INVESTIGATION OF POLYMER-SURFACTANT INTERACTIONS

Abstract

Surfactants have received significant attention in the last decades due to their tremendous industrial and medicinal applications. The addition of small quantity of polymer or electrolytes further enhances their potentials as their surface properties can be easily manipulated. Therefore, our objective was to investigate the surface behavior of cetyltrimethylammonium bromide (CTAB) surfactant and its interactions with Poly(ethyleneoxide) (PEO) having different molecular mass in the absent and presence of electrolytes. The surfactant was characterized by using various available techniques like surface tension, light scattering, viscosity and conductance measurement. Its CMC was obtained as 1mM which was reproducible and consistent. The aggregation behavior of three samples of poly (ethylene oxide) having 6, 12, 35 Kg/mol molecular mass was investigated using surface tension measurement and a relationship between molecular mass and surface tension was established. It was concluded that the characteristic concentration (CC) and critical aggregation concentrations (CAC) of PEO was decreased as the molecular mass of polymer was increased. The intrinsic viscosity, hydrodynamic radius, RH, and molecular mass relationship was also established. The impact of poly (ethylene oxide) over the micellization process of surfactant (CTAB) was explored, using the above stated techniques. It was concluded that the CMC of CTAB was increased by the addition of polymer. The three interaction ranges of the polymer PEO and surfactant CTAB were identified at surface tension plot with respect to CTAB concentration. It was observed that these points / ranges are polymer concentration dependent. The temperature effect over these interactions and micellization behavior of CTAB was also highlighted. It was also noted that the value of CMC, ΔH and flow activation energy of the PEO/CTAB system were smaller than for the mixture. It was noted that more the polymer added high the values of these parameters were. The value of CMC of CTAB was reduced with the increase in temperature. The RH and Rg/RH values obtained by light scattering also indicated such type of behavior. The CMC values were also obtained by viscosity and conductivity measurement. The results and conclusions drawn through all the techniques were consistent. New techniques have also been introduced to interpret the data obtained by surface tension, viscosity and conductance measurement and to get information about the point of interaction and saturation point of polymer with surfactant that were noted to be very useful and informative. Effect of electrolytes (LiCl, NaCl, KCl) and temperature over the micellization behavior of CTAB and its mixtures with polymer has also been discussed. It is concluded that the presence of electrolyte reduces hydrophilicity of CTAB, favoring micellization at relatively low concentration than in water at ambient temperature. The critical micelle concentration showed a marked decrease in the presence of electrolytes. This decrease in CMC in the presence of electrolytes was in the order of K+> Na+> Li+ and was explained on the basis of specific absorption of electrolytes, change in the structure of micelle, ionic strength and hence variation in the free energy of micellization. It was also concluded that CMC decreases with the increase in temperature of the system and was explained in term of solubility of surfactant, change in shape of micelle and free energy of the system with the temperature. Over all the study was found to be very useful to understand the surfactants and polymers interactions at molecular level in the absence or presence of electrolytes.