Modification of micro-channel filling flow by poly(dimethylsiloxane) surface functionalization with fluorine-Substituted aminonaphthols

Article abstract of DOI:10.1016/j.jfluchem.2009.11.017

Microfluidics based on the capillarity-induced filling of elastomeric channels by a suitable liquid or solution represents a useful route for realizing portable diagnostic devices designed without additional mechanical or electrical micropumps. In this study, an elastomeric mold made of poly(dimethylsiloxane) (PDMS), containing relief patterns placed in intimate contact with a silicon substrate, is utilized to create a continuous network of rectangular micro-channels for the motion of water fluid. The immobilization on activated PDMS surface of suitable functional molecules such as hydrophilic and hydrophobic fluorine-containing aminonaphthols, obtained through a straightforward and versatile synthetic procedure, allowed us to modulate PDMS surface properties depending on the structural characteristics of the employed derivative. In this context, the incorporation of fluorine groups is important for improving biocompatibility of the resulting device, providing surfaces that could be chemically and biologically inert as well as resistant to surface adhesion phenomena. The functionalization from liquid phase of PDMS replicas, involving a covalent derivatization via silanization reaction of the above mentioned compounds to an oxidized PDMS surface, resulted in a successful modification of microfluidic motion of water in rectangular capillaries, moreover contact angle values evidence also how wettability of PDMS films could be modulated, with the fluorinated aminonaphthols fuctionalized PDMS exhibiting higher contact angles.

Full text of DOI:10.1016/j.jfluchem.2009.11.017

Journal of Fluorine Chemistry 131 (2010) 357–363
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Modification of micro-channel filling flow by poly(dimethylsiloxane) surface
functionalization with fluorine—Substituted aminonaphthols
G. Cortese a, F. Martina a, G. Vasapollo a, R. Cingolani b, G. Gigli a,b, G. Ciccarella a,b,
*
a
`
Universita del Salento, Dipartimento di Ingegneria dell’Innovazione, via Arnesano, I-73100, Lecce, Italy
b National Nanotechnology Laboratory (NNL) of CNR, INFM, Distretto Tecnologico ISUFI, via Arnesano, I-73100, Lecce, Italy
A R T I C L E I N F O
A B S T R A C T
Article history:
Microfluidics based on the capillarity-induced filling of elastomeric channels by a suitable liquid or
solution represents a useful route for realizing portable diagnostic devices designed without additional
mechanical or electrical micropumps. In this study, an elastomeric mold made of poly(dimethylsiloxane)
(PDMS), containing relief patterns placed in intimate contact with a silicon substrate, is utilized to create
a continuous network of rectangular micro-channels for the motion of water fluid. The immobilization
on activated PDMS surface of suitable functional molecules such as hydrophilic and hydrophobic
fluorine-containing aminonaphthols, obtained through a straightforward and versatile synthetic
procedure, allowed us to modulate PDMS surface properties depending on the structural characteristics
of the employed derivative. In this context, the incorporation of fluorine groups is important for
improving biocompatibility of the resulting device, providing surfaces that could be chemically and
biologically inert as well as resistant to surface adhesion phenomena. The functionalization from liquid
phase of PDMS replicas, involving a covalent derivatization via silanization reaction of the above
mentioned compounds to an oxidized PDMS surface, resulted in a successful modification of microfluidic
motion of water in rectangular capillaries, moreover contact angle values evidence also how wettability
of PDMS films could be modulated, with the fluorinated aminonaphthols fuctionalized PDMS exhibiting
higher contact angles.
Received 30 April 2009
Received in revised form 19 November 2009
Accepted 20 November 2009
Available online 1 December 2009
Keywords:
Microfluidics
Poly(dimethylsiloxane)
Surface functionalization
Aminonaphthols
Fluorine groups
ß 2009 Elsevier B.V. All rights reserved.
1. Introduction
from the decreasing of the pressure [2]. A system based on capillary
action as driving force is suitable for portable diagnostic devices
Microfabrication is essential to modern science and technology.
Miniaturization and integration of a range of devices result in
portability, reduction in time, costs, reagents, sample size and
power consumption [1]. Furthermore, improvements in detection
limits and a series of other new functions are also observed. In
particular the possibility to implement mixers, diluters, and valves
as components of a PDMS-based microfluidic circuit opens new
perspectives for lab-on-chip applications such as bioassays and
chemical sensors. This is possible mainly having the capability of
modulating the filling flow of liquids within micro-channels by
adopting the consolidated microfabrication technology.
