Publications by authors named "Malgorzata Kowalik"

6 Publications

  • Page 1 of 1

Atomistic Mechanisms of Thermal Transformation in a Zr-Metal Organic Framework, MIL-140C.

J Phys Chem Lett 2021 Jan 15;12(1):177-184. Epub 2020 Dec 15.

Department of Mechanical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.

To understand the mechanisms responsible for thermal decomposition of a Zr-MOF (MIL-140C), we perform atomistic-scale molecular dynamics (MD) simulations and discuss the simulation data in comparison with the TEM images obtained for the decomposed Zr-MOF. First, we introduce the ReaxFF parameters suitable for the Zr/C/H/O chemistry and then apply them to investigate the thermal stability and morphological changes in the MIL-140C during heating. Based on the performed simulations we propose an atomic mechanism for the collapse of the MIL-140C and the molecular pathways for carbon monoxide formation, the main product of the MIL-140C thermal degradation. We also determine that the oxidation state of the ZrO clusters, evolved due to the thermal degradation, approximates the tetragonal phase of ZrO. Both simulations and experiments show a distribution of very small ZrO clusters embedded in the disrupted organic sheet that could contribute to the unusual high catalytic activity of the decomposed MIL-140C.
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http://dx.doi.org/10.1021/acs.jpclett.0c02930DOI Listing
January 2021

Graphene reinforced carbon fibers.

Sci Adv 2020 Apr 24;6(17):eaaz4191. Epub 2020 Apr 24.

Department of Mechanical and Aerospace Engineering, University of Virginia, 122 Engineer's Way, Charlottesville, VA 22904, USA.

The superlative strength-to-weight ratio of carbon fibers (CFs) can substantially reduce vehicle weight and improve energy efficiency. However, most CFs are derived from costly polyacrylonitrile (PAN), which limits their widespread adoption in the automotive industry. Extensive efforts to produce CFs from low cost, alternative precursor materials have failed to yield a commercially viable product. Here, we revisit PAN to study its conversion chemistry and microstructure evolution, which might provide clues for the design of low-cost CFs. We demonstrate that a small amount of graphene can minimize porosity/defects and reinforce PAN-based CFs. Our experimental results show that 0.075 weight % graphene-reinforced PAN/graphene composite CFs exhibits 225% increase in strength and 184% enhancement in Young's modulus compared to PAN CFs. Atomistic ReaxFF and large-scale molecular dynamics simulations jointly elucidate the ability of graphene to modify the microstructure by promoting favorable edge chemistry and polymer chain alignment.
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http://dx.doi.org/10.1126/sciadv.aaz4191DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7182419PMC
April 2020

Unveiling Carbon Ring Structure Formation Mechanisms in Polyacrylonitrile-Derived Carbon Fibers.

ACS Appl Mater Interfaces 2019 Nov 1;11(45):42288-42297. Epub 2019 Nov 1.

Department of Mechanical and Aerospace Engineering , University of Virginia , 122 Engineer's Way , Charlottesville , Virginia 22904 , United States.

As the demand for electric vehicles (EVs) and autonomous vehicles (AVs) rapidly grows, lower-cost, lighter, and stronger carbon fibers (CFs) are urgently needed to respond to consumers' call for greater EV traveling range and stronger safety structures for AVs. Converting polymeric precursors to CFs requires a complex set of thermochemical processes; a systematic understanding of each parameter in fiber conversion is still, to a large extent, lacking. Here, we demonstrate the effect of carbonization temperature on carbon ring structure formation by combining atomistic/microscale simulations and experimental validation. Experimental testing, as predicted by simulations, exhibited that the strength and ductility of PAN CFs decreased, whereas the Young's modulus increased with increasing carbonization temperature. Our simulations unveiled that high carbonization temperature accelerated the kinetics of graphitic phase nucleation and growth, leading to the decrease in strength and ductility but increase in modulus. The methodology presented herein using combined atomistic/microscale simulations and experimental validation lays a firm foundation for further innovation in CF manufacturing and low-cost alternative precursor development.
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http://dx.doi.org/10.1021/acsami.9b15833DOI Listing
November 2019

Atomistic Scale Analysis of the Carbonization Process for C/H/O/N-Based Polymers with the ReaxFF Reactive Force Field.

