Phenomena Associated with Gel鈥揥ater Interfaces. Analyses and Alternatives to the Long-Range Ordered Water Hypothesis
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- 作者：J. Michael Schurr
- 刊名：The Journal of Physical Chemistry B
- 出版年：2013
- 出版时间：June 27, 2013
- 年：2013
- 卷：117
- 期：25
- 页码：7653-7674
- 全文大小：513K
- 年卷期：v.117,no.25(June 27, 2013)
- ISSN：1520-5207
文摘
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鈥?00 渭m 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鈥?00 渭m wide at or near the gel鈥搒olution interface; and (4) a significantly lower proton T2 and an apparently reduced H2O self-diffusion coefficient over a zone 60 渭m wide at or near the gel鈥搒olution 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鈥?00 渭m 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鈥?/sup> (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鈥?/sup> (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.