Synthesis of an Open-Cage Structure POSS Containing Various Functional Groups and Their Effect on the Formation and Properties of Langmuir Monolayers

Article abstract of DOI:10.1002/chem.201602456

Recently, silsesquioxanes have been recognized as a new group of film-forming materials. This study has been aimed at determining the effect of the kind of functional groups present in two different open-cage structure POSS molecules on the possibility of the formation of Langmuir monolayers and their properties. To achieve this goal, two new POSS derivatives (of open-cage structures) containing polyether and fluoroalkyl functional groups have been synthesized on the basis of a hydrosilylation process. An optimization of the process was performed, which makes it possible to obtain the above-mentioned derivatives with high yields. In the next step, the Langmuir technique was applied to measurements of the surface pressure (π) ? the mean molecular area (A) isotherms during the compression of monolayers formed by molecules of the two POSS derivatives considered. Subsequently, the monolayers were transferred onto quartz plates according to the Langmuir–Blodgett technique. Both derivatives are able to form insoluble Langmuir films at the air–water interface, which can be transferred onto a solid substrate and effectively change its wetting properties.

Full text of DOI:10.1002/chem.201602456

DOI: 10.1002/chem.201602456
Full Paper
&
Silsesquioxanes
Synthesis of an Open-Cage Structure POSS Containing Various
Functional Groups and Their Effect on the Formation and
Properties of Langmuir Monolayers**
Michał Dutkiewicz,[b, c] Joanna Karasiewicz,[a] Monika Rojewska,[d] Marta Skrzypiec,[d]
Katarzyna Dopierała,[d] Krystyna Prochaska,[d] and Hieronim Maciejewski*[a, c]
Abstract: Recently, silsesquioxanes have been recognized as
a new group of film-forming materials. This study has been
aimed at determining the effect of the kind of functional
groups present in two different open-cage structure POSS
molecules on the possibility of the formation of Langmuir
monolayers and their properties. To achieve this goal, two
new POSS derivatives (of open-cage structures) containing
polyether and fluoroalkyl functional groups have been syn-
thesized on the basis of a hydrosilylation process. An optimi-
zation of the process was performed, which makes it possi-
ble to obtain the above-mentioned derivatives with high
yields. In the next step, the Langmuir technique was applied
to measurements of the surface pressure (p) ꢀ the mean
molecular area (A) isotherms during the compression of
monolayers formed by molecules of the two POSS deriva-
tives considered. Subsequently, the monolayers were trans-
ferred onto quartz plates according to the Langmuir–Blodg-
ett technique. Both derivatives are able to form insoluble
Langmuir films at the air–water interface, which can be
transferred onto a solid substrate and effectively change its
wetting properties.
Introduction
ple, polymers, thus creating organic–inorganic hybrid and
nanocomposite materials of specific and unprecedented prop-
erties.[1–4] In the group of cage derivatives one can additionally
name fully condensed silsesquioxanes, not fully condensed sil-
sesquioxane (open cage with one of the corner silicon atoms
missing), and heterosilsesquioxanes. Much less attention has
been paid to the application of POSS with open cage struc-
tures. Most of the published studies concern their application
to synthesis of fully condensed derivatives in the process of
corner capping, being in fact, the process of hydrolytic con-
densation of the respective trisilanol with trichloro- or trialkox-
ysilane. In this way, monofunctional derivatives containing
seven identical chemically passive groups (most frequently iso-
butyl or phenyl ones) and one reactive functional group are
formed.[1–3] Trisilanol-POSS derivatives have also been em-
ployed for the synthesis of complexes in the capacity of chelat-
ing ligands and for the synthesis of heterosilsesquioxanes con-
taining an atom of another element in one of the silicon–
oxygen core corners.[1,5–7] The reaction of hydrolytic condensa-
tion provides not only the possibility of end capping in trisila-
nols but also of attaching three reactive groups. For instance,
the condensation of trisilanol with three molecules of dime-
thylchlorosilane or vinyldimethylchlorosilane enables to obtain
derivatives with an open-cage structure having three substitu-
ents that contain terminal hydrogen atoms or vinyl groups, re-
spectively. Derivatives of this type can be applied as agents for
hydrophobization of plastic surfaces or printed surfaces after
their introduction into polymers or paint just by means of
mixing.[8,9] Also known are examples of the application of di-
Silsesquioxanes make a large group of organosilicon deriva-
tives of the general formula (RSiO1.5)n that attracts a constant
interest of researchers from many areas, such as chemistry,
physics, and even biology and medicine.[1] Predominant
among them are cage silsesquioxanes (POSS), which due to
their strictly defined structure (of nanometric dimensions) as
well as the presence of organic substituents, provide the possi-
bility for further modification and creation of new derivatives
or formation of durable bonding to other materials, for exam-
[a] Dr. J. Karasiewicz, Prof. Dr. H. Maciejewski
Faculty of Chemistry
Adam Mickiewicz University in Poznan
Umultowska 89 B, 61-614 Poznan (Poland)
E-mail: maciej@amu.edu.pl
´
´
[b] Dr. M. Dutkiewicz
Centre for Advanced Technologies
Adam Mickiewicz University in Poznan
Umultowska 89 C, 61-614 Poznan (Poland)
´
´
[c] Dr. M. Dutkiewicz, Prof. Dr. H. Maciejewski
´
Poznan Science and Technology Park
Adam Mickiewicz University Foundation
Rubiez˙ 46, 61-612 Poznan (Poland)
´
[d] Dr. M. Rojewska, M. Skrzypiec, Dr. K. Dopierała, Prof. Dr. K. Prochaska
Institute of Chemical Technology and Engineering
´
Poznan University of Technology
´
Berdychowo 4, 60-965 Poznan (Poland)
[**] POSS=polyhedral oligomeric silsesquioxane.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201602456.
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methylsiloxy group-containing derivatives as modifiers for pol-
ymethacrylates produced by means of free-radical polymeri-
zation[10] or after their functionalization with dithiocarbamyl
groups as initiators of methacrylate polymerization.[11] The de-
rivatives containing dimethylsiloxy and dimethylvinylsiloxy
groups can also be used for the synthesis of materials with
low dielectric constants, applied, for example, in the process of
the manufacture of liquid-crystal displays by means of hydrosi-
lylation of dienes or chain and cyclic derivatives of polysilox-
anes.[12,13] By using the process of hydrosilylation, it is possible
to perform functionalization with a large group of organic de-
rivatives and obtain silsesquioxanes with open-cage structures
having three reactive groups. Unfortunately, the open-litera-
ture reports on this subject are still very scarce and the most
of the available information is contained in patents, which de-
scribe the way of the synthesis and the direction of applica-
tions. For instance, the derivatives containing amino or poly-
ether groups are employed in the manufacture of liquid-crystal
displays, where they play the role of modifiers for protective
varnishes on the basis of polyimide or polyamine resins.[14] The
derivatives with 3-isocyanatepropyl groups can be used as
cross-linking agents in binders and hot-melt adhesives.[15] They
have also found an application in optical fibers and optical ma-
terials[16,17] as well as in the manufacture of photosensitive ma-
terials.[18–20] Compounds of this type having three functional
groups in the form of derivatives of succinic acid modified by
ethylenediamine and seven 2,2,4-trimethylhexyl groups play
the role of a stabilizer of quantum-dot binding ligands in
nanocrystalline electroluminescent materials.[21]
First, compound 1 was obtained in the reaction of a hydrolyt-
ic condensation between trisilanolisobutyl-POSS and dimethyl-
chlorosilane, that was later employed in hydrosilylation. The
synthesis of compounds 2 and 3 was based on the process of
hydrosilylation of olefins (allyl polyether with a terminal hy-
droxyl group and a 5-(allyloxy)-1,1,2,2,3,3,4,4-octafluoropen-
tane), respectively, by using 3,7,14-tris[dimethylsiloxy]-
1,3,5,7,9,11,14-heptaisobutyltricyclo[7.3.3.15,11]heptasiloxane (1)
(as a hydrosilylating agent) in the presence of a catalyst (Kar-
stedt’s catalyst—[Pt2{O[Si(CH3)2CH=CH2]2}3] or hexachloroplatin-
ic acid) according to Scheme 1.
