Flexible,stretchable, and patchable organic devices integrated on freestanding polymeric substrates

We present a novel technique for realizing an electrical circuit composed of organic devices on a highly flexible, stretchable, and patchable freestanding substrate, using a photo‐curable polyurethaneacrylate (PUA) mixture. Substrate structure was designed under consideration of enhanced mechanical strength in addition to flexibility, stretchability, and adhesive properties. The designed components facilitate the fabrication of highly flexible and stretchable electrodes without additional photolithography or patterning processes, and the fabricated organic circuits are substantially free from structural stress and strain induced from the substrate deformation. High flexibility and adhesive properties also enable mounting of the organic circuits onto nonflat surfaces with conformal contact. In addition, high light transmissivity of PUA suggests strong potential for a wide range of optoelectronic applications. We anticipate that these results will be applied to the development of various flexible, stretchable, and patchable organic devices, which can lead to further applications in many fields of science and engineering. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 453–460     

Stretchable and flexible resistive behavior of poly(3,4‐ethylenedioxythiophene):Poly(styrenesulfonate) thin film on ultra‐low modulus polydimethylsiloxane with trench‐type roughness

This study investigates the resistive behavior of rod‐coated micrometer thick films of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on ultra‐low modulus (120– 130 kPa) polydimethylsiloxane (PDMS) substrate having scratch or microtrench‐type roughness patterns. On average, the films were found to remain electrically functional up to 23% axial strain with an average increase of three times in the value of the normalized resistance. The films were also found to remain conductive up to bending diameter of 4 mm with an average increase of 1.12 times their initial resistance. The rod‐coated PEDOT:PSS films on ultra‐low modulus PDMS having microtrench‐type roughness were also found to remain functional even after 1000 bending cycles at a bending diameter of 4 mm and even smaller with an increase in resistance that was on average 1.15 times their initial resistance. The films were found to fail firstly by cracking and thereby debonding from the substrate under the application of axial strain. On the other hand, the films exhibit no delamination under bending strains. The results from this investigation suggest that the polymer–polymer laminate has potential applicability in stretchable and flexible electronics and related applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 226–233     

Facile non‐lithographic route to highly aligned silica nanopatterns using unidirectionally aligned polystyrene‐block‐polydimethylsiloxane films

Thin films (monolayer and bilayer) of cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) were shear aligned by the swelling and deswelling of a crosslinked PDMS pad that was physically adhered to the film during solvent vapor annealing. The nanostructures formed by self‐assembly were exposed to ultraviolet‐ozone to partially oxidize the PDMS, followed by calcination in air at 500 °C. In this process, the PS segments were fully decomposed, while the PDMS yielded silica nanostructures. The highly aligned PDMS cylinders were thus deposited as silica nanolines on the silicon substrate. Using a bilayer film, the center‐to‐center distance of these features were effectively halved from 38 to 19 nm. Similarly, by sequential shear‐alignment of two distinct layers, a rhombic array of silica nanolines was fabricated. This methodology provides a facile route to fabricating complex topographically patterned nanostructures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1058–1064     

Applying magnetic soft mold imprint technology with ultraviolet light‐emitting‐diode array on the fabrication of microlens arrays

This study proposed a novel technology, which uses exposed technology with ultraviolet light‐emitting‐diode (UV‐LED) arrays and the polydimethylsiloxane (PDMS) magnetic flexible soft mold imprint technology, to develop exposed equipments with UV‐LED arrays. This study used magnetic soft mold imprint technology to replicate the structure of microlens, providing a more effective alternative for imprint technology and application. The measurement results showed that PDMS with magnetic iron powder can precisely cast mold to replicate the structures of microlens. Electromagnetic plates were used to control even imprinting with magnetic force, in order to fill the mold of micro‐structure of the photo‐resist. Magnetic iron powder was added to PDMS to produce composite material, which can effectively avoid the transformation of pure PDMS during soft mold imprinting, and increase mechanical strength. Magnetic PDMS soft mold is easy to make, and the casting time is short, so that costs can be effectively reduced. Also with advantages of less free energy on its surface, and unlikely to adhere to the photo‐resist during imprinting, it can be combined with electromagnetic plates evenly to control the magnetic soft mold. This imprinting technology is a big advantage to the production process of micro‐structures during imprinting. Copyright © 2009 John Wiley & Sons, Ltd.     

