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Effects of Size and Coalescence on the Interfacial Dynamics of Nanoparticles: A Molecular Dynamics Study Open Access

Descriptions

Other title
Subject/Keyword
nanoparticle shape fluctuation
molecular dynamics
nanoparticles
string collective atomic motion
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Yang, Ying
Supervisor and department
Zhang, Hao (Department of Chemical and Materials Engineeering)
Examining committee member and department
Liu, Jinfeng (Department of Chemical and Materials Engineeering)
Chen, Weixing (Department of Chemical and Materials Engineeering)
Zeng, Hongbo (Department of Chemical and Materials Engineeering)
Deng, Chuang (Department of Mechanical Engineering, University of Manitoba)
Semagina, Natalia (Department of Chemical and Materials Engineeering)
Department
Department of Chemical and Materials Engineering
Specialization
Materials Engineering
Date accepted
2015-09-29T17:19:09Z
Graduation date
2015-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Normally chemically inert materials such as Au have been found to be catalytically active in the form of particles whose size is about 1 nm. Direct and indirect observations of various types of metal nanoparticles (NPs) in this size range, under catalytically relevant conditions for fuel-cell operation and catalysis, have indicated that such ‘small’ particles can exhibit large spontaneous shape fluctuations and significant changes in shape and chemical activity in response to alterations in environmental conditions. NPs also normally exhibit facile coalescence when in proximity, and these agglomations impact their stability and reactivity in applications. Our molecular dynamics simulations first focus on Ni nanoparticles, a commonly used NP in catalytic applications and carbon nanotube growth, in the ~ 1 nm size regime where large scale shape fluctuations have been observed experimentally. An analysis of the large scale shape fluctuations observed in our simulations of these ‘small’ NPs indicates that they are accompanied by collective migration motion of Ni atoms through the NP center and we quantify these dynamic structures and their impact on NP shape. In contrast, string-like collective atomic motion is confined to the NP interfacial region of NPs having a diameter greater than a few nm and, correspondingly, the overall NP shape remains roughly spherical, a case studied in our prior Ni NP simulations. Evidently, the large spontaneous NP shape fluctuations reflect a change in character of the collective atomic dynamics when the NPs become critically small in size. Meanwhile, we are aimed to investigate the NP sintering and coalescence phenomenon quantitatively to determine the string-like collective motions in the coalescence of ultra-small NPs and the crystallization process to form the crystalline nanoparticles. We identify the string-like collective motions accompany the evolvements of the local fcc structure, the local icosahedral structure and the liquid-like structure as well as the crystallization process, rather than the rotations of the NPs, in the coalescence of the multiple ultra-small NPs. The recognition of this phenomenon would help us understand the early stages of crystal growth and structural rearrangement of the relatively disordered ‘amorphous’ pre-nucleation clusters. Finally, we explore the NP behavior under the constraint of the graphene substrate as the supporting material. The results show that NP affected by the substrate has lower ratio of the local fcc structure than the single free NP, indicating that the substrate makes the NP more disordered and more active.
Language
English
DOI
doi:10.7939/R3RR1PS3P
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Y. Yang, H. Zhang and J. Douglas, "Origin and Nature of Spontaneous Shape Fluctuations in 'Small' Nanoparticles," ACS Nano, 8, 7465-7477 (2014).

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