Mixtures of pH-responsive microgels and temperature-responsive star-like copolymers; From heteroaggregation to gelation

Somjit Tungchaiwattana, Ruixue Liu, Silvia Halacheva, Nur Nabilah Shahidan, Andrew Kells, Brian R. Saunders

    Research output: Contribution to journalArticlepeer-review


    Heteroaggregation of dispersions has attracted much interest in the literature, especially when one or more components are stimulus responsive. Here, we study binary mixtures of microgels (MG) and star-like copolymers for the first time. The study investigated the use of complementary hydrogen bonding between carboxylic acid and amide groups to construct heteroaggregates and gels that contained temperature- and pH-responsive components. The pH-responsive MG contained methacrylic-acid and had an apparent pKa of 8.2. Two new star-like copolymers were introduced which comprised a cationic backbone with poly(N-isopropylacrylamide) side-chains. They are abbreviated as M1-PNP. A combination of complementary hydrogen bonding and hydrophobic interactions was shown to cause formation of heteroaggregates for mixed MG/M1-PNP dispersions at room temperature and at pH values less than the MG pKa. MG/M1-PNP heteroaggregate formation occurred over a wide pH-range and also in the presence of 0.2 M NaNO3. The heteroaggregates exhibited temperature-dependent hydrodynamic diameters and zeta potentials. Concentrated MG/M1-PNP dispersions formed self-supporting hybrid gels at 45 °C and gel formation also occurred over a wide pH range. The gels contained 80% MG with respect to total polymer content and were remarkably ductile. They had yield strains greater than or equal to 290%. There was evidence that the elasticity and ductility of the hybrid gels were controlled by the MG and M1-PNP components, respectively. The new M1-PNP star-like copolymers introduced here had superior temperature-triggered gel-formation properties compared to related copolymers and should be a versatile system for conferring temperature-responsive gelation properties to polymer colloids containing carboxylic acid groups. © 2013 The Royal Society of Chemistry.
    Original languageEnglish
    Pages (from-to)3547-3557
    Number of pages10
    JournalSoft Matter
    Issue number13
    Publication statusPublished - 9 Apr 2013


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