This paper describes the compatibility of poly(dimethylsiloxane) (PDMS) with organic solvents; this compatibility is important in considering the potential of PDMS-based microfluidic devices in a number of applications, including that of microreactors for organic reactions. We considered three aspects of compatibility: the swelling of PDMS in a solvent, the partitioning of solutes between a solvent and PDMS, and the dissolution of PDMS oligomers in a solvent. Of these three parameters that determine the compatibility of PDMS with a solvent, the swelling of PDMS had the greatest influence. Experimental measurements of swelling were correlated with the solubility parameter, delta (cal(1/2) cm(-3/2)), which is based on the cohesive energy densities, c (cal/cm(3)), of the materials. Solvents that swelled PDMS the least included water, nitromethane, dimethyl sulfoxide, ethylene glycol, perfluorotributylamine, perfluorodecalin, acetonitrile, and propylene carbonate; solvents that swelled PDMS the most were diisopropylamine, triethylamine, pentane, and xylenes. Highly swelling solvents were useful for extracting contaminants from bulk PDMS and for changing the surface properties of PDMS. The feasibility of performing organic reactions in PDMS was demonstrated by performing a Diels-Alder reaction in a microchannel.

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Creating a regular surface pattern on the nanometre scale is important for many technological applications, such as the periodic arrays constructed by optical microlithography that are used as separation media in electrophoresis, and island structures used for high-density magnetic recording devices. Block copolymer patterns can also be used for lithography on length scales below 30 nanometres (refs 3-5). But for such polymers to prove useful for thin-film technologies, chemically patterned surfaces need to be made substantially defect-free over large areas, and with tailored domain orientation and periodicity. So far, control over domain orientation has been achieved by several routes, using electric fields, temperature gradients, patterned substrates and neutral confining surfaces. Here we describe an extremely fast process that leads the formation of two-dimensional periodic thin films having large area and uniform thickness, and which possess vertically aligned cylindrical domains each containing precisely one crystalline lamella. The process involves rapid solidification of a semicrystalline block copolymer from a crystallizable solvent between glass substrates using directional solidification and epitaxy. The film is both chemically and structurally periodic, thereby providing new opportunities for more selective and versatile nanopatterned surfaces.

The development of pressure sensors that are effective over a broad range of pressures is crucial for the future development of electronic skin applicable to the detection of a wide pressure range from acoustic wave to dynamic human motion. Here, we present flexible capacitive pressure sensors that incorporate micropatterned pyramidal ionic gels to enable ultrasensitive pressure detection. Our devices show superior pressure-sensing performance, with a broad sensing range from a few pascals up to 50 kPa, with fast response times of <20 ms and a low operating voltage of 0.25 V. Since high-dielectric-constant ionic gels were employed as constituent sensing materials, an unprecedented sensitivity of 41 kPa in the low-pressure regime of <400 Pa could be realized in the context of a metal-insulator-metal platform. This broad-range capacitive pressure sensor allows for the efficient detection of pressure from a variety of sources, including sound waves, a lightweight object, jugular venous pulses, radial artery pulses, and human finger touch. This platform offers a simple, robust approach to low-cost, scalable device design, enabling practical applications of electronic skin.

Here, a facile route to fabricate thin ferroelectric poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA) blend films with very low surface roughness based on spin‐coating and subsequent melt‐quenching is described. Amorphous PMMA in a blend film effectively retards the rapid crystallization of PVDF upon quenching, giving rise to a thin and flat ferroelectric film with nanometer scale β‐type PVDF crystals. The still, flat interfaces of the blend film with metal electrode and/or an organic semi‐conducting channel layer enable fabrication of a highly reliable ferroelectric capacitor and transistor memory unit operating at voltages as low as 15 V. For instance, with a TIPS‐pentacene single crystal as an active semi‐conducting layer, a flexible ferroelectric field effect transistor shows a clockwise I–V hysteresis with a drain current bistability of 103 and data retention time of more than 15 h at ±15 V gate voltage. Furthermore, the robust interfacial homogeneity of the ferroelectric film is highly beneficial for transfer printing in which arrays of metal/ferroelectric/metal micro‐capacitors are developed over a large area with well defined edge sharpness.