Preparation And Emulsifying Performance Of Core Cross-Linked Amphiphilic Copolymer Colloidal Particles

Recently, the assembly of copolymer colloidal particles at liquid-liquid interface are extensively studied, amoug which the assembley behavior of colloidal particles at the oil-water interface to prepare Pickering emulsions has attracted much attention due to their potential applications in various areas. Therefore, sysmetically investigation of the assembly behavior of colloidal particles at the oil-water interfece has important research significance.Untill now most of the polymeric assemblies used as particulate emulsifiers were obtained by the solvent selected self-assembly of premade amphiphilic copolymers, which is tedious and time-consuming. Furthermore, the concentrations of the colloidal particles dispersion are raletively low. Thus, it is essential to develop an easy and scaled-up method to prepare multiple structures. In this paper, by using the direct polymerization reaction, responsive core cross-linked copolymer colloidal particles with surface activity were obtained and used as particulate emulsifiers. Furthermore, the influence of the structure of copolymer chains and colloidal particles on the surface activity and emulsifying performance of the copolymer colloidal particles were discussed. This work provides a convenient and feasible way to prepare effective particulate emulsifiers via the direct chemical reaction. Finally, the emulsifying properties of the copolymer colloidal particles in Pickering emulsion polymerization reaction system were discussed, extending the application of copolymer colloid particles.There are three parts in this paper:1. Preparation and emulsifying performance of core cross-linked colloidal particles PDVB@PASThe carboxyl-terminated poly(acrylic acid-r-styrene)-based macromolecular chain transfer agents(PAS-DMP) were synthesized using trithiocarbonate as an chain transfer agent, and then further applied in the RAFT polymerization of divinyl benzene to prepare the amphiphilic copolymer colloidal particles poly(divinyl benzene)@poly(acrylic acid-r-styrene)(PDVB@PAS) with crosslinked poly(divinyl benzene)(PDVB) as core and poly(acrylic acid-r-styrene)(PAS) as outer copolymer chains. The chemical structure of the macromolecular chain transfers were characterized by infrared spectroscopy(IR), proton nuclear magnetic resonance(1H-NMR), and gel permeation chromatography(GPC). Transmission electron microscope(TEM) and scanning electronic microscopy(SEM) confirmed the spherical-like morphology of the colloidal particles. Dynamic light scattering(DLS) and electrophoresis revealed the structure transition of the colloidal particles in response to pH change. The effects of the concentration of colloidal particles, salt concentration, pH in aqueous phase, volume ratio of oil to water, and oil type on the emulsifying performance of the colloidal particles were studied. The configuration of the colloidal particles on the oil-water interface was also investigated by solidifying the oil phase. The results show that the colloidal particles were effective particulate emulsifiers when homogenized with various oils. In addition, the white oil-in-water high internal phase emulsions(HIPEs) with a high oil volume fraction of 80% were formed when the colloidal particles were heavily flocculated. The HIPEs were pH-responsive and capable of demulsification with an addition of alkaline solution.2. The effects of the structure of core cross-linked colloidal particles PDVB@PAS on their emulsifying performanceOn the basis of the second chapter, copolymer colloidal particles PDVB@PAS with crosslinked poly(divinyl benzene)(PDVB) as core and poly(acrylic acid-r-styrene)(PAS) as outer copolymer chains were utilized as the model, regulating the size of the cross-linked core, the amphipathicity and length of the outer copolymer chains, to examine the effects of the structure on their emulsifying performance. The chemical structure of the macromolecular chain transfer agents were characterized by IR spectroscopy, 1H-NMR, and GPC. The size, morphology, and amphipathicity of the as-prepared colloidal particles were characterized by DLS, SEM, and water contact angle tests, respectively. The effects of the size of the cross-linked core, the chemical composition and the length of outer copolymer chains on the emulsifying performance of the colloidal particles under different pH and different oil-water ratio were studied. The results shows that the size, amphipathicity, and emulsibility of the colloidal particles could be regulated effectively by varying the chemical constitution of the outer copolymer chains. The colloidal particles, with the mole fraction of St content in the outer copolymer chains of 11%, could well stabilize the oil-in-water emulsions at a wide p H range(3~11), and the maximum volume fraction of oil in emulsions could reach 80%. Core cross-linked colloidal particles with moderate crosslinking degree, more hydrophilic outer copolymer chains, longer outer copolymer chains, have good emulsifiability.3. Pickering emulsion polymerization stabilized by core cross-linked colloidal particles PDVB@PASOn the basis of the third chapter, colloidal particles PDVB@PAS0.11-150 with good emulsifying performance were used as particles emulsifiers, to prepare Pickering emulsions. The polymerization monomer was used as oil phase. The preparation of polymer microspheres via Pickering emulsion polymerization in different reaction conditions were discussed. The effects of the concentration of colloidal particles, volume ratio of oil to water, and monomer type on the stability of the emulsions after polymerization and polymer microspheres morphology were studied. Meanwhile, the polymerization mechanism of the polymerization reaction in different initiator system were discussed. The results show that the colloidal particles can be used as emulsifiers in emulsion polymerization instead of the traditional small molecule emulsifiers. The type of initiator has significant influence on the stability of Pickering emulsion polymerization system. The emulsions of water-soluble initiator system could be stable for a period of time, while the product of oil-soluble initiator system layered. Polymerization conditions affected the morphology and size of polymer microspheres. The colloidal particles also could be used to stabilize Pickering emulsion polymerization of other common vinyl monomers.