Study of self-assembled nanostructures of amphiphilic molecules

Abstract

Self-assembled aggregates of amphiphilic molecules in aqueous media can vary their size and shape in response to thermodynamic variables, such as concentration and temperature. Often, the energy scale of the interactions between self-assembled aggregates in solution is comparable to the energy scales that determine the structure of a single aggregate. This leads to a rich variety of structures and phases that allow these materials to use in a variety of applications. In this study, we controlled the self-assembled micelle structures using additives and have studied their properties. At first, we studied the mixed micellar solution of $C_{12}E_5$(nonionic surfactant, penta-ethyleneglycol mono n-dodecyl ether) and DMPC (nonionic lipid, DL - α- phosphatidylcholine Dimyristol). We observed the increase in size of micelles by adding DMPC to $C_{12}E_5$ micellar solutions. A one dimensional growth model had been applied for mixed micelles of $C_{12}E_5$ and DMPC to explain the growth of the micelles. Based on the CMC (critical micellization concentration) and thermodynamic - molecular theory, the micellization free energies and end-cap energies of mixed micelles were estimated. The end-cap energy of mixed micelles increased as the amount of DMPC increase. The end-cap energy increase made the average contour length of mixed micelles grow. The estimated diffusion coefficients based on the one dimensional growth model from SLS (static light scattering) measurements, decreased with increasing the amounts of DMPC. These findings from SLS measurements were in an excellent agreement with diffusion coefficients obtained from DLS (dynamic light scattering) measurements. Furthermore, nonionic lipids (DOPC and DMPE) gave enhanced effects on the micellar growth in size and in the temperature dependence. On the other hand, the charged molecules (DOTAP, DTAB) decreased the size of micelles. The presence of salt also could control the micellar size by screening charge interacti...