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Ridings KM, Hendy SC. Nanowire melting modes during the solid-liquid phase transition: theory and molecular dynamics simulations. Sci Rep 2022; 12:20052. [PMID: 36414690 PMCID: PMC9681868 DOI: 10.1038/s41598-022-24654-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2022] [Accepted: 11/18/2022] [Indexed: 11/24/2022] Open
Abstract
Molecular dynamics simulations have shown that after initial surface melting, nanowires can melt via two mechanisms: an interface front moves towards the wire centre; the growth of instabilities at the interface can cause the solid to pinch-off and breakup. By perturbing a capillary fluctuation model describing the interface kinetics, we show when each mechanism is preferred and compare the results to molecular dynamics simulation. A Plateau-Rayleigh-type of instability is found and suggests longer nanowires will melt via an instability mechanism, whereas in shorter nanowires the melting front will move closer to the centre before the solid pinch-off can initiate. Simulations support this theory; preferred modes that destabilise the interface are proportional to the wire length, with longer nanowires preferring to pinch-off and melt; shorter wires have a more stable interface close to their melting temperature, and prefer to melt via an interface front that moves towards the wire centre.
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Affiliation(s)
- Kannan M. Ridings
- grid.9654.e0000 0004 0372 3343The MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Physics, The University of Auckland, Auckland, 1010 New Zealand
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Afkhami S. Challenges of numerical simulation of dynamic wetting phenomena: a review. Curr Opin Colloid Interface Sci 2022. [DOI: 10.1016/j.cocis.2021.101523] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Surface, Interface, and Temperature Effects on the Phase Separation and Nanoparticle Self Assembly of Bi-Metallic Ni0.5Ag0.5: A Molecular Dynamics Study. NANOMATERIALS 2019; 9:nano9071040. [PMID: 31330888 PMCID: PMC6669487 DOI: 10.3390/nano9071040] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 07/10/2019] [Accepted: 07/19/2019] [Indexed: 11/16/2022]
Abstract
Classical molecular dynamics (MD) simulations were used to investigate how free surfaces, as well as supporting substrates, affect phase separation in a NiAg alloy. Bulk samples, droplets, and droplets deposited on a graphene substrate were investigated at temperatures that spanned regions of interest in the bulk NiAg phase diagram, i.e., miscible and immiscible liquid, liquid-crystal, and crystal-crystal regions. Using MD simulations to cool down a bulk sample from 3000 K to 800 K, it was found that phase separation below 2400 K takes place in agreement with the phase diagram. When free surface effects were introduced, phase separation was accompanied by a core-shell transformation: spherical droplets created from the bulk samples became core-shell nanoparticles with a shell made mostly of Ag atoms and a core made of Ni atoms. When such droplets were deposited on a graphene substrate, the phase separation was accompanied by Ni layering at the graphene interface and Ag at the vacuum interface. Thus, it should be possible to create NiAg core-shell and layer-like nanostructures by quenching liquid NiAg samples on tailored substrates. Furthermore, interesting bimetallic nanoparticle morphologies might be tuned via control of the surface and interface energies and chemical instabilities of the system.
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Ridings KM, Aldershof TS, Hendy SC. Surface melting and breakup of metal nanowires: Theory and molecular dynamics simulation. J Chem Phys 2019; 150:094705. [PMID: 30849918 DOI: 10.1063/1.5086435] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We consider the surface melting of metal nanowires by solving a phenomenological two-parabola Landau model and by conducting molecular dynamics simulations of nickel and aluminum nanowires. The model suggests that surface melting will precede bulk melting when the melt completely wets the surface and the wire is sufficiently thick, as is the case for planar surfaces and sufficiently large nanoparticles. Surface melting does not occur if the melt partially wets or does not wet the surface. We test this model, which assumes that the surface energies of the wire are isotropic, using molecular dynamics simulations. For nickel, we observe the onset of anisotropic surface melting associated with each of the two surface facets present, but this gives way to uniform surface melting and the solid melts radially until the solid core eventually breaks up. For aluminum, while we observe complete surface melting of one facet, the lowest energy surface remains partially dry even up to the point where the melt completely penetrates the solid core.
