Molecular Simulations of Carbon- Polymer Interfaces: Potential for Multiscale Composite Design

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Oswald Lynch
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Baris Demir Institute for Frontier Materials

1 ICME, Melbourne, Feb Molecular Simulations of Carbon- Polymer Interfaces: Potential for Multiscale Composite Design Prof. Tiff Walsh and Dr. Baris Demir Institute for Frontier Materials Deakin University Phone: +61 (0)

CARBON NEXUS Carbon Nexus is an open-access research facility focused on carbon fibre & composite materials Owned and operated by Deakin University and opened in May 2014 Developed in collaboration

2 CARBON NEXUS Carbon Nexus is an open-access research facility focused on carbon fibre & composite materials Owned and operated by Deakin University and opened in May 2014 Developed in collaboration with the Victorian Centre for Advanced Materials Manufacturing (VCAMM) A nexus between industry, academia, research and training Vision: A world-class facility to attract global companies to research and invest in Australia The centre was established with A$34M of funding from Deakin University, Australian Federal Government and Victorian State Government as part of the Australian Future Fibres Research and Innovation Centre (AFFRIC)

3 WHAT MAKES CARBON NEXUS UNIQUE? Was the first world-wide to offer a pilot scale carbon fibre line in a university. Enables industrially relevant research and the ability to manufacture new carbon fibre materials in sufficient quantities to make prototype parts. Research at CN encompasses the entire carbon fibre and composite value chain, from molecules to materials. Deakin University CRICOS Provider Code: 00113B

4 Carbon Reinforced Polymer Composites: Benefits and Challenges Challenges for: Integrity Durability Repair/Maintenance Inherently multiscale *

5 Carbon Fibre: a multi-scale structure with many unknowns A. R. Bunsell, Fibre Reinforcement for Composite Materials. fibre long axis oriented microcrystallites turbostratic carbon & graphitised layers Behr et al, Carbon, 107, 525 (2016) Schimmelpfennig &, J Env Qual, 41, 1001 (2011)

6 Polymer resin: molecular-level details Thermoset polymers: precursor liquid 3-D cross-linked polymers EPON-862 Cross-linking takes place between the terminal Carbon atom of the EPON-862 and the Nitrogen atom of the DETDA molecules. DETDA (CROSS-LINKER) epoxy cross-linker cross-linked polymer In our simulations we dynamically cross-link the polymer (liquid) in the presence of the CF surface

7 The Carbon Fibre/Resin Interface and Interphase Bulk polymer chain packing Interphase polymer chain packing is not in bulk-like state handshake region Carbon Fibre Surface This handshake region is the interphase. We seek to tune the interphase to optimise stress transfer. Getty images

The soft-soft-hard interface provides a graded handshake region between the two very

8 Hard/Soft Composite Interfaces in Nature Nacre a natural composite with excellent mechanical properties. The soft-soft-hard interface provides a graded handshake region between the two very different phases of matter. Adapted from Sugawara-Narutaki, Polym. J Inspiration for improving fibre-to-matrix interactions in CF-epoxy composites?

9 Surface-Grafted Chains: a Tailored Handshake Region Grafted functionalised molecules = designer sizing with tailored interfacial properties. Carbon Fibre Surface

amine-bearing groups enables chemical bonding at the fibre-to-resin interface.

10 Surface Functionalisation of Carbon fibre: Tailoring the Resin/CF Interface CF surface is chemically inert CF needs to be functionalised polymer Carbon surface interphase Surface grafted molecules (SGMs): attachment of amine-bearing groups enables chemical bonding at the fibre-to-resin interface. How does the polymer matrix influence the SGMs? Do SGMs modify the interphase? If yes, how? How to design SGMs to optimise interfacial properties?

11 Interfacial Enrichment Carbon Fibre Surface Carbon Fibre Surface

12 Interfacial Enrichment Opportunities to tune the interphase Bulk-like precursor mixture at interface? Unlikely Interfacial enrichment of pre-cursor. Carbon Fibre Surface Carbon Fibre Surface

at the molecular level discovery using experimental techniques alone.

13 Why Molecular Simulation? Computer simulations can complement experimental characterisation efforts: It is challenging to investigate interfacial structure at the molecular level discovery using experimental techniques alone. Molecular dynamics (MD) simulations can provide practical guidance by guidance revealing links between the structure and properties of the polymer/carbon fibre interface. Molecular simulations provide inputs for the parametrisation of Finite Element translation approaches. SGMs on the CF surface

EPON and DETDA and equilibrate it. Cross-link dynamically.

