Silica-diblock fluoropolymer hybrids synthesized by surface-initiated atom transfer radical polymerization

Article abstract of DOI:10.1039/c3ra47393g

Silica/diblock fluoropolymer hybrids SiO₂-g-PMMA-b-P12FMA for coatings were synthesized by the silica surface-initiating atom transfer radical polymerization (SI-ATRP) of methylmethacrylate (MMA) and dodecafluoroheptyl methacrylate (12FMA). Silica surface initiator (SiO₂-initiator) was obtained by 10-25 nm fumed silica particles grafted hydrosilylated undec-10-enyl, 2-bromo-2-methyl propionate with a density of 0.573 mmol g ^-1. The SI-ATRP approach in this paper displays the diagnostic criteria of controlled radical polymerization by the analysis of ¹H NMR, ¹⁹F NMR and SEC-MALLS analysis, after comparing with the conventional initiator of ethyl 2-bromoisobutyrate (EBiB) for the E-PMMA-b-P12FMA diblock copolymer. Three mass ratios of SiO₂- initiator/MMA/12FMA as 1/72.50/18.15, 1/72.50/45.38 and 1/181.26/18.15 were used to obtain the SiO₂-g-PMMA-b-12FMA hybrids. The hybrids show 25-30 nm core-shell particles in CHCl₃ solution composed of a P12FMA core and PMMA shell, but densely twined together as agglomerated particles. The PMMA-b-P12FMA shell grafted onto silica particles obviously increases the surface roughness of the film (50-500 nm), more than the E-PMMA-b-12FMA film (30 nm), and thereby contributes to the hydrophobic (112-118°) and oleophobic (45-78°) properties of the films. Increasing the P12FMA concentration (1/72.50/45.38) could result in stronger migration of the P12FMA segments onto the film surface, and therefore led to a lower surface free energy (10.97 mN m^-1), increased advancing and receding for water contact angles (112° and 108°) and the highest cetane contact angles (74° and 70°), the lower water absorption and viscoelasticity, but a high thermostability at 420-450 °C. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c3ra47393g

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PAPER
Silica-diblock fluoropolymer hybrids synthesized
by surface-initiated atom transfer radical
polymerization†
Cite this: RSC Adv., 2014, 4, 13108
*
Hongpu Huang and Ling He
Silica/diblock fluoropolymer hybrids SiO2-g-PMMA-b-P12FMA for coatings were synthesized by the silica
surface-initiating atom transfer radical polymerization (SI-ATRP) of methylmethacrylate (MMA) and
dodecafluoroheptyl methacrylate (12FMA). Silica surface initiator (SiO2-initiator) was obtained by 10–25
nm fumed silica particles grafted hydrosilylated undec-10-enyl, 2-bromo-2-methyl propionate with a
density of 0.573 mmol gꢀ1. The SI-ATRP approach in this paper displays the diagnostic criteria of
controlled radical polymerization by the analysis of 1H NMR, 19F NMR and SEC-MALLS analysis, after
comparing with the conventional initiator of ethyl 2-bromoisobutyrate (EBiB) for the E-PMMA-b-P12FMA
diblock copolymer. Three mass ratios of SiO2-initiator/MMA/12FMA as 1/72.50/18.15, 1/72.50/45.38 and
1/181.26/18.15 were used to obtain the SiO2-g-PMMA-b-12FMA hybrids. The hybrids show 25–30 nm
core–shell particles in CHCl3 solution composed of a P12FMA core and PMMA shell, but densely twined
together as agglomerated particles. The PMMA-b-P12FMA shell grafted onto silica particles obviously
increases the surface roughness of the film (50–500 nm), more than the E-PMMA-b-12FMA film (30 nm),
and thereby contributes to the hydrophobic (112–118ꢁ) and oleophobic (45–78ꢁ) properties of the films.
Increasing the P12FMA concentration (1/72.50/45.38) could result in stronger migration of the P12FMA
segments onto the film surface, and therefore led to a lower surface free energy (10.97 mN mꢀ1),
increased advancing and receding for water contact angles (112ꢁ and 108ꢁ) and the highest cetane
contact angles (74ꢁ and 70ꢁ), the lower water absorption and viscoelasticity, but a high thermostability at
420–450 ꢁC.
Received 6th December 2013
Accepted 20th January 2014
DOI: 10.1039/c3ra47393g
www.rsc.org/advances
also increases the compatibility of the silica particles with the
polymer matrix.
