Publications (68)81.36 Total impact



Journal of the Chemical Society Perkin Transactions 2 01/2010; DOI:10.1002/chin.199304048

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ABSTRACT: We report in this paper detailed measurements of the linear and nonlinear optical properties of thin films of P(VDFTrFE) copolymers (with composition 70/30 mol%). The polymer films are cast from solutions using the spin coating technique and poled at saturation using very lowfrequency a.c. fields. The refractive index (n = 1.42) is determined from measurements of the Brewster incidence, and the thickness from measurements of the optical path close to the normal incidence. Recording of the Maker fringes and calibration of the setup with a quartz plate allow us to determine the secondharmonic coefficients: d33 = 4.3, d31 = 0.22 10−12 m/V and the optical dispersion n(2ω) − n(ω) = 0.0077 (ω is the frequency of the incident laser beam at 1060 nm). The spincoated copolymer films are optically unaxial due to a preferential orientation of the chain axes parallel to the plane of the film, and measurement of their birefringence gives ne − no = −0.0083. Therefore, this feature allows us to find a direction of phase matching along which the first and secondharmonic waves have an infinite coherence length. It is observed using an indexmatching liquid.EPL (Europhysics Letters) 07/2007; 9(7):657. DOI:10.1209/02955075/9/7/008 · 2.27 Impact Factor 
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ABSTRACT: Without application of an external electric field, the temperature dependence of the shear angle uxy, which is proportional to the spontaneous polarisation and therefore to the order parameter, has been measured by means of Bragg scattering of 412 keV gamma radiation in KH2PO4 and RbH2PO4. Simultaneously, optical observations of the domain structure were performed. The shape of the rocking curve of KDP and RbDP are compared and discussed. The ferroelectric transition in RbDP is of second order in contrast to KDP which exhibits a firstorder one. The modified Slater's theory provides for RbDP a good fit to the experimental data uxy(T) in the whole temperature range investigated. The fact that beta =0.5 near Tc can be understood as an effect of the dipolar interaction; so this system exhibits a cross over from a Slater behaviour to a dipolar behaviour.Journal of Physics C Solid State Physics 02/2001; 11(6):1203. DOI:10.1088/00223719/11/6/025 
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ABSTRACT: A phenomenological theory of the incommensurate phase transition which occurs close to the alpha  beta transition in quartz is presented. This theory assumes that the coupling between the soft optic mode of the alpha  beta transition and the acoustic modes play an important role in the formation of the modulated structure. According to the values of the phenomenological parameters, different kinds of incommensurate structures can form, in particular singlek or triplek structures. The available experimental data concerning the quartz transition are discussed.Journal of Physics C Solid State Physics 11/2000; 16(35):6705. DOI:10.1088/00223719/16/35/004 
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ABSTRACT: Monolayers of short chiral alcohols at the water surface provide a simple model for chiral interactions between molecules. This paper is focused on alcohols with two particular chain lengths, 2tridecanol (2C13) and 2tetradecanol (2C14). Thermodynamic and structural parameters were measured, varying the ratio of left and right enantiomers within monolayers. The evolution of melting temperatures and entropies is not consistent with the formation of a racemate. Grazing Xray diffraction, revealing the molecular stacking, shows clearly that there is no chiral separation. In these two compounds molecules spontaneously selfassemble at the water surface as a solid solution. The chiral polar headgroup is partially screened by the chain thermal disorder of the rotator phase. 2tridecanol exhibits a hexagonal rotator phase stable in time and independent of temperature. Experiments performed close to the melting point show pretransitional effects for mixtures different from 50/50. This broadening of the peak can be related to defects in 2D crystals, phenomena already observed for the melting of some 3D systems.The European Physical Journal E 08/2000; 3(1):6370. DOI:10.1007/s101890070042 · 2.18 Impact Factor 
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ABSTRACT: We formulate a simple Landau type model describing macroscopic behavior recently discovered in new smectic phases composed of achiral bentshaped molecules. Films of such smectics exhibit three types of ordering related to dipole polarization, molecular tilt, and chirality. However, due to specific thirdorder coupling of the order parameters, these three symmetrybreaking types are not independent and this fact leads to specific domain structures that are observed in experiments. (C) 2000 MAIK "Nauka/Interperiodica".Journal of Experimental and Theoretical Physics 04/2000; 90(5):826833. DOI:10.1134/1.559169 · 0.93 Impact Factor 
