Reactive layer-by-layer deposition of poly(ethylene imine) and a precursor of TiO2: influence of the sodium chloride concentration on the film growth, interaction with hexacyanoferrate anions, and particle distribution in the film.

Films prepared according to a layer-by-layer (LBL) manner find increasing importance in many applications such as coatings with dedicated optical or electronic properties, particularly when including nanomaterials. An alternative way to prepare such hybrid layer-by-layer coatings is to perform sol-gel chemistry in a layer-by-layer manner. In this article, we highlight the importance of the NaCl concentration as a parameter to control the growth as well as the properties of LBL films made from poly(ethylene imine) as the organic counterpart and titanium IV (bisammoniumlactato)dihydroxyde ([Ti(lac)(2)(OH)(2)](2-)) as the precursor of TiO(2). An increase in the sodium chloride concentration leads to the faster growth of the film and to a decrease in the number of hexacyanoferrate anions remaining in the film after a buffer rinse. This may be due to a progressive increase in the fraction of negatively charged TiO(2) as suggested by transmission electron microscopy. In the presence of 0.5 M NaCl, the fraction of TiO(2) is close to 60% in mass. As a surprising finding, the films produced from 0.15 M NaCl are not homogeneously filled with TiO(2) even if the film is produced in an LBL fashion. The increased concentration of TiO(2) at the film-solution interface could constitute a barrier for the incorporation of the negatively charged redox probe.

Polyelectrolyte multilayer films: A sponge for insulin?

Considering restrictive diabetes treatments, new insulin administration strategies constitute a huge medical challenge. This study aimed at developing a new support for insulin reservoirs, using polyelectrolyte multilayer films (PEM films), and thus studying this hormone release in a progressive manner. At first, insulin was loaded in (PDADMAC-PAA)n films, by immerging them for various periods of time (2, 14 and 24 h) in a solution containing this protein. Confocal laser scanning microscopy (CLSM) revealed that insulin-FITC could diffuse inside the film with a bigger concentration in the upper part of the film (after 2 and 14 h in contact with the polypeptide solution), and then in the whole film (after 24 h) from a solution at pH=4.3 (below insulin's isolelectric point). Environmental scanning electron microscopy (ESEM) and CLSM showed that the film swells upon insulin loading. We finally investigated the insulin release by ATR-FTIR spectroscopy. It revealed that a loaded (PDADMAC-PAA)15 film, immerged in distilled water, showed no measurable insulin release. In contrast, a slow unloading was observed in the presence of a NaCl 0.15 M solution (salinity close to physiological serum). This study could open the route for a new way of insulin delivery.

Composite films of polycations and TiO2 nanoparticles with photoinduced superhydrophilicity.

We apply herein the reactive layer-by-layer (LBL) spray deposition of a polycation (polyethyleneimine, PEI) and a water soluble initiator of titanium dioxide [Ti(IV) bis(ammoniumlactato)dihydroxide, TiBisLac] to produce thin hybrid films containing PEI and nearly monodisperse TiO(2) anatase nanoparticles. The thickness of these coatings can be finely adjusted by either changing the number of deposition steps or the TiBisLac concentration. These films display intense absorption in the UV range and nearly full transparency above 365 nm and they also display photoinduced superhydrophilicity. These coatings can be produced either by reactive LBL spray deposition or reactive LBL dipping and may offer a wide range of applications from biology, as antibacterial coatings, to photoactive materials.