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3. AFM observations of single polyolefin molecules on mica and graphiteстатья
- Автор: Valery Prokhorov
- Сборник: Structure and Properties of Polyolefin Materials
- Серия: ISBN: 978-81-7895-543-8
- Год издания: 2013
- Место издания: Transworld Research Network Kerala, India
- Первая страница: 53
- Последняя страница: 96
- Аннотация: Abstract. Single-molecule linear chain (LC) conformations and crystalline conformations consisting of a small number of polymer molecules (regular shaped nanocrystallites (NC), nanolamellae (NL) and isolated undulating lamellae) have been observed by atomic force microscopy (AFM) for a number of synthetic polyolefins on mica surface. The polyolefins (polyethylene, isotactic polypropylene, poly- 1-butene and their copolymer and block copolymer) were deposited from dilute solutions at elevated temperatures; the crystalline conformations formed due to rapid folding of polymer chains on the mica surface at samples cooling. The LC have both highly kinked sites as expected for flexible polymers, and sites of large lateral expansion with length ~10 nm due to local chain folding. The NC have rod-like or rectangular shapes with characteristic lamellar double-stripe morphology or more complex shapes consisting of independent, misaligned crystalline blocks. The polymer fold length fluctuates greatly in the NC populations. Two-dimensional networks have been observed for ultrahigh molecular weight polyethylene with crystalline block-type NL in the junctions linked by tie chains. Multiple anomalies in the AFM imaging (the negative height of LC and some lamellae and the apparent volume insufficiency of NC) have been observed; their explanation is proposed, based on the idea of immobilization of polymer molecules in a nm-thick salt layer that forms on the surface of mica. The general conformation of crystalline polyolefin molecules on the mica surface is found to be a sequence of crystalline bundles of variable dimensions, linked by randomcoil chain segments. Only isolated lamellae and monolayer lamellar domains were observed on graphite surface and only globular nanoparticles were observed for noncrystalline polystyrene. The coil-to-crystal intramolecular transition appears to be highly inhibited on mica in comparison with graphite, allowing the visualization of partially folded linear chains on the mica surface.
- Добавил в систему: Прохоров Валерий Васильевич