Click chemistry and electro-grafting onto colloidally templated conducting polymer arrays

Article abstract of DOI:10.1016/j.polymer.2012.05.040

Herein we developed a new approach of creating topologically and well-defined patterned polymeric surfaces via the "grafting to" approach. This was accomplished by either using colloidally templated "clickable" arrays, whereby the chemistry was performed

Full text of DOI:10.1016/j.polymer.2012.05.040

Polymer 53 (2012) 3124e3134
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Polymer
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Click chemistry and electro-grafting onto colloidally templated conducting
polymer arrays
,b,
Edward L. Foster a, Ajaykumar Bunha a, Rigoberto Advincula a
*
a Department of Chemistry and Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204-5003, United States
b Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein we developed a new approach of creating topologically and well-defined patterned polymeric
surfaces via the “grafting to” approach. This was accomplished by either using colloidally templated
“clickable” arrays, whereby the chemistry was performed directly onto the pattern or by subsequent
backfilling with azido terminated SAM’s. Similarly, direct grafting of electroactive temperature respon-
sive oligo(ethylene glycol) methacrylic polymers to colloidally templated surfaces allowed for tunable ion
gate formation.
Received 21 February 2012
Received in revised form
19 May 2012
Accepted 21 May 2012
Available online 30 May 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Colloidal templating
Electrodeposition
Ion gate
1. Introduction
More recently, click chemistry has become a popular technique
to covalently graft prefabricated polymers to surfaces. The most
Covalent tethering or chemical adsorption of macromolecules is
a robust approach to fine-tuning surface and interfacial properties
[1e3]. Although somewhat limited in terms of thickness and
grafting density, a primary advantage of the “grafting to” polymer
brush approach is the ability to fully characterize the preformed
polymer precursors prior to adsorption. To date, the majority of
research regarding the covalent tethering of polymers to substrates
has been based on the condensation of silane terminated linear
polymers on hydroxyl functionalized surfaces or by other self-
assembly methods [4e7]. Other novel techniques have been
reported to tether macromolecules. For example, Patton et al.
described a series of well-defined dendritic-linear copolymer
architectures prepared via the reversible addition-fragmentation
chain transfer (RAFT) polymerization technique [8]. Using
dendritic chain transfer agents (CTA)s, RAFT polymerization was
carried out to polymerize linear polystyrene (PS) and poly(methyl
methacrylate) (PMMA) chains. These linear dendron polymers
were then successfully grafted electrochemically onto the
conductive substrates via the electroactive carbazole moieties at
the periphery of the dendrons.
widely used click reaction is the copper-catalyzed azide alkyne
cycloaddition (CuAAC) reaction [9]. The CuAAC reaction is one
representative of a family of efficient chemical reactions, which are
modular, widely applicable, relatively insensitive to solvents, and
pH ranges, while resulting in high yields [10]. This coupling reaction
has been employed for the fabrication of grafted poly(ethylene
glycol) brushes onto alkyne-functionalized pseudobrushes and
mucin-like glycopolymers for microarray applications [11,12]
An important complement to polymer brushes are nano-
patterned polymeric surfaces. Nanopatterned polymeric surfaces
serve as excellent platforms for controlling interfacial chemical
interactions and biological component adsorption with applica-
tions ranging from biomaterials and micro/nanofluidic systems to
microelectromechanical devices and photonic crystal materials
[13]. Due to this high interest, various strategies including micro-
contact printing, photolithography, and electron beam lithography
have been developed for fabricating patterned polymer brushes
[14]. These techniques however, require complex procedures or
could only be applicable to specific surfaces via patterned self-
assembled monolayers (SAM). An underutilized technique for the
fabrication of two dimensional (2-D) surface patterning is the use of
ordered colloidal crystal templates. Porogenic templating has been
done on ordered colloidal crystals that serve as sacrificial templates
(colloidal templating) for structuring inverse three-dimensional
(3-D) colloidal arrays. Similarly, other sacrificial templates can
* Corresponding author. Department of Macromolecular Science and Engineering,
Case Western Reserve University, Cleveland, OH 44106, United States
E-mail address: rca41@case.edu (R. Advincula).
0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2012.05.040

E.L. Foster et al. / Polymer 53 (2012) 3124e3134
3125
come from a variety of materials including anodized alumina, block
copolymers, and inorganic or organic colloidal spheres [15e17].
Polymer colloidal spheres (PS microspheres) have drawn particular
attention due to the ease of handling, commercial availability, and
their ability to serve as sacrificial templates. Materials ranging from
metals to glassy carbon have been used to fillin the interstitial void
spaces in-between the ordered colloidal arrays. However, the use of
electroactive organic molecules and polymers is of high interest
because of their tunable electro-optical and electrochemical
properties [17e20].
Herein, we report the electrodeposition of a series of first
generation (G1) dendrons (Fig. 1aec) onto colloidally templated
substrates. The first part focuses on the grafting of linear poly-
styrene molecules (Fig. 1d and e) containing either an azide (PS-N3)
or terminal alkyne (PS-alkyne) via the CuAAC reaction onto
PPEGMEMA-CTA) and removal of the PS microspheres, novel
temperature responsive tuning of pore diameter was achieved.
