EFFECT OF TEMPERATURE ON THE INTERACTIONS BETWEEN NEUTRAL POLYMERS AND A CATIONIC AND A NONIONIC SURFACTANT IN AQUEOUS-SOLUTIONS

Many studies performed around 25 degrees C concluded that the interactions between nonionic polymers such as poly(oxyethylene) (POE) or poly(vinylpyrrolidone) (PVP) and cationic surfactants such as alkyltrimethylammonium halides or nonionic surfactants such as poly(oxyethylene) monoalkyl ethers are nonexistent or extremely weak. In the present work we have investigated the effect of temperature on these interactions by means of conductivity, spectrofluorometry and time-resolved fluorescence quenching. The results show that an interaction sets in between POE and the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) at a temperature T above 35 degrees C, resulting in the formation of POE-bound TTAB micelles which are smaller and more ionized than free TTAB micelles, the more so the larger the POE content of the system. This behavior is attributed to the decreased polarity of POE upon increasing temperature. Nevertheless, the decreased polarity of POE at high Tis not sufficient to induce interactions with the nonionic surfactant C(12)E(8) even at 60 degrees C, as indicated by the fact that the aggregation number of C(12)E(8) micelles remained unchanged by the addition of 2% POE in the whole temperature range. No interaction occurs between PVP and TTAP even at T = 60 degrees C because the polarity of this polymer is not reduced at high T. Some measurements of micelle aggregation numbers have also been performed in systems containing 1% POP (poly(oxypropylene glycol)), which is much less polar than POE at all temperatures. The results show a very strong interaction with TTAB but only a very weak interaction with C(12)E(8), in the range 5-20 degrees C.