The inner surfaces of a hexagonal mesoporous silica (HMS) are treated by chlorotrimethylsilane, either directly or through vapor or liquid endcapping. The directly treated inner surfaces have the highest effective interfacial tension, and the liquid endcapping treated surfaces have the largest accessible nanopore volume. The difference in the treatment results may be attributed to the distinct surface structures. (C) Koninklijke Brill NV, Leiden, 2011