Stability of Colloid-Polymer Mixtures

In the introductory chapter we saw that many systematic depletion studies were performed on mixtures of spherical colloids plus non-adsorbing or free polymers. The reason is obvious spherical colloids are of industrial and fundamental relevance, and can be prepared in a relatively controlled way (rather monodisperse, hard-sphere like), while polymers are ubiquitous, and are efficient depletants. 

To verify whether polymers adsorb or not there are various experimental methods. The typical adsorbed amount at saturation P 1 mg m [1]. It is possible to investigate whether a polymer adsorbs onto a colloid by measuring the friction coefficient that a sphere experiences by for instance sedimentation or dynamic light scattering [3, 4]. 

Lekkerkerfcer and R. Tuinier, Colloids and the Depletion Interaction, Lecture Notes in Physics, 833, DOI 10.1007/978-94-007-1223-2 4, 

Verify that the polymer concentration Cp (in g/L) required to fully cover all spheres with radii in a dispersion with volume fraction t can be expressed as 

Hint assume that all added polymer adsorbs. 

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In a mixture of hard spheres and depletants a phase transition occurs upon exceeding a certain concentration of colloidal spheres and/or depletants. This is the subject of Chaps. 3-6 in this book. A key parameter in describing the phase stability of colloid-polymer mixtures is the size ratio q,... 

The forces of attraction and repulsion that control the adsorption process also determine the stability of colloidal dispersions. The stability of any colloidal dispersion consisting of particles, polymer molecules, or mixtures of particles and polymer molecules dispersed in a medium is determined by the balance between the attractive van der Waals forces and repulsive (or attractive) electrostatic forces. 

Protective Colloids. Another approach in preparing and stabilizing metal colloids is by adsorption of macromolecules on their surfaces. A wide variety of materials have been used including gummy gelatinous liquids,(J 0) albumin,(27) Icelandic moss,(28) latex,(22) polyvinylpyrrolidone, (29) antibodies, ( 30 ) carbowax 20M, ( 31 ) polyvinylpyridine, (31 ) and various polymer-water/oil-water mixtures.( 2) These studies clearly indicate that "steric stabilization of metal colloids is also important (along with electronic stabilization).(33)... 

Theoretical studies of the role of polymer additives lag behind their analogs in electrostatic stability since polymer molecules have considerably more configurational freedom and since the interaction of the polymer molecules with the solvent is an inseparable part of phenomena in polymer-colloid mixtures. We begin with some of the general issues and a thermodynamic analysis of the role of polymer on stability in Section 13.5. 

Doublier, J.-L., and Llamas, G. (1993). A rheological description of amylose-amylopectin mixtures. In Food Colloids and Polymers Stability and Mechanical Properties, Dickinson, E., and Walstra, P. (Eds.), pp. 138-146. Royal Chem. Soc., London. 

I.V. Rao and E. Ruckenstein Phase behaviour of mixtures of sterically stabilized colloidal dispersions and free polymer, JOURNAL OF COLLOID AND INTERFACE SCIENCE 108 (1985) 389-402. 

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. 

Stability in mixtures of colloidal particles and polymer molecules, dispersed in a solvent, has been the subject of experimental and theoretical investigations for a long time and it has applications in diverse fields such as paint technology, wastewater treatment, emulsion polymerization, biology etc. It has now been well recognized that polymer molecules can be used to induce either stabilization or flocculation (phase separation) in colloidal dispersions. It is important to distinguish between polymers which are adsorbed on the particle surface and those that are free in solution because the two situations usually lead to qualitatively different effects. Stability imparted by adsorbed polymers is known as steric stabilization and the flocculation or phase separation caused by the free polymer is due... 

In our earlier work 113], the stability of mixtures of sterically stabilized colloidal particles and free polymer molecules in solution was examined theoretically by considering the total intcrparticle potential as the sum of contributions due to (i) the presence of the adsorbed polymer, (ii) the presence of free polymer in solution, and (iii) van der Waals attraction. 

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