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Affiliation(s)
- Kannan M Ridings
- Department of Physics, MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Auckland, Auckland 1142, New Zealand
| | - Thomas S Aldershof
- School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Shaun C Hendy
- Department of Physics, MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Auckland, Auckland 1142, New Zealand
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Maekawa Y, Shibuta Y. Dewetting dynamics of nickel thin film on alpha-quartz substrate: A molecular dynamics study. Chem Phys Lett 2016. [DOI: 10.1016/j.cplett.2016.06.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Yadavali S, Sandireddy VP, Kalyanaraman R. Transformation of irregular shaped silver nanostructures into nanoparticles by under water pulsed laser melting. NANOTECHNOLOGY 2016; 27:195602. [PMID: 27041091 DOI: 10.1088/0957-4484/27/19/195602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The ability to easily manufacture nanostructures with a desirable attribute, such as well-defined size and shape, especially from any given initial shapes or sizes of the material, will be helpful towards accelerating the use of nanomaterials in various applications. In this work we report the transformation of discontinuous irregular nanostructures (DIN) of silver metal by rapid heating under a bulk fluid layer. Ag films were changed into DIN by dewetting in air and subsequently heated by nanosecond laser pulses under water. Our findings show that the DIN first ripens into elongated structures and then breaks up into nanoparticles. From the dependence of this behavior on laser fluence we found that under water irradiation reduced the rate of ripening and also decreased the characteristic break-up length scale of the elongated structures. This latter result was qualitatively interpreted as arising from a Rayleigh-Plateau instability modified to yield significantly smaller length scales than the classical process due to pressure gradients arising from the rapid evaporation of water during laser melting. These results demonstrate that it is possible to fabricate a dense collection of monomodally sized Ag nanoparticles with significantly enhanced plasmonic quality starting from the irregular shaped materials. This can be beneficial towards transforming discontinuous Ag films into nanostructures with useful plasmonic properties, that are relevant for biosensing applications.
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Affiliation(s)
- S Yadavali
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN 37996, USA
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Zhang Z, Hilton GC, Yang R, Ding Y. Capillary rupture of suspended polymer concentric rings. SOFT MATTER 2015; 11:7264-7269. [PMID: 26287952 DOI: 10.1039/c5sm01537e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We present the first experimental study on the simultaneous capillary instability amongst viscous concentric rings suspended atop an immiscible medium. The rings ruptured upon annealing, with three types of phase correlation between neighboring rings. In the case of weak substrate confinement, the rings ruptured independently when they were sparsely distanced, but via an out-of-phase mode when packed closer. If the substrate confinement was strong, the rings would rupture via an in-phase mode, resulting in radially aligned droplets. The concentric ring geometry caused a competition between the phase correlation of neighboring rings and the kinetically favorable wavelength, yielding an intriguing, recursive surface pattern. This frustrated pattern formation behavior was accounted for by a scaling analysis.
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Affiliation(s)
- Zheng Zhang
- Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, Colorado 80309, USA.
