Pickering emulsions stabilized by self-assembled colloidal particles of amphiphilic branched random poly(styrene-co-acrylic acid)

• Branched copolymer BPSAA is synthesized by atom transfer radical polymerization.
• BPSAA self-assembled colloidal particles are used to stabilize Pickering emulsions.
• Branched structure improves hydrophilicity and emulsifiability of BPSAA particles.
• The structure and emulsifiability of BPSAA particles exhibit pH-responsiveness.
• High NaCl salinity makes BPSAA particles flocculate to enhance emulsifiability.

Amphiphilic branched random poly(styrene-co-acrylic acid) (BPSAA) is facilely synthesized by a one-pot atom transfer radical copolymerization of styrene and tert-butyl acrylate with 1-(chloromethyl)-4-ethenylbenzene as chain transfer monomer followed by hydrolysis of ester groups. Then the self-assembled colloidal particles of BPSAA are prepared by a selective solvent method and used to stabilize Pickering emulsions. The influences of pH, branching degree, and salinity on the structure and emulsifying performance of the colloidal particles are investigated. The results show that the BPSAA colloidal particles exhibit pH responsiveness. They can stabilize O/W emulsions effectively at strongly alkaline conditions rather than acidic or weakly alkaline conditions. It is probably due to the random distribution of hydrophobic and hydrophilic microdomains in the colloidal structure restrains the ionization of carboxyl groups and leads to high pKa. The branched structure of the copolymer plays an important role in the colloidal structure and emulsification. The colloidal particles of the BPSAA copolymer with higher degree of branching exhibit higher ionization of carboxyl groups at same pH condition, thus better hydrophilicity and emulsifying performance. In addition, a high NaCl salinity can reduce the electrostatic repulsion among the colloidal particles significantly by shielding effect, to make the colloidal particles flocculate. The formed flocs show an enhanced emulsifying performance. This study may contribute to understand the relationship between the structure and emulsifying performance of polymeric self-assembled colloidal particles.

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