A. Sacco, E. Belorizky, M. Jeannin, W. Gorecki, P. Fries
On etudie la dynamique de plusieurs paires d'ions attractifs et repulsifs en solution aqueuse a des forces ioniques atteignant 1 mol l -1 . La mesure des taux de relaxation nucleaire longitudinale des protons des ions diamagnetiques fournit l'information experimentale. On a choisi les solutions ioniques de sorte que le principal mecanisme de relaxation de ces protons soit les fluctuations temporelles de leur interaction dipolaire magnetique avec les spins electroniques des ions paramagnetiques. Cette interaction depend fortement du potentiel des forces moyennes (PMF) ion-ion et des coefficients d'auto-diffusion ioniques. On calcule les correlations spatiales ion-ion et les PMF associes a l'aide d'une nouvelle approximation des equations integrales de la mecanique statistique des liquides. Ce formalisme traite tous les ions comme des particules discretes. Il est fonde sur les PMF d'infinie dilution des differentes paires d'ions. Il melange une theorie de Born-Oppenheimer pour la dilution infinie avec une approximation de type McMillan-Mayer pour tenir compte de la concentration ionique. Il va au-dela du modele d'ecrantage de Debye-Huckel ou une distribution continue de charge rend compte des effets des ions discrets environnants. Il est relie au concept des constantes dielectriques locales qui generalisent la constante dielectrique macroscopique usuelle et sont fonction des distances ion-ion. On a mesure les coefficients d'auto-diffusion des ions diamagnetiques par des techniques RMN de gradients pulses de champ magnetique (PMFG), appliquees aux protons resonnants. Dans les solutions paramagnetiques contenant plusieurs especes protonees, les precautions particulieres a prendre sont discutees en detail. Dans toutes les solutions considerees la theorie rend bien compte des taux de relaxation en fonction des charges des ions, de leurs concentrations et de la frequence de resonance des protons. On compare les resultats de relaxation predits par la nouvelle approximation des PMF ion-ion a ceux deduits du formalisme d'ecrantage coulombien simple de Debye-Huckel, qui s'applique encore assez bien jusqu'a des forces ioniques moderees.
研究了离子强度为1 mol l -1的水溶液中几种吸引离子和排斥离子对的动力学。测量抗磁性离子质子的纵向核弛豫率提供了实验信息。离子溶液的选择使这些质子的主要弛豫机制是它们与顺磁离子电子自旋的磁偶极相互作用的时间波动。这种相互作用很大程度上取决于平均力势(PMF)和离子自扩散系数。利用液体统计力学积分方程的新近似，计算了离子-离子空间相关性和相关的PMF。这种形式主义将所有离子视为离散粒子。它是基于PMF对不同离子的无限稀释。它将无限稀释的波恩-奥本海默理论与考虑离子浓度的麦克米伦-梅耶近似相结合。它超越了Debye-Huckel屏蔽模型，在该模型中，连续电荷分布考虑了周围离散离子的影响。它与局部介电常数的概念有关，局部介电常数推广了通常的宏观介电常数，是离子-离子距离的函数。利用梯度磁场脉冲(PMFG) nmr技术测量了抗磁性离子的自扩散系数，并应用于共振质子。在含有几种质子的顺磁溶液中，详细讨论了应采取的特别预防措施。在所有考虑的解中，该理论都很好地考虑了弛豫率作为离子电荷、离子浓度和质子共振频率的函数。将PMF离子-离子的新近似所预测的松弛结果与Debye-Huckel的简单库仑散射形式所预测的松弛结果进行了比较，后者在中等离子力下仍然相当有效。
{"title":"Effective Forces Between Diamagnetic and Paramagnetic Ions in D 2 O at Low and Moderate Ionic Strengths: An NMR Relaxation Study","authors":"A. Sacco, E. Belorizky, M. Jeannin, W. Gorecki, P. Fries","doi":"10.1051/JP2:1997109","DOIUrl":"https://doi.org/10.1051/JP2:1997109","url":null,"abstract":"On etudie la dynamique de plusieurs paires d'ions attractifs et repulsifs en solution aqueuse a des forces ioniques atteignant 1 mol l -1 . La mesure des taux de relaxation nucleaire longitudinale des protons des ions diamagnetiques fournit l'information experimentale. On a choisi les solutions ioniques de sorte que le principal mecanisme de relaxation de ces protons soit les fluctuations temporelles de leur interaction dipolaire magnetique avec les spins electroniques des ions paramagnetiques. Cette interaction depend fortement du potentiel des forces moyennes (PMF) ion-ion et des coefficients d'auto-diffusion ioniques. On calcule les correlations spatiales ion-ion et les PMF associes a l'aide d'une nouvelle approximation des equations integrales de la mecanique statistique des liquides. Ce formalisme traite tous les ions comme des particules discretes. Il est fonde sur les PMF d'infinie dilution des differentes paires d'ions. Il melange