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ABSTRACT: We formulate a simple Landau type model describing macroscopic behaviour recently discovered new smectic phases composed of achiral bentshaped molecules. Films of such smectics exhibit three types of ordering related to dipole polarization, molecular tilt, and chirality. However due to specific third order coupling of the order parameters these three types of symmetrybreaking are not independent ones, and this fact leads to specific domain structures really observed in experiments. 
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ABSTRACT: Structural relaxations near surfaces and interfaces are analysed in a simple, generic model with first, second and thirdlayer interactions. The relaxations have exponential envelopes with three types of structural distortion: (i) ferrodistortive, (ii) antiferrodistortive, and (iii) modulated (incommensurable). Their stability conditions in the field of control parameters and their relationship with structural phase transitions is derived. A tricritical point is found for threelayer interactions and a transition to an incommensurate phase. All phase transitions to the ferrodistortive phase are firstorder in the model. The theory is applied to the analysis of lattice relations near internal interfaces in ionic polytypic materials (e.g. PbI2). Diffuse Xray scattering and the shift of diffraction angles are the typical fingerprints for such relaxations. The relevant structure factors are calculated. There is tentative agreement between the calculated and observed diffraction profiles.Journal of Physics Condensed Matter 12/1998; 4(49):9779. DOI:10.1088/09538984/4/49/006 · 2.22 Impact Factor 
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ABSTRACT: Biquadratic coupling between two order parameters Q1 Q2 can lead to transitions between a phase with only one of the two order parameters active (phase I or II) and a mixed phase III in which both order parameters are symmetry breaking. Domain walls for positive coupling energies are chiral under thermodynamic conditions close to the transition points IIII and IIIII. Annihilation of chirality in the wall leads to wall widening and wall bifurcations. The widths of the walls are different for the two order parameters leading to greater lattice distortions on either side of the wall than in the centre of the wall.Journal of Physics Condensed Matter 12/1998; 3(27):5163. DOI:10.1088/09538984/3/27/009 · 2.22 Impact Factor 
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ABSTRACT: The electrostatic quadrupolar interaction between spherical nematic droplets in an isotropic (and nonconducting) liquid is calculated. It is found to have an anisotropic form U q ∝1/R 5, where R is the distance between droplets, with repulsion for droplets having parallel orientation of the quadrupole moments and attraction at oblique angles around the orthogonal orientation. In an external magnetic field aligning the orientations of the quadrupole moments, a competition of the quadrupolar repulsion and van der Waals attraction (U vdW∝ 1/R 6) leads to a specific spatial organization of droplets which is in fact often reported in experimental observations (see the monograph by P. Drzaic, Liquid Crystal Dispersions, World Scientific, Singapore (1995) and references cited therein).JETP Letters 10/1998; 68(10):785791. DOI:10.1134/1.567946 · 1.36 Impact Factor 
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ABSTRACT: It has been shown previously [J. Lajzerowicz and A. P. Levanyuk, Phys. Rev. B 49, 15 475 (1994)] that in a perfect threedimensional crystal the commensurateincommensurate transition is always discontinuous due to a fluctuationinduced longrange attraction between domain walls. At the same time it has been concluded long ago that in real crystals a strong repulsion between the domain walls exists due to impurityinduced roughening of the domain walls. This poses the question whether the commensurateincommensurate transition becomes continuous in real crystals. We argue that the most important point to answer this question is that a very slow activation motion of domain walls over disorderinduced potential barriers is necessary for making the repulsion operative, so that over a reasonable time of experiment this interaction ‘‘propagates’’ to distances that are no more than one order of magnitude bigger than the domainwall width. Meanwhile the attractive interactions between the domain walls ‘‘propagate’’ almost instantaneously, thus leading to the conclusion that experimentally observed commensurateincommensurate transition will always be discontinuous. Our estimates show that for structural incommensurate systems the ‘‘equilibrium’’ distance between the domain walls near transition point has the same order of magnitude as the domainwall width. © 1996 The American Physical Society.Physical review. B, Condensed matter 12/1996; 54(17):1207312075. DOI:10.1103/PhysRevB.54.12073 · 3.66 Impact Factor 


