We present a systematic study of spiral waves in the Belousov-Zhabotinsky re- action in a spatial open reactor, where the concentrations of sulfuric acid, sodium bromate, and malonic acid are varied. Within this parameter space, three kinds of instabilities arise: two of them, which we identify as the retracting wavefront and convective instabilities, lead to the destruction of the spiral pattern, and mark the boundaries of the spiral existence domain in parameter space. Inside this domain, there exists a region where simply rotating spirals undergo the meandering instability. Quantitative measurements of the asymptotic characteristics of sim- ple spirals provide scaling relations between the observables: the pitch varies as the square root of the period. They both diverge with simple exponents at the retracting wavefront instability. This organization, reminiscent of a second order phase transition, allows us to consider the spi- ral a critical pattern. Comparison with several models and numerical simulations indicates the validity or discrepancies of applying these theoretical approaches to our experimental results. R esum e. |N ous pr esentons une etude syst ematique des ondes spirales dans la r eaction de Belousov-Zhabotinsky en r eacteur ouvert, en fonctions des concentrations d'acide sulfurique, de bromate de sodium et d'acide malonique. Dans cet espace de param etres, trois types d'insta- bilit es surviennent : deux d'entre elles, que nous appelons instabilit e de r etraction de front et instabilit e convective, nissent par d etruire les structures spirales, et marquent les limites de leur domaine d'existence. Il existe, dans ce domaine, une r egion o u les spirales en rotation simple bifurquent vers l'instabilit e de sinuage. Des mesures quantitatives des caract eristiques asymp- totiques des spirales simples fournissent des lois d' echelles entre les observables : le pas varie comme le carr ed e la p eriode ; tous deux divergent avec des exposants simples a l'instabilit ed e r etraction. Cette organisation, rappelant celle des transitions de phases du second ordre, nous autorise a consid erer la spirale comme une structure critique. La comparaison de nos r esultats exp erimentaux avec di erents mod eles et simulations num eriques montre accords et d esaccords des approches th eoriques.
我们提出了一个系统的研究螺旋波的别洛乌索夫- zhabotinsky反应在一个空间开放反应器，其中硫酸，溴酸钠和丙二酸的浓度是不同的。在这个参数空间中，产生了三种不稳定性:其中两种不稳定性，我们将其定义为回缩波前和对流不稳定性，它们导致螺旋图形的破坏，并标记了参数空间中螺旋存在域的边界。在这个区域内，存在一个简单旋转的螺旋经历蜿蜒不稳定的区域。简单螺旋的渐近特性的定量测量提供了可观测值之间的标度关系:螺距随周期的平方根而变化。在缩回波前不稳定性下，两者均以单指数发散。这种组织，使人联想到二阶相变，使我们能够考虑一个临界模式。与几种模型和数值模拟的比较表明了这些理论方法与实验结果的有效性或差异性。研究了不同浓度的硫酸、溴酸钠、溴酸钠和丙二酸盐的浓度，并对不同浓度的硫酸、溴酸钠和丙二酸盐的浓度进行了分析。Dans et space de parpareses, three types d'insta- biles幸存;deux d' entreselles, que nous appelons，不稳定，不稳定，不稳定，对流，不稳定，不稳定，结构螺旋，不稳定，不稳定，限制，leledomain d'existence。将会存在一种不稳定的、不稳定的、不稳定的、不稳定的、不稳定的、不稳定的、不稳定的区域。它测量了数量上的不对称现象——不对称现象——不对称现象——不对称现象——不对称现象——不对称现象——不对称现象——不对称现象——不对称现象——不对称现象——不对称现象——不对称现象;我们的双发散平均暴露简单一个'不稳定'或'不稳定'的抽吸。更清晰的组织，更清晰的细胞，更清晰的细胞，更清晰的细胞，更清晰的细胞，更清晰的细胞，更清晰的细胞，更清晰的结构。对不同模型模型的模拟结果进行了比较，并对不同模型模型的模拟结果进行了比较。
{"title":"Experimental Survey of Spiral Dynamics in the Belousov-Zhabotinsky Reaction","authors":"A. Belmonte, Ouyang Qi, J. Flesselles","doi":"10.1051/JP2:1997195","DOIUrl":"https://doi.org/10.1051/JP2:1997195","url":null,"abstract":"We present a systematic study of spiral waves in the Belousov-Zhabotinsky re- action in a spatial open reactor, where the concentrations of sulfuric acid, sodium bromate, and malonic acid are varied. Within this parameter space, three kinds of instabilities arise: two of them, which we identify as the retracting wavefront and convective instabilities, lead to the destruction of the spiral pattern, and mark the boundaries of the spiral existence domain in parameter space. Inside this domain, there exists a region where simply rotating spirals undergo the meandering instability. Quantitative measurements of the asymptotic characteristics of sim- ple spirals provide scaling relations between the observables: the pitch varies as the square root of the period. They both diverge with simple exponents at the retracting wavefront instability. This organization, reminiscent of a second order phase transition, allows us to consider the spi- ral a critical pattern. Comparison with several models and numerical simulations indicates the validity