Dip-coating is a common liquid deposition technique employed in research, but also for industrial production, to obtain polymer, hybrid and inorganic thin layers of controlled thickness.During liquid deposition, the substrate withdrawal speed allows in principle an easy tuning of deposited film thickness (first modeled by Landau and Levich). Yet, experimentally, unexplained thickness irreproducibility or strong fluctuations of the sol-gel films are often observed when coating large substrates, which is a critical issue for optical coatings such as antireflective/reflective coatings. In this study, we pointed out for the first time that uncontrolled solvent relative pressure gradients (coming from solvent evaporation) are responsible for these thickness fluctuation issues. We investigated and quantified their impact for various solutions (of sol-gel or polymer), and pointed out that the solvent evaporation rate is not constant but strongly depends on the geometric configuration of the dip-coating experiment. From this understanding, we demonstrated how an accurate tuning of processing atmosphere can provide a very good control on layer thickness in the practical case of the deposition of anti-reflective water repellent coating. In a second example, we used this phenomenon for developing a very easy synthesis strategy leading to giant and controlled thickness gradient profiles.

Mesoporous silica nanoparticles (MSNs) have seen a fast development as drug delivery carriers thanks to their tunable porosity and high loading capacity. The employ of MSNs in biomedical applications requires a good understanding of their degradation behavior both to control drug release and to assess possible toxicity issues on human health. In this work, we study mesoporous silica degradation in biologically relevant conditions through in situ ellipsometry on model mesoporous nanoparticle or continuous thin films, in buffer solution and in media containing proteins. In order to shed light on the structure/dissolution relationship, we performed dissolution experiments far from soluble silicate species saturation. Via a complete decorrelation of dissolution and diffusion contributions, we proved unambiguously that surface area of silica vectors is the main parameter influencing dissolution kinetics, while thermal treatment and open mesoporous network architecture have a minor impact. As a logical consequence of our dissolution model, we proved that the dissolution lag-time can be promoted by selective blocking of the mesopores that limits the access to the mesoporous internal surface. This study was broadened by studying the impact of the organosilanes in the silica structure, of the presence of residual structuring agents, and of the chemical composition of the dissolution medium. The presence of albumin at blood concentration was found affecting drastically the dissolution kinetics of the mesoporous structure, acting as a diffusion barrier. Globally, we could identify the main factors affecting mesoporous silica materials degradation and proved that we can tune their structure and composition for adjusting dissolution kinetics in order to achieve efficient drug delivery.