Silica hollow particles (microcapsules) are one of the exciting subjects in materials chemistry in both basic and applied researches. Our previous paper reported a new preparation method of silica hollow particles having unique shell with macropore holes, which resemble diatomaceous earth in morphology, by interfacial reaction method using W/O/W emulsion as a reaction field. The preparation procedure of these unusual silica particles inherently requires the addition of suitable amounts of sodium polymethacrylate to the sodium silicate solution as the internal water phase of the W/O/W emulsion. For revealing the detailed mechanism of the formation of the shells with macropore holes, silica thin films using the similar solutions were examined as a model system of the interfacial reaction method, because both processes produce silica thin matrices such as shell or as film, respectively. Some silica thin films with macropore dents were formed by immersing dip-coated films of sodium silicate and sodium polymethacrylate into NH4HCO3 aqueous solution. FE-SEM/EXD observation indicated that the modest phase separation of sodium silicate and the polymethacrylate occurred in the dip-coated films before the immersion into NH4HCO3 solution. Moreover, infrared spectrometry studies revealed that the addition of sodium polymethacrylate to sodium silicate changed the bonds of the silicate significantly to promote the condensation. The experimental observations in these model studies strongly suggested that the shell with macropore holes in diatomaceous earth like silica hollow particles are formed by the removal of the aggregated and the phase-separated polymethacrylate during the formation of silica matrix of the particle shell. (C) 2011 Elsevier B.V. All rights reserved.