Dielectric Spectroscopy Study On Molecular Self-organized Assembles

Surfactants in solution exhibit a complex aggregation behavior resulting from a delicate balance of opposing forces, forming into different structures, such as micelle, microemulsion, vesicle, liposome, liquid crystals, etc. by self-associating.. The size and shape of the aggregates not only depend on the chemical composition, but also dramatically change in response to variations in solution parameters, such as temperature, concentration, PH, or ionic strength. The study on molecular self-organized assembles has attracted a lot of attention in recent years, due to their theoretical and practical significance. Molecular self-organized assembles are of definite structure, which is very interesting and supernatural when the composition of system varies. So the phase behavior of many surfactant systems were investigated by several methods, such as Quasielastic Light Scattering (QLS), NMR Self-diffusion and Relaxation, time-resolved fluorescence quenching (TRFQ), small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) etc. In this thesis, dielectric relaxation spectroscopy method (DRSM) was also used to determine the structural, electric and dynamic properties of molecular self-organized assembles.Dielectric relaxation spectroscopy (DRS) method is known as a classical but useful technique to investigate molecular motions of functional groups with dipole moments. In some cases, DRA is also a powerful method to evaluate macroscopic electric properties of colloidal systems such as (oil in water (O/W) and water in oil (W/O) emulsions, vesicles, microcapsules, and biological cell dispersions, which have more than two electrically different components separated with insulation shells. The dielectric properties of these colloidaldispersion have been discussed with a Maxwell- Wagner theory based on macroscopic electric polarization on the interface between two different components.The phase diagram of the ternary system of sodium dodecyl trioxyethylene sulfate (SDES) / n-butanol / water is obtained at 30.0+0.1. There exists a clear, isotropic, and low-viscosity L phase, which could be divided into W/O micelle, bi-continuous (B.C.) phase and OAV micelle by conductivity measurements. Dielectric Relaxation Spectroscopy (DRS) measurements are applied to investigate microstructure changes of this system. For samples with a fixed weight ratio SDES / n-butanol of 3:7, DRS indicates a structure transition from W/O to O/W micelles via B.C. phase with the increase of water content. For samples with a fixed weight ratio SDES / H2O of 4:6, DRS presents that there only exists changes of onefold structure size of W/O micelles as n-butanol content increases. The results obtained from DRS and its analysis are in good agreement with those from phase diagram and conductivity measurements.Microemulsions are optically isotropic fluid mixtures, which form spontaneously in the presence of a surfactant, usually in combination with ' co-surfactant (alcohol), oil and water. Alkyl polyglucoside (APG) is a kind of green surfactant. APG / n-butanol / n- hexane / water microemulsion system was also determined by DRS. DRS can estimate the type of microemulsions primarily. The static and dynamic dielectric properties as a function of frequency and concentration of wa'ter, surfactant and cosurfactant are considered.Vesicles, which are single-bilayer-closed shells that encapsulate an aqueous interior, have become the preferred structure for use in most applications. There has been great effort devoted to using liposomes as model membranes and, morerecently, as drug delivery systems and microreactors for specialized chemistry. The vesicle suspension of cationic surfactants was also prepared, characterized TEM and investigated by DRS method. The effect of composition, salt content, solvent etc. to vesicle was determined by DRS.