2. Experimental section
2.1. Materials
Reagent chemicals (Sodium n-dodecylsulphate) (SDS), methyl
methacrylate (MMA, 99%), norbornene (99%), styrene (99%), tetra-
butylammonium hexafluorophosphate (TBAH, 99%), copper
bromide (99%), 2,20-azobisisobutyronitile (AIBN, 99%), and trie-
thylamine (TEA, 99%), were purchased from Aldrich and were used
without further purification unless otherwise indicated. Chemicals
N,N0-dicyclohexylcarbodiimide (DCC, 99%), 4-dimethylamino-
pyridine (DMAP, 99%), poly(ethylene glycol) methyl ether meth-
acrylate (PEGMEMA), N,N,N0,N00,N0-pentamethyldiethylenetriamine
(PMDETA), potassium thioacetate, sodium azide, 18-crown-6,
lithium aluminum hydride, carbazole (99%), 1,4 dibromobutane
(99%), methyl 2-bromo-2-methylpropionate (MBMP), tetraethylene
glycol (99%), 4-cyano-4-(thiobenzoylthio)pentanoic acid, sodium
hydroxide, and methyl-3,5-dihydroxybenzoate (99%) were all
purchased from Alfa Aesar and were used without further purifi-
cation. 2-bromoisobutyryl bromide (99%) was purchased from
Tokyo Chemical Industry (TCI) and also used without any purifi-
cation. The Polystyrene (PS) latex microspheres (500 nm sizes,
2.5 wt% solids in aqueous suspension) were purchased from Poly-
sciences, Inc. and used without further purification. Deionized
water (DI-H2O), methanol (MeOH), dicholoromethane (DCM),
dimethylformamide (DMF), acetonitrile (ACN), and tetrahydrofuran
(THF) were used in the formation of patterned indium tin oxide
(ITO) or gold slides, synthesis, and polymerization reactions.
Styrene and PEGMEMA monomers containing inhibitor were
colloidally templated conducting polymer arrays. Scheme
1
demonstrates how the successful grafting of the PS-N3 (Scheme 1,
Route 1) or PS-alkyne (Scheme 1, Route 2) was achieved either
through the use of the electroactive “clickable” molecule prop-2-
ynyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzoate (G1Cbz-alkyne),
or by backfilling an inverse colloidal 2-(2-(2-(2-hydroxy)ethoxy)
ethoxy)ethyl-3(4-(9H-carbazol-9-yl)butoxy)-5-(4-(9Hcarbazol-
9yl)butoxy)) benzoate (G1Cbz-TEG) array with azidoundecane-
thiolSAM, respectively. The second part of the paper examines an
alternative route (Scheme 1, Route 3) for the direct grafting of
electroactive linear polymers via electrodeposition onto colloidally
templated surfaces. This was achieved by first polymerizing a linear
poly((polyethylene glycol)3 methyl ether methacrylate) (PPEG-
MEMA) from an electroactive RAFT polymerizable reagent i.e. 3,5-
bis (4-(9H-carbazol-9-yl) butoxy) benzyl 4-cyano-4 (phenyl-
carbonothioylthio) pentanoate (G1Cbz-CTA). Following the elec-
trodeposition of the electroactive linear PPEGMEMA (G1Cbz-
Fig. 1. Structures of (a) prop-2-ynyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzoate (G1Cbz-alkyne), (b) 2-(2-(2-(2-hydroxy)ethoxy)ethoxy)ethyl-3(4-(9H-carbazol-9-yl)butoxy)-5-(4-
(9Hcarbazol-9yl)butoxy)) benzoate (G1Cbz-TEG), (c) electroactive dendritic-linear PPEGMEMA (G1Cbz-PPEGMEMA-CTA) molecule, (d) linear PS with terminal azide functional
group (PS-N3) and, (e) linear PS with terminal alkyne functional group (PS-alkyne).

3126
E.L. Foster et al. / Polymer 53 (2012) 3124e3134
Scheme 1. Fabrication of a highly ordered monolayer of colloidal arrays (500 nm diameter PS microspheres), inverse colloidal arrays, and patterned polymer brushes via the
“grafting to” approach using linear (Route 1) PS-N3, (Route 2) PS-alkyne or, (Route 3) G1Cbz-PPEGMEMA-CTA polymers.
passed through a column with alternating layers of activated basic
washed with water (2x) and brine solution (2ꢂ). The mixture was
alumina and inhibitor remover and were stored at ꢀ20 ꢁC.
then subjected to column chromatography using 1/4 hexanes/DCM.
2.2.4. Polymerization of styrene to form of PS-alkyne
PS-alkyne was prepared by RAFT ([Sty]/[AIBN]/[CTA-alkyne])
600:1:5, 50 vol % toluene) polymerization. The solution was sub-
jected to 3 freeze-pump-thaw cycles followed by backfilling with
nitrogen. The solution was heated at 70 ꢁC for 5 h. Afterwards the
solution was cooled to room temperature and the solvent was
minimized. The solution was then reprecipitated in MeOH (3ꢂ) and
dried.
2.2. Polymerization
2.2.1. Polymerization of styrene to form of PS-br
The polymerizations of styrene were conducted with conditions
modified from previously reported methods [21]. For all polymer-
izations, oxygen was removed by three freeze-pump-thaw cycles
followed by backfilling with nitrogen. Linear PS-Br was prepared by
atom transfer radical polymerization (ATRP) ([Sty]/[MBMP]/[CuBr]/
[PMDETA]) 100:1:1:1, 40 vol % toluene, 80 ꢁC). The polymerization
was stopped after 3 h by exposing the reaction mixture to air. The
mixture was diluted with THF and passed through a neutral
alumina column to remove the copper. The polymer was then
reprecipitated in MeOH (3ꢂ) and dried.
2.2.5. Synthesis of G1Cbz-CTA
The synthesis of G1Cbz-CTA was performed according to litera-
ture [8].
2.2.6. Polymerization of PEGMEMA to form G1Cbz-PPEGMEMA-CTA
G1Cbz-PPEGMEMA-CTA was prepared by RAFT ([PEGMEMA]/
[AIBN]/[G1Cbz-CTA]) 600:1:5, 50 vol % dry THF). The solution was
subjected to 3 freeze-pump-thaw cycles followed by backfilling
with nitrogen. The solution was heated at 70 ꢁC for 24 h. After-
wards, the solution was cooled to room temperature and the
solvent was minimized. The solution was then reprecipitated in
hexane (3ꢂ) and dried.
