Independent Control of Adhesive and Bulk Properties of Hybrid Silica Coatings on Polycarbonate

International audience; Transparent polymers are widely used in many 9 applications ranging from automotive windows to micro-10 electronics packaging. However, their intrinsic characteristics, 11 in particular their mechanical properties, are significantly 12 degraded with exposure to different weather conditions. For 13 instance, under humid environment or UV-irradiation, 14 polycarbonate (PC) undergoes depolymerization, leading to 15 the release of Bisphenol A, a molecule presumed to be a 16 hormonal disruptor, potentially causing health problems. This 17 is a serious concern and the new REACH (Registration, 18 Evaluation, Authorization and Restriction of Chemical 19 substances) program dictates that materials releasing Bisphenol A should be removed from the market by January 1st, 2015 20 (2012-1442 law). Manufacturers have tried to satisfy this new regulation by depositing atop the PC a dense oxide-like protective 21 coating that would act as a barrier layer. While high hardness, modulus, and density can be achieved by this approach, these 22 coatings suffer from poor adhesion to the PC as evidenced by the numerous delamination events occurring under low scratch 23 constraints. Here, we show that the combination of a N 2 /H 2-plasma treatment of PC before depositing a hybrid organic-24 inorganic solution leads to a coating displaying elevated hardness, modulus, and density, along with a very high adherence to PC 25 (> 20 J/m 2 as measured by double cantilever beam test). In this study, the sol-gel coatings were composed of hybrid O/I silica 26 (based on organoalkoxysilanes and colloidal silica) and designed to favor covalent bonding between the hybrid network and the 27 surface treated PC, hence increasing the contribution of the plastic deformation from the substrate. Interestingly, double-28 cantilever beam (DCB) tests showed that the coating's adhesion to PC was the same irrespective of the organoalkoxysilanes/ 29 colloidal silica ratio. The versatility of the sol-gel deposition techniques (dip-coating, spray-coating, etc.), together with the 30 excellent mechanical properties and exceptional adherence of this hybrid material to PC should lead to interesting new 31 applications in diverse fields: optical eyeglasses , medical materials, packaging, and so forth. 32