Dynamics of water state in nanoconfined environment

Abstract

To investigate water state in vitro conditions, cetyltrimethylammonium bromide/isooctane 1-hexanol reverse micellar system was used as a model for nanoscale medium. Using Fourier transform infrared spectroscopy and deconvolution technique, the water states in these systems were studied at several water/surfactant molar ratios, wo, with respect to time. The presence of four sub-peaks in deconvolution of FT-IR absorption spectra of OH stretching band certified four different states of water. The results showed time dependency of water state, especially in those systems having low wo, that are more dynamic. Also, exchange of water molecules between different states results in approaching each state to a final steady state value. Based on deconvolution results, it was found that mechanism of ionizing surfactant head group can control water bonded to the bromide counter ion. Moreover, more than 50% of water molecules are like frozen water in reverse micelles and they are not available for solubilization of hydrophilic compounds. Based on the results of this study, state and properties of water in nanoscale medium are quite different from bulk scale.