Polymer-Water Interfaces

For the model system considered in Eikerling et al., i the chemical composition and water content are fixed. Only minimal hydration could be considered. A more recently begun work aims explicitly at the understanding of structural correlations and dynamics at acid-functionalized interfaces between polymer and water in PEMs. It directly addresses the question of... 

More than 10 years ago, Ikada et al. evaluated the free energy (ylw) of the interface between polymer and water, and the work of adhesion (W12,w) in water of bovine serum albumin (BSA) to the polymer surface [12]. According to a well-known concept of surface chemistry, Ikada derived the following equations. 

MacKenzie, A. P., Rasmussen, D. H. Interactions in the water-polyvinylpyrrolidone system at low temperatures, In Jellinek, H. H. G. ed. Water Structure at the Water-Polymer Interface. New York Plenum Publishing, 1972, pp. 146-172. 

Polymer electrolyte fuel cell (PEFC) is considered as one of the most promising power sources for futurist s hydrogen economy. As shown in Fig. 1, operation of a Nation-based PEFC is dictated by transport processes and electrochemical reactions at cat-alyst/polymer electrolyte interfaces and transport processes in the polymer electrolyte membrane (PEM), in the catalyst layers consisting of precious metal (Pt or Ru) catalysts on porous carbon support and polymer electrolyte clusters, in gas diffusion layers (GDLs), and in flow channels. Specifically, oxidants, fuel, and reaction products flow in channels of millimeter scale and diffuse in GDL with a structure of micrometer scale. Nation, a sulfonic acid tetrafluorethy-lene copolymer and the most commonly used polymer electrolyte, consists of nanoscale hydrophobic domains and proton conducting hydrophilic domains with a scale of 2-5 nm. The diffusivities of the reactants (02, H2, and methanol) and reaction products (water and C02) in Nation and proton conductivity of Nation strongly depend on the nanostructures and their responses to the presence of water. Polymer electrolyte clusters in the catalyst layers also play a critical... 

Kakutani et al. described an ion-transfer voltammetry and potentiometry method for the determination of acetylcholine with the interface between polymer-nitrobenzene gel and water [13]. The PVC-nitrobenzene gel electrode was prepared as described by Osakai et al. [14]. The transfer of acetylcholine ions across the interface between the gel electrode and water was studied by cyclic voltammetry, potential-step chronoamperometry, and potentiometry. The interface between the two immiscible electrolyte solutions acted as the ion-selective electrode surface for the determination of acetylcholine ions. 

AP Mackenzie. In Water Structure at the Water-Polymer Interface (H.H. Jellinek, ed.). Plenum Press, New York, 1972, p. 146. 

Tail, M.J. Ablett, S. Franks, F. Water Structure at the Water-Polymer Interface Jellinek, H., Ed. Plenum Press New York, 1972 29-38. 

Kozarac, Z., A. Dhathathreyan, and D. Mobius (1989), Interaction of Nitrophenols with Lipids at the Air/Water Interface, Colloid Polym. Sci. 267, 722-729. 

Katz, L.E. 1993. Surface complexation modeling of cobalt ion sorption at the a-Al203-water interface Monomer, polymer and precipitation reactions. Ph.D. diss. Univ. Michigan, Ann Arbor, MI. 

The Structure of Water. Pertinent to the bound, non-freezing, or interface water in polymers, a subject of subsequent sections, are the studies of Angel et al. (see ref. in... 

We present here some aspects of the surface chemistry and some explanatory models for vrater-polymer and related Interfaces. The term "poljrmer" will be taken to mean an essentially organic material, of sufficiently high molecular weight and (or) sufficiently cross-linked that a stiff (as opposed to fluid) phase is Involved. The material Is Insoluble In water, so that the term "water-polymer" Interface refers to what Is macroscopIcally an ordinary phase boundary. Typical polymers In the present context will be polytetrafluorethylene (PTFE), and polyethylene (PE). Solutions of macromolecules are thus not considered, nor is the related topic of so-called hydrophobic bonding, although some of what Is discussed here is relevant to that subject. 

In the present paper, evidence is presented which indicates that all of the above assumptions are seriously in error for the water-polymer interface. The error is sufficient that a new modellstlc framework, rather than amendments to the existing one, is needed. 

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