The flow of a liquid in micro-channels is a thermodynamically
driven capillary process, explained in terms of interfacial free
energy between solid/vapour and solid/liquid interfaces. It occurs
because of a pressure difference between two hydraulically
connected regions of the liquid mass, the flow direction resulting
designed without additional mechanical or electrical micropumps
[3].
Microfluidics based on the capillarity-induced filling of elasto-
meric channels by a suitable liquid or solution represents a very
efficient method for patterning biomolecules and for the selective
delivery of proteins from aqueous solutions, such as blood and
saliva [4–6]. However, since the filling process depends on the
interfacial free energies of micro-channel walls, there are several
requirements for a successful patterning of such bio-derivatives
[7,8]: the micro-channels have to be sufficiently hydrophilic to
promote filling by capillary action and at the same time, they
should possess protein repellent surfaces, in order to prevent any
loss of proteins to micro-channels walls. Therefore, since water
motion strongly depends on the channel walls conditions, the
wetting of solid surfaces by the liquid can be controlled by varying
the interfacial free energies of one wall and/or all walls of the
micro-channels.
In general, the filling rate of the fluidic channels is proportional
to the reciprocal length of the capillary, z: dz/dt = R
where , R, , and indicate the liquid viscosity, the radius of the
capillary, the liquid–vapour interfacial free energy of the fluid and
gcos u/4hz,
* Corresponding author at: Universita` del Salento, Dipartimento di Ingegneria
dell’Innovazione, via Arnesano, I-73100, Lecce. Italy.Tel.: +39 0832 298233.
E-mail address: giuseppe.ciccarella@unisalento.it (G. Ciccarella).
h
g
u
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.11.017

358
G. Cortese et al. / Journal of Fluorine Chemistry 131 (2010) 357–363
the contact angle between the liquid and the surface of the
capillary, respectively. , whose cosine is proportional to the
difference between the solid–liquid and the solid–vapour interfa-
cial energies, determines whether the filling process is thermody-
namically favoured, i.e., if the channels can be wetted by water
the coagulation sequence [30]. The proposed study reports a PDMS
surface modification by hydrophilic and fluorinated hydrophobic
molecules, the last providing surfaces that could be chemically and
biologically inert as well as resistant to surface adhesion
phenomena involving biomolecular adsorption.
u
(cos
u
> 0) or not (cos
u
< 0). Filling rate of channels can be
The preparation of such new aminoalcohols, also known as Betti
bases [31–36], involved an inexpensive, efficient and versatile
synthetic procedure involving (in a first step) a simple and
straightforward condensation of 2-naphthol with an aldehyde and
an amine. The successive N-methylation [32–33], in a strategy that
involved the formation-cleavage of an oxazine ring, was employed
to obtain tertiary aminonaphthols; their reaction with 3-triethox-
ysilylpropylisocyanate allowed the preparation of the direct
precursors used in the surface modification of PDMS.
influenced by geometrical factors [9] (R and z) but also by suitable
derivatizations of the involved surfaces, that can modify their
wettability: the surface chemistry of PDMS can affect the
applicability of this material in microfluidic processes involving
pure water or water solutions. Among the numerous approaches
used to change the PDMS surface characteristics [10], covalent
modification has been providing successful results, since coating
with physically and chemically stable derivatives allows the
incorporation of suitable functional groups able to supply
desiderable properties. In particular, a covalent modification of
PDMS surface can be mainly performed through a photo-induced
chemical reaction involving vinyl monomers or polymers [11–18]
or by means of a silanization reaction [19–25] on activated PDMS
surface. Unlike radiation induced surface derivatization, that
necessitates the use of a vinyl compound, silanization allows
the immobilization of a variety of materials useful for specific
applications, thus resulting in improved microfluidic perfor-
mances.
In the present work, a covalent modification of PDMS surface
aimed to fulfil the above mentioned requirements is proposed: an
elastomeric mold made of poly(dimethylsiloxane) (PDMS) con-
taining relief patterns placed in intimate contact with a silicon
substrate, is utilized to create a continuous network of rectangular
micro-channels for the motion of water fluid (Figs. 1 and 5).
