Direct liquid crystal templating of mesoporous silica

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

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2003

Author dc:creator

• Gordon-Smith, Tobias James

Advisor dc:contributor.advisor

• Attard, George