Kinetic Model for Layer-by-Layer Crystal Growth in Chain Molecules

Bourque, Alexander J.

doi:10.1021/acs.macromol.5b02758

Cited by 8 publications

(14 citation statements)

References 33 publications

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“…Further discussion of surface nucleation rates and the relation to the mechanism of surface nucleation and crystal growth is presented in earlier work. 26,35 Crystalline nucleating agents possess a variety of low index lattice planes that can serve as distinct surfaces for nucleation and growth of crystallites within the surrounding liquid. The alignment of crystallized chains at the nucleating agent surface is shown in Figure 4.…”

Section: Resultsmentioning

confidence: 99%

“…26 Critical nucleus sizes, induction times, and rates for surface nucleation were estimated and used to parameterize a new kinetic model for crystallization in chain molecules. 35 In this work, we demonstrate the utility of MD simulation for screening systematically the activity of nucleating agents, and for characterizing their mechanism of action. As nucleating agents, we examine the entire family of tetrahedrally coordinated crystals described by the Stillinger-Weber (SW) potential.…”

Section: Introductionmentioning

confidence: 96%

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Heterogeneous Nucleation of an n-Alkane on Tetrahedrally Coordinated Crystals

Bourque

Locker

2017

J. Phys. Chem. B

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Heterogeneous nucleation refers to the propensity for phase transformations to initiate preferentially on foreign surfaces, such as vessel walls, dust particles or formulation additives. In crystallization, the form of the initial nucleus has ramifications for the crystallographic form, morphology and properties of the resulting solid. Nevertheless, the discovery and design of nucleating agents remains a matter of trial and error, due to the very small spatio-temporal scales over which formation of the critical nucleus occurs, and the extreme difficulty of examining such events empirically. Using molecular dynamics simulations, we demonstrate a method for the rapid screening of entire families of materials for activity as nucleating agents, and for characterizing their mechanism of action. The method is applied to the crystallization of n-pentacontane, a model surrogate for polyethylene, on the family of tetrahedrally coordinated crystals including diamond and silicon. Systematic variation of parameters in the interaction potential permits a comprehensive, physically-based screening of nucleating agents in this class of materials, including both real and hypothetical candidates. The induction time for heterogeneous nucleation is shown to depend strongly on crystallographic registry between the nucleating agent and the critical nucleus, indicative of an epitaxial mechanism in this class of materials. Importantly, the severity of this registry requirement weakens with decreasing rigidity of the substrate and increasing strength of attraction to the nucleating agent surface. Employing this method, high throughput computational screening of nucleating agents becomes possible, facilitating the discovery of novel nucleating agents within a broad, "materials genome" of possible additives.3

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Heterogeneous Nucleation of an n-Alkane on Tetrahedrally Coordinated Crystals

Bourque

Locker

2017

J. Phys. Chem. B

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“…Chain segment analysis gave rise to a broad length distribution of loops, which supports the "switchboard model" in the early stage of crystals formed in deep supercooling. Recently, refinements of the MD procedure and a kinetic model have been described to explain surface nucleation and crystal growth in C 50 systems [303,304].…”

Section: Crystallization From the Meltmentioning

confidence: 99%

Predicting experimental results for polyethylene by computer simulation

Ramos

Vega

Martínez‐Salazar

2018

European Polymer Journal

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This feature article reviews several aspects of computational approaches to polyethylene melt and solid state properties in relation to existing experimental results. Based on 40 years of experience in the field, we offer a personal view of how computer simulations are helping to understand the physics of polyethylene as a model polymer. The first issue discussed is the molten state of polyethylene, including static and dynamic properties and entanglement features along with their impacts on rheological behaviour. We then examine the glass transition, crystallization process and solid state structure, including the interlamellar region. This is followed by brief descriptions of the latest advances in simulating mechanical properties and of the various methodologies used to simulate the physics of polyethylene. Throughout the manuscript, references are made to our own work and also to studies by many other authors that have nicely contributed to developments in simulating the physics of polyethylene in close agreement with experimental results.