1. Introduction
Generally, there are two approaches to chemically attach
polymer chains to a silica surface:8,11 (1) the “graing to”
method, where the end-functionalized polymers react with an
appropriate surface and (2) the “graing from” method, where
polymer chains are grown from the surface of the initiators.12
The modication of silica particles via the substitution of
surface silanol groups with mono- or multifunctional silanes has
been proven to be a reliable approach to achieve satisfactory
surface coverage of the desired functional groups.13,14 Using the
graing from approach by controlled/“living” silica surface-
initiated atom transfer radical polymerization (SI-ATRP), many
silica hybrid particles are synthesized, such as the growth of
polystyrene (PS) from high-surface-area silica gels,15–17 the
multilayer organo–silica/polystyrene/polyaniline composite
particles,14 the core–shell silica–polypeptide composite parti-
cles,18 the core–shell structured silica encapsulated per-
ylenediimide (PDI) nanoellipsoids,19 and the silica nanoparticles
bearing vinyl groups and covered by uorinated chains.20
Therefore, the SI-ATRP technique has many advantages over
conventional radical polymerizations in controlling the polymer
architecture and molecular weight for obtaining hybrids.21–24
Inorganic/polymeric hybrids have attracted great interest in
improving the properties of nanostructured polymeric mate-
rials.1–4 Silica is one of the most investigated inorganic particles
for introducing into polymer matrices due to its easy prepara-
tion, controlled particle size and well-understood surface
chemistry.5–7 It is reported that the extreme nonwetting
behavior of lm surfaces could be obtained when silica particles
are embedded into the surface for multiple scales of roughness
and re-entrant curvature.8,9 Therefore, silica/polymer hybrids
have been extensively studied as coating materials. However,
the key point in controlling the properties of nal materials is
how the silica particles are dispersed in the polymer matrix. One
effective way is to gra polymer chains chemically onto the
silica particles to avoid agglomeration.10 This does not only
improve the stability of the silica particles in suspension, but
Department of Chemistry, School of Science, Xi'an Jiaotong University, Xianning West
Road, 28, Xi'an, 710049, China. E-mail: heling@mail.xjtu.edu.cn; Fax: +86-29-
82668559; Tel: +86-29-82668554
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c3ra47393g
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Introducing uorine-containing substituents into a silica/ catalyst (platinum–divinyltetramethyldisiloxane complex),
polymer could result in dramatic changes in the material prop- undecylenyl alcohol (10-undecen-1-ol, C11H22O), 2-bromo-2-
erties of low surface energy (typically 5 mN mꢀ1) and good methylpropionyl bromide (BMPB), methylene chloride, chloro-
chemical/thermal stability.25–27 Their “oleophobicity” acts as a form, dichloromethylsilane (DCMS), tetrahydrofuran (THF),
driving force for obtaining low surface free energy lms and is N,N,N9,N9,N0-pentamethyldiethylenetriamine (PMDETA), cop-
useful from a practical point of view. It is reported that such a per(I) bromide and 2-bromoisobutyrylbromide (BiBB) were used
modication also leads to signicant changes in the high as received. N,N-Dimethylformamide (DMF) was stirred over
thermal stability (up to 400 ꢁC) compared to physically absorbed CaH2 for 12 h at room temperature, and then distilled under
complexes,28 which ensures the successful development and reduced pressure prior to use.
application of uoroalkyl-functionalized silica hybrids in
producing durable nonwetting surfaces.29–32 On the other hand,
2.2 Synthesis of silica surface-initiator
the self-assembly of uorinated block copolymers could produce
The rst step was the synthesis of undec-10-enyl, 2-bromo-2-
signicant thin lms for coatings.29,30 In comparison to bulk
methyl propionate. 6.0 ml 10-undecen-1-ol (29.60 mmol), 20.0 ml
systems, self-assembled thin lms (ꢂ100 nm thickness) are
dry methylene chloride and 7.0 ml triethylamine (50.22 mmol)
strongly inuenced by the surface energies and roughness of the
were added to a 100 ml Schlenk ask. Then, 4.0 ml BMPB
lm surface via varying the molar mass of the constituent
(32.36 mmol) was added dropwise at 0 ꢁC. The reaction was
blocks.31–33 To our knowledge, the surface-initiated atom transfer
carried out under nitrogen protection at 0 ꢁC for 2 h and then at
radical polymerization (SI-ATRP) of uorinated chains graed
room temperature for 24 h. The crude product was isolated by
onto silica surface has never been described in the literature.
ltration and extraction using an aqueous-saturated ammonium
In this article, the synthesis and properties of the silica
chloride solution. The obtained undec-10-enyl, 2-bromo-2-
graing diblock uoroacrylate copolymer hybrids SiO2-g-
methyl propionate was then distilled at 55 ꢁC under reduced
PMMA-b-P12FMA are reported. The synthesis was performed in
pressure (6–7 mmHg) (yield: 75%).
two steps: (i) the preparation of monolayer SiO2-initiator by the
The second step was the hydrosilylation of undec-10-enyl,
reaction of fumed silica particles with hydrosilylated undec-10-
2-bromo-2-methyl propionate. A mixture of 1.2 ml undec-10-
enyl, 2-bromo-2-methyl propionate. (ii) the SI-ATRP synthesis of
enyl, 2-bromo-2-methyl propionate (6.27 mmol), 60 ml Karstedt's
poly(methylmethacrylate) (PMMA) and poly(dodecauoroheptyl
catalyst and 9.0 ml DCMS (86.06 mmol) was added to a 100 ml
methacrylate) (P12FMA) to obtain silica graed diblock copol-
dried Schlenk ask, and was allowed to react in the dark for 24 h
ymer hybrid SiO2-g-PMMA-b-P12FMA in the mass ratio of SiO2-
at 40 ꢁC under nitrogen protection. The catalyst was removed by
initiator/MMA/12FMA
¼
1/72.50/18.15, 1/72.50/45.38 and
quickly ltering the product through a short plug of dry silica,
and the excess DCMS was removed under reduced pressure.
