Polymers adsorption onto particle

Polymer charge density increase Extends polymer chains in solution under suitable conditions Decreases adsorption onto particles of the same charge sign... 

The adsorption behavor of surfactant onto particles in the absence and presence of pre-adsorbed polymer was determined. Electrokinetic studies of the system were made. Contact angle measurements yielded information on the level of hydrophobicity achieved at various additions of polymer and collector. 

There are very important phenomena originated when a polymer is on one interface or close to one interface. Such phenomena include adsorption, adhesion, monolayer formation, coating and colloidal stabilization. In the majority of circumstances a polymer adsorbed onto colloidal particles will increase the stability of a dispersion [8], The essential feature of polymer or steric stabilization is... 

Three emission bands (a, p and y in the order of decreasing energy) are observed in CH2CI2 solution and are found to be the emission from the excited state of 1, from the excited state of a solute-solvent complex and from a relaxed twisted excited state of the solute-solvent complex, respectively. Model compound studies show that squaraine forms strong solute-solvent complexes with alcoholic solvent molecules. Analogous complexation process between 1 and the OH groups in PVF is also shown to occur. A model for the stabilization of particles of 1 in polymer solution is put forward where we propose that the stabilization mechanism is a steric effect achieved by adsorption of PVF macromolecules onto particles of 1 via the formation of the PVF 1 complex. 

State (h) represents the case whereby the particles are not completely covered by the polymer chains. In this situation, the simultaneous adsorption of one polymer chain onto more than one particle occurs, leading to bridging flocculation. If the polymer adsorption is weak (low adsorption energy per polymer segment), the flocculation may be weak and reversible, but if the adsorption of the polymer is strong then tough floes will be produced and the flocculation will be irreversible. The latter phenomenon is used for soUd/Uquid separation, for example in water and effluent treatment... 

Adsorption onto colloidal polystyrene results in very different behavior because of the hydrophobic nature of that surface. The addition of even a small amount of polystyrene particles to the polymer solution results in the complete disappearance of the excimer emission (Figure 6). In this case, the hydrophobic pyrene groups are strongly attracted to the polystyrene surface thus, the formation of excimers is precluded. A similar disappearance of the excimer was observed upon complexation with PMAA, a result indicating that the hydrophobic character of that polymer may hinder the formation of excimers by adsorbing the pyrene groups into a hydrophobic pocket. This observation is further supported by the fluorescence excitation spectra, presented in the next section. 

This chapter is concerned with just one of this class of thickeners, namely a hydrophobically modified (hydroxyethyl)cellulose (HMHEC), Hercules WSP D-47. Gelman and Barth (i) reported on the viscosity of such HMHECs. This sample contained up to four hexadecyl chains grafted to the cellulose backbone. The preparative route was that described by Landoll (2). The dilute solution properties were characterized by capillary viscom-etry, whereas the more concentrated solutions were characterized by continuous-shear viscometry, forced oscillation measurements, and shear-wave propagation. In addition, the adsorption onto polymer latex particles was investigated. 

The HMHECs used in these experiments provided good examples of an associative thickener, in that clear evidence of a critical aggregation concentration was seen from the dilute-solution behavior. Although some limited molecular aggregation may occur below this concentration, once this concentration is achieved, a three-dimensional network starts to form. This network formation leads to a significant enhancement of adsorption onto polymer latex particles from which the surfactant has been removed. The adsorption density is high for a cellulosic polymer of the equivalent molecular weight. 

The formation of floes due to bridging flocculation has a dramatic effect on sedimentation rates, sediment volumes and on the ease of filtration. Effective flocculation may occur over a narrow range of polymer concentration because too little polymer will not permit floe formation, while too much polymer adsorption will eliminate the fraction of free particle surface needed for the bridging action (i.e. the polymer molecules will adsorb onto single particles in preference to bridging several particles). It has been proposed that the optimum degree of bridging flocculation may occur when particle surfaces are half covered with adsorbed polymer. 

Gibson, J. B., Chen, K., and Chynoweth, S. Simulation of particle adsorption onto a polymer-coated surface using the dissipative particle dynamics method. J Colloid Interface 5cz., 206,464-74 (1998). 

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