or discrepancies of applying these theoretical approaches to our experimental results. R esum e. |N ous pr esentons une etude syst ematique des ondes spirales dans la r eaction de Belousov-Zhabotinsky en r eacteur ouvert, en fonctions des concentrations d'acide sulfurique, de bromate de sodium et d'acide malonique. Dans cet espace de param etres, trois types d'insta- bilit es surviennent : deux d'entre elles, que nous appelons instabilit e de r etraction de front et instabilit e convective, nissent par d etruire les structures spirales, et marquent les limites de leur domaine d'existence. Il existe, dans ce domaine, une r egion o u les spirales en rotation simple bifurquent vers l'instabilit e de sinuage. Des mesures quantitatives des caract eristiques asymp- totiques des spirales simples fournissent des lois d' echelles entre les observables : le pas varie comme le carr ed e la p eriode ; tous deux divergent avec des exposants simples a l'instabilit ed e r etraction. Cette organisation, rappelant celle des transitions de phases du second ordre, nous autorise a consid erer la spirale comme une structure critique. La comparaison de nos r esultats exp erimentaux avec di erents mod eles et simulations num eriques montre accords et d esaccords des approches th eoriques.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"29 1","pages":"1425-1468"},"PeriodicalIF":0.0,"publicationDate":"1997-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78526259","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 theoretically analyze the behavior of membranes presenting a nematic susceptibility, induced by the presence of anisotropic phospholipids having a quadrupolar nematic symmetry. This kind of anisotropic phospholipids is either naturally found in some biological membranes, or can be chemically tailored by linking pairs of single surfactants at the level of their polar heads, giving rise to so-called “gemini” surfactants. We predict that such membranes can acquire a non-zero paranematic order induced by the membrane curvature, which in turn produces curvature instabilities. We call the resulting paranematic order para-antinematic, since it is opposite on opposite sides of the membrane. We find phase transitions toward sponges (L3), tubules, or modulated “egg-carton” phases.
{"title":"Sponges, Tubules and Modulated Phases of Para-Antinematic Membranes","authors":"J. Fournier, P. Galatola","doi":"10.1051/JP2:1997199","DOIUrl":"https://doi.org/10.1051/JP2:1997199","url":null,"abstract":"We theoretically analyze the behavior of membranes presenting a nematic susceptibility, induced by the presence of anisotropic phospholipids having a quadrupolar nematic symmetry. This kind of anisotropic phospholipids is either naturally found in some biological membranes, or can be chemically tailored by linking pairs of single surfactants at the level of their polar heads, giving rise to so-called “gemini” surfactants. We predict that such membranes can acquire a non-zero paranematic order induced by the membrane curvature, which in turn produces curvature instabilities. We call the resulting paranematic order para-antinematic, since it is opposite on opposite sides of the membrane. We find phase transitions toward sponges (L3), tubules, or modulated “egg-carton” phases.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"46 1","pages":"1509-1520"},"PeriodicalIF":0.0,"publicationDate":"1997-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89225159","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}
Microphase separation in multiblock (AB) n copolymer melts at equilibrium is considered theoretically. It is shown that any finite polydispersity of the block molecular weights results in a set of novel super 2 -structures which are characterized by two levels of microdomains, one on the top of the other. The typical size of the second-level microdomains is governed by the polydispersity degree δ, and is much larger than the size of ordinary microdomains if δ is small. The theoretical description involves the second order parameter field φ(r) (in addition to the normal order parameter ψ related to the local composition) which is proportional to the local excess of longer blocks over shorter blocks. A scaling picture including the main characteristics of the super 2 -structures is built for both weak and strong segregation regimes.