2.2.2. Synthesis of PS-N3
The PS-Br (0.05 M) molecules were reacted with NaN3 (1.1
equiv) at room temperature in DMF to yield PS-N3, The polymers
were isolated by precipitation into MeOH.
2.2.3. Synthesis of prop-2-ynyl 4-(benzodithioyl)-4-
cyanopentanoate (CTA-alkyne)
In a one-necked flask, 4-cyano-4-(thiobenzoylthio)pentanoic
acid (500 mg, 1.8 mmol), propargyl alcohol (201 mg, 3.6 mmol), and
DMAP (22 mg, 0.18 mmol) were combined. The mixture was dis-
solved in 50 ml of DCM, bubbled with nitrogen, and placed in an ice
bath. After which, a solution of DCC (743 mg, 3.6 mmol) in DCM was
added dropwise to the reaction mixture. This was then stirred
vigorously for 30 min, warmed to room temperature and stirred
overnight. The solid by-product was filtered off and the filtrate was
2.3. Surface preparation and electrodeposition
The solution used for layering, contained 1 wt % PS microspheres
and 34.7 mM SDS (spreading agent) in Milli-Q water. The layering
of PS microspheres was accomplished using a procedure previously
described by Grady and co-workers [22]. The method is called the
LB-like technique because it forms a monolayer of PS microspheres
onto flat surfaces without using the conventional LB setup that

E.L. Foster et al. / Polymer 53 (2012) 3124e3134
3127
employs floating barriers. The substrate was attached into the
dipper motor via a Teflon clip and was dipped into an aqueous
solution containing PS microspheres (1 wt %) and SDS (34.7 mM).
The substrate was withdrawn vertically from the solution at a rate
of 0.3 mm/min. Finally, the substrate was dried by suspending it in
air for a few minutes. The PS microspheres were removed from the
surface after electropolymerization by dipping the PS microsphere
coated substrate in THF twice for 30 min. This is done to create the
inverse colloidal crystals of conducting polymer pores and arrays
(also called inverse opals or PS-templated film). The substrate then
was allowed to dry naturally under ambient conditions.
between 0.8 and 1.0 lines/s. Commercially available tapping mode
tips (TAP300, Silicon AFM Probes, Ted Pella, Inc.) were used on
cantilevers with
a resonance frequency in the range of
290e410 kHz was performed. The scanning of the electro-
polymerized films was performed under ambient and dry condi-
tions. All AFM topographic images (AAC tapping mode) were
filtered and analyzed using SPIP (Scanning Probe Image Processor,
Imagemet.com) or Gwyddion 2.19 software. Cyclic voltammetry
(CV) was performed in a conventional three-electrode cell, using an
Autolab PGSTAT 12 potentiostat (Brinkmann Instruments (now
MetroOhm USA)). The potentiostat was controlled using GPES
The electropolymerization of the monomer was done using both
chronoamperometry and cyclic voltammetry (CV) using an Autolab
PGSTAT 12 potentiostat (Metro Ohm) in a standard three-electrode
measuring cell, a fabricated electrochemical cell with a diameter of
1.0 cm and volume of 0.785 cm3, made of Teflon) with platinum
wire as the counter electrode, Ag/AgCl wire as the reference elec-
trode, and PS microsphere coated gold or ITO substrates as the
working electrode. For CV, a potential of 0e1.1 V, scan rate 50 mV/s
or 100 mV/s, and 20 cycles was used. For chronoamperometry, the
potential was kept constant at 1.3 V for 3 min. After the electro-
deposition, the resulting film was washed with ACN thrice, and
a monomer free scan was performed, using a range of 0e1.3 V at
50 mV/s scan rate but for only one CV cycle. The electropolymerized
substrate was dried with nitrogen gas.
software (version 4.9). The deionized water (18.2 M
the dilution of PS microspheres was purified by a Milli-Q Academic
system (Millipore Corporation) with a 0.22 m Millistack filter at
the outlet. The attenuated total reflectance fourier transform
infrared (ATR-FTIR) spectra were obtained on a Digilab FTS 7000
equipped with a HgCdTe detector from 4000 to 600 (cmꢀ1) wave-
numbers. All spectra were taken with a nominal spectral resolution
of 4 cmꢀ1 in absorbance mode. All films were measured under
ambient and dry conditions.
Ucm) used for
m
3. Results and discussions
3.1. Synthesis of PS-N3 and PS-alkyne
The inverse colloidal G1Cbz-PPEGMEMA-CTA arrayed ITO
substrates were immersed in the solution at room temperature for
60 min prior to CV. For the elevated temperature scans, the elec-
trochemical cell was placed in a temperature-controlled water bath
at 70 ꢁC for 60 min prior to electrochemical testing.
The “grafting to” approach on colloidally templated surfaces
relies on the preparation of polymers having either a terminal azide
(PS-N3) or alkyne (PS-alkyne) functional group that can react
sequentially by CuAAC reaction. Atom transfer radical polymeri-
zation (ATRP) was employed for controlled living radical polymer-
ization to enable monodispersed samples. The precursor PS-Br
molecule was synthesized via ATRP using styrene and MBMP along
with CuBr/PMDETA as the catalyst system (Scheme 2a). Using Gel
permeation chromatography (GPC), we determined the molecular
weight (Mn) and polydispersity index (PDI) of the PS-Br molecule to
be 2019 g/mol and 1.017 respectively. A good correlation between
GPC Mn and 1H NMR spectroscopy (Mn ¼ 1997 g/mol) was also
observed. To synthesize the PS-alkyne another popular and well
controlled living polymerization technique, RAFT polymerization,
was used (Scheme 2b). Here polymerization of styrene to yield PS-
alkyne was carried out in toluene at 70 ꢁC, yielding a rather low
molar mass (Mn ¼ 3084 g/mol) and narrow PDI (1.15). Once again,
1H NMR analysis data supported GPC data (Mn ¼ 3103 g/mol).