14 Our in-situ dynamic cross-linking procedure EPON Demir and Walsh, Soft Matter, (2016), 12, 2453 Generate a liquid mix of EPON and DETDA and equilibrate it. Cross-link dynamically. Cool it down to room temperature and test under strain. DETDA polymer matrix

15 polymer in-situ computational cross-linking at CF interfaces Cross-linked CFRP sample ready for computational mechanical testing Surface functionalised (with SGM) CF surface polymer matrix SGM CF

16 in-situ computational cross-linking for CF interfaces Demir, Henderson and Walsh, ACS Appl. Mater. Interfaces, (2017), 9, polymer matrix SGM CF interphase bulk polymer SGM conformations on the CF surface in liquid precursor Allignment of spatial arrangements: SGM conformations and liquid mixture structure.

17 Computational mechanical testing: Pull-out tests We displaced the CF with a constant velocity out of the simulation cell and register the potential energy change interfacial shear stress (ISS) Pull-out Displacement = 0 Å Pull-out Displacement = 20 Å ISS from our simulations matches the trend in IFSS from experimental SFFT ISS / GPa Bare Unreac ve Reac ve Demir, Henderson and Walsh, ACS Appl. Mater. Interfaces, (2017), 9,

Further comparisons of SGM design and interfacial additives Different

, Fox, Walsh and Henderson, Carbon, (2017) Ionic liquid in bare and

Sci. Technol, (2018) SGM chain rigidity Demir et. al.

18 Further comparisons of SGM design and interfacial additives Different SGM chemistries Different SGM chain architectures Demir et al., Fox, Walsh and Henderson, Carbon, (2017) Ionic liquid in bare and grafted CF models Demir et. al., Fox, Henderson and Walsh, Compos. Sci. Technol, (2018) SGM chain rigidity Demir et. al., Walsh and Henderson, J. Mat. Chem. A, (2018) Demir, Henderson, Walsh & co-workers, in preparation.

Next steps: Use outcomes of molecular simulations and experimental single-fibre characterisation to parametrise mesoscale models of the composite performance for grafted Multi-scale opportunities:

19 Next steps: Use outcomes of molecular simulations and experimental single-fibre characterisation to parametrise mesoscale models of the composite performance for grafted Multi-scale opportunities: Link Single-Fibre tests to Composites The ISS is not directly comparable to the IFSS misses effects on the macro lengthscale: plastic flow, resin shrinkage, etc. Single fibre fragmentation tests do not test the mechanical response of a composite.

20 Multi-scale opportunities: Improved Carbon Fibre models fibre long axis oriented microcrystallites turbostratic carbon & graphitic layers Behr et al, Carbon, 107, 525 (2016) Schimmelpfennig &, J Env Qual, 41, 1001 (2011) Tomas et al, Carbon, 119, 1 (2017)

21 Summary and Outlook Our MD simulation procedures are incorporated into opensource software packages. Outcomes from our simulations are consistent with single-fibre experimental characterisation for a growing range of SGM chemistries, architectures, and different resins. Extended our procedure to other systems with multi-scale relevance: graphene-nanoplatelet-reinforced nanocomposites, polymer/polymer interfaces (Bremen), hydrogel materials (HUST), and next: polymer-grafted surfaces (ARC DP18). Our long-term goal: incorporate our findings into higher-scale models of composites capture influence of sample features (e.g. composite lay-up) and phenomena on longer lengthscales and timescales (e.g. plastic flow during deformation).

Acknowledgements: High Performance Computing

22 Acknowledgements: High Performance Computing facilities: NCI & Pawsey centre. The experimental team: Luke Henderson, Bronwyn Fox, Luke O Dell, Sally McArthur, Linden Servinis, Kathleen Beggs. Group contributions: Dr. Baris Demir. The ARC, CSIRO, Deakin University and Carbon Nexus for support.

Supporting Information for: Design Rules for. Enhanced Interfacial Shear Response in. Functionalized Carbon Fiber Epoxy Composites

Supporting Information for: Design Rules for Enhanced Interfacial Shear Response in Functionalized Carbon Fiber Epoxy Composites Baris Demir, Luke C. Henderson, and Tiffany R. Walsh Institute for Frontier