Article: Melting of Short 1Alcohol Monolayers on Water: Thermodynamics and XRay Scattering Studies
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ABSTRACT: From surface tension measurements we extract the melting entropy Deltas2D of fattyalcohol monolayers on water. Deltas2D is found to be 4kB/mol lower than in the bulk. Because of the role of the conformational entropy, the melting transition is discontinuous for long chains, but tends to be continuous for molecules shorter than 1nonanol. For 1decanol Deltas2D is sufficiently small to allow observation of critical fluctuations; the diffraction peak, measured with a high resolution synchrotron experiment, is described by a powerlaw singularity which broadens as the temperature approaches the melting point.Physical Review Letters 10/1994; 73(12):16521655. DOI:10.1103/PhysRevLett.73.1652 · 7.73 Impact Factor 
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ABSTRACT: Owing to macroscopic electric fields arising from thermal fluctuations of a ferroelectric domain wall, the attraction energy of two parallel walls decays at large distances between the walls (h) as h2 with a prefactor that is proportional to T and to a ratio of dielectric constants that is equal to unity for the isotropic medium. For proper ferroelectrics, and improper ones with a quadratic dependence of the spontaneous polarization on the order parameter, this law is valid for all h greater than the domain wall thickness (which is the minimum length of the problem). For improper ferroelectrics with cubic (or higherorder) dependence of the polarization on the order parameter, there exists a region with a logarithmic dependence of the interaction energy on h. This attraction, which proves to prevail over the Van der Waals one, leads to a discontinuity of the ferroelectricincommensurate transition. Estimation of the period of the incommensurate phase at the transition provides a reasonable order of magnitude and shows that this period does not depend much on the crystal parameters other than the width of the domain wall. The interaction of the ferromagnetic and ferroelastic domain walls is qualitatively analogous to that of the ferroelectric ones. The role of quantum fluctuations becomes important at not very low temperatures. For nonferroelectric, nonferroelastic, nonferromagnetic domain walls the powerlaw fluctuationinduced attraction is shown to arise as well.Physical review. B, Condensed matter 07/1994; 49(22):1547515484. DOI:10.1103/PhysRevB.49.15475 · 3.66 Impact Factor 
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ABSTRACT: We argue that any commensurateincommensurate phase transition in a crystalline media is discontinuous due to powerlaw attraction of the domain walls. The main origin of this attraction are the thermal fluctuations of the walls which are always accompanied, in a crystal, by at least one of the longrange fields: electric, magnetic, elastic.Ferroelectrics 07/1994; 157(1):6368. DOI:10.1080/00150199408229483 · 0.38 Impact Factor 
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ABSTRACT: Some analogies exist between parametrically driven dynamical system and anisotropic XY model. We discuss one aspect of this analogy : the existence of domain walls, their different structures and the existence of “wetting” like transitions. The work is done in a LandauGinzburg framework.Ferroelectrics 02/1993; 140(114):8187. DOI:10.1080/00150199308008267 · 0.38 Impact Factor 
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ABSTRACT: The problem of winding of a long polymer chain around an attractive rigid rod is studied in relation with the localization transition exhibited by this system. The role of chiral and polar interactions is considered. The results are compared with previous models of adsorption of a polymer and of helixcoil transition. On étudie le problème de l'enroulement d'une longue chaîne de polymère autour d'une barre rigide, en relation avec la transition de localisation présentée par ce système. Le rôle des interactions chirales et polaires est considéré. Ces résultats sont comparés à des modèles précédemment proposés pour décrire l'adsorption d'un polymère et la transition hélicepelote.Journal de Physique I 10/1992; DOI:10.1051/jp1:1992250
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763  Citations  
81.36  Total Impact Points  
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1989–2010

University Joseph Fourier  Grenoble 1
Grenoble, RhôneAlpes, France


1988

University of Grenoble
Grenoble, RhôneAlpes, France
