*2.1. Sol Synthesis*

All chemicals were purchased from Aldrich and used without further purification. Two variations of Tween® non-ionic long chain surfactants were used as pore directing agents for sol-gel processing; Tween® 20 and Tween® 40. Each surfactant was added in varying concentrations as listed in Table 1. Preparation of the TiO2 sol involved initial incorporation of the surfactant into the solvent, isopropanol (69 mL) with vigorous stirring until a homogeneous suspension was obtained. Acetylacetone (0.61 mL) was then added dropwise with continuous stirring, to act as a stabilising agent in order to control the speed of the hydrolysis and subsequent condensation reactions. The titania precursor, titanium tetraisopropoxide (TTIP, 6 mL) was then added dropwise to the solution with continuous stirring. The resulting transparent solution was stirred for a further 30 min before adding acetic acid (6.86 mL) dropwise. The solution was stirred for an additional 30 min, and then the sol was ready for use in dip-coating. The molar ratio of surfactant/TTIP/acetylacetone/isopropanol/acetic acid was *R* 0.2:0.06:9:0.04, where the surfactant concentration *R* was varied from 0 to 0.0006 mol·dm<sup>í</sup><sup>3</sup> . Sols were typically transparent, pale yellow in colour, homogeneous and stable for several weeks.
