Structure and Properties of Gels

5 Change of the Structure and Properties of Hair that is Independent of the Chemical Changes of SS Bonds 162 

4 Gelation Behavior and Conformational Order in i-PS/Solvent System 188 

2 Viscoelasticity and Its Evaluation Technique of Vibration Damping Gels 331 

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Lakeman, C. D. E. Guistolise, D. J. Tani,T. Payne, D. A. 1994. Effect of thermal processing conditions on the structure and properties of sol-gel derived PZT thin layers. Br. Ceram. Proc. 52 70-76. 

In general, the structure of sol gel materials evolves sequentially as the product of successive and/or simultaneous hydrolysis and condensation and their reverse reactions (esterification and depolymerization). Thus, in principle, by chemical control of the mechanisms and kinetics of these reactions, namely the catalytic conditions, it is possible to tailor the structure (and properties) of the gels over a wide range. For example, stable silica xerogels of tailored particle dimensions, pore morphology, density and porosity, from relatively... 

Surface-initiated ATRP was applied not only on planer substrates but also on various kinds of flne particles. The latter systems will be reviewed separately in Sect. 5.1. Porous materials are also fascinating targets for chromatographic application making use of the unique structure and properties of high-density polymer brushes. Wirth et al. were the first to report the grafting of poly(acrylamide) (PAAm) on a porous silica gel [109,110]. 

Jarvis, M. C. (1984). Structure and properties of pectin gels in plant cell walls. Plant, Cell and Environment, 7, 153-164. 

SedlXCek, B. Structure and properties of hydrophylic polymers and their gels. VII. Turbidity changes of polymeric gels poly (ethylene glycol methacry-Iate) -glycol-water. Collection Czech. Chem. Comm tin. 32, 1368 (1967). 

In biological systems molecular assemblies connected by non-covalent interactions are as common as biopolymers. Examples are protein and DNA helices, enzyme-substrate and multienzyme complexes, bilayer lipid membranes (BLMs), and aggregates of biopolymers forming various aqueous gels, e.g., the eye lens. About 50% of the organic substances in humans are accounted for by the membrane structures of cells, which constitute the medium for the vast majority of biochemical reactions. Evidently organic synthesis should also develop tools to mimic the structure and properties of biopolymer, biomembrane, and gel structures in aqueous media. 

The physical and chemical properties of photoisomerizable molecular films or photoisomerizable polymers are controlled by light. Photochemical control of the formation of liquid crystal phases, or sol-gel transitions,137 381 of polymers containing photoisomerizable components demonstrates signal regulation of the structure and properties of microscopic and macroscopic phases. Physicochemical properties of photoisomerizable membrane-mimetic assemblies such as liposomes,1241 mono-... 

In the 1970s, the fluid mosaic concept emerged as the most plausible model to account for the known structure and properties of biological membranes [41]. The fact that membranes exist as two-dimensional fluids (liquid disordered) rather than in a gel state (solid ordered) was clearly demonstrated by Frye and Ededin [42], who showed that the lipid and protein components of two separate membranes diffuse into each other when two different cells were fused. Since that time, numerous studies have measured the diffusion coefficient of lipids and proteins in membranes, and the diffusion rates were found to correspond to those expected of a fluid with the viscosity of olive oil rather than a gel phase resembling wax. 

The relative rates of reaction for the hydrolysis and condensation dictate the structure and properties of an alkoxide gel. These reaction rates are schematically described in Figure 8.18 [43] for the example of a silicon ethoxide. In acidic solutions, hydrolysis is achieved by a bimolecular displacement mechanism that substitutes a hydronium ion (H" ) for an alkyl [44]. Under these conditions the hydroljreis is rapid compared to the condensation of the hydrolyzed monomers and promotes the development of larger and more linear molecules, as is described in Figure 8.19. Under basic conditions, hydrolysis occurs by nucleophilic substitution of hydrojgrl ions (OH ) for alkyl groups [45]. Here the condensation is rapid relative to hydrolysis, promoting the precipitation of three-dimensional colloidal particles as shown in Figure 8.17(b) and 8.19. 

Patel HK, Rowe RC, McMahon J, Stewart RE A comparison of the structure and properties of ternary gels containing cetrimide and cetostearyl alcohol obtained from both natural and synthethic sources. Acta Pharm Technol 1985 31(4) 243-247. 

Structure and properties of the films formed by organic substances on silica gel surface. Investigations by inverse gas chromatography (IGC)... 

We note here that systematic studies of the melting transition of dry or nearly dry phospholipids bilayers (e.g., vesicles) have been scarce. While there is an abundant experimental and theoretical literature concerning the structure and properties of bilayers in water, less is known about their behavior when water is removed. We have therefore initiated a systematic experimental study of the gel-liquid crystal transition of pure DPPC and DPPC-cholesterol vesicles freeze-dried with and without disaccharides and oxyanion-disaccharide complexes. Some of our results to date are shown in Figure 9.3. 

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