Viscoelastic gel

T Tanaka, LO Hocker, GB Benedek. Spectrum of light scattered from a viscoelastic gel. J Chem Phys 59 5151-5159, 1973. 

The organized structures give to the aqueous phases new macroscopic properties like iridescent colors, viscoelasticity, gel character, a yield stress, and, between crossed polarizers, beautifully colored patterns that make the order in the samples visible. The self-organization of the surfactant molecules is simply a result of the hydrophobic and electrostatic interaction between the individual molecules and the micellar structures. The size of the micellar structures, as in the case of small imUamellar vesicles, can be extremely monodisperse, even though one vesicle consists of hrmdreds of surfactant molecules. 

The vitreous humor volume is about 4 ml in an adult. Its viscosity is 2-4 times that of water and is dependent on the concentration of sodium hyaluronate. Although it has the outward appearance of a transparent, viscoelastic gel, it contains fine diameter type II collagen fibers (8-12 nm diameter) that entrap the large coiled hyaluronic acid molecules. These fibers give the gel a spherical structure with a dent in the anterior surface (the hyaloid fossa). The main constituent of the vitreous is water (98%) with a refractive index of 1.33, but the gel is... 

The bitumen comes as a residue from the refining of conventional or heavy crude oil, or from natural deposits of oil (tar) sand. Bitumen, being a complex mixture of more than 1000 different molecules, is itself a colloidal suspension of asphaltenes in a continuous phase of saturated parrafins, aromatic oils and resins [774], Descriptions of different kinds of asphalts are given in Refs. [775,776], At low asphaltene concentration the suspension is Newtonian. Once the concentration increases above about 8 % v/v, however, the asphaltenes form a three-dimensional network and the suspension can become a viscoelastic gel [774]. The asphaltenes interact through van der Waals forces so that a bitumen containing 15% asphaltenes is solid at room temperature and liquid above about 60-100 °C. 

Mucus possesses both solid-like (elastic) and liquid-like (viscous) attributes simultaneously and is therefore termed a viscoelastic gel. The viscoelastic properties arise from the non-covalent interactions (entanglements) between the predominantly anionic mucin molecules, although weak hydrogen-bonding and ligand-like attractions between protein regions of adjacent molecules may also play a role. Gel properties are affected by ... 

Various chitosan derivatives of enhanced solubility, mucoadhesive, and permeation properties were developed. V-Trimethyl chitosan chloride (TMC) is a quater-nized derivative of chitosan with superior aqueous solubility over a broader pH range and penetration-enhancing properties under physiological conditions [78]. Carboxymethylated chitosan (CMChi) is a polyampholytic polymer able to form viscoelastic gels in aqueous environments. CMChi appears to be less potent compared with the quaternized derivative. Neither TMC nor CMChi have been found to provoke damage of the cell membrane, and therefore, they should not alter the viability of nasal epithelial cells [79],... 

Besides taking part in acquired pellicle formation on tooth (denture, implant) surfaces, MUC5B type mucins cover all oral surfaces with a 10-20- im thick layer. In addition, MUC5B type mucins form a hydrophilic viscoelastic gel (already in low concentration) that causes a high viscosity matrix of saliva. 

Chapter five introduces highly organized, quasi one-dimensional crystals, namely micellar rod and vesicular tubular fibres. They are compared to equally fascinating liquid threads found in viscoelastic gels and to phospholipid tubules. These membraneous assemblies build a bridge to the secondary structures of... 

Polysaccharides with Surfactant Micelles. Consider a solution of a fairly hydrophobic polysaccharide, such as a cellulose ether. The hydrophobic groups cause a weak attractive interaction, leading to a somewhat increased viscosity at low shear rates. If an anionic small-molecule surfactant is added, say SDS (sodium dodecyl sulfate), at a concentration above the CMC (critical micellization concentration), micelles are formed that interact with the polymer more specifically, one or a few polymer chains can pass through a micelle. In this way, polymer chains can be cross-linked. If now the polymer concentration c is below c (the chain overlap concentration), mainly intramolecular junctions are formed. If c > c, however, a gel results. In this manner, viscoelastic gels can be made with a modulus of the order of 10 Pa. 

Sofia P, Fiilber C, Demco DE, Bliimlich B, Spiess FTW (1996) Effect of residual dipolar interactions on the NMR relaxation in cross-linked elastomers. Macromolecules 29 6222-6230 Suzuki M, Hirasa O (1993) An approach to artificial muscle using polymer gels formed by microphase separation. Adv Polym Sci 110 241-261 Tanaka T, Fillmore DJ (1979) Kinetics of swelling of gels. J Chem Phys 70 1214—1218 Tanaka T, Hooker LO, Benedek GB (1973) Spectrum of light scattered from a viscoelastic gel. J Chem Phys 59 5151-5159... 

Most biological systems are predominantly water, with other components conferring important structural and mechanical properties. The complexity of the fluid can have a substantial impact on rates of diffusional transport. For example. Chapter 5 discusses the consequences of having self-organized phospholipid phases (i.e., membrane bilayers) in systems that are primarily composed of water. Membranes separate the medium into smaller aqueous compartments, which remain distinct because the membrane permits the diffusion of only certain types of molecules between the compartments. Complex fluid phases have diverse roles in biological systems hyaluronic acid forms a viscoelastic gel within the eye (vitreous humor) that provides both mechanical structure and transparency actin monomers and polymers within the cytoplasm control cell shape and internal architecture. Drug molecules often must diffuse through these complex fluids in order to reach their site of action. 

Grant, J.W. and Cotton, J.R. 1991. A model for otolith dynamic response with a viscoelastic gel layer. /. Vestib. Res. 1 139-151. 

Munch, J. P., Candau, S., Duplexxis, R., Picot, C., Herz, J., and Benoit, H., 1976, Spectrum of light scattered from viscoelastic gels, 7. Polym. Sci. Polym. Phys. Ed. 14 1097-1109. 

CMHEC is also very tolerant of Ca + and consequently readily dissolves in seawater. Unlike HEC, CMHEC in solution may be cross-linked with trivalent cations such as Fe + and AP+ to give greatly increased viscosity or three-dimensional viscoelastic gels (97). 

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