Prof Laurence Brassart, Department of Engineering Science, Univeristy of Oxford, UK

Micromechanics of near-ideal polymer networks
When Jan 27, 2020
from 02:00 PM to 03:00 PM
Where LR1
Contact Name
Contact Phone 01865 273651
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Many soft materials, such as elastomers and hydrogels, are made of long chain molecules crosslinked to form a three-dimensional network. Their mechanical properties depend on network parameters such as chain density, chain length distribution and the crosslink coordination. Understanding the relationships between the structure of polymer networks and their mechanical properties is important for the design of advanced soft materials with optimal properties. In recent years, a new paradigm for network formation has emerged, whereby near-ideal hydrogels are produced by the cross-coupling of branched macromolecules with well-defined chain length [1]. Such ideal networks constitute an excellent model system to investigate structure-property relationships in hydrogels, as well as a promising platform for the design of new materials with tuneable properties.

In this work, we investigate the relative contributions of various network parameters to the elasticity of near-ideal polymer networks using a computational approach based on random discrete networks. In this approach, a polymer network is represented as an assembly of non-linear springs connected at nodes representing crosslinking points. We performed an extensive parametric study by systematically varying the network parameters independently. We also compared discrete networks predictions to analytical estimates such as the 3-chain, 8-chain and full-network models of rubber elasticity. Scaling relations between the elastic properties and network parameters predicted by discrete network simulations were found to contradict the predictions of classical rubber elasticity theories [2]. The discrepancy is explained by the coupling between chain pre-strain and network parameters in the computational model, which is not considered in rubber elasticity theories. The results also highlight the critical role of topological features such and dangling ends and loops on the mechanical properties. Our results have implications for the interpretation of experimental data for near-ideal polymer networks.

References:

[1] Sakai, T., Matsunaga, T., Yamamoto, Y., Ito, C., Yoshida, R., Suzuki, S., Sasaki, N., Shibayama, M., Chung, U.-I., 2008. Design and fabrication of a high-strength hydrogel with ideally homogeneous network structure from tetrahedron-like macromonomers. Macromolecules 41, 5379-5384.

[2] Alame, G., Brassart, L., 2019. Relative contributions of chain density and topology to the elasticity of two-dimensional networks. Soft Matter 15, 5703-5713.