Immobilization of polymer-decorated liquid crystal droplets on chemically tailored surfaces.

Materials Linear poly(ethylene imine) (LPEI) was synthesized by hydrolysis of the side chains of poly(2-ethyloxazoline) [MW = 50,000; obtained from Polysciences, Inc., Warington, PA] and purified prior to use in analogy to procedures described previously. 42 4-(2-Hydroxyethyl-1-piperazineethanesulfonic acid) (HEPES), sodium chloride, methanol, ethanol, dimethyl sulfoxide (DMSO), ethyl acetate, chloroform, dichloromethane, hexanes, trifluoroacetic acid, and glass cover slips were purchased from Fisher Scientific (Pittsburgh, PA). Acryloyl chloride, n -decylamine, 3-(dimethylamino)-1-propylamine, 1,3-diaminopropane, di- tert -butyl dicarbonate, branched poly(ethylene imine) [BPEI, MW = 25,000], fluorescein isothiocyanate labeled dextran [FITC-dextran, MW = 2,000,000], and 2,2'-azobisisobutyronitrile were purchased from Sigma-Aldrich (St. Louis, MO). 2-Vinyl-4,4-dimethylazlactone (VDMA) was a generous gift from Dr. Steven Heilmann (3M Corporation, St. Paul, MN). N -Decylacrylamide, N -[3-(dimethylamino)propyl]acrylamide, N -[3-( tert -butoxycarbonylamino)propyl]acrylamide, and poly(VDMA) (PVDMA) were synthesized in analogy to previously described procedures. 43 - 45 Carboxytetramethylrhodamine succinimidyl ester (TMR-NHS) was purchased from Molecular Probes (Carlsbad, CA). The LC 4-cyano-4′-pentylbiphenyl (5CB) was obtained from EMD Chemicals (Hawthorne, NY). Glass beads (diameter = 3-10 μm) were purchased from Polysciences, Inc. Deionization of a distilled water source was performed using a Milli-Q system (Millipore, Bedford, MA) yielding water with a resistivity of 18.2 MΩ. All materials were used as received and without additional purification unless otherwise noted. General Considerations Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AC+ 300 spectrometer (300.135 MHz for proton; Billerica, MA). Chemical shift values are given in ppm and are referenced with respect to residual protons from solvent. Polarized light, bright-field, and fluorescence microscopy images of 5CB droplets were acquired using an Olympus IX-71 inverted microscope equipped with a 100 W mercury lamp and filter cube with a 560 nm excitation filter and a 645 nm emission filter. Images were captured using a Hamamatsu 1394 ORCA-ER-CCD camera controlled with SimplePCI software (Hamamatsu Inc., Sewickly, PA) Laser scanning confocal microscopy (LSCM) was performed using a Bio-Rad Radiance 2100 MP Rainbow laser scanning confocal microscope. Tetramethylrhodamine and fluorescein were excited sequentially using laser lines at 543 nm and 488 nm, respectively, and fluorescence emission was collected individually from the red and green channels. Silicon substrates used for reflective infared spectroscopy experiments were prepared by depositing thin layers of titanium (10 nm) and gold (200 nm) sequentially onto silicon wafers (Si-Tech, Inc., Topsfield, MA) using an electron-beam evaporator (Tek-Vac Industries, Brentwood, NY).

Characterization of multilayered films by polarization-modulation infrared reflectance-absorbance spectroscopy

