Preparation of colloidosome microcapsules based on particle stabilized photo-crosslinkable Pickering emulsions

Abstract

In this work, we studied the preparation and emulsification behavior of nanoparticles with photo-sensitive polymer brushes and presented a method for the preparation of novel colloidosome microcapsules based on single Pickering emulsion template, which is stabilized by surface-modified silica nanoparticles with photodimerizable coumarin group. Firstly, silica nanoparticles were self-made by using a stöber method with a diameter of about 180 nm, following aminated by 3-aminopropyltriethoxysilane (APS) and further modified by 2-bromo-2-methylpropionyl bromide, endowing these nanoparticles with ATRP-initiator reactive group. After that, silica nanoparticles with photo-sensitive polymer brushes (SiO2-PMMA-PCMA) were obtained through graft reaction of methyl methacrylate (MMA) and 7-(2-methacryloyloxyethoxy)-4-methylcoumarin (CMA) monomers (with a molar fraction of 4:1) onto silica nanoparticles by surface-initiated atom transfer radical polymerization (SI-ATRP) method. Here, CMA was synthesized via a two-step method and was detected by UV-visible spectrophotometer. Secondly, the as-prepared hydrophobic SiO2-PMMA-PCMA nanoparticles were dispersed in 2 mL of toluene with a ultrasonic for 5 min (with an interval of 30 s per min), then 0.5 mL of deionized water was rapidly added, afterwards, water-in-oil type Pickering emulsions were prepared by hand-shake for 3 min. Finally, colloidosome microcapsules were produced through cross-linking reaction of the coumarin group of CMA initiated by UV irradiation, in this step, the SiO2-PMMA-PCMA nanoparticles were locked. The average size and size distribution of as-synthesized Pickering emulsion droplets and colloidosomes were observed with an optical microscope. The results show that both CMA and SiO2-PMMA-PCMA nanoparticles can be initiated to cross-link through the dimerization of the coumarin groups of CMA from different SiO2-PMMA-PCMA nanoparticles via UV irradiation, the dimerization rate of CMA reached about 80% in 6 min and the UV absorption peak of coumarin group of SiO2-PMMA-PCMA nanoparticles was blue-shifted. Besides, the Pickering emulsion droplets can be stored for a long time without breaking up and the average size of as-produced colloidosome microcapsules were about 170 μm. In theory, this method can be scaled up to produce large quantity of colloidosomes. © 2012 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.