Using PYS, TraPPE, OPLS-L, and Flexible-Williams (FW) force field models, atomistic simulations at temperatures ranging from 450 K to 600 K are performed to predict the melt density ρ, the persistence length Np, the nematic coupling constant α, and crystallization dynamics for pentacontane (C50). The coupling constant α arises from packing entropy of rodlike Kuhn segments and increases with increasing ρ and Np. Together with a self-consistent field theory, Np and α are then used to predict the isotropic-to-nematic (IN) transition temperature for polyethylene (PE) oligomers as a function of chain length. The nematic phase is found to be metastable since the IN transition temperature lies below the crystal melting temperatures for C50 in simulations using different force fields. Finally, isothermal simulations of crystallization for PE C50 oligomers and C1000 polymers show that crystal nucleation may be much accelerated by quenching below the IN transition temperature, where chains in the isotropic state first rapidly form nematic ordered domains, within which crystalline order then grows. We also find that the PYS, TraPPE, and FW models overpredict the melting temperature for C50 by around 50 K, while the most flexible OPLS-L model gives a melting temperature within around 10 K of the experimental value. Although giving a more accurate melting temperature, the slow crystallization kinetics of the OPLS-L model may limit its application in direct simulations of PE crystallization.
REFERENCES
1.
B.
Crist
, C. J.
Fisher
, and P. R.
Howard
, “Mechanical properties of model polyethylenes: Tensile elastic modulus and yield stress
,” Macromolecules
22
, 1709
–1718
(1989
).2.
I. M.
Ward
, “Optical and mechanical anisotropy in crystalline polymers
,” Proc. Phys. Soc.
80
, 1176
(1962
).3.
F.
Su
, Y.
Ji
, L.
Meng
, Z.
Wang
, Z.
Qi
, J.
Chang
, J.
Ju
, and L.
Li
, “Coupling of multiscale orderings during flow-induced crystallization of isotactic polypropylene
,” Macromolecules
50
, 1991
–1997
(2017
).4.
Z.
Wang
, J.
Ju
, J.
Yang
, Z.
Ma
, D.
Liu
, K.
Cui
, H.
Yang
, J.
Chang
, N.
Huang
, and L.
Li
, “The non-equilibrium phase diagrams of flow-induced crystallization and melting of polyethylene
,” Sci. Rep.
6
, 32968
(2016
).5.
A. J.
Ryan
, J. P. A.
Fairclough
, N. J.
Terrill
, P. D.
Olmsted
, and W. C. K.
Poon
, “A scattering study of nucleation phenomena in polymer crystallisation
,” Faraday Discuss.
112
, 13
–29
(1999
).6.
R. H.
Gee
, N.
Lacevic
, and L. E.
Fried
, “Atomistic simulations of spinodal phase separation preceding polymer crystallization
,” Nat. Mater.
5
, 39
(2006
).7.
M.
Anwar
, F.
Turci
, and T.
Schilling
, “Crystallization mechanism in melts of short n-alkane chains
,” J. Chem. Phys.
139
, 214904
(2013
).8.
M.
Anwar
, J. T.
Berryman
, and T.
Schilling
, “Crystal nucleation mechanism in melts of short polymer chains under quiescent conditions and under shear flow
,” J. Chem. Phys.
141
, 124910
(2014
).9.
T.
Shimada
, M.
Doi
, and K.
Okano
, “Concentration fluctuation of stiff polymers. III. Spinodal decomposition
,” J. Chem. Phys.
88
, 7181
(1988
).10.
P. D.
Olmsted
, W. C. K.
Poon
, T. C. B.
McLeish
, N. J.
Terrill
, and A. J.
Ryan
, “Spinodal-assisted crystallization in polymer melts
,” Phys. Rev. Lett.
81
, 373
(1998
).11.
P. D.
Olmsted
and P.
Goldbart
, “Theory of the nonequilibrium phase transition for nematic liquid crystals under shear flow
,” Phys. Rev. A
41
, 4578
(1990
).12.
H.
See
, M.
Doi
, and R.
Larson
, “The effect of steady flow fields on the isotropic–nematic phase transition of rigid rod-like polymers
,” J. Chem. Phys.
92
, 792
–800
(1990
).13.
R.
Greco
and G.
Ragosta
, “Isotactic polypropylenes of different molecular characteristics: Influence of crystallization conditions and annealing on the fracture behaviour
,” J. Mater. Sci.
23
, 4171
(1988
).14.
W.
Paul
, D. Y.
Yoon
, and G. D.
Smith
, “An optimized united atom model for simulations of polymethylene melts
,” J. Chem. Phys.
103
, 1702
–1709
(1995
).15.
M. G.
Martin
and J. I.
Siepmann
, “Transferable potentials for phase equilibria. 1. United-atom description of n-alkanes
,” J. Phys. Chem. B
102
, 2569
–2577
(1998
).16.
D. J.
Tobias
, K.
Tu
, and M. L.
Klein
, “Assessment of all-atom potentials for modeling membranes: Molecular dynamics simulations of solid and liquid alkanes and crystals of phospholipid fragments
,” J. Chim. Phys.
94
, 1482
–1502
(1997
).17.
S. W. I.
Siu
, K.
Pluhackova
, and R. A.
Böckmann
, “Optimization of the OPLS-AA force field for long hydrocarbons
,” J. Chem. Theory Comput.
8
, 1459
–1470
(2012
).18.
W. L.
Jorgensen
, D. S.
Maxwell
, and J.
Tirado-Rives
, “Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids
,” J. Am. Chem. Soc.
118
, 11225
–11236
(1996
).19.
G. C.
Rutledge
, “Molecular simulation of crystal nucleation in n-octane melts
,” J. Chem. Phys.