(PM-IRRAS) was conducted in analogy to previously reported methods. 46 All experiments involving the use of 5CB were performed at ambient room temperature (~25 °C), well below the nematic/isotropic transition temperature of 5CB (33.5 °C) 21 unless otherwise noted. Synthesis of Polymer 1 The synthesis of polymer 1 was performed by the conjugate addition of LPEI to acrylamide compounds in analogy to previously published methods. 44 , 45 N -[3-( tert- Butoxycarbonylamino)propyl]acrylamide (13.1 mg, 0.058 mmol) was added to a solution of LPEI (50 mg, 1.16 mmol) in methanol in a screw-capped vial equipped with a magnetic stir bar. The reaction solution was stirred at 50 °C for 7 days at which time N -decylacrylamide (98.2 mg, 0.46 mmol) was added. The reaction mixture was stirred for an additional 7 days at which time N -[3-(dimethylamino)propyl]acrylamide (218 mg, 1.39 mmol) was added and the reaction mixture was allowed to stir for an additional 7 days. The resulting reaction product was isolated by repeated precipitation into a mixture of hexanes and diethyl ether (9:1, v/v) to yield the Boc-protected polymer. Removal of the Boc protecting group was achieved by dissolving the polymer in a mixture of dichloromethane and trifluoroacetic acid (1:1, v/v) in a screw-capped vial equipped with a magnetic stir bar. The reaction mixture was stirred for two hours at room temperature. The resulting reaction product was isolated by precipitation into a mixture of hexanes and diethyl ether (5:1, v/v) to yield polymer 1 as a tacky, viscous oil. M n = 29,500; PDI=3.7. 1 H NMR (CDCl 3 ) δ (ppm) 0.877 (t, -NHCH 2 CH 2 (CH 2 ) 7 C H 3 ), 1.17 (br, -NHCH 2 CH 2 (C H 2 ) 7 CH 3 ), 1.38 (m, -NHCH 2 C H 2 (CH 2 ) 7 CH 3 ), 1.80-1.85 (b, -NHCH 2 C H 2 CH 2 N(CH 3 ) 2 , -NHCH 2 C H 2 CH 2 N 2 ), 2.81 (s, -NHCH 2 CH 2 CH 2 N(C H 3 ) 2 ), 2.87-3.27 (br m), 3.36-3.42 (b, m, -NHC H 2 CH 2 (CH 2 ) 7 CH 3 , -NHC H 2 CH 2 CH 2 N(CH 3 ) 2 , -NHC H 2 CH 2 CH 2 NH 2 ). Synthesis of Fluorescently Labeled Polymer 1 A fluorescently-labeled analog of polymer 1 (Polymer 1 TMR ) was synthesized using the following procedure. Polymer 1 (16.9 mg, 30.7 μmol) was weighed into a screw-capped vial equipped with a magnetic stir bar. DMSO (0.93 mL) and TEA (3.0 μL) were added to the vial and the solution was stirred for four hours at room temperature. TMR-NHS (7.4 mg, 14 μmol) was dissolved in 74 μL of DMSO and added to this solution. The reaction solution was stirred at room temperature for 50 h. The DMSO was removed by maintaining the vial under low pressure at 50 °C for two days. The polymer was isolated by dialysis against DI water (MW cutoff = 3500) for three weeks and lyophilized to produce a pink solid that was used without further purification.

