Porous materials having a dual surface are disclosed. Also disclosed is a method for their preparation. An example of such a material is silica gel reacted with 1,1,1-trifluoropropyldimethylsilyl-N-methylacetamide and then, with N-trimethylsilyl-N-methylacetamide to give a dual treated material having 1,1,1-trifluoropropyldimethylsilyl groups on the exterior surface and trimethylsilyl groups on the porous interior surface.