Permeability thickness dependence of polydimethylsiloxane (PDMS) membranes

Surface-pattern engineering, as a key strategy to fabricate high-performance Nafion membranes for fuel cells, plays an important role in surface functionalization of the membrane, optimization of the three-phase boundary, water management, proton transport, etc. Considerable efforts have been dedicated to developing advanced-patterned Nafion membranes with single-scale (nanoscale or microscale) and multiscale-patterned structures which are believed to improve the performance of membrane electrode assemblies (MEAs) for fuel cells. In this review, the recent progress in surface-patterned Nafion membranes (SPNMs) equipped with single-scale-patterned structures (including nanostructured and microstructured Nafion membranes) is firstly highlighted. The structural features and construction methods of SPNMs are discussed in detail. The effects of single-scale SPNMs on the construction and performance of fuel cells are also analyzed. Followed is an overview of the recent advances in fabricating multiscale SPNMs based on different strategies with a specific introduction on the membrane related effects on fuel cells. Finally, the future development direction and certain perspectives on the current issues of SPNMs are presented.

A critical review on surface-pattern engineering of nafion membrane for fuel cell applications

With advances in technology, hyperelastic materials are seeing increased use in varied applications ranging from microfluidic pumps, artificial muscles to deformable robots. They have also been proposed as materials of choice in the construction of components undergoing dynamic excitation such as the wings of a micro-unmanned aerial vehicle or the body of a serpentine robot. Since the strain energy potentials of various hyperelastic materials are more complex than quadratic, exploration of their nonlinear dynamic response lends itself to some interesting consequences. In this work, a structure made of a Mooney-Rivlin hyperelastic material and undergoing planar vibrations is considered. Since the stresses developed in a Mooney-Rivlin material are at least a quadratic function of strain, a possibility of 1:2 internal resonance is explored. A Finite Element Method (FEM) formulation implemented in Matlab is used to iteratively modify a base structure to get its first two natural frequencies close to the ratio 1:2. Once a topology of the structure is achieved, the linear modes of the structure can be extracted from the finite element analysis, and a more complete Lagrangian formulation of the hyperelastic structure can be used to develop a nonlinear two-mode model of the structure. The nonlinear response of the structure can be obtained by application of perturbation methods such as averaging on the two-mode model. It is shown that the strain energy potential for the Mooney-Rivlin material makes it possible for internal resonance to occur in such structures.Copyright © 2013 by ASME

Design for 1:2 Internal Resonances in In-Plane Vibrations of Plates With Hyperelastic Materials

Nano-imprinting lithography of P(VDF-TrFE-CFE) for flexible freestanding MEMS devices

Buckling membrane micro-actuators based on relaxor ferroelectric polymer poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF–TrFE–CFE)) were fabricated and actuated near their resonant frequency. The devices produced displacements of several microns under applied biases of ⩽60 V μm−1. In this buckling actuator configuration the electrodes are located only at the membrane’s circumference and do not coat the entire membrane. Besides for preserving the optical transparency of the polymer, the critical advantage of this configuration is that the unique electro-mechanical properties of the polymer can be exploited without constriction of displacements by the metal electrodes which have a comparatively higher Young’s modulus.Electrical characterization of P(VDF–TrFE–CFE) thin films was performed through the use of micro-capacitor test structures. Dielectric properties were examined as a function of temperature (25–115 °C), frequency (6 kHz–2 MHz) and processing conditions, most notably thermoplastic nano-imprint lithography (T-NIL).

A study toward the development of an electromechanical poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) buckling membrane actuator

We report on a novel fabrication process based on thermal imprinting for the formation of micron-scale, freestanding, dielectric layers of poly(dimethylsiloxane). This technique is the basis for three-dimensional elastomeric membrane micro-electro-mechanical system applications where the structural material is part of the actuator and the lateral expansion is by vertically applied bias. We have fabricated freestanding smooth defect-free membranes with thicknesses in the range of 0.4?4.8 ?m and with diameters of centimeters order of magnitude. A curve was plotted to calibrate the thickness of the elastomer layer to the pressure of the imprint. The adhesion between the polymer and the silicon (Si) chip's surface was reduced by the deposition of a hydrophobic dodecyl-trichlorosilane monolayer on the chips prior to imprinting. The ability to detach the membrane from the chips after imprinting is critical for the production of layers that are freestanding. Additionally, we demonstrate the feasibility of patterning the membranes at the time of imprinting to create freestanding patterned micron-scale membranes. A simple device made up of a freestanding circular membrane with electrodes on the circumference demonstrating the application of the method is presented here. The device's electromechanical characteristics are presented as well.

https://iopscience.iop.org/article/10.1088/0960-1317/22/4/045003/pdf

Freestanding smooth micron-scale polydimethylsiloxane (PDMS) membranes by thermal imprinting

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Freestanding smooth micron-scale polydimethylsiloxane (PDMS) membranes by thermal imprinting