Synergism between Cationic Alkyltrimethylammonium Bromides (C_nTAB) and Nonionic n-Octanol in the Foamability of Their Mixed Solutions

Abstract

In this study, the foamability of pure solutions of alkyltrimethylammonium bromides (C n TAB with n = 8, 12, and 16) of various concentrations and their mixtures with n-octanol was studied. It was found from the results that n-octanol behaved as a foamability enhancer, depending on the C n TAB solution concentration. A similar foam height was obtained in C n TAB/octanol systems compared to pure C n TAB solutions with a greatly reduced amount of cationic surfactants. This synergistic effect between C n TAB and n-octanol was quite significant, and it could be observed for systems where the C n TAB concentration differed even by two orders of magnitude. Such behavior was observed only below some characteristic concentration of C n TAB, called a critical synergistic concentration (CSC), above which the synergistic effect was either no longer visible or significantly reduced. Moreover, it was found that the presence of n-octanol affected only the solution foamability without significant changes in the stability of the foams. A possible origin of this effect was analyzed and discussed on the basis of the magnitude of the surface elasticity forces induced in the foam films during the foam generation period and while operating during foam decay.

Critical Synergistic Concentration of Binary Surfactant Mixtures

“…There are additionally plotted (as horizontal lines) dσ values for non-ionic SAS solutions of given concentrations used as the additives for preparation of the binary mixtures. As seen, these lines delimit two dσ regimes, which are crucial for determination of the CSC value and was discussed in detail in our previous paper for n-octanol [7]. It was concluded there that n-octanol as the non-ionic additive to the cationic surfactant solution in a binary mixture, participates in the mixed adsorption layer formation at the rising bubbles surface and causes an increase in the E value of the liquid/gas interface.…”

“…As a consequence, the solution foamability is enhanced. This effect, however, is significant only for the dσ lying below the threshold value, indicated by the horizontal line, above which the n-octanol molecules start to be a minor component of the adsorption layer [7], and where E values are determined mainly by the mixture main constituent. The way of determining the CSC values on the basis of dσ is presented in Figure 4b.…”

“…The results presented in Figure 2 directly indicate that the non-ionic SAS addition to the C n TAB solutions caused a strong synergistic effect-foamability in binary mixtures is much higher compared to the one-component solution. However, this conclusion holds below the threshold concentration, which was called as critical synergistic concentration (CSC) [7].…”

“…where σ water is the water surface tension and σ (c) is the surface tension of SAS of a given concentration [7,21]. Calculated dσ values for each studied SAS (one-component system) are presented in Figure 4 as a function of their solution concentration.…”

“…Thus, the goal of our paper is to present and validate a simple method for determination of the critical synergistic concentration (CSC), that is the concentration below which the synergism between binary surfactants in their foamability occurs [7]. Values of CSC can be easily predicted based on the surface tension data on individual components, which can be either found in a myriad of published papers or easily determined.…”