une theorie de Born-Oppenheimer pour la dilution infinie avec une approximation de type McMillan-Mayer pour tenir compte de la concentration ionique. Il va au-dela du modele d'ecrantage de Debye-Huckel ou une distribution continue de charge rend compte des effets des ions discrets environnants. Il est relie au concept des constantes dielectriques locales qui generalisent la constante dielectrique macroscopique usuelle et sont fonction des distances ion-ion. On a mesure les coefficients d'auto-diffusion des ions diamagnetiques par des techniques RMN de gradients pulses de champ magnetique (PMFG), appliquees aux protons resonnants. Dans les solutions paramagnetiques contenant plusieurs especes protonees, les precautions particulieres a prendre sont discutees en detail. Dans toutes les solutions considerees la theorie rend bien compte des taux de relaxation en fonction des charges des ions, de leurs concentrations et de la frequence de resonance des protons. On compare les resultats de relaxation predits par la nouvelle approximation des PMF ion-ion a ceux deduits du formalisme d'ecrantage coulombien simple de Debye-Huckel, qui s'applique encore assez bien jusqu'a des forces ioniques moderees.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"17 1","pages":"1299-1322"},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85873270","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 experimental results of Cladis et al. ill about the behaviour of smectic-C liquid crystal free-standing films subjected to a two-dimensional shear flow are reproduced via a Ginzburg-Landau model which is simulated numerically. The model takes into account effects that were first neglected in the theoretical analysis made by Cladis et al. particular emphasis is put on the influence of the elastic anisotropy and the nonrotational part of the flow.
{"title":"Flow Alignment in Smectic Liquid Crystal","authors":"C. Chevallard, T. Frisch, J. Gilli","doi":"10.1051/JP2:1997185","DOIUrl":"https://doi.org/10.1051/JP2:1997185","url":null,"abstract":"The experimental results of Cladis et al. ill about the behaviour of smectic-C liquid crystal free-standing films subjected to a two-dimensional shear flow are reproduced via a Ginzburg-Landau model which is simulated numerically. The model takes into account effects that were first neglected in the theoretical analysis made by Cladis et al. particular emphasis is put on the influence of the elastic anisotropy and the nonrotational part of the flow.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"29 1","pages":"1261-1272"},"PeriodicalIF":0.0,"publicationDate":"1997-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87075346","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 report the modification of the bending elastic modulus kc of lipid bilayers (here DMPC) by small amounts (c ≤5 mol %) of (i) small amphiphiles which exchange between the bilayer and the aqueous phase (e.g. the ion carrier valinomycin and the Ca++ carrier A23187) and (ii) amphiphiles solubilized in the membrane (cholanic acid). Large reductions of the bending stiffness may be induced by a few percent of the solutes, e.g. 1 mol % of valinomycin reduce kc by a factor of two. The effect is rationalised in terms of local thinning of the bilayer. The strong effect of solutes on kc contrasts with its weak dependence on the lipid structure since the C18:0/C18:1-lipid stearoyl-oleoyl-phosphatidyl-choline (SOPC) exhibits only a 15% higher value of kc than DMPC. The effect of temperature on the flicker behaviour was analysed in order to establish correlations between the effective tension and the excess area of the quasi-spherical vesicles. The temperature dependence of the bilayer excess area for a DMPC vesicle leads to the thermal expansion coefficient, β, for which a value of β= 10.4 ×10-3 K-1 is obtained. A much stronger tendency for budding on μm-scale (micro budding) during thermal area expansion of POPC and SOPC compared to DMPC was observed.
