Phenomena Associated with Gel–Water Interfaces. Analyses and Alternatives to the Long-Range Ordered Water Hypothesis

Abstract

Interfacial regions between certain gels and their surrounding solutions were observed by Pollack and co-workers to exhibit several unexpected phenomena: (1) long-range exclusion of charged microspheres out to typical distances of ~100-200 μm from the gel surface; (2) significant electrostatic potentials extending over comparable distances; (3) a reduced intensity of upward spontaneous thermal IR emission over a region 300-500 μm wide at or near the gel-solution interface; and (4) a significantly lower proton T2 and an apparently reduced H2O self-diffusion coefficient over a zone ~60 μm wide at or near the gel-solution interface in high resolution NMR imaging experiments. To account for such observations, they proposed that a region of long-range ordered water bearing a net negative charge, but lacking mobile charge carriers, extended ~100-200 μm outward from the gel surface. In this paper, various problems associated with the ordered water hypothesis, including contradictions by experiments from many other laboratories, are briefly discussed, and testable alternative explanations for the observed phenomena are proposed. Exclusion zones are suggested to arise from chemotaxis of the microspheres in long-range diffusion gradients of OH(-) (or H(+)) and salt, the theory of which was developed and compared with the observations on non-ionic gels in a companion paper. The same theory together with the expected directions of ion transfers between gel and solution are now used to predict qualitatively the exclusion/attraction behavior of microspheres in the presence of ionic gels and ionomers. The electrostatic potentials are interpreted as long-range liquid-junction potentials arising from the same long-range diffusion gradients of OH(-) (or H(+)) and salt in the unstirred solutions of Pollack and co-workers. Alternative explanations in terms of plausible experimental artifacts are suggested for both the reduced intensity of IR thermal emission and the lower proton T2 and apparent H2O diffusion coefficient in the NMR imaging experiments.