Scheme 1. Synthesis of products 2 and 3 based on hydrosilylation of allyl
polyether or 5-(allyloxy)-1,1,2,2,3,3,4,4-octafluoropentane with 3,7,14-tris[di-
methylsiloxy]-1,3,5,7,9,11,14-heptaisobutylotricyclo[7.3.3.15,11]heptasiloxane.
The hydrosilylation process was monitored with the use of
real-time infrared spectroscopy. The reaction progress was
quantified by observing changes in the area of the band at n˜ =
904 cmꢀ1 (ascribed to the stretching vibrations of the SiꢀH
bond) with time. The obtained results have clearly shown a sig-
nificant effect of the employed catalyst on the course of the
hydrosilylation reaction.
Despite more and more numerous examples of applications,
this group of derivatives (and particularly their properties) is
still little known. In the last few years, polyhedral oligomeric sil-
sesquioxanes (POSS) have been recognized as a new group of
materials forming stable Langmuir monolayers, which could be
transferred onto the solid substrate as Langmuir–Blodgett (LB)
or Langmuir–Schaefer (LS) thin films and modify the substrate
properties.[22–25] However, it is obvious that the modification
effect as well as the character of the monolayer formed by
POSS molecules strongly depend on the type of POSS com-
pound.[26] Therefore, it is interesting to know the effect of the
type and the structure of different substituents present in
POSS molecules on their ordering, and the tendency to form
self-aggregates in monolayers at the air–water and air–solid
substrate interfaces. This is why our study was aimed at syn-
thesizing two new silsesquioxane derivatives with an open-
cage structure, containing polyether or fluoroalkyl groups and
determining their properties including the possibility of form-
ing stable Langmuir monolayers and their further use for pro-
ducing coatings and hybrid materials.
Figure 1 presents the dependence of the change in the in-
tensity of the studied band (i.e., n˜ =904 cmꢀ1) during the hy-
drosilylation of 5-(allyloxy)-1,1,2,2,3,3,4,4-octafluoropentane in
the presence of hexachloroplatinic acid and Karstedt’s catalyst
(Figures 1a and b, respectively) and allyl polyether in the pres-
ence of the same catalysts (Figures 1c and d, respectively). To
emphasize changes occurring in the first step of the process,
only the first two hours of the process duration are presented
in Figure 1.
To more precisely present the effect of the catalyst and the
kind of the parent compound on the course of the hydrosilyla-
tion, changes in SiꢀH bond conversion with time for various
reaction systems are shown in the Supporting Information.
In the case of both reactions, the activity of the Karstedt’s
catalyst considerably surpasses that of hexachloroplatinic acid.
The obtained products, after their isolation from the post-re-
action mixture, have been subjected to spectroscopic analyses,
namely nuclear magnetic resonance (1H, 13C, and 29Si NMR
spectroscopy) (see the Supporting Information). The formation
of the products of the desired structures has also been con-
firmed by the analysis of the FTIR spectra of the products 2
and 3 and the parent compounds employed for their synthesis
(Figures 2 and 3).
Results and Discussion
At the initial stage of the study, syntheses of two new organo-
silicon compounds that were derivatives of cage silsesquiox-
anes with one open corner were performed. They contained
polyether and fluoroalkyl groups (that are mutually opposite)
as substituents.
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In the spectrum of product 2 a band is visible at n˜ =
3500 cmꢀ1, which can be ascribed to stretching vibrations of
the hydroxyl group. The presence of this band in the product
spectrum and the decay of the bands at n˜ =2100 and
903 cmꢀ1, originating from stretching vibrations of the SiꢀH
group (present in the parent compound spectrum), testify the
formation of the hydrosilylation product and not to the occur-
rence of a condensation reaction between the SiꢀH and OH
groups. The structure of the product has also been confirmed
by the presence of bands attributed to symmetric and asym-
metric stretching vibrations characteristic of CꢀH bonds of
methyl and methylenic groups in the region n˜ =2700–
3000 cmꢀ1, as well as bands ascribed to stretching vibrations
of C-O-C bonds present in the polyether chains and asymmet-
ric stretching vibrations of Si-O-Si groups in the region n˜ =
1000–1200 cmꢀ1.
The spectrum of the product 3, which is shown in Figure 3,
although somewhat poorer in signals, also makes it possible to
correctly verify the structure of the obtained product. Similarly,
as it was in the case of the spectrum of product 2 presented
in Figure 2, also in this case one can notice the absence of
bands at n˜ =2100 and 903 cmꢀ1, originating from stretching vi-
brations of the SiꢀH group, which were present in the spec-
trum of the parent compound. Also present are bands attribut-
ed to symmetric and asymmetric vibrations of CꢀH bonds of
methyl and methylenic groups in the region n˜ =2700–
3000 cmꢀ1, as well as bands originating from stretching vibra-
tions of CꢀF bonds present in the chains of the fluoroalkyl
groups and asymmetric stretching vibrations of Si-O-Si groups
in the region n˜ =1000–1200 cmꢀ1.
Figure 1. Analysis of real-time FTIR measurements showing changes in the
intensity of the band at n˜ =904 cmꢀ1 with time during the hydrosilylation of
5-(allyloxy)-1,1,2,2,3,3,4,4-octafluoropentane in the presence of a) hexachlor-
oplatinic acid and b) Karstedt’s catalyst as well as allyl polyether catalyzed
by c) hexachloroplatinic acid and d) Karstedt’s catalyst.
To shed light on the relation between the chemical structure
of the obtained POSS derivatives and their potential ability to
modify solid substrates, we have performed a multi-step inves-
tigation. In the first step, we have applied the Langmuir tech-
nique to measure the surface pressure (p) ꢀ the mean molecu-
lar area (A) isotherms during the compression of monolayers
formed by molecules of the two POSS derivatives considered.
