Within the framework of the continuum elastic theory of biaxial nematic liquid crystals, we have addressed ourselves to the structure, stability and energetics of some singular and non-singular topological defects, and certain director configurations. We find that certain non-singular hybrid disclinations could be energetically favourable relative to certain half-strength disclinations. The interaction between singular hybrids depends strongly on the biaxial elastic anisotropy. We suggest possible defect structures that can exist in spherical droplets of biaxial nematics. Further we find structural instabilities, in confined geometries, arising due to the inherent biaxiality of the system.
{"title":"On Some Elastic Instabilities in Biaxial Nematics","authors":"Sreejith Sukumaran, G. Ranganath","doi":"10.1051/JP2:1997146","DOIUrl":"https://doi.org/10.1051/JP2:1997146","url":null,"abstract":"Within the framework of the continuum elastic theory of biaxial nematic liquid crystals, we have addressed ourselves to the structure, stability and energetics of some singular and non-singular topological defects, and certain director configurations. We find that certain non-singular hybrid disclinations could be energetically favourable relative to certain half-strength disclinations. The interaction between singular hybrids depends strongly on the biaxial elastic anisotropy. We suggest possible defect structures that can exist in spherical droplets of biaxial nematics. Further we find structural instabilities, in confined geometries, arising due to the inherent biaxiality of the system.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"309 10","pages":"583-601"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72564320","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present the first evidence for spatio-temporal merging dynamics in thin gap electroless deposition experiments. The influence of both the gap thickness and the buoyancy forces on these phenomena is analyzed. The occurrence of this reverse cascading dynamical process is discussed in terms of the interaction of two counter rotating buoyancy driven convection rolls.
{"title":"Convection Induced Self-Organization in Electroless Deposition Experiments","authors":"F. Texier, G. Gadret, C. Léger, F. Argoul","doi":"10.1051/JP2:1997150","DOIUrl":"https://doi.org/10.1051/JP2:1997150","url":null,"abstract":"We present the first evidence for spatio-temporal merging dynamics in thin gap electroless deposition experiments. The influence of both the gap thickness and the buoyancy forces on these phenomena is analyzed. The occurrence of this reverse cascading dynamical process is discussed in terms of the interaction of two counter rotating buoyancy driven convection rolls.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"93 1","pages":"663-675"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91464710","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ce travail presente une etude theorique de l'indice de refraction pour une onde de matiere se propageant dans un gaz. Le calcul de l'indice prend en compte le mouvement des atomes du gaz et met en evidence les effets Doppler et Fizeau. Le cas ou les atomes du gaz et ceux de l'onde ont un spin 1/2 est egalement discute, ce qui permet le calcul du pouvoir rotatoire et du dichroisme circulaire d'un gaz optiquement pompe. Finalement, l'indice de l'helium, du neon, de l'argon, du krypton et du xenon est calcule pour une onde de sodium. Ces calculs montrent l'importance des effets de gloire et de la moyenne thermique. Ces effets doivent donc etre pris en compte pour l'interpretation precise des resultats experimentaux. De plus, il apparait que l'indice depend fortement du parametre quantique B = 2μD e σ 2 (en unite atomique). En utilisant les potentiels sodium-gaz rares disponibles dans la litterature, nous obtenons un accord raisonnable entre l'indice calcule et les resultats experimentaux. Cependant, il reste difficile de rendre compte de certaines valeurs experimentales avec les meilleurs potentiels actuellement disponibles.