J Phys Chem B 2019 Jun 13;123(25):5357-5367. Epub 2019 Jun 13.

During the carbonization process of raw polymer precursors, graphitic structures can evolve. The presence of these graphitic structures affects mechanical properties of the carbonized carbon fibers. To gain a better understanding of the chemistry behind the evolution of these structures, we performed atomistic-scale simulations using the ReaxFF reactive force field. Three different polymers were considered as a precursor: idealized ladder PAN (polyacrylonitrile), a proposed oxidized PAN, and poly( p-phenylene-2,6-benzobisoxazole). We determined the underlying molecular details of polymer conversion into a carbon fiber structure. Because these are C/H/O/N-based polymers, we first developed an improved force field for C/H/O/N chemistry based on the density functional theory data with a particular focus on N formation kinetics and its interactions with polymer-associated radicals formed during the carbonization process. Then, using this improved force field, we performed atomistic-scale simulations of the initial stage of the carbonization process for the considered polymers. On the basis of our simulation data, the molecular pathways for the formation of low-molecular-weight gas species and all-carbon ring formation were determined. We also examined the possible alignment of the developed all-carbon 6-membered ring clusters, which is crucial for the further graphitic structure evolution.
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http://dx.doi.org/10.1021/acs.jpcb.9b04298DOI Listing
June 2019

[Secrets of the red-headed].

Pol Merkur Lekarski 2016 Dec;41(246):306-309

Medical University of Wrocław Poland: Students of Medical Faculty.

Only 1-2% of people is red-headed but in the Russian Udmurt Republic or United Kingdom they can be met more often. A specific variant of MC1R gene (R allele) is responsible for the red hair. The gene encodes a receptor for melanocortins. These substances stimulate melanocytes to product melanin- a dye of the skin which is transported to keratinocytes. It protects a cellular nucleus from ultraviolet radiation. Melanin has two types: eumelanin which is dark brown or even black and red/orange pheomelanin. The second one is mostly observed in red-headed which is caused by R allele. The DNA damage occurs more easily because of worse protecting ability of pheomelanin. Moreover this allele is connected with inefficient DNA repair. People with R allele have not only flaming red hairstyle but also very fair skin (often with freckles) and blue eyes. Unfortunately this phenotype is more exposed to harmful effects of UV rays. It means that too extensive exposition to solar light leads to sunburn and development of cancerous skin diseases with melanoma as the worst. R allele is a recessive variant of the gene so only in homozygous persons this characteristic phenotype is observed. Nevertheless blond- or auburn-haired carriers of this allele are also more prone to develop carcinomas. The red-headed also differ from the others in sensitivity to anaesthetics, what is shown by increased MAC. On the other hand these persons less often suffer from vitamin D deficiency. The aim of the article is to present facts and myths of red-headed.
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December 2016

Oscillations and dynamics in a two-dimensional prey-predator system.

Phys Rev E Stat Nonlin Soft Matter Phys 2002 Dec 9;66(6 Pt 2):066107. Epub 2002 Dec 9.

Department of Physics, A. Mickiewicz University, 61-614 Poznań, Poland.

Using Monte Carlo simulations we study two-dimensional prey-predator systems. Measuring the variance of densities of prey and predators on the triangular lattice and on the lattice with eight neighbors, we conclude that temporal oscillations of these densities vanish in the thermodynamic limit. This result suggests that such oscillations do not exist in two-dimensional models, at least when driven by local dynamics. Depending on the control parameter, the model could be either in an active or in an absorbing phase, which are separated by the critical point. The critical behavior of this model is studied using the dynamical Monte Carlo method. This model has two dynamically nonsymmetric absorbing states. In principle both absorbing states can be used for the analysis of the critical point. However, dynamical simulations which start from the unstable absorbing state suffer from metastablelike effects, which sometimes renders the method inefficient.
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http://dx.doi.org/10.1103/PhysRevE.66.066107DOI Listing
December 2002