showing 7 related works from this author
Low-temperature specific heat of orientational glasses
1992
This review summarizes specific heat data measured at low temperatures (T<1 K) on orientational glasses. Three species of mixed molecular crystals exhibiting orientational disorder are considered, namely (KBr)1−x (KCN) x , (NaCN)1−x (KCN) x (Rb)1−x (NH4) x H2PO4. For intermediate concentrations of the anisotropic components, glass-like excitations have been observed. It is demonstrated that with respect to thermal properties, orientational disorder leads to the same “universal” behaviours than for structural disorder, i.e. a specific heat which varies below 1 K and for times 10−4 s–10 s as:C p(T,t)∞T 1×ln(t). The variation of the glass-like anomaly with compositional disorder is also discus…
Inelastic and quasi-elastic light scattering in (NaCN)1?x(KCN)x quadrupolar glasses
1990
The elastic constantsc11 andc44, and the attenuation of longitudinal phonons along (100)-direction in (NaCN)1−x(KCN)x mixed crystals have been determined by brillouin spectroscopy in the temperature range fromT=10K−300K. Minima inc44 (T) which determine the freezing tempratureTF in these orientational glasses appear at lower temperatures compared to neutron scattering results. The coupling of molecular reorientations to longitudinal phonons in NaCN-rich smaples shows up in dispersion effects inc11 (T) and the appearence of a dynamical central peak nearTF.
Anomalous thermoelastic behavior of (KI)1-x(NH4I)x
1990
Abstract An anomalous softening of the shear mode c 44 is observed in (KI) 1- x (NH 4 I) x with Brillouin scattering (10 K ⩽ T ⩽ 300 K ). It is caused by the weak quadrupolar moment of the NH 4 + ion, induced by the C 3 v symmetry of the potential. A parallel decrease of the lifetime of this transverse phonon at lower temperatures is observed. Static random strain fields due to admixing KI with NH 4 I are small. The results have been treated in terms of a mean field theory. The c 11 elastic constant does not show any anomalous behavior. Also are given the elastic constants c 11 and c 44 for x =0.14, 0.43 and 1 and 1 at T = 300 K and 10 K .
Magnetic microrods as a tool for microrheology
2015
International audience; Dynamics of superparamagnetic rods in crossed constant and alternating magnetic fields as a function of field frequency are studied and it is shown that above the critical value of the amplitude of the alternating field the rod oscillates around the direction of the alternating field. The fit of the experimentally measured time dependence of the mean orientation angle of the rod allows one to determine the ratio of magnetic and viscous torques which act on the rod. The protocol of microrheological measurements consists of recording the dynamics of the orientation of the rod when the magnetic field is applied at an angle to the rod and observing its relaxation due to …
Dynamics of paramagnetic nanostructured rods under rotating field
2011
International audience; The dynamical rotational behavior of magnetic nanostructured rods based on the auto-association of maghemite nanoparticles and block-copolymers is probed by optical microscopy under rotating fields i n a s imple l iquid. The reorientation of the rods by a field rotated by 90° is first studied. The measured relaxation is characteristic of param-agnetic objects. Under a stationnary rotating field, a synchronous rotational regime is observed at low field frequency. Above a frequency threshold which scales as H^2 , the dynamics becomes asynchronous with back-and-forth rotations. These behaviors are well predicted by the presented model.
Magnetic wire-based sensors for the micro-rheology of complex fluids
2013
We propose a simple micro-rheology technique to evaluate the viscoelastic properties of complex fluids. The method is based on the use of magnetic wires of a few microns in length submitted to a rotational magnetic field. In this work, the method is implemented on a surfactant wormlike micellar solution that behaves as an ideal Maxwell fluid. With increasing frequency, the wires undergo a transition between a steady and a hindered rotation regime. The study shows that the average rotational velocity and the amplitudes of the oscillations obey scaling laws with well-defined exponents. From a comparison between model predictions and experiments, the rheological parameters of the fluid are det…