In the case of the PS-alkyne no further modification was
required because the “clickable” terminal alkyne was present after
polymerization. In the case of the PS-Br molecule additional steps
were required to create the azido functional group necessary for
CuAAC. Nucleophilic substitution of the resulting Br end groups was
achieved by reaction with NaN3 in DMF at room temperature [23].
1H NMR analysis (Fig. 2) also confirmed the conversion of PS-Br to
2.4. Copper catalyzed click reactions
In a typical experiment, a solution of PS-N3 or PS-alkyne (0.1 M)
was dissolved in DMF. Afterwards PMDETA (0.5 equiv) was added
and the solution was degassed. After degassing, the solution was
transferred to a second degassed schlenk tube containing CuBr (0.5
equiv), and the substrates containing either the colloidally tem-
plated G1Cbz-alkyne arrays or the azidoundecanethiolfilms. The
reactions were allowed to go for 24 h. Afterwards the substrates
were removed and rinsed with DMF, water, and MeOH followed by
drying under vacuum before characterization.
2.5. Characterization
Nuclear magnetic resonance (NMR) spectra were recorded on
a General Electric QE-500 spectrometer operating at 500 MHz for
1H NMR. The UV spectrum was recorded on an HP-8453 UVeVis
spectrometer in the range between 300 and 800 nm. The electro-
polymerized film on ITO was directly scanned onto the spectrom-
eter with ITO used as a blank. The films were completely dried
under vacuum prior to the UVeVis measurements. X-ray Photo-
electron Spectroscopy (XPS) was done using a PHI 5700 X-ray
photoelectron spectrometer was equipped with a monochromatic
PS-N3 due to the shift of the
u
-terminal methine from
d
¼ 4.5 ppm
(Ha) to
d
¼ 3.9 ppm (Hb) [21,24].
3.2. Formation of inverse colloidal G1Cbz-alkyne arrays
Al KR X-ray source (h
n
¼ 1486.7 eV) incident at 90ꢁ, relative to the
axis of a hemispherical energy analyzer. The spectrometer was
operated both at high and low resolutions with pass energies of
23.5 and 187.85 eV, respectively, a photoelectron take off angle of
45ꢁ from the surface, and an analyzer spot diameter of 1.1 mm. All
spectra were collected at room temperature with a base pressure of
1 ꢂ 10ꢀ8 Torr. The peaks were analyzed first by background
subtraction, using the Shirley routine. All the samples were
completely dried in argon gas prior to XPS measurements. Atomic
Force Microscopy (AFM) measurements were carried out in a piezo
scanner from Agilent Technologies. The scanning rate was set
The procedure for the formation of patterned polymer brush
surfaces is illustrated in Scheme 1 (Route 1). First, PS microspheres
(500 nm) immersed in a water SDS solution, were deposited onto
a
conducting ITO substrate using a vertical motor via the
LangmuireBlodgett (LB)-like technique, forming a hexagonally closed-
packed monolayer [22]. The colloidal pattern then becomes a mask
for the in-situ electrodeposition of an electroactive monomer to
form an inverse opal of a conducting polymer (polycarbazole). It
should be mentioned that the use of a compatible solvent like ACN
is important to successfully electrodeposit electroactive molecules in

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E.L. Foster et al. / Polymer 53 (2012) 3124e3134
Scheme 2. Polymerization of styrene via (a) ATRP from MBMP and post nucleophilic substitution, (b) RAFT polymerization from 4-cyano-4-(thiobenzoylthio)pentanoic acid.
order to maintain the hexagonally closed-packed monolayer of PS
microspheres. During electrodeposition, solvents such as water, THF,
DCM, or toluene tend to wash the microspheres or destroy the
order of the patterned surface.
Electrodeposition of G1Cbz-alkyne was achieved via chro-
noamperometry using a constant potential of 1.3 V for 3 min. To
confirm the successful electrodeposition a monomer-free scan was
performed (Fig. 3a). UVeVis spectrum (Fig. 3b) of the electro-
deposited film after removal of the PS microspheres, by soaking in
THF, reveals the signature peaks of a typical crosslinked poly-
carbazole network film on ITO with peaks centered at 430 and
The advantage of using electrodeposition is that G1Cbz-alkyne is
only deposited at the interstitial void spaces between the hexago-
nally packed PS microspheres (Fig. 4a). The PS microspheres were
then removed by washing with THF (2ꢂ, 30 min), creating the 2-D
inverse colloidal G1Cbz-alkyne arrays. AFM topography measure-
ments of the inverse colloidal G1Cbz-alkyne arrays depict a high
periodicity of the PS particle imprinted film (Fig. 4b). The size of the
cavity matches the size of the PS particle template as determined by
the AFM line profile (Fig. 4d and e). The AFM line profile also
showed that the average height of the cavity before polymerization
was 9.2 ꢃ 0.8 nm (Fig. 4e).
>750 nm. These peaks are assigned to the
p to p
* transition of the
polycarbazole and the polaronic band formation of the conjugated
polycarbazole and their redox ion couple with the hexa-
fluorophosphate ions respectively, further confirming the
successful formation of the inverse colloidal G1Cbz-alkyne array
[25,26].
3.3. Grafting of PS-N3 onto inverse colloidal G1Cbz-alkyne arrays
To create a highly ordered patterned grafted polymer film, the
CuAAC reaction was performed on the inverse colloidal G1Cbz-
alkyne arrays (Fig. 4c). From the AFM topography image the
Fig. 2. 1H NMR spectra and peak labels for bromine-terminated polystyrene (PS-Br) and, azido-terminated polystyrene (PS-N3).

E.L. Foster et al. / Polymer 53 (2012) 3124e3134
3129
were then backfilled with either a 1-octadecanethiol or ATRP-silane
initiator SAMs on gold or ITO substrates respectively [30]. Based on
this it should also be possible to backfill the cavities with “clickable”
materials i.e. azidoundecanethiol.
