Lower flocculation temperature

A decrease in temperature may also lead to flocculation at a lower flocculation temperature (l.f.t.), partly because the Brownian motion can no longer maintain the dispersed state and partly... 

Flocculation studies were performed by lowering the temperature of PMMA dispersions in a binary mixture of n-heptane and... 

Weakly flocculated gels are less strain sensitive than the strongly flocculated gels discussed above. Figure 7-17 shows the elastic modulus G versus strain y for two gels made from weakly flocculated octadecyl-coated silica spheres (Chen and Russel 1991). For the more weakly flocculated of the two, obtained by lowering the temperature to 29 C, nonlinearity occurs above a critical strain yc of around 10%, while for a somewhat more... 

Alternatively, the 0-condition may be reached by increasing the temperature. Here the interactions between the medium and the segments of the polymer decrease because of the decreasing density of the medium, and segment-segment interactions dominate when an upper flocculation temperature (u.f.t.) is reached. This is analogous to the lower consolutc behaviour of those polymer solutions which undergo a phase separation as the temperature is raised. 

Experimental observation of selective flocculation. Croucher and Hair (1980a) have demonstrated the phenomenon of selective flocculation in mixtures of heterosterically stabilized dispersions. They prepared particles of poly(vinyl acetate) stabilized by polystyrene and polyacrylonitrile particles stabilized by polyisobutylene, both in cyclopentane. The value of X23 for polystyrene and polyisobutylene is known to be positive (Hyde and Tanner, 1968), corresponding to mutually incompatible polymers. The poly(vinyl acetate) particles stabilized by polystyrene exhibited both upper and lower critical flocculation temperatures whereas the polyisobutylene stabilized particles only flocculated on heating. 

When a mixture of the two different types of particles dispersed in cyclopentane was cooled to the lower critical flocculation temperature (280 K) of the poly(vinyl acetate) particles stabilized by polystyrene, those... 

Another recently demonstrated separation application of SPs is flocculation. A thermosensitive polysaccharide was synthesised by graft-polymerisation of pNIPAM onto pullulan, a polysaccharide polymer consisting of maltotriose units, using Ce(IV) as the initiator. The thermosensitive polysaccharide induced flocculation of clay particles both below and above the lower critical temperature. This process, however, was more efficient with larger floes forming above the LCST (Ghimici and Constantin, 2011). 

The principal consideration in selecting an appropriate soluble polymeric component for the steric barrier is that it should be freely soluble in the dispersion medium to be usedo This had been recognised empirically for some years before Napper (4) undertook quantitative studies which showed that sterically stabilised latexes flocculated at or around the theta point for the soliible polymer in the dispersion medium. Later studies have shown that both upper and lower critical flocculation temperatures may occur in organic solventso... 

These are necessary in water-based paints to prevent coagulating or flocculating when the paints are subjected to freezing temperatures. Stabilizers, such as ethylene or propylene glycol, are added to lower the temperature at which paint freezes. An additive that improves the stability of the emulsion can also be used. 

In other words, the lower the mass of the particle, the higher its velocity, because the average energy of any particle at a given temperature is constant, kT. A dispersed particle is always in random thermal motion (Brownian motion) due to coUisions with other particles and with the walls of the container (4). If the particles coUide with enough energy and are not well dispersed, they will coagulate or flocculate. 

The rate of flocculation of selenium sols by solutions of potassium or barium chloride of various concentrations at temperatures between 15° and 20° C. has been determined.8 Results show that a very high concentration of these electrolytes is necessary for rapid flocculation. Smoluchowski s theory holds when the velocity of flocculation is not far removed from that obtaining when the colloidal particles are totally discharged. The results, however, deviate largely from this theory when the concentrations of the electrolytes are lower.3... 

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