Photolithographically patterned surface modification of poly(dimethylsiloxane) via UV-initiated graft polymerization of acrylates

Patterned surface modification of poly(dimethylsiloxane) (PDMS) is achieved by combining ultraviolet-initiated graft polymerization (UV-GP) and photolithography. Poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) patterns were grafted onto PDMS with micrometer-scale feature edge resolution. The morphology and chemical composition of the grafted layers were assessed by optical and atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and XPS imaging. AFM section analyses demonstrated the deposition of 33 +/- 1 and 62 +/- 8 nm thick patterned films of PAA and PMAA, respectively. Spatially resolved C 1s XPS provided images of carboxylic acid functionalities, verifying the patterned deposition of acrylate films on PDMS. These observations demonstrate the general usefulness of UV-GP and photolithography for micropatterning.     

Grafting of light‐activated antimicrobial materials to nylon films

Protoporphyrin IX and zinc protoporphyrin IX were grafted to the surface of nylon‐6,6 films via an ethylene diamine bridge and a poly(acrylic acid) (PAA) scaffold. X‐ray photoelectron spectroscopy showed that approximately 57% of the nylon surface was covered by PAA and approximately 6% of the carboxylic acid groups in PAA were grafted to the ethylene diamine derivative of protoporphyrin IX or its zinc salt. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 41–47, 2003     

Surface modification of glass beads with poly(acrylic acid)

Non‐porous P₂ glass beads were etched with sodium hydroxide to increase the number of silanol groups that could be used to modify the surface. The etched glass beads were then functionalized with 3‐aminopropyltriethoxysilane (APS) and/or glycidoxypropyltrimethoxysilane (GPS). The surface of the glass beads were further modified with poly(acrylic acid) (PAA) by reacting the carboxyl groups on PAA with the amino groups of the pregrafted APS. The chemical modifications were characterized by FT‐IR spectroscopy, particle size analyzer and tensiometry for contact angle and porosity measurements. Five different molecular weight PAA polymers ranging from 2000 to 3,000,000 were grafted with less than expected increase of grafted PAA with molecular weight. The amount of APS and PAA on the surface was determined from thermogravimetric analysis and elemental analysis data. The surface properties of the surface modified glass beads were determined by measuring water and hexane penetration rate and contact angle. The surface morphology was examined by scanning electron microscopy. Copyright © 2006 John Wiley & Sons, Ltd.     

Suppression of surface pattern formation in spin‐coated polymer films by the addition of polydimethylsiloxane‐grafted silica nanoparticles

Polydimethylsiloxane (PDMS)‐grafted nanoparticles and PDMS were added, respectively, to inhibit the dewetting of polymer films and the formation of surface patterns in spin coating. Uniform and flat films were successfully achieved with the addition of PDMS‐grafted silica nanoparticles or PDMS. Time‐of‐flight secondary ion mass spectrometry depth profiling indicated that PDMS‐grafted silica nanoparticles and PDMS preferentially segregated to the surface. A high concentration of bromine end groups was observed at the interface. The surface layer of PDMS or PDMS‐grafted silica nanoparticles can decrease the surface tension of the polymer solutions and reduce the evaporation rates of the solvents, providing more time for the bromine end groups to anchor themselves at the silicon substrates. Copyright © 2016 John Wiley & Sons, Ltd.     

A Simple Method for Fabricating Patterned Curvilinear Microstructures in Poly(dimethylsiloxane) by Selective Wetting

