title: Thermodynamic, structural, and nanomechanical properties of a fluorous biphasic material.
abstract: The dynamics of the amphiphilic semifluorinated F(CF2)12(CH2)12H (F12H12) alkane that undergoes two condensed phase transitions have been investigated by Brillouin light spectroscopy, shear rheometry, small- (SAXS) and wide-angle (WAXS) X-ray scattering, and thermodynamic PVT measurements. The solid (I)-solid (II) transition (Ts) is marked by a stronger temperature dependence of the sound velocity in phase II and by a 2 orders of magnitude drop of the shear modulus. Between the Ts and the melting transition (Tm), the presence of two phonons implies a coexistence of solid (II) and amorphous (liquid) regions in the submicrometer range at thermal equilibrium as revealed by the SAXS pattern of a single reflection superimposed on a very broad amorphous halo. This intriguing finding of a transient, very slow (over 10 h) solid/liquid coexistence within phase II is rationalized by a two-stage mechanism for melting of the smectic phase (II) of F12H12. A refinement of the known packing motifs for the two solid-state structures is proposed.
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Núñez
authors.forename: C G
authors.initials: CG
authors.lastname: Clark
authors.forename: W
authors.initials: W
authors.lastname: Cheng
authors.forename: A
authors.initials: A
authors.lastname: Best
authors.forename: G
authors.initials: G
authors.lastname: Floudas
authors.forename: A N
authors.initials: AN
authors.lastname: Semenov
authors.forename: G
authors.initials: G
authors.lastname: Fytas
authors.forename: K
authors.initials: K
authors.lastname: Müllen
mesh_terms: D002152:Calorimetry, Differential Scanning; D036103:Nanotechnology; D012212:Rheology; D012542:Scattering, Radiation; D013816:Thermodynamics