Subsequently, the monolayers were transferred onto a quartz
plate by using the Langmuir–Blodgett technique (this method
provides the best control over the parameters of thin films for-
mation) and finally the water contact angle (WCA) on the
modified substrates was measured.
Figure 2. FTIR spectra of the parent compounds and the product 2.
p–A isotherms
The PEG-POSS (2, PEG=[w-(hydroxy)(polyethoxy)propyl]dime-
thylsiloxy) and OFP-POSS (3, OFP= [3-(2,2,3,3,4,4,5,5-octafluor-
opentyloxy)propyl]dimethylsiloxy) molecules formed insoluble
Langmuir films at the air–water interface. The monolayers
formed by molecules of these two POSS derivatives were
spread on pure water (pH 6.5, subphase temperature=(25ꢁ
0.1)8C) and the p–A isotherms were recorded. The obtained re-
sults are plotted in Figure 4, which also presents the depend-
ence of the compression modulus (Csꢀ1) on the surface pres-
sure (p) (insert of Figure 4a). The compression modulus CSꢀ1
,
which is the reciprocal of the compressibility, is defined as
given in Equation (1):[29]
Figure 3. FTIR spectra of the parent compounds and the product 3.
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A isotherms recorded for both POSS derivatives: Ao =average
area occupied by closely packed molecules in the monolayer
state determined by extrapolating the linear part of the con-
densed state in the p–A isotherms to zero pressure; pcollapse
=
value of the surface pressure at which the inflection of the
monolayer takes place; Acollapse =value of the area per molecule
corresponding to the film collapse, and maxCSꢀ1 =maximum
value of the compression modulus.
As one can note, the type of substituents R attached to the
silica cage in the POSS molecules has a dramatic influence on
the behavior of the silsesquioxane molecules at the air–water
interface during compression. Therefore, the results should be
analyzed separately for each POSS compound studied.
PEG-POSS (2)
As one can see, the isotherm of PEG-POSS starts to rise at ap-
proximately 550 ꢁ2 moleculeꢀ1. This area value, named Alift-off
,
corresponds to the end of the submonolayer regime (p=
0 mNmꢀ1) at which the film is likely to be biphasic with the
co-existence of gaseous- and liquid-like domains. The further
course of the isotherm indicates the liquid state of the mono-
layer. Upon compression, the surface pressure raises monotoni-
cally until the film collapses, which occurs slightly above
46 mNmꢀ1.
The collapse area determined from the p–A isotherm is ap-
proximately 132 ꢁ2. It can be assumed that this value corre-
sponds to monolayer disruption and formation of 3D struc-
tures.
According to optimization of the molecular geometry made
with the Vega ZZ 3.0.1 software[36] and shown in Figure 5a, it
was found that the initial area occupied by PEG-POSS mole-
cules is determined by three hydrophilic PEG chains and it is
equal to 580 ꢁ2. This value is close to the Alift-off value of PEG-
POSS. It seems that at the beginning of monolayer formation
the PEG chains are spaced widely at the interface with the hy-
droxyl groups immersed into the aqueous subphase, whereas
the silsesquioxane cage is oriented toward the air. Upon com-
pression, the PEG moieties approach each other and in the
condensed monolayer the molecules reach the limiting area
equal to 232 ꢁ2. The initial area could also be decreased due
to partial dissolution of the PEG chains in the water subphase.
However, the results of a relaxation experiment shown in
Figure 7 did not reveal a significant area loss with time. Thus,
the loss in area caused by the interaction of the PEG moieties
with the water subphase can be probably neglected.
Figure 4. a) p–A isotherms of PEG-POSS (2) and OFP-POSS (3). The inset
shows the compression modulus as a function of the surface pressure.
b,c) Surface pressure–area and electric surface potential (DV)–area isotherms
of PEG-POSS (2) and OFP-POSS (3), respectively.
dp
dA
Csꢀ1 ¼ ꢀAð Þt
ð1Þ
ꢀ1
where CS is a rheological quantity related to the monolayer
rigidity and it is a measure of the elastic energy stored in the
monolayer upon compressive deformation of the surface. The
inflexion points in the plot of Csꢀ1 versus p indicate the surface
pressure at which significant reorganization of the surface film
takes place in the course of the film compression. The magni-
ꢀ1
tude of CS provides information about the elasticity of the
As mentioned above, the state of the monolayer can be
quantified with the compression modulus values. As the maxi-
monolayers and indirectly about their physical state as well as
about the phase transition. For CSꢀ1 <50 mNmꢀ1, the state of
a given monolayer is classified as liquid expanded (LE, iso-
tropic liquid), for 50<CSꢀ1 <250 mNmꢀ1, the state is
liquid condensed (LC, liquid crystalline; monolayer often
diffracts X-ray radiation), and for CSꢀ1 >250 mNmꢀ1, the
monolayer is described as solid, according to the criterion
Table 1. Characteristic parameters of the Langmuir monolayers of the PEG-
POSS (2) and OFP-POSS (3) derivatives.
Compound A0
pcollapse
Acollapse
MaxCSꢀ1 A(maxCSꢀ1)
given by Davies and Rideal.[30]
[ꢁ2 moleculeꢀ1] [mNmꢀ1] [ꢁ2 moleculeꢀ1] [mNmꢀ1] [ꢁ2 moleculeꢀ1
]
2
3
232
311
46.1
11.8
131.7
216.6
130.5
34.1
164.8
229
Table 1 presents the values of characteristic parameters
of Langmuir monolayers estimated on the basis of the p–
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tween the molecules present at the subphase, the stronger is
the intermolecular interaction between the PEG moieties. On
the other hand, the stronger the interactions of PEG moieties
with water, the deeper the shift of molecules into the water
subphase. In consequence, a slight increase in the measured
value of the surface potentials up to approximately 0.2 V can
be observed (Figure 4b). On the other hand, the plot of DV
versus the molecular area (Figure 4b) indicates that the PEG-
POSS molecules increase the surface potential of water. The
measured values of DV are positive in the whole range of mon-
olayer compression.
The extrapolated cross-sectional area obtained from the p–A
isotherm (limiting area Ao) indicates that closely packed PEG-
POSS molecules occupy about 230 ꢁ2 of the interface. Taking
into account that the cubic structure of the POSS cage is
about 5 ꢁ in size,[31] it seems that the value of Ao suggests
such an orientation of the PEG-POSS molecules in which the
hydrophilic moieties (i.e., the PEG groups) lie on the water sur-
face, whereas the silica cage is located above, without direct
contact with the subphase. Thus, the limiting area of the PEG-
POSS molecules is determined by the dimensions of the hydro-
philic PEG moieties. Besides, the value of A0 seems to be rea-
sonable, if one compares it with the cross-sectional area esti-
mated for a molecule of trisilanolisobutyl POSS (Ao =(177ꢁ
4) ꢁ2) or trisilanol-cyclohexyl POSS (Ao =181 ꢁ2), that is, the de-
rivatives possessing much shorter moieties attached to the sili-
con–oxygen partially condensed open cage.[23,24]
Figure 5. Graphical representation of a) PEG-POSS (2) and b) OFP-POSS (3)
molecules at the interface according to the space-filling model (a colored
version of this graphic is given in the Supporting Information).