The fabrication of patterned microstructures in poly(dimethylsiloxane) (PDMS) is a prerequisite for soft lithography. Herein, curvilinear surface relief microstructures in PDMS are fabricated through a simple three‐stage approach combining microcontact printing (μCP), selective surface wetting/dewetting and replica molding (REM). First, using an original PDMS stamp (first‐generation stamp) with linear relief features, a chemical pattern on gold substrate is generated by μCP using hexadecanethiol (HDT) as an ink. Then, by a dip‐coating process, an ordered polyethylene glycol (PEG) polymer‐dot array forms on the HDT‐patterned gold substrate. Finally, based on a REM process, the PEG‐dot array on gold substrate is used to fabricate a second‐generation PDMS stamp with microcavity array, and the second‐generation PDMS stamp is used to generate third‐generation PDMS stamp with microbump array. These fabricated new‐generation stamps are utilized in μCP and in micromolding in capillaries (MIMIC), allowing the generation of surface micropatterns which cannot be obtained using the original PDMS stamp. The method will be useful in producing new‐generation PDMS stamps, especially for those who want to use soft lithography in their studies but have no access to the microfabrication facilities.     

Exploring the effect of radiation crosslinking on the physico‐mechanical,dynamic mechanical and dielectric properties of EOC–PDMS blends for cable insulation applications

This work focuses on the effect of electron beam irradiation on the physico‐mechanical, dynamic mechanical and dielectric properties of blends based on ethylene octene copolymer (EOC) and poly dimethyl siloxane (PDMS) rubber. It is found that electron beam irradiation caused considerable improvement in the physico‐mechanical properties; the tensile strength was enhanced by nearly 35% for 70:30 EOC:PDMS blend. Phase morphology of the blends analyzed before irradiation by scanning electron microscopy (SEM) exhibited droplet/matrix morphology with sizes of the PDMS rubber domain varying from 0.55 µm to 0.47 µm as the amount of PDMS rubber decreased from 30 wt% to 10 wt%. This reduction in the PDMS rubber domain has been correlated with the physico‐mechanical properties of the blends. Further, the dynamic mechanical properties and creep behavior of these EOC:PDMS blends before and after irradiation has been studied. It is inferred that the 70:30 blend after radiation crosslinking shows a 17% decrease in the creep compliance, i.e. higher creep resistance compared to neat blends. All the radiation crosslinked blends exhibited lower dielectric constant, lower dielectric loss and higher electrical resistivity as compared to the virgin blends which makes it suitable for cable insulating application. Copyright © 2016 John Wiley & Sons, Ltd.     

Ultrastretchable,Tough, and Notch‐Insensitive Hydrogels Formed with Spherical Polymer Brush Crosslinker

Spherical polymer brushes, poly(acrylic acid) (PAA)‐grafted polystyrene nanoparticle (PAA@PS), are employed as the macro‐crosslinker to prepare PAA hydrogels. Benefitting from the innumerable hydrogen bonds between highly entangled PAA chains both in bulk and on the polymer brush, the PAA/PAA@PS hydrogels combine desirable stretchability, toughness, and notch‐insensitivity. The uniaxial tensile tests show a very high fracture elongation up to 9.1 × 10³% while the fracture toughness reaches 3.0 MJ m⁻³ and the maximum swelling ratio of the hydrogel can be 2.0 × 10³ as well. After being loaded with silver nanoparticles, the PAA/PAA@PS hydrogels are employed as a recyclable catalyst successfully.     

Glass bead grafting with poly(carboxylic acid) polymers and maleic anhydride copolymers

Glass beads were etched with acids and bases to increase the surface porosity and the number of silanol groups that could be used for grafting materials to the surfaces. The pretreated glass beads were functionalized using 3‐aminopropyltriethoxysilane (APS) coupling agent and then further chemically modified by reacting the carboxyl groups of carboxylic acid polymers with the amino groups of the pregrafted APS. Several carboxylic acid polymers and poly(maleic anhydride) copolymers, such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), poly(styrene‐alt‐maleic anhydride) (PSMA), and poly(ethylene‐alt‐maleic anhydride) (PEMA) were grafted onto the bead surface. The chemical modifications were investigated and characterized by FT‐IR spectroscopy, particle size analysis, and tensiometry for contact angle and porosity changes. The amount of APS and the different polymer grafted on the surface was determined from thermal gravimetric analysis and elemental analysis data. Spectroscopic studies and elemental analysis data showed that carboxylic acid polymers and maleic anhydride copolymers were chemically attached to the glass bead surface. The improved surface properties of surface modified glass beads were determined by measuring water and hexane penetration rates and contact angle. Contact angles increased and porosity decreased as the molecular weights of the polymer increased. The contact angles increased with the hydrophobicity of the attached polymer. The surface morphology was examined by scanning electron microscopy (SEM) and showed an increase in roughness for etched glass beads. Copyright © 2007 John Wiley & Sons, Ltd.     

