Adsorption polymer + surfactant complex

Recent investigations have shown that the behavior and interactions of surfactants in a polyvinyl acetate latex are quite different and complex compared to that in a polystyrene latex (1, 2). Surfactant adsorption at the fairly polar vinyl acetate latex surface is generally weak (3,4) and at times shows a complex adsorption isotherm (2). Earlier work (5,6) has also shown that anionic surfactants adsorb on polyvinyl acetate, then slowly penetrate into the particle leading to the formation of a poly-electroyte type solubilized polymer-surfactant complex. Such a solubilization process is generally accompanied by an increase in viscosity. The first objective of this work is to better under-stand the effects of type and structure of surfactants on the solubilization phenomena in vinyl acetate and vinyl acetate-butyl acrylate copolymer latexes. 

Anionic sulfonated polyacrylamide (PAMS) is also found to increase amine flotation of quartz. Although PAMS does not adsorb on the negatively charged quartz and cause no direct activation of amine adsorption, the polymer-surfactant electrostatic interaction can lead to the formation of complexes. This polymer-surfactant complex can reduce the armoring of bubbles and lead to flotation. The anionic polymer can also bridge the adsorbed amine to the amine on the bubble surface and enhance flotation under saturated adsorption conditions. The hydration effect of the polymer may also be responsible for the enhanced flotation in this case. 

The interfacial behaviour of surfactant-polymer mixtures, utilized for example in the stabilization of suspensions, depends on a complex interplay between different pair interactions. Addition of a polymer can either remove surfactant from a surface or enhance its adsorption, and vice versa, depending on the relative stability of the polymer-surfactant complexes in solution and at the interface. 

At relatively low polymer adsorption levels, oscillatory force profiles similar to those observed for micellar solutions are also seen in polyelectrolyte-containing systems. As with micellar structuring, these oscillations originate from an inhomogenous density distribution of polymer (or polymer/surfactant complexes) within the film. Furthermore, the characteristic length-scale of the oscillatory forces indicate that this structuring is controlled by electrostatic interactions. To date, no complete theory describing this phenomenon exists ... 

Polymer and surfactant interact in solution. Adsorption of polymer/surfactant complex results in beneficial effects (or unwanted problems) at solid/liquid interface. 

Carbon adsorption Solvent extraction Complexing with surfactant Distillation Reverse osmosis Polymer adsorption Liquid membrane Foam... 

The aim of this chapter is to present the fundamentals of adsorption at liquid interfaces and a selection of techniques, for their experimental investigation. The chapter will summarise the theoretical models that describe the dynamics of adsorption of surfactants, surfactant mixtures, polymers and polymer/surfactant mixtures. Besides analytical solutions, which are in part very complex and difficult to apply, approximate and asymptotic solutions are given and their range of application is demonstrated. For methods like the dynamic drop volume method, the maximum bubble pressure method, and harmonic or transient relaxation methods, specific initial and boundary conditions have to be considered in the theories. The chapter will end with the description of the background of several experimental technique and the discussion of data obtained with different methods. 

A fundamental question as to the nature of polymer-surfactant interaction arises from the large difference between the mass of polymer and that of surfactant molecules. The adsorption concept emphasizes that the polymer is a large unit and it has many sites available for surfactant binding. In the complex formation model, the stress is on the elementary process between one polymer site and the surfactant molecule, disregarding the fact that the polymer sites are linked with each other in the polymer chain. 

Proteins are themselves surface-active compounds with an amphiphilic nature. The interfacial behavior of proteins is different from that of low-molecular-weight amphiphiles with a simple structure, namely, detergents, because proteins are highly complex polymers made up of a combination of 20 different amino acids (this point is described in detail in Chapter 3 of this book). Normally, proteins take on the folded compact structure, in which nonpolar amino acid residues are located in the interior and hydrophilic residues are exposed to molecular surfaces. Since hydrophobic interactions play dominant roles in the adsorption of surfactants to the air-water and oil-water interfaces, such a native structure of proteins should be modified to make fiiU use of the surface activity of proteins [1]. 