Then, the product was used directly for the silanization step to
obtain hydrosilylated undec-10-enyl, 2-bromo-2-methyl propio-
nate (purity: 90%).
1/181.26/18.15. Meanwhile, for comparison, the conventional
initiator of ethyl 2-bromoisobutyrate (EBiB) was also used to
produce the diblock copolymers E-PMMA-b-P12FMA in this
paper. Their chemical structures were characterized by 1H NMR,
19F NMR spectroscopy and size exclusion chromatography-
multiangle laser light scattering (SEC-MALLS). The obtained
SiO2-g-PMMA-b-P12FMA hybrids were observed by transmission
electron microscopy (TEM). The surface properties of the lms
were investigated by static contact angle (SCA) and dynamic
contact angle (DCA) measurements, atomic force microscope
(AFM) and X-ray photoelectron spectroscopy (XPS). The water
absorption of the lm was monitored by the quartz crystal
microbalance with dissipation (QCM-D). The thermostablity
was further analyzed by thermo gravimetric analysis (TGA).
Meanwhile, the results for SiO2-g-PMMA-b-P12FMA and
E-PMMA-b-P12FMA were compared.
The last step was the synthesis of silica surface-initiator
ꢁ
(SiO2-initiator). Silica particles were dried in vacuum at 110 C
for 6–7 h and were dispersed in dry THF by ultrasonication.
15 ml silica particle solution in THF was added to a 200 ml dried
Schlenk ask. Then, 0.25 g hydrosilylated undec-10-enyl,
2-bromo-2-methyl propionate (0.576 mmol) was introduced
through a cannula, followed by the dropwise addition of 1.25 ml
triethylamine (8.97 mmol). The reaction was carried out under
N2 atmosphere at 40 ꢁC for 40 h. The particles were isolated by
centrifugation and puried by Soxhlet extraction exposed to
reuxing 50/50 (v/v) methylene chloride/diethyl ether for 8 h.
The puried particles were redispersed in 10 ml of DMF. The
solution was used as the silica initiator for ATRP. The synthesis
scheme of the SiO2-initiator is given in Scheme 1(I).
2. Experimental
2.1 Materials
2.3 Synthesis of SiO2-g-PMMA-b-P12FMA hybrids by SI-ATRP
Fumed silica (VK-SP15) with an average diameter of 10–25 nm
and a specic area of 230 m2 gꢀ1 was supplied by the Hang Zhou The mixture of 0.4546 mmol CuCl, 0.0358 mmol CuCl2, 32.96
New Material Company of China. Dodecauoroheptyl methac- mmol MMA and 0.4546 mmol PMDETA were added to a 100 ml
rylate (C11H8O2F12, 12FMA, liquid) was supplied by XEOGIA dried Schlenk ask under N2 atmosphere, which was sealed
Fluorine-Silicon Chemical Co. Ltd. (China). Methyl methacry- with a rubber septum prior to three vacuum/N2 cycles. The
late (MMA, 99% wt, Aldrich) was puried by extraction with 5% mixture was stirred until a homogeneous medium formed.
aqueous sodium hydroxide and distilled from calcium hydride Then, 10 ml SiO2-initiator (0.4546 mmol in DMF) was added to
prior to use. Triethylamine was puried by distillation. Karstedt the ask by cannula transfer and the reaction mixture was
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polymerization procedure was the same as for the SiO2-initiator.
The polymerization conditions and detailed values are listed in
Table 1.
2.5 Characterization
Nuclear magnetic resonance (1H NMR and 19F NMR) spectros-
copy was used to characterize the chemical structures of SiO2-g-
PMMA and SiO2-g-PMMA-b-P12FMA by a BrukerAC500 NMR
spectrometer using the solvent peak as reference (CDCl3). The
molecular weights and molecular weight distribution of the
resultant copolymers were measured using a DAWN EOS size
exclusion chromatography-multiangle laser light scattering
(SEC-MALLS) instrument equipped with a viscometer (Wyatt
Technology, USA) using the SEC/DAWN EOS/Optilab rEX/QELS
model at 25 ꢁC, aer SiO2-g-PMMA and SiO2-g-PMMA-b-P12FMA
were treated by HF to isolate SiO2. DMF was used as the eluent
at a ow rate of 0.5 ml minꢀ1. The individual particles of
obtained SiO2-g-PMMA-b-P12FMA hybrid were observed by
transmission electron microscopy (TEM) with a JEM-3010 TEM
at an acceleration voltage of 100 kV. Samples were prepared by
drop-casting micelle in CHCl3 solution onto carbon-coated
copper grids, and then air-drying at room temperature before
measurement.
