Effect of biological buffers on the colloidal behavior of sodium dodecyl sulfate (SDS)

Abstract

This study investigates the influence of three commonly used buffers (TRIS, TES and TAPS) on the conductivities and the colloidal behavior of the aqueous solutions containing a surfactant, sodium dodecyl sulfate (SDS). To find the effect of these buffers on the aggregation behavior of the aqueous SDS solutions, we experimentally determined the conductivities of the solutions containing different concentrations of SDS (0.002M–0.025M) in water and in 0.2M, 0.5M, and 1.0M TRIS, TES, and TAPS buffers, respectively, at 298.2K under atmospheric pressure. To get insight into the effect of the buffers on the aggregation behavior of the aqueous SDS solutions, the critical micelle concentration (CMC) values of the aqueous solutions are estimated from the experimental results of conductivity measurements. Interestingly, in comparison with the CMC of SDS in water, the presence of TRIS is found to increase the CMC, whereas the addition of TES or TAPS is found to decrease the CMC, especially at higher concentration (1.0M). The influence of the buffers on the CMC or aggregation of the SDS is further characterized by calculating various aggregation parameters such as the degree of ionization of the micelle (αm), the degree of counter ion binding in micelle (fm), and the standard Gibbs free energy of micellization (ΔG°m) for all the studied systems. Moreover, the outcomes from the conductivities measurement are reconfirmed by using the fluorescence probe analysis.