NOVELTY - Preparation (P1) of a thin film composite involves applying to a porous support a liquid phase containing at least one polyfunctional acyl halide having at least two acid halide groups in an inert solvent; and contacting the porous support with a second fluid phase comprising at least one polyfunctional amine having at least two amine functional groups, so as to form a thin film composite.    USE - For preparation of thin film composite, which is used in osmotic processes, gas separation, nanofiltration, reverse electro dialysis and/or fuel cells; and for desalination of water or pressurization of water for power production (claimed).    ADVANTAGE - The process allows the use of highly hydrophilic supports previously not usable for the formation of thin film composites. The thin film composite exhibits excellent selective permeability properties and therefore has applications as osmotic membranes, e.g. reverse osmosis membranes and pressure retarded osmosis, and in gas separation in general. The process produces improved thin film composite (TFC) membranes, which show very positive osmotic properties. The produced TFC membranes have a lower flow resistance of water on the interface between the two layers because the selective membrane faces the more hydrophilic surface towards the support. The TFC membrane exhibits improved fouling properties.    DETAILED DESCRIPTION - Preparation (P1) of a thin film composite involves applying to a porous support a first liquid phase containing at least one polyfunctional acyl halide having at least two acid halide groups in an inert solvent; and contacting the porous support with a second fluid phase comprising at least one polyfunctional amine having at least two amine functional groups, so as to form a thin film composite, where the support has pores small enough for sufficient immobilization of first reactant so that a polyamide film is formed when the second reactant is contacted with the support; and the solvent or solvent mixture used for two liquid phases is immiscible, miscible or is same for the two liquids, where each solvent dissolves the species. INDEPENDENT CLAIMS are included for the following:    (1) a thin film composite obtainable by the process (P1); and    (2) desalination of water or pressurization of water for power production involving passing water through the thin film composition.