本文对气体中物质波的折射率进行了理论研究。指数的计算考虑了气体原子的运动，突出了多普勒和菲索效应。本文还讨论了气体原子和波原子自旋为1/2的情况，从而计算了光泵气体的旋转功率和圆二色性。最后计算了钠波中氦、氖、氩、氪和氙的指数。这些计算表明了荣耀效应和热平均效应的重要性。因此，在精确解释实验结果时，必须考虑到这些影响。此外，该指数与量子参数B = 2μD e σ 2(原子单位)密切相关。利用文献中可用的稀有钠气势，得到了计算指标与实验结果的合理一致。然而，仍然很难用目前可用的最佳潜力来解释一些实验值。
{"title":"Refractive index for atomic waves: Theory and detailed calculations","authors":"C. Champenois, É. Audouard, P. Duplaa, J. Vigué","doi":"10.1051/JP2:1997144","DOIUrl":"https://doi.org/10.1051/JP2:1997144","url":null,"abstract":"Ce travail presente une etude theorique de l'indice de refraction pour une onde de matiere se propageant dans un gaz. Le calcul de l'indice prend en compte le mouvement des atomes du gaz et met en evidence les effets Doppler et Fizeau. Le cas ou les atomes du gaz et ceux de l'onde ont un spin 1/2 est egalement discute, ce qui permet le calcul du pouvoir rotatoire et du dichroisme circulaire d'un gaz optiquement pompe. Finalement, l'indice de l'helium, du neon, de l'argon, du krypton et du xenon est calcule pour une onde de sodium. Ces calculs montrent l'importance des effets de gloire et de la moyenne thermique. Ces effets doivent donc etre pris en compte pour l'interpretation precise des resultats experimentaux. De plus, il apparait que l'indice depend fortement du parametre quantique B = 2μD e σ 2 (en unite atomique). En utilisant les potentiels sodium-gaz rares disponibles dans la litterature, nous obtenons un accord raisonnable entre l'indice calcule et les resultats experimentaux. Cependant, il reste difficile de rendre compte de certaines valeurs experimentales avec les meilleurs potentiels actuellement disponibles.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"302 1","pages":"523-541"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89228927","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
For a two-dimensional model of pattern formation the interplay between a broken up down symmetry and a weakly broken rotational symmetry is investigated. Both symmetries may be broken, for instance, in chemical reactions with an applied electric field or in thermal convection of planarly aligned nematic liquid crystals. In a system with rotational symmetry and a broken up down symmetry hexagonal patterns are favored in a certain parameter range. With increasing values for the anisotropies, by keeping the up down symmetry broken, hexagons may be deformed to centered rectangular patterns. Hence, breaking both symmetries is an alternative mechanism leading to rectangular patterns. Finally, at larger values of the anisotropies a bifurcation to stripes takes place.
{"title":"Deformed Hexagonal Patterns in a Weakly Anisotropic System","authors":"R. Schmitz, W. Zimmermann","doi":"10.1051/JP2:1997151","DOIUrl":"https://doi.org/10.1051/JP2:1997151","url":null,"abstract":"For a two-dimensional model of pattern formation the interplay between a broken up down symmetry and a weakly broken rotational symmetry is investigated. Both symmetries may be broken, for instance, in chemical reactions with an applied electric field or in thermal convection of planarly aligned nematic liquid crystals. In a system with rotational symmetry and a broken up down symmetry hexagonal patterns are favored in a certain parameter range. With increasing values for the anisotropies, by keeping the up down symmetry broken, hexagons may be deformed to centered rectangular patterns. Hence, breaking both symmetries is an alternative mechanism leading to rectangular patterns. Finally, at larger values of the anisotropies a bifurcation to stripes takes place.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"81 1","pages":"677-683"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80994533","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Y. Hemar, N. Herrmann, P. Lemarechal, R. Hocquart, F. Lequeux
In this article, we deal with the propagation of ultrasonic waves in monodisperse concentrated oil-in-water emulsions. Using the approximation of Isakovich, we propose two different models, a mirror model and a core-shell model, aiming to describe the temperature field in the dense medium and to supply a correct expression of the ultrasonic wave vector. The comparison between experimental data and theoretical models shows that the core-shell model leads to a very accurate description of the ultrasonic attenuation, in a wide range of frequencies and concentrations, in the case where the thermo-elastic effect, due to the scattering of thermal waves by the particles, is the dominant loss mechanism.
{"title":"Effective Medium Model for Ultrasonic Attenuation Due to the Thermo-Elastic Effect in Concentrated Emulsions","authors":"Y. Hemar, N. Herrmann, P. Lemarechal, R. Hocquart, F. Lequeux","doi":"10.1051/JP2:1997148","DOIUrl":"https://doi.org/10.1051/JP2:1997148","url":null,"abstract":"In this article, we deal with the propagation of ultrasonic waves in monodisperse concentrated oil-in-water emulsions. Using the approximation of Isakovich, we propose two different models, a mirror model and a core-shell model, aiming to describe the temperature field in the dense medium and to supply a correct expression of the ultrasonic wave vector. The comparison between experimental data and theoretical models shows that the core-shell model leads to a very accurate description of the ultrasonic attenuation, in a wide range of frequencies and concentrations, in the case where the thermo-elastic effect, due to the scattering of thermal waves by the particles, is the dominant loss mechanism.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"31 1","pages":"637-647"},"PeriodicalIF":0.0,"publicationDate":"1997-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76043859","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We consider a blend of two polymers of different chemical nature in the presence of an adsorbing surface. We assume that the surface adsorbs strongly one or both species at high temperature. This constrains the system to a quenched composition on the surface. We assume that phase separation occurs at lower temperature. We discuss the influence of the quenched surface fluctuations on the critical properties of the mixture. We generalize to these mixtures the characteristic critical adsorption that is present in simple fluid mixtures. The composition profile is calculated in all cases.
