ABSTRACT
A simple double thin-film coating-based device is proposed to quantify the ethanol content in humid air featuring a 10 ppm resolution and spanning a dynamic range from 0 to 1000 ppm. The transduction involves the measurement of the direct optical reflection intensity, changing upon refractive index variations induced by water and ethanol adsorption within the coatings. The first thin-film coating is a microporous methyl-functionalized, silica xerogel material more sensitive to alcohol, and the second one is a microporous pure silica xerogel material more sensitive to water. The precision of the sensor is achieved through a mathematical treatment applied on the time resolved adsorption period. Reflection signals of both the ethanol- and water-sensitive coatings are taken into account in the treatment to correct for differences in ambient conditions (temperature, relative humidity, presence of volatile organic compounds) within the same chamber previous to data analysis, which corresponds to realistic operating conditions. As the adsorption mechanism is governed by molecular dynamic equilibrium, these sensors are fast and instantaneously regenerated in ambient air. The sensor is easy to assemble and was reusable for a period exceeding 1 year (maximal tested time).
ABSTRACT
Metal oxide (MOX) surface nanopatterns can be prepared using Soft-Nano-Imprint-Lithography (soft-NIL) combined with sol-gel deposition processing. Even if sol-gel layers remain gel-like straight after deposition, their accurate replication from a mould remains difficult as a result of the fast evaporation-induced stiffening that prevents efficient mass transfer underneath the soft mould. The present work reports a detailed investigation of the role of the xerogel layer conditioning (temperature and relative humidity) prior to imprinting and its influence on the quality of the replication. This study is performed on four different systems namely titania, alumina, silica and yttria-stabilised zirconia. We demonstrate that the quality of the replica can be considerably improved without the use of sacrificial stabilising organic agents, but by simply applying an optimal aging at controlled temperature and relative humidity specific to each different reported MOX. In each case this condition corresponds to swelling the initial xerogels of around 30%vol by water absorption from humidity. We show that this degree of swelling represents the best compromise for sufficiently increasing the xerogel fluidity while limiting the shrinkage upon final thermal curing.
ABSTRACT
A straightforward crack-patterning method is reported allowing the direct formation of periodic cracks in metal-organic framework (MOF) nanoparticle films during dip-coating deposition. The crack propagation and periodicity can be easily tailored by controlling the evaporation front and the withdrawal speed. Several MOF-patterned films can be fabricated on large surfaces and on several substrates (flat, curved or flexible) including the inner surface of a tube, not achievable by other lithographic techniques. We demonstrate that the periodic cracked arrays diffract light and, due to the MOF sorption properties, photonic vapor sensors are fabricated. A new concept of "in-tube", MOF-based diffraction grating sensors is proposed with outstanding sensitivity that can be easily tuned "on-demand" as function of the desired detection range.
