A space‐charge model for electrolyte transport in charged capillary pores was examined experimentally with aqueous solutions of alkali chlorides and MgCl2 in track‐etched mica membranes. The model combines the Gouy‐Chapman view of the double layer with the Nernst‐Planck and Navier‐Stokes transport equations. The pores of experimental membranes were uniform capillaries with a well‐characterized cross section. The pore sizes ranged from an order of magnitude smaller to an order of magnitude larger than the Debye screening lengths of solutions. Three independent quantities were measured: streaming potential, for which an applied pressure across the membrane is the driving force for transport; pore conductivity, for which an applied electrical potential is the driving force; and concentration potential, for which an electrolyte concentration difference is the driving force. Data follow the trends of model predictions but indicate that chloride ions affect the pore wall charge. For monovalent cations, the pore wall charge deduced from pore conductivity measurements yielded theoretical predictions for the streaming potential and for the concentration potential that agree quite well with the data. Such agreement was not obtained with Mg2+, probably because these divalent cations adsorbed onto the negative pore wall. We conclude that, in the absence of strong interaction between the charged pore wall and free ions in solution, the model is quantitatively accurate for pores larger than 30Å in radius and for aqueous electrolyte concentrations of 0.1M or lower.

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In this paper we present our results from a molecular dynamics study of n-octane liquids confined between planar bcc solid surfaces. The systems studied were wide enough to develop a bulklike region throughout the middle portion of the film and two well-separated interfaces. Our work focused on segmental dynamics and relaxation of ‘‘adsorbed’’ octane molecules. In particular, we investigated the role of architectural and dynamical features peculiar to short chain molecules (almost fixed bend angles and restricted torsional rotations) on the dynamics of ‘‘adsorbed’’ chains. We found that the relaxation of octane molecules exhibits the same qualitative trends as those observed in molecular simulations of generic ‘‘bead-spring’’ oligomer films. The most important effect is the dramatic slow down of rotational motions (up to a factor of 1000) for chains adsorbed on strongly physisorbing surfaces (adhesion energy per segment of 1–2 kT). Despite the qualitative similarities with bead-spring chains, the dynamics of realistic short hydrocarbon chains are affected much more strongly by the interfacial environment than their bead-spring counterparts. These stronger effects originate largely from the suppression of torsional angle transitions inside the extremely dense first layer (in cases of strong physisorption). The frequency of torsional transitions was found to be correlated directly with the amount of ‘‘free volume’’ available inside the crowded first layer.

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The effects of micelle/pore interactions (e.g., electrostatic, hydrodynamic, and steric) on intrapore micelle diffusion coefficients were studied experimentally and compared with calculations for the hindered diffusion of charged spheres in charged cylindrical pores. Interactions between the micelle and the pore wall were important, since micelle diffusion was studied in pores whose radii were as small as 10 times the micelle radius and in solutions with low ionic strengths, where the Debye length was significant when compared to the pore size.