Bubble-size dependence of the critical electrolyte concentration for inhibition of coalescence

Effects of surfactant and electrolyte concentrations on bubble formation and stabilization

“…However, a surfactant concentration above the CMC is generally a prerequisite for achieving maximum efficiency, as discussed above. Electrolytic salts are known to be effective in reducing the CMC [14][15][16], and they are believed to prevent gaseous bubbles from coalescing and to improve bubble stability [25]. Thus, it is important to characterize the effect of electrolyte addition on the formation and stabilization of microbubbles.…”

“…It has previously been found that in a froth system stabilized by a nonionic surfactant, the stability was improved by the addition of low KCl concentrations (<10 −4 M), while it was reduced by the addition of high KCl concentrations (>10 −3 M) [14]. It has been experimentally proven that there is a critical concentration of salt that prevents coalescence of millimeter-sized bubbles, and this concentration increases with decreasing bubble size [25]. Since no coalescence was observed in the present system, a different destabilization mechanism is probably involved for the bubbles of micrometer size.…”

Inhibition of bubble coalescence: Effects of salt concentration and speed of approach

“…Examples include observation of freely rising bubbles in vertical columns with two bubbles rising sideby-side [11][12][13], and a bubble rising to approach the liquid surface [14][15][16][17][18][19][20][21][22] (in this case the air phase above the liquid surface can be considered as an infinitely-large bubble). Some studies have used a bubble contacting device where pairs of bubbles are formed from two adjacent or two directly opposed nozzles [23][24][25][26][27][28][29][30][31][32][33][34][35]. In these studies, coalescence characteristics were examined with bubbles approaching each other at relatively high speeds, i.e.…”

“…Most studies in bubble coalescence deal with the effects of factors such as surfactants [11,12,14,18,20,28,30,32,38,[41][42][43]47,48,[51][52][53], electrolytes [3][4][5][8][9][10]20,21,25,29,[32][33][34][35]38,43,46,[54][55][56][57][58][59][60][61], their concentrations [4,5,11,12,14,20,25,[28][29][30]…”

A theory on bubble-size dependence of the critical electrolyte concentration for inhibition of coalescence

“…Experimental studies have shown that transition from coalescence to noncoalescence of bubbles occurs within a small range of electrolyte concentration [1,4]. Many investigators have attempted to model the coalescence behavior, however there has been no direct comparison between experiments and theory on the critical salt concentration which is bubble-size dependent.…”