Correction: Concentration and temperature dependent interactions and state diagram of dispersions of copolymer microgels.

Correction for 'Concentration and temperature dependent interactions and state diagram of dispersions of copolymer microgels' by José Ruiz-Franco et al., Soft Matter, 2023, 19, 3614-3628, https://doi.org/10.1039/D3SM00120B.

Concentration and temperature dependent interactions and state diagram of dispersions of copolymer microgels.

We investigate by means of small angle neutron scattering experiments and numerical simulations the interactions and inter-particle arrangements of concentrated dispersions of copolymer poly(N-isopropylacrylamide)-poly(ethylene glycol methyl ether methacrylate) (PNIPAM-PEGMA) microgels across the volume phase transition (VPT). The scattering data of moderately concentrated dispersions are accurately modeled at all temperatures by using a star polymer form factor and static structure factors calculated from the effective potential obtained from simulations. Interestingly, for temperatures below the VPT temperature (VPTT), the radius of gyration and blob size of the particles significantly decrease with increasing the effective packing fraction in the non-overlapping regime. This is attributed to the presence of charges in the system associated with the use of an ionic initiator in the synthesis. Simulations using the experimentally corroborated interaction potential are used to explore the state diagram in a wide range of effective packing fractions. Below and slightly above the VPTT, the system undergoes an arrest transition mainly driven by the soft repulsion between the particles. Only well above the VPTT the system is found to phase separate before arresting. Our results highlight the versatility and potential of copolymer PNIPAM-PEGMA microgels to explore different kinds of arrested states balancing attraction and repulsion by changing temperature and packing fraction.

Link between Morphology, Structure, and Interactions of Composite Microgels.

We combine small-angle scattering experiments and simulations to investigate the internal structure and interactions of composite poly(N-isopropylacrylamide)-poly(ethylene glycol) (PNIPAM-PEG) microgels. At low temperatures the experimentally determined form factors and the simulated density profiles indicate a loose internal particle structure with an extended corona that can be modeled as a starlike object. With increasing temperature across the volumetric phase transition, the form factor develops an inflection that, using simulations, is interpreted as arising from a conformation in which PEG chains are incorporated in the interior of the PNIPAM network. This gives rise to a peculiar density profile characterized by two dense, separated regions, at odds with configurations in which the PEG chains reside on the surface of the PNIPAM core. The conformation of the PEG chains also have profound effects on the interparticle interactions: Although chains on the surface reduce the solvophobic attraction typically experienced by PNIPAM particles at high temperatures, PEG chains inside the PNIPAM network shift the onset of attractive interaction at even lower temperatures. Our results show that by tuning the morphology of the composite microgels, we can qualitatively change both their structure and their mutual interactions, opening the way to explore new collective behaviors of these objects.