Nonaqueous dispersions contributions

Besides temperature and addition of non-solvent, pressure can also be expected to affect the solvency of the dispersion medium for the solvated steric stabilizer. A previous analysis (3) of the effect of an applied pressure indicated that the UCFT should increase as the applied pressure increases, while the LCFT should be relatively insensitive to applied pressure. The purpose of this communication is to examine the UCFT of a nonaqueous dispersion as a function of applied pressure. For dispersions of polymer particles stabilized by polyisobutylene (PIB) and dispersed in 2-methylbutane, it was observed that the UCFT moves to higher temperatures with increasing applied pressure. These results can qualitatively be rationalized by considering the effect of pressure on the free volume dissimilarity contribution to the free energy of close approach of the interacting particles. 

Steric and Electrostatic Contributions to the Colloidal Properties of Nonaqueous Dispersions... 

The signs of the contributions of the various enthalpy and entropy components to the free energy of flocculation in many nonaqueous dispersions... 

A dispersion that flocculates on heating, as was mentioned previously, must be enthalpically stabilized just below the UCFT. For nonaqueous dispersions, the origin of the enthalpy contribution that imparts stability in these circumstances is readily pinpointed from Table 7.4. The only enthalpy contribution that is positive is that associated with the free volume dissimilarity. It is therefore this term that imparts stability just below the UCFT. 

When the temperature is raised, the contact dissimilarity term, which favours stability, is signiflcantly reduced. Although the combinatorial contribution to the overall free energy of interpenetration increases on heating, it would be expected, by analogy with nonaqueous dispersions, that the absolute magnitude of the free volume term (which favours flocculation) would increase. The net effect of a reduced contact dissimilarity contribution to... 

The thermodynamic contributions to steric stabilization according to the free volume theory for nonaqueous (and some aqueous) dispersions... 

The tendency of decreasing the contribution of the concentration factor and increasing the contribution of the factor of the micellar microenviromnent is also observed for the reverse nonaqueous micellar solutions. For the case of aminolysis of phosphonates 1-4 in the polyethylene glycol-600-monolaurate (PM) reverse micelles, both factors are shown to contribute positively to the micellar rate effect, with F higher than Fc (Table 15.1). In nonaqueous systems micellization is mainly contributed by dispersion interactions and results in the formation of small aggregates with a low solubilization capacity towards the substrates. ... 

Pattabi et al. reported obtaining self-standing flexible nanocomposite films based on PVP capped CdS NPs embedded in a PVA matrix with photoluminescence properties (Pattabi et al. 2007) and electrical conductivity (Amma et al. 2014). CdS NPs were obtained from cadmium nitrate and hydrogen sulfide by a nonaqueous method and then were dispersed in a PVA matrix. With an average particle size of approximately 3-5 nm, they contributed to the obtaining of photoluminescence emission spectra with two peaks, at 502 and 636 mn (Pattabi et al. 2007). The electrical conductivity of the (PVP-CdS) PVA films was seen to increase with temperature (Amma et al. 2014). 

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