Amphiphilic Colloidal Particles Prepared Via Concentrated Emulsions

Amphiphilic particles can be prepared by jointing hydrophilic polymer chains and hydrophobic chains. The jointing methods include blocking, grafting, and random copolymerization. The amphiphilic particles prepared by these methods contain hydrophilic and hydrophobic chains combined by chemical bonds. The jointing portions, however, are neither hydrophilic nor hydrophobic. Thus, the amphiphilicity of the particles is reduced. In order to overcome this shortcoming, a novel and simple method to prepare amphiphilic colloidal particles with hydrophobic core/hydrophilic shell is proposed.In the first step, the individual polystyrene (PS) colloidal particles (Fig. 1) were obtained by using a concentrated emulsion as precursor. Divinyl benzene (DVB) was employed as a crosslinker, and AIBN, an initiator. Sodium dodecyl sulfate (SDS) was used as the emulsifier and water as the continuous phase.Subsequently, amphiphilic monomer, acrylamide (AM) was introduced into the polymerized concentrated emulsion with N, N -methylenebisacrylamide (DMA) as its crosslinker, water as a diluent and Ferrous Sulfate (FS) a reductant initiator. FS and Cumene Hydroperoxide (CHPO), which was introduced into the PS core particles during the first step, formed an ox-reduction initiator system. CHPO diffused into the surface of the PS core, reacted with the FS in the continuous phase, and released free radicals. Under the proper conditions, polyacrylamide shells could encapsulate PS cores, and the shells possessed a porous (Fig.2) or wrinkle structure (Fig.3).A notable feature of the work is that no copolymer jointing portions exist. The hydrophobic cores were just encapsulated by hydrophilic shells.The porous shell (Fig.2) ensured the hydrophobic cores accessible to the outside media. As a result, such particles could be dispersed in both water and organic solvents. That is to say, they were compatible with both polar and nonpolar solvents.Scanning electron microscope (SEM) photographs confirmed the shell structure. The amphiphilicity of the particles was characterized by their water and diesel oil absorbabilities.It was found that polymerization recipes and reaction conditions, such as the amount of ox-reduction initiator, diluent, hydrophilic monomer, DAM and the temperature of polymerization could adjust the structure and thickness of the hydrophilic shells.The stability of the concentrated emulsions was studied. Other monomer, such as methyl methacrylate, was also employed.Such amphiphilic colloidal particles can be used widely in drug delivery and catalytic processes.