Surface latex

Deco Turf acryhc latex surface for tennis Koch Materials ... 

The influence of the surfactant in the modified polymers of Figure 1 on n (aqueous solutions, Table I) is not overpowering. The surfactant s influence is diminished by the amphiphilic oxyethylene units which lie interfacially flat at the aqueous-air interface. The hydrophobes are structurally similar to the surfactants providing stability to commercial latices and should be capable of competing with the classical surfactants at the latex surface, but this ability is not reflected in 7T values. The oxyethylene units have been demonstrated(18) to provide osmotic stabilization to latex particles. 

In recent papers (1-2), we have shown how the thermodynamics of adsorption of nonionic surfactants on latex surfaces can be described in terms of a few simple parameters that may be used to predict the relative strength of adsorption of surfactants with different hydro-philic/hydrophobic balance on surfaces of different polarity. 

We have shown that the main driving force of adsorption of surfactants in monolayers on latex surfaces is the (cooperative) inter-... 

These results indicate that it should be possible to make rough predictions of competitive adsorption of different surfactants on latex surfaces without any detailed knowledge about the properties of the surface. The major difference in adsorption strength should be due to differences in the hydrophilic/hydrophobic balance of the surfactants, i.e. to differences in their solution properties. 

In this paper we apply basic solution thermodynamics to both the adsorption of single surfactants and the competitive adsorption of two surfactants on a latex surface. The surfactant system chosen in this model study is sodium dodecyl sulfate (SDS) and nonylphenol deca (oxyethylene glycol) monoether (NP-EO o) These two surfactants have very different erne s, i.e. the balance between their hydrophobic and hydrophilic properties are very different while both are still highly soluble in water. 

For the adsorption of water on the latex surface. Equations 1 and 2 give... 

This represents the difference in the second adsorption free energy term in Equation 21, i.e. the two terms on the right hand side each represent the change in free energy when a water-surface molecular contact is replaced with a surfactant-surface molecular contact. It is very reasonable to assume that, at close packing, both surfactants adsorb with only their hydrocarbon moieties (or part of these moieties) in direct contact with the surface. Hence, the two surfactants interact with the latex surface with the same strength and the last term in Equation 17 is equal to zero. 

Adsorption on Polystyrene Latex. Figure 3 shows the adsorption isotherms of the two single surfactants, NP-EO q and SDS, on the polystyrene latex surface. Both isotherms reach a limiting value when the cmc is approached. The lines drawn in the figure are calculated from the fitting Equation 19. The adsorption free energies, as obtained from Equation 21, are shown in Table I. The table also shows the two contributions to Ap, according to Equation 21, where the first contribution is obtained from the cmc s and the second from the difference between the two terms in Equation 21. 

Table II presents the experimental data, obtained from using bulk solutions of different NP-EO q/SDS ratios. Figure 6 shows the surfactant composition on the polystyrene latex surface as a function of the surfactant composition in the bulk solution at concentrations corresponding to the onset of micellization. If the surfactant composition on the surface were the same as that in the bulk solution, the experimental points would fall on the dashed line in the figure. Thus, the...

In particular, we would like to point out two conclusions of practical importance. Firstly, a surface analysis of the serum (bulk solution) cannot give direct information on either the surfactant composition on the latex surface or in the total system. This is an important conclusion since such analyses are frequently carried out in industrial laboratories. Secondly, Figure 6 shows that if NP-EOiq is added to a system stabilized with SDS, the latter will desorb. In practice, this causes foaming problems. Such problems can be predicted, as is shown below. 

Monodisperse Polystyrene Latexes Surface Charge and Number of Sulfate Endgroups/Polymer Molecule (3,5,9)... 

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. 

It was reported earlier (1) that surfactant adsorption at a polymer/water interface can be related to the polarity of the polymer surface. The model used in that study was tested satisfactorily by using the available literature data on polymer polarity and sodium lauryl sulfate adsorption on latex surfaces. 

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. 

Figure 2 shows adsorption isotherms of two sulfated ethoxy-late type anionics - Alipal EP-110 and Alipal EP-120 - on the 85/15 VA/BA latex surface. Again it is soen that the lower molecular weight EP-110 shows a C type isotherm similar to NaLS while the higher molecular weight EP-120 exhibits a normal saturation type isotherm. 

Presence of non-ionic surfactants such as Igepal CO-630 seems to prevent the thickening of PVAC latex by NaLS, as shown in Table IV. This can be interpreted as to show that the presence of non-ionic surfactant at the PVAC latex surface prevents the penetration of NaLS into the particle. 

Table VI shows the adsorption data of Igepal CO-630 surfactant at the three latex/water interfaces. The isotherms were of the normal type and no thickening of the latex in the presence of surfactant was observed. A typical adsorption isotherm of Igepal CO-630 on a 85/15 VA/BA latex surface is shown in Figure 4. Area per molecule was calculated according to equation - 1 (14).

POLARITY OF LATEX SURFACE BY CONTACT ANGLE MEASUREMENTS (17)... 

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 interaction parameter, as expected, decreases with increase in polarity of the latex surface (12). It shows that at saturation adsorption, the extent of interaction of Igepal CO-630 with the PVAC homopolymer and the two VA/BA co-polymer latexes is 29%, 49%, and 57% respectively of the theoretical limit corresponding to a close packed monolayer adsorption. 

Figure 5 shows a plot of log A vs polarity (xP) of latex surface. It is readily seen that the plot is quite linear and fits equation 2.in good agreement with the results on the adsorption of sodium lauryl sulfate at various latex/water interfaces (1). 

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). 

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... 

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. 

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