Ionotropic gels

The flow enhancement effect is completely suppressed in the presence of trivalent cations. Even at the preparation stage for aluminium sulfate (Al2(SOi)3), the polymer is precipitated at a concentration of c = 5 ppm the flakes thus formed can be clearly seen, suspended in solution. Consequently, no drag-reduction effect can be expected and the experimental solution behaves as a Newtonian fluid (Fig. 31). Therefore, it is likely that multivalent cations from complexes or ionotropic gels and that by exceeding a critical value they may precipitate out of solution. 

Ionotropic gels are more acid-stable than the sols (Guiseley et al., 1980) because of protonation of the electrolyte-sensitive acidic groups and immobilization of the molecules in the network. 

The operational stability of Trigonopsis variabilis cells with D-amino acid oxidase activity, entrapped in standard and hardened ionotropic gels, was also investigated by means of the FMC [39]. The activity of the biocatalyst packed in the FMC column was continuously monitored by the FMC signal measurement... 

Many techniques have been proposed for making capillary-pore membranes including laser beams, electroforming, photochemical etching, and ionotropy to orient anisotropic gel particles to form ionotropic-gel membranes.3... 

Alginates form ionotropic gels via selective binding of cations, and it forms gel-like networks with the polycation chitosan. 

For the acidic gels, an increase in the fraction of homopolymeric G-block yields higher shear modulus, similar to the influence of this residual sequence on the ionotropic gels. Homopolymeric M-block also forms jimctions under acidic conditions however, their contribution is smaller than those of the G-block. Alternating MG-block, with an approximately degree of polymerization of 15, does not contribute to form junctions and rather perturb gel formation [62]. 

Bi- and trivalent cations can also lead to the formation of ionotropic gels [see McCormick p 336 in 5 ]. In these gels, the metal ions... 

A simple example of gel formation is provided by chitosan tripolyphosphate and chitosan polyphosphate gel beads the pH-responsive swelling abihty, drug-release characteristics, and morphology of the gel bead depend on polyelectrolyte complexation mechanism and the molecular weight. The chitosan beads gelled in pentasodium tripolyphosphate or polyphosphoric acid solution by ionotropic cross-hnking or interpolymer complexation, respectively. 

Kulicke and Nottelmann (1989) divided gels into three generic classes, viz., physical, ionotropic, and covalent. Physical gels are held together by hydrogen bonds and molecular entanglements they expand when hydrated and contract when dehydrated to Silberberg (1989) they are swollen me-... 

Entrapment methods have been used almost exclusively to immobilize plant cells (17). They can be classified into three general groups (24,25) a. gel formation by ionic crosslinking of a charged polymer (ionotropic) b. gel formation by cooling of a heated polymer (thermal), and c. gel formation by chemical reaction (cross-linking, radical polymerization). 

Whatever the technique used (thermal or ionotropic gelation), gel particles are generally formulated in a two-step procedure involving a droplet formation and hardening. The droplet formation step determines the mean size and the size distribution of the resulting gel particles. In the following, the main procedures used for droplet formation—droplet extrusion, nebulization (spray), and emulsification—are described. 

Agulhon P, Robitzer M, David L, Quignatd F (2012) Structural regime identification in ionotropic alginate gels influence of the cation nature and alginate structure. Biomacromolecules 13 215-220... 

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