The approach described in this paper consists of a modulation of
the filling rate of the rectangular capillaries by water. For this
purpose, suitable derivatizations of PDMS surface were realized
introducing a series of new synthesized molecules via silanization
reaction onto activated micro-channel walls. In particular, the
immobilization on activated PDMS surface [26–28] of hydrophilic
and hydrophobic fluorine-containing aminonaphthols was per-
formed and the resulting modifications in terms of surface
wettability and channel’s filling rate by water was evaluated:
different surface properties were achieved depending on the
structural characteristics of the employed derivative. In this
context, it is reported [29] that incorporation of fluorine groups
remarkably enhances hemocompatibility of the device, the
presence of C–F containing substituents leading to a more
biocompatible surface. As well known, material biocompatibility
is closely related to protein adsorption process, that may trigger
2. Theoretical model for rectangular channel
The thermodynamics of filling in capillaries [3] can be explained
in terms of interfacial free energy and contact angle. A liquid fills in
capillaries in order to minimize interfacial free energies of solid/
vapour and solid/liquid interfaces.
In the laminar regime, the rate of liquid flow in the capillary can
be approximated using the Hagen-Poiselle equation, obtaining:
dz
dt
DP
8mz
¼
RH2
(1)
where RH is the hydraulic radius (the ratio between the volume and
the surface area of the capillary, e.g., whz/2(w + h)z; in our model
RH is 0.62
mm, being w = 28.00 mm and h = 1.3 mm), m the viscosity
of the liquid (the viscosity value is 1.00 ꢀ 10ꢁ3 kg/(m ꢀ s) at 20 8C),
z the length of the column of liquid, and
DP (the pressure drop is
represented by the capillary pressure for microfluidic channels of
small dimensions, < 1 mm) is the difference of pressure of the
liquid mass between inside and outside the channel.
DP can be
calculated using the Laplace equation which, for a rectangular
capillary of width w and height h, approximately is:
ꢀ
ꢁ
cos uSi þ cos uPDMS 2cos uPDMS
D
P ¼ gLG
þ
(2)
h
w
This expression [4] reveals that micro-channels filling is highly
sensitive to the surface tension of the liquid, LG, and to the contact
g
angles uPDMS and usi of the liquid with each of the walls of the
micro-channel (Fig. 2).
The integration of Eq. (1) defines the displacement of the fluid
filling the channel after a time t. Thus, the capillary dynamics for
the length coordinate is described by a power law model
zðtÞ ¼ a þ bt1=2
(3)
where
ꢂ
ꢀ
ꢁꢃ
1=2
R2HgLG
cos uSi þ cos uPDMS 2cos uPDMS
b ¼
þ
(4)
4m
h
w
and a depends on operative measurement beginning. Eq. (3) is in
agreement with the experimental data describing micro-channels
Fig. 2. A scheme for surface tension – driven flow of water in a rectangular micro-
channel.
Fig. 1. Rectangular microfluidic channels for the capillary flow of water.

G. Cortese et al. / Journal of Fluorine Chemistry 131 (2010) 357–363
359
filling and the coefficient b, evaluated by a non-linear regression fit,
F, can be compared with the one calculated using Eq. (4), bCA
b
m
.
3. Results and discussion
3.1. Synthesis of Betti-type aminonaphthols
The main distinctive feature of Betti-type aminonaphthols
[31,32] is represented by a simple and high yield synthesis (the
condensation of 2-naphthol with an aldehyde and an amine). The
starting materials involved supply the surface modifiers adopted in
the following experiments without significant amount of side
products.
The first step proceeds through the formation of the Schiff base;
in presence of 2-naphthol, a Mannich-like condensation takes
place with the obtainment of the aminonaphthols 1-4. The
subsequent reaction takes place by adding an excess of parafor-
maldehyde in ethanol solution, with the obtainment of the oxazine
derivatives 1a–4a. The successive cleavage of oxazine ring under
N-methylation conditions (reduction by NaBH4 in THF and
subsequent hydrolysis with trifluoroacetic acid) supplies the
tertiary aminonaphthols 1b and 3b–4b. The reaction with 3-
(triethoxysilylpropyl-isocyanate) in the presence of triethylamine
in dichloromethane solution [31] gives the surface modifiers 1c–4c
(Scheme 1).
Scheme 2. Step 1. PDMSox was obtained by a few minutes of O2 plasma. Step 2.
