Effect of chain stiffness on the competition between crystallization and glass-formation in model unentangled polymers

Abstract

We map out the solid-state morphologies formed by model soft-pearl-necklace polymers as a function of chain stiffness, spanning the range from fully flexible to rodlike chains. The ratio of Kuhn length to bead diameter (lK/r0) increases monotonically with increasing bending stiffness kb and yields a one-parameter model that relates chain shape to bulk morphology. In the flexible limit, monomers occupy the sites of close-packed crystallites while chains retain random-walk-like order. In the rodlike limit, nematic chain ordering typical of lamellar precursors coexists with close-packing. At intermediate values of bending stiffness, the competition between random-walk-like and nematic chain ordering produces glass-formation; the range of kb over which this occurs increases with the thermal cooling rate |Ṫ| implemented in our molecular dynamics simulations. Finally, values of kb between the glass-forming and rodlike ranges produce complex ordered phases such as close-packed spirals. Our results should provide a useful initial step in a coarse-grained modeling approach to systematically determining the effect of chain stiffness on the crystallization-vs-glass-formation competition in both synthetic and colloidal polymers.

Isostaticity and the solidification of semiflexible polymer melts

“…[15,18] It is comparable to the Kremer-Grest bead-spring model, [22] but possesses crystalline ground states. All monomers have mass m and interact via the truncated and shifted Lennard-Jones potential…”

“…As detailed in Ref. [15], the model's solid morphologies -formed by cooling from the isotropic liquid state -range from random-walk close-packed crystals to glasses to nematic close-packed crystals over this range of k bend . Since its soldification dynamics [24] also vary strongly with k bend , the model is suitable for studying connections between solidification and isostaticity in a very general way.…”

“…These studies focused on liquids of fully flexible [9][10][11][12] or infinitely stiff [12] chains, for which the definition of Z iso nc is straightforward. However, finite chain stiffness is well known to strongly and nontrivially affect polymer soldification in both thermal [13][14][15] and athermal [16,17] systems. Here we examine the connection of isostaticity to polymer solidification using molecular dynamics simulations of a simple crystallizable bead-spring model [18] with continuously variable chain stiffness.…”

Constant-pressure nested sampling with atomistic dynamics

“…Here we present results for a bead-spring polymer model (see Appendix D 4) with a harmonic bond and cosine angle potential parameterized by stiffnesses k b and k a , respectively, and a non-bonded LJ interaction with energy . This model has been used to study crystallization in polymers [24], and is similar to the model used in a previous Wang-Landau study [20]. sitions.…”

“…The bead-spring models used to study long molecule chains are based on those used by Nguyen et al to study polymer crystallization [24]. The energy of a bond between two monomers along the backbone of a polymer chain…”