The lm was prepared by casting 10% wt homogeneous
solution of SiO2-g-PMMA-b-P12FMA in CHCl3 on a glass slide
and drying at ambient temperature for 72 h. The lm properties
were investigated by X-ray photoelectron spectroscopy (XPS),
atomic force microscope (AFM), static contact angle (SCA),
dynamic contact angle (DCA) and surface free energy. XPS
measurements were processed on the air exposed lm surface
by an AXIS ULTRA (England, KRATOS ANALYTICAL Ltd) using
an Al-Ka monochromatic X-ray source (1486.6 eV) operated at
150 W. The overview scans were obtained with a pass energy of
160 eV and acquisition time of 220 s. NT-MDT new Solver-Next
was used to characterize the surface topographies and rough-
ness (root-mean-square roughness) of the same lm samples.
The measurements were taken at room temperature under 38–
42% R.H. Tip information: radius <10 nm, cantilever length 90
ꢃ 5 mm; width 40 ꢃ 3 mm; thickness 2.0 ꢃ 0.5 mm, resonant
frequency 330 kHz, force constant 48 N mꢀ1. SCA measure-
ments for both the deionized water and hexadecane on the air-
exposed lm surfaces were performed on a JY-82 contact angle
goniometer (Hebei Chengde Testing Machine Co. Ltd China) by
Scheme 1 Synthesis of the SiO2-initiator (I) and SiO2-g-PMMA-b-
P12FMA (II).
heated to 90 ꢁC and was kept for 12 h. In this case, the
appearance of the reaction system varied from light green to
turquoise blue, indicating a change in the nature of the copper
complexes. Finally, 8.250 mmol 12FMA was added and was
allowed to continue the reaction for 12 h. When the polymeri-
zation was stopped, THF was added to dilute the mixture, and
the nanoparticles were isolated by centrifugation. The particles
were repeatedly dispersed in THF, isolated by centrifugation to
remove physically adsorbed polymers and the product SiO2-g-
PMMA-b-P12FMA was dried in a vacuum oven at 40 ꢁC over-
night. The conversion of MMA aer 12 h reaction was 82% aer
12 h reaction and the conversion of 12FMA aer 12 h reaction
was 35%. The detailed synthesis route for SiO2-g-PMMA-b-
P12FMA is given in Scheme 1(II). In this paper, three mass
ratios of SiO2–Br/MMA/12FMA ¼ 1/72.50/18.15, 1/72.50/45.38
and 1/181.26/18.15 for sample S1, S2 and S3 were used to obtain
SiO2-g-PMMA-b-P12FMA hybrid particles, as shown in Table 1.
2.4 Synthesis of E-PMMA and E-PMMA-b-P12FMA with the
EBiB initiator
In order to compare the differences of the SiO2-initiator and the sessile drop method with a microsyringe at 25 ꢁC. The
normal initiator, EBiB was selected as the initiator, instead of instrument error is ꢃ0.50ꢁ. An average of nine readings of
the SiO2-initiator to obtain E-PMMA-b-P12FMA (sample S4). The contact angles was used as the nal value for each sample (error
Table 1 Component values for the preparation of SiO2-g-PMMA-b-12FMA and E-PMMA-b-12FMA
SiO2–Br/MMA/12FMA
(molar ratios)
SiO2–Br
(mmol)
EBiB
(mmol)
MMA
(mmol)
12FMA
(mmol)
CuCl
(mmol)
CuCl2
(mmol)
PMDETA
(mmol)
DMF
(ml)
Samples
S1
S1
S3
S4
1/72.50/18.15
1/72.50/45.38
1/181.26/18.15
E-PMMA-P12FMA
(1/77.92/22.0)
0.4546
0.4546
0.4546
—
—
—
—
0.5127
32.96
32.96
82.40
39.95
8.250
20.63
8.250
10.00
0.4546
0.4546
0.4546
0.5132
0.0358
0.0358
0.0358
—
0.4546
0.4546
0.4546
0.5132
15
15
15
15
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about 2–3%). The surface free energies of the samples were
evaluated by applying the Owens and Wendt method based on
static contact angle values.
A quartz crystal microbalance with dissipation (QCM-D)
monitoring (Q-Sense E1, Sweden) at 25 ꢁC was performed to
discuss the water adsorption and viscoelasticity of SiO2-g-
PMMA-b-P12FMA lms. AT-cut piezoelectric quartz crystals
covered with gold were used with a fundamental frequency of
5 MHz and a diameter of 14 mm. The lm samples for the
measurements were prepared by dropping 2 ml of the polymer
solutions (5% wt, ltering through 0.45 mm disposable PA
membrane) on the surfaces of quartz crystals and drying in a
vacuum oven at 30 ꢁC for 12 h. The Df and DD were recorded at
15 MHz with air as the baseline.
The thermal stabilities of the SiO2-g-PMMA-b-P12FMA hybrid
particles were evaluated by thermo gravimetric analysis (TGA)
performed under N2 atmosphere with the rate of temperature
rise 10 ꢁC minꢀ1 at a high temperature of 800 ꢁC using TGA
analyzer (STA449C Jupiter from NETZSCH).