Electroless Deposition of Nickel on Photografted Polymeric Microscale Patterns

This report demonstrates the electroless deposition of Ni onto micropatterns of poly (acrylic acid) (PAA) photografted to phthalimide‐terminated self‐assembled monolayers (SAMs). PAA is spin‐coated onto phthalimide SAMs and covered with a photomask. UV irradiation selectively binds PAA to exposed regions of the surface, allowing PAA on unexposed regions to be rinsed off. A Pd catalyst is then selectively adsorbed to regions of the surface where PAA is bound. The adsorbed catalyst selectively initiates Ni plating upon immersion of the substrate into a Ni(SO₄) bath.

     

Formation of long‐range stripe patterns with sub‐10‐nm half‐pitch from directed self‐assembly of block copolymer

We have demonstrated directed self‐assembly of poly(styrene‐b‐dimethylsiloxiane) (PS‐b‐PDMS) down to sub‐10‐nm half‐pitch by using grating Si substrate coated with PDMS. The strong segregation between PS and PDMS enables us to direct the self‐assembly in wide grooves of the grating substrate up to 500 nm in width. This process can be applied to form various type of sub‐10‐nm stripe pattern along variety of grating shape. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Synthesis,characterization, and swelling behaviors of chitosan‐g‐poly(acrylic acid)/poly(vinyl alcohol) semi‐IPN superabsorbent hydrogels

A series of granulated semi‐interpenetrating polymer network (semi‐IPN) superabsorbent hydrogels composed of chitosan‐g‐poly(acrylic acid) (CTS‐g‐PAA) and poly(vinyl alcohol) (PVA) were prepared by solution polymerization using ammonium persulfate (APS) as an initiator and N,N′‐methylenebisacrylamide (MBA) as a crosslinker. The effects of reaction conditions such as the concentration of MBA, the weight ratio of AA to CTS, and the content of PVA on water absorbency were investigated. Infrared (IR) spectra and differential scanning calorimetry (DSC) analyses confirmed that AA had been grafted onto CTS backbone, and PVA semi‐interpenetrating into CTS‐g‐PAA networks. SEM analyses indicated that CTS‐g‐PAA/PVA has improved porous surface and PVA was uniformly dispersed in CTS‐g‐PAA network. The semi‐IPN hydrogel containing 10 wt% PVA shows the highest water absorbency of 353 and 53 g g^?1 in distilled water and 0.9 wt% NaCl solution, respectively. Swelling behaviors revealed that the introduction of PVA could improve the swelling rate and enhance the pH stability of the superabsorbent hydrogel. Copyright © 2009 John Wiley & Sons, Ltd.     

Micropatterning of Covalently Attached Biotin on Poly(lactic acid) Film Surfaces

A two‐step approach was used to micropattern covalently attached biotin on the surface of poly(lactic acid) (PLA) film. Poly(acrylic acid) (PAA) was micropatterned on PLA using photolithography in step 1, followed by carbodiimide wet chemistry to covalently attach biotin to acid groups in step 2. The PAA micropatterning reaction progression was monitored using attenuated total reflectance‐Fourier transform infrared (ATR‐FT‐IR) spectroscopy, water contact angle goniometry, and atomic force microscopy (AFM). The PAA‐biotin conjugation reaction characterization using XPS confirmed the carbodiimide mediated amidation reaction. The resultant PLA film was then immersed into a solution of fluorescence‐conjugated streptavidin and examined under fluorescence microscopy to reveal various micropatterns

     

