Molecular Model of Rupture of a Macromolecular Chain of a Loaded Oriented Crystalline Polymer

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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Toward an alignment of the actin molecule within the actin filament

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100075981 ◽

1983 ◽

Vol 41 ◽

pp. 450-451

Author(s):

P.R. Smith ◽

W.E. Fowler ◽

U. Aebi

Keyword(s):

Actin Filament ◽

Diffraction Data ◽

Quantitative Estimate ◽

Molecular Model ◽

Quantitative Comparison ◽

Regulatory Proteins ◽

Essential Information ◽

X Ray ◽

Maximum Resolution ◽

Lack Of Information

An understanding of the specific interactions of actin with regulatory proteins has been limited by the lack of information about the structure of the actin filament. Molecular actin has been studied in actin-DNase I complexes by single crystal X-ray analysis, to a resolution of about 0.6nm, and in the electron microscope where two dimensional actin sheets have been reconstructed to a maximum resolution of 1.5nm. While these studies have shown something of the structure of individual actin molecules, essential information about the orientation of actin in the filament is still unavailable.The work of Egelman & DeRosier has, however, suggested a method which could be used to provide an initial quantitative estimate of the orientation of actin within the filament. This method involves the quantitative comparison of computed diffraction data from single actin filaments with diffraction data derived from synthetic filaments constructed using the molecular model of actin as a building block. Their preliminary work was conducted using a model consisting of two juxtaposed spheres of equal size.

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Structure-property relations of liquid crystalline polymers

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100127013 ◽

1987 ◽

Vol 45 ◽

pp. 460-463

Author(s):

Linda C. Sawyer

Keyword(s):

Solid State ◽

Liquid Crystalline ◽

Structural Model ◽

Crystalline Polymer ◽

Liquid Crystalline Polymers ◽

Mechanical Anisotropy ◽

Structure Property ◽

Preparation Methods ◽

Crystalline Polymers ◽

Extended Chain

Recent liquid crystalline polymer (LCP) research has sought to define structure-property relationships of these complex new materials. The two major types of LCPs, thermotropic and lyotropic LCPs, both exhibit effects of process history on the microstructure frozen into the solid state. The high mechanical anisotropy of the molecules favors formation of complex structures. Microscopy has been used to develop an understanding of these microstructures and to describe them in a fundamental structural model. Preparation methods used include microtomy, etching, fracture and sonication for study by optical and electron microscopy techniques, which have been described for polymers. The model accounts for the macrostructures and microstructures observed in highly oriented fibers and films.Rod-like liquid crystalline polymers produce oriented materials because they have extended chain structures in the solid state. These polymers have found application as high modulus fibers and films with unique properties due to the formation of ordered solutions (lyotropic) or melts (thermotropic) which transform easily into highly oriented, extended chain structures in the solid state.

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Exploration of cell wall architecture with the rapid-freeze deep-etch technique

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100146485 ◽

1993 ◽

Vol 51 ◽

pp. 128-129

Author(s):

Béatrice Satiat-Jeunemaitre ◽

Chris Hawes

Keyword(s):

Plant Cell ◽

Cell Walls ◽

Cell Biology ◽

Molecular Model ◽

Three Dimensional ◽

Secretory Activity ◽

Wall Structure ◽

Specimen Preparation ◽

Molecular Architecture ◽

Plant Cell Walls

The comprehension of the molecular architecture of plant cell walls is one of the best examples in cell biology which illustrates how developments in microscopy have extended the frontiers of a topic. Indeed from the first electron microscope observation of cell walls it has become apparent that our understanding of wall structure has advanced hand in hand with improvements in the technology of specimen preparation for electron microscopy. Cell walls are sub-cellular compartments outside the peripheral plasma membrane, the construction of which depends on a complex cellular biosynthetic and secretory activity (1). They are composed of interwoven polymers, synthesised independently, which together perform a number of varied functions. Biochemical studies have provided us with much data on the varied molecular composition of plant cell walls. However, the detailed intermolecular relationships and the three dimensional arrangement of the polymers in situ remains a mystery. The difficulty in establishing a general molecular model for plant cell walls is also complicated by the vast diversity in wall composition among plant species.

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Observing the relaxation of molecular orientation in sheared liquid crystalline polymer solutions

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100178598 ◽

1990 ◽

Vol 48 (4) ◽

pp. 1092-1093

Author(s):

Wendy Putnam ◽

Christopher Viney

Keyword(s):

Molecular Orientation ◽

Liquid Crystalline Polymer ◽

Liquid Crystalline ◽

Crystalline Polymer ◽

Polymer Processing ◽

Molecular Alignment ◽

Global Alignment ◽

Shear Direction ◽

Axial Strength ◽

Strength And Stiffness

Liquid crystalline polymers (solutions or melts) can be spun into fibers and films that have a higher axial strength and stiffness than conventionally processed polymers. These superior properties are due to the spontaneous molecular extension and alignment that is characteristic of liquid crystalline phases. Much of the effort in processing conventional polymers goes into extending and aligning the chains, while, in liquid crystalline polymer processing, the primary microstructural rearrangement involves converting local molecular alignment into global molecular alignment. Unfortunately, the global alignment introduced by processing relaxes quickly upon cessation of shear, and the molecular orientation develops a periodic misalignment relative to the shear direction. The axial strength and stiffness are reduced by this relaxation.Clearly there is a need to solidify the liquid crystalline state (i.e. remove heat or solvent) before significant relaxation occurs. Several researchers have observed this relaxation, mainly in solutions of hydroxypropyl cellulose (HPC) because they are lyotropic under ambient conditions.

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