Gel membranes

MONITORING WATER CONCENTRATION IN ORGANIC SOLVENT WITH FLUORESCENT DYES IN A SOL-GEL MEMBRANE... 

Several standard DNA isolation kits are commercially available, including the QIAamp DNA Stool Mini Kit and the DNeasy Plant Mini Kit made by Qiagen. Both of these products are based on silica gel membrane technology and allow for the extraction of total DNA from processed foods and raw foodstuffs, respectively. In... 

A composite polymer membrane has also been used as an effective amperometric detector for ion exchange chromatography [42] and showed detection limits similar to those obtained with a conductivity detector. An advantage of the amperometric detector based on micro-ITIES over the conductometric detector is that selectively can be tailored by proper choice of the ionophore. For instance, the selectivity of the membrane toward ammonium in the presence of an excess of sodium could be substantially increased by introducing an ammonium-selective ionophore (such as valinomycin) in the gel membrane [42]. 

One effect of the electrochemical reactions in an aqueous system is a local pH change around the electrodes. By water electrolysis, hydronium ions (H30+) are generated at the anode, while hydroxyl ions (OH ) are produced at the cathode. These changes have been utilized for controlling the permeability of polyelectrolyte gel membrane or on-off solute release via ion exchange or surface erosion of interpolymer complex gels. 

An electrically activated membrane which reversibly expands and contracts in pore size has been designed by other researchers [8], The gel membrane used was a PAMPS gel. The water permeability through the membrane was controlled by electrical signals. 

Lobnik A., Majcen N., Niederreiter K., Uray G., Optical pH sensor based on the absorption of antenna generated europium luminescence by bromothymolblue in a sol-gel membrane, Sensors and Actuators B 2001 74 200-206. 

J. Yu, S. Liu, and H.X. Ju, Glucose sensor for flow injection analysis of serum glucose based on immobilization of glucose oxidase in titania sol-gel membrane. Biosens. Bioelectron. 19, 401—409 (2003). 

J. Yu and H.X. Ju, Pure organic phase phenol biosensor based on tyrosinase entrapped in a vapor deposited titania sol-gel membrane. Electroanalysis 16, 1305-1310 (2004). 

L. De Backer, S. Devlemnick, R. Willaert, G. Baron (1992) Reaction and diffusion in a gel membrane reactor containing immobilized cells. Biotech. Bioeng, 40 322-328... 

D. A. Nivens, M.V. Schiza and S.M. Angel, Multilayer sol-gel membranes for optical sensing applications single layer pH and dual layer C02 and NH3 sensors, Talanta, 58(3) (2002) 543-550. 

A series of crosslinked copolymer gels composed of DMAEMA and AAm were prepared using methylenebisacrylamide as a crosslinker for the preparation of polymer membrane. The feed compositions for the polymer membranes are listed in Tables 1 and 2. The polymerization was carried out between two Mylar sheets separated by a rubber gasket (1-mm diameter) and backed by glass plates. After polymerization, the gel was immersed in distilled water for 3 days to remove unreacted compound. The thickness of gel membrane was 1 mm in swollen state (20°C). 

The permeation of hydrocortisone across the gel membrane composed of copolymer II was observed in response to pulsatile temperature changes between 20 and 40°C. As shown in Figure 7, higher permeation was observed... 

Figure 8 Permeation of hydrocortisone across the poly(DMAEMA-cc>-AAm) gel membrane in response to pulsatile temperature change. 

To address the zinc dendrite problem in nickel-zinc cells, eVionyx claims to have developed a proprietary membrane system that is nonporous, has very high ionic conductivity, is of low cost, and can block zinc dendrite penetration even in high concentrations of KOH. The polymeric membrane has an ionic species contained in a solution phase thereof. The ionic species behaves like a liquid electrolyte, while at the same time the polymer-based solid gel membrane provides a smooth impenetrable surface that allows the exchange of ions for both discharging and charging of the cell. 

Nonporous gel membranes - these membranes do not contain a porous structure and thus diffusion occurs through the space between the polymer chains (the mesh). Obviously in this case, molecular diffusion rather than convective transport is the dominant mechanism of diffusion in these membranes. 

The theories developed for transport in microporous membranes cannot be applied to nonporous gel membranes. The pore structure in microporous membranes is not analogous to the mesh of the nonporous gels. Thus a different set of theories had to be developed for the treatment of nonporous polymer gel membranes. These theories are based on the idea of the existence of free volume in the macromolecular mesh. As a result, diifusion through nonporous membranes is said to occur through the space in the polymer gel not occupied by polymer chains. 

The first theory of transport through nonporous gels was presented by Yasuda et al. [150] and was proposed as a result of previous experimental results [151, 152]. This theory relates the ratio of diffusion coefficient in the polymer membrane and diffusion coefficient in the pure solvent to the volume fraction of solvent in the gel membrane or in Yasuda s terminology, the degree of hydration of the membrane, H (g water/g swollen polymer). Yasuda et al. use the... 

As seen, diffusion in nonporous gel membranes differs from that in macro-porous or microporous membranes. Various theories based on solute diffusion through the macromolecula r free volume in the membrane have been proposed. It is clear from these theories that structural parameters of the polymer network such as degree of swelling, molecular weight between crosslinks, and crystallinity in addition to factors such as solute size and solvent free volume play important roles in this type of transport. 

The actual blotting process may be accomplished by one of two methods passive (or capillary) transfer and electroblotting. In passive transfer, the membrane is placed in direct contact with the polyacrylamide gel and organized in a sandwich-like arrangement consisting of (from bottom to top) filter paper soaked with transfer buffer, gel, membrane, and more filter paper. The sandwich is compressed by a heavy weight. Buffer passes by capillary ac-... 

Assemble the gel/membrane transfer sandwich and place in transfer tank (see Basic Protocol 1, steps 7 to 10). 

During electrotransfer, proteins migrate out of gels in an electric field according to the charge on the protein. Most electrotransfers employ a tank transfer apparatus (Fig. B3.2.2) in which the gel/membrane transfer sandwich is mounted in a cassette and placed in a tank of Tris/glycine/methanol transfer buffer. The... 

Although for highly selective membranes the first explanation seems to be the most plausible one, it is feasible that for membranes with a high water content and a rather low capacity (such as the homogeneous gel membranes with which Meares and co-workers experimented) the second explanation is the right one. 

Concentration Gradient Across a Membrane. J. S. Mackie and P. Meares (88) tested the equation (30), derived by them. They measured the diffusion of five different salts through a homogeneous gel membrane of the sulphonated phenolformaldehyde type. The osmotic flow during diffusion was measured too. For the mobilities in the resin the values in free solution were taken, multiplied with the factors Aa [equation (73)] and Q [equation (78)]. 

The measurements were made at a homogeneous gel membrane, a condensation product of phenolsulfonic-acid and formaldehyde, with the ion pairs Na+/H+, Na+/K+ and Na+/Sr++. 

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