{"title":"Effects of Fully and Partially Solubilized Amphiphiles on Bilayer Bending Stiffness and Temperature Dependence of the Effective Tension of Giant Vesicles","authors":"W. Haeckl, U. Seifert, E. Sackmann","doi":"10.1051/JP2:1997177","DOIUrl":"https://doi.org/10.1051/JP2:1997177","url":null,"abstract":"We report the modification of the bending elastic modulus kc of lipid bilayers (here DMPC) by small amounts (c ≤5 mol %) of (i) small amphiphiles which exchange between the bilayer and the aqueous phase (e.g. the ion carrier valinomycin and the Ca++ carrier A23187) and (ii) amphiphiles solubilized in the membrane (cholanic acid). Large reductions of the bending stiffness may be induced by a few percent of the solutes, e.g. 1 mol % of valinomycin reduce kc by a factor of two. The effect is rationalised in terms of local thinning of the bilayer. The strong effect of solutes on kc contrasts with its weak dependence on the lipid structure since the C18:0/C18:1-lipid stearoyl-oleoyl-phosphatidyl-choline (SOPC) exhibits only a 15% higher value of kc than DMPC. The effect of temperature on the flicker behaviour was analysed in order to establish correlations between the effective tension and the excess area of the quasi-spherical vesicles. The temperature dependence of the bilayer excess area for a DMPC vesicle leads to the thermal expansion coefficient, β, for which a value of β= 10.4 ×10-3 K-1 is obtained. A much stronger tendency for budding on μm-scale (micro budding) during thermal area expansion of POPC and SOPC compared to DMPC was observed.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"64 1","pages":"1141-1157"},"PeriodicalIF":0.0,"publicationDate":"1997-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87636234","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}
Off-lattice Monte Carlo simulations of both the single chain structure factor h(q) and the inter-chain structure factor HD(q) of flexible polymers in solutions are presented over a wide range of both wavenumber q and concentration c from the dilute to the concentrated regime, for chain lengths up to N = 256. The single chain properties ${$gyration radius 〈Rg2〉, $h(q)}$ are in reasonable agreement with the expected theoretical behavior, showing a crossover from swollen chains ${langle R_{rm g}^2rangle propto N^{2nu} ,~ h(q) propto q^{-1/nu}}$ to Gaussian chains, and the data comply with a scaling description, with a correlation length ξ∝c-ν/(3ν-1). However, the inter-chain structure factor HD(q) disagrees with the corresponding predictions, we find a behaviour HD(q)∝q-3 only in an intermediate range but this is accidental: rather it is found that HD(q) smoothly bends over from its saturation value at small q to a behavior close to q-4 at q≈1/l, l being the length of effective bonds. This failure is traced back to the condition that the law HD(q)∝q-3 should only be observed for ξ-1≪q ≪l-1, a condition reached neither in the simulation nor in experiments. We also compare our results for HD(q) with the random phase approximation and find strong deviations.
{"title":"Inter-chain structure factors of flexible polymers in solutions : A Monte Carlo investigation","authors":"V. Yamakov, A. Milchev, K. Binder","doi":"10.1051/JP2:1997176","DOIUrl":"https://doi.org/10.1051/JP2:1997176","url":null,"abstract":"Off-lattice Monte Carlo simulations of both the single chain structure factor h(q) and the inter-chain structure factor HD(q) of flexible polymers in solutions are presented over a wide range of both wavenumber q and concentration c from the dilute to the concentrated regime, for chain lengths up to N = 256. The single chain properties ${$gyration radius 〈Rg2〉, $h(q)}$ are in reasonable agreement with the expected theoretical behavior, showing a crossover from swollen chains ${langle R_{rm g}^2rangle propto N^{2nu} ,~ h(q) propto q^{-1/nu}}$ to Gaussian chains, and the data comply with a scaling description, with a correlation length ξ∝c-ν/(3ν-1). However, the inter-chain structure factor HD(q) disagrees with the corresponding predictions, we find a behaviour HD(q)∝q-3 only in an intermediate range but this is accidental: rather it is found that HD(q) smoothly bends over from its saturation value at small q to a behavior close to q-4 at q≈1/l, l being the length of effective bonds. This failure is traced back to the condition that the law HD(q)∝q-3 should only be observed for ξ-1≪q ≪l-1, a condition reached neither in the simulation nor in experiments. We also compare our results for HD(q) with the random phase approximation and find strong deviations.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"68 1","pages":"1123-1139"},"PeriodicalIF":0.0,"publicationDate":"1997-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81356048","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}
Jeremy I. Martin, Zhen‐Gang Wang, D. Zuckerman, R. Bruinsma, P. Pincus
We study the interaction forces between two plates in a semi-dilute solution of polymers each having one weakly adsorbing end-group. We show that this system exhibits both repulsive and attractive interactions of comparable magnitude and well-separated length scales: when the plate separation is within a range of order the end-to-end distance of the end-adsorbed polymer, repulsion arises with a magnitude off ∈ Φ/Na 3 where ∈ is the end-adsorption energy, N is the degree of polymerization, a is the Kuhn length and Φ the volume fraction of the polymer. This repulsion is due to desorption of the end-adsorbed chains. At plate separations of order the correlation length of the solution, a depletion attraction sets in with a magnitude that scales with the bulk osmotic pressure.
