Adsorption vinyl acrylic latex surface

It is seen that the adsorption of Igepal CO-630 at the three latex/water interfaces decreases with increase in polarity of the vinyl acrylic latex surface. Explanation for such a decrease in surfactant adsorption at a polymer/water interface with increase in polymer polarity has been discussed in detail elsewhere (1). Briefly, increased polarity of the polymer lowers the interfacial free energy of the polymer latex/water interface and this, in turn, reduces the free energy of adsorption for a simple saturation type adsorption process of a surfactant at a latex surface in aqueous media. Such a lowering in free energy of surfactant adsorption at a polymer latex/water interface with increase in polymer polarity leads to the observed results, namely, decrease in the adsorption of Igepal CO-630 with polarity increase of the VA/BA latex particle. 

The polarity and adsorption data discussed above reveal some interesting aspects of the surface chemistry of vinyl acrylic latex surfaces. It is quite likely that the polarity of the latex films, expecially of the two co-polymers, determined by contact angle measurements may not correspond exactly with their respective latex surfaces in the dispersed state due to reorientation of polymer chains during film formation. But the surfactant adsorption data shows clearly that the three latex surfaces in their dispersed state do exhibit varying polarity paralleling the trend found from contact angle measurements. The result also shows that the surface of the co-polymer latex surface is a mixture of vinyl acetate and acrylate units. This result is somewhat unexpected in a vinyl acrylic latex, prepared by a batch... 

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. 

In order to achieve the above objectives, three vinyl acrylic latexes of varying butyl acrylate content have been prepared and cleaned1 for use in the study. Several anionic and nonionic surfactants commonly usod in emulsion polymerization have been used to investigate the effects of surfactant structure and polymer composition on the solubilization process. Polarity of latex surface estimated from contact angle measurements have been used to study the effect of polymer polarity on surfactant adsorption. 

Polarity of Vinyl Acrylic Latex and Surfactant Adsorption Contact angle measurements, dispersion and polar contribution to latex film surface tension and polarity of polymer calculated according to the method of Kaelble (10) of the three latex films are whown in Table V. It is seen that the polarity of the latex film decreases with increase in butyl acrylate content of the vinyl acrylic co-polymer. The polarity of the 70/30 (VA/BA) latex is very similar to that of the polybutyl acrylate homopolymer estimated to be about 0.21 (1). ... 

In agreement with our earlier studies (1,15), the adsorption results of Igepal CO-630 on the three vinyl acrylic latexes show that the area per molecule of surfactant can be related to the polarity of polymer surface. Further, the results show that one can employ the techniques discussed above to characterize the polarity of co-polymer latex surfaces. 

It is also shown that the adsorption of non-ionic surfactants at a vinyl acrylic latex/water interface that exhibit a saturation type isotherm can be related to the polarity of the polymer surface, in agreement with earlier sufactant adsorption studies. 

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