ꢀ1
mum value CS can take is 131 mNmꢀ1, the monolayer charac-
ꢀ1
terized by this value of CS can be regarded as condensed
liquid.
On the other hand, the compression modulus reaches its
maximum value for pꢂ32.5 mNmꢀ1. It is worth mentioning
that this value is the best for Langmuir–Blodgett film deposi-
tion.
OFP-POSS (3)
According to the Csꢀ1 criterion, the OFP-POSS molecules form
a liquid expanded Langmuir monolayer at the air–water inter-
face because of the maxCsꢀ1 value, which is equal to
34 mNmꢀ1. The limiting area Ao of the OFP-POSS p–A isotherm
is approximately 311 ꢁ2 and the monolayer collapses at about
12 mNmꢀ1 and an area of 216 ꢁ2 moleculeꢀ1. After the collapse
point, the OFP-POSS exhibits a long plateau at p of approxi-
mately 12 mNmꢀ1. The collapse of the monolayer causes
a transfer from a 2D to a 3D structure and the formation of
a multilayer at the air–water interface.
ꢀ1
Moreover, the molecular area at the maxCS value is equal
to 164.8 ꢁ2 and it corresponds to the most compact arrange-
ment of PEG-POSS molecules at the interface. Comparing this
value with the calculated cross-sectional area, one can con-
clude that PEG-POSS shows larger compressibility in compari-
son with trisilanolisobutyl-POSS reported by Yin et al.[32] This
effect will be discussed later, together with the dilational vis-
coelasticity of the PEG-POSS monolayer.
The chemical structure of the PEG-POSS molecules should
be analyzed, taking into account that the three substituents,
that is, the PEG moieties, show hydrophilic character, which
counter-balances the hydrophobicity of the silica cage with
seven corners substituted with isobutyl groups and makes the
whole molecule amphiphilic. Such a design corresponds to the
classical amphiphiles having a hydrophilic head and a hydro-
phobic tail. It can be supposed that the PEG-POSS molecules
behave like typical amphiphiles and assume the orientation
with the hydrophobic tails (i.e., the cage) towards air and the
hydrophilic head groups (i.e., the PEG moieties) anchored to
the water subphase.
The three fluorinated moieties present in the structure of
the OFP-POSS molecules show hydrophobic character, the
same as a partly open silica cage. Thus, the OFP-POSS mole-
cules are built of hydrophobic fragments only and do not con-
tain any polar group. So, the orientation of these molecules at
the air–water interface is not limited by any tendency to inter-
action with the subphase of any of the groups. Admittedly,
usually it is assumed that the molecules (existing in the mono-
layer state), which include perfluorinated moieties have their
strongly hydrophobic moieties in contact with air.[33] However,
the OFP-POSS seem highly probable to have a mosaic struc-
ture of the monolayer with domains containing alternately di-
rected molecules. Such a mosaic structure has been pro-
posed[34,35] for semi-fluorinated n-alkane molecules. Additional-
ly, this assumption of a mosaic model seems to be supported
by the measured values of the surface potential for the OFP-
POSS, which are negative but very close to zero (Figure 4c). It
Moreover, the formation of hydrogen bonds between the
PEG moieties and water molecules seems to be very likely.
Upon monolayer compression, the PEG-POSS molecules
assume an orientation tending to perpendicular to the inter-
face, which is reflected by their molecular area decrease to A
equal to approximately 232 ꢁ2. The shorter the distance be-
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is noteworthy that, for the monolayer formed by the molecules
with their perfluorinated substituents exposed towards air, the
values of the surface potential should be clearly negative,
much smaller than zero,[35] whereas in the mosaic model, the
values of the surface potential should be around zero because
of the cancellation of oppositely directed dipole vector mo-
ments.
The optimization of the molecular structure made for the
OFP-POSS by using the VEGA ZZ software[36] (shown in Fig-
ure 5b) revealed that the cross-sectional area of the single
molecule is equal to approximately 343 ꢁ2, which is in agree-
ment with the Alift-off value and it is only a little larger than the
limiting area determined from the p–A isotherm (Figure 4a).
However, for the OFP-POSS, the more informative parameters
are the value of A at maxCsꢀ1 and the area at collapse, which
are equal to 229 and 216.6 ꢁ2, respectively. Both values are
much lower than the calculated cross-sectional area (343 ꢁ2)
suggesting that the OFP-POSS changes the orientation of the
fluorinated chains from a vertical to a titled one (the perpen-
dicular orientation of the molecules at the interface was ex-
cluded during the calculations). It must also be emphasized
that larger volume and cross-section area values for fluorocar-
bon chains in comparison with those for hydrocarbon chains
are crucial for the explanation of their behavior at the inter-
face. Here, the titling of the OFP-POSS may be governed by
the repulsive interactions between the fluorinated chains and
the isobutyl substituents attached to the SiꢀO cage. However,
usually the variation in the orientation causes noticeable re-
sponse of the surface potential. As mentioned above, for OFP-
POSS we observed a DV value, which is surprisingly small in
comparison with the values for typical fluorinated amphiphiles.
This decrease was observed mainly in the gas phase and re-
sults from an increasing number of molecules under the meas-
uring sensor.[50] Upon further compression, the surface poten-
tial is almost constant. The key factor leading to the collapse
of OFP-POSS is a weak interaction of the isobutyl groups with
the water subphase in the expanded film.
Figure 6. BAM images recorded upon compression of a) OFP-POSS and
b) PEG-POSS monolayers at room temperature.
layer takes place. Upon collapse, a multilayer is formed, which
is manifested by the appearance of bright rod-like domains in
the background.[51,52] Thus, the BAM images show significant
differences in the morphology of the monolayers formed at
the air–water interface by the two investigated POSS deriva-
tives, stemming from the nature of these molecules, that is, of
strong hydrophobicity of OFP-POSS and an amphiphilic charac-
ter of PEG-POSS.
The evidently different course of the p–A and DV–A iso-
therms (Figures 4a and c) as well as the different BAM images
(Figures 6a and b) obtained for the PEG-POSS and OFP POSS
derivatives indicate a quite different behavior as well as orien-
tation of the molecules of these two compounds at the air–
water interface upon monolayer compression, but does not
give any information about the time stability of these two
Langmuir monolayers.
The strongly hydrophobic character of the OFP-POSS mole-
cules is the reason for their very weak interaction with the sub-
phase. In consequence, the removal of OFP-POSS molecules
from the air–water interface required much lower p values
than for the PEG-POSS molecules. As one can see, the PEG-
POSS (with PEG moieties anchored probably to the water sub-
phase) has a much higher (near four-fold) dynamic collapse
surface pressure (pcollapse ꢂ46 mNmꢀ1) at a smaller Acollapse value
of approximately 131.7 ꢁ2 moleculeꢀ1 than OFP-POSS (pcollapse
ꢂ12 mNmꢀ1 and Acollapse ꢂ216.6 ꢁ2 moleculeꢀ1). Moreover, their
p–A isotherms reveal a vastly different behavior in the collaps-
ing regime.
