报告题目：Structural analysis of crystalline polymers byelectron microscopy, electron diffraction and AFM

报告人：Prof. Bernard Lotz

Institut Charles Sadron (CNRS), 23, Rue duLœss, 67034 Strasbourg (France)

报告时间：2016年05月30日（星期一）下午14:00

报告地点：独墅湖校区 907楼1445室

报告摘要：Crystalline polymers are made ofsmall (several micrometers) and thin (ten to several tens of nanometers)lamellae, which amounts to ≈ 10^-10 to 10^-12 grams ofmaterial. Electron microscopy is therefore an ideal tool for theirinvestigation, in spite of the sensitivity of polymers to the beam ofelectrons. Upon crystallization from the bulk, crystalline polymers producespherulites with a complex structure. They are made of radial lamellae,frequently twisted in space, which renders their investigation difficult.However, crystallization from solution or in thin films generates singlecrystals that are well adapted for structural investigations. It is alsopossible to take advantage of epitaxial crystallization on foreign substrates(usually low molecular weight organic crystals) to produce thin films withsingle crystal characteristics, and in which the chains lay in the plane of thefilm. The presentation will illustrate several contributions of electronmicroscopy (imaging mode in bright field and dark field, electron diffraction)in the investigation of crystalline polymers (structure and crystallizationprocesses of polymers, mostly commodity polymers: polyethylene and isotacticpolypropylene). The presentation will bevery didactic. It will insist on some problematics that have beenencountered in the field and on the ways that have been developed to solvethem:

-         The structural analysis of metastable phases that cannot be obtained in an oriented, fiber form byclassical (usually mechanical) means, as illustrated with  the combined use of epitaxialcrystallization, electron diffraction and AFM to observe the structure ofpolymers with methyl group resolution (≈ 4Å)

-         The concept of frustratedpacking in crystalline polymers

-         The use of dark fieldimaging to visualize and investigate the growth mechanism of, and thecrystal-crystal transformations in, single crystals

The investigation of the fold structure, i.e. of the amorphouslayer that sandwiches the crystalline core of the lamellae, and in which theoutgoing stems fold back to reenter the crystalline core. Due to its largervolume requirement, this folding generates surface stresses that, in turn,induce twisted and scrolled lamellar morphologies.

报告人简介：Prof.Bernard Lotz received his PhD in physical sciences from Université LouisPasteur, Strasbourg in1968. He then went to USA as a technical staff atATT-Bell Laboratories for 2 years. In 1970, he went back to France and workedin Institut Charles Sadron (CNRS) and has been a director of research from 1982to 2004. Prof. Lotz’s main research interests include the following aspects:(1) Structure and morphology of biopolymers (determination of the structure ofvarious polymers, polypeptides and fibrous proteins); (2) Crystal structure,morphology, phase transitions, crystallization and melting of syntheticpolymers, mostly technichnologically relevant polymers (e.g. polyethylene,isotactic and syndiotactic polypropylene, polyesters and polyamides, polylactides).His major investigation techniques are electron microscopy and electrondiffraction, atomic force microscopy, modeling by conformational and packingenergy analysis. He has published over 310 papers of original work, bookchapters and reviews. His work earned him many awards including the Grand Prixof the Groupe Français des Polymères; “Fraser P. Price” award of the Universityof Massachusetts, Amherst; Fellow of the American Physical Society, Division ofPolymer Physics.

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