Premelting features and acoustic mode softening in the rotator phases of linear telomers: C₁₇H₃₆

Abstract

The polymer induced ali@ment (PIA) tcchniqne is presented as B new technique to grow single-crystalline films of linear telomers. Combining the PIA technique with special high-resolution Brillouin techniques. it is possible 10 determine the coefficienls of Ihe elastic stiffness tenwr of the crystalline state of linear lelomen. especially in their rotator phases. As model systems we have chosen the perfluoroalkane Ca~Fhz and the linear n-alkane C17H36. A comparison of elaslic data obtained from classically and PIA grown samples proves their equivdenee as well as their complemenlarity. Precursors of critical melting discovered xn the rataiotOr phase of C17Hy axe discussed in terms of the anomalous temperature dependence of cefiain elastic tensor coefficients and of related n-telomers.

Phase-transition behavior ofn-alkanes on nanostructured polytetrafluorethylene films: Brillouin spectroscopic and calorimetric investigations on pentacosane

“…As has been shown for many systems, [6][7][8]10,11 the elastic properties of plastic systems are strongly affected by the morphology and the morphological changes during the different phase transitions. In the following, we will demonstrate the efficiency of high-resolution BS in connection with modulated differential scanning calorimetry ͑MDSC͒ investigations for the understanding of the dynamical properties of the system under study throughout its different phase transitions.…”

“…Usually, even a second crystallographic axis is positioned within the PIA plane. 7,8 The aim of the current paper is to show that the transcrystallization mechanism on the PIA substrate still works for C 25 H 52 and that the created morphology corresponds to that of solution-or melt-grown crystals of that material. Moreover, we want to relate our Brillouin and calorimetric investigations to the phase transition sequence and the related phase-transition mechanisms.…”

“…This is reflected by acoustic as well as by thermal properties. [6][7][8][9] The competitive influences of the stiff covalent bonded chain molecules and the weak intermolecular interactions between the molecular chains as well as between the crystal lamellas on the elastic properties have been demonstrated for different types of alkanes. [5][6][7]10,11 Consequently, investigations of the static and dynamic elastic properties, combined with investigations of the thermal properties, will give essential information about the interrelations between these properties on one hand, and the molecular structure, the molecular dynamics, and the morphology on the other.…”

“…7,8 This crystal growth method uses the polytetrafluoroethylene ͑PTFE͒ induced alignment ͑PIA͒ technique, to obtain oriented crystal plates of n-alkanes or perfluoroalkanes. The PIA technique, originally developed by Wittmann and Smith, 21 allows one to obtain highly structured crystal mats of very different materials including n-alkanes and perfluoroalkanes.…”

“…The PIA technique, originally developed by Wittmann and Smith, 21 allows one to obtain highly structured crystal mats of very different materials including n-alkanes and perfluoroalkanes. 7,8,[22][23][24][25][26] Although the organization mechanism of the nanostructured PIA substrate on the deposited sample material is not well understood, it is clear that the PIA substrate induces a preferential orientation of the sample crystallites with their c axes parallel to the preferential orientation of the PTFE. Usually, even a second crystallographic axis is positioned within the PIA plane.…”