Adsorption layer of polymers

According to this concept, it is expected that polymer molecules, especially high molecular weight polymers, give an increased adsorption at a temperature close to the cloud point, and particles with the thick(or dense) adsorption layer of polymer formed out of a poor solvent would show strong protection against flocculation. 

Adsorption behavior and the effect on colloid stability of water soluble polymers with a lower critical solution temperature(LCST) have been studied using polystyrene latices plus hydroxy propyl cellulose(HPC). Saturated adsorption(As) of HPC depended significantly on the adsorption temperature and the As obtained at the LCST was 1.5 times as large as the value at room temperature. The high As value obtained at the LCST remained for a long time at room temperature, and the dense adsorption layer formed on the latex particles showed strong protective action against salt and temperature. Furthermore, the dense adsorption layer of HPC on silica particles was very effective in the encapsulation process with polystyrene via emulsion polymerization in which the HPC-coated silica particles were used as seed. 

Also, here, the effect of the adsorption layer of HPC on encapsulation of silica particles in polymerization of styrene in the presence of silica particles has been investigated. Encapsulation is promoted greatly by the existence of the adsorption layer on the silica particles, and the dense adsorption layer formed at the LCST makes composite polystyrene latices with silica particles in the core (7.). This type of examination is entirely new in polymer adsorption studies and we believe that this work will contribute not only to new colloid and interface science, but also to industrial technology. 

It was apparent that the dense adsorption layer of HPC which was formed on the silica particles at the LCST plays a part in the preparation of new composite polymer latices, i.e. polystyrene latices with silica particles in the core. Figures 10 and 11 show the electron micrographs of the final silica-polystyrene composite which resulted from seeded emulsion polymerization using as seed bare silica particles, and HPC-coated silica particles,respectively. As may be seen from Fig.10, when the bare particles of silica were used in the seeded emulsion polymerization, there was no tendency for encapsulation of silica particles, and indeed new polymer particles were formed in the aqueous phase. On the other hand, encapsulation of the seed particles proceeded preferentially when the HPC-coated silica particles were used as the seed and fairly monodisperse composite latices including silica particles were generated. This indicated that the dense adsorption layer of HPC formed at the LCST plays a role as a binder between the silica surface and the styrene molecules. 

Another kind of wall-effect was proposed by El perin (1967). He suggested that an adsorbed layer of polymer molecules could exist at the pipe wall during flow and this could lower the viscosity, create a slip, dampen turbulence pulsations, and prevent any initiation of vortices at the wall. Later work (Little 1969), however, with a transparent pipe and dyed polymer, showed that the adsorption could in be fact an experimental artifact (a quantity of polymer solution, trapped in pressure gage piping, slowly diffused back into the solvent flow). Although polymer molecules do more or less adhere to clean surfaces in thin films, there is no interaction with the bulk of the solution which could alter the flow properties (Gyr, 1974). Thus, it is evident that adsorption of the additives on surfaces is not the reason for the drag reducing effect. 

The adsorption from solution of polymers has been studied extensively. The amount of polymer adsorbed usually reaches a limiting value as the concentration of polymer in solution is increased, but this value is usually well in excess of that which would be expected for a monomolecular layer of polymer adsorbed flat on the solid surface. This suggests that the adsorbed polymer is anchored to the surface only at a few points, with the remainder of the polymer in the form of loops and ends moving more or less freely in the liquid phase179. 

Fig. 3. Interfacial slip of an entangled melt at a non-adsorbing perfectly smooth surface, where the dots represent an organic surface (e.g., obtained by a fluoropolymer coating), which invites little chain adsorption. Lack of polymer adsorption produces an enormous shear rate jiat the entanglement-free interface between the dots and the first layer of (thick) chains. y-x=vs/a is much greater than the shear rate y present in the entangled bulk. This yields an extrapolation length b, which is too large in comparison to the chain dimensions to be depicted here...

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 an adsorbed polymer layer, the Interaction of the chains with the solvent remains very important. Therefore, before discussing the adsorption behaviour of polymers and polyelectrolytes, we review briefly some properties of these molecules in solution. In the following sections, we follow roughly the outline of a recent monograph on polymers at interfaces... 

Li (2007) observed that the adsorption of a hydrophobically associating water-soluble polymer, AP-2, did not follow the Langmuir-type isotherm. Figure 5.37 shows that the adsorption increased to a maximum and then decreased as the polymer concentration was increased. The reason is probably that the hydrophobic polymer has an adsorption layer of multiple molecules on rock surfaces. When the polymer concentration is increased, the adsorption layer becomes thicker because of more adsorption. When the polymer concentration is further increased, the molecular interaction in the liquid is stronger than that between the adsorbed molecules and rock surfaces. Then the adsorbed molecules may leave the rock surfaces and redissolve into the liquid. Thus, the adsorption decreases. 

