Direct liquid crystal templating of mesoporous silica

The work described in this thesis is concerned with the development of orderedmesoporous silicas by direct templating from lyotropic liquid crystal phases of thesurfactants Pluronic PI23, Pluronic F127, CTAB and Brij 78. The factors affecting theregularity, morphology, pore diameter and wall thickness of the templated mesoporoussilicas were examined by exploring the reaction composition space and plotting thestructural properties on TMOS/surfactant/water ternary diagrams. The silicas werestudied 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 phaseof CTAB were prepared from fumed silica/CTAB/water/NaOH mixtures underhydrothermal conditions. The mesostructure showed very good long-range order andvery narrow pore size distributions, with -3.4 mn diameter pores and -1.4 mn thickwalls.In addition, mesoporous silicas were prepared using a sol-gel route fromTMOS/surfactant/0.5 M HCl(aq) mixtures at 45°C. The central regions of the ternarydiagrams of these mixtures were explored. Using Pluronic PI23, mesoporous silicas withhexagonal (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 poremorphologies were formed with pore diameters in the range of 2.9 - 4.5 mn and 4 - 1 0nm for Brij 78 and Pluronic F127 respectively.The mesoporous silicas produced via the sol-gel route had the most ordered structureswith a TMOS:water molar ratio in the range of 1:5 to 1:7, leaving little water presentafter hydrolysis. For ordered silicas, the sum of the pore diameter and wall thickness isroughly constant, where the pore diameter decreases with increasing TMOS content anddecreasing 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 23and F127 micelles, allowing the templating of mesoporous silica with pore diameters upto 14 nm