Computer Simulations of Crystallization Mechanism in Polymeric Materials

Anwar, Muhammad

Reference : Computer Simulations of Crystallization Mechanism in Polymeric Materials


	Document type :	Dissertations and theses : Doctoral thesis
	Discipline(s) :	Physical, chemical, mathematical & earth Sciences : Physics
	To cite this reference:	http://hdl.handle.net/10993/19993

Title :	Computer Simulations of Crystallization Mechanism in Polymeric Materials
Language :	English
Author, co-author :	Anwar, Muhammad [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit >]
Publication date :	22-Dec-2014
Institution :	University of Luxembourg, Luxembourg
Name of the degree :	PhD in Physics
Number of pages :	125
Supervisor :	Schilling, Tanja
President of the jury :	Sanctuary, Roland
Member of the jury :	Malvetti, Massimo
	Wagner, Christian
	Messina, René
Keywords :	[en] Crystallization ; Nucleation & Growth ; Simulations
Abstract :	[en] In this work, we have studied crystallization in short polymer chains using molec- ular dynamics simulations. We use a realistic united atom model which is able to reproduce the physical quantities related to phase transitions. We present a study of crystal nucleation from undercooled melts of n-alkanes and identify the molec- ular mechanism of homogeneous crystal nucleation under quiescent conditions and under shear flow. We choose n-eicosane (C20) the length of which is below the en- tanglement length and n-pentacontahectane (C150) the length of which is above the entanglement length so that we can compare results for unentangled and entangled polymer chains. We also provide the crystal growth mechanism of n-eicosane under quiescent conditions. For C150, we present crystal lamellae structure and compare our results with published simulation results. We use a mean first passage time analysis and a committor analysis to determine the critical nucleus size and then to compute the nucleation rate. We observe that the critical nucleus is of cylindrical shape. We report on the effects of shear rate and temperature on the nucleation rates and estimate the critical shear rates, beyond which the nucleation rate in- creases with the shear rate. We show that the critical shear rate corresponds to a Weissenberg number of order unity which is in agreement with previous experimen- tal observation and theoretical work. We also show that the power law behaviour between nucleation rate and shear rate is in agreement with experiments and theory. We compute the viscosity of the system during the formation of crystalline nuclei and we show that the viscosity of the system is not affected by the crystalline nuclei. Finally, we present results of crystallization in the polyethylene (C500) melt under quiescent conditions.
Research centres :	University of Luxembourg
Funders :	Fonds National de la Recherche - FnR
Name of the research project :	F1R-PHY-PFN-10POLY > POLYSHEAR : Structure formation in sheared polymer systems > 01/02/2011 - 31/01/2014 > SCHILLING Tanja
Target :	Researchers ; Professionals ; Students ; General public ; Others
Permalink :	http://hdl.handle.net/10993/19993

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