{"title":"Forces between surfaces with weakly end-adsorbed polymers","authors":"Jeremy I. Martin, Zhen‐Gang Wang, D. Zuckerman, R. Bruinsma, P. Pincus","doi":"10.1051/JP2:1997175","DOIUrl":"https://doi.org/10.1051/JP2:1997175","url":null,"abstract":"We study the interaction forces between two plates in a semi-dilute solution of polymers each having one weakly adsorbing end-group. We show that this system exhibits both repulsive and attractive interactions of comparable magnitude and well-separated length scales: when the plate separation is within a range of order the end-to-end distance of the end-adsorbed polymer, repulsion arises with a magnitude off ∈ Φ/Na 3 where ∈ is the end-adsorption energy, N is the degree of polymerization, a is the Kuhn length and Φ the volume fraction of the polymer. This repulsion is due to desorption of the end-adsorbed chains. At plate separations of order the correlation length of the solution, a depletion attraction sets in with a magnitude that scales with the bulk osmotic pressure.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"82 1","pages":"1111-1121"},"PeriodicalIF":0.0,"publicationDate":"1997-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80144143","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}
H. Finkelmann, I. Kundler, E. Terentjev, M. Warner
We present an experimental and theoretical investigation of the critical formation of stripe domains in monodomain nematic elastomers. Domains with alternating sense of director rotation are formed when the material is stretched perpendicular to the initial director alignment. A wide range of differing samples are shown to have a singular onset to director rotation at a threshold deformation and a second singular point at the end of the stripe domain region. All the data collapses onto a master plot revealing a universal behaviour. We analyse theoretically the threshold properties of the stripe phase. The analysis of free energy yields a first order transition into a fully-coarsened texture without any intermediate state of sinusoidal modulation.
{"title":"Critical Stripe-Domain Instability of Nematic Elastomers","authors":"H. Finkelmann, I. Kundler, E. Terentjev, M. Warner","doi":"10.1051/JP2:1997171","DOIUrl":"https://doi.org/10.1051/JP2:1997171","url":null,"abstract":"We present an experimental and theoretical investigation of the critical formation of stripe domains in monodomain nematic elastomers. Domains with alternating sense of director rotation are formed when the material is stretched perpendicular to the initial director alignment. A wide range of differing samples are shown to have a singular onset to director rotation at a threshold deformation and a second singular point at the end of the stripe domain region. All the data collapses onto a master plot revealing a universal behaviour. We analyse theoretically the threshold properties of the stripe phase. The analysis of free energy yields a first order transition into a fully-coarsened texture without any intermediate state of sinusoidal modulation.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"308 1","pages":"1059-1069"},"PeriodicalIF":0.0,"publicationDate":"1997-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91551020","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 studied the "collective" diffusion of a concentrated solution of "living polymers" in brine, which in certain concentration conditions exhibit superdiffusive (L4vy flight) behaviour when tracer diffusion is considered. The concentration profile of the diffusion front is monitored over time using a Michelson interferometer. We show how a concentration dependent diffusion constant can be extracted from the fringe pattern. We find that the diffusion constant decreases linearly with increasing concentration, at variance with a power-law dependence, ex- pected when the interaction between chains is neglected.
{"title":"Collective Diffusion of “Living Polymers”","authors":"A. Ott, J. Bouchaud, W. Urbach, D. Langevin","doi":"10.1051/JP2:1997174","DOIUrl":"https://doi.org/10.1051/JP2:1997174","url":null,"abstract":"We have studied the \"collective\" diffusion of a concentrated solution of \"living polymers\" in brine, which in certain concentration conditions exhibit superdiffusive (L4vy flight) behaviour when tracer diffusion is considered. The concentration profile of the diffusion front is monitored over time using a Michelson interferometer. We show how a concentration dependent diffusion constant can be extracted from the fringe pattern. We find that the diffusion constant decreases linearly with increasing concentration, at variance with a power-law dependence, ex- pected when the interaction between chains is neglected.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"53 1","pages":"1099-1109"},"PeriodicalIF":0.0,"publicationDate":"1997-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77888393","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}
In this experimental study we give results concerning the shear thickening behavior exhibited by an aqueous cationic surfactant solution of CTAB in the presence of added NaTOS. We carefully investigate the rheological characteristics of this phenomenon corresponding to a shear induced state (SIS), the reproductibility and also the transient regimes. We show that with steady experiments there exist no hysteresis effect. Finally we give the evolution of the shear thickening characteristics against temperature.
