Polymer concentration effect dispersions

Our model predicts destabilization of colloidal dispersions at low polymer concentration and restabilisation in (very) concentrated polymer solutions. This restabilisation is not a kinetic effect, but is governed by equilibrium thermodynamics, the dispersed phase being the situation of lowest free energy at high polymer concentration. Restabilisation is a consequence of the fact that the depletion thickness is, in concentrated polymer solutions, (much) lower than the radius of gyration, leading to a weaker attraction. 

Experimentally it is difficult to detect the occurrence of polymer shear degradation since concentration effects, increased peak dispersion, and ultrafiltration of high molecular weight components may also distort the peak profile or shift the distribution towards the low molecular weight region. Furthermore,... 

Another experimental aspect investigated by Stenkamp et al. was the effect of the concentration of the polymer initially dissolved in solution (Figure 2). In general, by decreasing the initial concentration of the polymer, the probability for restabilization to occur decreases. For LiCl and KNO3, a decrease from 60 x 10 3 to 0.6 x 10 3 g/L of the initial concentration of the polymer causes the loss of restabilization. KC1 had a stronger propensity for restabilization and could restabilize the colloidal dispersion for a 0.6 x 10 3 g/L initial polymer concentration, but not for a 0.01 x 10 3 g/L concentration. 

Most food systems are of a colloidal as well as a polymeric nature. The presence of a nonadsorbing polymer in a skim milk dispersion induces an effective attraction between the casein particles, called depletion interaction, resulting in phase separation at sufficiently high polymer concentration. Tuinier et al. (2003) discussed the influence of colloid-polymer size ratio, polymer concentration regime, size, poly-dispersity and charges in colloid/biopolymer mixtures, demonstrating the challenging complexity of the subject. 

At the same stress amplitude, rubber modified polymers fail sooner in fatigue than do the unmodified polymers even though they have superior resistance to fatigue crack propagation. This is a result of much earlier initiation of crazing, localized plastic deformation, and subsequent crack development due to the stress concentrating effect of the dispersed second phase particles. 

When the surfeclant concentration is high relative to the polymer concentration sufRdent sui ctant may be adsorbed on individual polymer molecules to prevent their coalescence to form latex particles or indeed to disperse prdbrmed polymer to form clear solutions in which the solute behaves as a po yelectro yte, But the influence of such effects on tbe course of emulsion polymerization reactions has not been elucidated. Sata and Saito (1952) showed that poly(vinyl acetate) preeptated from acetone solution with water could be solubibzed in sodium dodecyl sulfate solutions after removal of the acetone by dialysis. To obtain a clear solution at 20°C, a wdght of surfactant S-10 times that of pol ner was required. Althou this greatly exceeds the surfactant concentrations normally used in emulsion... 

It has been seen in Chapter 7 that the use of macromolecules as dispersion stabilisers depends in part on the osmotic forces arising from the interaction of solvated polymer chains as neighbouring particles approach (see Fig. 7.7). It is thus important to know how factors such as temperature and additive affect this interaction. Flory has given the free energy of dilution (the opposite process to the concentration effect discussed in section 7.2)... 

The above results of phase behavior as summarized in Table I suggest that the observed macroscopic phase separation is directly related to the structure of the surfactant solution. There is no phase separation when the solutions are isotropic. But the added polymer induces phase separation only when a single liquid crystalline phase or a stable dispersion of liquid crystal particles in brine is present in the absence of polymer. The effect is the same for two different types of polymer and is independent of the polymer concentration over a fair range of composition. 

Majority of dispersed dyes, used for PETP dyeing, are instable themselves [284, 286]. That is why it may be supposed that increase of dye concentration leads to accumulation of being formed radicals in the thin surface layer of the sample without mixing, as a result of which the rate of chain break rises and suppresses chain photooxidation of polymer. This effect was called by the authors [175] effect of concentration inhibition, which was observed in the case of polycaproamide light stabilization by action dyes. 

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