کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5180112 | 1502535 | 2015 | 11 صفحه PDF | دانلود رایگان |
- Monotonic shear thinning with exponent â0.57 from 10 sâ1 to 1000 sâ1.
- Negative extrudate swell showing a minimum at a critical shear rate γËc.
- No full nematic alignment along the flow, even at 1000Â sâ1.
- 2 fluids morphology formed under shear in the slit die.
- Stress relaxation upon flow cessation coincides with growth of bands widths.
The rheological and structural characteristics of acetoxypropylcellulose (APC) nematic melt are studied at shear rates ranging from 10 sâ1 to 1000 sâ1 which are relevant to extrusion based processes. APC shows a monotonic shear thinning behavior over the range of shear rates tested. The negative extrudate-swell shows a minimum when a critical shear rate γËc is reached. For shear rates smaller than γËc, the flow-induced texture consists of two set of bands aligned parallel and normal to the flow direction. At shear rates larger than γËc, the flow induced texture is reminiscent of a 2 fluids structure. Close to the shearing walls, domains elongated along the flow direction and stacked along the vorticity are imaged with POM, whereas SALS patterns indicate that the bulk of the sheared APC is made of elliptical domains oriented along the vorticity. No full nematic alignment is achieved at the largest shear rate tested. Below γËc, the stress relaxation is described by a stretched exponential. Above γËc, the stress relaxation is described by a fast and a slow process. The latter coincides with the growth of normal bands thicknesses, as the APC texture after flow cessation consists of two types of bands with parallel and normal orientations relative to the flow direction. Both bands thicknesses do not depend on the applied shear rate, in contrast to their orientation.
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Journal: Polymer - Volume 71, 5 August 2015, Pages 102-112