Relation between molecular properties and macroscopic performance of interpenetrating networks

Dnr:

SNIC 2016/1-467

Type:

SNAC Medium

Principal Investigator:

Christer Elvingson

Affiliation:

Uppsala universitet

Start Date:

2016-11-28

End Date:

2017-12-01

Primary Classification:

10402: Fysikalisk kemi

Secondary Classification:

10105: Beräkningsmatematik

Tertiary Classification:

10407: Teoretisk kemi

Webpage:

http://www.kemi.uu.se/forskning/fysikalisk-kemi/forskargrupper/christer-elvingson-group/

Allocation

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, in terms of modulus, stiffening, and damage properties. Understanding the mechanical properties of IPNs is thus of fundamental importance in polymer mechanics, but many phenomena are still not well understood. One such phenomenon is the Mullins effect, in which the damage of the networks leads to a stress-induced softening that gives rise to high toughness. The behaviour depends on the strain history, and already the first network deformation causes a significant change in the mechanical properties. Although studied for decades, it is still a major obstacle for understanding rubber-like material behaviour and there is no general agreement on the physical explanation or the mechanical modelling of this effect, although several theories have been proposed. One of these is that the breaking of the short chains in the short-chain network leads to softening, but it is not clear how this quantitatively relates to polymer chain lengths and densities. Some gels also show necking instability in tensile tests, although the exact mechanism is not clear. 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[1], relevant for e.g. drug delivery applications. Applications in the form of the collapse transition of core-shell nanoparticles have also been studied using a similar type of algorithm[2]. In the proposed project, our aim is to study the various mechanical phenomena of IPN:s during deformation using molecular simulations. We want to systematically investigate the mechanical strength and deformational behaviour during multiple cyclic 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 need for cpu-time would be in the range 35 000 cpu hours per month, and the disk space needed to store the resulting trajectories during the analysis stage would 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)