Engineering Thermoresponsive Emulsions with Branched Copolymer Surfactants. Issue 10 (21st August 2022)

• Record Type: Journal Article
• Authors: da Silva, Marcelo Alves; Rajbanshi, Abhishek; Opoku‐Achampong, Daniel; Mahmoudi, Najet; Porcar, Lionel; Gutfreund, Philipp; Tummino, Andrea; Maestro, Armando; Dreiss, Cecile A.; Cook, Michael T.
• Is Part Of: Macromolecular materials and engineering. Volume 307:Issue 10(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-21
• Subjects: emulsion engineering -- small angle neutron scattering -- thermoreversible gels; Plastics -- Periodicals; Polymers -- Periodicals; Polymerization -- Periodicals; 547.705
• DOI: 10.1002/mame.202200321
• Languages: English
• ISSNs: 1438-7492

Abstract

Abstract: This study describes thermo‐rheological properties of branched copolymer surfactants (BCSs) stabilizing oil‐in‐water emulsions to generate materials exhibiting temperature‐dependent gelation with the ability to solubilize a broad range of molecules. Four poly(N‐isopropylacrylamide‐ ran ‐poly(ethylene glycol) methacrylate) (poly(NIPAM‐ ran ‐PEGMA)) BCSs with varying molecular weight (Mn ), 4.7; 7.0; 7.8 and 9.0 kg mol −1, are investigated via oscillatory shear rheology, small angle neutron scattering (SANS), and neutron reflectivity (NR). Rheological thermoscans show that emulsions stabilized by the BCS with the lowest Mn (4.7 kg mol −1 ) are thermo‐thinning, while with the other BCSs the emulsions display a thermo‐thickening behavior. Emulsions stabilized with the BCS with Mn = 7.8 kg mol −1 form gels within a precise temperature window depending on BCS concentration. Small angle neutron scattering data analysis suggests that the BCS is present in two forms in equilibrium, small aggregates dispersed in the bulk water and an adsorbed polymeric layer at the oil/water interface. Changes in dimensions of these structures with temperature correlate with the macroscopic thermo‐thinning/thermo‐thickening behavior observed. Neutron reflectivity is conducted at the oil/water interface to allow further elucidation of BCS behavior in these systems. Abstract : Thermoresponsive branched copolymer surfactants allow the generation of "engineered emulsions" which switch from a low viscosity state to a gel upon warming. This phenomenon is shown to be highly dependent on molecular weight, with larger macromolecules promoting gel formation. Small‐angle neutron scattering and neutron reflectivity at the oil–water interface reveal the mechanisms underpinning thermoreversible gelation.