{"title":"Shear Thickening of an Aqueous Micellar Solution of Cetyltrimethylammonium Bromide and Sodium Tosylate","authors":"V. Hartmann, R. Cressely","doi":"10.1051/JP2:1997173","DOIUrl":"https://doi.org/10.1051/JP2:1997173","url":null,"abstract":"In this experimental study we give results concerning the shear thickening behavior exhibited by an aqueous cationic surfactant solution of CTAB in the presence of added NaTOS. We carefully investigate the rheological characteristics of this phenomenon corresponding to a shear induced state (SIS), the reproductibility and also the transient regimes. We show that with steady experiments there exist no hysteresis effect. Finally we give the evolution of the shear thickening characteristics against temperature.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"7 1","pages":"1087-1098"},"PeriodicalIF":0.0,"publicationDate":"1997-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76278526","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 steady-state nonlinear rheology of wormlike micellar systems is thought to be subject to shear banding (the underlying shear stress vs. strain rate curve σ(γ) is nonmonotonic). Shear banding may result in a plateau (σ(γ) = σp) in the measured flow curve (at controlled mean strain rate γ). We present new rheological data for aqueous CPyCl/NaSal (100 mM /60 mM). Steady-state flow curves published previously for this system (Rehage H. and Hoffmann H., Mol. Phys. 74 (1991) 933) have since been interpreted as shear-banded flow with top-jumping, in which the steady-state shear rate γ1 in the low shear band is the largest possible (γ 1 = γ 1 max , σ p = σ max ). That would rule out the existence of a metastable branch with a stress larger than σp. We show that such a branch does, however, exist (for temperatures in the range 20 - 25 °C). Similar results are found for a 100 mM/75 mM system. The time scale for relaxation of a metastable state onto true steady state flow, τ ss , is far longer than the Maxwell time of the fluid; this is consistent with shear banding. We observe τ ss ∼ (γ - γ c ) -P in the metastable regime (γ > γ 1 ), with p an exponent that depends on composition and temperature. The critical shear rate γ c is in some cases less than γ 1 so that no actual divergence of τ ss occurs. In at least one case, though, there is evidence for a physical divergence (γ c > γ 1 ) accompanied by a small window of shear rates, γ 1 < γ < γ c , for which τ ss is effectively infinite. In some respects the observed behaviour resembles that reported previously (Berret J.-F., Roux D.C. and Porte G., J. Phys. II Prance 4 (1994) 1261) for equimolar CPyCl/NaSal in 0.5 M NaCl. Those results were interpreted in terms of nucleation and growth of a shear-induced nematic phase. However the same explanation is unlikely for the low weight fractions (Φ ≤ 5%) used in our study.
