arXiv subjects

L. K. R. Duarte

Publications and source records attributed to L. K. R. Duarte.

4 recordsLinked to original sources

arXiv2025

Comment on "Solvent-Induced Negative Energetic Elasticity in a Lattice Polymer Chain''

In a recent Letter, Shirai and Sakumichi [Phys. Rev. Lett. 130, 148101 (2023), arXiv:2202.12483] presented a study focusing on the origin of a temperature-dependent negative contribution $G_U(T)$ to the elastic modulus $G(T)$ of hydrogels [Yoshikawa et al., Phys. Rev. X 11, 011045 (2021)]. The authors support their findings through an energy-related stiffness $k_U(r,T)$ obtained from a single chain, with $r$ being the end-to-end distance of a random walk on a 3D lattice. It is argued that the parameter $\varepsilon$ related to polymer-solvent interactions is positive, so the energy $E_s$ of an elongated state should be smaller than the energy $E_b$ of a more compact state. We believe that the analogy between $G_U(T)$ and $k_U(r,T)$ might have misled their claim that $G_U(T)<0$ when $\varepsilon>0$.

cond-mat.soft↗

arXiv2024

Revisiting the strain-induced softening behaviour in hydrogels

Usually, the strain-induced softening behaviour observed in the differential modulus $K(T,γ)$ of hydrogels has been attributed to the breakage of internal structures of the network, such as the cross-links that bind together the polymer chains. Here we consider a stress-strain relationship that we have recently derived from a coarse-grained model to demonstrate that no rupture of the network is needed for rubber-like gels to present such behaviour. In particular, we show that, in some cases, the decreasing of $K(T,γ)$ as a function of the strain $γ$ is closely related to the energy-related contribution to the elastic modulus that has been experimentally observed, e.g., for tetra-PEG hydrogels. Thus, our results suggest that, instead of the breakage of structures, the softening behaviour can be also related to the effective interaction between the chains in the network and their neighbouring solvent molecules. Comparison to experimental data determined for several hydrogels is included to illustrate that behaviour and to validate our approach.

cond-mat.soft↗

arXiv2023

On the origin of the negative energy-related contribution to the elastic modulus of rubber-like gels

We consider a coarse-grained polymer model in order to investigate the origin of a recently discovered negative energy-related contribution to the elastic modulus $G(T)$ of rubber-like gels. From this model, we are able to compute an exact expression for the free energy of the system, which allows us to evaluate a stress-strain relationship that displays a non-trivial dependence on the temperature $T$. We validate our approach through comparisons between the theoretical results and the experimental data obtained for tetra-PEG hydrogels, which indicate that, although simple, the present model works well to describe the experiments. Importantly, our approach unveiled aspects of the experimental analysis which turned out to be different from the conventional entropic and energetic analysis broadly used in the literature. Also, in contrast to the linear dependence predicted by the traditional, {\it i.e.}, purely entropic, models, our results suggest that the general expression of the elastic modulus should be of the form $G(T) \propto k_BT w(T)$, with $w(T)$ being a temperature-dependent correction factor that could be related to the interaction between the chains in the network and the solvent. Accordingly, the correction factor allows the expression found for the elastic modulus to describe both rubber and rubber-like gels.

cond-mat.soft↗

arXiv2021

Microrheology of semiflexible filament solutions based on relaxation simulations

We present an efficient computational methodology to obtain the viscoelastic response of dilute solutions of semiflexible filaments. By considering an approach based on the fluctuation-dissipation theorem, we were able to evaluate the dynamical properties of probe particles immersed in solutions of semiflexible filaments from relaxation simulations with a relatively low computational cost and higher precision in comparison to those based on stochastic dynamics. We used a microrheological approach to obtain the complex shear modulus and the complex viscosity of the solution through its compliance which was obtained directly from the dynamical properties of a probe particle attached to an effective medium described by a mesoscopic model, i.e., an effective filament model (EFM). The relaxation simulations were applied to assess the effects of the bending energy on the viscoelasticity of semiflexible filament solutions and our methodology was validated by comparing the numerical results to experimental data on DNA and collagen solutions.

cond-mat.soft↗