The prediction of the mesoscale morphology of complex polymer systems is very important for the final product properties. The application area of the proposed method includes computer simulation of such processes as emulsion copolymerization, copolymer melts and softened polymer melts, polymer blends, polymer surfactant stabilized emulsions, and adsorption phenomena in aqueous surfactant systems. 

This section will deal with the above interfacial aspects starting with the equilibrium aspects of surfactant adsorption at the air/water and oil/water interfaces. Due to the equilibrium aspects of adsorption (rate of adsorption is equal to the rate of desorption) one can apply the second law of thermodynamics as analyzed by Gibbs (see below). This is followed by a section on dynamic aspects of surfactant adsorption, particularly the concept of dynamic surface tension and the techniques that can be applied in its measurement. The adsorption of surfactants both on hydrophobic surfaces (which represent the case of most agrochemical solids) as well as on hydrophilic surfaces (such as oxides) will be analyzed using the Langmuir adsorption isotherms. The structure of surfactant layers on solid surfaces will be described. The subject of polymeric surfactant adsorption will be dealt with separately due to its complex nature, namely irreversibility of adsorption and conformation of the polymer at the solid/liquid interface. 

Another promising domain of investigation on polymer—surfactant interactions concerns the adsorption behavior at the solid-liquid interface of the different partners of the interaction (i.e., surfactant, polymer, and resulting complex). Increasing effort is devoted in understanding what happens at the solid-liquid interfaces, as numerous commercial applications of polymer-surfactant mixtures are a consequence of their interaction with... 

The concentration regime at which polymer—surfactant interaction is studied. For a low-concentration regime, studies are focused on the mechanism of interaction between the polymer and the surfactant. The adsorption behavior of polymers, surfactants, and their possible resulting complexes at various interfaces (liquid-air, solid-liquid) primarily concern those dilute conditions. On the other hand, the association between polymers and surfactants for high-concentration ranges finds broad practical applications as a consequence of complex phase behaviors [9,11]. 

It is generally accepted that surfactant-polymer interactions may occur between individual surfactant molecules and the polymer chain (i.e., simple adsorption), or in the form of polymer-surfactant aggregate complexes. In the latter case, there may be a complex formation between the polymer chain and micelles, premiceUar or submiceUar aggregates, liquid crystals, and bicontinuous phases—that is, with any and all of the various surfactant aggregate structures described in Chapters 4 and 5. Other association mechanisms may result in the direct formation of what are sometimes called hemimicelles along the polymer chain. The term hemimicelle may be defined, for present purposes, as a surfactant aggregate formed... 

The ability of surfactants to form complexes with polymer chains may also affect the ultimate properties and stability of the resulting polymer, especially when the macromolecule exhibits some affinity for or reactivity with water. Perhaps the best documented case of the effect of surfactant on latex stability is that of polyvinyl acetate. The stability of PVAc latexes has been found to vary significantly depending on the surfactant employed in its preparation. It has also been found that PVAc could be dissolved in concentrated aqueous solutions of SDS and that it did not precipitate on dilution. The results suggest that, in this case at least, solubilization did not occur in the micelle, but that extensive adsorption of surfactant onto the polymer chain was required. They also indicate that a strong, stable PVAc-SDS complex is formed that produces a water-soluble structure that is essentially irreversible, imlike normal micelle formation. Cationic and nonionic surfactants had little or no solubilizing effect under identical conditions, indicating the specific nature of many, if not most, polymer-surfactant interactions. 

Attempts to correlate the adsorption data of other surfactants such as Alipal EP-110 and NaLS on the three latex surfaces in a similar manner failed because of the more complex and specific interactions observed in these systems. Equation 2 can adequately describe the adsorption data of surfactants at polymer/ water interfaces, provided that the free energy of the interface is related to the free energy of adsorption and there are no specific interactions between surfactant and interface (15). 

---