To get information about the stability of the monolayer
formed by PEG-POSS and OFP-POSS molecules an additional
experiment was performed, in which the monolayers were first
compressed until
a desired surface pressure value (i.e.,
10 mNmꢀ1), which was afterwards kept constant, and a de-
crease in the area was monitored with time (Figure 7). As can
be seen, in both systems no area loss was observed with time.
Thus, the obtained results can be a proof of the stability of
both films.
For comparison and more detailed explanation of the mor-
phology of OFP-POSS and PEG-POSS, the monolayers were vi-
sualized with Brewster angle microscopy (BAM) and the repre-
sentative images are presented in Figure 6. The PEG-POSS film
remains homogeneous throughout the whole compression.
The changes in the morphology of this monolayer are clearly
visible only for values of the surface pressure corresponding to
the collapse, whereas for OFP-POSS a gradual formation of bi-
To test the stability of the PEG-POSS and OFP-POSS mono-
layers under dynamic conditions, area deformation was in-
duced by means of the oscillating barriers method.[37,38] Ac-
cording to this method, it is possible to evaluate the modulus
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Figure 8. Dilatation rheological parameters for a) PEG-POSS and b) OFP-POSS
Figure 7. Static stability experiments of PEG-POSS and OFP-POSS monolay-
ers—a description is given in the text.
monolayers as a function of the frequency at different surface pressures,
that is, 5, 10, and 25 mNmꢀ1
.
of the complex dilatational viscoelasticity (E), which is derived
from the change in the surface pressure (dilatational stress)
dp, resulting from a small change in the surface area (dilata-
tional strain) dA. The modulus E can be calculated from the re-
lation given in Equation (2).
tion of elastic films by the two studied monolayers. Thus, al-
though for both OFP-POSS and PEG-POSS films the viscoelastic
response appeared, nevertheless these films have more elastic
character. In the more compressed monolayer the stronger in-
termolecular interactions should exist, which is consistent with
the results obtained. As shown for the PEG-POSS monolayer,
the value of elastic modulus E’ significantly increases with an
increasing surface pressure, which may be caused by the for-
mation a more stable monolayer upon compression. As men-
tioned above, we can conclude that the three PEG moieties
present in the PEG-POSS molecules, were anchored in the
water subphase and enhanced the stability of the monolayer
formed at the air–water interface but did not impact the inter-
molecular interactions between the POSS molecules. A similar
behavior was reported for closed-cage 1,2-propanediolisobutyl
POSS.[25]
dp
d ln A
ð2Þ
E ¼ ꢀð
ÞT
The dilatational modulus obtained in the oscillating barrier
experiment is a complex quantity and is composed of the real
component, that is, the elastic modulus (E’), and the imaginary
component, that is, the viscous modulus (E’’). For a perfectly
viscous monolayer, the real part is equal to zero, whereas for
a perfectly elastic one, the imaginary part is zero. The ratio of
E’’ to E’ is defined as the tangent of the loss angle, tanq,
where q is the phase shift between the imaginary component
and the real component of the dilatational modulus. A value
of tanq lower than 1 implies elastic properties of the monolay-
er, whereas a value of tanq greater than 1 reveals a more vis-
cous character.[37,39]
In the case of the OFP-POSS monolayer, the rheological char-
acteristics were considered only for low surface pressures that
is, 5 and 10 mNmꢀ1, due to its low value of collapse of approx-
imately 11.8 mNmꢀ1. It should be noted that the values of the
elastic modulus E’ determined for the OFP-POSS monolayer are
higher when compared with the values of E’ characterizing the
PEG-POSS film under the same conditions of study. This may
be due to a strongly hydrophobic nature of the OFP-POSS mol-
ecules forming a more insoluble monolayer in the LE phase at
the air–water interface.
The surface viscoelastic properties of the POSS monolayers
spread on the air–water interface, as a function of the frequen-
cy of oscillations, were investigated at different surface states
characterized by given values of the surface pressure. The
changes in the surface elastic modulus (E’) and the viscous
modulus (E“) as a function of the deformation rate (i.e., the fre-
quency of oscillations) are presented in Figure 8. For the OFP-
POSS monolayer (Figure 8a) the experiments were conducted
at 5 and 10 mNmꢀ1, which corresponded to the LE state and
the onset of collapse, respectively, whereas for the PEG-POSS
monolayer (Figure 8b) the experiments were conducted at 5,
10, and 25 mNmꢀ1, that is, before and after the LE–LC phase
transition region and at the maximal static elasticity, respec-
tively.
As shown in Figure 9, the tangent of the loss angle for both
monolayers (under all studied conditions) assumed low values,
which did not exceed 0.4 for the highest deformation rate at
the highest surface pressure studied. The obtained results
permit concluding that the monolayers formed by molecules
of both POSS derivatives revealed rheological behavior (under
dilatational conditions) that are essentially elastic.
The dilatational elasticity (E’) depended very weakly on the
frequency of oscillations in the studied range, in all considered
monolayers states, whereas the dilatational viscosity (E“) in-
creased with increasing of the frequency in an almost linear
way. The results presented show that the values of E’ exceed
the values of the viscous modulus E”, which indicates forma-
To conclude, the oscillating barrier experiment has shown
that irrespectively of the dynamic conditions resulting both
from high and low deformation rates, both PEG-POSS as well
as OFP-POSS monolayer behave like elastic material.
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In the case of OFP-POSS, the mosaic structure of the mono-
layer produced at the air–water interface remained in the
same form after the deposition of this film onto the solid sub-
strate. The presence of domains with oppositely directed OFP-
POSS molecules, which are aligned at the surface, that is,
direct contact of both the hydrophobic cores and the hydro-
phobic fluorinated groups with the molecules of wetting water
results in the higher hydrophobicity of this layer than that of
the PEG-POSS monolayer. Moreover, it is worth mentioning
that the measured value of the contact angle for the substrate
modified by deposition of the OFP-POSS film is clearly lower
(by about 208) in comparison with the wettability of the mate-
rial modified by typical fluorinated polyhedral oligomeric silses-
quioxanes (F-POSS).[48,49] Thus, the results obtained seem to
confirm the proposed mosaic structure and simultaneously ex-
clude the orientation of the OFP-POSS molecules forming a LB
film with the fluorinated moieties exposed towards the air.
Deposited Langmuir–Blodgett monolayers of both substan-
ces were also investigated by using an atomic force micro-
scope in order visualize them the in nanometric scale. Repre-
sentative images are presented in Figures 10a–d.
Figure 9. Frequency dependence of the tangent of the loss angle for PEG-
POSS and OFP-POSS at different surface pressures. Amplitude of deforma-
tion=1%.
