Surface-Dependent Effect of Functional Silica Fillers on Photocuring Kinetics of Hydrogel Materials Mariola Sadej, 1 Ewa Andrzejewska, 1 Beata Kurc, 1 Hubert Gojzewski, 2,3 Teofil Jesionowski 1 1 Faculty of Chemical Technology, Poznan University of Technology, Berdychowo 4, PL-60965 Poznan, Poland 2 Faculty of Technical Physics, Poznan University of Technology, Nieszawska 13A, PL-60965 Poznan, Poland 3 Department of Theory & Bio-Systems, Max Planck Institute of Colloids and Interfaces, Am M€ uhlenberg 1 Golm, D-14476 Potsdam, Germany Correspondence to: E. Andrzejewska (E- mail: ewa.andrzejewska@put.poznan.pl) Received 6 July 2014; accepted 10 September 2014; published online 00 Month 2014 DOI: 10.1002/pola.27412 ABSTRACT: Two types of silica: precipitated (P, prepared in non-polar media, a new type, submicrometer sized) and fumed (F, nanosized), both unmodified and surface modified are investigated as functional fillers for potential applications in nanocomposites with poly(2-hydroxyethyl methacrylate) matrix. Special attention is paid to the kinetics of composite formation in an in situ photopolymerization process. Silica- containing formulations polymerize faster; this effect is much stronger for silica P having much larger particle size than silica F. Surface treatment leads to further acceleration of the poly- merization in case of silica P but to retardation in case of silica F; the effect of modification of the filler surface on properties of composites is different for each of the silicas. The obtained results are discussed in terms of effects of curvature of silica particles, surface properties, solvation cell, interphase region, viscosity changes, and morphology of the resulting compo- sites. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 00, 000–000 KEYWORDS: interfaces; kinetics (polym.); nanocomposites; pho- topolymerization; silica INTRODUCTION A new class of materials based on organic and inorganic species combined at a nanoscale level has attracted significant attention during the last decade. 1 These materials, so-called nanocomposites or hybrid materials, exhibit novel and excellent properties, e.g. mechanical, 2 ther- mal, 2–4 electrical, 5,6 magnetic, 5,7 optical, 5 and catalytic. 8 The resulting properties of the nanocomposites are influenced by the filler properties as well as properties of their surface. The chemical, pharmaceutical, cosmetic, and food processing industries need a vast range of highly dispersed and pow- dered substances. Among them of considerable importance are the synthetic silicas that can be produced in a number of chemical processes. 9–12 The spherical shape of the particles can be achieved in many ways, e.g. by the use of aerosols. The particles obtained in this way have surface area high and wide particle size distribution. 13–15 Another popular method of silica production is by combustion of silicon tetra- chloride at 1200  C. The product of oxidation/reduction is of high purity, made of nanosized particles with developed sur- face area. There is also a method based on the preparation of two emulsions and direct precipitation of silica from one of them: then the product has spherical shape particles of different degree of polydispersity and of a wide range of pos- sible applications. 16–19 Silica is also produced by hydrolysis/ condensation reaction of tetraalkoxysilanes, commonly known as St€ ober method. 16–18 New methods are continu- ously sought to get products of improved quality and target properties. One of the recently proposed methods is that of precipitation of silica from the emulsion system by introduc- ing mineral acids to solutions of sodium silicate. 19–21 To improve the adhesion between the polymer and the nano- filler often modification of the filler surface is needed. 22–24 The modifying groups can be inactive, leading e.g. to hydro- phobization of the surface and to interaction with the poly- mer matrix only through secondary forces or reactive (like methacryloxy) which results additionally in covalent bonding between the filler and the polymer matrix. Poly(2-hydroxyethyl methacrylate) (poly-HEMA) belongs to the class of polymers known as hydrogels. 25–28 The unique properties of hydrogels stem from a combination of the properties of the polymer phase and aqueous phases, because they adsorb large amounts of water or biological fluids without dissolutions. Due to the high capability of water uptake, nontoxicity, and favorable compatibility to tis- sues and blood, poly-HEMA is an attractive biomaterial for V C 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 00, 000–000 1 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE