The Effect of Surface Features on Nanorheology of LCP Melts in Nanochannels by MD Simulation

The effects of wall surface features on the rheological properties and phase orientation of liquid crystalline polymer (LCP) melts flowing in a nanochannel have been first investigated by molecular dynamics (MD) simulations. The surfaces are modeled as rough atomic serrated walls whereby the roughness is characterized by the period and amplitude of serration. The molecular chains of LCPs are depicted by a newly developed molecular model named the GB-spring-bead model. Through simulating the phase formation of LCP melts, the new model was evaluated and the results have shown the new model is efficient and accurate to describe semi-flexible main-chain LCP molecules. MD simulations of the effect of wall surface features on the LCP shear flow were conducted and the results have revealed the surface features affect greatly the rheological properties and phase orientations of LCP melts in a nanochannel (the distance between the upper wall and the lower wall is 12.8nm). Findings in this study provide very useful information in the injection molding of plastic products with nanofeatures.

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A New Simulation Method of Interaction Between a Liquid Crystalline Polymer and Two Serrated Walls

World Tribology Congress III, Volume 2 ◽

10.1115/wtc2005-64033 ◽

2005 ◽

Author(s):

Lan He ◽

K. L. Yung ◽

Yan Xu ◽

Yun Wen Shen

Keyword(s):

Liquid Crystalline Polymer ◽

Liquid Crystalline ◽

Md Simulation ◽

Molecular Model ◽

Computational Cost ◽

Crystalline Polymer ◽

Simulation Method ◽

Boundary Problems ◽

Nonlinear Springs ◽

Improved Model

This paper presents a new molecular model to define the interactions of a liquid crystalline polymer (LCP) flowing between two serrated walls. The wall is modeled by a rough atomic serrated wall. The roughness characteristics are given by the space and height of the serrated wall. Molecular model of the liquid crystalline polymer is described by an improved model that consists of GB (Gay-Berne) sites as rigid segments and LJ (Lennard-Jones) sites. There are two nonlinear springs each connecting from a GB site to a LJ site that situate between two GB sites as flexible segments. This improved model is newly developed to reduce the computational cost from that of the hybrid GB/LJ model, which has provided an effective way to investigate the boundary problems and flowing behaviors of LCPs at nano-scale. The molecular dynamics (MD) simulation using this reduced computational cost method to study the effect of boundary conditions on alignment and rheological properties of the LCP is shown in the result.

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Effects of Surface Conditions on Rheological Properties and Phase Orientation of Sheared LCP Melts in Nanochannels by MD Studies

Materials Science Forum ◽

10.4028/www.scientific.net/msf.532-533.624 ◽

2006 ◽

Vol 532-533 ◽

pp. 624-627

Author(s):

Lan He ◽

Kai Leung Yung ◽

Yun Wen Shen ◽

Yan Xu

Keyword(s):

Surface Roughness ◽

Rheological Properties ◽

Shear Viscosity ◽

Order Parameter ◽

Liquid Crystalline ◽

Orientational Order ◽

Crystalline Polymer ◽

Md Simulations ◽

Isotropic Phase ◽

Orientational Order Parameter

The rheological properties and phase orientation of liquid crystalline polymer (LCP) melts flowing in a nanochannel with different surface roughness are investigated by molecular dynamics (MD) simulations. Simulation results show the surface roughness has great impact on the rheological properties and phase orientation of LCP melts in the nanochannel (cross section is 12nm). As the amplitude of serrations increases, the shear viscosity increases nonlinearly and the value of orientational order parameter decreases. When the serration amplitude is larger than 1.1nm, a phase transition (from nematic to isotropic phase) of LCP melt happens, which makes flowing in nanochannels more difficult. On the other hand, the influence of serration period on the shear viscosity and orientational order parameter are found not so obvious. Findings in this study will be helpful for injection molding plastic products with nanofeatures.

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