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Mechanical Properties of 2D Flexyne and Reflexyne Polyphenylacetylene Networks: A Comparative Computer Studies with Various Force-Fields

100%

Trapani L. , Gatt R. , Mizzi L. , Grima J. N.

tom Vol. 19, No 3

237--296

Auxetic materials exhibit the very unusual property of becoming wider when stretched and narrower when compressed, – they have a negative Poisson’s ratio. This unusual behaviour is the source of many desired effects in the materials’ properties and it is therefore, no wonder that auxetics are described as being superior to conventional materials in many practical applications. Here we make use of force-field based molecular modelling simulations in order to investigate the mechanical properties of polypehyleacetylene systems known as (n, m)-flexyne and (n, m)-reflexyne in an attempt to extend the existing knowledge there is regarding these systems. These systems have already attracted considerable consideration since negative on-axis Poisson’s ratios have been discovered for the reflexynes. We first developed a methodology for the modelling and property determination of flexyne and reflexyne network systems which we validated against existing published data. Then, extended the study to prove the simulated results were independent of the modelling methodology or the force-field used. In particular, we showed that on-axis auxeticity in the reflexynes is a force-field independent property, i.e. a property which is not an artefact of the simulations but a property which is likely to be present in the real materials if these were to be synthesised. We also studied and reported the shear behaviour of these systems were we show that the flexynes and reflexynes have very low shear moduli, a property which regrettably limits the prospects of these systems in many practical applications. Finally we examine the in-plane off-axis mechanical properties of the systems and we report that in general, these mechanical properties are highly dependent on the direction of loading. We also find that the auxeticity exhibited by the reflexynes on-axis is lost when these systems are loaded off axis since the Poisson’s ratios becomes positive very rapidly as the structure is stretched slightly off-axis (e.g. 15deg off-axis). This is once again of great practical significance as it highlights another major limitation of these systems in their use as auxetics.

From the Dynamic Lattice Liquid Algorithm to the Dedicated Parallel Computer – mDLL Machine

88%

Jung J. , Kiełbik R. , Rudnicki K. , Hałagan K. , Polanowski P. , Sikorski A.

Computational Methods in Science and Technology

2018

tom Vol. 24, No. 4

235--247

The designing, production and testing of the mDLL machine led to the development of such a structure in which operational cells (e.g. KDLL) were located in the nodes of a three-dimensional torus network and the device was scalable. Thus, the future expansion of this device with additional Printed Circuit Boards (PCB) will not result in lengthened wire connections between Field-Programmable Gate Arrays (FPGA) or slow down the operation of the machine. The conducted tests confirmed the correctness of the adopted design assumptions and showed that by using mDLL one can effectively perform molecular simulations. Despite some structural shortcomings, the mDLL machine was a prototype that has already been sufficiently tested to allow the technology used in it to be used to build a device with a number of 1 million to 5 million KDLL cells. Such a device would already be suitable for simulating multi-particle systems with unprecedented speed.