3. Results and discussion
3.1 Synthesis of the SiO2-g-PMMA-b-P12FMA hybrid
Fig. 1 1H NMR spectra of undec-10-enyl, 2-bromo-2-methyl propi-
onate (I) and the hydrosilylated undec-10-enyl, 2-bromo-2-methyl
propionate (II).
The procedures for the synthesis of the SiO2-initiator and SiO2-
g-PMMA-b-P12FMA are shown in Scheme 2. The SiO2-initiator
was prepared by the hydrosilylation of undec-10-enyl, 2-bromo-
2-methyl propionate (UBMP) and silica nanoparticles. The
carbon–carbon double bonds of UBMP serve as the growth polymerized onto the SiO2 particle's surface of the SiO2-initi-
sites during the subsequent hydrosilylation with dichlor- ator. Furthermore, the TGA curves (ESI, S2†) indicate that the
omethylsilane (DCMS). This is conrmed in Fig. 1(I) for UBMP weight retention at 800 ꢁC is 99.7% for SiO2 particles due to the
by d 1.29 (2H, CH2), 1.67 (2H, CH2), 1.93 [6H, (CH3)2], 2.04 (2H, water loss, but the initiator particles have 78.9% weight reten-
ꢁ
tion. If the mass percentage of the residue at 800 C is used as
CH2), 4.16 (2H, CH2), 4.91–5.01 (2H, CH2) and 5.80 (1H, CH),
and in Fig. 1(II) for hydrosilylated UBMP by d 0.50 [3H, CH3], the reference, the weight increase of SiO2-initiator particles
0.86 (2H, CH2), 1.28–1.31 [18H, (CH2)8], 1.68 (2H, CH2), 1.92 relative to that of SiO2 would be 20.8%. Therefore, the density of
[6H, (CH3)2] and 4.17 (2H, CH2).
the SiO2-initiator is 0.573 mmol per gram SiO2-initiator.
The end groups of –SiCH3Cl2 in hydrosilylated undec-10- Furthermore, the density of Br on the SiO2 surface is calculated
enyl, 2-bromo-2-methyl propionate formed chemical bonds as 0.05% (i.e. 0.625 mmol per gram SiO2-initiator) from the XPS
with the –OH groups on the surface of silica particles to obtain a data of SiO2–Br (Fig. 5a).
monolayer of the anchored silica particles ATRP-initiator (SiO2-
initiator). The FTIR spectrum for the SiO2-initiator (ESI, S1†)
SiO2-g-PMMA-b-P12FMA hybrids were obtained by the SI-
ATRP of PMMA-b-P12FMA shell on the surface of the silica core.
shows the absorption at 2983 and 2899 cmꢀ1 due to the alkyl C– The 1H NMR spectrum of SiO2-g-PMMA (Fig. 2I), SiO2-g-PMMA-
H stretching vibration, but these absorptions are non-existent b-P12FMA (Fig. 2II) and 19F-NMR spectrum of SiO2-g-PMMA-b-
in the SiO2 particles, which indicates that the initiator has been P12FMA (Fig. 2III) reveal the characteristic signals at d 0.841 &
Scheme 2 Formation of the SiO2-g-PMMA-b-P12FMA hybrids.
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1.020 ppm, 1.832–1.960 ppm and 3.600 ppm in Fig. 2I for the PMMA (1/181.26) and E-PMMA (1/77.92), respectively. For the
PMMA segment, the signals at 4.456 ppm and 5.513 ppm in two initiators to obtain diblock copolymers, the poly-
Fig. 2II for the P12FMA segment, and uorine multiple peak dispersity index (PDI) of 1.12–1.25 in Fig. 3b reveals a narrow
signals in the 19F-NMR in Fig. 2III for P12FMA. These results distribution of molecular weight, which illustrates that the
indicate that SiO2-g-PMMA-b-P12FMA was successfully prepared polymerization initiated both by SiO2-initiator and EBIB are
by SI-ATRP.
typically controllable ATRP. The monomodal molecular
The SEC-MALLS results of the SiO2-g-PMMA and SiO2-g- weight distributions in Fig. 3b are 11 700, 18 000, 21 300 g
PMMA-b-P12FMA are given in Fig. 3 and Table 2. PMMA and molꢀ1 for SiO2-g-PMMA-b-P12FMA (SiO2/MMA/12FMA ¼ 1/
E-PMMA-b-P12FMA (E/MMA/12FMA ¼ 1/77.92/22.00) are 72.50/18.15, 1/72.50/45.38 and 1/181.26/18.15), respectively.
used for comparison in order to conrm the controlled Table 2 indicates that the obtained Mn is lower than the
radical polymerization of the SI-ATRP approach. Fig. 3a theoretical value for all the samples, and that Mn for
shows that the molecular weights were 7558.7 g molꢀ1
,
E-PMMA-P12FMA (13 500 g molꢀ1) is higher than SiO2-g-
molꢀ1), which
17 810.75 g molꢀ1 and 7786.67 g molꢀ1 for PMMA (1/72.5), PMMA-P12FMA (1/72.50/18.15) (11 700
g
shows the lower activity of the SiO2-initiator. All the results
from the 1H-NMR, 19F-NMR and SEC-MALLS conrm that
the synthesis of SiO2-g-PMMA-P12FMA proceeded as Table 1
for the monomer feed ratios, reactant concentrations, reac-
tion conditions employed and synthetic routes as expected.