Incubation of PDMSox into dichloromethane solutions containing compounds 1c–4c
resulted in surface-modified PDMS-X.
The immobilization of compounds c and 1c–4c was detected by
FT-IR. The band at 2270 cmꢁ1, typical of –N55C55O moiety, and the
peaks at 2928 cmꢁ1 and 2887 cmꢁ1, corresponding to –CH–
vibrations of the grafted isocyanate, are remarkable in IR spectrum
of PDMSc.
Similarly, the functionalization process on PDMS1c–PDMS4c
surfaces was evaluated. The band corresponding to carbamoyloxy
group was evidenced at 1675 cmꢁ1 (PDMS1c), 1723 cmꢁ1
(PDMS2c), 1695 cmꢁ1 and 1696 cmꢁ1 (PDMS3c and PDMS4c
respectively); The peaks around 1625 cmꢁ1
,
1500 cmꢁ1
,
1370 cmꢁ1 and 1250 cmꢁ1, belonging to aminonaphtol moiety,
are also remarkable.
Subsequently, the microfluidic behaviour of such surfaces
towards water was evaluated. As a first step, 3-triethoxysylilpropyl
isocyanate was covalently linked to PDMS–OH; the time to
completely fill the capillaries by water (filling times refer to a
10 mm length) was decreased by a factor 1.5 (from 93 to 62 s) with
respect to untreated PDMS (Fig. 3). The decreasing of contact angle
value (from 1098 to 838) was in agreement with the microfluidic
behaviour (Table 1).
The wettability of channels was further enhanced by linking on
activated PDMS the tertiary aminonaphtol 1c; the time to fill the
capillaries was decreased by a factor 2 respect to untreated PDMS
(Table 1) and contact angle reached 798. The basicity of the tertiary
nitrogen in the structure of 1c makes the surface more hydrophilic.
On the other hand, the compound 2c, was found to be less polar
because of the increasing of the contact angle (948) and of the
filling time (84 s). The more hindered nitrogen, belonging to the
oxazine ring, is probably less available to interact with the water
molecules. Fig. 4 reports the experimental (z, t) curves describing
the capillary motion of water in functionalised microchannels.
Indeed, oxidized PDMS can be exploited as a base layer to link a
series of isocyanates bearing variously substituted amino-
3.2. Microfluidic tests and contact angle measurements
Micro-channel water filling performances can be modulated
by introducing variously substituted aminonaphthols on acti-
vated PDMS walls [31–33] (PDMS–OH). PDMS consists of
repeating (–OSi(CH3)2–) units which provide a hydrophobic,
low interfacial energy, chemically inert surface. Even if the
hydrophobic nature of the surface could be advantageous,
however, in many diagnostic applications, it is necessary to
make the surface of PDMS hydrophilic to improve wetting of
aqueous solvents and ensure micro-channel filling by capillary
action. Therefore, we covered the walls of PDMS micro-channels
with polar –OH functionalities by exposure to O2 plasma [26–
28]. Subsequently, PDMSox was employed as base layer to
chemically bind molecules having suitable characteristics
(Scheme 2).
The structures of the new surface-modified samples PDMSc and
PDMS1c–PDMS4c, obtained upon the first mentioned functiona-
lization process, are reported in Chart 1.
Scheme 1. Synthesis of the surface modifiers 1c–4c.

360
G. Cortese et al. / Journal of Fluorine Chemistry 131 (2010) 357–363
Fig. 3. Microfluidic tests for PDMS (black line) and PDMSc (red line) (10 mm channel
length) (For interpretation of the references to color in this figure legend, the reader
is referred to the web version of the article).
Fig. 4. Microfluidic tests for PDMS and PDMS1c–PDMS4c (10 mm channel length).
carbon–fluorine bonds [37,38] allows to obtain more hydrophobic
surfaces, with a decreased capillarity-induced micro-channel
filling and reduced chemical and physical interactions with
aqueous medium. Furthermore, the low polarity of C–F bonds
allow to minimize the surface free energy.
In summary, a simple and versatile process allows us to obtain
differently substituted aminonaphthols, able to influence micro-
fluidic performances depending on the hydrophilic or hydrophobic
nature of the resulting structures. Contact angle measurements,
reported in Table 1, represent a useful indicator of surface
characteristics and of the efficiency of surface treatments
performed on PDMS flats.
