Crystallinity Increases in Semi Crystalline Polymers During High Rate Testing

Palladium single-crystal films have been prepared by Matthews in ultra-high vacuum by evaporation onto (001) NaCl substrates cleaved in-situ, and maintained at ∼ 350° C. Murr has also produced large-grained and single-crystal Pd films by high-rate evaporation onto (001) NaCl air-cleaved substrates at 350°C. In the present work, very large (∼ 3cm2), continuous single-crystal films of Pd have been prepared by flash evaporation onto air-cleaved (001) NaCl substrates at temperatures at or below 250°C. Evaporation rates estimated to be ≧ 2000 Å/sec, were obtained by effectively short-circuiting 1 mil tungsten evaporation boats in a self-regulating system which maintained an optimum load current of approximately 90 amperes; corresponding to a current density through the boat of ∼ 4 × 104 amperes/cm2.

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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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SEM/FESEM imaging of lamellar structures in melt extruded polyethylene films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130341 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1142-1143

Author(s):

R.T. Chen ◽

M.G. Jamieson ◽

R. Callahan

Keyword(s):

Imaging Techniques ◽

Membrane Surface ◽

High Stress ◽

Extrusion Direction ◽

Polymeric Membranes ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Crystalline Polymers ◽

Lamellar Structures ◽

Resolution Imaging

“Row lamellar” structures have previously been observed when highly crystalline polymers are melt-extruded and recrystallized under high stress. With annealing to perfect the stacked lamellar superstructure and subsequent stretching in the machine (extrusion) direction, slit-like micropores form between the stacked lamellae. This process has been adopted to produce polymeric membranes on a commercial scale with controlled microporous structures. In order to produce the desired pore morphology, row lamellar structures must be established in the membrane precursors, i.e., as-extruded and annealed polymer films or hollow fibers. Due to the lack of pronounced surface topography, the lamellar structures have typically been investigated by replica-TEM, an indirect and time consuming procedure. Recently, with the availability of high resolution imaging techniques such as scanning tunneling microscopy (STM) and field emission scanning electron microscopy (FESEM), the microporous structures on the membrane surface as well as lamellar structures in the precursors can be directly examined.The materials investigated are Celgard® polyethylene (PE) flat sheet membranes and their film precursors, both as-extruded and annealed, made at different extrusion rates (E.R.).

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