Aerosol flame technology has been used for decades to fabricate on an industrial scale a range of inorganic (nano)particles, including carbon blacks, titania, and fumed silica. Nevertheless, the high local temperatures inherent to this technique prevent direct organic functionalization or loading by organic derivatives, which is essential in many applications to achieve specific properties and optimal dispersion within an organic matrix. We describe herein a novel eco-friendly UV process allowing a single-step manufacture of high-value silica and organosilica particles at ambient temperature. Atomized alkoxysilane precursor droplets are produced within an annular photoreactor including 6 fluorescent UV lamps (maximum emisson: 312 nm), and photocondensed continuously after a 1 min single pass. Droplet condensation is controlled by the release of a photoacid catalyst localized in the droplets, affording spherical polydisperse powder particles with a mean diameter ranging around 400-700 nm. In the presence of amphiphilic block copolymer template, a silica/surfactant mesostructured film was deposited using this UV aerosol technology, resulting in a wormlike mesoporous structure after calcination.

Designing sustainable and industrially viable processing methods to synthesize ordered mesoporous films is a necessary condition to tap their full potential of applications. In order to respond to this challenge, well-established photoacid-catalyzed sol-gel photopolymerization has been harnessed to prepare large (> 100 cm 2) and micrometer-thick porous silica films possessing a 2D hexagonal mesostructure. Our UV irradiation system consists of two inexpensive and low radiant power fluorescent UV tubes (3 mW cm-2 , 280-380 nm) enclosed in a hygrometric chamber. Precise conditions to promote copolymer/silica hybrid film mesostructuration have been determined as regards relative humidity, film thickness and templating agent concentration. The mesostructured films have been analyzed using an extensive range of techniques including electron microscopy, grazing-incidence small-angle X-ray scattering (GISAXS), and N 2 sorption measurements, and solidstate NMR spectroscopy. Mesoporous silica films with a specific surface area up to 314 m 2 g-1 have been achieved with a very low level of microporosity. Coupling of X-ray diffraction (XRD) and FTIR spectroscopy has enabled to shed light into the photoinduced self-assembly mechanism.

Abstract. We describe a novel combination of orthogonal reactions based on UV-driven thiol-ene and alkoxysilyl condensation reactions to form a single-step route toward thioether-bridged silsesquioxane films. Our chemical strategy consists of using two bifunctional (meth)acrylate (E) and propanethiol (T) trimethoxysilyl precursors containing two complementary functional moieties for thiol-ene coupling and sol-gel process. The reaction kinetics revealed that c.a. 85% of thiol and ene conversions were consumed concomitantly. Meanwhile, a complete hydrolysis was accomplished, affording ultimately a high degree of condensation (81%). Emphasis was placed on differences of mechanical properties between sol-gel hybrids resulting from thiol-ene reaction (E-T mixture) and ene homopolymerization (E only) using scratch test measurements. For the methacrylate system, the formation of thioether linkages within a vitreous silica network emerged as a useful strategy for the formation of a uniform, low-stress and flexible crosslinked hybrid structure. Enhanced mechanical properties were manifested by an expanded elastic domain, and better resistance to cracking. Moreover, there are clear indications that mechanical properties can be easily tuned upon varying the ratio of the two hybrid precursors.

We describe a fast photocalcination process to prepare highly ordered silica mesoporous films through the use of a low-pressure amalgam arc (λ: 185 / 254 nm). Because radiant power is 2-3 times higher than conventional low-pressure UV lamps, the elimination of the PEO-b-PPO-b-PEO copolymer template in the 2D hexagonal hybrid film has been completed within 50 min, without damage to the mesostructure. The degradation kinetics are impacted by film thickness and irradiance, but hardly copolymer concentration. Compared to thermocalcination, a narrower pore size distribution and lower energy consumption have been found. Photodegradation mostly originates from a photoablation mechanism induced by radiation at 185 nm, while oxidation due to photogenerated reactive oxygen species plays a minor role. Photocalcination has been combined with an initial photoinduced mesostructuration (detailed in Part 1: Microporous Mesoporous Mater., 257 (2017) 42-50), resulting in an unprecedented "all UV" method to mesoporous silica films. The final process relies on dual wavelength photoactivation: UV B to form the hybrid copolymer/silica network, a flash intermediate thermal consolidation, and UV C to decompose the copolymer chains.

In the context of increasing use of nanostructured materials, finding innovative characterization methods able to assess precisely the level of ordering is essential. To this end, a range of model organic-inorganic copolymer-silica films is synthesized using poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) amphiphilic triblock copolymer as supramolecular template. Upon increasing copolymer concentration (10 -100 wt%), the order can be gradually enhanced from short-range to long-range as proved by conventional techniques such as X-ray diffraction and electron microscopy. To evaluate the level of mesoscopic organization, the same series of samples is also analyzed by solid-state nuclear magnetic resonance (NMR) spectroscopy. The disorder-to-order transition is probed by 1 H and 13 C magic angle spinning NMR spectra through the increase in chemical environment uniformity and chain mobility respectively, which both result from the self-assembly mechanism. 1 H NMR relaxation measurements (T 2 ) using low-field NMR spectroscopy are instrumental to identify the threshold template concentration where ordering takes place.