Chart 1. Structures of the surface-modified samples PDMSc and PDMS1c–PDMS4c.
naphthols, thus modulating microfluidic performances by using
aminonaphtol-based structures having polar or non polar groups.
In particular, the introduction on PDMS surface of the fluorine-
containing structures 3c and 4c resulted in a increase in the filling
time of the micro-channels by water fluid (111 s and 142 s
respectively), as shown in the experimental curves reported in
Fig. 4 the highest value of contact angle (1238) was observed when
the isocyanate 4c, having six fluorine atoms as substituents on
aromatic rings, was immobilized on PDMS surface. Therefore, the
functionalization of PDMS walls with derivatives containing
Furthermore, for each PDMS functionalization, the agreement
between experimental microfluidic results and the ones obtained
from contact angle measurements was evaluated. To this purpose,
the coefficient bCA (Eq. (4) in theoretical model), which only
depends on functionalized PDMS contact angle values (being
u
Si = 27.98), was compared with b F (Eq. (3) in theoretical model),
m
evaluated by a non-linear regression fit of the experimental (t, z)
curves.
First of all, the two coefficients of untreated PDMS have been
compared: bCA_PDMS (1.71) resulted higher than b
(1.003),
F_PDMS
m

G. Cortese et al. / Journal of Fluorine Chemistry 131 (2010) 357–363
361
Table 1
rectangular capillaries: the filling rate of fluidic channels by water
fluid increases upon customizing PDMS walls with more hydro-
philic structures (PDMSc, PDMS1c–PDMS2c), while decreases
upon covering PDMS with more hydrophobic molecules containing
a series of C–F bonds (PDMS3c–PDMS4c), thus suggesting a
reduced chemical and physical interaction of micro-channel walls
with aqueous medium. Furthermore, contact angle values evi-
dence how wettability could be modulated depending on the
different surface modifier, with the fluorinated aminonaphthols
fuctionalized PDMS exhibiting the higher contact angles.
Finally, the functionalization process proposed in this paper
offers the opportunity to develop systems where surface wetta-
bility have to be precisely and reproducibly adjusted and where a
selective patterning of biomolecules from an aqueous medium
could be realized through an anisotropic modification of PDMS
walls.
Contact angles, fill time values and fill time ratio with respect to untreated PDMS for
PDMS, PDMSc, PDMS1c–PDMS4c.
Sample
CA
Fill time (s)
Fill time ratio
PDMS
109.18 ꢂ 1.218
83.38 ꢂ 1.608
79.38 ꢂ 1.368
94.28 ꢂ 1.668
116.28 ꢂ 0.738
122.78 ꢂ 1.808
94
1.00
0.66
0.52
0.93
1.18
1.51
PDMSc
PDMS1c
PDMS2c
PDMS3c
PDMS4c
62
49
87
111
142
Table 2
b values for PDMS, PDMSc, PDMS1c–PDMS4c.
bCA (mm/s0.5
)
b
(mm/s0.5
)
bCA_cor (mm/s0.5
)
F
m
PDMS
1.71
2.34
2.42
2.08
1.45
1.26
1.00
1.26
1.33
1.06
0.92
0.81
1.00
1.37
1.42
1.22
0.85
0.74
PDMSc
PDMS1c
PDMS2c
PDMS3c
PDMS4c
5. Experimental
5.1. General
thus confirming what described by Delamarche et al. about the 40%
reduction in velocity of the liquid in closed channels compared to
their open counterparts [5]. To evaluate the presence of features
not considered in the theoretical model and/or due to experimen-
tal measurements, it was calculated an empirical corrective factor
All experiments were carried out under ambient laboratory
conditions (20–25 8C and 40–45% humidity).
Contact angle of liquids was measured on a Rame-Hart Model
100 goniometer (Dataphysics OCA 20) at room temperature and
ambient humidity. The filling flow was followed in real time by an
optical microscope.
c = b F-PDMS/bCA-PDMS approximate to 0.586. In fact, for what
m
concerns untreated PDMS, it is obvious that, unlike modified
Mass spectrometry analyses were carried out using an Agilent
technologies HPLC mass spectrometer (1100 Series) equipped with
an Electrospray (ESI) and an APCI (Atmospheric Pressure Chemical
Ionization) interfaces. FT-IR spectra were recorded on a JASCO FT-
IR 660Plus spectrometer, in ATR (Attenuated Total Reflectance)
mode. 1H NMR spectra were recorded on a Bruker Avance 400 at
room temperature and chemical shifts are reported relative to
tetramethylsilane.
