Solution interface, hydrogel

The second approach is based on using a microprobe to perturb equilibrium in one of the phases near the interfacial boundary. The transfer of electrochemically active ions and neutral molecules across the liquid/liquid interface can be studied with a metal tip positioned near the phase boundary (56). The interfacial flux was induced by using a disk-shaped UME to deplete the concentration of transferred species in one of two phases. The transfer processes at an air/water and hydrogel/solution interfaces can be studied similarly (56). 

The interfacial flux was induced by using a disk-shaped UME to deplete the concentration of transferred species in one of two phases. The transfer processes at an air-water and hydrogel-solution interfaces can be studied similarly [73],... 

R - Rq C. = C (concentration continuity at hydrogel-bulk solution interface)... 

Formation of microlens at interface between oil and aqueous solution. Interface is pinned stably at a hydrophobic-hydrophilic boundary along circular aperture. Volumetric changes of hydrogel microposts cause flexible aperture slip to bend in the z direction. The pinned water-oil interface is pressed downward or upward, thus tuning the focal length. (Source Dong, L. and H. Jiang. 2006. Applied Physics Letters, 89(21), 211120. With permission.)... 

In the present section, the behavior of a hydrogel strip in a solution bath with applied electric field is investigated. As discussed in Sect. 2, the application of an electric field results in local variations of the concentrations at the gel-solution interface in both gel and solution phase. Due to the higher conductivity corresponding to the larger number of mobile ions in the gel than in the solution, the increase of the electric potential - from the cathode to the anode side - in the gel is smaller than in the solution. The smaller increase of the electric potential in the gel is compensated... 

Membranes made by interfacial polymerization have a dense, highly cross-linked interfacial polymer layer formed on the surface of the support membrane at the interface of the two solutions. A less cross-linked, more permeable hydrogel layer forms under this surface layer and fills the pores of the support membrane. Because the dense cross-linked polymer layer can only form at the interface, it is extremely thin, on the order of 0.1 p.m or less, and the permeation flux is high. Because the polymer is highly cross-linked, its selectivity is also high. The first reverse osmosis membranes made this way were 5—10 times less salt-permeable than the best membranes with comparable water fluxes made by other techniques. 

In a rather unnecessary attempt to define the interface between the ion-selective membrane and the dielectric, an internal hydrogel layer saturated with, for example, a buffer solution, has been interposed between these two layers. It mirrors the miniaturization of conventional symmetrical membrane ion sensors. The volume of the hydrogel layer is very small. This approach creates more problems than it solves. What is the major problem ... 

FIGURE 51.8 Schematic diagram of using PCSLs to interface microfluidics with ion-permeable membranes, (a) APCSL-protected microchannel substrate is bonded to a PMMA cover piece having a membrane reservoir, (b) Prepolymer solution is poured into the membrane reservoir, (c) An ion-permeable hydrogel is photopolymerized. (d) The PCSL is melted and removed from the channel. (Adapted from Kelly, R. T., et al., Anal. Chem., 78, 2565, 2006. Copyright 2006. With permission from American Chemical Society.)... 

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