Study On The Interaction Between PVP And Quaternary Ammonium-type Surfactant By NMR

The interaction of Polyvinylpyrrolidone (PVP) with Quaternary Ammonium-type Gemini surfactant (G12-3-12, G12-6-12) and zwitterionic surfactant Dodecyl Dimethyl Betaine (C12BE) had been studied through1H NMR, relaxation time, self-diffusion coefficient measurements and2D NOESY. TEM studied the morphology of the mixed aggregates was characterized by transmission electron microscope (TEM). Then, we designed the model of the interaction process with NMR data and TEM figures.1. The interaction between PVP and Gemini surfactant G12-3-12The critical micelle concentrations (cmc), the critical aggregation concentration (cac) and the adsorption reached saturated concentration (C2) have been studied by1H NMR, respectively. Relaxation time measurements of G12-3-12show that the motion of the ionic head N+-CH3proton (G6of G12-3-12) is seriously restricted in solution and it should be situated in the hydrophilic layer of micelle. Relaxation time measurements also show that there is interaction between G12-3-12and PVP.2D NOESY spectra of the PVP/G12-3-12system indicate that the precise interaction site is located between the hydrophobic tail (Gl, G2) of G12-3-12and (P1,P2, P3) of PVP ring. Meanwhile there are all kinds of micellar morphologies in PVP/G12-3-12solution by TEM, such as spherical, rod-like, dendritic micelles. According to NMR and TEM experiment results, the interaction model of the PVP/G12-3-12has been built. When [G12-3-12]>cac, G12-3-12have started association to PVP through the hydrophobic effect, G12-3-12molecules are dispersed on the stretch of PVP chain. When [G12-3-12]>>C2, the association of surfactant and PVP is saturated, the excess G12-3-12molecules were continuing to gather lamellar micelles on PVP/G12-3-12mixed aggregations backbone to make the branches of dendritic aggregations spreading around and forming a huge "dendritic structure" like-micelle aggregation which coexists with the spherical and rod-like free micelles of G12-3-12in solution.2. The interaction between PVP and Gemini surfactant G12-6-12The cac and C2value of PVP/G12-6-12system is0.52mM (cac) and1.0mM (C2) respectively through1H NMR. In presence of PVP, the TR values are smaller than absence of PVP solution. Then, the TR of ionic head N+-CH3*proton (G6’of G12-6-12) first increased to the highest point (cac) and then decreased with a change in trend, this shows that the addtion of PVP had a great influence on hydrophilic group of surfactant.The cross peaks of G6’-P1, G6’-P2can be observed in2D NOESY, it can be seen that the precise interaction site is located between the hydrophilic head of G12-6-12and the methyl protons near the amide groups of PVP ring. The TEM images of mixed system show that the structure of the mixed aggregates change from spherical to linear winding aggregates. Combining with the NMR data, we imitated the model of the interaction between PVP and G12-6-12is "linear winding" model.3. The interaction between PVP and zwitterionic surfactant C12BEThe cac and C2values of C12BE increased as concentration of PVP increased by1H NMR. The measurements of relaxation time and self-diffusion coefficient showed that different content of PVP had different influences on the motion of C12BE moleculer. The more content of PVP is, the more limited of C12BE molecular motion is. In addition, the presence of PVP impact on the the hydrophilic group B7proton than hydrophobic group B2proton.The self-diffusion coefficient data also showed that the larger aggregates have formed in mixed solution. And the B7-P1, B7-P2cross peaks can be observed in2D NOESY indicated that the major interaction site is located between the hydrophilic head of C12BE and the methyl protons near the amide groups of PVP ring, and the electrostatic interaction was considered to be the leading driving force. The images of TEM showed that there are fiber bundle aggregates in mixed system. So, we imitated the interaction model of the PVP/C12BE is similar to the "pearl necklace" model.