arXiv subjects

Takuya Katashima

Publications and source records attributed to Takuya Katashima.

3 recordsLinked to original sources

arXiv2022

Percolation induced gel-gel phase separation in a dilute polymer network

Cosmic large-scale structures, animal flocks, and living tissues are non-equilibrium organized systems created by dissipative processes. Despite the uniqueness, the realization of dissipative structures is still difficult. Herein, we report that a network formation process in a dilute system is a dissipative process, leading to percolation induced gel-gel phase separation (GGPS) in a prominent miscible polymer-water system. The dilute system, which forms a monophase structure at the percolation threshold, eventually separates into two gel phases in a longer time scale as the network formation progresses. The dilute hydrogel with GGPS exhibits an unexpected mesoscale co-continuous structure and induces adipose growth in subcutaneous. The formation mechanism of GGPS and a cosmic large-scale structure is analogous, in terms of attractive interactions in a diluted system driving phase separation. This unique phenomenon unveils the possibility of dissipative structures enabling advanced functionalities and will stimulate research fields related to dissipative structures.

cond-mat.soft↗

arXiv2021

Temperature Dependence of Polymer Network Diffusion

The swelling dynamics of polymer gels are characterized by the (collective) diffusion coefficient $D$ of the polymer network. Here, we measure the temperature dependence of $D$ of polymer gels with controlled homogeneous network structures using dynamic light scattering. An evaluation of the diffusion coefficient at the gelation point $D_{\mathrm{gel}}$ and the increase therein as the gelation proceeds $ΔD\equiv D-D_{\mathrm{gel}}$ indicates that $ΔD$ is a linear function of the absolute temperature with a significantly large negative constant term. This feature is formally identical to the recently discovered "negative energy elasticity" [Y. Yoshikawa et al., Phys. Rev. X 11, 011045 (2021) (arXiv:1912.13191)], demonstrating a nontrivial similarity between the statics and dynamics of polymer networks.

cond-mat.soft↗

arXiv2021

Tri-branched gels: Rubbery materials with the lowest branching factor approach the ideal elastic limit

Unlike hard materials such as metals and ceramics, rubbery materials can endure large deformations due to the large conformational degree of freedom of the crosslinked three-dimensional polymer network. However, the effect of the branching factor of the network on the ultimate mechanical properties of rubbery materials has not yet been clarified. This study shows that tri-branching, which entails the lowest branching factor, results in a large elastic deformation near the theoretical upper bound. This ideal elastic limit is realized by reversible strain-induced crystallization, providing on-demand reinforcement. The findings indicate that the polymer chain is highly orientated along the stretching axis, whereat enhanced reversible strain-induced crystallization is observed in the tri-branched and not in the tetra-branched network. A mathematical theory of structural rigidity is used to explain the difference in the chain orientation. Although tetra-branched polymers have been preferred since the development of vulcanization, these findings highlighting the merits of tri-branching will prompt a paradigm shift in the development of rubbery materials.

cond-mat.mtrl-sci↗