EVAPORATION AND AGGREGATION IN AQUEOUS MONODODECYLTRIMETHYLAMMONIUM N-DODECANEPHOSPHANATE SOLUTIONS

Electrobalance evaporation rate measurements were used to measure solu te weights in the aqueous catanionic system onododecyltrimethylammoniu m-n-dodecanephosphonate. At very low concentration premicelles compose d of ion pairs between 3.6 and 7 were found, which increased with conc entration. Above the cmc the aggregates increased in size with concent ration much more rapidly. Aggregates had 54 ion pairs at the higher st udied concentration (6 x 10(-3) mol dm(-3)). This value agrees with li terature data of other similar systems. Since the system is probably p olydisperse and the evaporation rate method gives number average weigh ts, the true aggregation numbers are probably higher than those found. In this system the cmc did not indicate the starting point of aggrega tion, but a change in the aggregates structure and growing regime.