Tuning the selectivity and sensitivity of mesoporous dielectric multilayers by modifiying the hydrophobic-hydrophilic balance of the silica layer

We investigate the possibility of tuning the selectivity and sensitivity of SiO2/TiO2 mesoporous dielectric multilayers for the adsorption of analytes with different chemical polarities. The hydrophilic-hydrophobic balance of the mesoporous SiO2 layer was controlled by one-pot co-condensation of mixtures of methyltriethoxysilane (MTES) and tetraethyl orthosilicate (TEOS) in variable contents. Infrared spectroscopy analysis combined with water contact angle measurement confirmed the gradual increase of the hydrophobic behavior of the hybrid silica layer obtained by increasing the MTES content, without losing its porosity. Hybrid silica layers included into the dielectric multilayer material enabled controlling the surface properties of the Bragg stacks. UV-visible spectroscopy showed a Bragg peak red-shift. This shift depends on the affinity of the adsorbed molecule toward the functional groups present on the surface of the constituting materials. This procedure enabled the dramatic change of the adsorption properties of the mesoporous dielectric multilayer and correspondingly the optical response of the photonic crystal.