Structure of gels

Chul, M Phillips, R McCarthy, M, Measurement of the Porous Microstructure of Hydrogels by Nuclear Magnetic Resonance, Journal of Colloid and Interface Science 174, 336, 1995. Cohen, Y Ramon, O Kopeknan, IJ Mizrahi, S, Characterization of Inhomogeneous Polyacrylamide Hydrogels, Journal of Polymer Science Part B Polymer Physics 30, 1055, 1992. Cohen Addad, JP, NMR and Statistical Structures of Gels. In The Physical Properties of Polymeric Gels Cohen Addad, JP, ed. Wiley Chichester, UK, 1996 39. 

The structure of gels can be controlled by the selection of the optional chain length of the prepolymer. 

Te Nijenhuis, K. (1997) Thermoreversible networks. Viscoelastic properties and structure of gels. Advances in Polymer Science, 130, 1-267. 

Louden JD, Patel HK, Rowe RC. A preliminary examination of the structure of gels and emulsions containing cetostearyl alcohol and cetrimide using laser Raman spectroscopy. Int J Phann 1985 25 179-190. 

The influence of homogeneity of structure of gels on the phase transitions was studied by us for the networks of copolymers of methacrylamide with SMA in the mixtures of water with isopropanol [17]. The specific feature of these gels is the microinhomogeneity of their structure, which is manifested in intensive light scattering. For this type of system, it would be natural to expect an absence of... 

The collapse of P(DEAAm/MNa) gels in pure water cannot be described by the theory due to the formation of associated structures in the collapsed state (turbid structure of gels). 

Some small-angle X-ray scattering techniques have also been applied to polysiloxane elastomers. One examples is the characterization of the structures of gels.343 The most important example, however, has been the characterization of fillers precipitated into polysiloxane elastomers, and the corresponding incorporation of such elastomers into ceramic matrices (in both cases to improve mechanical properties).92,344,345 Some of this work is described in Chapter 8. 

Figure 23.5 Structure of gel components (a) poly(amideacid) azobenzene, (b) 1,3-dibutylimidazolium...

Structure of Gels There is still a difference of opinion about the structure of gels. Various theories have, however, been proposed to explain the structure of gels. 

It is known from Table 1 that gel time increases with the increase of water volume for hydrolysis. Transparent gel body can be obtained under 10 ml or 20 ml of water, whereas it would become opaque and show light white when water volume increases to 40 ml. The structure of gel body will become loosen and a little solution will bleed under the following drying, gel can not be formed when water volume rises up to 50 ml, white... 

The structure of gels depends on the components and the process parameters. Proteins containing over 30% hydrophobic residues form coagulum-type gels, e.g., hemoglobin and egg white albumin. The gelling-type proteins contain less hydrophobic residues and are represented by some soybean proteins, ovomucoid, and gelatin. 

Depending on the method used for membrane processing, colloidal or polymeric, two main structures of gel layers before drying and sintering can be described according to the literature ... 

Fig. 7,2. Influence of colloidal sol stability on the porous structure of gel layers (a) stable sol with non-aggregated particles (b) partially aggregated sol with weakly charged particles.

Moreover, the structure of gels produced depends substantially on precipitation conditions and is determined by the precipitation temperature, pH of the medium, initial composition of solution, its concentration, of sequential mixing of solutions or conditions of introduction of precipitating agent [7]. It should be noted here that even in the production of one-component gel, periodicity of precipitation gives a product with a non-homogeneous structure which, as a rule, forms adsorbents with a set of pores different in size. Therefore, strict observance of all the conditions of sample synthesis enumerated above is absolutely necessary. 

The network structure of gels is generally highly heterogeneous from the structural and dynamic points of view. The existence of solid-like domains from the cross-linked region is characteristic of the formation of the gel network. Such a domain in polysaccharide gels is ascribed to formation of cross-links due to the physical association of chains adopting an ordered conformation. It is now obvious that the secondary structure of such ordered polysaccharide chains is readily determined on the basis of the conformation-... 

This means that the network structures of gels consisting of (1 3)-)8-d-glucans are different from each other with respect to the linear and branched forms. The C-1 and C-3 chemical shifts from the liquid-like domain of... 

Apart from a discussion of functional properties, this section will be divided according to the network structure of gels. Flory gave the following structural classification ... 

Finally, the surface and pore structure of gels obtained after dehydrating sols may be affected by the presence of oligomeric silica. This effect will be particularly evident with sols of small particle size in which partial particle coalescence may occur, together with the generation of small micropores (<2 nm), as has been previously observed (18). 

Bastide J, Candau SJ (1996) Structure of gels as investigated by means of static scattering techniques. In Cohen Addad JP (ed) Physical properties of polymeric gels. Wiley, New York... 

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