Heterogeneous collapse in thermoresponsive copolymer microgels varying molar composition

Jacopo Vialetto; Francesco Brasili; Letizia Tavagnacco; Gavino Bassu; Elena Buratti; Stephen King; Emanuela Zaccarelli; Marco Laurati

arXiv · 2609.03571

Heterogeneous collapse in thermoresponsive copolymer microgels varying molar composition

Jacopo Vialetto·Francesco Brasili·Letizia Tavagnacco·Gavino Bassu·Elena Buratti·Stephen King·Emanuela Zaccarelli·Marco Laurati

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Abstract

Understanding the internal architecture of copolymer microgels is crucial for establishing how nanoscale polymer organization controls their stimuli-responsive behavior. Here we focus on thermoresponsive P(N-isopropylacrylamide-co-N-isopropyl-methacrylamide), P(NIPAM-co-NIPMAM), microgels with varying mole fraction of the components, synthesized via radical precipitation polymerization, and we demonstrate that changes in their volume phase transition and equilibrium swelling are governed by composition-dependent internal heterogeneity. Comparison between small-angle neutron scattering (SANS) with isotopic labeling and monomer-resolved simulations show a block-like monomer distribution of the two components. SANS analysis reveals a universal maximum in the polymer mesh correlation length near the transition, evidencing coexistence of collapsed NIPAM-rich and swollen domains. The correlation length increases with increasing NIPMAM content, with a maximum for 75 mol \% NIPMAM, implying sparse collapsed regions within the network and thus a large degree of heterogeneity induced by the presence of an increasingly large fraction of intercalated, non-collapsing PNIPMAM. The maximum heterogeneity correlates with the equilibrium swelling ratio, indicating that collapsed microgels retain a structural memory of the transition and present a less-compliant structure in response to temperature variations. Overall, these insights highlight a complex effect of the block-like monomer distribution on the responsive properties of copolymer microgels with different compositions, thus providing a design rule for tailoring responsive colloids for functional soft materials.

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Jacopo Vialetto, Francesco Brasili, Letizia Tavagnacco, Gavino Bassu, Elena Buratti, Stephen King, Emanuela Zaccarelli, Marco Laurati. 2026-09-03. Heterogeneous collapse in thermoresponsive copolymer microgels varying molar composition. https://arxiv.org/abs/2609.03571

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