Polymer electrolyte membrane definition

Looking back, the only unequivocal membrane improvement, in spite of all these efforts, has been the reduction of thickness from 200 jjim in 1995 to <50 (jun in 2005. In terms of chemical or morphological modifications at the microstructural level, no definite recommendations could be discerned so far. The focus of the works reviewed herein has been exploring the fundamental relations between micromorphology and transport from micro- to macroscales for prototypical polymer electrolyte membranes and the understanding of their major principles of operation. 

Because water is ubiquitous both in the sensing environment and inside many sensors (especially electrochemical sensors), the hydrophobic or hydrophilic nature of a polymer used in a sensor is often crucial. For example, a polymer that is to be used as a hydrogel is by definition hydrophilic. On the other hand, gas-permeable membranes are often made of hydrophobic polymers to prevent passage of water through the membrane. These conventions are not always the case, however. An electrolyte for a sensor operating with non-aqueous electrochemistry may be less hydrophilic. Similarly, an in situ sensor to analyse polar degradation products in motor oil may use a hydrophilic membrane to allow passage of the analyte into the aqueous electrolyte from the non-polar hydrocarbon sample [14]. 

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