Direct liquid crystal templating of mesoporous silica

The work described in this thesis is concerned with the development of ordered mesoporous silicas by direct templating from lyotropic liquid crystal phases of the surfactants Pluronic PI23, Pluronic F127, CTAB and Brij 78. The factors affecting the regularity, morphology, pore diameter and wall thickness of the templated mesoporous silicas were examined by exploring the reaction composition space and plotting the structural properties on TMOS/surfactant/water ternary diagrams. The silicas were studied using the complementary techniques of small angle X-ray diffraction, transmission electron microscopy and N? adsorption isotherms. Mesoporous silicas with hexagonal (H,) pore morphologies templated from the Hi phase of CTAB were prepared from fumed silica/CTAB/water/NaOH mixtures under hydrothermal conditions. The mesostructure showed very good long-range order and very narrow pore size distributions, with -3.4 mn diameter pores and -1.4 mn thick walls. In addition, mesoporous silicas were prepared using a sol-gel route from TMOS/surfactant/0.5 M HCl(aq) mixtures at 45°C. The central regions of the ternary diagrams of these mixtures were explored. Using Pluronic PI23, mesoporous silicas with hexagonal (Hi) pore morphologies were formed with pore diameters in the range of 5 - 10 nm. With Brij 78 and Pluronic F127, mesoporous silicas with 3d cubic pore morphologies were formed with pore diameters in the range of 2.9 - 4.5 mn and 4 - 1 0 nm for Brij 78 and Pluronic F127 respectively. The mesoporous silicas produced via the sol-gel route had the most ordered structures with a TMOS:water molar ratio in the range of 1:5 to 1:7, leaving little water present after hydrolysis. For ordered silicas, the sum of the pore diameter and wall thickness is roughly constant, where the pore diameter decreases with increasing TMOS content and decreasing surfactant content there is commensurate increase in wall thickness. Finally, 1,3,5 trimethyl benzene was used to swell the hydrophobic core of Pluronic PI 23 and F127 micelles, allowing the templating of mesoporous silica with pore diameters up to 14 nm.EThOS - Electronic Theses Online ServiceGBUnited Kingdo