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“…Alkanes are modeled with two different united-atom (UA) force fields: PYS [14][15][16] and OPLS [17,18]. These force fields have been widely used to investigate the structure, interfacial properties and phase transitions of alkanes [4,12,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Water is modeled with the monatomic water model, mW [38], which has been extensively used to study the structure, thermodynamics, interfacial properties, and phase transitions of water .…”

Section: Methodsmentioning

confidence: 99%

“…A recent simulation study of crystallization of pentacontane (C50) finds that it crystallizes heterogeneously at solid silicon-like templating surfaces, resulting in crystals with the chains oriented parallel to the interface, and that the nucleation is faster for more strongly interacting surfaces [12,19,20]. Based on these results, it may be expected that increasing ε wc between alkane and the water fluid may increase the ordering of the molecules parallel to the interface, and could result in a new region of heterogeneous nucleation at high ε wc .…”

Section: Strength Of the Alkane-solvent Attraction Determines Whethermentioning

confidence: 99%

Strength of Alkane–Fluid Attraction Determines the Interfacial Orientation of Liquid Alkanes and Their Crystallization through Heterogeneous or Homogeneous Mechanisms

Qiu

Molinero

2017

Crystals

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Abstract:Alkanes are important building blocks of organics, polymers and biomolecules. The conditions that lead to ordering of alkanes at interfaces, and whether interfacial ordering of the molecules leads to heterogeneous crystal nucleation of alkanes or surface freezing, have not yet been elucidated. Here we use molecular simulations with the united-atom OPLS and PYS alkane models and the mW water model to determine what properties of the surface control the interfacial orientation of alkane molecules, and under which conditions interfacial ordering results in homogeneous or heterogeneous nucleation of alkane crystals, or surface freezing above the melting point. We find that liquid alkanes present a preference towards being perpendicular to the alkane-vapor interface and more parallel to the alkane-water interface. The orientational order in the liquid is short-ranged, decaying over~1 nm of the surface, and can be reversed by tuning the strength of the attractions between alkane and the molecules in the other fluid. We show that the strength of the alkane-fluid interaction also controls the mechanism of crystallization and the face of the alkane crystal exposed to the fluid: fluids that interact weakly with alkanes promote heterogeneous crystallization and result in crystals in which the alkane molecules orient perpendicular to the interface, while crystallization of alkanes in the presence of fluids, such as water, that interact more strongly with alkanes is homogeneous and results in crystals with the molecules oriented parallel to the interface. We conclude that the orientation of the alkanes at the crystal interfaces mirrors that in the liquid, albeit more pronounced and long-ranged. We show that the sign of the binding free energy of the alkane crystal to the surface, ∆G bind , determines whether the crystal nucleation is homogeneous (∆G bind ≥ 0) or heterogeneous (∆G bind < 0). Our analysis indicates that water does not promote heterogeneous crystallization of the alkanes because water stabilizes more the liquid than the crystal phase of the alkane, resulting in ∆G bind > 0. While ∆G bind < 0 suffices to produce heterogeneous nucleation, the condition for surface freezing is more stringent, ∆G bind < −2 γ xl , where γ xl is the surface tension of the liquid-crystal interface of alkanes. Surface freezing of alkanes is favored by their small value of γ xl . Our findings are of relevance to understanding surface freezing in alkanes and to develop strategies for controlling the assembly of chain-like molecules at fluid interfaces.

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Kinetic Model for Layer-by-Layer Crystal Growth in Chain Molecules

Cited by 8 publications

References 33 publications

Heterogeneous Nucleation of an n-Alkane on Tetrahedrally Coordinated Crystals

Heterogeneous Nucleation of an n-Alkane on Tetrahedrally Coordinated Crystals

Predicting experimental results for polyethylene by computer simulation

Strength of Alkane–Fluid Attraction Determines the Interfacial Orientation of Liquid Alkanes and Their Crystallization through Heterogeneous or Homogeneous Mechanisms

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