| This Ph.D. project addresses the structure, dynamics and some applications of amphiphilic block copolymers, poly(ethylene oxide)-poly(propylene oxide) poly(ethylene oxide) (known as Pluronic or Poloxamer).; We start from the small-angle neutron scattering (SANS) investigation of the micellization of block copolymers in solvents ranging in polarity, including water, formamide, as well as water/formamide, water/glycerol and water/ethanol mixtures of different water/cosolvent compositions and at different temperatures. We present the results on the critical micellization concentration and temperature, the thermodynamic parameters of micellization, and the micelle structure.; We then study the lyotropic liquid crystalline structures, formed by block copolymer micelles. The structures and the structure transitions are investigated at rest and under different shear patterns. The flow mechanism of block copolymer liquid crystal under shear is investigated.; Based on the understanding of the physical properties of Pluronic lyotropic liquid crystal, we investigate the applications of Pluronic block copolymers for drug delivery. We study the release kinetics of hydrophilic drug from Pluronic gel (Pluronic + water) and tablet (bulk Pluronic) and correlate the release mechanisms to drug diffusion and gel matrix erosion. The diffusion coefficient of drug in Pluronic gel and the erosion rate of the gel matrix are found to be two parameters critical for the drug release process. The effects of Pluronic gel concentration, different drug formulations, drug loading and release medium on drug release are studied. The objective of the application study is to optimize the performance of Pluronic gel as a controlled drug release substrate.; Finally, the transport phenomena of the solvent diffusion, block copolymer phase separation and dissolution are investigated. Mathematical models are established, from which we can obtain the concentration profile of the solvent in each observed lyotropic liquid crystal (LLC) phase, as well as the solvent diffusion coefficient and polymer dissolution rate to quantify the block copolymer dissolution and corresponding solvent diffusion process. The influences of the polymer molecular weight, block composition, LLC phase structure, and temperature on solvent diffusion & polymer dissolution process are also investigated. |