Both films cover the quartz substrates almost completely de-
spite the fact that there are defects in the substrates visible as
lines (polishing grooves) and black areas (point defects), which
are typical of these type of substrates.[41] In the images of the
PEG-POSS (Figures 10a and b) many small 3D aggregates, visi-
ble as bright spots against the homogenous monolayer, can
be seen. The aggregate lateral dimensions do not exceed
100 nm, protruding typically 2–5 nm above the monolayer.
Emergence of these forms can be explained by the tendency
to aggregation of the PEG-POSS molecules described in the lit-
erature.[25,42] In addition to that, the PEG-POSS include highly
polar groups, which, we concluded, lie on the water surface
oriented parallel to each other. In close proximity, dipolar inter-
actions between them also contribute to repellence of the
molecules out of the contact with the water surface.
Thin films of POSS at the solid substrates
The Langmuir monolayers formed by molecules of the two
POSS studied were deposited onto quartz surfaces according
to the Langmuir–Blodgett technique (LB) to form a layer struc-
ture and then (after drying the quartz plate) the wettability of
the modified substrates was determined. Table 2 details the re-
sults obtained for the water contact angle. The wetting angle
measurements of such prepared materials confirmed the suc-
cessful deposition of the POSS monolayers. In both cases a sig-
nificant increase in the water contact angle was observed
(measured values varied from around 70 to 1018 for the differ-
ent POSS) when compared to quartz (i.e., (15ꢁ0.1)8).
As follows from the above data, the wettability of the solid
substrate modified by deposition of the PEG-POSS monolayer
is significantly lower than that of the quartz covered by a thin
film of the OFP-POSS. This result reflects the differences in the
orientation of these two types of POSS molecules forming
films on the solid substrate. It confirms that within the PEG-
POSS film the hydrophilic head (i.e., the PEG moieties) was in
contact with water and, after the film transfer, with the solid
substrate, whereas the hydrophobic tail (i.e., the POSS cage)
was exposed towards air. The measured value of the water
contact angle for the quartz substrate modified with the PEG-
POSS film is in good agreement with the data reported for 1,2-
propanediolisobutyl POSS, that is, a POSS derivative with
a silica cage substituted with seven isobutyl group similarly as
the PEG-POSS molecule.[25]
Table 2. Values of the water contact angle (WCA) on the modified quartz
substrate.
Compound Transfer surface pressure [mNmꢀ1
]
Water contact angle [8]
Figure 10. Topography AFM images of a,b) PEG-POSS and c,d) OFP-POSS
Langmuir–Blodgett films deposited on quartz substrates. The image scale is
a,c) 5ꢂ5 mm2 and b,d) 1ꢂ1 mm2.
2
3
30
10
(70.4ꢁ0.1)
(101.1ꢁ0.1)
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In contrast to a large number of aggregates in the PEG-
POSS image (56 mm2) covering about 2% of the total substrate
surface, only single spots (<1 mm2) can be seen for the OFP-
POSS monolayer (Figures 10c and d) with a negligible total
coverage (0,04%). Inhibited aggregation of OFP-POSS stems
the Langmuir monolayers formed on the water surface (i.e.,
packing density, orientation of the molecules, stability, electric
surface potential) depend strongly on the chemical structure
of the POSS compound.
The successful preparation of LB films by using the PEG-
POSS and OFP-POSS suggests that these two types of silses-
quioxanes can be good candidates for obtaining nanostruc-
tured hybrid materials and coatings and can be applied to
other types of thin film technology.
from the above-mentioned smaller molecular packing (Csꢀ1
34.1 mNmꢀ1) when compared to that of PEG-POSS (Csꢀ1
=
=
130.5 mNmꢀ1). Longer intermolecular distances in the per-
fluorinated OFP-POSS are a result of the substitution of the
silica cage with groups containing strongly electronegative
atoms. In this way, fluorination (substitution with strongly elec-
tronegative atoms in general) prevents aggregation into 3D
forms.[43]
Experimental Section
Materials: All commercially available (Sigma–Aldrich) chemicals
were used as received without any further purification. 5-(Allyloxy)-
1,1,2,2,3,3,4,4-octafluoropentane was synthesized by a Williamson
As is well known, the geometry of the surface can have
a great impact on wettability.[44,45] Roughness, represented by
the root-mean-square (Sq), is identical for both investigated
films (Table 3); however, its value results from imperfection of
the substrate rather than from the character of the surfaces of
the monolayer. On the other hand, the values of the Wenzel
factor[46,47] for both PEG-POSS as well as for OFP-POSS are very
close to unity. This is due to the fact that in both cases the ap-
parent surface area of the monolayers is almost equal to the
projected surface area. Therefore, considering the difference in
the hydrophobicity of these two sample surfaces we can con-
clude that it derives entirely from its chemical nature and is
not a geometric effect.
reaction.[27]
1,3,5,7,9,11,14-Heptaisobutyltricyclo[7.3.3.15,11]hepta-
siloxane-endo-3,7,14-triol was synthesized by hydrolytic condensa-
tion of isobutyltrimethoxysilane under basic conditions according
to a procedure described elsewhere.[28]
Synthesis of 3,7,14-tris[dimethylsiloxy]-1,3,5,7,9,11,14-heptaiso-
butyltricyclo[7.3.3.15,11]heptasiloxane—SiH-POSS (1): The synthe-
sis was based on the hydrolytic condensation of 1,3,5,7,9,11,14-
heptaisobutyltricyclo[7.3.3.15,11]heptasiloxane-endo-3,7,14-triol with
chlorodimethylsilane carried out in the presence of trimethylamine
under an argon atmosphere. To a Schlenk flask, placed on an ice
bath, were introduced dry hexane (50 mL), 1,3,5,7,9,11,14-hepta-
isobutyltricyclo[7.3.3.15,11]heptasiloxane-endo-3,7,14-triol
(10 g,
0.0126 mol), chlorodimethylsilane (3.7 g, 0.0388 mol) followed by
dropping trimethylamine (4 g, 0.0395 mol) to the obtained solu-
tion. The reaction mixture became cloudy as a result of hydrochlo-
ride formation. After one hour, the mixture was warmed to room
temperature while stirring for two more hours. Then the post-reac-
tion mixture was subjected to filtration in order to remove the
formed triethylamine hydrochloride and the filtrate was evaporat-
ed under reduced pressure. The raw product was washed three
times with methanol to remove any possible hydrochloride resi-
due. The obtained 3,7,14-tris[dimethylsiloxy]-1,3,5,7,9,11,14-heptai-
sobutyltricyclo[7.3.3.15,11]heptasiloxane (11.8 g, 97%) was subjected
to spectroscopic analysis, which confirmed its structure. 1H NMR
(400 MHz, C6D6, 258C, TMS): d=0.40 (d, J=2.8 Hz, 18H; Si(CH3)2),
0.86–0.80 (m, 14H; SiCH2), 1.09 (d, J=3.3 Hz, 42H; CH3), 2.16–1.98
(m, 7H; CH), 5.18–5.13 ppm (m, 3H; SiH); 13C NMR (75.5 MHz, C6D6,
258C, TMS): d=0.41 (Si(CH3)2), 22.90 (SiCH2), 24.45 (CH), 26.18 ppm
(CH3); 29Si NMR (59.6 MHz, C6D6, 258C, TMS): d=ꢀ67.53, ꢀ67.33,
ꢀ66.58, ꢀ5.06 ppm.