131
, 134902
(2009
).20.
P.
Yi
, C. R.
Locker
, and G. C.
Rutledge
, “Molecular dynamics simulation of homogeneous crystal nucleation in polyethylene
,” Macromolecules
46
, 4723
–4733
(2013
).21.
N.
Wentzel
and S. T.
Milner
, “Crystal and rotator phases of n-alkanes: A molecular dynamics study
,” J. Chem. Phys.
132
, 044901
(2010
).22.
G.
Dee
, T.
Ougizawa
, and D.
Walsh
, “The pressure-volume-temperature properties of polyethylene, poly(dimethyl siloxane), poly(ethylene glycol) and poly(propylene glycol) as a function of molecular weight
,” Polymer
33
, 3462
–3469
(1992
).23.
J.
Ramos
, J. F.
Vega
, and J.
Martínez-Salazar
, “Molecular dynamics simulations for the description of experimental molecular conformation, melt dynamics, and phase transitions in polyethylene
,” Macromolecules
48
, 5016
–5027
(2015
).24.
W.
Zhang
, E. D.
Gomez
, and S. T.
Milner
, “Predicting nematic phases of semiflexible polymers
,” Macromolecules
48
, 1454
–1462
(2015
).25.
X. J.
Wang
and M.
Warner
, “Theory of nematic backbone polymer phases and conformations
,” J. Phys. A: Math. Gen.
19
, 2215
(1986
).26.
A.
Ramírez-Hernández
, S.-M.
Hur
, J.
Armas-Pérez
, M.
Olvera de la Cruz
, and J.
de Pablo
, “Demixing by a nematic mean field: Coarse-grained simulations of liquid crystalline polymers
,” Polymers
9
, 88
(2017
).27.
Q.
Chen
, E. B.
Sirota
, M.
Zhang
, T. C. M.
Chung
, and S. T.
Milner
, “Free surfaces overcome superheating in simulated melting of isotactic polypropylene
,” Macromolecules
48
, 8885
–8896
(2015
).28.
W.
Zhang
, E. D.
Gomez
, and S. T.
Milner
, “Surface-induced chain alignment of semiflexible polymers
,” Macromolecules
49
, 963
–971
(2016
).29.
W.
Zhang
, E. D.
Gomez
, and S. T.
Milner
, “Using surface-induced ordering to probe the isotropic-to-nematic transition for semiflexible polymers
,” Soft Matter
12
, 6141
–6147
(2016
).30.
W. F.
Seyer
, R. F.
Patterson
, and J. L.
Keays
, “The density and transition points of the n-paraffin hydrocarbons
,” J. Am. Chem. Soc.
66
, 179
(1944
).31.
M. G.
Broadhurst
, “Extrapolation of the orthorhombic n-paraffin melting properties to very long chain lengths
,” J. Chem. Phys.
36
, 2578
–2582
(1962
).32.
A.
Hammami
and A. K.
Mehrotra
, “Liquid-solid-solid thermal behaviour of n-C44H90 + n-C50H102 and n-C25H52 + n-C28H58 paraffinic binary mixtures
,” Fluid Phase Equilib.
111
, 253
–272
(1995
).33.
B.
Wunderlich
, “Motion in polyethylene. I. Temperature and crystallinity dependence of the specific heat
,” J. Chem. Phys.
37
, 1203
–1207
(1962
).34.
S.
Auer
and D.
Frenkel
, “Numerical prediction of absolute crystallization rates in hard-sphere colloids
,” J. Chem. Phys.
120
, 3015
–3029
(2004
).35.
W.
Zhang
and R. G.
Larson
, “Direct all-atom molecular dynamics simulations of the effects of short chain branching on polyethylene oligomer crystal nucleation
,” Macromolecules
51
, 4762
–4769
(2018
).36.
S. T.
Milner
, “Polymer crystal–melt interfaces and nucleation in polyethylene
,” Soft Matter
7
, 2909
–2917
(2011
).37.
Q.
Chen
, D.
Kozuch
, and S. T.
Milner
, “‘Plunger’ method for simulating crystal–melt interfacial free energies
,” Macromolecules
50
, 4797
–4806
(2017
).38.
J. A.
Koutsky
, A. G.
Walton
, and E.
Baer
, “Nucleation of polymer droplets
,” J. Appl. Phys.
38
, 1832
–1839
(1967
).39.
J. D.
Hoffman
and R. L.
Miller
, “Kinetic of crystallization from the melt and chain folding in polyethylene fractions revisited: Theory and experiment
,” Polymer
38
, 3151
–3212
(1997
).40.
H.
Kraack
, M.
Deutsch
, and E. B.
Sirota
, “n-Alkane homogeneous nucleation: Crossover to polymer behavior
,” Macromolecules
33
, 6174
–6184
(2000
).41.
J. D.
Hoffman
and J. J.
Weeks
, “Rate of spherulitic crystallization with chain folds in polychlorotrifluoroethylene
,” J. Chem. Phys.
37
, 1723
–1741
(1962
).42.
L. J.
Fetters
, D. J.
Lohse
, D.
Richter
, T. A.
Witten
, and A.
Zirkel
, “Connection between polymer molecular weight, density, chain dimensions, and melt viscoelastic properties
,” Macromolecules
27
, 4639
–4647
(1994
).43.
A. R.
Khokhlov
and A. N.
Semenov
, “Liquid-crystalline ordering in the solution of long persistent chains
,” Physica A
108
, 546
–556
(1981
).44.
L.
Onsager
, “The effects of shape on the interaction of colloidal particles
,” Ann. N. Y. Acad. Sci.
51
, 627
–659
(1949
).© 2019 Author(s).
2019
Author(s)
You do not currently have access to this content.
