A coated microcapillary column for high performance electrophoresis is disclosed. A preferred microcapillary includes a column; a universal sub-layer of coating material that has been highly crosslinked using a crosslinking agent and attached covalently or non-covalently to the column wall; and a variable top layer of a monomer or polymer, preferably crosslinked, attached to the sub-layer. The microcapillary preferably is prepared by covalently bonding a highly crosslinked siloxanediol sub-layer to the inner surface of the microcapillary wall and then causing a mixture of monomers or polymers to react in the bore of the microcapillary to form a top layer. The bilayer coating as used in a microcapillary prevents adsorption of solutes during electrophoresis and eliminates or controls electroosmotic flow. The disclosed coating may also be formed on other kinds of surfaces where similar surface modification is desired. The sub-layer, which can be formed from other siloxane derivatives having two nucleophilic end groups, e.q., diamino or dithiol, may be used independently, or as a base layer for bilayer or even multilayer surface formation.