Table 3. Values of the root-mean-square roughness (Sq), number of 3D
aggregates per 1 mm2 (NAGG), percentage area covered by aggregates
(%AGG), and Wenzel factor (r) calculated for the investigated monolayers.
Compound
Sq [nm]
NAGG [mmꢀ2
]
%
AGG
r [a.u.]
2
3
0.49
0.49
56
<1
2.23
0.04
1.0006
1.0009
Conclusion
Two new silsesquioxane derivatives with open-cage structures,
containing three fluoroalkyl groups (OFP-POSS) or hydroxy ter-
minated polyether functional groups (PEG-POSS), have been
synthesized on the basis of a hydrosilylation process. While
synthesizing the above-mentioned derivatives, the effects of
the kind of olefin and catalyst employed on the course of the
hydrosilylation process have been determined. The reaction
proceeds more effectively in the case of olefins with strongly
hydrophobic properties (i.e., fluoroalkyl-allyl ether) and in the
presence of the Karstedt’s catalyst. The obtained derivatives
were isolated and characterized spectroscopically. The men-
tioned POSS derivatives were subsequently subjected to an
analysis of their surface properties followed by a study of the
interfacial behavior of both derivatives at the air–water inter-
face. The obtained results indicate that the PEG-POSS mole-
cules as well as the OFP-POSS molecules are able to form in-
soluble Langmuir films at the air–water interface, which can be
transferred onto a solid substrate and effectively change its
wetting properties. It has been shown that the properties of
Synthesis of 3,7,14-tris{[w-(hydroxy)(polyethoxy)propyl]dime-
thylsiloxy}-1,3,5,7,9,11,14-heptaisobutyltricyclo[7.3.3.15,11]hepta-
siloxane—PEG-POSS (2): The reaction was based on a hydrosilyla-
tion process. In a round-bottom flask equipped with a magnetic
stirrer and a reflux condenser, were placed toluene (20 mL), 3,7,14-
tris[dimethylsiloxy]-1,3,5,7,9,11,14-heptaisobutyltricyclo[7.3.3.15,11]-
heptasiloxane (5 g, 5.18ꢂ10ꢀ3 mol), and allyl polyether with termi-
nal hydroxyl groups (6 g, 0.0171 mol) of an average molecular
weight of 350 gmolꢀ1. This was followed by adding Karstedt’s cata-
lyst to the mixture at room temperature. The amount of the cata-
lyst corresponded to 5ꢂ10ꢀ5 mol Pt per one mol of SiꢀH present
in
3,7,14-tris[dimethylsiloxy]-1,3,5,7,9,11,14-heptaisobutyltricy-
clo[7.3.3.15,11]heptasiloxane and then the whole mixture was heated
to 908C and maintained at this temperature for 7 h. The process
was monitored by infrared spectroscopy, observing the disappear-
ance of the band at n˜ =904 cmꢀ1 originating from the SiꢀH bond
present in the parent compound (i.e., 3,7,14-tris[dimethylsiloxy]-
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1,3,5,7,9,11,14-heptaisobutyltricyclo[7.3.3.15,11]heptasiloxane). After
completion of the process, the post-reaction mixture was cooled
down followed by evaporation of the solvent and olefin excess
under reduced pressure. It resulted in 10.2 g (97.7%) of the prod-
uct 2. The obtained product was subjected to spectroscopic analy-
ring with time in the area of the band at n˜ =904 cmꢀ1 originating
from stretching vibrations of the SiꢀH bond.
Isotherm measurements: Langmuir trough (KN 0033, KSV Nima)
with a surface area of 273 cm2 (LꢂWꢂD, 364ꢂ75ꢂ4 mm3) and
a subphase volume of 190 mL was used for the preparation of the
monolayers. Before the experiments the Teflon trough was cleaned
with chloroform and ethanol and rinsed with ultrapure water. At
the beginning of the experiment, a double-barrier trough was
filled with ultrapure water (18.2 MWcm, 71.98ꢁ0.01 mNmꢀ1) and
then the surface of the water was cleaned by using a suction
pump until the change in the surface pressure after maximum
compression was below 0.2 mNmꢀ1. In the next step of the experi-
ment, the POSS derivatives studied (dissolved in chloroform) were
spread evenly onto the surface of the subphase with a Hamilton
microliter syringe. After evaporation of chloroform (ꢂ20 min) the
monolayers were compressed with a rate of 5 mmminꢀ1. A plati-
num Wilhelmy plate (KSV Nima) connected with the balance was
1
sis. H NMR (400 MHz, C6D6, 258C, TMS): d=0.21 (s, 18H; Si(CH3)2),
0.64–0.58 (m, 6H; (CH3)2SiCH2), 0.71–0.65 (m, 6H; SiCH2), 0.98 (d,
J=5.5 Hz, 42H; CH3), 1.69–1.60 (m, 6H; CH2), 2.02–1.84 (m, 7H;
CH), 3.34–3.28 (m, 6H; CH2O), 3.50–3.35 (m, 84H; OCH2CH2O), 3.54
(s, 3H; OH), 3.63–3.58 ppm (m, 6H; CH2OH); 13C NMR (75.5 MHz,
C6D6, 258C, TMS): d=0.17 (Si(CH3)2), 14.09 ((CH3)2SiCH2), 22.40
(SiCH2), 23.53 (CH2), 24.09 (CH), 25.67 (CH3), 61.29 (CH2OH), 70.39
(OCH2CH2O), 72.78 (OCH2), 73.76 ppm (CH2O); 29Si NMR (59.6 MHz,
C6D6, 258C, TMS): d=ꢀ68.06, ꢀ67.68, ꢀ67.03, 9.75 ppm.
Synthesis of 3,7,14-tris{[3-(2,2,3,3,4,4,5,5-octafluoropentyloxy)-
propyl]dimethylsiloxy}-1,3,5,7,9,11,14-heptaisobutyltricy-
clo[7.3.3.15,11]heptasiloxane—OFP-POSS (3): The reaction was
based on a hydrosilylation process. In a round-bottom flask
equipped with a magnetic stirrer and a reflux condenser, were
placed toluene (20 mL), 3,7,14-tris[dimethylsiloxy]-1,3,5,7,9,11,14-
heptaisobutyltricyclo[7.3.3.15,11]heptasiloxane (5 g, 5.18ꢂ10ꢀ3 mol),
and 5-(allyloxy)-1,1,2,2,3,3,4,4-octafluoropentane (4.7 g, 0.0173 mol).
This was followed by adding Karstedt’s catalyst to the mixture at
room temperature. The amount of the catalyst corresponded to
5ꢂ10ꢀ5 mol Pt per one mole of SiꢀH present in 3,7,14-tris[dime-
thylsiloxy]-1,3,5,7,9,11,14-heptaisobutylotricy-
used to record the surface pressure
p to a resolution of
ꢁ0.01 mNmꢀ1. The mean molecular area (A) was recorded in [ꢁ2].
