Abstract
We investigate the temperature dependent phase behaviour of mixtures of poly(Nisopropylacrylamide) (pNIPAM) microgel colloids and a triblock copolymer (PEOPPO-PEO) surfactant. Usually, gelation in these systems results from an increase in temperature. Here we investigate the role of the heating rate and, surprisingly, we find that this causes the mechanism of aggregation to change from one which is driven by depletion of the microgels by the micelles at low temperatures, to the association of the two species at high temperatures. We thus reveal two competing mechanisms for attractions between the microgel particles which can be controlled by changing the heating rate. We use this heating rate-dependent response of the system to access multiple structures for the same system composition. Samples were found to demix into phases rich and poor in microgel particles at temperatures below 33◦C, under 1 conditions where the microgels particles are partially swollen. Under rapid heating full demixing is bypassed and gel networks are formed instead. The temperature history of the sample, therefore, allows for kinetic selection between different final structures, which may be metastable.
| Original language | English |
|---|---|
| Number of pages | 9 |
| Journal | Langmuir |
| Volume | 39 |
| Issue number | 3 |
| Early online date | 9 Jan 2023 |
| DOIs | |
| Publication status | E-pub ahead of print - 9 Jan 2023 |
Bibliographical note
Funding Information:S.F. was supported by a studentship provided by the Bristol Centre for Functional Nanomaterials (EPSRC grant EP/L016648/1). C.P.R. acknowledges support from EPSRC (grant GR/M32320/01 and ERC consolidator grant NANOPRS, project no. 617266). The authors thank Craig Davies, Croda, for supplying the Synperonic PE/P105.
Publisher Copyright:
© 2023 The Authors. Published by American Chemical Society.