Effect of Polymers on Colloid Stability

GREGORY, J., Effects of polymers on colloid stability , in Scientific Basis of Flocculation (see reference 100), pp. 101-130... 

The role of polymers on colloid stability is considerably more complicated than electrostatic stability due to low molecular weight electrolytes considered in Chapter 11. First, if the added polymer moieties are polyelectrolytes, then we clearly have a combination of electrostatic effects as well as effects that arise solely from the polymeric nature of the additive this combined effect is referred to as electrosteric stabilization. Even in the case of nonionic... 

Scheutjens-Fleer (SF) Theory. A conceptual model for the effects of NOM on colloidal stability can be developed by using existing theoretical and experimental investigations of polymer and polyelectrolyte adsorption on solid surfaces and of the effects of macromolecules on colloidal stability. The modeling approach begins with the work of Scheutjens and Fleer for uncharged macromolecules, termed here the SF theory (3-5). This approach has been extended to the adsorption of linear flexible strong polyelectrolytes by van der Schee and Lyldema (6), adapted to weak polyelectrolytes (7-9), and applied to particle-particle interactions (8, 10). 

The study of polymer solutions at interfaces has most often been motivated by the effects of polymers on the stability of colloidal suspensions. 

E. Ruckenstein and LV. Rao Effect of solvent on the stability of mixtures of sterically stabilized dispersions and free polymers, COLLOIDS AND SURFACES 17 (1986) 185-205. 

Tadros, T.F. (1982) Polymer adsorption and colloid stability, in The Effect of Polymers on Dispersion Properties (ed. T.F. Tadros), Academic Press, London. Thompson, W. (Lord Kelvin) (1871)... 

To ascertain the effect of anchor polymer on colloid stability, Napper (1970a) measured the UCFTs of five poly(vinyl acetate) latices stabilized by poly(oxyethylene) of molecular wei t 10000 in 0-39 M MgS04. The stabilizing moieties were covalently attached to five different anchor polymers. The results are presented in Table 5.2. 

The Effects of Free Polymer on Colloid Stability Theories of Depletion Flocculation and Depletion Phase Separation... 

During the past few decades the increase in activity in polymer colloids [100-104] and with it methods for the formation of veiy monodisperse spherical particles has provided a variety of polymeric substrates for adsorption or chemical attachment of polymers or surfactants. They have also provided quite well-defined systems for investigating the effects of these molecules on colloidal stability. Added to this has been a complementaiy growth in the synthesis of various type of surfactants and macromolecules in well-defined, often pure, form. On the theoretical front the rapid development of computers has also provided ways of simulating both molecular structures in solution and at surfaces. This has meant a rapid growth of the literature on adsorption of various molecules on polymer colloids and on the effects of this adsorptioi colloid stability. Much of this is now summarized in review articles, conferences and books [105-107] which are too extensive to discuss in this chapter hence rally the salient points will be covered. 

The various regimes and effects obtained for the interaetion of polymer solutions between two surfaces have recently been reviewed [55]. It transpires that force-microscope experiments done on adsorbed polymer layers form an ideal tool for investigating the basic mechanisms of polymer adsorption, colloidal stabilization, and flocculation. 

J. F. Joanny, L. Leibler, P. G. de Gennes. Effects of polymer solutions on colloid stability. J Polym Sci Polym Phys Ed 77 1073-1084, 1979. 

Vincent, B., Luckham, P.F. and Waite, F.A. (1980) The effect of free polymer on the stability of sterically stabilized dispersions. Journal of Colloid and Interface Science, 73 (2), 508-521. 

Adsorption behavior and the effect on colloid stability of water soluble polymers with a lower critical solution temperature(LCST) have been studied using polystyrene latices plus hydroxy propyl cellulose(HPC). Saturated adsorption(As) of HPC depended significantly on the adsorption temperature and the As obtained at the LCST was 1.5 times as large as the value at room temperature. The high As value obtained at the LCST remained for a long time at room temperature, and the dense adsorption layer formed on the latex particles showed strong protective action against salt and temperature. Furthermore, the dense adsorption layer of HPC on silica particles was very effective in the encapsulation process with polystyrene via emulsion polymerization in which the HPC-coated silica particles were used as seed. 

In this study, adsorption behavior of water soluble polymers and their effect on colloid stability have been studied using polystyrene latices plus cellulose derivatives. As the aqueous solution of hydroxy propyl cellulose(HPC) has a lower critical solution temperature(LCST), near 50 °C(6 ), an increased adsorption and strong protection can be expected by treating the latices with HPC at the LCST. 

Polymer molecules are often employed to stabilize colloids [1]. In most theoretical treatments of the effect of polymer adsorption [2-5], only the steric force is taken into account, and the steric force and the traditional double-layer force for particles devoid of hairs are assumed to be additive. The steric force is a short-range interaction which acts only when the chains on the surfaces of the two particles interpenetrate [6-8]. However, in addition to this short-range interaction, a hairy surface can also generate another effect, because it can change the dielectric constant in the vicinity of the surface. 

Addition of polymers can both stabilize and destabilize a solution. If the polymer contains ionizable units it is usually referred to as a polyelectrolyte. In this report we will focus on the effect from polyelectrolytes on the colloidal stability. In high dielectric media like water, where the monomers are ionized, the behavior of a polyelectrolyte is mainly governed by electrostatics and the connectivity of the monomers. Therefore, in theoretical studies, many important features of the polyelectrolyte behavior in water solution can be studied by a schematic description of the polyelectrolyte as a linear chain of charged monomers connected with springs. The bonding interaction between two monomers is Ub=K(r —a)2, where K is the spring constant, a is the equilibrium value and r is the distance between the two monomers (see Fig. 11). 

Li, Ch., Yu, X., and Somasundaran, P., Effect of a comb-like amphiphihc polymer on the stability of alumina dispersions, Colloids Surf., 69, 155, 1992. 

Furusawa, K., Shou, Z., and Nagahashi, N., Polymer adsorption on fine particles the effect of particles size audits stability. Colloid Polym. Sci., 2IQ, 212, 1992. 

Vincent B. The effect of adsorbed polymers on dispersion stability. Adv Colloid Interface Sci 1974 4 193-277. 

The spontaneous crystallization temperature of each sample of treated wine (Table 1.16) was also determined using the same procedure. Examination of the results shows that a wine filtered on a 10 Da Millipore membrane, i.e. a wine from which all the colloids have been removed, has the lowest value for the supersaturation field (Tsat - Tcso), closest to that of the model dilute alcohol solution. Therefore, the difference between the results for this sample and the higher values of the supersaturation fields of fined samples define the effect of the protective colloids. It is interesting to note that the sample treated with metatartaric acid had the widest supersaturation field, and cold stabilization was completely ineffective in this case. This clearly demonstrates the inhibiting effect this polymer has on crystallization and, therefore, its stabilizing effect on wine (Section 1.7.6). Stabilization by this method, however, is not permanent. 

The chart presented in Table 1.4 provides a road map to the structure and organization of this book. The effects of attached polymer will be discussed first, followed by consideration of the influence of free polymer. Note that an alternative schematic representation of the effects of polymeric chains on colloid stability is presented in Chapter 17, Section 17.7. 

---