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Nurse AK, Coriell SR, McFadden GB. On the Stability of Rotating Drops. JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY 2015; 120:74-101. [PMID: 26958440 PMCID: PMC4730680 DOI: 10.6028/jres.120.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Accepted: 03/24/2015] [Indexed: 06/05/2023]
Abstract
We consider the equilibrium and stability of rotating axisymmetric fluid drops by appealing to a variational principle that characterizes the equilibria as stationary states of a functional containing surface energy and rotational energy contributions, augmented by a volume constraint. The linear stability of a drop is determined by solving the eigenvalue problem associated with the second variation of the energy functional. We compute equilibria corresponding to both oblate and prolate shapes, as well as toroidal shapes, and track their evolution with rotation rate. The stability results are obtained for two cases: (i) a prescribed rotational rate of the system ("driven drops"), or (ii) a prescribed angular momentum ("isolated drops"). For families of axisymmetric drops instabilities may occur for either axisymmetric or non-axisymmetric perturbations; the latter correspond to bifurcation points where non-axisymmetric shapes are possible. We employ an angle-arc length formulation of the problem which allows the computation of equilibrium shapes that are not single-valued in spherical coordinates. We are able to illustrate the transition from spheroidal drops with a strong indentation on the rotation axis to toroidal drops that do not extend to the rotation axis. Toroidal drops with a large aspect ratio (major radius to minor radius) are subject to azimuthal instabilities with higher mode numbers that are analogous to the Rayleigh instability of a cylindrical interface. Prolate spheroidal shapes occur if a drop of lower density rotates within a denser medium; these drops appear to be linearly stable. This work is motivated by recent investigations of toroidal tissue clusters that are observed to climb conical obstacles after self-assembly [Nurse et al., Journal of Applied Mechanics 79 (2012) 051013].
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Nurse AK, Colbert-Kelly S, Coriell SR, McFadden GB. Equilibrium and stability of axisymmetric drops on a conical substrate under gravity. PHYSICS OF FLUIDS (WOODBURY, N.Y. : 1994) 2015; 27:10.1063/1.4927697. [PMID: 33311971 PMCID: PMC7727205 DOI: 10.1063/1.4927697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Accepted: 07/18/2015] [Indexed: 06/12/2023]
Abstract
Motivated by recent investigations of toroidal tissue clusters that are observed to climb conical obstacles after self-assembly [Nurse et al., Journal of Applied Mechanics 79 (2012) 051013], we study a related problem of the determination of the equilibrium and stability of axisymmetric drops on a conical substrate in the presence of gravity. A variational principle is used to characterize equilibrium shapes that minimize surface energy and gravitational potential energy subject to a volume constraint, and the resulting Euler equation is solved numerically using an angle/arclength formulation. The resulting equilibria satisfy a Laplace-Young boundary condition that specifies the contact angle at the three-phase trijunction. The vertical position of the equilibrium drops on the cone is found to vary significantly with the dimensionless Bond number that represents the ratio of gravitational and capillary forces; a global force balance is used to examine the conditions that affect the drop positions. In particular, depending on the contact angle and the cone half-angle, we find that the vertical position of the drop can either increase ("the drop climbs the cone") or decrease due to a nominal increase in the gravitational force. Most of the equilibria correspond to upward-facing cones, and are analogous to sessile drops resting on a planar surface; however we also find equilibria that correspond to downward facing cones, that are instead analogous to pendant drops suspended vertically from a planar surface. The linear stability of the drops is determined by solving the eigenvalue problem associated with the second variation of the energy functional. The drops with positive Bond number are generally found to be unstable to non-axisymmetric perturbations that promote a tilting of the drop. Additional points of marginal stability are found that correspond to limit points of the axisymmetric base state. Drops that are far from the tip are subject to azimuthal instabilities with higher mode numbers that are analogous to the Rayleigh instability of a cylindrical interface. We have also found a range of completely stable solutions that correspond to small contact angles and cone half-angles.