A Simple Imprint Method for Multi‐Tiered Polymer Nanopatterning on Large Flexible Substrates Employing a Flexible Mold and Hemispherical PDMS Elastomer

This work reports a facile method to fabricate multi‐tiered polymer nanopatterns on SU‐8 by the combination of imprint‐ and photo‐lithography. First, SU‐8 is imprint patterned using a polymeric flexible mold with an anti‐adhesion coating that is deposited on a transparent and flexible substrate, at room temperature under low pressure. Next, the resulting SU‐8 nanopatterns are exposed to UV light through a chromium mask by a photolithographic process. Removal of the unexposed SU‐8 leaves behind multi‐tiered structures. The use of a hemispherical poly(dimethylsiloxane) pad facilitates the evacuation of trapped air during the imprinting process. Line/space patterns of 500 nm with the smallest line width of 200 nm were homogeneously imprint‐patterned on SU‐8 on a large flexible substrate, and three‐tiered structures, ranging in thickness from 300 nm to 2 µm, were successfully formed.

     

Degradation mechanisms of polyfluorene‐based organic semiconductor lasers under ambient and oxygen‐free conditions

In this communication we investigate the degradation mechanisms of different highly fluorescent polyfluorenes for applications as active organic semiconductor material in laser devices. Using various analytical methods, like Ultraviolet‐Visible (UV‐Vis) absorption spectroscopy, Fourier‐transform infrared spectroscopy (FT‐IR) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), we investigate photo‐induced degradation mechanisms. It is shown that the photo‐oxidation rate decreases with an increasing number of benzothiadiazole units within the conjugated polymer. Photooxidation is much more distinct for poly[9,9‐dioctylfluorenyl‐2,7‐diyl] (PFO) than for poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐alt‐co‐(1,4‐benzo‐{2,1′,3}‐thiadiazole)] (F8BT). The influence of the photooxidation on the lifetime of the organic laser devices is not as profound as previously assumed, since the laser shuts down before any evidence of photo‐oxidation in F8BT manifests. We observe that the solubility of the material is different at various degradation levels and we consider chain scission of excited bonds and cross‐linking as dominant degradation factors. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1029–1034     

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     

Determining thermo‐mechanical properties of polydimethylsiloxanes from their strain‐induced spectral fingerprints

Adaptive properties and complex shapes of modern day soft matter components create a challenge for materials applications where mechanical properties of intricate fabricated components cannot be determined from conventional invasive and destructive mechanical tests. In particular, challenges arising from variable mechanical properties of polydimethylsiloxanes (PDMSs) constantly attract wide‐scale attention in the fields of material sciences, biological systems, and microfluidics. Herein, a noninvasive and nondestructive strain‐induced infrared spectroscopic method (S‐FTIR) is developed. S‐FTIR is a method that maps thermo‐mechanical response of PDMS to its strain‐induced spectral fingerprint. From the results of this study, strong correlations of up to 95% between spectral fingerprint of PDMS and its corresponding nonlinear thermo‐mechanical response is seen. Given the nature of these results, it is expected that S‐FTIR will provide an interesting new analytical approach to understand soft materials and allow for the characterization of micro and nanoscale devices composed of these polymeric materials as well. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 359–367     

A novel fabrication technique to minimize poly(dimethylsiloxane)‐microchannels deformation under high‐pressure operation

PDMS is one of the most common materials used for the flow delivery in the microfluidics chips, since it is clear, inert, nontoxic, and nonflammable. Its inexpensiveness, straightforward fabrication, and biological compatibility have made it a favorite material in the exploratory stages of the bio‐microfluidic devices. If small footprint assays want to be performed while keeping the throughput, high pressure‐rated channels should be used, but PDMS flexibility causes an important issue since it can generate a large variation of microchannel geometry. In this work, a novel fabrication technique based on the prevention of PDMS deformation is developed. A photo‐sensible thiolene resin (Norland Optical Adhesive 63, NOA 63) is used to create a rigid coating layer over the stiff PDMS micropillar array, which significantly reduces the pressure‐induced shape changes. This method uses the exact same soft lithography manufacturing equipment. The verification of the presented technique was investigated experimentally and numerically and the manufactured samples showed a deformation 70% lower than PDMS conventional samples.     

