The morphologies and crystalline structures of melt-crystallized ultrathin isotactic poly(1-butene) films have been studied with transmission electron microscopy and electron diffraction. It is demonstrated that a bypass of form II crystallization can be achieved with an increase in its crystallization temperature. Electron microscopy observations show that melt-grown isotactic poly(1-butene) single crystals have a well-shaped hexagonal form, whereas form I crystals converted from form II display the morphologies of their tetragonal precursors. Electron diffraction results indicate that, instead of the twinned hexagonal pattern of the converted form I crystal, the directly formed form I single crystals exhibit an untwinned hexagonal pattern.
Distributed optical fiber sensors (DOFS) offer unprecedented features, the most unique one of which is the ability of monitoring variations of the physical and chemical parameters with spatial continuity along the fiber. Among all these distributed sensing techniques, optical frequency domain reflectometry (OFDR) has been given tremendous attention because of its high spatial resolution and large dynamic range. In addition, DOFS based on OFDR have been used to sense many parameters. In this review, we will survey the key technologies for improving sensing range, spatial resolution and sensing performance in DOFS based on OFDR. We also introduce the sensing mechanisms and the applications of DOFS based on OFDR including strain, stress, vibration, temperature, 3D shape, flow, refractive index, magnetic field, radiation, gas and so on.
Poly(vinylidene fluoride) (PVF2) exhibits at least four crystalline forms, c~, fl, 7 and 6, among which the/~ phase is the most important because of its extensive applications in piezoelectric and pyroelectric properties. Many attempts have been made to prepare /~-form PVF2 by various methods which include growth from solution [1], mechanical deformation [2-5], crystallization at elevated pressures [6][7][8], application of a strong electric field [9][10][11] and the copolymerization with other fluorocarbons (i.e. trifluoro-or tetrafluoroethylene) [12,13]. Generally, in the sample of PVF 2 cooled from the melt, the e phase is predominant and transition to the /3 form has to be performed by stretching. It would be very important if it were possible to prepare directly the fl phase from the melt. The only reported/~ crystallization of pure PVF 2 from the melt at atmospheric pressure was described by Lovinger [14] based on epitaxial growth on the surface of potassium bromide. However, no systematic investigation has been carried out on the temperature dependence of melt-grown/?-crystals.The purpose of this letter is to focus on the effects of quenching and then annealing on the /~-phase formation from the melt of PVF2 by means of FTIR, X-ray diffraction and electron microscopy.The PVF 2 (mol. wt = 5 x 105 ) utilized in this work was supplied by Polysciences, Inc. Films were either cast from cyclohexanone solutions on to glass plates or compression moulded. The thickness of the samples is about 5/~m for FTIR and X-ray diffraction analysis and about 100nm for electron microscopy studies. The two types of films were supported on a thin sheet of mica and were melted at 210°C for 10rain and then quenched quickly in a bath in the
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