1. Fabrication of Concussion Resistant Nanocomposites
Tong Zuo, Kuangyu Shen, Xiaoliang Li, Isaac Macwan, Prabir Patra
Department of Biomedical Engineering
University of Bridgeport, Bridgeport, CT
Introduction
Impact testing
Chronic Traumatic Encephalopathy (CTE) is a common degenerative brain disease found in people who have suffered hundreds or thousands of head impacts over the course of many years, such as, football players, military veterans and other people who have repetitive brain trauma. Polydimethylsiloxane (PDMS) based nanomaterials are gaining widespread attention in this regard.
We propose a vibration-absorbing PDMS-graphene nanocomposite manufactured by using PDMS (Sylgard 184) as a base polymer and graphene oxide/graphene as nanoparticle reinforcement. A well-controlled pore structure has been used for improve impact absorption properties as a function of porosity.
Visual Molecular Dynamics (VMD), Dynamic Mechanical Analyzer (DMA) and JMP Software has been used for sample test and data analysis.
The impact test show the energy absorption of the materials. All of the samples are under the same weight impact of the object. Increase the object height to increase the energy until the sample is broken. Result shows that the sample will absorb more energy by increasing the amount of the graphene Nano platelets. The bubble group has a significant increase of energy absorption than other groups.
Materials and Methods
PDMS based nanocomposite was fabricated by swelling the PDMS in chloroform/Tetraethyl orthosilicate (TEOS) mixture followed by ultra sonication of the graphene oxide(GO) or graphene Nano platelets in the same solvent that swells the polymer. Various factors, such as temperature, curing agent (Sylgard 184 kit and Polymethylhydrosiloxane), nanoparticle size, solvent and filler concentrations that influence the nanoparticle-polymer interface has been studied in the experiment.
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Fig.3: The energy absorption analysis graph(a) recorded by the impact test machine(b).
Visual Molecular Dynamics(VMD)
In here, VMD has been used to analysis the interface and the micro force between PDMS and Graphene. Protein Data Bank (PDB) files get from the PubChem or building by software. PSF files build by the Automatic PSF builder of VMD. And, it was using the VEGA ZZ to build the solvent box for the non-water solvent. The
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molecular dynamic analysis will generate by NAMD. After all those work, it will show the result of the hydrogen bond, molecular energy, Timeline and other data in Nano level.
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Fig.1: The basic experiment procedure using ball-and-stick molecule model(a) different size of the nanocomposite fabricated include thin film(b) and Round cake(c) could support different type of tests.
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Dynamic Mechanical Analyzer (DMA)
Fig.4: The interface and micro force between PDMS and Graphene analysis by VMD.
The stiffness of PDMS-Graphene nanocomposites and pure PDMS were measured using DMA. The modulus of elasticity is often one of the primary properties considered when selecting a material. A high modulus of elasticity is sought when deflection is undesirable, while a low modulus of elasticity is required when flexibility is needed.
Discussion and Conclusion
Graphene Nano platelets could make composite harder than Graphene oxide(GO), GO plays a role of both filler and curing agent. More filler added into composite, higher elasticity and crisp properties could be achieve. PMHS have faster curing time than Dow Corning kit. High temperature could rush the curing process but also make the material more “hard”.
However, faster time usually come with Inhomogeneous situation which means bubbles. Decrease curing agent percentage will need longer time to finish curing process but could produce more “soft” material. Nanocomposite with uniform bubble structure have twice impact absorb properties than usual.
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Application and Future Plan
The detailed understanding of dynamic stiffness along with loss and storage modulus of the nanocomposites will enable its potential use as concussion resistant materials. Resulting nanocomposite may find its application as compliant heart valve mimicking biomaterials as our future plan.
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Fig.2: The result of the DMA test. Compare the stiffness with different graphene concentrate group(a,b), when we add the graphene to the PDMS, the stiffness will increase. Once the graphene proportion reach the limit point, the stiffness will start decrease. Different graphene proportion groups have a significant difference(c).
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Acknowledgements
Thanks to  Dr. Pulickel Ajayan, ChandraSekhar Tiwary, Samora Peter from Rice University Department of Mechanical Engineering for impact testing and DMA analyze result support.
University of Bridgeport Department of Biomedical Engineering for the research opportunity provided.