Nanopatterning and micropatterning of cobalt containing block copolymers via phase‐separation and lithographic techniques

Reversible addition fragmentation transfer (RAFT) agent functionalized polydimethylsiloxane (PDMS‐RAFT) was used as a macro‐RAFT agent to polymerize a mixed sandwich cobaltocene containing monomer featuring η⁵‐cyclopentadienyl‐cobalt‐η⁴‐cyclobutadiene. High molecular weight block copolymers (BCP) consisting of a metallic block and a PDMS block with excellent control over molecular weight and polydispersity were prepared. Solid‐state self‐assembly of this BCP resulted in hexagonal domains of metallopolymer phase‐separated from PDMS. In solution, spherical micelles with a metallic core, stabilized by a PDMS corona were prepared. Pyrolysis of the BCP resulted in magnetic nanoparticles with 30% char yield. The BCP was used as an ink material for microcontact printing (μCP) to transfer long‐ranged patterns. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2747–2754     

Synthesis,self‐assembly,and thermosensitivity of amphiphilic POEGMA‐PDMS‐POEGMA triblock copolymers

In this article, the synthesis and self‐assembly of a novel well‐defined biocompatible amphiphilic POEGMA‐PDMS‐POEGMA triblock copolymer were studied. The copolymer was synthesized by atom transfer radical polymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) using α,ω‐dibromo polydimethylsiloxane macroinitiator (Br‐PDMS‐Br). Br‐PDMS‐Br was synthesized through the esterification of α,ω‐hydroxypropyl polydimethylsiloxane and 2‐bromoisobutyryl bromide. The structures of the copolymers were confirmed by proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The copolymers showed reversible aggregation in response to temperature cycles with a lower critical solution temperature (LCST) between 61 and 66 °C, as determined by ultraviolet‐visible spectrophotometry and dynamic light scattering. The LCST values increased in proportion to the length of the hydrophilic block and were lower than that of the POEGMA homopolymer. The self‐assembly behavior of the copolymers in aqueous solution was investigated by fluorescence spectroscopy and transmission electron microscopy. The critical micelle concentration value (1.08–0.26 10^?6 mol L^?1) decreased as the length of the POEGMA chain increased. The POEGMA‐PDMS‐POEGMA copolymers can easily self‐assemble into spherical micelles in aqueous solution. Such biocompatible block copolymers may be attractive candidates as ‘‘smart'' thermo‐responsive drug delivery systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2684‐2691     

Deformable strain sensors based on patterned MWCNTs/polydimethylsiloxane composites

Patterned MWCNT/polydimethylsiloxane (PDMS) nanocomposite strain sensors were achieved by a microelectromechanical system assisted electrophoretic deposition (EPD) technique. With the combined effect of superior intrinsic piezoresistivity of the individual MWCNT and the tunneling effect of the MWCNT network, the stretchable composite demonstrates high sensitivity to the tensile strain. The gauge factor shows a strong dependence on both the initial resistance of the CNT/PDMS composite and the applied strain level. The mechanism is elucidated by analyzing the structure‐property‐function of patterned CNT networks. When the entanglement of a MWCNT network allows effective load transfer, the sensitivity is primarily dominated by the intrinsic piezoresistivity of individual MWCNTs. Conversely, when the MWCNTs interpenetrate loosely, the tunneling effect prevails. The sensitivity of the device can be tailored by the proposed technique since MWCNT film thickness/density can be readily controlled by means of the patterning parameters of the EPD process. The work provides useful guidance for design and development of strain/stress sensors with targeted sensitivity for flexible electronics applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1505–1512     

