Abstract
Thermoresponsive microgels are polymeric colloidal networks that can change their size in response to a temperature variation. This peculiar feature is driven by the nature of the solvent-polymer interactions, which triggers the so-called volume phase transition from a swollen to a collapsed state above a characteristic temperature. Recently, an advanced modelling protocol to assemble realistic, disordered microgels has been shown to reproduce experimental swelling behavior and form factors. In the original framework, the solvent was taken into account in an implicit way, condensing solvent-polymer interactions in an effective attraction between monomers. To go one step further, in this work we perform simulations of realistic microgels in an explicit solvent. We identify a suitable model which fully captures the main features of the implicit model and further provides information on the solvent uptake by the interior of the microgel network and on its role in the collapse kinetics. These results pave the way for addressing problems where solvent effects are dominant, such as the case of microgels at liquid-liquid interfaces.
Highlights
Thermoresponsive microgels are polymeric colloidal networks that can change their size in response to a temperature variation
When PNIPAM chains are crosslinked with bisacrylamide (BIS), microgel particles can be prepared in a range of sizes of 10–1000 nm by standard synthesis methods[4], and even reach much larger scale with microfluidic techniques[5]
We report the comparison for the two cases where the agreement is found to be fully satisfactory for all χeff, namely the Dissipative Particle Dynamics (DPD) and Molecular Dynamics (MD) Vλ models
Summary
Thermoresponsive microgels are polymeric colloidal networks that can change their size in response to a temperature variation. When PNIPAM chains are crosslinked with bisacrylamide (BIS), microgel particles can be prepared in a range of sizes of 10–1000 nm by standard synthesis methods[4], and even reach much larger scale (up to 100 μm) with microfluidic techniques[5] These particles undergo a Volume Phase Transition (VPT) in water at a temperature of ≈305 K, from a swollen state at low temperatures to a collapsed one at high temperatures. Fully-bonded configurations are obtained by introducing a swapping mechanism[17] that makes it possible to equilibrate the system even at the strong attractions required to maximize the bonding In this protocol there are two parameters controlling the topology of the resulting network: the concentration of crosslinkers and the confinement radius. A thorough discussion on how the internal structure of the microgels depends on these parameters can be found in Refs.[15,16]
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