Membrane polymer network

Concentration of Electrolyte Myer and Sievers"" applied the Donnan equilibrium to charged membranes and developed a quantitative theory of membrane selectivity. They expressed this selectivity in terms of a selectivity constant, which they defined as the concentration of fixed ions attached to the polymer network. They determined the selectivity constant of a number of membranes by the measurement of diffusion potentials. Nasini etal and Kumins"" extended the measurements to paint and varnish films. 

When the Donnan equilibrium is operative the entry of ions into the membrane is restricted. Consequently as the concentration of ions in the solution increases the resistance of the membrane remains constant until the concentration of ions in the solution reaches that of the fixed ions attached to the polymer network. At this point their effect will be swamped and the movement of ions will be controlled by the concentration gradient. 

Interpellet porosity, 25 294 Interpenetrated wall matrix, in hollow-fiber membranes, 76 15 Interpenetrating polymer networks (IPNs), 79 834... 

Olfaction, research in, 18 383-384 Olfactory membrane, 11 567 Olfactory perceptions, 11 510-511 Olfactory receptors, 18 383-384 Olfactory response, 11 566-567 01igo(2-propenyloxy)methyloxyirane, sulfonation of, 23 720 Oligocyclic lattice host inclusion compounds, 14 177-179 Oligocyclic lattice hosts, 14 177 01igo(y-caprolactone)dimethylacrylate, in shape- memory polymer networks, 22 364... 

Hydrogels are crosslinked polymer networks with entrapped solvent. In the case of hydrogels containing polyectrolytes, in addition to solvent, ions and salt can be found in the gel as determined by the Dorman partition. This arises from the exclusion of ions of the same charge that sets a membrane potential at the gel/external electrolyte interface. 

Mediators can exist free in solution physically entrapped behind a membrane - immobilized in a matrix along with the biocatalyst or covalently bound to a surface or polymer network, wherein the polymer can be conductive or insulating. - Detailed discussion of the various formats is outside scope of this review paper. However, selected immobilization chemistries reported in relation to enzymatic biofuel cells are reviewed in the sections below. 

Such a significant gain in membrane productivity at higher operating pressures can be attributed to an Increased mechanical strength of the upper membrane layer, which is caused by the densely crosslinked tridimensional polymer network in it. 

Several theories have been proposed to calculate the molecular weight between crosslinks in a hydrogel membrane. Probably the most widely used of these theories is that of Flory and Rehner [5]. This theory deals with neutral polymer networks and assumes a Gaussian distribution of polymer chains and tetrafunctional crosslinking within the polymer network. 

Polymer network structure is important in describing the transport through biomedical membranes [139, 140]. The mechanism of diffusion in membranes may be that of pure diffusion or convective transport depending on the mesh size of the polymer network. With this in mind, polymer membranes are typically divided into three major types described below [141]. 

Thus the factor (Mc — M )/(Mn — M ) may be thought of as the sieving term mentioned in the theory of Yasuda et al. [150], In the Peppas-Reinhart theory, the sieving mechanism takes an understandable form which is a function of the structure of the network. It must be noted that the presence of semicrystalline regions in the polymer membrane leads to deviations from the predicted dependencies in this theory. These researchers found that as the crosslinking density in the polymer membrane increased, the solute diffusion coefficient decreased, further illustrating the importance of structural parameters of the polymer network in predicting the solute diffusion coefficient [156],... 

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. 

In general, but not as a rule, the smaller the target compounds to be separated, the denser should be the polymer network in order to give the most intense membrane-solute interactions during permeation. The driving force for the separation to take place should then act on the most significant difference... 

Enzymes, when immobilized in spherical particles or in films made from various polymers and porous materials, are referred to as immobUized enzymes. Enzymes can be immobilized by covalent bonding, electrostatic interaction, crosslinking of the enzymes, and entrapment in a polymer network, among other techniques. In the case of batch reactors, the particles or films of immobilized enzymes can be reused after having been separated from the solution after reaction by physical means, such as sedimentation, centrifugation, and filtration. Immobilized enzymes can also be used in continuous fixed-bed reactors, fluidized reactors, and membrane reactors. 

A number of liquid crystalline polyphosphazenes with mesogenic side groups have been prepared (48—50). Polymers with nonlinear optical activity have also been reported (51). Polyphosphazene membranes have been examined for gas, liquid, and metal ion separation, and for filtration (52—54). There is interest in phosphazene—organic copolymers, blends, and interpenetrating polymer networks (IPNs) (55—61) to take advantage of some of the special characteristics of phosphazenes such as flame retardance and low temperature flexibility. A large number of organic polymers with cydophosphazene substituents have been made (62). 

E. Ruckenstein, L. Liang, Pervaporation of ethanol-water mixtures through poly(vinyl alcohol)-poly(acrylamide) interpenetrating polymer network membranes unsupported and supported on polyether-sulfone ultrafiltration membranes a comparison, J. Membr. Sci. 110... 

In 2003, Ksiqzczak et al. [42] used water TPM for the characterization of nitrocellulose prepared by nitration of natural cellulose. The hydrophobic nature of the membrane made the measurements difficult and only partial conclusions were drawn. Despite this, pore size distributions were measured which showed good consistency and confirmed the value of TPM for such studies. Even more recently, Rohman et al. used water TPM to measure pore size distributions in porous polymers networks [43]. 

Turner JS, Cheng YL (2000) Preparation of PDMS-PMAA Interpenetrating polymer network membranes using the monomer immersion method. Macromolecules 33( 10) 3714—3718... 

Miyata T et al. (1996) Preparation of polydimethylsiloxane/polystyrene interpenetrating polymer network membranes and permeation of aqueous ethanol solutions through the membranes by pervaporation. J Appl Poly Sci 61(8) 1315—1324... 

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