Amphiphilic thermoset elastomers from metal‐free,click crosslinking of PEG‐grafted silicone surfactants

The hydrophobicity of silicone elastomers can compromise their utility in some biomaterials applications. Few effective processes exist to introduce hydrophilic groups onto a polysiloxane backbone and subsequently crosslink the material into elastomers. This problem can be overcome through the utilization of metal‐free click reactions between azidoalkylsilicones and alkynyl‐modified silicones and/or PEGs to both functionalize and crosslink silicone elastomers. Alkynyl‐functional PEG was clicked onto a fraction of the available azido groups of a functional polysiloxane, yielding azido reactive PDMS‐g‐PEG rake surfactants. The reactive polymers were then used to crosslink alkynyl‐terminated PDMS of different molecular weights. Using simple starting materials, this generic yet versatile method permits the preparation and characterization of a library of amphiphilic thermoset elastomers that vary in their composition, crosslink density, elasticity, hydrogel formation, and wettability. An appropriate balance of PEG length and crosslink density leads to a permanently highly wettable silicone elastomer that demonstrated very low levels of protein adsorption. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1082–1093     

A two‐stage surface treatment for the long‐term stability of hydrophilic SU‐8

The use of SU‐8 photoresist as a structuring material for portable capillary‐flow cytometry devices has been restricted by the near‐hydrophobic nature of the SU‐8 surface. In this work, we evaluate the use of chemical and plasma treatments to render the SU‐8 surface hydrophilic and characterise the resulting surface utilising a combination of techniques including contact angle goniometry, atomic force microscopy and X‐ray photoelectron spectroscopy. In particular, for low‐power plasma treatments, we find that the chemistry of the plasma used to modify the SU‐8 surface and the incorporation of O₂ on that modified surface are paramount for improved surface wettability, whilst plasma‐induced surface roughness is not a necessary requirement. We demonstrate a technique to obtain a hydrophilic SU‐8 surface with contact angle as low as 7° whilst controlling and significantly reducing the level of surface roughness generated via the applied plasma. An additional chemical treatment step is found to be essential to stabilise the activated SU‐8 surface, and incubation of the samples with ethanolamine is demonstrated as an effective second‐stage treatment. Application of the optimised two‐stage surface treatment to cross‐linked SU‐8 is shown to result in a smooth hydrophilic surface that remains stable for over 3 months. Copyright © 2015 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.     

High‐performance thin film composite membranes with well‐defined poly(dimethylsiloxane)‐b‐poly(ethylene glycol) copolymer additives for CO2 separation

A series of well‐defined diblock copolymers (BCPs) consisting of poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) were synthesized and blended with commercially available PEBAX® 2533 to form the active layer of thin‐film composite (TFC) membranes, via spin‐coating. BCPs with a PEG component ranging from 1 to 10 kDa and a PDMS component ranging from 1 to 10 kDa were synthesized by a facile condensation reaction of hydroxyl terminated PEG and carboxylic acid functionalized PDMS. The BCP/PEBAX® 2533 blends up to 50 wt % on cross‐linked PDMS gutter layers were tested at 35 °C and 350 kPa. TFC membranes containing BCPs of 1 kDa PEG and 1–5 kDa PDMS produced optimal results with CO₂ permeances of approximately 1000 GPU which is an increase up to 250% of the permeance of pure PEBAX® 2533 composite membranes, while maintaining a CO₂/N₂ selectivity of 21. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1500–1511     

Fabrication of photo‐cross‐linked polyethyleneimine‐based barriers for CO2 capture

In this study, first, polyethyleneimine was acrylated and mixed with polyvinyl alcohol solution to prepare photo‐crosslinked polyethyleneimine (PEI)‐based nanofibers by utilizing ultraviolet and electrospinning technique at the same time. For CO₂ permeability testing, same formulations were prepared by using solvent casting technique and exposed to ultraviolet light to have polyethyleneimine‐based membrane films. The chemical structures of the nanofibers were characterized by Fourier transform infrared spectroscopy. The thermal properties of nanofibers were examined by thermal gravimetric analysis and differential scanning calorimeter. The morphology of nanofibers was investigated by scanning electron microscopy. CO₂ permeabilities of samples were also measured. Copyright © 2015 John Wiley & Sons, Ltd.     

