Madhavan Unni P K
Department of Physics, Indian Institute of Science, Bangalore 560 012, India.
J Chem Phys. 2006 Feb 7;124(5):054505. doi: 10.1063/1.2167640.
The system 3-methylpyridine(3MP) + water(H2O)+NaBr has been the subject of an intense scientific debate since the work of Jacob et al. [Phys. Rev. E. 58, 2188 (1988)] and Anisimov et al. [Phys. Rev. Lett. 85, 2336 (2000)]. The crossover critical behavior of this system seemed to show remarkable sensitivity to the weight fraction (X) of the ionic impurity NaBr. In the range X< or =0.10 the system displayed Ising behavior and a pronounced crossover to mean-field behavior in the range 0.10< or =X< or =0.16. A complete mean-field behavior was observed at X=0.17, a result that was later attributed to the existence of long-living nonequilibrium states in this system [Kostko et al., Phys. Rev. E. 70, 026118 (2004)]. In this paper, we report the near-critical behavior of osmotic susceptibility in the isotopically related ternary system, 3MP+heavy water(D2O)+NaBr. Detailed light-scattering experiments performed at exactly the same NaBr concentrations as investigated by Jacob et al. reveal that the system 3MP + D2O + NaBr shows a simple Ising-type critical behavior with gamma approximately 1.24 and nu approximately 0.63 over the entire NaBr concentration range 0< or =X< or =0.1900. The crossover behavior is predominantly nonmonotonic and is completed well outside the critical domain. An analysis in terms of the effective susceptibility exponent (gammaeff) reveals that the crossover behavior is nonmonotonic for 0< or =X< or =0.1793 and tends to become monotonic for X>0.1793. The correlation length amplitude xio, has a value of approximately 2 A for 0.0250< or =X< or =0.1900, whereas for X=0, xio approximately 3.179 A. Since isotopic H-->D substitution is not expected to change the critical behavior of the system, our results support the recent results obtained by Kostko et al. [Phys. Rev. E. 70, 026118 (2004)] that 3MP + H2O + NaBr exhibits universal Ising-type critical behavior typical for other aqueous solutions.
自雅各布等人[《物理评论E》58, 2188 (1988)]和阿尼西莫夫等人[《物理评论快报》85, 2336 (2000)]开展研究工作以来，3 - 甲基吡啶(3MP)+水(H₂O)+溴化钠(NaBr)体系一直是激烈科学争论的主题。该体系的交叉临界行为似乎对离子杂质溴化钠的重量分数(X)表现出显著的敏感性。在X≤0.10的范围内，该体系呈现伊辛行为，而在0.10≤X≤0.16的范围内则明显转变为平均场行为。在X = 0.17时观察到完全的平均场行为，该结果后来被归因于该体系中存在长寿命非平衡态[科斯泰科等人，《物理评论E》70, 026118 (2004)]。在本文中，我们报告了同位素相关的三元体系3MP +重水(D₂O)+ NaBr中渗透磁化率的近临界行为。在与雅各布等人所研究的完全相同的溴化钠浓度下进行的详细光散射实验表明，在整个溴化钠浓度范围0≤X≤0.1900内，3MP + D₂O + NaBr体系呈现简单的伊辛型临界行为，其中γ约为1.24，ν约为0.63。交叉行为主要是非单调的，并且在临界区域之外就已完成。根据有效磁化率指数(γeff)进行的分析表明，对于0≤X≤0.1793，交叉行为是非单调的，而对于X > 0.1793则趋于单调。对于0.0250≤X≤0.1900，关联长度振幅ξ₀的值约为2 Å，而对于X = 0，ξ₀约为3.179 Å。由于预计同位素H→D替换不会改变该体系的临界行为，我们的结果支持了科斯泰科等人[《物理评论E》70, 026118 (2004)]最近获得的结果，即3MP + H₂O + NaBr呈现出其他水溶液典型的普适伊辛型临界行为。
