Shear-induced adsorption

Since we are considering shear-induced adsorption, the adsorption rate constant can be approximated from Smoluchowski s theory [14] for the collision between two... 

The decrease in expansion seems to occur at moisture levels above 30°/o moisture for both cereal (starch-based) polymer systems, and protein (soy grits). This corresponds to a point on their adsorption curves where water activity rises rapidly with added moisture that is, at a level where the water added to a mix has little effect on primary hydration of polymers, but behaves as a diluent. In mechanical terms, this may be explained by proposing that at above levels of 25°/o-30% water plasticisation of the polymers is complete, and further added water acts as a lubricant, reducing the shear-induced temperature rise and particle damage necessary for the formation of homogeneous melts. 

The object of this study was to clarify some aspects of the mechanism of shear-induced flocculation in colloidal dispersions. Vinyl chloride homopolymer and copolymer latices were prepared by emulsion polymerization using sodium dodecyl sulphate as emulsifier. Agglomeration behavior in these latices was studied by measuring the mechanical stability using a high speed stirring test. The latex particle size was measured by an analytical centrifuge. Molecular areas of emulsifier in the saturated adsorption layer at the surface of homopolymer and copolymer latex particles were estimated from adsorption titration data. 

In the previous sections, the impact of the material properties of emulsions and spray process parameters on the dispersion was described. It provided information about the dispersion of secondary droplet of DE, rather than the release of an encapsulated component. The release of functional components during spray processing may also be influenced by shear-induced diffusion and osmotic pressure. Therefore, an iron-salt (FeS04) encapsulated DE was sprayed and the retained amount of iron in the sprayed emulsion detected. Conductivity and Atomic Adsorption Spectroscopy (AAS) methods were used for measuring the concentration of iron. The retained amount of iron is defined as follows (23.15) ... 

Stock composition, kinetics of adsorption and hydrodynamic shear dictate the point at which a cationic polymer is added to a papermaking furnish in order to induce flocculation. Flocculation of cellulose fibers in turbulent flow proceeds very rapidly and is completed in less than two seconds.120-123 Flocks form due to charge interactions through a patch-type or a bridging-type mechanism. However, these flocks will be sensitive to shear force and deflocculation and reflocculation might occur. 

In nematic liquid crystals, the viscosity depends on the relative orientation between the shear gradient and the orientation of the nematic phase. Close to a surface, the orientation is usually governed by surface orientational anchoring [77]. Anchoring transitions, for instance induced by the adsorption of an analyte molecule to the surface [78], can therefore be easily detected with the QCM [79,80]. This reorientation induced by adsorption amounts to an amplification scheme the expected shift in the resonance frequency and bandwidth... 

Electroosmosis. Electroosmosis occurs in systems with applied potentials and results from preferential adsorption of charges at a fixed surface, such as a column wall. This ionic adsorption results in the build-up of a charged counter layer at the surface, which migrates electrophoretically. This flux along the wall induces a convective flux in the bulk due to viscous shear. If... 

Limitations for the applicability of SEC for certain molecules are the high shear forces due to the dense column packing, which may influence molecular assemblies and lead to degradation. Furthermore, the column packing material can induce unwanted interactions between the stationary phase and the molecules, thus shifting the separation mechanism from pure size exclusion towards separation by enthalpic interactions. Especially in cases of multifunctional polymers like dendritic molecules with a high number of end groups, delayed elution or complete adsorption can be observed. 

Electrokinetic phenomena, namely electrophoresis, electro-osmosis and streaming potential are discussed in Vol. 1 at a fundamental level. These effects arise because of charge separation at the interface that is induced for example by application of an electric field. The plane at which the liquid starts to move is defined as the shear plane and the potential at this plane is defined as the electrokinetic or zeta potential. A schematic picture is given that describes the shear plane and zeta potential. The latter is mostly assumed to be equal to the Stern potential and in the absence of specific adsorption it can be equated to the surface potential, which is the parameter... 

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