arXiv subjects

Sonali Vasant Kawale

Publications and source records attributed to Sonali Vasant Kawale.

3 recordsLinked to original sources

arXiv2026

Stiffness-dependent Dielectric Relaxation in Thermoreversible Microgels: Effects of Temperature and Strain

We investigate how particle stiffness governs length-scale-dependent relaxation dynamics in dense suspensions of thermoresponsive PNIPAM microgels subjected to temperature variations and large amplitude oscillatory shear. By combining dielectric spectroscopy with rheometric measurements, we directly correlate microscopic polarization fluctuation dynamics with macroscopic mechanical relaxation. Highly crosslinked, stiffer microgels exhibit longer dielectric relaxation times across a broad temperature range and strain-induced slowing down, whereas softer, open-network microgels exhibit nearly strain-independent dielectric dynamics. Below the volume phase transition temperature (VPTT), macroscopic bulk stress relaxation experiments reveal that suspensions of the softest particles relax most rapidly. For the stiffer microgel suspensions, however, the dynamics decouple: bulk stress relaxation speeds up with increasing stiffness even as dielectric relaxation slows down. Above the VPTT, softer particles undergo greater volume collapse, leading to very rapid bulk stress relaxation. Besides exhibiting slower stress decay, stiffer microgel suspensions also undergo shear-induced structural regeneration during the later stages of deformation. These findings demonstrate that particle stiffness and internal architecture govern relaxation pathways across microscopic and macroscopic length scales, thereby providing a framework for designing adaptive soft metamaterials, stress-dissipative coatings, and self-healing robotic materials.

cond-mat.soft↗

arXiv2025

Thermal History Asymmetry and Dissipation in Dense Colloidal Microgel Glasses

Microstructurally arrested matter, from molecular glasses to soft glassy materials, can retain a memory of their thermal or mechanical (shear) histories. Their history-dependent and nonlinear microstructural recoveries have been studied within the Kovacs framework. Here, we applied the temperature ramps of varying magnitudes to dense colloidal suspensions of thermoresponsive, deformable and compressible microgel particles should serve as an effective strategy to probe the nonlinear path-dependent structural recovery of these systems. We synthesised Poly (N-isopropyl acrylamide) (PNIPAM) microgel particles using the free radical precipitation polymerisation method. Using oscillatory rheology, we studied the relaxations of the viscoelastic moduli of dense PNIPAM suspensions that were heated and cooled at various temperature ramp rates. Path-dependent structural recovery was quantified by studying the asymmetric approach of the suspension elastic modulus toward the target temperature during the heating and cooling temperature ramps. The loss modulus peaks, observed at the times of initiation and termination of the temperature ramps, were understood to arise from energy dissipation due to microgel rearrangement events. The heights of the peaks were found to be inversely correlated with the asymmetry in the elastic response. Our work highlights the important role of energy dissipation through microgel rearrangements in eliminating path-dependent asymmetries in the storage moduli of dense PNIPAM suspensions subjected to thermal shocks. By tuning the applied temperature ramp rate and particle packing density, therefore, asymmetric storage modulus relaxations in dense systems can be modulated via adjustments of the accessible free volume.

cond-mat.soft↗

arXiv2024

Role of microgel stiffness in particle self-assembly and suspension rheology across the lower consolute solution temperature

We synthesize thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) colloidal microgel particles of different stiffnesses by controlling the concentration of crosslinker in a one-pot synthesis method. We employ oscillatory rheology and cryogenic scanning electron microscopy to study the temperature and stiffness-induced mechanical properties and microscopic structures of dense aqueous suspensions of the synthesized PNIPAM microgels. Using Fourier transform infrared (FTIR) spectroscopy, we show that particle hydrophobicity increases with increasing suspension temperature and decreasing particle stiffness. Our zeta potential measurements of soft PNIPAM particles and those of intermediate stiffnesses demonstrate that these particles are electrostatically unstable and prone to aggregation even at temperatures below the lower consolute solution temperature (LCST). In contrast, stiff PNIPAM particles in dilute aqueous suspensions are electrostatically stabilized at all temperatures explored in this study. Interestingly, our frequency and strain amplitude sweep rheology experiments reveal that the linear viscoelastic moduli and yield stresses of all the PNIPAM suspensions increase when the temperature is raised above the LCST. Combining cryogenic scanning electron microscopy (cryo-SEM) and rheology, we demonstrate that dense suspensions of soft PNIPAM microgels show a gel-liquid-gel transition with increase in temperature across the LCST. Suspensions of stiff particles, in contrast, exhibit a glass-glass transition under the same temperature sweep conditions and do not pass through an intermediate liquid state.

cond-mat.soft↗