The formation of the laterally patterned binary composite
surface is illustrated in Scheme 1, Route 2. First the inverse colloidal
G1Cbz-TEG polymer array was created on gold substrates according
to previous literature [30]. The second step involved back-filling the
cavities of the inverse colloidal G1Cbz-TEG arrays with a “clickable”
azidoundecanethiol. This step was then followed by grafting PS-
alkyne to the azidoundecanethiolSAM’s via CuAAC. AFM topog-
raphy images (Fig. 6aec) and line profiles (Fig. 6def), confirms the
success of the various stages of film development. For example, the
adsorption of azidoundecanethiol into the inner holes is clearly
seen in the AFM topography image (Fig. 6b). Changes in surface
morphology are also evident after grafting the PS-alkyne into the
cavities of the G1Cbz-TEG arrays via the CuAAC reaction (Fig. 6c).
Further verification of film development can be seen in the AFM
line profiles in Fig. 6def. For example, the successful immobiliza-
tion of the azidoundecanethiol inside the cavities of G1Cbz-TEG
arrays was determined by the difference in height before (Fig. 6d)
and after immobilization of azidoundecanethiol (1.8 ꢃ 0.4 nm). This
value is equivalent to the experimental length found in literature
[31]. The AFM line profile analysis provides further evidence of the
successful grafting of PS-alkyne onto the azidoundecanethiolSAM
(Fig. 6f). For example, by comparing Fig. 6e and f, a clear increase in
thickness from 1.8 ꢃ 0.4 nm to 8.8 ꢃ 1.3 nm is evident.
High resolution X-ray photoelectron spectroscopy (XPS) spectra
of the azide-terminated SAM further established the presence of
the azide functionality and the thiolate bond, and provided
a benchmark for comparison after the CuAAC. Fig. 7a shows an XPS
high resolution scan in the binding energy (BE) range (158e168 eV)
of the thiolate sulfur (S 2p) of the azidoundecanethiolSAM [32]. The
N 1s photoelectron spectrum is given in Fig. 7b. Two distinct peaks
at 399.5 and 403.5 eV are observed in the high resolution scan. The
lower BE peak (399.5 eV) is attributed to the electron-rich outer
nitrogen(s) of the azide and the higher BE peak (403.5 eV) to the
electron deficient inner nitrogen [33]. Comparing the N 1s spec-
trum on the surface before and after the CuAAC reaction of PS-
alkyne, the azide peak at 404.5 eV was reduced significantly after
the reaction (Fig. 7b). This indicates the conversion of azide groups
to the triazole ring during the cycloaddition reaction [34].
Based on these results it should be clear that a number of
possible binary systems could be fabricated. For example, herein we
reported the CuAAC reaction of PS-N3 or PS-alkyne onto “clickable”
colloidally templated surfaces, however any previously reported
clickable arrays could also be theoretically covalently grafted to
these surfaces. Examples include biotin, proteins, carbohydrates,
and nanomicrospheres [35].
Fig. 3. (a) Representative I-T curve of the electrodeposition via chronoamperometry at
a constant potential of 1.3 V for 3 min and the subsequent monomer free scan (inset).
(b) UVeVis spectrum of inverse colloidal G1Cbz-alkyne arrays after electrodeposition.
morphology has changed from the hexagonal array (Fig. 4b), to
a relatively spherical void with a more granular appearance on the
periphery of the patterned area (Fig. 4c). The AFM line profiles
(Fig. 4f) before and after grafting PS-N3 also show an increase in the
patterned film thickness from 9.2 ꢃ 0.8 nm to 13.4 ꢃ 1.8 nm.
Further evidence of the successful grafting of PS-N3 via CuAAC
reaction comes from attenuated total reflectance infrared spec-
troscopy (ATR-IR). In Fig. 5 an increase in intensity of the charac-
teristic peaks of PS is evident upon grafting the PS-N3 onto the
G1Cbz-alkyne arrays (gray) when compared to the ATR-IR spectra of
the G1Cbz-alkyne film (black). For example, the ATR-IR spectrum of
the grafted PS-N3 showed the expected peaks at 3034 cmꢀ1
,
2932 cmꢀ1, 1600 cmꢀ1, 1500 cmꢀ1, and 1456 cmꢀ1 corresponding to
the aromatic CeH stretch, aliphatic CeH stretch of the polymer
backbone, two bands for C]C (in ring) stretches, and CeC aromatic
stretch (in ring), respectively [27]. Also comparison of the PS-N3
grafted film to the G1Cbz-alkyne reveals a disappearance of the
terminal alkyne signature peak at 3300 cm-1 (inset). This is
attributed to the formation of the triazole product upon grafting
the PS-N3 to the G1Cbz-alkyne array [9].
3.5. Temperature responsive PPEGMEMA
Porous membranes that predictably respond to pH [36],
temperature [37], or electric fields [38] have been the focus of
research for the last few decades. These responsive membranes
present potential applications including controlled drug release,
catalysis, sensors and separation of macromolecules including
biological molecules such as proteins. One of the most widely used
approaches to create membranes with controlled porosity is to
graft stimuli-responsive macromolecules onto the surfaces of
porous membranes. Recently, oligo(ethylene glycol)- methacrylic
polymers have attracted interest because of their biocompatibility
and thermo-responsive properties [39].