{"title":"Phase Separation in Polymer Blends Near a Surface","authors":"A. Saout-Elhak, M. Benhamou, M. Daoud","doi":"10.1051/JP2:1997141","DOIUrl":"https://doi.org/10.1051/JP2:1997141","url":null,"abstract":"We consider a blend of two polymers of different chemical nature in the presence of an adsorbing surface. We assume that the surface adsorbs strongly one or both species at high temperature. This constrains the system to a quenched composition on the surface. We assume that phase separation occurs at lower temperature. We discuss the influence of the quenched surface fluctuations on the critical properties of the mixture. We generalize to these mixtures the characteristic critical adsorption that is present in simple fluid mixtures. The composition profile is calculated in all cases.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"139 1","pages":"503-516"},"PeriodicalIF":0.0,"publicationDate":"1997-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89475846","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Fontaine, J. Daillant, P. Guenoun, M. Alba, A. Braslau, J. Mays, J. Petit, F. Rieutord
We present results of the adsorption of charged diblock copolymers at the free interface between air and solution. These copolymers are water soluble and act as surfactants above some concentration. Through thermodynamic and diffuse X-ray surface scattering measurements, we demonstrate the influence of the concentration on the formed adsorbed layer. While sufficiently long copolymers adsorb by forming structures which do not deform the interface, short copolymers are shown to induce buckling of the interface due to interchain interactions.
{"title":"Spontaneous Buckling Induced by the Adsorption of Charged Copolymers at the Air-Water Interface","authors":"P. Fontaine, J. Daillant, P. Guenoun, M. Alba, A. Braslau, J. Mays, J. Petit, F. Rieutord","doi":"10.1051/JP2:1997133","DOIUrl":"https://doi.org/10.1051/JP2:1997133","url":null,"abstract":"We present results of the adsorption of charged diblock copolymers at the free interface between air and solution. These copolymers are water soluble and act as surfactants above some concentration. Through thermodynamic and diffuse X-ray surface scattering measurements, we demonstrate the influence of the concentration on the formed adsorbed layer. While sufficiently long copolymers adsorb by forming structures which do not deform the interface, short copolymers are shown to induce buckling of the interface due to interchain interactions.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"126 1","pages":"401-407"},"PeriodicalIF":0.0,"publicationDate":"1997-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76836286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The internal structure (the monomer density profiles) of weakly charged polyelectrolyte brushes of different morphologies has been analyzed on the basis of the self-consistent-field approach. In contrast to previous studies based on the local electroneutrality approximation valid for sufficiently strongly charged or densely grafted (osmotic) brushes we consider the opposite limit of sparse brushes which are unable to retain the counterions inside the brush. We have shown that an exact analytical solution of the SCF-equations is available in the case of a planar brush. In contrast to Gaussian monomer density profile known for osmotic polyelectrolyte brushes we have found that weakly charged brushes are characterized by constant monomer density. At the same time free ends of grafted polyions are distributed throughout the brush. Thus, the structural cross-over between polyelectrolyte mushrooms and dense brush regimes is established.