Preparation of LC Emulsions

A dispersion of LC droplets was formed by alternately sonicating a mixture of 5CB in an aqueous buffer (1 vol%; 10 mM HEPES, pH 7.0) for 10 seconds followed by agitation with a vortex mixer for 10 seconds. This process was repeated a minimum of five times. A volume of the LC emulsion (150 μL) was added to a solution of polymer 1 (1:2 v/v, respectively) dissolved in HEPES buffer. The LC emulsion was rotated gently end-over-end using a laboratory rotator for up to 25 hours. Excess polymer solution was removed from the bulk aqueous phase by using the following washing procedure. A dispersion of LC droplets (200 μL) was combined with HEPES buffer (1 mL) in a microcentrifuge tube. The sample was centrifuged for 10 minutes at 500 g. The supernatant was removed and the droplets were resuspended in HEPES buffer (200 μL). Microscopy images of the droplets were collected by placing the dispersion of LC droplets (10 μL) on a glass coverslip (either untreated or modified with multilayered polymer films, see text). For experiments designed to investigate the immobilization of droplets on multilayered films, droplets were allowed to settle to the surface of these substrates for a period of 10 minutes. Freely suspended droplets were then removed from the solution by flowing buffer over the surface using a micropipette at a rate of approximately 20 μL/s. Layer-by-Layer Fabrication of Polymer Thin Films Multilayer films composed of BPEI and PVDMA were fabricated in analogy to previously reported methods. 46 , 47 Briefly, solutions of BPEI and PVDMA were prepared in acetone (20 mM with respect to the molecular weight of the repeat unit). Glass and silicon substrates were cleaned with deionized water, methanol, ethanol, and acetone and dried under a stream of filtered, compressed air prior to the fabrication of multilayered films. Films were deposited layer-by-layer on glass or silicon manually according to the following general procedure: 1) Substrates were submerged in a solution of BPEI for 30 seconds, 2) substrates were removed and immersed in an initial acetone bath for 30 seconds followed by a second acetone bath for 30 seconds, 3) substrates were submerged in a solution of PVDMA for 30 seconds, and 4) substrates were rinsed in the manner described above. This cycle was repeated until four layer pairs (or ‘bilayers’) of BPEI/PVDMA were deposited to yield thin films (approximately 30 nm thick) terminated with a final layer of PVDMA. Films were dried under a stream of filtered, compressed air and were either used immediately or stored in a vacuum desiccator prior to use. Additional modification of these azlactone-functionalized reactive films to design amine-functionalized or carboxylate-functionalized surfaces was performed by either (i) submerging the substrates into a solution of BPEI for 30 seconds to terminate the film with a final layer of BPEI, followed by rinsing as described above, or (ii) hydrolyzing residual azlactone functionality in the films by placing the substrate in a closed vessel under complete saturation of water vapor at 37 °C for 48 hours. Complete hydrolysis of the residual azlactone functionality was confirmed by PM-IRRAS. To fabricate surfaces with spatially-defined chemical patterns, BPEI/PVDMA films terminated with a final layer of BPEI were treated with a small drop of a PVDMA solution (20 mM in DMSO) for two minutes. Films were then rinsed with cold acetone (approximately −50 °C) and dried under filtered air.

Materials Linear poly(ethylene imine) (LPEI) was synthesized by hydrolysis of the side chains of poly(2-ethyloxazoline) [MW = 50,000; obtained from Polysciences, Inc., Warington, PA] and purified prior to use in analogy to procedures described previously. 42 4-(2-Hydroxyethyl-1-piperazineethanesulfonic acid) (HEPES), sodium chloride, methanol, ethanol, dimethyl sulfoxide (DMSO), ethyl acetate, chloroform, dichloromethane, hexanes, trifluoroacetic acid, and glass cover slips were purchased from Fisher Scientific (Pittsburgh, PA). Acryloyl chloride, n -decylamine, 3-(dimethylamino)-1-propylamine, 1,3-diaminopropane, di- tert -butyl dicarbonate, branched poly(ethylene imine) [BPEI, MW = 25,000], fluorescein isothiocyanate labeled dextran [FITC-dextran, MW = 2,000,000], and 2,2'-azobisisobutyronitrile were purchased from Sigma-Aldrich (St. Louis, MO). 2-Vinyl-4,4-dimethylazlactone (VDMA) was a generous gift from Dr. Steven Heilmann (3M Corporation, St. Paul, MN). N -Decylacrylamide, N -[3-(dimethylamino)propyl]acrylamide, N -[3-( tert -butoxycarbonylamino)propyl]acrylamide, and poly(VDMA) (PVDMA) were synthesized in analogy to previously described procedures. 43 - 45 Carboxytetramethylrhodamine succinimidyl ester (TMR-NHS) was purchased from Molecular Probes (Carlsbad, CA). The LC 4-cyano-4′-pentylbiphenyl (5CB) was obtained from EMD Chemicals (Hawthorne, NY). Glass beads (diameter = 3-10 μm) were purchased from Polysciences, Inc. Deionization of a distilled water source was performed using a Milli-Q system (Millipore, Bedford, MA) yielding water with a resistivity of 18.2 MΩ. All materials were used as received and without additional purification unless otherwise noted.

Supplementary Material 1_si_001