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Molecular simulation of crystal nucleation in -octane melts
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10.1063/1.3240202
/content/aip/journal/jcp/131/13/10.1063/1.3240202
http://aip.metastore.ingenta.com/content/aip/journal/jcp/131/13/10.1063/1.3240202

Figures

Image of FIG. 1.
FIG. 1.

A snapshot of 480 -octane chains simulated at 200 K. The -octane chains are rendered as line models. (a) Viewed along the -axis of the triclinic unit cell. (b) Viewed along the -axis of the triclinic unit cell. (c) Viewed along chain direction. This figure was rendered by VMD (Ref. 39).

Image of FIG. 2.
FIG. 2.

The chain-orientation distribution for a system of 480 -octane chains at 200 K in the rotator phase. The chain orientation is defined as the azimuthal angle of a vector in the plane. This vector points from the average of the projection of all odd beads on one chain on the plane to that of all even beads on the same chain.

Image of FIG. 3.
FIG. 3.

Determination of the equilibrium melting temperature with a crystal-melt interface. Boundaries are periodic in all three directions. Two periodic images in the horizontal direction are shown to emphasize more clearly the interfaces between the amorphous melt and ordered crystalline regions. (a) At , the interface moves toward the melt region. (b) At , the interface stays stationary for at least 3 ns. (c) At , the interface moves toward the crystalline region, and melting of the crystal can be seen. This figure was rendered by VMD (Ref. 39).

Image of FIG. 4.
FIG. 4.

Global orientation order parameter as a function of time at five different temperatures, for a system of 480 -octane chains with a crystal-melt interface. Within the precision achievable in 3 ns, the equilibrium melting temperature is .

Image of FIG. 5.
FIG. 5.

Evolution of characteristic variables for a system of 960 -octane chains during a typical MD simulation, after quenching from 250 to 170 K at . (a) Potential energy and volume per chain. (b) Size of the largest nucleus, , and the global orientation order parameter, . (c) Fraction of trans states, .

Image of FIG. 6.
FIG. 6.

The maximum nucleus size as a function of time, using three different sets of cutoff angle and cutoff radius in the definition of nucleus by Esselink et al. (Ref. 10). Vertical offsets were made for purposes of clarity.

Image of FIG. 7.
FIG. 7.

The MFPT of maximum nucleus size from 24 MD simulations of a system of 960 -octane chains quenched from 250 to 170 K at . The open circles are simulation data, and the solid line is the formula of Eq. (19), with , , and parameterized to fit the simulation data.

Image of FIG. 8.
FIG. 8.

The free energy of formation for a crystal nucleus in a melt of -octane chains at 170 K. System with 480 chains (filled squares); system with 960 chains (open circles). In both cases the critical nucleus size is 18 chains and the free energy barrier height is .

Image of FIG. 9.
FIG. 9.

The free energy of formation for a crystal nucleus in a melt of 960 -octane chains at 170 K. Simulation data (filled circles); spherical nucleus model using surface free energy of Uhlmann et al. (Ref. 8) (triangles); spherical nucleus model using surface free energy of Oliver et al. (Ref. 7) (inverted triangle); spherical nucleus model fit using surface free energy , chosen to match the critical nucleus free energy from simulation (dashed curve); cylindrical nucleus model using surface free energies for the end surface and for the lateral surface, chosen to fit both the critical nucleus free energy and the critical nucleus size of the simulation data (solid curve).

Image of FIG. 10.
FIG. 10.

A snapshot of a crystal nucleus that consists of 18 -octane chains from a MC simulation of a melt of 960 -octane chains at 170 K. (a) Side view. (b) Top view. This figure was rendered by VMD (Ref. 39).

Image of FIG. 11.
FIG. 11.

The free energy of formation for a crystal nucleus in a melt of 960 -octane chains at 170, 180, and 190 K, respectively. Simulation data (open symbols); fixed-length cylindrical nucleus model using Eq. (12) (solid curves). The values of the interfacial free energy and used in generating the modeled curves are presented in Table IV.

Tables

Generic image for table
Table I.

Crystal structure of -octane at 200 K.

Generic image for table
Table II.

Potential energy per chain and average density of -octane systems at pressure and several different temperatures.

Generic image for table
Table III.

The crystal nucleation free energy as a function of nucleus size for an -octane melt containing 960 chains.

Generic image for table
Table IV.

Crystal-liquid interfacial free energy of -octane molecules.

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/content/aip/journal/jcp/131/13/10.1063/1.3240202
2009-10-06
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Molecular simulation of crystal nucleation in n-octane melts
http://aip.metastore.ingenta.com/content/aip/journal/jcp/131/13/10.1063/1.3240202
10.1063/1.3240202
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