{"title":"Structure of weakly charged polyelectrolyte brushes: Monomer density profiles","authors":"O. Borisov, E. Zhulina","doi":"10.1051/JP2:1997137","DOIUrl":"https://doi.org/10.1051/JP2:1997137","url":null,"abstract":"The internal structure (the monomer density profiles) of weakly charged polyelectrolyte brushes of different morphologies has been analyzed on the basis of the self-consistent-field approach. In contrast to previous studies based on the local electroneutrality approximation valid for sufficiently strongly charged or densely grafted (osmotic) brushes we consider the opposite limit of sparse brushes which are unable to retain the counterions inside the brush. We have shown that an exact analytical solution of the SCF-equations is available in the case of a planar brush. In contrast to Gaussian monomer density profile known for osmotic polyelectrolyte brushes we have found that weakly charged brushes are characterized by constant monomer density. At the same time free ends of grafted polyions are distributed throughout the brush. Thus, the structural cross-over between polyelectrolyte mushrooms and dense brush regimes is established.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":" 3","pages":"449-458"},"PeriodicalIF":0.0,"publicationDate":"1997-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72560996","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Adamson, A. Zaitsevskii, Andrei Dement’Ev, N. Stepanov
Potential energy and non-adiabatic coupling functions for the two lowest 1 Σ + states of LiF were calculated using the recently proposed perturbative approach, based on the multiple partitioning of the full Hamiltonian, and the difference-dedicated CI method. The results are compared with MRDCI and available full CI data for the same AO basis set. A high accuracy was achieved with a semiempirical perturbative scheme combining the direct calculations at second order with an approximate estimation of higher-order local contributions.
{"title":"Multi-partitioning QDPT and difference-dedicated CI calculations of non-adiabatic couplings : Application to charge transfer in LiF system","authors":"S. Adamson, A. Zaitsevskii, Andrei Dement’Ev, N. Stepanov","doi":"10.1051/JP2:1997132","DOIUrl":"https://doi.org/10.1051/JP2:1997132","url":null,"abstract":"Potential energy and non-adiabatic coupling functions for the two lowest 1 Σ + states of LiF were calculated using the recently proposed perturbative approach, based on the multiple partitioning of the full Hamiltonian, and the difference-dedicated CI method. The results are compared with MRDCI and available full CI data for the same AO basis set. A high accuracy was achieved with a semiempirical perturbative scheme combining the direct calculations at second order with an approximate estimation of higher-order local contributions.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"20 1","pages":"393-399"},"PeriodicalIF":0.0,"publicationDate":"1997-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74562199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We consider the problem of polymer chains confined between two parallel plates (a slit). The interactions between the polymer and the plates are assumed to be repulsive. A variational theory is used to derive the size of the chain as a function of the distance between plates, D, for both hard impenetrable walls as well as for soft walls. In both cases it is shown that for large and small values of D, the results coincide with the predictions of the scaling theory. For intermediate values of D the size of the polymer depends on the strength of interaction, C 0 , between the monomers and the walls. The cross-over from the fully squeezed regime (D → 0) to the case when the plate separation is infinite is non-monotonic for good solvents. In particular the mean square end-to-end distance has a minimum (the depth of which depends on C 0 ) at moderate values of D. The theoretical predictions are in accord with Monte-Carlo simulations. When the solvent quality is poor the cross-over from two-dimensional behavior to three-dimensional case is monotonic. The effect of interaction strength between the polymer and the plates is also examined. It is argued that for moderate values of D a slit of given size with a specified interaction has the same effect as one of larger slit size but with stronger interactions.
{"title":"Shape of Confined Polymer Chains","authors":"C. Cordeiro, M. Molisana, D. Thirumalai","doi":"10.1051/JP2:1997136","DOIUrl":"https://doi.org/10.1051/JP2:1997136","url":null,"abstract":"We consider the problem of polymer chains confined between two parallel plates (a slit). The interactions between the polymer and the plates are assumed to be repulsive. A variational theory is used to derive the size of the chain as a function of the distance between plates, D, for both hard impenetrable walls as well as for soft walls. In both cases it is shown that for large and small values of D, the results coincide with the predictions of the scaling theory. For intermediate values of D the size of the polymer depends on the strength of interaction, C 0 , between the monomers and the walls. The cross-over from the fully squeezed regime (D → 0) to the case when the plate separation is infinite is non-monotonic for good solvents. In particular the mean square end-to-end distance has a minimum (the depth of which depends on C 0 ) at moderate values of D. The theoretical predictions are in accord with Monte-Carlo simulations. When the solvent quality is poor the cross-over from two-dimensional behavior to three-dimensional case is monotonic. The effect of interaction strength between the polymer and the plates is also examined. It is argued that for moderate values of D a slit of given size with a specified interaction has the same effect as one of larger slit size but with stronger interactions.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"1 1","pages":"433-447"},"PeriodicalIF":0.0,"publicationDate":"1997-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89827491","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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