PDMS, the disagreement between bCA and b
values can not
F
m
depend on the surface functionalization process neither on the
resulting modifiers immobilized surface density (the number of
immobilized molecules in a unit surface).
In light of these considerations, for each functionalization, the
term bCA_cor was introduced (see Table 2) as result of the product of
the corrective factor c and bCA values.
In particular, the introduction of the parameter bCA_cor
remarked how inhomogeneities, impurities and changes in the
wettability of modified microfluidic channels could provide
further limits in real cases. In fact, as reported in Table 2, for
hydrophobic surfaces (PDMS3c–PDMS4c), bCA_cor (which take
5.2. Synthesis of chemical modifiers
5.2.1. Preparation of compounds 1–4
To an ethanol solution of 2-naphthol (10 mmol, 1.24 g in 5 ml),
an excess of aldehyde (14 mmol) and an equimolar amount of
amine (10 mmol, 1.21 g) was added for obtaining the amono-
naphthols 1–2; the synthesis of the fluorinated aminonaphthols 3–
4 was carried out by adding a substoichiometric amount of amine
(8.5 mmol). Then the mixtures were stirred at 50 8C for six days
and the crude products crystallized from ethanol solution.
into account of the corrective term c = b F/bCA for untreated
m
PDMS), are slightly lower than the corresponding b F values thus
m
suggesting that the slow filling of micro-channels is influenced by
surface inhomogeneities coming from the functionalization
process (the presence of not functionalized PDMS portions
slightly increases
PDMS1c–PDMS2c are slightly higher than the corresponding
F, since experimental b F values take into account the effect of
b
value); similarly, bCA_cor values for
F
m
b
5.2.2. Preparation of compounds 1a–4a
m
m
the linked hydrophilic molecules but also the influence of not
modified PDMS (Table 2).
To an ethanol solution of 1–4 (10 mmol in 25 ml), paraformal-
dehyde (50 mmol, 1.50 g) was added. The mixture was stirred at
50 8C for 4 h. Then the crude product was centrifuged to remove
the excess of paraformaldhyde and the liquid phase concentrated
under reduced pressure.
Anyway, a relative comparison between the surface properties
of functionalized PDMS samples, PDMSc–PDMS4c, is possible and
the influence of the PDMS surface derivatizations by aminonaph-
tol-based isocyanates 1c–4c on micro-channel filling perfor-
mances by water fluid can be evaluated.
5.2.3. Preparation of compounds 1b, 3b–4b
To a THF solution of 1a, 3a–4a (10 mmol in 40 ml), NaBH4
(40 mmol, 1.51 g) was added. Subsequently a solution of TFA
(10 ml) in THF (60 ml) was added dropwise and the resulting
mixture stirred at 65 8C for 6 h. After acid workup, the crude
product was dissolved in diethyl ether, the precipitate removed by
centrifugation and the liquid phase concentrated under reduced
pressure.
4. Conclusion
An approach for modulating micro-channel filling rate through
suitable chemical modifications of PDMS walls is reported. It
involves a straightforward and versatile synthetic procedure that
supplies a library of hydrophilic and hydrophobic aminonaphthols,
depending on the substituents on aromatic rings. The functiona-
lization from liquid phase of PDMS replicas, involving a covalent
grafting of the above mentioned derivatives to activated PDMS
surface, allows to modify microfluidic motion of water in
5.2.4. Preparation of compounds 1c–4c
Under nitrogen atmosphere, 3-(triethoxysilylpropyl-isocya-
nate) (11 mmol, 2.72 g) was added dropwise to a solution of 1b,

362
G. Cortese et al. / Journal of Fluorine Chemistry 131 (2010) 357–363
2a, 3b–4b (10 mmol) in dichloromethane (12.5 ml), in presence
of triethylamine (33 mmol, 1.82 g, 2.5 ml). The mixture was
stirred at room temperature for 8 h thus obtaining the surface
modifiers 1c–4c. Compounds 1c–4c have been purified by
5.4. Preparation of PDMS samples
An elastomeric mold was fabricated from poly(dimethylsilox-
ane) (PDMS, Sylgard 184, Dow Corning, Midland, MI) by casting
PDMS against a master (prepared as previously reported) that
contained a three-dimensional relief pattern to be replicated. The
master was used a number of times to fabricate multiple copies of
the elastomeric mold.