Secondary electron contrast modulation in SU‐8 photoresist films exposed holographically

We report a Secondary Electron (SE) contrast modulation observed in scanning electron microscope photographs of the cross‐section of SU‐8 photoresist films exposed holographically. The modulation occurs along the whole depth of the sample and its contrast disappears when the samples are submitted to the post exposure bake (PEB). Diffraction and atomic force microscopy measurements of the samples were performed before and after PEB to investigate this modulation. The results indicate that this SE emission contrast modulation comes from the spatial chemical modulation generated by the photolysis during the exposure of the SU‐8 films. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 226–230, 2010     

Mass‐Spectrometric Observation of Counter Anion Production in SU‐8 Exposed to UV Light and its Use for Dill C Parameter Determination

Photopolymerization is a phenomenon that is the basis of much of today's microfabrication technology and intense research is conducted to improve its control and the characteristics of end products for a variety of applications. The design of microscopic structures often relies on the accurate knowledge and modeling of photopolymer's behavior upon exposure, i.e. the Dill parameters, for each radiation species of interest and therefore the development of flexible characterization techniques is of great importance. SU‐8 is a popular compound that is representative of a whole class that relies on cationic polymerization, where an acid is obtained via photolysis of an onium salt during exposure. Here we report on the observation of SbF₆^? via laser desorption mass spectrometry on SU‐8 exposed to UV light at the wavelength of 365 nm and demonstrate that the yield of this counter‐anion as a function of exposure is consistent with the Dill C parameter value available in the literature. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 967–972     

Synthesis of hyperbranched polyacetals via an + b2‐type polyaddition (n = 3, 8, 18, and 21): Candidate resists for extreme ultraviolet lithography

Polyaddition (A_n + B₂) reactions of 1,1,1‐tris(4‐hydoxyphenyl) ethane (THPE; A₃‐type monomer), calix[4]resorcinarene (CRA[4]; A₈‐type monomer), α‐cyclodextrin (α‐CD; A₁₈‐type monomer), and β‐cyclodextrin (β‐CD; A₂₁‐type monomer) with 1,4‐bis(4‐vinyloxy)cyclohexane (BVOC; B₂‐type monomer) afforded corresponding soluble hyperbranched polyacetals. The physical properties, including solubility, thermal stability, and film‐forming ability, the ultraviolet‐induced degradation reactivity, and the solubility‐switch in an extreme ultraviolet (EUV) exposure tool indicated that poly(THPE‐co‐BVOC) and poly(CRA[4]‐co‐BVOC) are candidate next‐generation photo‐resists. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2343–2350     

Flexible transparent fluorinated nanohybrid with innovative heat‐resistance property—new technology proposal for fabrication of transparent materials using “crystalline” polymer

A new technology for the production of transparent material, using a “crystalline” polymer, is proposed in this study. In addition, a heat‐resistant transparent flexible plastic film with a high hydrophobic surface and a thermal decomposition temperature near 400 °C was created. Partially fluorinated crystalline polymer with switchboard‐type lamellae results high transparency as a consequence of the formation of a high‐density amorphous structure based on high‐temperature drawing just below the melting point at 250 °C. Melt‐compounding with montmorillonite modified by the long‐chain quaternary phosphonium with high coverage induces formation of a nanohybrid that retains transparency and also results in an increase in the thermal degradation temperature by over 50 °C. Through this technology, which results in heat‐resistance, transparency, and flexibility, the nano‐micro‐millimeter structures of solid‐state polymers are hierarchically controlled, which enables the creation of new materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1674–1690