Physical Gelation of Biopolymers

Abstract

Polymer networks can be divided into two main classes, those formed at high segment concentrations by the topological entanglement of polymer chains and those formed formally by the covalent cross-linking of preformed linear chains. The former are networks at frequencies higher than some typical entanglement lifetime, and are viscoelastic liquids, whereas the latter are of infinite molecular weight, and have an equilibrium modulus-they are viscoelastic solids. However, there are many intermediate systems of chains which are "physically" cross-linked, the cross-links themselves being of small but finite energy, and/or of finite lifetime; these are called physical networks. Specific systems include both biological and synthetic polymers. Amongst the former are gelatin, and the seaweed polysaccharides such as agarose and the carrageenans. Such biopolymers form physical gels involving junction zones of known, ordered secondary structure. Models are presented that relate the modulus and geltime kinetics to properties of the macromolecular chains. Covalent and Entanglement NetworksPolymer gels or networks can be divided into two main classes, chemically cross-linked materials (including bulk elastomers), and "entanglement networks". The covalently cross-linked materials are formed by a variety of routes including cross-linking high molecular weight linear chains, either chemically or by radiation, by end-linking react ant chains with a branching unit, or by step-addition polymerisation of oligomeric multi-functional precursors. They are true macromolecules, where the molecular weight is nominally infinite, and they therefore possess an infinite relaxation time

Effect of degree of deacetylation on physicochemical and gelation properties of konjac glucomannan

“…At lower frequencies, molecular chains disentangle during a long period of oscillation; yet at higher frequencies, KGM molecules can't disentangle during a short period of oscillation and form a temporary network structure. Therefore, the solution change from liquid-like behavior at low frequencies (G′ b G″) to solid-like behavior at higher frequencies (G′ > G″) (Ross-Murphy, 1987). However, the crossover frequency of G′ and G″ shifted gradually to a lower value with increasing DD of KGM, indicating an enhancement of temporary network structures of KGM chains at 25°C.…”

Biopolymer and Water Dynamics in Microbial Biofilm Extracellular Polymeric Substance

“…The biofilm EPS is composed of cellular byproduct, including nucleic acids and proteins, but is thought to be predominantly polysaccharides 4,7,8. The rheology and polymer dynamics of polysaccharide gels have been extensively studied experimentally3,9 and theoretically10,11 due to their prevalence, however, such studies in biofilms are more recent 6-8,12,13…”

Effects of Temperature on Viscoelastic Properties and Activation Energies of Whey Protein Gels

“…If disulfide bonds are the predominant cross-links between the protein molecules, the linkages are permanent and such gels should possess rubber-like elasticity, whereas, if the cohesive attractive forces involve mainly noncovalently stabilized and/or topological interactions (Clark and Lee-Tuffnel, 1986;Mitchell, 1980;Ross-Murphy, 1987), the rheological properties of such gels are influenced by temperature.…”