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Organic Phase Change Materials (PCMs) 鈥� as cheap, non-toxic, and stable technical-grade paraffins - are starting to play an important role in heat storage. Though promising, their widespread implementation is limited by their rather low thermal conductivity. We propose to address this problem by augmenting the paraffin system by small amounts of high-aspect ratio carbon-based nanofillers that have much higher conductivity. The enhanced thermal conductivity in such hybrid systems would permit a much larger heat flux to be sustained between a source or sink of heat and the augmented paraffin system. Recent experiments report that a relatively low fraction of carbon nanotubes (CNTs), can significantly (factor 2-3) increase the thermal conductivity of some organic fluids. For concentrations well above the percolation threshold (below 0.2%), or for very anisotropic nanofillers (aspect ratio above 1000) simple geometrical considerations provide estimates for the paraffin-CNT composite thermal conductivity a full 100 times larger than that of pristine paraffin. The marked disparity between this theoretical limit and the recent experimental findings suggests there is ample room for further optimization. We believe that this disparity is mainly due to the poor filler-filler contacts.
The focus of this proposal is on solving this problem and exploiting the full potential of augmented paraffin systems. In Wax+ project we suggest to study 2D graphene colloids as potentially interesting candidate nanofillers.         

Using heterogeneous multiscale paraffin nanocomposite modelling and experimentation, we will

• simulate and advise on the ideal filler-filler contacts and filler-matrix interface structure; this interface should be such that the fillers are hierarchically dispersed in the matrix, yet still enabling good filler-filler contacts;
• connect sub-micron, atomistic properties of the interface to macroscopic network scales, predict thermal conductivity, and develop practical strategies to increase thermal conductivity drastically;
• concentrate on the functionalization of the nanofiller surface and the properties of the filler-matrix interface.

We will investigate routes towards ideal PCM paraffin-nanofiller mixtures, performing according to the following specifications:

• Large thermal conductivity;
• Low interfacial thermal resistance; Large filler shape anisotropy and proper dispersal in the paraffin matrix;
• Interfacial polymer matrix layers providing good phonon coupling and good filler contacts;

We will also investigate and steer the nanofiller agglomeration. We will identify conditions such that the nanofiller particles 鈥榓ssemble spontaneously鈥�, creating heat conducting pathways over longer distances.

• Large (network) scales: Synthesis and experimental testing of the samples (H. Friedrich, H. Huinink), Computational Fluid Dynamics modelling of the resulting composite from the fully resolved to the coarsest scales (B. Geurts);
• Molecular scales, interfacial and contact properties: Fully atomistic and coarse-grained classical molecular-dynamics modelling of the interfacial thermal conductivity, filler-filler and filler-matrix interactions (A. Lyulin);
• Atomistic scales, phonon scattering: quantum (Density-Functional Theory) calculations (P. Bobbert).

• Alexey Lyulin (PI), Group Theory of Polymers and Soft Matter (TPS), Eindhoven University of Technology and Center for Computational Energy Research (CCER)
• P.A. Bobbert, Group Molecular Materials and Nanosystems (M2N), Eindhoven University of Technology (TUE) and Center for Computational Energy Research (CCER)
• H. Friedrich, Group Physical Chemistry (SPC), Eindhoven University of Technology (TUE) and Center for Multiscale Electron Microscopy
• B.J. Geurts, Multiscale Modeling and Simulation Group (MMS), Faculty EEMCS, University of Twente (UT) and Center for Computational Energy Research (CCER)
• H.P. Huinink, Group Transport in Permeable Media (TPM), Eindhoven University of Technology (TUE) and Center for Computational Energy Research (CCER)
• Bosch Thermotechniek Deventer, The Netherlands
• TNO-ECN
• Nanocyl
• MDP Srl

This Wax+ project is granted by the OTP Programme of the NWO TTW Domain. The mission of this NWO domain is to facilitate applied research that yields applications and impact for people and society. The aim of the NWO 鈥� TTW 鈥� OTP program is to stimulate projects that combine science with concrete application possibilities of the results. The TTW Domain of NWO provides funding up to a maximum of 850,000 euros. If the total project costs exceed 600,000 euro, co-funding by users (industrial partners) is compulsory. It amounts to 25% of the sum in excess of 600,000 euro.