Understanding Molecular Epitaxial Mechanism and Chain Folding in Determining Chain Packing and Crystalline Morphology of Isotactic Polypropylene
Dr. Yan Cao, Ph.D.
The University of Akron
About the speaker
Dr. Cao obtained a master of polymer engineering at South China University of technology in 2003. In 2012, she was awarded Ph. D. of polymer physics (Adviser: Prof. Stephen Z. D. Cheng) at The University of Akron. She joined the Takahara ERATO project as a postdoc researcher at Kyushu University.
We investigate how the epitaxial domination of the crystal morphologies takes place in the γ-form of the chain-folded crystals using high molecular weight isotactic polypropylene (i-PP) samples with a controlled number of stereodefects. Two different morphologies were identified via transmission electron and atomic force microscopies (TEM and AFM). One is needle-like and the other is "flat''. Based on the tilted selected area electron diffraction (SAED) results, the microscopic formation mechanism of the "needle" and "flat'' morphology was discussed and it revealed that in the "flat'' γ-form crystal, the initial α-form single crystal had a stem orientation tilted away from the lamellar normal within the ac-plane around the b-axis. Elongated α2-form lath-like single crystals were grown from thin film melt at Tx =145oC -155oC using commercial sample. This 17o-stem tilt in the α2-form single crystals favors the (10-2) fold surface and appears to depend upon both conformational and chain folding constraints.
时间: 2014年12月3日 上午9:30-10:30
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