3.4. Formation of inverse colloidal G1Cbz-TEG arrays
Another component of surface patterning is the fabrication of
laterally patterned binary polymer composites. It should be
mentioned however that there are only a limited number of ways to
produce such surfaces [28]. Recently our group has shown that
laterally patterned binary polymer surfaces can be produced via
successive SIP from the colloidally templated G1Cbz-CTA and SAM’s
of 11-(2-Bromo-2-methyl)propionyloxy) undecyltrichlorosilane
(ATRP-silane initiator) [29]. Similarly successful colloidally tem-
plated binary composites have also been fabricated from the
inverse colloidal G1Cbz-TEG arrays. From these arrays, the cavities
Based on the interest in porous membranes, herein we present
a novel approach to combine the “grafting to” approach of the

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E.L. Foster et al. / Polymer 53 (2012) 3124e3134
Fig. 4. AFM topography 2-D images (4 ꢂ 4
m
m): (a) 500 nm PS particle monolayer array, (b) after electrodeposition of G1Cbz-alkyne and washing of PS microspheres (inverse
colloidal G1Cbz-alkyne arrays), and (c) after grafting PS-N3. Line profile analysis of (d) single PS particle, (e) cavities after electrodeposition of G1Cbz-alkyne and PS microspheres
removal, and (f) G1Cbz-alkyne arrays before and after CuAAC reaction with PS-N3.
electroactive and thermo-responsive G1Cbz-PPEGMEMA-CTA and
colloidal templating. Scheme 3 depicts the fabrication of G1Cbz-
PPEGMEMA-CTA from the G1Cbz-CTA and the subsequent thermo-
responsive arrays following electrodeposition and removal of the
PS microspheres. Here polymerization of PEGMEMA to yield G1Cbz-
PPEGMEMA-CTA was carried out in THF at 70 ꢁC, yielding relatively
high molar mass (Mn ¼ 13,087 g/mol) and PDI (1.29).
100 mV/s (Fig. 8c). In the first CV cycle, the oxidation peak has an
onset potential at w1.0 V. This onset is attributed to the formation
of electron in the nitrogen atom of the N-substituted carbazole
monomer [41]. This reactive radical cation combines with another
radical cation to form the poly(carbazole). In the second cycle,
a new oxidation peak appears between 0.7 V and 1.0 V due to the
formation of a more stable dication (bipolaron) with extended
p-
1H NMR analysis data shows the typical peaks of the PPEG-
MEMA further confirming successful formation via RAFT polymer-
ization (Fig. 8a) [40]. As seen in Fig. 8b one can see from the zoomed
in aromatic region of the 1H spectra that the electroactive carbazole
and the terminal CTA moieties are still present [8]. End group
analysis to find molar mass (Mn ¼ 12,900 g/mol) from the 1H
spectra are also consistent with GPC data.
conjugation. The corresponding reduction peak in the reverse scan,
from 0.6 V to 0.9 V is also evident. As time progresses the current
increases at this reduction oxidation (redox) peak, indicating the
formation of more p-conjugated species as a result of further cross
linking between the carbazole molecules and electrodeposition of
more G1Cbz-PPEGMEMA-CTA onto the ITO electrode substrate.
UVeVis was used to further prove the presence of the G1Cbz-
PPEGMEMA-CTA arrays (see Supporting information).
Investigations into the swelling and collapsing nature of PPEG-
MEMA brushes due to their lower critical solution temperature
Electrodeposition of G1Cbz-PPEGMEMA-CTA on colloidally
templated ITO was achieved via cyclic voltammetry (CV) using
a scanning potential of 0e1.1 V for 20 cycles at a scan rate of

E.L. Foster et al. / Polymer 53 (2012) 3124e3134
3131
Fig. 5. ATR-IR spectra of before and after grafting PS-N3 via CuAAC reaction to the
inverse colloidal G1Cbz-alkyne array from (a) 1250e4000 cmꢀ1 and 3100e3400 cmꢀ1
(inset).
(LCST) transition have been thoroughly examined [42]. Herein, the
thermo-responsive properties of the colloidally templated G1Cbz-
PPEGMEMA-CTA arrays were investigated by comparing the AFM
topography images at either 22 ꢁC (Fig. 9a) or 70 ꢁC (Fig. 9b). As can
be seen in Fig. 9a, at 22 ꢁC the water temperature is below the LCST
of PPEGMEMA, leading to the swollen morphology of the colloidal
arrays. What can also be seen from the AFM images is that the pores
of the inverse colloidal arrays are partially covered by the swollen
polymer array. When the temperature is increased to 70 ꢁC,
Fig. 7. High resolution XPS scans of (a) S 2p and, (b) N 1s peaks before and after
grafting PS-alkyne to azidoundecanethiol.
Fig. 6. AFM topography 2-D images (4 ꢂ 4
mm): (a) inverse colloidal G1Cbz-TEG array, (b) after backfilling cavities with azidoundecanethiol, and (c) after grafting PS-alkyne via
CuAAC reaction to azidoundecanethiol. Line profile analysis: (d) inverse colloidal G1Cbz-TEG array, (e) after backfilling cavities with azidoundecanethiol, and (f) after grafting PS-
alkyne via CuAAC reaction to azidoundecanethiol.

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E.L. Foster et al. / Polymer 53 (2012) 3124e3134
a collapse of the colloidal G1Cbz-PPEGMEMA-CTA array is evident,
leading to a progressive opening of the pores. This collapse can be
attributed to the thermo-responsive nature of PEGMEMA mole-
cules. For example, hydrogels are exposed to an aqueous solution at
a temperature that is below their LCST, water polymer interactions
dominate and the hydrogel swells. Above the LCST however,
hydrophobic interactions between the polymer chains dominate
and the hydrogel structure collapses, releasing water from the
hydrogel matrix [43]. Similarly, peak-to-baseline AFM line profile
analysis (Fig. 9c) was also performed in order to get more insight
into the swelling deswelling behavior. As seen from Fig. 9c,
a collapse is evident is the swollen case (22 ꢁC) where the baseline
is no longer evident. This data means that the thermo-responsive
material fills in (less porous) the cavities of the hexagonally
closed packed arrays (note: in the peak-to-baseline AFM line profile
analysis, swelling in the z-axis (vertical swelling) was ignored). In
the case when the temperature was above the LCST (70 ꢁC), the
patterns return to a more familiar hexagonally closed pack array,
and a clearer baseline is also evident (Fig. 9c).
