Colloid-polymer surface layers, determined

Up to date, besides the SFA, several non-interferometric techniques have been developed for direct measurements of surface forces between solid surfaces. The most popular and widespread is atomic force microscopy, AFM [14]. This technique has been refined for surface forces measurements by introducing the colloidal probe technique [15,16], The AFM colloidal probe method is, compared to the SFA, rapid and allows for considerable flexibility with respect to the used substrates, taken into account that there is no requirement for the surfaces to be neither transparent, nor atomically smooth over macroscopic areas. However, it suffers an inherent drawback as compared to the SFA It is not possible to determine the absolute distance between the surfaces, which is a serious limitation, especially in studies of soft interfaces, such as, e.g., polymer adsorption layers. Another interesting surface forces technique that deserves attention is measurement and analysis of surface and interaction forces (MASIF), developed by Parker [17]. This technique allows measurement of interaction between two macroscopic surfaces and uses a bimorph as a force sensor. In analogy to the AFM, this technique allows for rapid measurements and expands flexibility with respect to substrate choice however, it fails if the absolute distance resolution is required. 

Rudoy VM, Dement eva OV, Yaminskii IV, Sukhov VM, Kartseva ME, Ogarev VA, Metal Nanoparticles on Polymer Surfaces 1. A New Method of Determining Glass Transition Temperature of the Surface Layer, Colloid J., 64, 746-54 (2002). 

The model proposed by Harkins and Yurzhenko doesn t take into accotmt, the intermolecular interactions on the interface, the most important factor determining behaviour of the colloidal system. Thus, this model assiunes that the molecule area of an emulsifier in a micelle and in an adsorption layer of a polymer-monomer particle have identical values, and the newly formed surface is stabilized immediately after its formation. As a result, the surface of particles per unit volume is defined as the surface oc-... 

In addition to giving information about the shape and internal structure of colloidal aggregates, SANS studies can also be used profitably to determine the thickness and conformation of polymer layers adsorbed onto the surface of colloidal particles such as latex nanoparticles, and in some special cases, the surface of emulsion droplets. ° In such studies, the particles on which the polymer is adsorbed must generally be very accurately contrast matched to the solvent so as to allow information to be obtained only about the adsorbed layer. SANS studies have also been recently used in combination with differential scanning calorimetry and visual inspection of the solutions, to draw up a (simplified) partial phase diagram of the aggregation behavior of a polymeric surfactant in water.t ... 

Churaev, Nikologorodskaya, and co-workers (33) investigated the Brownian and electrophoretic motion of silica hydrosol particles in aqueous solutions of an electrolyte at different concentrations of poly(ethylene oxide) (PEO) in the disperse medium. The adsorption isotherms of PEO on the surface of silica particles were obtained. The thickness of the adsorption layers of PEO was determined as a function of the electrolyte concentration and the pH of the dispersed medium. The results can be used in an analysis of the flocculation and stabilization conditions for colloidal dispersions of silica (with non-ionogenic water-soluble polymers of the PEO type). 

It is convenient from a conceptual viewpoint to delineate three domains of close approach for sterically stabilized colloidal particles (Evans and Napper, 1973a). These zones delimit domains in which different phenomenology is clearly recognizable. They are determined by the relative sizes of the spans of the attached polymer chains (assumed for simplicity to be monodisperse) and the separation between the particles. The span can be defined in this context as specifying the conformational average distance normal to the surface that the furthermost segment meanders from the surface. The span thus sets the absolute limit to the average conformational thickness of the steric layers. 

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