Sylgard 184 silicone elastomer was supplied as a two-part
liquid component kit comprised of base and curing agent. PDMS
samples were prepared mixing the silicone base and its curing
agent (containing cross-linker and catalytic amount of a Pt
catalyst) in a 10:1 weight ratio, pouring onto Si masters and
allowing to stand for 30 s, to favour the emersion of trapped air
bubbles. The degassed mixture was cured at 140 8C for 15 min and
then gently peeled away.
The PDMS mold was made sufficiently thin (approximately
1 mm in thickness) to follow the imbibition front when it advances
in microcapillaries during microfluidic experiments. A typical size
of the mold is 2.0 cm ꢀ 1,0 cm and the length of the channels in the
mold ꢃ1.5 cm. Only one end of the channels in the mold was open
to allow a liquid to enter. The high solubility of such gases as N2 and
crystallization from dichloromethane–hexane mixture: to
a
dichloromethane solution of compound 1c–4c, hexane was added
dropwise under stirring, until precipitation of solid was observed.
The solid was then filtered and dried. The obtained molecules
were characterized by LC–MS, FT-IR and 1H NMR spectroscopies
(Table 3).
5.3. Preparation of masters
Photolithography was employed to fabricate Si substrates for
PDMS replication.
A standard photoresist (SU-8-2000, MicroChem) [39] was spun
on Si substrate, exposed to UV radiation and developed. Then the
substrate was etched using NH4F/HF/H2O and the obtained mask
employed to etch silicon using a 6.0 M H2O/iPrOH solution of KOH
at 80 8C.
A ruler was integrated in the masters, side by side with the
channels, to exactly determine by optical microscopy the length
covered by the water fluid during the filling process.
O2 in PDMS makes the term of the internal pressure (Dpint), due to
Table 3
Spectroscopic data of compounds 2a, 1b, 3b–4b, 1c–4c.
Compound
Yield (%)
79
LC–MS (m/z)
FT-IR (cmꢁ1
)
1H NMR (400 MHz, CDCl3)
2a
m/z = 382 [M + 1]+
3333, 3060, 2974, 2926, 2898, 1681,
1622, 1598, 1514, 1485, 1467, 1453,
1436, 1402, 1353, 1263, 1231, 1154,
1071, 1018, 998, 860
d=7.67–7.05 (Ar, 12H), 6.92 (d, Ar, 1H), 6.68 (d, Ar, 2H), 5.28
(s, HOC6H4CH–N–, 1H), 5.18 (dd, –N–CH2–O–, 2H, J = 10.8 Hz),
4.98 (dd, N–CH2–O–, 2H, J = 10.8 Hz), 4.09 (q, CH3–CH–N–, 1H,
J = 6.6 Hz), 1.57 (d, CH3–CH–N–, 3H, J = 6.6 Hz) ppm
1b
3b
4b
1c
82
76
89
81
m/z = 368 [M + 1]+
m/z = 458 [M + 1]+
m/z = 462 [M + 1]+
m/z = 616 [M + 1]+
3064, 2926, 2853, 1674, 1624, 1518,
1456, 1438, 1338, 1269, 1241, 1200,
1136, 973, 900, 834
d
=7.77–7.05 (Ar, 15H), 6.85 (Ar, d, 1H), 5.29 (s, Ar1Ar2–CH–N, 1H),
4.22 (q, Ar1Me–CH–N, 1H, J = 6.6 Hz), 2.13 (s, CH3–N, 3H),
1.59 (d, CH3–CH–N, 3H, J = 6.6 Hz) ppm
3330, 1674, 1627, 1601, 1518, 1499,
1465, 1436, 1401, 1355, 1304, 1274,
1232, 1206, 1141, 1122, 1018, 992, 928
d=7.82–7.07 (m, Ar, 10H), 6.87 (Ar, d, 1H), 5.31 (s, Ar–CH–N–, 1H),
4.18 (q, CH3–CH–N–, 1H, J = 6.6 Hz), 2.32 (s, CH3–N–, 3H),
1.59 (d, CH3–CH–N–, 3H, J = 6.6 Hz) ppm.
