Branched copolymer surfactants impart thermoreversible gelation to LAPONITE® gels

• Published in: Soft matter 2023-12, Vol.2 (1), p.13-114
• Main Authors: Rajbanshi, Abhishek, Da Silva, Marcelo Alves, Mahmoudi, Najet, Janeczek, Agnieszka, Shaw, Allison, Dawson, Jonathan, Cook, Michael Thomas
• Format: Article
• Language: English
• Subjects: Body temperature; Clay; Copolymers; Ethylene glycol; Functional materials; Gelation; Gels; Glycol dimethacrylates; Heating systems; Molecular weight; Nanocomposites; Neutron scattering; Polyethylene glycol; Polymers; Rheological properties; Rheology; Self-assembly; Sol-gel processes; Surfactants
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/d3sm01271a

This investigation seeks to integrate LAPONITE® clay gels with thermoresponsive branched copolymer surfactants (BCSs) to develop advanced functional materials with temperature-induced sol-gel behaviour. It is known that a diverse range of molecules adsorb strongly to clays which may be used to control liberation of the species in healthcare applications, and as such the development of polymer/clay hybrid materials which can add function to the native clay behaviour are of great interest. BCS were synthesised with a structure that encompasses poly(ethylene glycol)methacrylate (PEGMA), ethylene glycol dimethacrylate (EGDMA), and dodecanethiol (DDT), conferring versatile and tuneable thermoresponsive attributes. Systematic modulation of the monomer : DDT/initiator ratio was used to facilitate the synthesis of BCS architectures spanning a range of molecular weights. Through application of small-amplitude oscillatory shear (SAOS) rheology and small-angle neutron scattering (SANS) in conjunction with controlled temperature variations, the sol-gel transition dynamics of these nanocomposite materials were elucidated. Complementary insights into the mechanisms underpinning this transition and temperature-induced alterations in the constituents are gleaned through the utilization of SANS techniques employing contrast-matching methodologies to mitigate clay and polymer scattering interference. It is found that heating systems from room- to body- temperature induces self-assembly of BCS in the bulk aqueous phase with concurrent structuration of clay in gel-forming samples with lower number average molecular weight ( M n ). SANS study unpicks this phenomenon to find that gelation occurs with concurrent aggregation of BCS in the bulk, inducing clay-clay interactions only in lower M n BCS systems with large nanoaggregates. Composite solutions of LAPONITE® and branched copolymer surfactants give thermoreversible sol-gel transitions due to nanostructural assembly processes.