Elastic properties of thin ultraoriented poly(ε‐caprolactone) films grown on ptfe substrates as revealed by Brillouin spectroscopy

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

“…This order-disorder effect destroys the all-trans conformation of the chain molecules. The value and the temperature dependence of ⌫ 22 ϭ(q 2 /4) 22 suggests the appearance of a rather high structural viscosity 41 22 within the rotator phases when compared with the values in the orthorhombic crystalline phase, being almost independent of temperature. As a matter of fact, the 22 values in the rotator phase are also higher than those of other plastic crystals in their rotator phases.…”

“…Obviously, there exists a strong coupling between the driving order parameters at the transitions at T k and T m leading to significant discontinuities of the longitudinal elastic stiffness coefficients c 22 and c 33 and the shear stiffness c 44 . Of course, these discontinuities are not just due to the related density anomalies but reflect strong morphologic influences.…”

“…The PIA technique to prepare sandwich samples has been described in detail in previous papers. 7,8,[22][23][24][25] Here we only want to stress the most important aspects relevant for the present work. The PIA substrate consists of a highly oriented and highly crystalline PTFE layer of about 10 nm thickness usually deposited on a conventional glass substrate.…”

“…39 Taking into account the orientation of the pentacosane crystals on the PIA substrate and the shortened Voigt's notation 39 of the elastic constants, it is straightforward to correlate the longitudinal polarized phonon mode propagating along the crystallographic c axis ͑three axis͒ with the elastic constant c 33 and that propagating along the crystallographic b axis ͑two axis͒ with the elastic constant c 22 . The elastic constants c 44 , c 55 , and c 66 are the shear constants related to the sample plane ͑see Fig.…”

“…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.…”