Abstract
Dodecyltrimethylammonium triflate (DTATf) micelles possess lower degree of counterion dissocn. (α), lower hydration, and higher packing of monomers than other micelles of similar structure. Addn. of sodium triflate ([NaTf] > 0.05 M) to DTATf solns. promotes phase sepn. This phenomenon is commonly obsd. in oppositely charged surfactant mixts., but it is rare for ionic surfactants and relatively ...
Abstract
Dodecyltrimethylammonium triflate (DTATf) micelles possess lower degree of counterion dissocn. (α), lower hydration, and higher packing of monomers than other micelles of similar structure. Addn. of sodium triflate ([NaTf] > 0.05 M) to DTATf solns. promotes phase sepn. This phenomenon is commonly obsd. in oppositely charged surfactant mixts., but it is rare for ionic surfactants and relatively simple counterions. While the properties of DTATf have already been reported, the driving forces for the obsd. phase sepn. with added salt remain unclear. Thus, we propose an interpretation for the obsd. phase sepn. in cationic surfactant solns. Addn. of up to 0.03 M NaTf to micellar DTATf solns. led to a limited increase of the aggregation no., to interface dehydration, and to a progressive decrease in α. The viscosity of DTATf solns. of higher concn. ([DTATf] ≥ 0.06 M) reached a max. with increasing [NaTf], though the aggregation no. slightly increased, and no shape change occurred. We hypothesize that this max. results from a decrease in interaggregate repulsion, as a consequence of increased ion binding. This redn. in micellar repulsion without simultaneous infinite micellar growth is, probably, the major driving force for phase sepn. at higher [NaTf]. [on SciFinder(R)]
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