INTERACTIONS OF TRIBLOCK COPOLYMERS WITH IONIC SURF ACT ANTS

Abstract

The interactions of triblock copolymers E30B lOE30 and E48B lOE48 with anionic surfactant SDS and cationic surfactant CTAB were studied employing surface tensiometry, electrical conductivity, pyrene fl uorescence probe and dynamic laser light scattering techniques. Using surface tensiometry and electrical conductivity teclmiques Critical Micelle Concentration (CMC) were determined. Electrical Conductivity technique was used to determine CMC, degree of ionization (a.), degree of cow1ter ion binding ( ~) and free energy of micellization (.0.Gm) . The increase trend in CMC for ternary system both in the case of SDS and CTAB were observed. The increase in CMC in case of concentrated polymer solution is more as compare to dilute polymer solution both in the case of SDS and CTAB. In our case among the two triblock copolymers, E30B lOE30 is more hydrophobic (BIE = 0.166) as compare to E48BlOE48 (BIE = 0.104) that is why E48B lOE48 cause more delay in the CMC of surfactants and greater increase were observed in this case. The CMC of the mixed system determined by surface tensiometry and electrical conductivity are in close agreement with an increasing trend. The increase trends were observed for degree of ionization in case of SDS as compare to CTAB. Degree of counter ion binding increase in case of CTAB as compare to SDS. The free energy of micellization remains negative both in the case of SDS and CT AB predicting that the process is spontaneous. Pyrene Fluorescence technique was used to calculate first and third vibronic ratio l lll), micelle aggregation number (Nagg), Binding sites (n), Binding constant (Kb) and free energy of binding (.0.Gb) . The 1 sl and 3rd vibronic ratio for pure CT AB is more as compare to SDS confirming more hydrophobic nature of CT AB. In the presence of triblock copolymers the 11 /13 ratio is more for SDS as compare to CT AB, predicting that the micro polarity of the solvent decrease in the case of CTAB. The aggregation number decrease both in the case of SDS and CT AB. Dynamic laser light scattering was used to determine the apparent hydrodynamic radius (Rh). Decrease in the aggregates size (Rh) in the presence of surfactants (SDS) were confirmed from dynamic laser light scattering.