Electrostatic effects, polymer adsorption

If only electrostatic effects are responsible for polymer adsorption and flocculation, our results can be explained according to the same scheme as that used by Furusawa et Al.(20) to interprete the destabilization of negatively charged latex by a cationic polymer. In a first step, the adsorption of the polymer leads to the neutralization of the particles which are no more stabilized by electrostatic repulsions and there is flocculation (we have not studied this step since in our experiments polymer was always in large excess with respect to Al(0H)3). In a second step the adsorption inverses the charge and (we have indeed measured by... 

In general, the adsorption of a surfactant on particles with previously adsorbed polymer can be influenced by (i) a reduction of surface area available for adsorption as a result of the presence of adsorbed polymer, (ii) possible interactions between polymer and surfactant in the bulk solution or in the interfacial region (that is, surfactant with loops, tails or trains of adsorbed polymer molecules), (iii) the steric effect of adsorbed polymer, preventing approach of surfactant molecules for adsorption at the surface, or (iv) possible electrostatic effects if polymer and/or surfactant are charged species. 

It was shown [21] that polyelectrolytes having hydrophobic functionalities show higher efficiency for such systems due to the synergetic effect of electrostatic and hydrophobic interactions promoting the polymer adsorption at solid/liquid or liquid/hquid interface. 

Chemosensory applications will normally take place in an environment of complex composition. Humidity and other varying ambient conditions are in sharp contrast to the well-defined environment most typically found in related applications of imprinted polymers. Moreover, the trend in sensor technology towards miniaturisation, with the aim of future nano-scale dimensions, is a primary reason for rising perturbation sensitivity, such as new interfering forces that can be neglected in the macro range. Chemical sensors can be influenced by numerous factors, such as electrostatic effects (ChemFETs) or non-specific adsorption (SAW, surface plasmon resonance). 

The choice of eluent system depends on the polymer type. For most non-ionic hydrophilic polymers, water can be used. However much more complex eluent systems are needed, for anionic and cationic polymers where interactions with the column based on ion exclusion, inclusion and exchange, adsorption by hydrogen bonding or hydrophobic interactions and intramolecular electrostatic effects, are possible. This can often make method development in aqueous SEC extremely difficult and time-consuming. 

We now consider the effect of electrostatics on initial adsorption rates. Our first example [26] is again for the polycationic polymer PVP+ adsorbing at pH 8 on Ti02, which is negatively charged under these conditions see Figure 5. It is the same system as considered in Figure lb. Two sets of... 

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],... 

Surface properties can be adjusted by the adsorption of surfactants and polymers. Adsorption itself can essentially be considered to be preferential partitioning of the adsorbate into the into the interfacial region. It is the result of one or more contributing forces arising from electrostatic attraction, chemical reaction, hydrogen bonding, hydro-phobic interactions, and solvation effects. 

Fleer GJ, Cohen Stuart MA, Scheutjens JMHM et al (1993) Electrostatic effects charged surfaces and polyelectrolyte adsorption. In Polymers at interfaces. Chapman Hall, London... 

Electrostatic and adsorption effects conspire to make aqueous GPC more likely to be nonideal than organic solvent GPC. Thus, universal calibration is often not obeyed in aqueous systems. Elence, it is much more critical that the standard chosen for calibration share with the polymer being analyzed chemical characteristics that affect these interactions. Because standards that meet this criterion are often not available, it is prudent to include in each analysis set a sample of a secondary standard of the same composition and molecular weight as the sample. Thus, changes in the chromatography of the analyte relative to the standards will be detected. 

In the following paper, the possibility of equilibration of the primarily adsorbed portions of polymer was analyzed [20]. The surface coupling constant (k0) was introduced to characterize the polymer-surface interaction. The constant k0 includes an electrostatic interaction term, thus being k0 > 1 for polyelectrolytes and k0 1 for neutral polymers. It was found that, theoretically, the adsorption characteristics do not depend on the equilibration processes for k0 > 1. In contrast, for neutral polymers (k0 < 1), the difference between the equilibrium and non-equilibrium modes could be considerable. As more polymer is adsorbed, excluded-volume effects will swell out the loops of the adsorbate, so that the mutual reorientation of the polymer chains occurs. 

In fact this "unhydrolyzed" polyacrylamide sample is slightly charged and its low polyectrolyte character is confirmed by a slight difference of red values at pH 7 and 5, for salt free solutions. A really neutral polymer should be necessary to differentiate low effects of electrostatic interactions from non ionic interactions. coordination binding at low pH and hydrogen bonds at pH 7. Nevertheless, at this pH, the adsorption of the chain on Al(0H)3 aggregates can probably be considered as the main origin of the loss of viscosity. 

The effects of calcium on polymer-solvent and polymer-surface interactions are dependent on polymer ionicity a maximum intrinsic viscosity and a minimum adsorption density as a function of polymer ionicity are obtained. For xanthan, on the other hand, no influence of specific polymer-calcium interaction is detected either on solution or on adsorption properties, and the increase in adsorption due to calcium addition is mainly due to reduction in electrostatic repulsion. The maximum adsorption density of xanthan is also found to be independent of the nature of the adsorbent surface, and the value is close to that calculated for a closely-packed monolayer of aligned molecules. 

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