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Molecular to Continuum Investigation of Anisotropic Thermal Transport in Polymers

Periodic Reporting for period 1 - MCIATTP (Molecular to Continuum Investigation of Anisotropic Thermal Transport in Polymers)

Reporting period: 2017-10-16 to 2019-10-15

This project addresses the gaps in scientific knowledge pertaining the understanding of thermal transport in polymer melts during manufacturing processes such as injection molding or 3D printing through Filament Deposition Manufacturing (FDM). Improvement of such processes requires macroscopic simulation of the flows involved. To this end, a molecular-to-continuum methodology is proposed to connect the current state of the art experimental findings with newly developed results from MD simulations and macroscopic network models to create the tools required for macroscopic (CFD) simulation of industrially relevant flows.
The outcomes described in the project final report will benefit the EU plastics industry, economy and society through the development of more competitive products and the creation of jobs. Specifically, completion of the project’s goals:
1)Facilitates tuning of current manufacturing processes and makes possible the development of new ones in a cost efficient manner.
2)Allows optimization of polymer melt performance in current applications by controlling thermal conductivity to make better polymeric heat insulators (or conductors).
3)Expedites the development of new applications/technologies based on enhanced (or reduced) thermal conductivity (i.e. fast cooling flexible electronics, improved efficiency thermo-electric devices and super-insulators).
The overall objectives of the project are tightly connected to the description the goals for each of the WP in the project proposal:
First goal (WP1): Implement macroscopic network models able to predict the rheological behaviour of melts. The stress obtained through flow simulation of complex polymeric materials is then used together with the stress-thermal rule to provide predictions for the anisotropy in thermal conductivity. In WP1 the stress-thermal rule coefficient can be extracted for a limited number of chemistries from experimentally available data.
Second goal (WP2): Develop the necessary molecular dynamics simulation tools to: (1) reproduce and extend current experimental dataset on thermal transport of entangled polymer melts. (2) improve the basic understanding of the structure-property relations leading to anisotropy in the thermal conductivity in polymers subjected to deformation or flow.
Third goal (WP3): Combine the modelling developed in WP1 and the knowledge gained through WP2. Validation of the microscopic study of thermal transport in WP2 against experimental data allows extraction of the stress-thermal coefficients from molecular simulation. Comparison of experimental and simulation results can also help improve the understanding of the mechanism driving thermal transport in polymers.
Forth goal (WP4): Develop the tools necessary for macroscopic (CFD) simulation of industrially relevant (non-isothermal and non-homogeneous) flows.
The work performed during the project follows the Work Package scheme presented in the original project proposal. Additional details on the Tasks included on each WP have been described in the Project Final Report document. Here only a summary of the work carried out and the main results achieved in each WP is given.

WP1 Main Results: Implementation of macroscopic networks models and connection of the simulated stress to predict anisotropy in thermal conductivity through application of the stress thermal rule. Deliverables: 1 scientific publication, 1 paper in preparation, 2 oral and 1 poster presentations at scientific meetings and 1st draft for the data management plan.

WP2 Main Results: The work performed in WP2 has provided: 1) a method to determine stress in deformed molecular melts; 2) The necessary tools to test anisotropy in TC induced by deformation and the stress-thermal rule using MD; 3) A check on the TC dependence on molecular weight, an observation that is fundamental to the key hypothesis supporting the STR. Significantly, our results have highlighted the important role of entanglements as phonon dispersion centers in polymeric materials. Deliverables: 1 publication under review, 1 paper in preparation and sufficient findings for a 3rd publication using a deformation field in CAMC simulations to slowly deform entangled PE melts. 3 Oral presentations at scientific meetings.

WP3 Main Results: Comparison of anisotropy in TC as obtained from experiments and simulations. Comparison of the stress-thermal and stress-optic rule. Validation of the thermal transport framework proposed in WP1. Deliverables: 1 scientific paper in preparation. 1 Oral presentation at scientific meetings.

WP4 Main Results: Simulation of an anisotropic solid for visualization of the effect that anisotropic thermal transport has on the temperature distribution in the presence of temperature gradients. Deliverables: Sufficient material for a publication discussing manipulation of the heat flux direction through molecular orientation. 1 oral and 1 poster presentation at scientific meetings. Final report document.
The main project objective aims to improve the understanding of the connections between the micro-structure in polymer melts subjected to deformation and the exhibited macroscopic properties, specifically the thermal conductivity. To that end a molecular-to-continuum methodology is proposed to connect the current state of the art experimental findings with results from MD simulations and coarse-graining models to facilitate the macroscopic simulation of industrially relevant flows.
During the project realization, we have developed an approach to overcome the current limitations in the field following an ambitious molecular-to-continuum multidisciplinary approach that combines experiments and molecular simulation to perform macroscopic modelling and the development of tools for macroscopic CFD simulation. This approach has allowed robust validation of the different modelling/simulation stages with available results from experimental studies of anisotropy in thermal conductivity induced by deformation in polymeric materials. The simulation of fully realistic non-isothermal polymer manufacturing flows remains a challenge, but the advancements in the understanding of thermal transport in polymers at the microscale and the implementation of prediction models suitable for CFD represent significant stepping stones in the right direction.
The impact of the project has been augmented by communication of the results at a number of scientific meetings (8 oral and 2 poster presentations) and a number of scientific publications. The quality of the ER’s work in the field has been recognized in a poster prize awarded by the Iberian Society of Rheology and a travel grant awarded by the Polymer Processing Society for the ER to attend the last regional PPS meeting celebrated in South Africa after the completion of the project.
In addition, to communicate the scientific results, the project has devoted important efforts to disseminate science to non-expert audiences and the general public. In this regard we highlight organization, coordination and teaching of a rheology workshop oriented for young audiences as part of the European Researchers Night celebrated at CENIEH institute in Burgos.
All these outcomes will benefit the EU plastics industry, economy and society not only through the development of more competitive products and the creation of jobs, but also through an increased general interest in science.
MCIATTP Project General Scheme