In this study a type of colloidal particles with a cross-linked poly(divinylbenzene) (poly(DVB)) core and a poly(acrylic acid- r -styrene) (PAS) shell were directly prepared by reversible addition-fragmentation chain transfer (RAFT)-mediated cross-linking copolymerization. The particle size, morphology, zeta potential and pH responsibility were studied. The emulsification study showed that PAS-Poly(DVB) colloidal particles were effective particulate emulsifiers when homogenized with various oils including toluene, white oil, isooctyl palmitate, dicaprylyl carbonate, silicone oil, and propylheptyl caprylate. Additionally, the emulsification performance of PAS-Poly(DVB) colloidal particles at different pH values were investigated. Gelled white oil- in -water high internal phase emulsions (HIPEs) were formed at a high oil volume fraction of 80% when the colloidal particles were flocculated at low pH value. The addition of base can trigger the demulsification of the HIPEs, exhibiting a pH-responsive behavior. The effects of oil phase volume fraction on emulsion rheological properties were investigated. Both the emulsion viscosity and storage modulus (G′) progressively increased with the increasing of oil phase volume fraction. These results suggest that our work provides a convenient and feasible way to prepare effective particulate emulsifiers via the direct chemical reaction, and the PAS-Poly(DVB) colloidal particles have promising potential application in the oil industry and preparation and exploitation of smart materials.
Yuanyuan Xu,Youcheng Li,Xueteng Cao,Qijing Chen,Zesheng An
Reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization in cononsolvents of poly(N-isopropylacrylamide) (PNIPAM) was developed as a versatile strategy for the synthesis of thermoresponsive nanogels with controlled composition, functionality and architecture. Cononsolvents composed of mixtures of methanol, ethanol and isopropanol with water were first screened for their suitability as the media for dispersion polymerization of NIPAM, and water–ethanol (75 : 25, v : v) solution was selected due to good RAFT control, efficient formation of nanogels and low toxicity. RAFT dispersion polymerization of NIPAM in the cononsolvent using poly(N,N-dimethylacrylamide) (PDMA) as the macromolecular chain transfer agent (Macro-CTA) showed good control over the molecular weight, polydispersity and pseudo linear polymerization kinetics, as characterized by gel permeation chromatography (GPC) and 1H NMR. The effect of the molecular weight of Macro-CTA, the degree of polymerization of PNIPAM, the molar ratio of [crosslinker] : [Macro-CTA] and the solid content on the formation and size of nanogels was investigated. The thermal profiles of nanogels were characterized by dynamic light scattering (DLS) both in cononsolvents and water. This cononsolvency strategy for dispersion polymerization was shown to be compatible with the incorporation of hydrophilic comonomers of N-(2-hydroxyethyl)acrylamide (HEAM) and diacetone acrylamide (DAAM). The nanogel containing DAAM was demonstrated for postpolymerization modification using ketone–alkoxyamine chemistry. More importantly, dispersion polymerization in cononsolvents allowed various hydrophobic components, e.g. butyl acrylate (BA), fluorescein O-acrylate (FLA), and 1,6-hexanediol diacrylate (HDDA), to be reliably copolymerized with NIPAM, showing well controlled polymerization, composition, nanogel size and colloidal stability. Finally, an amphiphilic block copolymer PDMA-b-PBA was used as a Macro-CTA to produce the PDMA-b-PBA-b-PNIPAM triblock copolymer and triple-layered nanogel, taking advantage of the solubility of PDMA-b-PBA and the insolubility of PNIPAM in the water–ethanol solution at the polymerization temperature.
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