Interaction of poly(vinylpyrrolidone) with cationic and nonionic surfactants in aqueous solution studied by 1H NMR

Aqueous solutions of surfactant at various concentrations with 0.2% poly(vinylpyrrolidone) (PVP) were studied by H-1 NMR methods, including relaxation time and self-diffusion coefficient measurements and two-dimensional nuclear Overhauser enhancement spectroscopy. Two surfactants were concerned: cationic cetyltrimethylammonium bromide (CTAB) and nonionic Triton X-100 (TX-100). In the presence of 0.2% PVP, the variation of the T-2 values of CTAB protons is similar to that in the absence of PVP. Relaxation times of PVP protons are not significantly affected by the increasing concentration of CTAB. This indicates that no interaction between PVP and CTAB could be detected. However, in the presence of 0.2% PVP, TX-100 micelles are formed at a concentration lower than its normal critical micellization concentration. According to the results of relaxation time measurement of water protons, the presence of 0.2% PVP also induces the contraction of the hydrophilic layer of the TX-100 micelle. This indicates some interaction between PVP and TX-100, but the mechanism of this interaction needs further investigation.