Molecular orientation of a liquid‐crystalline polymer solution in mixed shear‐extensional flows

1996 ◽  
Vol 40 (2) ◽  
pp. 235-257 ◽  
Author(s):  
Bruce D. Bedford ◽  
Wesley R. Burghardt
Keyword(s):  
Polymer Solution ◽  
Molecular Orientation ◽  
Liquid Crystalline Polymer ◽  
Liquid Crystalline ◽  
Crystalline Polymer ◽  
Extensional Flows

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

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.

Flow Induced Unstable Structure of Liquid Crystalline Polymer Solution in L-Shaped Slit Channels

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
Takatsune Narumi ◽  
Jun Fukada ◽  
Satoru Kiryu ◽  
Shinji Toga ◽  
Tomiichi Hasegawa
Keyword(s):  
Polymer Solution ◽  
Liquid Crystalline Polymer ◽  
Liquid Crystalline ◽  
Flow Behavior ◽  
Crystalline Polymer ◽  
Test Fluid ◽  
Radius Of Curvature ◽  
Unstable Behavior ◽  
Corner Flow ◽  
Side Flow

An experimental study has been conducted on unstable structures induced in two-dimensional slit flows of liquid crystalline polymer solution. 50wt% aqueous solution of hydroxyl-propylcellulose (HPC) was utilized as a test fluid and its flow behavior in L-shaped slit channels with a cross section of 1mm height and 16mm width was measured optically. The inner corner of the L-shaped channel was rounded off in order to clarify the influence of the radius of curvature on the unstable behavior. A conversing curved channel was also tested. The flow patterns of the HPC solution in the channels were visualized with two crossed polarizers and we observed that typical wavy textures generated in the upstream of the corner almost disappeared after the corner flow. However, an unstable texture was developed again only from the inner corner in downstream flow. The fluctuation of the orientation angle and dichroism were also measured with a laser opto-rheometric system and it was found that the unstable behaviors of the HPC solution have periodic oscillatory characteristics at a typical frequency. In the inner side flow after the corner, the periodic motion became larger toward the downstream and then higher harmonic oscillations were superimposed. Larger rounding off of the inner corner suppressed the redevelopment of unstable behavior, and it is considered that the rapid regrowth of unstable behavior was caused by rapid deceleration at the corner flow. Moreover, the unstable structure was stabilized with an accelerated (elongated) region in the corner flow and the converging channel was helpful to obtain a stable structure in the downstream region.

correlations of mechanical properties and microstructural parameters in annealed drawn film of liquid crystalline polymer in situ reinforced PP

e-Polymers ◽  
2011 ◽  
Vol 11 (1) ◽  
Author(s):  
Sayant Saengsuwan
Keyword(s):  
Mechanical Properties ◽  
Annealing Time ◽  
Crystalline Phase ◽  
Molecular Orientation ◽  
Liquid Crystalline Polymer ◽  
Liquid Crystalline ◽  
Crystalline Polymer ◽  
Relative Level ◽  
Microstructural Parameters

AbstractDrawn composite thin film based on thermotropic liquid crystalline polymer (TLCP) and polypropylene (PP) was annealed at 130 °C at different times. The influence of annealing time on microstructural and mechanical properties of the composite film has been studied. The correlation in mechanical properties and their microstructural parameters has also been investigated. X-Ray diffraction results reveal that the smectic mesophase transforms progressively into the monoclinic phase as annealing time is increased. Consequently, the true crystallinity (Xc), crystal thickness (L) as well as relative level of molecular orientation of PP crystalline phase in the annealed TLCP/PP films are increased significantly. Also, the TLCP fibrils have no influence on the microstructure of PP crystalline phase. The apparent crystallinity (Xc,a) of PP phase evaluated by DSC also increase significantly with annealing time. As a result, the increases of these microstructural parameters coupled with the reinforcement of TLCP fibrils could be contributed directly to the remarkable enhancement of mechanical properties of the annealed TLCP/PP film in both machine (MD) and transverse (TD) directions. The correlation of moduli with microstructural parameters (Xc, Xc,a and L) exhibits nonlinear relations. However, the relative level of molecular orientation is a more suitable parameter to correlate with the improvement of mechanical properties of the annealed TLCP/PP film. Finally, this work presents that the mechanical properties of the TLCP in situ reinforced thermoplastics can be significantly enhanced via a simple thermal treatment.

Mechanism of the Occurrence of Wavy Texture in Slit Flows of a Liquid Crystalline Polymer Solution

2002 ◽  
Vol 2002.77 (0) ◽  
pp. _13-49_-_13-50_
Author(s):  
Masatada SHINDOU ◽  
Noriyasu MORI ◽  
Tsutomu TAKAHASHI ◽  
Kiyoji NAKAMURA
Keyword(s):  
Polymer Solution ◽  
Liquid Crystalline Polymer ◽  
Liquid Crystalline ◽  
Crystalline Polymer ◽  
Wavy Texture
Sign in / Sign up

Export Citation Format

Share Document