Enhanced Microchip Electrophoresis of Neurotransmitters on Glucose Oxidase Modified Poly(dimethylsiloxane) Microfluidic Devices

In this paper, glucose oxidase (GOx) was employed to construct a functional film on the poly(dimethylsiloxane) (PDMS) microfluidic channel surface and apply to perform electrophoresis coupled with in‐channel electrochemical detection. The film was formed by sequentially immobilizing poly(diallyldimethylammonium chloride) (PDDA) and GOx to the microfluidic channel surface via layer‐by‐layer (LBL) assembly. A group of neurotransmitters (5‐hydroxytryptamine, 5‐HT; dopamine, DA; epinephrine, EP; dobuamine, DBA) as a group of separation model was used to evaluate the effect of the functional PDMS microfluidic devices. Electroosmotic flow (EOF) in the modified PDMS microchannel was well suppressed compared with that in the native one. Experimental conditions were optimized in detail. As expected, these analytes were efficiently separated within 110 s in a 3.7 cm long separation channel and successfully detected at a single carbon fiber electrode. Good performances were attributed to the decreased EOF and the interactions of analytes with the immobilized GOx on the PDMS surface. The theoretical plate numbers were 2.19×10⁵, 1.89×10⁵, 1.76×10⁵, and 1.51×10⁵ N/m at the separation voltage of 1000 V with the detection limits of 1.6, 2.0, 2.5 and 6.8 μM (S/N=3) for DA, 5‐HT, EP and DBA, respectively. In addition, the modified PDMS channels had long‐term stability and excellent reproducibility.     

Properties of poly(dimethylsiloxane)/hydrogel multicomponent systems

The properties of surface‐ and bulk‐modified poly(dimethylsiloxane) (PDMS) were examined. Laser‐induced surface grafting of poly(2‐hydroxyethyl methacrylate) (PHEMA) on PDMS and a sequential method for preparation of interpenetrating polymer networks of PDMS/PHEMA were, respectively, used for surface and bulk modifications. The hydrogel content and water‐uptake capability of the modified samples were also investigated. The modified PDMS samples were examined by performing attenuated total reflection/Fourier transform infrared spectroscopy, dynamic mechanical thermal analysis, scanning electron microscopy, and water contact‐angle measurements. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2145–2156, 2003     

Preparation and mechanical properties of poly(chitosan‐g‐DL‐lactic acid) fibrous mesh scaffolds

DL ‐lactic acid was grafted onto chitosan to produce poly(chitosan‐g‐DL ‐lactic acid)(PCLA) without using a catalyst. These PCLAs were then spun into filaments and further fabricated into fibrous mesh scaffolds using an improved wet‐spinning technique. The diameter of filaments in different scaffolds could vary from a few micrometers to several tens of micrometers. The scaffolds exhibited various pore sizes ranging from about 20 µm to more than 200 µm and different porosities up to 80%. The several main processing conditions were optimized for obtaining the desired scaffolds with well‐controlled structures. The tensile and compressive mechanical properties of the mesh scaffolds in both dry and hydrated states were mainly examined. Significantly improved tensile strength and modulus, enhanced compressive modulus, and stress as well as the dimensional stability for these mesh scaffolds in their hydrated state were observed. Copyright © 2007 John Wiley & Sons, Ltd.     

Improving mechanical properties and chemical resistance of ink‐jet printer color filter by using diblock polymeric dispersants

The diblock copolymers of polystyrene and poly(tert‐butyl acrylate) (PSt‐b‐PtBA) with various molecular weights and hydrophobic/hydrophilic (styrene/acrylic acid) chain length were prepared by atom transfer radical polymerization (ATRP). Selective hydrolysis of the diblock copolymers (PSt‐b‐PtBA) resulted in amphiphilic block copolymers of polystyrene and poly(acrylic acid) (PSt‐b‐PAA). The amphiphilic block copolymers of PSt‐b‐PAA with average molecular weight (M_n) <7500 were proved to be critical in dispersing the pigments of UV curable ink‐jet inks for manufacturing the color filter. Incorporating DB2 diblock copolymer dispersants with styrene/acrylic acid ratio at 1.5 allowed more UV curable compositions in the red and blue inks without deteriorating pigment dispersing stability and jetting properties of the ink‐jet inks. The ink drops can be precisely ejected into the tiny color area. Better properties of the cured red stripe such as nanoindentation hardness and chemical resistance were found. The competing absorption of UV light by the blue pigment hindered the through cure of monomers near the interface between glass substrate and the blue stripe. This leads to lower hardness and poor chemical resistance of the UV cured blue stripe. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3337–3353, 2005     