3330, 2954, 1655, 1625, 1591, 1519,
1498, 1467, 1436, 1401, 1365, 1306,
1252, 1232, 1141, 1122, 1076, 1018, 995
d=7.88-7.08 (Ar, 6H), 6.91 (Ar, d, 1H), 6.84-6.77 (Ar, 3H),
5.30 (s, Ar-CH-N-, 1H), 3.72 (s, m-FC6H4-CH2-N-, 2H),
2.33 (s, CH3-N-, 3H) ppm
2976, 2928, 2887, 1690, 1564, 1478,
d
=7.97–7.07 (Ar, 15 H), 6.85 (Ar, d, 1H), 5.26 (s, Ar1Ar2–CH–N,
1445, 1391, 1251, 1200, 1168, 1070, 956
1H), 4.18 (q, Ar1Me–CH–N, 1H, J = 6.6 Hz), 3. 79 (q, –OCH2–CH3,
6H, J = 7.00 Hz), 3.19 (t, NH–CH2–CH2–, 2H, J = 6.5 Hz),
2.50 (s, CH3–N, 3H), 1.69 (–NHCH2CH2CH2Si–, 2H, J = 7.00 Hz),
1.60 (d, CH3–CH–N, 3H, J = 6.6 Hz), 1.33 (t, –OCH2–CH3,
9H, J = 7.00 Hz), 0.61 (t, –CH2Si, 2H, J = 8.1 Hz) ppm
2c
80
m/z = 630 [M +1]+
2973, 2926, 2885, 2734, 1724, 1624,
1600, 1514, 1482, 1441, 1389, 1210,
1165, 1077, 950, 864
d=7.78–6.91 (Ar, 15H), 5.28 (s, –OC6H4CH–N–, 1H), 5.18
(dd, –N–CH2–O–, 2H, J =10.8 Hz), 4.98 (dd, N–CH2–O–, 2H,
J = 10.8 Hz), 4.10 (q, CH3–CH–N–, 1H, J = 6.6 Hz), 3.82
(q, O–CH2–CH3, 6H, J = 7.00 Hz), 3.25 (t, NH–CH2–CH2–,
2H, J = 6.5 Hz), 1.69 (m, –NH–CH2–CH2–CH2–Si–, 2H,
J = 7.00 Hz), 1.54 (s, CH3–CH–N, 3H, J = 6.6 Hz), 1.26
(t, –OCH2CH3, 9H, J = 7.00 Hz), 0.64 (t, –CH2Si–,
2H, J = 8.1 Hz) ppm
3c
66
m/z = 705 [M + 1]+
2978, 1695, 1627, 1519, 1505, 1466,
1437, 1397, 1365, 1305, 1276, 1233,
1203, 1160, 1121, 1075, 1018, 993
d=7.73–7.09 (m, Ar, 10H), 6.89 (Ar, d, 1H), 5.32 (s, Ar–CH–N–,
1H), 4.15 (q, Ar1Me–CH–N, 1H, J = 6.6 Hz), 3.82 (q, –OCH2–CH3,
6H, J = 7.00 Hz), 3.19 (m, –NH–CH2–, 2H, J = 6.5 Hz),
2.22 (s, CH3–N–, 3H), 1.67 (m, –NHCH2CH2H2Si–,
2H, J = 7.00 Hz), 1.58 (d, CH3–CH–N, 3H, J = 6.6 Hz),
1.32 (t, –OCH2CH3, 9H, J = 7.00 Hz), 0.69 (t, –CH2Si, 2H,
J = 8.1 Hz) ppm
4c
72
m/z = 709 [M + 1]+
2985, 2937, 1696, 1655, 1625, 1591,
1520, 1500, 1466, 1437, 1401, 1366,
1306, 1251, 1198, 1123, 1019, 995
d=7.90–7.09 (m, Ar, 6H), 6.92 (Ar, d, 1H), 6.84–6.78
(Ar, 3H), 5.37 (s, Ar–CHN, 1H), 3.79 (q, OCH2CH3, 6H, J =7.00 Hz),
3.70 (s, m-FC6H4–CH2–N–, 2H), 3.17 (m, –NH–CH2–, 2H,
J = 6.5 Hz), 2.22 (s, CH3–N–, 3H), 1.67 (m, CH2CH2CH2, 2H,
J = 7.00 Hz), 1.40 (t, OCH2CH3, 9H, J = 7.00 Hz), 0.66
(t, -CH2Si, 2H, J = 8.1 Hz) ppm

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