The p–A isotherms were obtained upon symmetrical compression
caused by the movement of two barriers. During all measurements
the temperature of the subphase was kept constant on the level of
(25.0ꢁ0.1)8C by using a Julabo water circulating bath. A floating
optical table (Standa) under the Langmuir trough and all other de-
vices, minimized the vibrations. A Laminar flow hood surrounding
the equipment ensured a dust-free environment with a relative hu-
midity kept around 60–70%. Each isotherm was repeated at least
three times to ensure the reproducibility of the curves to ꢁ2 ꢁ2.
The cross-sectional areas and space-filling models for both mole-
cules were obtained by using the VEGA ZZ software.[36]
clo[7.3.3.15,11]heptasiloxane and then the whole mixture was heated
to 908C and maintained at this temperature for 3 h. The process
was monitored by infrared spectroscopy, observing the disappear-
ance of the band at n˜ =904 cmꢀ1 originating from the SiꢀH bond
present in the parent compound (i.e., 3,7,14-tris[dimethylsiloxy]-
1,3,5,7,9,11,14-heptaisobutyltricyclo[7.3.3.15,11]heptasiloxane). After
completion of the process, the post-reaction mixture was cooled
down followed by evaporation of the solvent and olefin excess
under reduced pressure. It resulted in 8.8 g (95.4%) of the product
3. The obtained product was subjected to spectroscopic analysis.
1H NMR (400 MHz, C6D6, 258C, TMS): d=0.37 (s, 18H; Si(CH3)2),
0.76–0.67 (m, 6H; (CH3)2SiCH2), 0.89–0.81 (m, 14H; SiCH2), 1.16 (d,
J=4.7 Hz, 42H; CH3), 1.79–1.66 (m, 6H; CH2), 2.19–2.01 (m, 7H;
CH), 3.44–3.29 (m, 6H; CH2O), 3.66 (t, J=13.9 Hz, 6H; OCH2), 5.74–
5.37 ppm (m, 3H; CF2H); 13C NMR (75.5 MHz, C6D6, 258C, TMS): d=
0.41 (Si(CH3)2), 14.13 ((CH3)2SiCH2), 22.89 (SiCH2), 23.65 (CH2), 24.58
CH), 26.02 (CH3), 67.63 (OCH2), 75.70 (CH2O), 108.14, 110.67, 116.02,
(CF2), 111.52 ppm (CF2H); 29Si NMR (59.6 MHz, C6D6, 258C, TMS): d=
ꢀ67.57, ꢀ67.20, ꢀ66.85, 9.45 ppm.
Brewster angle microscopy (BAM): The morphology of the mono-
layers was visualized with a Brewster angle microscope (Micro
BAM; KSV Nima) coupled with the Langmuir trough and installed
on an anti-vibration table. Different domain shapes and sizes ob-
served as different reflection density or gray levels indicate the
monolayer phases. These morphologies are also related to changes
in the thickness of the monolayer due to the formation of three-di-
mensional aggregates. BAM images were taken with a CCD camera
during the monolayer compression. The light source was a laser
diode (l=659 nm). The field of view was 3.6ꢂ4 mm2 and the reso-
lution was approximately six microns per pixel (i.e., better than
twelve microns resolution according to Rayleigh’s criterion; the
system is not diffraction limited). During the experiment, a flat
black glass plate was placed under the subphase to absorb the re-
fracted beam.
NMR spectroscopy: 1H NMR (400 MHz), 13C NMR (75 MHz), and
29Si MNR (59 MHz) spectra were recorded on a Bruker Ascend
400 MHz NanoBay spectrometer at room temperature by using
C6D6 as a solvent.
Surface potential: The surface potential (DV) was measured by
using the non-contact and non-destructive vibrating capacitor
method. The surface potential meter (SPOT, KSV Nima) recorded
the DV simultaneously with the p–A isotherm by using two elec-
trodes; the first one was placed just above the water surface,
whereas the counter electrode was immersed into the subphase.
The dynamic range of the measurement was ꢀ5 to +5 V with the
sensitivity ꢁ1 mV.
Substrate preparation: Quartz slides (purchased from PHASIS, Lꢂ
WꢂD 25ꢂ25ꢂ1 mm3) were used as substrates for the LB film dep-
osition. Prior to starting the Langmuir–Blodgett experiments, the
quartz slides were prepared by heating to (75ꢁ5)8C in a 5:1:1 by
volume mixture of H2O/NH4OH (27% concentrated)/H2O2 (30% by
volume) for 0.5 hour. After rinsing with an abundant amount of ul-
trapure water and drying in the atmosphere, the hydrophilic sub-
strates were ready (with a contact angle equal to 158) for the LB
film deposition.
FTIR spectroscopy: FT-R spectra were recorded on a Bruker Tensor
27 Fourier transform infrared spectrometer equipped with
a Specac Golden Gate diamond ATR unit. In all cases, sixteen scans
with a resolution of 2 cmꢀ1 were collected for a spectrum.
Real-time FTIR spectroscopy: Real-time infrared spectroscopy has
been applied to monitor the hydrosilylation of the olefins with
3,7,14-tris[dimethylosiloxy]-1,3,5,7,9,11,14-heptaisobutyltricy-
clo[7.3.3.15,11]heptasiloxane. The measurements were performed on
a Mettler-Toledo ReactIR 15 spectrometer equipped with a 9.5 mm
AgX DiComp (diamond) probe and a liquid nitrogen-cooled MCT
detector. The spectra were taken with a resolution of 4 cmꢀ1 col-
lecting fifty scans for each spectrum at intervals of 15 s. The reac-
tion progress in the studied systems of parent compounds and
catalysts was quantified by observing the rate of changes occur-
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Center (Poland), Project UMO-2012/05/B/ST 02200. The authors
wish to thank Dr. Jarosław Makowiecki for fruitful discussion
and his assistance in the realization of the AFM measurements.
Keywords: hydrosilylation · Langmuir–Blodgett films · POSS ·
silsesquioxanes · surface chemistry
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Received: May 23, 2016
Published online on && &&, 0000
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FULL PAPER
&
Silsesquioxanes
M. Dutkiewicz, J. Karasiewicz,
M. Rojewska, M. Skrzypiec, K. Dopierała,
K. Prochaska, H. Maciejewski*
&& – &&
Two POSS derivatives with open-cage
structures, containing fluoroalkyl- or hy-
droxy-terminated polyether groups
have been synthesized and were sub-
jected to the analysis of their surface
properties and interfacial behavior (see
figure). The properties of monolayers
formed on the water surface depend
strongly on the chemical structure of
the POSS compound. The results sug-
gest that they can be good candidates
for obtaining nanostructured thin film
coatings.
Synthesis of an Open-Cage Structure
POSS Containing Various Functional
Groups and Their Effect on the
Formation and Properties of Langmuir
Monolayers
Chem. Eur. J. 2016, 22, 1 – 13
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers! ÞÞ