3.2 The particles of SiO2-g-PMMA-b-P12FMA in CHCl3
solution
It is known that the self-assembled aggregates formed by
block copolymers strongly depend on the composition of
the segments. Herein, the inuence of different SiO2/
PMMA/P12FMA mass ratios as 1/72.50/18.15, 1/72.50/45.38
and 1/181.26/18.15 on the morphology of SiO2-g-PMMA-b-
P12FMA aggregates in CHCl3 solution is explored by TEM
(Fig. 4), based on the different solubilities of the segment
PMMA (good) and the segment P12FMA (poor) in CHCl3
solution. In order to better understand the morphology of
SiO2-g-PMMA-b-P12FMA particles, the particles of E-PMMA-b-
P12FMA in CHCl3 solution were used for comparison
(Fig. 4a). E-PMMA-b-P12FMA could produce about 100–150
nm spherical particles composed of the dark core and the
light shell observed. As the unsolvable chains in CHCl3
solution could aggregate into the harder cores and the solv-
able chains into the shells of the micelles or vesicles,32 the
inner dark core should be formed by P12FMA, and the outer
light shell should be formed by PMMA. However, for the
morphology of the three SiO2-g-PMMA-b-P12FMA samples,
25–30 nm core–shell spherical particles composed of the
dark core and the light shell are observed in Fig. 4b–d by the
particle shells densely twining together as the agglomerated
particles. Comparatively, the relatively fewer PMMA and
P12FMA segments in S1 (1/72.50/18.15) makes the particles
arrange closely (Fig. 4b), the poor solubility of P12FMA
segment enables S2 (1/72.50/45.38) to form congested
aggregates (Fig. 4c), but the higher content of PMMA segment
in S3 (1/181.26/18.15) leads to the formation of uniformly
distributed particles and less agglomeration (Fig. 4d) attrib-
uted to the sufficient solubility of PMMA in CHCl3 solution. It
can also be found that the size of the SiO2-g-PMMA-b-P12FMA
hybrids (25–30 nm) are much smaller than the E-PMMA-b-
P12FMA particles (100–150 nm), indicating that SiO2 has
been graed by the dense PMMA-b-P12FMA via the SI-ATRP
Fig. 2 1H-NMR spectra of the SiO2-g-PMMA (I), SiO2-g-PMMA-b-
P12FMA (II), and 19F-NMR spectrum of the SiO2-g-PMMA-b-P12FMA (III). approach.
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Fig. 3 GPC curves of (a) PMMA, and (b) diblock copolymer of E-PMMA-P12FMA (S4), the PMMA-b-P12FMA cleaved from SiO2-g-PMMA-b-
P12FMA in S1 (1/72.50/18.15), S2 (1/72.50/45.38) and S3 (1/181.26/18.15).
3.3 The surface composition, morphology and wettability of
the SiO2-g-PMMA-b-P12FMA lms
These aggregates are expected to inuence the surface compo-
sition, morphology, and therefore the resulting hydrophobic
character of the lms. The chemical compositions on the lm
top surface were analyzed by XPS in Fig. 5. The SiO2-initiator
(Fig. 5a) and E-PMMA-b-P12FMA were used for comparison
(Fig. 5e). In Fig. 5a, the electron binding energy of O1s, C1s, Si2p
and Br3d at 530.1 eV, 283.0 eV, 101.2 eV and 68.6 eV, respec-
tively, indicate that the SiO2-initiator has been successfully
prepared. For the XPS spectrum of the SiO2-g-PMMA-b-P12FMA
lms of S1 (Fig. 5b, 1/72.50/18.15), S2 (Fig. 5c, 1/72.50/45.38)
and S3 (Fig. 5d, 1/181.26/18.15), the lms are mainly composed
of the elements F, O, C and Si, but the peak of Si is much
weaker. Comparing with the stronger characteristic signal of
the F element in E-PMMA-b-P12FMA Fig. 5e, b(S1) and c(S2)
show less characteristic signals than Fig. 5e, but stronger
signals than Fig. 5d(S3). This has been proven by the chemical
composition in Table 3. The migration of P12FMA segments
Fig. 4 TEM images for E-PMMA-b-P12FMA (a, S4) and SiO2-g-PMMA-
b-P12FMA for S1 (b, 1/72.50/18.15), S2 (c, 1/72.50/45.38) and S3 (d, 1/
onto the lm surface leads to the higher uorine content of S1
(26.67%) and S2 (26.96%) because of the higher contribution of
the P12FMA segments, but the lower uorine content of S3
(18.21%) due to the lower P12FMA content.
