Cast film crystallization

A series of aggregation structures of bilayer forming azobenzene amphiphiles, CnAzoCmN+Br, both in single crystals and cast films was determined by the X-ray diffraction method and uv-visible absorption spectroscopy. From the relationship between chemical structures and their two-dimensional supramolecular structure, factors determining the molecular orientation in bilayer structure were discussed. Some unique properties based on two-dimensional molecular ordering were also discussed. 

In this paper, UV-visible absorption spectra and X-ray diffraction experiments of single crystals and solvent cast films of the azobenzene amphiphiles, CnAzoCmN+Br, were systematically investigated. Structural characterization of the cast bilayer films are discussed in comparison with aqueous solutions and single crystals. Some novel functional properties of the cast films are described, too. We also emphasize that the two-dimensional molecular assemblies, cast films and crystals of bilayer-forming amphiphiles, are suitable candidates for "crystal engineering" because of their simple structures compared with usual three-dimensional molecular crystals. 

Organic compounds which show reversible color change by a photochemical reaction are potentially applicable to optical switching and/or memory materials. Azobenzenes and its derivatives are one of the most suitable candidates of photochemical switching molecular devices because of their well characterized photochromic behavior attributed to trans-cis photoisomerization reaction. Many works on photochromism of azobenzenes in monolayers LB films, and bilayer membranes, have been reported. Photochemical isomerization reaction of the azobenzene chromophore is well known to trigger phase transitions of liquid crystals [29-31]. Recently we have found the isothermal phase transition from the state VI to the state I of the cast film of CgAzoCioN+ Br induced by photoirradiation [32]. 

The morphology of spin-cast film, thickness of 180 nm, from polycaprolactone shows many spherulitic structures with fibrillar nanostructures formed of lamellae lying edge on (about 10 nm thick) and areas with lamellar sheets lying flat on. Different crystalline structures are found when the sample is melted and crystallized as a function of temperature. These two studies reinforce the complex inner relationship between physical treatment and nanostructure. 

The crystallization tendency of polycarbonate is enhanced by the action of solvents. For example, crystallization may be accomplished by slow evaporation of solvent from cast film (14, 17) or by treatment with swelling agents such as ethyl acetate or acetone. 

The films prepared by melt prosing are very rapidly cooled to room temperature. Under these conditions no detectable crystallization in the polymer can develop, as is proved by x-ray examination. On the other hand, in the solvent-cast films chain mobility of the polycarbonate is enhanced by the presence of solvent and crystallinity can occur. In some extreme cases the solvent cast films are turbh ana the a ystallmn. can be a. nonstrated by x-ray photograms which showr x-ray patterns characteristic of crystallized polycarbonate. It is assumed that... 

Addition of DPP to growing MPP at 60° C produced still another type of copolymer. Solvent-cast films of this material are transparent. The copolymer does not crystallize on heating, forms stable solutions in m-xylene, and has a single glass transition, at 190°C. The thermal behavior is similar to that of a random copolymer, but the NMR spectrum (Figure 7) is more nearly that expected of a block copolymer. The methyl proton peak is rather sharp with the chemical shift expected for... 

The polyethylene samples examined are shown in Table III slowly cooled or quenched from melt, original monofilament, annealed, over drawn, cold drawn, single crystal, cast film, extended chain crystal, etc. The sample-probe distance can be chosen from TO to 260 mm. The setting angle is defined as the angle between the molecular plane and the be plane according to Bunn (1 1) as shown in Figure 12. 

Figure 13. Cell dimensions plotted against the lattice distortion parameter of polyethylene (40) ((O) melt crystallized, A (9) melt crystallized, B (Is) single crystal ( ) cast film high pressure crystallized, C)...

In the case of solution-crystallized UHMW-PE, it is possible to make solution-cast films in which the lamellar crystals are regularly stacked,... 

A well-defined amount of co-crystallization is possible across the interface of two adjacent crystals by annealing two stacked, completely wetted, solution-cast films of UHMW-PE [32]. It was found that doubling of the lamellae across the interface enhances the peel energy to such a level that the films could not be separated anymore. By contrast, pre-annealing one side of the film prohibited co-crystallization across the interface and these films could still be separated easily. It was therefore concluded that a limited amount of chain diffusion across the interface occurs during doubling of the lamellae, as facilitated by the well-defined structure of the interphase due to the adjacent reentry that occurs upon crystallization from solution. 

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