Ion permeability studies were also performed using the colloi-
dally templated G1Cbz-PPEGMEMA-CTA arrays (Fig. 9d). To test the
effects of temperature on ion permeability, Fe(CN6)3ꢀ anions were
used as molecular probes. After scanning at room temperature
(22 ꢁC) the electrochemical cell was immersed in a preheated water
bath at a temperature of 70 ꢁC, in order to maximize the collapse of
the colloidally templated PPEGMEMA array and hence increase its
porosity. Comparison of the room temperature and elevated
temperature experiments indicated an increase in the maximum
current density by 20% at the elevated temperature 70 ꢁC. This is
Scheme 3. (a) RAFT polymerization of PEGMEMA to form G1Cbz-PPEGMEMA-CTA and
(b) demonstration of thermo-responsive opening and closing of the inverse colloidal
G1Cbz-PPEGMEMA-CTA arrays.
Fig. 8. 1H NMR spectra from (a) 0.6 ppme8.3 ppm (b) 6.8 ppm to 8.3 ppm. (c) Cyclic voltammetry scan of the electrodeposition of G1Cbz-PPEGMEMA-CTA onto colloidally
templated ITO substrate.

E.L. Foster et al. / Polymer 53 (2012) 3124e3134
3133
Fig. 9. AFM topography images of the inverse colloidal G1Cbz-PPEGMEMA-CTA arrays at (a) 22 ꢁC and (b) 70 ꢁC. (c) AFM line profiles of the inverse colloidal G1Cbz-PPEGMEMA-CTA
arrays at 22 ꢁC and 70 ꢁC (d) Cyclic voltammetry comparative scan of inverse colloidal G1Cbz-PPEGMEMA-CTA arrays at 22 ꢁC and 70 ꢁC.
[3] Pyun J, Matyajaszewski K. Chem Mater 2001;13(10):3436e48.
[4] Geoghegan M, Clarke CJ, Boue F, Menelle A, Russ T, Bucknall DG. Macromol-
a consequence of the collapse of the PPEGMEMA array which
enhances the ion transport through the exposed ITO surface.
ecules 1999;32(15):5106e14.
Temperature changes the permeability of the membrane primarily
by limiting ion transport. In principle, smart colloidal arrays can be
designed to have temperature-dependent properties with respect
to ion and electron transport properties for practical applications.
[5] Yang Z, Galloway JA, Yu H. Langmuir 1999;15(24):8405e11.
[6] Tran Y, Auroy P. J Am Chem Soc 2001;123(16):3644e54.
[7] Cecchet F, Meersman BD, Demoustier-Champagne S, Nysten B, Jonas AM.
Langmuir 2006;22(3):1173e81.
[8] Patton LD, Taranekar P, Fulghum T, Advincula R. Macromolecules 2008;
41(18):6703e13.
[9] Nandivada N, Chen HY, Bondarenko L, Lahann J. Angew Chem Int Ed 2006;
45(20):3360e3.
4. Conclusions
[10] Kolb HC, Finn MG, Sharpless KB. Angew Chem Int Ed 2001;40(11):2004e21.
[11] Ostaci RV, Damiron D, Grohens Y, Légar L, Drockenmuller E. Langmuir 2010;
26(2):1304e10.
[12] Godula K, Rabuka D, Nam KT, Bertozzi CR. Angew Chem Int Ed 2009;48(27):
4973e6.
[13] (a) Xu FJ, Neoh KG, Kang ET. Prog Polym Sci 2009;34(8):719e61;
(b) Nie Z, Kumacheva E. Nat Mater 2008;7(4):277e90;
(c) Geissler M, Xia Y. Adv Mater 2004;16(15):1249e69.
[14] (a) Chen T, Chang DP, Zauscher S. Small 2010;6(14):1504e8;
(b) Jones DM, Smith JR, Huck WTS, Alexander C. Adv Mater 2002;14(16):
1130e4;
In conclusion, we have developed new approaches of creating
topologically and well-defined “clickable” colloidally templated
arrays: the grafting chemistry can be performed onto an electro-
deposited pattern or by subsequent backfilling with azido
terminated SAM’s on templated conducting polymer arrays.
Another approach enabled the fabrication of ion gates by electro-
grafting colloidally templated electroactive thermo-responsive
oligo(ethylene glycol)-methacrylic polymers. Future work will
focus on the incorporation of binary biological arrays, e.g.
controlled or tunable absorption of various molecules into the
templated G1Cbz-PPEGMEMA-CTA cavities with proteins or other
biological macromolecules.
(c) Konradi R, Rühe J. Langmuir 2006;22(2):8571e5;
(d) Prucker O, Schimmel M, Tovar G, Knoll W, Rühe J. Adv Mater 1998;10(14):
1073e7;
(e) Zhou F, Jiang L, Liu W, Xue Q. Macromol Rapid Commun 2004;25(23):
1979e83;
(f) Rastogi A, Paik M, Tanaka M, Ober C. ACS Nano 2010;4(2):771e80;
(g) Ahn SJ, Kaholek M, Lee W, LaMattina B, LaBean T, Zauscher S. Adv Mater
2004;16(23e24):2141e5;
(h) Brough B, Christman KL, Wong TS, Kolodziej CM, Forbes JG, Wang K, et al.
Soft Matter 2007;3(5):541e6.
Appendix A. Supporting information
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.polymer.2012.05.040.
[15] (a) Martin CR. Science 1994;266(23):1961e6;
(b) Yuan ZH, Huang H, Dang HY, Cao JE, Hu BH, Fan S. Appl Phys Lett 2001;
78(20):3127e9;
(c) Rahman S, Yang H. Nano Lett 2003;3(4):439e42.
