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Kowalik, Malgorzata

Publications and source records attributed to Kowalik, Malgorzata.

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Cost-effective carbon fiber precursor selections of polyacrylonitrile-derived blend polymers: carbonization chemistry and structural characterizations

Blending polyacrylonitrile (PAN) with plastic wastes and bio-based polymers provides a convenient and inexpensive method to realize cost-effective carbon fiber (CF) precursors. In this work, PAN-based blend precursors are investigated using ReaxFF reactive molecular dynamics simulations with respect to the formation of all-carbon rings, the evolutions of oxygen-containing and nitrogen-containing species, and the migration of carbon atoms to form turbostratic graphene. From these simulations, we identify that PAN/cellulose (CL) blend manifests the highest carbon yield and the most substantial all-carbon ring formation. This ReaxFF-based finding is confirmed by Raman and TEM experiments indicating high crystallinity for PAN/CL-derived blend CFs. We trace the pathway of gasification and carbonization of PAN/CL to elaborate the mechanism of the formation of all-carbon ring networks. We discover that the acetals of CL can catalyze the cyclization of the blend precursor, allowing for the search for CL derivatives or the other kinds of bio-based polymers with similar functionalities as alternative blends. In addition, we examine the structural characteristics using the carbon–carbon (C–C) radial distribution functions, C–C bond length distributions, and sp2 C atom ratios for the four representative precursors, i.e., PAN, oxidized PAN, PAN/nylon 6,6, and PAN/CL. Our simulation results show the most extensive all-carbon ring cluster and graphitic structure growths for PAN/CL. Here, we propose PAN/CL as a cost-effective alternative CF precursor, since (a) CL is naturally abundant and eco-friendly for production, (b) the blend precursor PAN/CL does not require oxidation treatment, (c) PAN/CL has a high carbon yield with substantial all-carbon ring formation, and (d) PAN/CL based CFs potentially provide a mechanical property enhancement.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Atomistic-Scale Simulations on Graphene Bending Near a Copper Surface

Molecular insights into graphene-catalyst surface interactions can provide useful information for the efficient design of copper current collectors with graphitic anode interfaces. As graphene bending can affect the local electron density, it should reflect its local reactivity as well. Using ReaxFF reactive molecular simulations, we have investigated the possible bending of graphene in vacuum and near copper surfaces. We describe the energy cost for graphene bending and the binding energy with hydrogen and copper with two different ReaxFF parameter sets, demonstrating the relevance of using the more recently developed ReaxFF parameter sets for graphene properties. Moreover, the draping angle at copper step edges obtained from our atomistic simulations is in good agreement with the draping angle determined from experimental measurements, thus validating the ReaxFF results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Low-temperature carbonization of polyacrylonitrile/graphene carbon fibers: A combined ReaxFF molecular dynamics and experimental study

Graphene inclusion in a polymer matrix is a promising route to significantly enhance the mechanical properties of low-grade carbon fibers (CFs). Using ReaxFF molecular dynamics simulation, the atomistic mechanism leading to this enhancement is investigated. We demonstrate that the graphene edges along with the nitrogen and oxygen functional groups play a catalytic role and act as seeds to expedite alignment of the all-carbon rings, which are starting sites for the growth of graphitic structures. To examine the role of this proposed mechanism that enhances the graphitic structure of PAN/graphene CFs, we discuss the experimental results wherein the PAN/graphene CFs carbonized at 1250 C demonstrate 91% (from 632 to 1207 MPa) increase in strength and 101% (from 88 to 177 GPa) enhancement in Young’s modulus compared to PAN-based CFs carbonized at 1500 C. In conclusion, these enhanced mechanical properties of low-grade carbon fibers achieved via graphene inclusion at decreased carbonization temperature provide a means to realize both energy savings and cost reduction.

42 ENGINEERING↗