Relation between molecular properties and macroscopic performance of interpenetrating networks
Abstract
Soft materials are an important area of great technological interest. The use of many gel materials is, however, often restricted due to their weak mechanical performance. One way of improving their properties is by forming interpenetrating networks. An interpenetrating network (IPN) consists of at least two polymer networks that are formed together but not covalently bonded to each other. These networks have important application areas, e.g., in organic solar cells, drug delivery, and tissue engineering. To be able to improve the mechanical properties, one needs to be able to correlate the mechanical properties with the network structure. The difference in cross-linking density means that the two networks that constitute the IPN will behave differently during the deformation. Understanding the mechanical properties of IPNs is thus of fundamental importance in polymer mechanics. The behaviour depends on the strain history, and already the first network deformation causes a significant change in the mechanical properties.
To investigate more general types of networks, we previously developed a novel algorithm to create a closed network with an unbiased distribution of crosslinking nodes, which has been used to investigate the diffusion of small molecules in crosslinked networks[1]. Applications in the form of the collapse transition of core-shell nanoparticles have also been studied using a similar type of algorithm[2].
Recently, we have also shown that a homogeneous bimodal gel (one network with two types of chains) can show improved mechanical properties compared to a network with chains corresponding the average chain length[3], and that inhomogeneities in the gel structure, in most cases, make the gel weaker, in accordance with experimental observations[4]. (Project SNIC 2016/1-252)
In the proposed project (a continuation of SNIC 2016/1-467), our aim is the study of various mechanical phenomena of interpenetrating networks during deformation using molecular simulations. We want to systematically investigate the mechanical strength and deformational behaviour during compressions and extensions for IPN:s of different cross-linking densities. The mechanical properties will mainly be investigated by analysing the stress-strain and the stress-relaxation curves. This will further be linked to polymer chain orientation and the local deformation in the material on a molecular level, in order to investigate the interplay of the two networks.
The initial simulations were done by a master student during spring 2017. During the autumn, N. Kamerlin has mainly been working on her thesis and refs. 3-4, but a new PhD student has now been appointed, and N. Kamerlin will also have the possibility to initially work on this project during the beginning of 2018
The need for cpu-time would be in the range 12 000 cpu hours per month, and the disk space needed to store the resulting trajectories during the analysis stage would still be 800Gb-1Tb during the present part of the project.
1. N. Kamerlin & C. Elvingson, J. Phys. Condens. Matter, 28, 475101 (2016)
2. N. Kamerlin & C. Elvingson, Macromolecules, 49, 5740 (2016)
3. N. Kamerlin & C. Elvingson, Macromolecules, 50, 7628, 2017
4. N. Kamerlin & C. Elvingson, Macromolecules, accepted for publication