[16] (a) Park M, Harrison C, Chaikin PM, Register RA, Adamson DH. Science 1997;
276(5342):1401e4;
References
[1] Advincula RC, Brittain WJ, Caster KC, Rühe J, editors. Polymer brushes:
synthesis, characterization, applications. Weinheim: Wiley-VCH; 2004.
[2] Zhao B, Brittain WJ. Prog Polym Sci 2000;25(5):677e710.
(b) Morey MS, O’Brien S, Schwarz S, Stucky GD. Chem Mater 2000;12(4):
898e911;
(c) Cheng W, Baudrin E, Dunn B, Zink JIJ. J Mater Chem 2001;11(1):92e7.

3134
E.L. Foster et al. / Polymer 53 (2012) 3124e3134
[17] (a) Holland BT, Blanford CF, Stein A. Science 1998;281(5388):538e40;
(b) Jiang P, Bertone JF, Colvin VL. Science 2001;291(5541):453e7;
(c) Norell MA, Makovicky P, Clark JM. Nature 1997;389(6659):447e8.
[18] (a) Velev OD, Tessier PM, Lenhoff AM, Kaler EW. Nature 1999;401(6761):548;
(b) Jiang P, Cizeron J, Bertone JF, Colvin VL. J Am Chem Soc 1999;121(34):
7957e8.
[33] Wollman EW, Kang D, Frisbie CD, Lorkovic IM, Wrighton MS. J Am Chem Soc
1994;116(100):4395e404.
[34] Radhakrishnan C, Lo MKF, Warrier MV, Garcia-Garibay MA,
Monbouquette HG. Langmuir 2006;22(11):5018e24.
[35] (a) Qin G, Santos C, Zhang W, Li Y, Kumar A, Erasquin UJ, et al. J Am Chem Soc
2010;132(46):16432e41;
[19] Zakhidov AA, Baughman RH, Iqbal Z, Cui C, Khayrullin I, Dantas SO, et al.
Science 1998;282(5390):897e901.
(b) Broyer RM, Schopf E, Kolodziej CM, Chen Y, Maynard HD. Soft Matter
2011;7(21):9972e7;
[20] Deutsch M, Vlasov YA, Norris DJ. Adv Mater 2000;12(16):1176e80.
[21] Vogt AP, Sumerlin BS. Macromolecules 2006;39(16):5286e92.
[22] Marquez M, Grady BP. Langmuir 2004;20(25):10998e1004.
[23] Coessens V, Pintauer T, Matyjaszewski K. Prog Polym Sci 2001;26(3):337e77.
[24] Tsarevsky NV, Sumerlin BS, Matyjaszewski K. Macromolecules 2005;38(9):
3558e61.
(c) Zhang Y, Luo S, Tang Y, Yu L, Hou K-Y, Cheng J-P, et al. Anal Chem 2006;
78(6):2001e8;
(d) Gassensmith JJ, Erne PM, Paxton WF, Valente C, Stoddart JF. Langmuir
2011;27(40):1341e5.
[36] Lee D, Nolte AJ, Kunz AL, Rubner MF, Cohen RE. J Am Chem Soc 2006;128(26):
8521e9.
[25] Kaewtong C, Jiang CG, Park Y, Fulghum T, Baba A, Pulpoka B, et al. Chem Mater
2008;20(15):4915e24.
[26] Fulghum T, Karim A, Baba A, Taranekar P, Nakai T, Masuda T, et al. Macro-
molecules 2006;39(4):1467e73.
[27] Tria MC, Park JY, Advincula R. Chem Commun 2011;47(8):2393e5.
[28] Zhou F, Zheng Z, Yu B, Liu W, Huck WTS. J Am Chem Soc 2006;128(50):
16253e8.
[37] Chu LY, Li Y, Zhu JH, Chen WM. Angew Chem Int Ed 2005;44(14):2124e7.
[38] Lee SB, Martin CR. J Am Chem Soc 2002;124(40):11850e1.
[39] (a) Jonas AM, Hu Z, Glinel K, Huck WTS. Nano Lett 2008;8(11):3819e24;
(b) Yavus MS, Buyukserin F, Zengin Z, Camli ST. J Polym Sci Part A Polym Chem
2011;49(22):4800e8;
(c) Tria MCR, Grande CDT, Ponnapati RR, Advincula RC. Biomacromolecules
2010;11(12):3422e31.
[29] Foster LE, Tria MCR, Pernites RB, Addison SJ, Advincula RC. Soft Matter 2012;
8(2):353e9.
[30] (a) Pernites RB, Felipe MJL, Foster EL, Advincula RC. ACS Appl Mater Interfaces
2011;3(3):817e27;
(b) Pernites RB, Foster EL, Felipe ML, Robinson M, Advincula RC. Adv Mater
2011;23(10):1287e92.
[31] Zirbs R, Kienberger F, Hinterdorfer P, Binder WH. Langmuir 2005;21(18):
8414e21.
[40] (a) Lutz J-F, Börner HG, Weichenhan K. Macromolecules 2006;39(19):6376e83;
(b) Han S, Hagiwara M, Ishizone T. Macromolecules 2003;36(22):8312e9.
[41] (a) Ambrose JF, Nelson RFJ. Electrochem Soc 1968;115(11):1159e64;
(b) Xia C, Advincula RC. Chem Mater 2001;13(5):1682e91.
[42] (a) Li D, Jones GL, Dunlap JR, Hua F, Zhao B. Langmuir 2006;22(7):3344e51;
(b) Boyer C, Whittaker MR, Luzon M, Davis TP. Macromolecules 2009;42(18):
6917e26.
[43] Meenach SA, Anderson KW, Hilt JZ. J Polym Sci Part A Polym Chem 2010;48:
3229e35.
[32] Tarlov MJ, Burgess DRF, Gillen G. J Am Chem Soc 1993;115(12):5305e6.