{"title":"Super2- Structures in Polydisperse Multiblock-Copolymers","authors":"A. Semenov","doi":"10.1051/JP2:1997197","DOIUrl":"https://doi.org/10.1051/JP2:1997197","url":null,"abstract":"Microphase separation in multiblock (AB) n copolymer melts at equilibrium is considered theoretically. It is shown that any finite polydispersity of the block molecular weights results in a set of novel super 2 -structures which are characterized by two levels of microdomains, one on the top of the other. The typical size of the second-level microdomains is governed by the polydispersity degree δ, and is much larger than the size of ordinary microdomains if δ is small. The theoretical description involves the second order parameter field φ(r) (in addition to the normal order parameter ψ related to the local composition) which is proportional to the local excess of longer blocks over shorter blocks. A scaling picture including the main characteristics of the super 2 -structures is built for both weak and strong segregation regimes.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"20 1","pages":"1489-1497"},"PeriodicalIF":0.0,"publicationDate":"1997-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78592362","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}
Applying laser tweezers to cylindrical vesicles of lipid bilayers produces an instability which propagates down the vesicle leaving behind it a peristaltic state, which appears under the microscope as pearls on a string. We investigate the late stages of this “pearling” instability, where the pearls are observed to drift slowly towards the laser trap (the spot at which the tweezers are applied, into which the surfactant is drawn) where they jam up. We model the hydrodynamics of the drifting pearls as a combination of translation of the string of pearls, and “slipping” of the bilayer skin over the pearls, to relate the speed of the pearls to the underlying flux of surfactant into the trap. We find that the pearl drift is slower than the skin-slip speed by a factor of order a/R where a is the radius of the tethers connecting the pearls, and R is the pearl radius.
{"title":"Late Stages of the “Pearling\" Instability in Lipid Bilayers","authors":"J. L. Coveas, S. Milner, W. Russel","doi":"10.1051/JP2:1997180","DOIUrl":"https://doi.org/10.1051/JP2:1997180","url":null,"abstract":"Applying laser tweezers to cylindrical vesicles of lipid bilayers produces an instability which propagates down the vesicle leaving behind it a peristaltic state, which appears under the microscope as pearls on a string. We investigate the late stages of this “pearling” instability, where the pearls are observed to drift slowly towards the laser trap (the spot at which the tweezers are applied, into which the surfactant is drawn) where they jam up. We model the hydrodynamics of the drifting pearls as a combination of translation of the string of pearls, and “slipping” of the bilayer skin over the pearls, to relate the speed of the pearls to the underlying flux of surfactant into the trap. We find that the pearl drift is slower than the skin-slip speed by a factor of order a/R where a is the radius of the tethers connecting the pearls, and R is the pearl radius.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"15 1","pages":"1185-1204"},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91293345","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}
Nous etudions la phase cubique du systeme binaire C 12 (EO) 6 /eau. La structure periodique tridimensionnelle de cette phase correspond au groupe d'espace Ia3d. Dans ce cas, la phase cubique est centree et les molecules de surfactant s'organisent en deux labyrinthes tridimensionnels interpenetres, separes par un milieu continu d'eau. Nous presentons des resultats recents obtenus en utilisant le spectrometre spin-echo IN 11 a l'I.L.L. Nos experiences ont permis de mettre en evidence, pour la premiere fois, le caractere dynamique des fluctuations observees dans la phase cubique etudiee. Pour ce faire, des mesures ont ete effectuees sur un monocristal (∼ 0,1 cm 3 ). La fonction de diffusion S(q 1 t) a ete mesuree pour differents vecteurs de diffusion q. Pour des vecteurs q qui ne correspondent pas a des reflexions de Bragg, la diffusion des neutrons est quasi-elastique et la fonction associee, S(q, t), decroit avec un temps caracteristique d'environ 20 ns. Les fluctuations dynamiques sont probablement apparentees a des modes collectifs de deformation des labyrinthes.
