Three-dimensional colloidal crystal films with large-area and robust mechanical properties can be successfully fabricated via the roomtemperature film-formation of ''soft'' polymer spheres latex with the aid of nanosilica particles.

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BACKGROUND: Polyacrylate/silica nanocomposite latexes have been fabricated using blending methods with silica nanopowder, in situ polymerization with surface‐functionalized silica nanoparticles or sol–gel processes with silica precursors. But these approaches have the disadvantages of limited silica load, poor emulsion stability or poor film‐forming ability. RESULTS: In this work, poly[styrene‐co‐(butyl acrylate)‐co‐(acrylic acid)] [P(St‐BA‐AA)]/silica nanocomposite latexes and their dried films were prepared by adding an acidic silica sol to the emulsion polymerization stage. Morphological and rheological characterization shows that the silica nanoparticles are not encapsulated within polymer latex particles, but interact partially with polymer latex particles via hydrogen bonds between the silanol groups and the COOH groups at the surface of the polymer particles. The dried nanocomposite films have a better UV‐blocking ability than the pure polymer film, and retain their transparency even with a silica content up to 9.1 wt%. More interestingly, the hardness of the nanocomposite films increases markedly with increasing silica content, and the toughness of the films is not reduced at silica contents up to 33.3 wt%. An unexpected improvement of the solvent resistance of the nanocomposite films is also observed. CONCLUSION: Highly stable P(St‐BA‐AA)/silica nanocomposite latexes can be prepared with a wide range of silica content using an acidic silica sol. The dried nanocomposite films of these latexes exhibit simultaneous improvement of hardness and toughness even at high silica load, and enhanced solvent resistance, presumably resulting from hydrogen bond interactions between polymer chains and silica particles as well as silica aggregate/particle networks. Copyright © 2009 Society of Chemical Industry

In a recent paper, 1 there was our previous paper 2 that should have been referenced in the Introduction. To make the readers understand the two papers more clearly, there are big differences between these two papers which could be briefly summarized as follows: 1. The preparation methods for nanocomposite latex were totally different. In the J. Phys. Chem. B paper, 2 the nanocomposite latex was synthesized by the in-situ emulsion polymerization method. Nanosilica particles, monomers, initiator, and water were mixed first, and then the polymerization was carried out to get the nanocomposite latex; In the Macromolecules paper, 1 the nanocomposite latex was prepared by the blending method. That is, monomers, initiator, and water were mixed first, and then the polymerization was carried out to synthesize polymer latex; this latex was then blended with nanosilica particles to get the nanocomposite latex. In the in-situ emulsion polymerization method, the Si-OH groups of the nanosilica surfaces could react with acrylic acid under reaction temperature first and then the CdC groups of acrylic acid on the surfaces of nanosilica particles polymerized with butyl acrylate and styrene. But this reaction did not happen in the blending method. As a result, two different preparation methods caused two nanocomposite latexes with different extent of interaction between nanosilica particles and polymer beads: the nanocomposite latex from the in-situ method should have much stronger interaction between nanosilica particles and polymer beads than that from the blending method. 2. The structures and properties of the obtained ordered porous films are different. It is the different extent of interaction that the nanocomposite latex from the blending method formed the ordered porous structure much more easily than that from the in-situ method. The former formed the ordered porous structure in the whole bulk, namely, three-dimensionally ordered porous structure. But for the film from in-situ method, the ordered porous structure was only observed on the surface of the film, namely, two-dimensionally ordered porous structure. Just due to the big difference in structure, the three-dimensionally ordered porous structure in the Macromolecules paper can display different colors, while the two-dimensionally ordered porous structure in the J. Phys. Chem. B paper cannot. In fact, for optical crystals, the three-dimensionally ordered structure is more important than the two-dimensionally ordered structure. Moreover, the three-dimensionally ordered porous structure has more potential applications than the two-dimensionally ordered porous structure. References and Notes (1) You, B.; Shi, L.; Wen, N.; Liu, X.; Wu, L.; Zi, J. Macromolecules 2008, 41, 6624-6626. (2) You, B.; Wen, N.; Zhou, S.; Wu, L.; Zhao, D.