蠕虫状胶束体系的稳态非线性流变被认为服从于剪切带(潜在的剪切应力-应变率曲线σ(γ)是非单调的)。在控制的平均应变率γ下，剪切带可能导致流动曲线出现平台(σ(γ) = σp)。我们提出了新的CPyCl/NaSal (100 mM /60 mM)的流变学数据。先前发表的稳态流动曲线(Rehage H.和Hoffmann H.， Mol. Phys. 74(1991) 933)被解释为具有顶跃的剪切带流动，其中低剪切带的稳态剪切速率γ1可能最大(γ 1 = γ1 max， σ p = σ max)。这将排除应力大于σp的亚稳分支的存在。然而，我们表明，这样的分支确实存在(温度在20 - 25°C范围内)。在100毫米/75毫米系统中发现了类似的结果。亚稳态弛豫到真正稳态流动的时间尺度τ ss远长于流体的麦克斯韦时间;这与剪切带一致。我们观察到τ ss ~ (γ - γ c) - p处于亚稳区(γ > γ 1)， p是一个指数，取决于成分和温度。在某些情况下，临界剪切速率γ c小于γ 1，因此τ ss不会发生实际的发散。然而，至少在一种情况下，有证据表明物理散度(γ c > γ 1)伴随着一个小的剪切率窗口，γ 1 < γ < γ c，其中τ ss实际上是无限的。在某些方面，观察到的行为与以前报道的相似(贝雷特j - f。， Roux D.C.和Porte G.， J. Phys。II Prance 4(1994) 1261)在0.5 M NaCl中测定等摩尔CPyCl/NaSal。这些结果被解释为剪切诱导的向列相的成核和生长。然而，同样的解释不太可能用于我们研究中使用的低权重分数(Φ≤5%)。
{"title":"Slow Transients and Metastability in Wormlike Micelle Rheology","authors":"C. Grand, J. Arrault, M. Cates","doi":"10.1051/JP2:1997172","DOIUrl":"https://doi.org/10.1051/JP2:1997172","url":null,"abstract":"The steady-state nonlinear rheology of wormlike micellar systems is thought to be subject to shear banding (the underlying shear stress vs. strain rate curve σ(γ) is nonmonotonic). Shear banding may result in a plateau (σ(γ) = σp) in the measured flow curve (at controlled mean strain rate γ). We present new rheological data for aqueous CPyCl/NaSal (100 mM /60 mM). Steady-state flow curves published previously for this system (Rehage H. and Hoffmann H., Mol. Phys. 74 (1991) 933) have since been interpreted as shear-banded flow with top-jumping, in which the steady-state shear rate γ1 in the low shear band is the largest possible (γ 1 = γ 1 max , σ p = σ max ). That would rule out the existence of a metastable branch with a stress larger than σp. We show that such a branch does, however, exist (for temperatures in the range 20 - 25 °C). Similar results are found for a 100 mM/75 mM system. The time scale for relaxation of a metastable state onto true steady state flow, τ ss , is far longer than the Maxwell time of the fluid; this is consistent with shear banding. We observe τ ss ∼ (γ - γ c ) -P in the metastable regime (γ > γ 1 ), with p an exponent that depends on composition and temperature. The critical shear rate γ c is in some cases less than γ 1 so that no actual divergence of τ ss occurs. In at least one case, though, there is evidence for a physical divergence (γ c > γ 1 ) accompanied by a small window of shear rates, γ 1 < γ < γ c , for which τ ss is effectively infinite. In some respects the observed behaviour resembles that reported previously (Berret J.-F., Roux D.C. and Porte G., J. Phys. II Prance 4 (1994) 1261) for equimolar CPyCl/NaSal in 0.5 M NaCl. Those results were interpreted in terms of nucleation and growth of a shear-induced nematic phase. However the same explanation is unlikely for the low weight fractions (Φ ≤ 5%) used in our study.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"13 11","pages":"1071-1086"},"PeriodicalIF":0.0,"publicationDate":"1997-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91447083","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}
This paper discusses the elastic behavior of a single polyelectrolyte chain. A simple scaling analysis as in self avoiding walk chains are not possible, because three interplaying relevant length scales are involved, i.e., the Debye screening length and the Pincus blob size. Therefore a self-consistent computation of an effective variational propagator is employed. It is shown that the elastic force as a function f of the distance R behaves as f R for small f. For larger forces we find a new regime, characterized by deformations larger than a computed electrostatic blob size. These results are supported by simulations and intuitive physical arguments.
{"title":"On the Elastic Behavior of a Single Polyelectrolyte Chain","authors":"P. Haronska, J. Wilder, Thomas A. Vilgis","doi":"10.1051/jp2:1997186","DOIUrl":"https://doi.org/10.1051/jp2:1997186","url":null,"abstract":"This paper discusses the elastic behavior of a single polyelectrolyte chain. A simple scaling analysis as in self avoiding walk chains are not possible, because three interplaying relevant length scales are involved, i.e., the Debye screening length and the Pincus blob size. Therefore a self-consistent computation of an effective variational propagator is employed. It is shown that the elastic force as a function f of the distance R behaves as f R for small f. For larger forces we find a new regime, characterized by deformations larger than a computed electrostatic blob size. These results are supported by simulations and intuitive physical arguments.","PeriodicalId":14774,"journal":{"name":"Journal De Physique Ii","volume":"82 1","pages":"1273-1285"},"PeriodicalIF":0.0,"publicationDate":"1997-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79333574","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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