Sodium lauryl sulfate adsorption

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. 

Figure 2. Effect of surface polarity on the limiting area per molecule for sodium lauryl sulfate adsorption on various polymers. (Vijayendran, Ref. 15).

It is well known (3,5,6) that sodium lauryl sulfate interacts with some polymers such as polyvinyl acetate causing solubilization of the insoluble polymer leading to an increase in viscosity. In Figure 3, viscosity of the homopolymer and 70/30 VA/BA at various NaLS/polymer ratio is shown. It is seen that the viscosity of the 2% latex dispersion increases with increase in NaLS/polymer ratio. Similar visoosity data for the 85/15 VA/BA was intermediate between the homopolymer and 70/30 VA/BA latexes. Surfactants that showed a normal saturation type adsorption behavior did not show any significant visoosity increase of the latex. 

Edelhauser (3) has explained his results on the interaction of anionic surfactants (sodium lauryl sulfate and sodium dodecyl-benzene sulfonate) with a PVAC latex as a two-step mechanism involving surface adsorption followed by surfactant penetration into... 

Figure 1. Adsorption isotherms of NaLS and Aerosol A-102 surfactants at 85/15 VA /BA latex /water interface (17) ((O) sodium lauryl sulfate (A) Aerosol A-102)...

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). 

Wilson, A., Epstein, M.B. and Ross, J. (1957) The adsorption of sodium lauryl sulfate and lauryl alcohol at the air-liquid interface. J. Colloid Sci., 12, 345-55. 

Rykke M, Rolla G, Sanju T Effect of sodium lauryl sulfate on protein adsorption to hydroxyapatite in vitro and on pellicle formation in vivo. Scand J Dent Res 1990 98 135-143. 

Hannah et al. [44] have shown that polymer JR deposits on hair in the presence of excess sodium lauryl sulfate. This deposited complex is highly substantive to hair and resists removal from the hair surface by either water or 3% sodium lauryl sulfate solution. Therefore, adsorption complexes of polymeric cations also resist shampooing from hair. 

Sykes and Hammes [43] have described the adsorption of both of these cationic polymers onto hair from solutions of different amphoteric and anionic surfactants. Analogous to the adsorption of polymer JR, uptake values were greater onto bleached hair than onto unbleached hair, and greater from amphoteric systems like cocobetaine or cocoamphyglycinate than from anionic surfactants like sodium lauryl sulfate or triethanolam-monium lauryl sulfate. 

Figure 3.3.7. (a) Surface tension vs. concentration of a surfactant, sodium lauryl sulfate, in water, (b) Surface adsorption isotherm in a gas-liquid system. 

In the interfacial tension theory, the adsorption of a surfactant lowers the interfacial tension between two liquids. A reduction in attractive forces of dispersed liquid for its own molecules lowers the interfacial free energy of the system and prevents the coalescence of the droplets or phase separation. Therefore the surfactant facilitates the stable emulsion system of the large interfacial area by breaking up the liquid into smaller droplets. However, the emulsions prepared with sodium dodecyl (lauryl) sulfate separate into two liquids upon standing even though the interfacial tension is reduced. The lowering of the interfacial tension in the stabilization of emulsions is not the only factor we should consider. 

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