Polymer adsorption structure

Of particular interest has been the study of the polymer configurations at the solid-liquid interface. Beginning with lattice theories, early models of polymer adsorption captured most of the features of adsorption such as the loop, train, and tail structures and the influence of the surface interaction parameter (see Refs. 57, 58, 62 for reviews of older theories). These lattice models have been expanded on in recent years using modem computational methods [63,64] and have allowed the calculation of equilibrium partitioning between a poly-... 

We think, therefore, that the conformation, chain and segment mobilities in the attached macromolecules can play a significant role in the shielding behavior of the polymeric stationary phase as well as in the processes of its formation of complexes with solutes. Obviously, the chromatographic studies relevant to composite supports suffer from a lack of information on the structure of the attached polymer. Nevertheless, we will attempt to point out some relevant data from independent studies on polymer adsorption and/or graft polymerization. 

Highly branched polymers, polymer adsorption and the mesophases of block copolymers may seem weakly connected subjects. However, in this review we bring out some important common features related to the tethering experienced by the polymer chains in all of these structures. Tethered polymer chains, in our parlance, are chains attached to a point, a line, a surface or an interface by their ends. In this view, one may think of the arms of a star polymer as chains tethered to a point [1], or of polymerized macromonomers as chains tethered to a line [2-4]. Adsorption or grafting of end-functionalized polymers to a surface exemplifies a tethered surface layer [5] (a polymer brush ), whereas block copolymers straddling phase boundaries give rise to chains tethered to an interface [6],... 

These differences in the effect of polymers on various flocculation responses have important theoretical and practical implications and can be explained in terms of various characteristics of floes and floc-aggregates. Polymer adsorption or attachment of particles to polymer can occur in any number of configurations, and as a result the aggregation of particles also can take place in many ways, leading to different floe and suspension structures which will respond differently to different tests. 

Kim H, Guiochon G. Adsorption on molecularly imprinted polymers of structural analogues of atemplate. Single-component adsorption isotherm data. Anal Chem 2005h 77 6415-6425. 

In the last 10-15 years, neutron reflectometry has been developed into a powerful technique for the study of surface and interfacial structure, and has been extensively applied to the study of surfactant and polymer adsorption and to determine the structure of a variety of thin films [14, 16]. Neutron reflectivity is particularly powerful in the study of organic systems, in that hydrogen/deu-terium isotopic substitution can be used to manipulate the refractive index distribution without substantially altering the chemistry. Hence, specific components can be made visible or invisible by refractive index matching. This has, for example, been extensively exploited in studying surfactant adsorption at the air-solution interface [17]. In this chapter, we focus on the application of neutron reflectometry to probe surfactant adsorption at the solid-solution interface. 

This publication arranges the published papers on adsorption of polymers with special regard to experiment and theory. A summary of all investigated systems is given. The experimental methods are outlined and the amounts adsorbed are discussed as a function of the system and experimental parameters (polymer, adsorbent, solvent, molecular, concentration, time, weight and temperature). Calculated and experimental amounts of saturation, the number of contact points per molecule adsorbed, the thickness of the adsorbed layer, the adsorption isotherms, the heats of adsorption, the effects of desorption are compared. Assumptions on the structur of the adsorbed layer and the mechanism of polymer adsorption are made and discussed. 

The contention that polymer adsorption can result in oleophobic (low yc ) and water stable films is given support by the results using the ETES polymer-monomer solution (Figure 10). In this case preformed polymer was present in the solution along with the monomer ETES, and the resulting films had a wettability not unlike those formed by the 1% and 5% VTES solutions on flamed silica. The water stability of these films can be explained by a film structure that is predominately polymer units. Desorption then requires the simultaneous breaking of many bonds which is a statistically unlikely event. 

Photoreaction 63 Photosynthesis 171 Plastic sulfur 43 Poly electrolytes 174 Polymer adsorption 174 -, preparation 87 -, rate of formation 90 -, structure 42 Polymerization theory 81 Polysulfanes 92-93 Polysulfide 176, 179, 183 -, oxidation 184... 

The effects of polymer molecular weight on the rate and extent of adsorption on carbon black at equilibrium is fundamentally no different from other polymeric adsorbate-adsorbent systems (95). When microporosity is present in carbon black, the adsorption is governed by the external surface area (96), but with very high molecular weight polymers adsorption is also limited by the inability of the molecular coils to penetrate the internal void space of the primary structure aggregates (95). 

Improved understanding of the mechanism, energetics, and structure of the bonding of water to surfaces is needed. Such information is a key to fundamental clarification of the interfacial structure at solid-liquid surfaces. Poor understanding of the thermodynamics of polymer adsorption at interfaces is impeding scientific progress on corrosion inhibition, colloidal stability, alteration of membrane selectivity, and electrocrystallization additives. 

The colloidal stabilization of aqueous dispersions by polymer surfactants is believed to be a result of the adsorption of the amphiphilic macromolecules on the particle surface. This adsorption results in the formation of mono- or multi-layers of certain structure and thickness which provide sterical and/or electrostatic stabilization effects [1-5], Polymer adsorption from aqueous solution on a particle surface is a result of specific interactions of various active sites on the particle surface with corresponding sites (groups) of the macromolecule. Therefore the adsorption behaviour and the colloidal stabilization may be used as a sensitive approach (tool) to elucidate the effects of the polymers structural differences on their behaviour on the liquid-solid interface [6-9],... 

The evidence of the polymer adsorption on the surface of pigment particles and the formation of protective layers has been obtained by ESA method by experiments on measuring the -potential of the TiC>2 surface in aqueous dispersions in the presence of EFIEC (Table 2). It can be seen from the table that -potential becomes less negative in the presence of EHEC and still more approaches zero as a result of the treatment of dispersions in an ultrasonic field. This indicates the activation of polymer adsorption and the formation of stabilizing layers due to mechanochemical modification of particles. From the table it is also seen that as a consequence of mechanochemical treatment, the size of pigment particles in dispersions decreases, and dispersion becomes structurally more uniform, which leads to an increase of its stability even at increased temperature (experiment 4). 

It seems impossible that general theories can be developed to describe polymer adsorption in an universal way. There are molecules which can unfold after adsorption at the interface while others remain in a compact structure (Fig. 4.17). 

The measurement of the variation of A(AV(t)) often does not give us a direct information on changes in the surfactant or polymer adsorption. So far the models are more or less qualitative. A quantitative model should be able to describe the complex structure of the electric double layer in the interfacial region and to explain peculiarities, such as the surface potential of a bare interface and changes in the potential due to adsorption of nonionic surfactants. 

Fig. 8.10 Principle of polymer adsorption and flocculation [B.29] a) adsorption of polymer molecule on the particle b) rearrangement of adsorbed chain c) collisions between destabilized particles and bridging to form aggregates (floes) d) break-up of floes Fig. 8.11 Structure of a flocculate (floe) bonded by a polymer [B.48]...

Surveying the literature, it appears that the interfacial behavior of proteins is a controversial subject. The main reason is that many studies have been performed under insufficiently defined conditions and/or that conclusions have been drawn on the basis of too scanty experimental evidence. Furthermore, the theoretical description of adsorbed layers of simple, flexible polymers is still in its infancy (5,6). As the structure of proteins is much more complex than that of those simple polymers, theories of polymer adsorption need to be greatly extended to become applicable to proteins. Clearly, our current knowledge of protein adsorption mechanisms and of the structure of the adsorbed layer is far from complete. 

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