{"title":"Dynamics of a Lyotropic Cubic Phase","authors":"M. Clerc, Y. Hendrikx, B. Farago","doi":"10.1051/JP2:1997181","DOIUrl":"https://doi.org/10.1051/JP2:1997181","url":null,"abstract":"Nous etudions la phase cubique du systeme binaire C 12 (EO) 6 /eau. La structure periodique tridimensionnelle de cette phase correspond au groupe d'espace Ia3d. Dans ce cas, la phase cubique est centree et les molecules de surfactant s'organisent en deux labyrinthes tridimensionnels interpenetres, separes par un milieu continu d'eau. Nous presentons des resultats recents obtenus en utilisant le spectrometre spin-echo IN 11 a l'I.L.L. Nos experiences ont permis de mettre en evidence, pour la premiere fois, le caractere dynamique des fluctuations observees dans la phase cubique etudiee. Pour ce faire, des mesures ont ete effectuees sur un monocristal (∼ 0,1 cm 3 ). La fonction de diffusion S(q 1 t) a ete mesuree pour differents vecteurs de diffusion q. Pour des vecteurs q qui ne correspondent pas a des reflexions de Bragg, la diffusion des neutrons est quasi-elastique et la fonction associee, S(q, t), decroit avec un temps caracteristique d'environ 20 ns. Les fluctuations dynamiques sont probablement apparentees a des modes collectifs de deformation des labyrinthes.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"111 1","pages":"1205-1214"},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79627778","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}
Nous presentons la synthese et l'etude des proprietes structurales de nouveaux materiaux dimesogenes polaires non symmetriques constitues de deux unites mesogenes differentes reliees par un espaceur flexible. L'influence de la longueur de l'espaceur est etudiee. L'architecture moleculaire a ete concue pour stabiliser les phases smectiques et nous montrons que les proprietes structurales se rapprochent fortement de celles des celebres smectiques polaires. Nous en deduisons que ces nouveaux systemes sont gouvernes par la competition entre plusieurs longueurs microscopiques incommensurables (modele de frustration). La nouveaute importante est que le parametre de couplage entre ces longueurs peut etre ajuste chimiquement par la longueur de l'espaceur.
{"title":"From Segregation to Intercalation in Smectic Organization of Polar Non-Symmetric Dimesogens","authors":"V. Faye, H. Nguyen, P. Barois","doi":"10.1051/JP2:1997184","DOIUrl":"https://doi.org/10.1051/JP2:1997184","url":null,"abstract":"Nous presentons la synthese et l'etude des proprietes structurales de nouveaux materiaux dimesogenes polaires non symmetriques constitues de deux unites mesogenes differentes reliees par un espaceur flexible. L'influence de la longueur de l'espaceur est etudiee. L'architecture moleculaire a ete concue pour stabiliser les phases smectiques et nous montrons que les proprietes structurales se rapprochent fortement de celles des celebres smectiques polaires. Nous en deduisons que ces nouveaux systemes sont gouvernes par la competition entre plusieurs longueurs microscopiques incommensurables (modele de frustration). La nouveaute importante est que le parametre de couplage entre ces longueurs peut etre ajuste chimiquement par la longueur de l'espaceur.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"37 1","pages":"1245-1260"},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79649750","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 have measured the shear modulus of three-dimensional aqueous foam under a small oscillating stress. The foam structure has also been characterized by measurements of the optical transmission. Each of these physical properties depends on a characteristic length, related to the bubble size distribution. We have shown that both lengths follow the same evolution as a function of foam age. They grow according to a parabolic law, in agreement with theoretical predictions.
