Organosilicon-based membranes are promising candidates for the detection of harmful vapors [1], or separation of diluted VOC from water by pervaporation [2,3]. The adsorption of species at the surface of the membranes, as well as their absorption and diffusion within the membrane bulk are the two main mechanisms that condition performances. Nevertheless, the extreme surface is seldom known and very few models have been developed in order to describe sorption [4]. In the present study, we propose to present the first developments of our original methodology that combines experiments and atomistic calculations. PDMS-like thin films were deposited in a microwaves PECVD reactor [5] at low pressure from HMDSO precursor. The morphological and chemical characterization by SEM, FTIR, XRR, water contact angle, AFM and XPS, are completed by surface atomistic calculations that help to understand adsorption mechanisms of such membrane material as a function of the PECVD process parameters to interact with specific vapors for their detection and/or elimination by separation.