181.26/18.15) in CHCl3 solution.
roughness of 500 nm is observed on the surface of S2 (Fig. 6c,
1/72.50/45.38), but a few individual heaves (the lighter points)
The surface morphology of the SiO2-g-PMMA-b-P12FMA
lms cast from CHCl3 solution was investigated by AFM for the as domains of approximately 40–60 nm height are scattered on
surface roughness (Fig. 6). Compared with the compact smooth the lm surface of S3 to form 50 nm root mean square rough-
surface of 30 nm root mean square roughness for E-PMMA-b- ness (Fig. 6d, 1/181.26/18.15).
P12FMA lm (Fig. 6a), three SiO2-g-PMMA-b-P12FMA lms were
distributed with nanoscale particle agglomerates. Island type
structures as 250 nm root mean square roughness are formed
on the lm surface of S1 (Fig. 6b, 1/72.50/18.15), the obvious
honeycomb structure as 1–2 mm domains as a root mean square
Actually, this composition and roughness will contribute
much to the surface wettability, as shown in Table 3 evaluated
by the static contact angles (SCAs) measurements for water and
cetane, and the calculated surface free energy (gS). The SCAs
indicate that the three lm surfaces are not only sufficiently
Table 2 GPC characterization of PMMA-b-P12FMA cleaved from the SiO2 surface
Sample
Mw/Mn
Mn (ꢄ 104) g molꢀ1
Mw (ꢄ 104) g molꢀ1
Mn (ꢄ 104)(theo) g molꢀ1
S1 (1/72.50/18.15)
S2 (1/72.50/45.38)
S3 (1/181.26/18.15)
S4 (1/77.92/22.00)
1.21
1.25
1.15
1.12
1.17
1.80
2.13
1.35
1.42
2.25
2.45
1.51
1.49
2.58
2.58
1.57
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Fig. 5 XPS scanning spectrum for the powder of SiO2–Br (a), the air-side surface of SiO2-g-PMMA-b-P12FMA for S1 (b, 1/72.50/18.15), S2 (c,
1/72.50/45.38) and S3 (d, 1/181.26/18.15) and E-PMMA-b-P12FMA (e, S4).
hydrophobic (112–118ꢁ) compared with the S4 lm (108ꢁ), but also suggest that the graing of uorinated copolymers onto
also that the S1 and S2 lm are more oleophobic (73–78ꢁ) than silica nanoparticles could obtain, not only the oleophobic
the S4 lm (56ꢁ). The obviously higher SCAs could lead to the property of lm surface, but also an increase in the hydropho-
lower surface energy for S1 and S2 (12.46 mN mꢀ1 and 10.97 mN bicity of such lms, and thus the lower surface free energy.
mꢀ1) than the E-PMMA-b-P12FMA lm (17.48 mN mꢀ1), Additionally, the dynamic contact angle (DCA) measurements
contributed to by the higher F content on the top surface and of water (WCA) and cetane (CCA) for the lms are measured in
higher surface roughness. Although S3 is less oleophobic (45ꢁ) Table 3. The surface of the S3 lm obtains the highest qa (114ꢁ)
than others, it is the most hydrophobic (118ꢁ), and gets the and qr (106ꢁ) for WCA, but the lowest qa (44ꢁ) and qr (38ꢁ) for
highest surface energy (22.33 mN mꢀ1) due to the lower uorine CCA, and the biggest qh of WCA and HAC (6ꢁ) among the three
content of S3 (18.21%). Compared with S1 and S4, the results hybrids, revealing that increasing the PMMA content favors a
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Table 3 Contact angles, surface free energy, and chemical compositions of the filmsa
Element content/% wt
gS/mN mꢀ1
F
Si
C
O
ꢁ
ꢁ
Sample
qH O
/
qcetane
/
2
SiO2–Br
—
—
—
—
65.54
1.34
0.63
1.56
—
16.94
53.84
54.21
58.87
55.68
17.47
18.15
18.20
20.98
20.45
S1 (1/72.50/18.15)
S2 (1/72.50/45.38)
S3 (1/181.26/18.15)
S4 (1/77.92/22.0)
112 (110 106, 4)*
114 (112 108, 4)
118 (114 108, 6)
108 (105, 97, 8)
73 (72, 67, 5)*
78 (74,70, 4)
45 (44,38, 6)
56 (52,44, 8)
12.46
10.97
22.33
17.48
26.67
26.96
18.21
23.87
a
Where, * the numbers in brackets refer to the advancing angle (qa), receding angle (qr) and hysteresis angle (qh ¼ qa ꢀ qr), respectively.
higher contact angle hysteresis, and therefore better hydro- equilibrium, showing the uoride side chains are vertically
phobic, but less oleophobic properties than increasing the distributed on the surface for a relatively ordered structure, so
P12FMA content in S2. The highest qh of WCA and HAC for the that the adsorbed water forms a relatively loose adsorption layer
S4 lm (8ꢁ for WCA and HCA) indicates that the SiO2 involved in on the lm surface. This process is suggested in the adsorption
the copolymer is favourable for obtaining lower contact angle model of Fig. 7I. In order to explain the uorine-containing
hysteresis.
