Porosity control and surface sensitivity of titania/silica mesoporous multilayer coatings: applications to optical Bragg resonance tuning and molecular sensing

1D photonic defect structures based on colloidal porous frameworks: Reverse pore engineering and vapor sorption

“…A variety of modification schemes have been explored to enhance the response toward environmental changes including the variation of the morphology of the constituting layers such as porosity, size or shape of the building blocks [5,6,11,12]. The sensitivity of solegel derived architectures could thus be improved by the use of mesoporous oxides [7,13]. Another possibility is the fabrication of cavity structures whose symmetry is disrupted by a defect layer deposited either inside or on top of a regular BS (referred to as "sandwich" and "top" defect structure, respectively) [6,9,10,14].…”

Flexible metal–organic framework-based one-dimensional photonic crystals

“…2 With the change in wavelength of maximum reectance, the color changes depending on the thickness and associated RI caused by an ex-stimulus. Many efforts have been devoted for implementing functionality within 1DPC by the bottom-up assembly of tailor-made inorganic or hybrid materials, such as dielectric and conductive metal oxides, 4-7 sol-gel-based materials, [8][9][10] zeolites, 11 clays, [12][13][14] super-paramagnetic colloidal particles, 15,16 liquid crystals, 17,18 organic polymers, [19][20][21] and hydrogels. These features make 1DPCs excellent platforms for a variety of physical, chemical, and biological sensors.…”

Theoretical condition for transparency in mesoporous layered optical media: Application to switching of hygrochromic coatings

“…By suitably selecting layer thicknesses, porosities, and host materials with adequate refractive indexes, the Bragg peak is positioned in the visible range, producing a specific color, which then varies upon liquid infiltration or displacement. 12 Although this recipe has been applied many times, it has only been adapted recently for switching from transparency to coloration by tailoring porosities of adjacent layers in a mixed oxide Bragg stack. 13 Indeed, transparency corresponds to the peculiar case in which the effective refractive index contrast between adjacent layers cancels out and, consequently, the photonic crystal behaves as an effective homogeneous, transparent material.…”

“…Chemical surface functionalization can be used to make pores hydrophilic or hydrophobic in specific layers, and capillary attraction due to controlled pore size variations between adjacent layers can be used to promote infiltration of the liquid across the whole layer stack. 12 Electro-wetting can be used to force displacement of the liquid across adjacent layers. 17 Hygrochromic coatings (deposited on glass substrate) consisting of Bragg stacks (N ¼ 3 bilayers) of mesoporous oxides (L 1 layers: xTiO 2 (1 -x)Al 2 O 3 , L 2 layers: SiO 2 ) were fabricated by a modified sol-gel method according a procedure described previously.…”