{"title":"Time Evolution of the Elastic Properties of Aqueous Foam","authors":"Hussein Hoballah, R. Höhler, S. Cohen-Addad","doi":"10.1051/JP2:1997182","DOIUrl":"https://doi.org/10.1051/JP2:1997182","url":null,"abstract":"We have measured the shear modulus of three-dimensional aqueous foam under a small oscillating stress. The foam structure has also been characterized by measurements of the optical transmission. Each of these physical properties depends on a characteristic length, related to the bubble size distribution. We have shown that both lengths follow the same evolution as a function of foam age. They grow according to a parabolic law, in agreement with theoretical predictions.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"2 1","pages":"1215-1224"},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87311660","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 finite chain backbone stiffness in polymers gives rise to a number of novel behaviors described on short length scales. We analyze the semiflexible polymer phases near surfaces using a new scaling theory, incorporating the surface attraction in terms of its range and depth. It is found that the phase diagram includes five different phases: desorbed, weakly- adsorbed with both isotropic and nematic-type distribution of polymer segments inside the potential well, strongly-adsorbed states with the isotropic and nematic-type distribution. We draw conclusions on the orders of the transitions between the phases. The stiffness of polymer chain backbone means the presence of an orientation "memory" be- tween segments along the chain. A rigid rod is the very stiff polymer, for which the persistence length is much larger than the total contour length. This polymer can not be crumpled without breakage. On the other hand a very flexible chain can be crumpled practically on any length scales. It can be crumpled as a whole (as in so-called globule-to-coil transition iii and in the ideal limit it can be crumpled on smaller and smaller length scales (down to the microscopic scales of chain diameter order), carrying a self-similar or fractal structure. For the intermediate cases of semiflexible chain, which are probably the most interesting for applications including biophysical problems, the persistence length is much smaller than the total polymer contour length, so it can be crumpled as a whole in a similar way as a flexible chain. In general, we can treat a semiflexible polymer chain as a flexible one, when we are interested in the universal macroscopic polymer properties measured over the scales of whole macromolecule dimensions. But on the scales smaller than the persistence length the semiflexible structure can be con- sidered as an array of rigid rods interconnected at a fixed angle. (Naturally, the semiflexible wormlike chain can be viewed as the continuous limit of the discrete model iii.) Therefore, on these scales already, semiflexible polymer can not be crumpled without breakage and its properties are essentially different from those of flexible polymer. A wide class of synthetic and
{"title":"A New Scaling Theory of Semiflexible Polymer Phases Near Attracting Surfaces","authors":"D. V. Kuznetsov, W. Sung","doi":"10.1051/JP2:1997187","DOIUrl":"https://doi.org/10.1051/JP2:1997187","url":null,"abstract":"The finite chain backbone stiffness in polymers gives rise to a number of novel behaviors described on short length scales. We analyze the semiflexible polymer phases near surfaces using a new scaling theory, incorporating the surface attraction in terms of its range and depth. It is found that the phase diagram includes five different phases: desorbed, weakly- adsorbed with both isotropic and nematic-type distribution of polymer segments inside the potential well, strongly-adsorbed states with the isotropic and nematic-type distribution. We draw conclusions on the orders of the transitions between the phases. The stiffness of polymer chain backbone means the presence of an orientation \"memory\" be- tween segments along the chain. A rigid rod is the very stiff polymer, for which the persistence length is much larger than the total contour length. This polymer can not be crumpled without breakage. On the other hand a very flexible chain can be crumpled practically on any length scales. It can be crumpled as a whole (as in so-called globule-to-coil transition iii and in the ideal limit it can be crumpled on smaller and smaller length scales (down to the microscopic scales of chain diameter order), carrying a self-similar or fractal structure. For the intermediate cases of semiflexible chain, which are probably the most interesting for applications including biophysical problems, the persistence length is much smaller than the total polymer contour length, so it can be crumpled as a whole in a similar way as a flexible chain. In general, we can treat a semiflexible polymer chain as a