groups migrating onto the lm surface during the lm forma-
Furthermore, in order to understand the surface water tion, the uorinated brush segment upon contact with water is
adsorption of E-PMMA-P12FMA and SiO2-g-PMMA-P12FMA placed further towards the Si-particle surface, and the PMMA
lms casting from CHCl3 solutions, the water adsorption curves region is placed closer to the Si-particle surface in the adsorp-
investigated by QCM-D are obtained in Fig. 7. The Df in the tion model of Fig. 7. The adsorbed amount of water and the
adsorption curves is used to indicate the adsorbed amounts of viscoelasticity of the adsorbed layer for both of them at the end
probe liquids and the DD is used to evaluate the viscoelasticity of absorption are similar (Df ¼ 450, DD ¼ 130 and 170) due to
of the adsorbed layer. In Fig. 7a for E-PMMA-P12FMA (S4) and the similar uorine content (26.67% and 23.87%). For S1
Fig. 7d for S3 (1/181.26/18.15) with fewer P12FMA segments, (1/72.50/18.15) with the same PMMA and P12FMA segments in
similar absorption curves are observed. When water is absorbed Fig. 7b, SiO2 plays a role of supporting the copolymer chains in
on the surface of lms, Df and DD quickly reach the adsorption the lm, but uorine-containing chains are migrating onto the
Fig. 6 AFM images of E-PMMA-P12FMA (a, S4) and SiO2-g-PMMA-b-P12FMA for S1 (b, 1/72.50/18.15), S2 (c, 1/72.50/45.38) and S3 (d, 1/181.26/
18.15).
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Fig. 7 Frequency (Df) and dissipation changes (DD) for water by QCM-D measurements for E-PMMA-P12FMA (S4) and SiO2-g-PMMA-b-P12FMA
for S1 (1/72.50/18.15), S2 (1/72.50/45.38), S3 (1/181.26/18.15), and water adsorption models on the film surface (I–III).
lm surface, which will lead to the uoride side chains forming PMMA-P12FMA in Fig. 8a shows the starting degradation at
a disordered structure Fig. 7(II). With water owing over the 250 ꢁC. But S1 (Fig. 8b, 1/72.50/18.15) and S2 (Fig. 8c, 1/72.50/
lm surface, the disordered structure transforms to an ordered 45.38) gave similar decomposition temperatures at 320 ꢁC with
structure and the adsorbed water begins to leave the surface, the weight losses of 85.7% wt and 85.9% wt, respectively. For
which causes a small increase in the Df and DD, but nally S3, a decomposition temperature at 280 ꢁC with the weight loss
reaches the adsorption equilibrium at Df ¼ 550 and DD ¼ 180, of 83.2% wt has a slightly lower thermostability than S1 and
showing high amounts of adsorbed water and a higher visco- S2. These results indicate that a higher PMMA content in S3
elasticity of the adsorbed layer than S4 and S3. However, for the will result in the reduction of the decomposition temperature,
SiO2-g-PMMA-b-P12FMA of S2 (1/72.50/45.38), a very different but increasing the P12FMA content in SiO2-g-PMMA-b-P12FMA
adsorption behavior is observed (Fig. 7c). Many more P12FMA from S1 to S2 could not obviously improve the thermostability.
segments make the uorine-containing chains migrate inten- Furthermore, the end decomposition temperatures are
sively crowdedly and nally form a rather rough surface observed at 430 ꢁC for S1 and S2, and 410 ꢁC for S3. Therefore,
(Fig. 6c). Therefore, when water is owing continually over this in the case of the “graing from” polymerization of SI-ATRP,
lm surface, the DD increases with the increases of Df, indi- the thermostabilities of SiO2-g-PMMA-b-P12FMA hybrids are
cating that a relatively ordered and loosely absorbed structure is much higher than E-PMMA-P12FMA, and the higher content
formed in Fig. 7(III) with the highest viscoelasticity of DD ¼ 268. of the 12FMA segment in SiO2-g-PMMA-b-P12FMA (1/72.50/
45.38) could provide the higher end decomposition tempera-
tures due to the thermostabilities of the P12FMA segments.
3.4 The thermostability of the SiO2-g-PMMA-b-P12FMA
hybrid
This was also proven by Nelly Durand9 et al. in their research
that silica nanoparticles activated with vinyl groups show an
The thermostabilities of the E-PMMA-P12FMA and SiO2-g- onset decomposition temperature around 300 ꢁC, but
PMMA-b-P12FMA hybrids were evaluated by TGA (Fig. 8). E- silica modied with “graing from” polymerization exhibits
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Acknowledgements
This work has been nancially supported by the National
Natural Science Foundation of China (NSFC Grants no.
51373133 and 51073126), by the National Basic Research
Program of China (973 Program, no. 2012CB720904), and by the
State Administration of Cultural Heritage (20110128). The
authors also wish to express their gratitude for the MOE Key
Laboratory for Non-equilibrium Condensed Matter and
Quantum Engineering of Xi'an Jiaotong University.
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