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). 

To attain this goal, we used ATR techniques which have been described previously (6). A liquid ATR cell can be used to circulate protein solutions (or blood) through the cell while spectrally monitoring the adsorption of proteins onto the surface of the ATR crystal. In addition, the ATR crystal can be coated with a thin layer of polymer, permitting us to follow the adsorption of pro-... 

A combination of two surfactants was studied in [279] ethoxylated nonylphenol of 150 moles EO (DNP 150) and adsorbing on the coal particle surface, and a water-soluble polymer polyethylene oxide (POE) the adsorption of which on the particles was not fixed. At a closely packed adsorption layers of DNP 150 on the surface of the coal particles and a minimum POE addition, a suspension was obtained which did not settle for 2 weeks. After this time, the suspension exhibited minimum settling without large increases in suspension viscosity. 

EDM with experiments using l.d.c. emulsions and s.d.e. may result in (1) the quantification of emulsion film stability, namely, the establishment of the coalescence time dependence on the physicochemical specificity of the adsorption layer of a surfactant (polymer), its structure, and the droplet dimensions. This quantification can form a basis for the optimization of emul-sifier and demulsiner selection and synthesis for emulsion technology applications, instead of the current empirical level applied in this area and (2) the elaboration of a commercial device for coalescencetime measurement, which in combination with EDM will represent a useful approach to the optimization of emulsion technology with respect to stabilization and destabilizatioa... 

If we study the composition of the surface of a pol)mier solution or a polymer mixture we should expect to find that the composition of the region near the surface is not the same as that of the bulk. The same applies to an interface between such a system and a solid for example a colloidal particle suspended in a polymer solution will often be coated with a layer of polymer, that may well be able to stabilise the colloid, preventing its aggregation. In polymer solutions this phenomena is known as adsorption, if the polymer accumulates at the surface, or depletion, if it is the solvent that is favoured there in polymer blends one often refers to the surface segregation or surface enrichment of one component of the mixture. However, these different names describe what is essentially the same phenomenon, the subject of this chapter. 

When two metal nanoparticles covered by a layer of adsorbed soluble polymer chains approach to a distance less the total thickness of adsorption layers, the polymer layers start to interact (Fig. 1). The interaction brings about steric stabilization and leads, in a majority of cases, to repulsion between the colloidal particles. It was repeatedly attempted to clarify its nature and determine its magnitude. Most frequently the problem is studied in terms of changing the Gibbs s energy when two particles are covered by an adsorbed polymer that are approaching one another from irffinity. 

A broad review of the effects of macromolecular compounds in disperse systems has been presented by Heller (311). He discusses the adsorption characteristics of polymer. molecules which on the one hand, are adsorbed at the surface with a terminal segment only, with the remainder of the chain protruding from the surface radially, and on the other hand, are adsorbed lying flat with all segments attached to the surface. Both situations can occur, of course, depending on the nature of the polymer and how much of an excess over the amount required to form a flat monomolecular layer is present. 

Effect of Precontamination on PLL(375)-g[5.6]-PEG-(5) Adsorption. Metal oxide surfaces that exhibited large amounts of hydrocarbon surface contamination nevertheless adsorbed a layer of PLL(375)-g[5.6]-PEG(5) that suppressed subsequent serum adsorption. Titanium dioxide waveguides that were not cleaned according to the procedure described in section 1.4.1 exhibited substantial hydrocarbon surface contamination (see Tables 2 and 3 and Figure 2). However, these XPS data also indicate that an additional layer of PLL(375)-g[5.6]-PEG-(5) does, indeed, adsorb onto this contaminated surface. Furthermore, OWLS experiments showed that the typical adsorbed areal density of 120 ng/cm forms on contaminated titanium dioxide waveguides and that this adsorbed layer of polymer suppresses subsequent serum protein adsorption by about 95%. That is, the adsorption and performance characteristics of PLL(375)-g[5.6]-PEG(5) are identical in the case of both contaminated and cleaned titanium dioxide surfaces. 

In analogy to the adsorption problem, one can characterize the wetting transition by the surface excess of polymer. If the polymer only partially wets the surface, O <0< 180 , there is only a miaoscopically thin enrichment layer of polymer at the surface and the surface excess... 

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