Preparation of porous polyimide/in‐situ reduced graphene oxide composite films for electromagnetic interference shielding

Herein we report an easy and efficient approach to prepare lightweight porous polyimide (PI)/reduced graphene oxide (RGO) composite films. First, porous poly (amic acid) (PAA)/graphene oxide (GO) composite films were prepared via non‐solvent induced phase separation (NIPS) process. Afterwards PAA was converted into PI through thermal imidization and simultaneously GO dispersed in PAA matrix was in situ thermally reduced to RGO. The GO undergoing the same thermal treatment process as thermal imidization was characterized with thermogravimetric analysis, Raman spectra, X‐ray photoelectron spectroscopy and X‐ray diffraction to demonstrate that GO was in situ reduced during thermal imidization process. The resultant porous PI/RGO composite film (500‐µm thickness), which was prepared from pristine PAA/GO composite with 8 wt% GO, exhibited effective electrical conductivity of 0.015 S m^?1 and excellent specific shielding efficiency value of 693 dB cm² g^?1. In addition, the thermal stability of the porous PI/RGO composite films was also dramatically enhanced. Compared with that of porous PI film, the 5% weight loss temperature of the composite film mentioned above was improved from 525°C to 538°C. Moreover, tensile test showed that the composite film mentioned above possessed a tensile strength of 6.97 MPa and Young's modulus of 545 MPa, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of polybutadiene‐graft‐poly(dimethylsiloxane) and polyethylene‐graft‐poly(dimethylsiloxane) copolymers with hydrosilylation reactions

We report preliminary results for the synthesis of polyethylene‐graft‐poly(dimethylsiloxane) copolymers obtained by catalytic hydrogenation of polybutadiene‐graft‐poly(dimethylsiloxane) copolymers (PB‐g‐PDMS). These last copolymers were synthesized by hydrosilylation reactions between commercial polybutadiene and ω‐silane poly(dimethylsiloxane). The reaction was carried in solution catalyzed by cis‐dichloro bis(diethylsufide) platinum(II) salt. The PB‐g‐PDMS copolymers were analyzed by ¹H and ¹³C NMR spectroscopies, and the relative weight percentages of the grafted poly(dimethylsiloxane) macromonomer were determined from the integrated peak areas of the spectra. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2920–2930, 2004     

Micropatterned designs of thermoresponsive surfaces for modulating cell behaviors

The chemistry and topography of the material surfaces have an important effect on cell behaviors. In this study, we reported the preparation of thermoresponsive micropatterned surfaces (TS) and galactosylated TS for modulating the adhesion/detachment of cells. A thickness of 1 µm of poly(N‐isopropylacrylamide) grafted layer was fabricated on the polystyrene surface with microgrooves using ultraviolet‐induced copolymerization. The thick grafted layer was in favor of the interactions between cells and materials. The following immobilization of galactose ligand with specific affinity to hepatocyte onto TS promoted the adhesion of human hepatocyte line (HL‐7702 cells). The microgrooves structure could facilitate cell adhesion and regulate the oriented growth of cells. Moreover, narrow grooves accelerated the spontaneous detachment of cells only by reducing temperature. Thus, micropatterned biofunctional designs with controlled geometrical features presented in this study have sufficient biofunctional activities in facilitating cell sheet engineering and regenerative medicine. Copyright © 2013 John Wiley & Sons, Ltd.