flexible one, when we are interested in the universal macroscopic polymer properties measured over the scales of whole macromolecule dimensions. But on the scales smaller than the persistence length the semiflexible structure can be con- sidered as an array of rigid rods interconnected at a fixed angle. (Naturally, the semiflexible wormlike chain can be viewed as the continuous limit of the discrete model iii.) Therefore, on these scales already, semiflexible polymer can not be crumpled without breakage and its properties are essentially different from those of flexible polymer. A wide class of synthetic and","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"36 1","pages":"1287-1298"},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82237514","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 use the Landau-de Gennes theory of a nematic liquid crystal to investigate anew aspects of the properties of the interface between the isotropic and nematic liquid crystal phases of the same fluid. The equations of the static interface have been solved, both numerically and using asymptotic analysis, with an emphasis on the effect of inclusion of the order parameter biaxiality on the physical properties. We have compared the results of the exact solutions to the commonly used de Gennes ansatz, which assumes positive and uniform unixiality through the interface. Although the de Gennes ansatz in general gives good results, when bend and splay elastic constants dominate over the twist constants, it can lead to errors of up to 10% in the surface energy. The asymptotic analysis also shows that, by contrast with the de Gennes ansatz, the order parameter wings in the isotropic phase exhibit negative order parameter, with principal axis perpendicular to the surface. For moving interfaces, using an approximation which at this stage does not yet include hydrodynamic coupling, we have compared our results with the analogue of the de Gennes ansatz used by the present authors in an earlier paper. We find that including biaxiality leads to larger effects in the dynamic than in the static properties, and that whereas this is essentially a perturbation to the energy, the velocity of the moving interface can be significantly slowed down. The slowing down effects are strongly correlated with surface biaxiality, but both effects seem to be diminished when the isotropic phase is advancing.
{"title":"Statics and Kinetics at the Nematic-Isotropic Interface: Effects of Biaxiality","authors":"V. Popa-Nita, T. Sluckin, A. A. Wheeler","doi":"10.1051/JP2:1997183","DOIUrl":"https://doi.org/10.1051/JP2:1997183","url":null,"abstract":"We use the Landau-de Gennes theory of a nematic liquid crystal to investigate anew aspects of the properties of the interface between the isotropic and nematic liquid crystal phases of the same fluid. The equations of the static interface have been solved, both numerically and using asymptotic analysis, with an emphasis on the effect of inclusion of the order parameter biaxiality on the physical properties. We have compared the results of the exact solutions to the commonly used de Gennes ansatz, which assumes positive and uniform unixiality through the interface. Although the de Gennes ansatz in general gives good results, when bend and splay elastic constants dominate over the twist constants, it can lead to errors of up to 10% in the surface energy. The asymptotic analysis also shows that, by contrast with the de Gennes ansatz, the order parameter wings in the isotropic phase exhibit negative order parameter, with principal axis perpendicular to the surface. For moving interfaces, using an approximation which at this stage does not yet include hydrodynamic coupling, we have compared our results with the analogue of the de Gennes ansatz used by the present authors in an earlier paper. We find that including biaxiality leads to larger effects in the dynamic than in the static properties, and that whereas this is essentially a perturbation to the energy, the velocity of the moving interface can be significantly slowed down. The slowing down effects are strongly correlated with surface biaxiality, but both effects seem to be diminished when the isotropic phase is advancing.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"19 1","pages":"1225-1243"},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91528364","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}
J. Dembczyński, S. Bouazza, G. Szawioła, J. Ruczkowski
The fine structure of the low configurations of the atomic hafnium has been analysed by simultaneous parametrization of one and two body interactions for the model space (5d + 6s) 4 . Using the calculated eigenfunctions the magnetic-dipole A and electric-quadrupole B hyperfine constants were predicted to stimulate the experimental work concerning the energy level structure of 179 Hf.
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