Gel-like networks

Kuroiwa K, Shibata T, Takada A, Nemoto N, Kimizuka N. Heat-set gel-like networks of lipophilic Co(II) triazole complexes in organic media and their thermochromic structural transitions. J Am Chem Soc 2004 126 2016-2021. 

Some petroleum products, especially those containing higher-molecular-weight compounds such as waxes, do not crystallize rapidly when cooled. Instead, they form a gel-like network throughout the fuel matrix. This network can begin forming at temperatures well above the pour point of a fuel and may render the product unpumpable. 

Fig. 10 a-d Optical images of polypseudorotaxane formed by a-CD and PEI gel-like network formed at gelation temperature a, equilibrated hydrogel at gelation temperature b, and crystalline precipitate formed by thermal process c and the schematic illustration of the transition process from the hydrogels to the crystalline precipitates d [81]... 

Proteins are considered to adsorb at the interface, partially unfold and interact to form molecular "gel-like" networks (Wilde et ak, 2004). Collapse of emulsions or foams involves the stretching of the interface and the elasticity of the protein structure is supposed to oppose this effect. For mobile surfactants or lipids stretching of the interface will lead to concentration gradients and rapid diffusion of the molecules to restore the status quo (Wilde et al., 2004). A source of instability for most foods is the presence of both proteins and small mobile molecules at the interface. The incompatibility of the two mechanisms means that mixed interfaces are less stable than interfaces containing pure protein or pure surfactant or lipid (Wilde et al., 2004). If there is sufficient surfactant or lipid present then they will eventually displace the protein. It is the structures formed during the battle for control of the interface that gives rise to instability. 

A characteristic feature of surfactants belonging to both of these groups is inability to form spatial gel-like networks both at interfaces and in the bulk. 

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

Similar metallopolymers based on diphenylphosphine-terminated macromonomers in combination with Rh" or Ir ions resulted in the formation of gel-like networks when the building blocks were combined in a solvent such as dichloromethane or chloroform [91]. These gels could be liquehed upon ultrasonication (Fig. 27) as a result of ligand exchanges that preserved the coordination stoichiometry of the metal centers while reducing the number of cross-links. After sonication, the equilibrium network reformed almost immediately in the case of Rh" (gel phase after 1 h at -i-20°C), whereas the process was much slower in the case of the Ir -based gel (sol phase still present after 3 days at —20°C). 

It is probable that crazing occurs when the volume of dried NaHSiOj is insufficient to fill the spaces or pores between the spherical colloidal particles as they become packed together upon drying. If the residual solid ionic silicate does not fill the pores, then the gel-like network of particles shrinks, and cracks develop in the film. Thus the greater the tendency to micro-crack, the lower the strength of the dried film. 

The sol-gel process is a wet-chemical technique used for the fabrication of both glassy and ceramic materials. In this process, the sol (or solution) evolves gradually toward the formation of a gel-like network containing both a liquid phase and a solid phase. In other words the sol-gel process is the formation of an oxide network through polycondensation reactions of a molecular precursor in a liquid. A sol is a stable dispersion of colloidal particles or polymers in a solvent. These particles may be amorphous or crystalline. A gel consists of a three-dimensional continuous network, which encloses a liquid phase. In a colloidal gel, the network is built from agglomeration of colloidal particles... 

E. Gel-Like Networks Self-Assembled from Lipophilic Complexes and Unique Thermal Transitions... 

Fig. 5. 22 Schematic of how hyper-(PAA23-PSi4-PAA23)n chains undergo interchain association to form a gel-like network, where PAA blocks from different chains are represented by different colors...

The dynamics of concentration fluctuations expressed by eqn [161] (or eqn [34]) of the Omstdn-Zemike type exhibits the diflrrsion coeflrdent D =feT/(6nj 0), eqn [72], which can also be derived from fluctuations of gel-like networks with screening of hydrodynamic interactions. Thus, it is often rderred to as the gd mode. A decrease in mesh size increases the rdaxation rate of the gel mode. Experimentally, DLS for semidilute solutions rrsually exhibits another mode of motions with a very slow decay rate. This slow mode may be assodated with some inhomogeneity depending on solvent quality and sample preparation, or may be rdated to the translational... 

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