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The surface morphology of hollow silica microspheres has influence on their applications. After a thorough investigation of the deposition of silica nanoparticles on polystyrene (PS) beads and the surface morphology and texture of the resultant hollow silica shells with scanning electron microscopy, transmission electron microscopy, and N2-sorption measurements, the influence of surfactant [cetyltrimethylammonium bromide (CTAB)] concentration on the surface morphology of hollow silica microspheres templated by PS beads is explained. Previously, CTAB was believed to turn the surface charge of PS beads from negative into positive so that negatively charged silica could be deposited on the PS template. Here, we show CTA+ cations preferentially assemble with silica species to form silica-CTA+ composite nanoparticles. Since the zeta potential of silica-CTA+ composite nanoparticles is smaller than that of pure silica nanoparticles, these composite nanoparticles encounter less repulsion when they are deposited on the surface of PS beads and close to each other. As more CTAB is added, the silica-CTA+ nanoparticles are less negatively charged, and more compact and smooth hollow silica microspheres are obtained. [ABSTRACT FROM AUTHOR]

Abstract: The nature of core template has significant influences on the synthesis of hollow silica microspheres via the polystyrene (PS) beads templating route. Our present study indicates that the silica forming medium determines whether a surfactant is needed in the synthesis. It is shown that in a medium which itself gives discrete silica microspheres, hollow silica microspheres can only be templated by PS beads with the addition of cetyltrimethylammonium bromide surfactant. In contrast, in a medium which itself generates highly aggregated silica microspheres, hollow silica microspheres successfully templated by PS beads without any cationic surfactant. A unified mechanism for the formation of hollow silica shells with and without the surfactant is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Cage-like hollow silica microspheres composed of mesoporous silica nanoparticles and macroporous interparticle voids were fabricated via the latex–surfactant dual templates route, simply by controlling the surfactant additions below its critical micelle concentration. The surface area, pore volume increase, and both the mesopore and macropore sizes decrease with the increase in surfactant amount. The surfactant cations preferentially assemble with negatively charged silica species generated by the hydrolysis and condensation of tetraethyl orthosilicate to form composite silica–surfactant nanoparticles. The electrostatic repulsion between the silica–surfactant composite nanoparticles and negatively charged polystyrene (PS) beads is smaller than that between surfactant–free silica and PS, favoring the deposition of composite nanoparticles on the surface of PS template. In the meantime, the deposited nanoparticles also have reduced repulsion from their neighbors, favoring their bridging to form silica shells. The more the surfactant is used, the less the repulsion exists among the composite particles and the smaller the interparticle macroporous voids are. [Copyright &y& Elsevier]