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European Training Network to Accelerate the Development Chain of Nanostructured Polymers

Periodic Reporting for period 2 - TheLink (European Training Network to Accelerate the Development Chain of Nanostructured Polymers)

Reporting period: 2016-11-01 to 2018-10-31

TheLink provided interdisciplinary training to 15 ESRs covering the whole development chain for nanostructured polymers. The development of such materials for 3 case studies (phase separated polymers, separation membranes and conductive polymer composites) was advanced through interlinked PhD projects in the disciplines of simulation, production and characterization.

This interdisciplinary approach is important as several steps, spanning various disciplines, are needed from the concept of a nanostructured material and the generation of a desired functionality through to the final product. Often, the specialized focus of university education does not provide the necessary space to examine adjacent disciplines.

The development of functional nanostructured polymers paves the way towards new, competitive products. The faster the innovation cycles, the greater the competitiveness of EU industry. TheLink’s ESRs gained the interdisciplinary skills needed for effective innovation in this key development field.
Electrically conductive composites:

Simulation techniques establish correlations between the nano- and microstructure of materials and their macroscopic properties e.g. electrical conductivity, EMI shielding, optical and mechanical properties. The simulation techniques are based on models that were developed, improved and applied in TheLink. On an atomic scale, the chemical functionalization of CNTs helps improve their interaction with the embedding matrix. For this purpose, the load transfer between functionalized CNTs and a polyethylene matrix was calculated using a hybrid approach combining quantum mechanical methods and classical molecular dynamics. On a mesoscopic scale, a 3D model was elaborated to calculate the conductivity, EMI shielding and the optical properties, describing the composite as a resistor/capacitor network. The effective conductivity of polymer/CNT composites at larger length scales, together with mechanical and strain-sensing capabilities, was calculated using a finite element analysis based on representative volume elements.

The cost-effective characterization of the nano- and microstructure of composites is an unsolved problem. Measurement of the dielectric properties and the use of optical coherence tomography (OCT) can overcome this. A model to describe the effective dielectric properties of 2-phase materials, depending on the volume fraction of the phases, particle aspect ratio and particle orientation, was elaborated and experimentally verified. The speed, robustness and compactness, as well as the measurement accuracy and sensitivity of an OCT system were significantly improved by using chip-scale frequency comb generators as optical sources and by dedicated signal processing techniques. Reference measurement techniques were applied and further developed, also to evaluate material compatibility with the techniques. Polarized Raman spectroscopy, SEM, FIB-SEM and 3view-SEM including advanced preparation techniques like plasma etching were used.
The production of conductive composites based on CNTs and graphene was also addressed. The percolation curves of graphene in epoxy, PVC plastisol, PP and PA6 were determined. TPU/graphene composites with different reduced graphene oxides were produced and characterized to study the effect of oxygen content. The production process for graphene oxide was improved to minimize defects. For the spatial orientation of CNTs in media with low viscosity due to electric fields, experimental setups were built to produce composite samples. Various matrix/filler systems were tested with a range of processing parameters. To find the electromagnetic interference shielding effectiveness of conductive injection-moulded polymer composites, a measurement setup was designed and validated using electromagnetic wave FEM simulation software. Preliminary measurements of injection moulded polycarbonate/carbon nanotubes (PC/CNTs) composites were performed.

Separation membranes:

Wearable artificial kidneys increase the comfort of dialysis patients but require highly sophisticated separation membranes. The modelling of membranes accelerates their development to achieve the necessary separation/removal performance and the flux through the membrane. A 3D computer simulation model of a membrane with an attached cell monolayer of immortalized living proximal tubule epithelial cells (ciPTEC) was built using the Comsol Multiphysics software. The stochastic porous topology of a mixed matrix membrane was generated by an algorithm. Property calculations taking account of the toxin transport through MMMs and the adsorption of the toxin on the embedded sorbent were performed. Two strategies were adopted to produce dialysis membranes: (i) chitosan-based adsorbents incorporated as particles in MMM and (ii) positively charged nanofiltration membranes. To remove endotoxins a further concept consisting of MMM composed of activated carbons dispersed in a polymeric matrix was developed. Furthermore PVDF hydrophilic and hydrophobic membranes using non-solvent induced phase separation were developed and a hydrophilic PES membrane, produced by vapor induced phase inversion, was optimized.

Phase separated polymers:

A model to simulate the formation of phase separated polymers was developed using quantum chemistry, molecular dynamics and mesoscopic simulation. The viscosity, density and the measured IR spectra of the precursor alkyl-diiscocyanurate trimers (ADI) could be predicted with a good accuracy. Mono- and diisocyanate trimers with 4-7 carbon atoms in the isocyanate structures were synthesized as precursors of phase separated polyurethanes. Viscosity studies of various monomer HDI-trimers and derivatives were carried out and the findings explained based on simulations. The processing and analysis of HDI-trimer based network structures was initiated.
17 exploitable results were defined for TheLink and exploitation strategies were developed by the ESRs. Dissemination took the form of scientific publications (13 by October 2018; 7 more which are accepted or under review). Furthermore, 24 contributions were made to conferences (oral presentations and posters).
In simulation, new models for different types of composites were developed, partly by combining simulation techniques over various length scales or by using 3D models of the microscopic structure of materials derived from measurements of the real material structure.

For newly synthesized chemical species useful as precursors to produce phase separated polymers, the density, the optical behavior and viscosity could be predicted with a high accuracy.
Models to predict the removal of specific species from blood by porous membranes and mixed matrix membranes were developed and tested by initial calculations.
In the area of characterization, measurement techniques were improved in view of their accuracy (OCT) or successfully applied to various material combinations (SEM and polarized Raman spectroscopy). Measurement setups were built for EMI shielding and dielectric properties.

In the area of processing, several setups for the spatial orientation of nanostructures in the composites were built and successfully tested for low viscous matrix systems. New insights were gained on the influence of processing parameters and the oxidation state of graphenes on the mechanical, thermal and electrical properties of their thermoplastic and thermoset composites.