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Affiliation(s)
- A K Nurse
- National Institute of Standards and Technology Gaithersburg, MD 20899
| | - S Colbert-Kelly
- National Institute of Standards and Technology Gaithersburg, MD 20899
| | - S R Coriell
- National Institute of Standards and Technology Gaithersburg, MD 20899
| | - G B McFadden
- National Institute of Standards and Technology Gaithersburg, MD 20899
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Wu Y, Dong N, Fu S, Fowlkes JD, Kondic L, Vincenti MA, de Ceglia D, Rack PD. Directed liquid phase assembly of highly ordered metallic nanoparticle arrays. ACS APPLIED MATERIALS & INTERFACES 2014; 6:5835-5843. [PMID: 24689648 DOI: 10.1021/am500695h] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Directed assembly of nanomaterials is a promising route for the synthesis of nanoscale materials. In this paper, we demonstrate the directed-assembly of highly ordered two-dimensional arrays of hierarchical nanostructures with tunable size, spacing and composition. The directed assembly is achieved on lithographically patterned metal films that are subsequently pulse-laser melted; during the brief liquid lifetime, the pattened nanostructures assemble into highly ordered primary and secondary nanoparticles, with sizes below that which was originally patterned. Complementary fluid-dynamics simulations emulate the resultant patterns and show how the competition of capillary forces and liquid metal-solid substrate interaction potential drives the directed assembly. As an example of the enhanced functionality, a full-wave electromagnetic analysis has been performed to identify the nature of the supported plasmonic resonances.
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Affiliation(s)
- Yueying Wu
- Department of Materials Science and Engineering, The University of Tennessee , Knoxville, Tennessee 37996, United States
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Nguyen TD, Carrillo JMY, Matheson MA, Brown WM. Rupture mechanism of liquid crystal thin films realized by large-scale molecular simulations. NANOSCALE 2014; 6:3083-3096. [PMID: 24264516 DOI: 10.1039/c3nr05413f] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The ability of liquid crystal (LC) molecules to respond to changes in their environment makes them an interesting candidate for thin film applications, particularly in bio-sensing, bio-mimicking devices, and optics. Yet the understanding of the (in)stability of this family of thin films has been limited by the inherent challenges encountered by experiment and continuum models. Using unprecedented large-scale molecular dynamics (MD) simulations, we address the rupture origin of LC thin films wetting a solid substrate at length scales similar to those in experiment. Our simulations show the key signatures of spinodal instability in isotropic and nematic films on top of thermal nucleation, and importantly, for the first time, evidence of a common rupture mechanism independent of initial thickness and LC orientational ordering. We further demonstrate that the primary driving force for rupture is closely related to the tendency of the LC mesogens to recover their local environment in the bulk state. Our study not only provides new insights into the rupture mechanism of liquid crystal films, but also sets the stage for future investigations of thin film systems using peta-scale molecular dynamics simulations.
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Affiliation(s)
- Trung Dac Nguyen
- National Center for Computational Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
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Nguyen TD, Fuentes-Cabrera M, Fowlkes JD, Rack PD. Coexistence of spinodal instability and thermal nucleation in thin-film rupture: insights from molecular levels. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:032403. [PMID: 24730848 DOI: 10.1103/physreve.89.032403] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Indexed: 06/03/2023]
Abstract
Despite extensive investigation using hydrodynamic models and experiments over the past decades, there remain open questions regarding the origin of the initial rupture of thin liquid films. One of the reasons that makes it difficult to identify the rupture origin is the coexistence of two dewetting mechanisms, namely, thermal nucleation and spinodal instability, as observed in many experimental studies. Using a coarse-grained model and large-scale molecular dynamics simulations, we are able to characterize the very early stage of dewetting in nanometer-thick liquid-metal films wetting a solid substrate. We observe the features characteristic of both spinodal instability and thermal nucleation in the spontaneously dewetting films and show that these two macroscopic mechanisms share a common origin at molecular levels.
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Affiliation(s)
- Trung Dac Nguyen
- National Center for Computational Sciences, Oak Ridge National Laboratory, Tennessee 37831
| | - Miguel Fuentes-Cabrera
- Center for Nanophase and Materials Science, Computer Science and Mathematics Division, Oak Ridge National Laboratory, Tennessee 37831 and Center for Nanophase and Materials Science, Oak Ridge National Laboratory, Tennessee 37831
| | - Jason D Fowlkes
- Center for Nanophase and Materials Science, Computer Science and Mathematics Division, Oak Ridge National Laboratory, Tennessee 37831
| | - Philip D Rack
- Center for Nanophase and Materials Science, Oak Ridge National Laboratory, Tennessee 37831 and Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996
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