37 research outputs found
Structure and relaxation processes of an anisotropic molecular fluid confined into 1D nanochannels
Structural order parameters of a smectic liquid crystal confined into the
columnar form of porous silicon are studied using neutron scattering and
optical spectroscopic techniques. It is shown that both the translational and
orientational anisotropic properties of the confined phase strongly couple to
the one-dimensional character of the porous silicon matrix. The influence of
this confinement induced anisotropic local structure on the molecular
reorientations occuring in the picosecond timescale is discussed
Sliding and translational diffusion of molecular phases confined into nanotubes
The remaining dynamical degrees of freedom of molecular fluids confined into
capillaries of nano to sub-nanometer diameter are of fundamental relevance for
future developments in the field of nanofluidics. These properties cannot be
simply deduced from the bulk one since the derivation of macroscopic
hydrodynamics most usually breaks down in nanoporous channels and additional
effects have to be considered. In the present contribution, we review some
general phenomena, which are expected to occur when manipulating fluids under
confinement and ultraconfinement conditions.Comment: 17 pages, 8 fig
Incoherent Quasielastic Neutron Scattering Study of Molecular dynamics of 4-n-cyano-4'-octylbiphenyl
We report incoherent quasielastic neutron scattering experiments on the
thermotropic liquid crystal 4-n-cyano-4'-octylbiphenyl. The combination of
time-of-flight and backscattering data allows analyzing the intermediate
scattering function over about three decades of relaxation times. Translational
diffusion and uniaxial molecular rotations are clearly identified as the major
relaxation processes in respectively the nanosecond and picosecond time scales.
The comparison with literature data obtained by other techniques is discussed.Comment: Accepted in Phys. Chem. Chem. Phy
Etudes structurales et dynamiques d'un composite d'inclusion incommensurable sous pression hydrostatique
Les changements de phase et les propriétés dynamiques du nonadécane-urée ont été étudiés par différentes techniques sous pression (P 4kbars) une nouvelle phase orthorhombique gardant la métrique hexagonale apparaît. A 300 K, par diffraction neutronique, le paramètre d'incommensurabilité varie sous l'effet de la pression et une déformation différente des sous-réseaux d'alcane et d'urée est constatée au dessus de 1 kbar. Les défauts de conformation des chaînes étudiés par différentes spectroscopies montrent une variation de leur concentration qui offre d'étonnantes similarités avec la périodicité du sous-réseau d'alcane. Ils expliquent en grande partie, la translation anormalement grande des alcanes le long des canaux.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF
Structural transformation with spatial and temporal high resolution
International audienc
Landau Theory for Non-Symmetry-Breaking Electronic Instability Coupled to Symmetry-Breaking Applied to Prussian Blue Analogue
International audienceDifferent types of ordering phenomena may occur during phase transitions, described within the universal framework of the Landau theory through the evolution of one, or several, symmetry-breaking order parameter . In addition, many systems undergo phase transitions related to an electronic instability, in the absence of a symmetry-breaking and eventually described through the evolution of a totally symmetric order parameter q linearly coupled to volume change. Analyzing the coupling of a non-symmetry-breaking electronic instability, responsible for volume strain, to symmetry-breaking phenomena is of importance for many systems in nature and here we show that the symmetry-allowed q 2 coupling plays a central role. We use as case study the rubidium manganese hexacyanoferrate Prussian blue analogue, exhibiting phase transitions with hysteresis that may exceed 100 K, and based on intermetallic charge transfer (CT). During the phase transition, the intermetallic CT described through the evolution of q is coupled to cubic-tetragonal ferroelastic symmetry-breaking described through the evolution of . In this system, the symmetry-breaking and non-symmetry breaking deformations have similar amplitudes but the large volume strain is mainly due to CT. We analyze both the ferroelastic and the CT features of the phase transition within the frame of the Landau theory, taking into account the q 2 coupling, stabilizing concomitant CT and Jahn-Teller distortion. The results show that the phase transition and its wide thermal hysteresis originate from the coupling between both processes and that the elastic coupling of each order parameter with the volume strain is responsible for the q 2 coupling. The phase diagrams obtained with this model are in good qualitative agreement with various experimental findings and apply to diverse families of materials undergoing Mott transition, spin-crossover, neutral-ionic transition…, for which isostructural electronic instability driving volume strain can couple to symmetry-breaking or not, create phase transition lines and drive cooperative phenomena