Hydrophobic association mechanisms

The amount of small molecules in the permeate at low alkalinity increased with the relative concentration of small molecules (Figure 3). If hydrophobic bonding or simple solubility was the dominant mechanism for the association, the solubility of lignin molecules should be solely a function of pH regardless of the MWD of the parent solution. Consequently, the permeate MWD should be approximately the same and not a function of the MWD of the parent solution. Since the experimental permeate MWD varied with the parent MWD, the solubility or hydrophobic interaction mechanism was no longer accepted. 

The only aggregate enhanced in D20 is the IIS species. This specific enhancement is additional support for our previous suggestion that the IIS aggregate is favored under conditions that are associated with a hydrophobic force mechanism, and the 7S is not. It appears then that comparative studies of aggregation phenomena in H20 and D20 are a convenient method for indicating aggregation processes favored by hydrophobic forces. 

Ben-Naim (1972b, c) has examined hydrophobic association using statistical mechanical theories of the liquid state, e.g. the Percus-Yevick equations. He has also examined quantitative aspects of solvophobic interactions between solutes using solubility data for ethane and methane. The changes in thermodynamic parameters can be calculated when two methane molecules approach to a separation of, 1-533 x 10-8 cm, the C—C distance in ethane, and the solvophobic quantities 8SI/i, s 2 and 8SiS2 can be calculated. In water (solvophobic = hydrophobic) 5si/i is more negative than in other solvents and decreases as the temperature rises both 8s iH%... 

Low charge density, hydrophobically modified polybetaines were shown to interact and comicellize with nonionic, anionic, cationic, and amphoteric surfactants [181-183] and many ionic organic dyes [264,265]. The association mechanism of hydrophobically modified polymers and surfactants in dependence on the concentration of interacting components can be modeled by two pathways (Scheme 21) [183]. 

Thickening Mechanism of HMWSPs. HMWSPs exhibit enhanced solution viscosity as compared to their unmodified counterparts. Figure 1 compares the Brookfield viscosity of a hydrophobically modified HEC (CigHMHEC) with that of a similar molecular weight HEC. The enhanced solution viscosity of HMWSPs is the result of intermolecular associations via the hydrophobic groups (Figure 2). These hydrophobic associations can be viewed as pseudo-cross-links. A three-dimensional network results because of the tendency of the hydrophobes to cluster and thereby minimize the disruption of water structure. This network leads to an apparent increase in the hydrodynamic volume, which is reflected in enhanced solution viscosities. 

The associative mechanism of thickening has been variously described, but is generally thought to result from nonspecific hydrophobic association of water-insoluble groups in water-soluble polymers 34, 35). For associative ASTs, the terminal hydrophobes of the ethoxylated side chains are considered to be the primary interactive components. These hydrophobes can interact with each other via intermolecular association, and can also interact with hydrophobic particle surfaces when present. The specific interaction with dispersed-phase components such as latex particles has been shown to be one of surface adsorption (36). In essence, the associative component of thickening in dispersed-phase systems also has dual character resulting from the building of structure within the aqueous phase and interaction with particle surfaces. 

From previous research, it is know that the coacervation mechanism for the system in Figure 10 is ion-exchange and hydrophobic association. Given this information, the No Salt diagram can be used as a baseline for understanding the effects of salt order of addition. 

This chapter discusses formation conditions as well as rheological and mechanical properties of hydrogels formed via hydrophobic associations in micellar solutions it also discusses why the dynamic and mechanical properties of such... 

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