Title:	Investigating the roles of hydrophobicity and electrostatics in the particle-scale dynamics and rheology of dense microgel suspensions
Authors:	Chanda, Sayantan Chandeshwar, Misra Ranjini, Bandyopadhyay
Keywords:	Colloids Electrostatics Metamaterials Microgels Polymers Scanning electron microscopy Viscoelasticity Hydrophobic effect, Rheology and fluid dynamics, Carbohydrates
Issue Date:	18-Mar-2026
Publisher:	Journal of Applied Physics
Citation:	Journal of Applied Physics, 2026, Vol. 139 (111), AR No. 114701
Abstract:	Colloidal microgel particles such as poly(N-isopropylacrylamide) (PNIPAM) shrink reversibly in an aqueous medium due to the expulsion of water at a volume phase transition temperature (VPTT) ~ 33  * C. Romeo et al. [Adv. Mater. 2010, 22, 3441–3445] had previously shown that dense aqueous PNIPAM suspensions transformed from one viscoelastic solid-like phase to another when suspension temperature was increased, with an intermediate viscoelastic liquid-like phase near the VPTT. They attributed this observation to a change in the inter-particle interaction from hydrophilic to hydrophobic. Here, we show using a combination of experimental techniques that particle hydrophobicity can become significant even below the VPTT. We achieve this by incorporating dissociating additives such as sodium chloride and potassium chloride, or non-dissociating additives such as sucrose, into the aqueous medium. Above the VPTT, we observe that suspension rigidity is the highest in the presence of salts because of the combined effects of electrostatic and hydrophobic attractions. In the presence of non-dissociating sucrose, in contrast, the inter-microgel interaction remains hydrophobic across the VPTT. Such easy tunability of interactions by incorporating commonly available chemicals into the suspension medium opens up new avenues for the synthesis of novel metamaterials.
Description:	Open Access.
URI:	http://hdl.handle.net/2289/8707
ISSN:	1089-7550
Alternative Location:	https://doi.org/10.48550/arXiv.2509.16651 https://doi.org/10.1063/5.0309685
Copyright:	© 2026 Author(s)
Additional information:	Special Collection: Mechanical Metamaterials
Appears in Collections:	Research Papers (SCM)

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