Grafted polymer, rheology

Several recent studies demonstrate convincingly the possibilities for adjusting the rheology of colloidal dispersions through the incorporation of polymer. Here we briefly review the effects of grafted polymer, adsorbing homopolymer, and nonadsorbing polymer. The literature abounds with other and more complicated phenomena. 

Keywords Colloidal dispersions Colloidal glasses Dynamics Grafted particles Hairy particles Micelles Nanoparticle-polymer hybrids Phase diagrams Polymers Rheology Soft colloids- Softness Stars... 

PP is probably the most thoroughly investigated system in the nanocomposite field next to nylon [127-132]. In most of the cases isotactic/syndiotactic-PP-based nanocomposites have been prepared with various clays using maleic anhydride as the compatibilizer. Sometimes maleic anhydride-grafted PP has also been used [127]. Nanocomposites have shown dramatic improvement over the pristine polymer in mechanical, rheological, thermal, and barrier properties [132-138]. Crystallization [139,140], thermodynamic behavior, and kinetic study [141] have also been done. 

Winter, H.H. Evolution of rheology during chemical gelation. Prog. Colloid Polym. Scl,15,104—110,1987. Hempenius, M.A. et al. Melt rheology of arborescent graft polystyrenes. Macromolecules, 31, 2299, 1998. 

Grafting and Stabilizers. The degree of grafting of poly(vinyl acetate) (PVAc.) on poly(vinyl alcohol) (PVA) and other stabilizers during emulsion polymerization strongly affects latex properties such as viscosity, rheology, and polymer solubility. 

An important group of surface-active nonionic synthetic polymers (nonionic emulsifiers) are ethylene oxide (block) (co)polymers. They have been widely researched and some interesting results on their behavior in water have been obtained [33]. Amphiphilic PEO copolymers are currently of interest in such applications as polymer emulsifiers, rheology modifiers, drug carriers, polymer blend compatibilizers, and phase transfer catalysts. Examples are block copolymers of EO and styrene, graft or block copolymers with PEO branches anchored to a hydrophilic backbone, and star-shaped macromolecules with PEO arms attached to a hydrophobic core. One of the most interesting findings is that some block micelle systems in fact exists in two populations, i.e., a bimodal size distribution. 

Polymer silicate nanocomposites offer unique possibilities as model systems to study confined polymers or polymer brushes. The main advantages of these systems are (a) the structure and dynamics of nanoconfined polymer chains can be conveniently probed by conventional analytical techniques (such as scattering, DSC, NMR, dielectric spectroscopy, melt rheology) (b) a wide range of different polymers can be inserted in the interlayer or end-grafted to the silicate... 

The grafted layer also affects two other features of the rheology. First, thicker polymer layers enhance the elasticity due to the longer range of the repulsion relative to the hard core size. Thus, samples formulated at 4>cff mo possess easily measurable static elastic moduli. Second, the softer repulsion apparently suppresses the shear thickening observed at high volume fractions for the harder particles, in accordance with earlier measurements by Willey and Macosko (1978). 

The most widely used synthetic and natural enhanced oil recovery polymers, such as partially hydrolyzed polyacrylamide, carboxymethyl(ethyl) cellulose, polysaccharides, or xanthan gums, are not suitable for high-temperature reservoirs (> 90 °C) with high-density brine fluid due to excessive hydrolysis and precipitation [277]. The main advantages of polymeric betaines over the mentioned standard polymers are (1) thermostability (up to 120 °C) (2) brine compatibility and (3) viscosification in brine solution [278]. Carbobetaines grafted onto hydroxyethyl cellulose were tested as a drilling-mud additive for clay hydration inhibition and mud rheological control [279]. An increase in the content of carbobetaine moieties resulted in an enhanced inhibitive abiUty, especially for sahne mud. 

Figure 7.9 Shear-stress dependence of the relative viscosity for dispersions in white spirit of acrylic copolymer particles of radius a = 157 nm at a volume fraction of p =0.40 for differing concentrations of nonadsorbing polyisobutylene polymer of molecular weight 411,000. The particles had been stabilized by addition of a comb-graft copolymer of PMMA backbone (which adsorbed to the particles) with non-adsorbing poly(12-hydroxystearic acid) teeth. The con-centrations (in weight per unit volume) of polyisobutylene are 1.0% ( ), 0.85%(B), 0.6%(D), 0.5%(V), 0.4%( ), and 0.1 %(0)- (From Bus-call et al. 1993, with permission from the Journal of Rheology.)...

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