利用调制差分量热法和同步辐射 X 射线衍射测量法对二元嘧啶液晶混合物进行热分析和结构分析。

IF 2.3 4区 物理与天体物理 Q3 PHYSICS, CONDENSED MATTER
Smriti Mitra, Akhileshwar Prasad, Malay Kumar Das, Banani Adhikari Das, Anuj Upadhyay, Archana Sagdeo, A Yogi
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引用次数: 0

摘要

我们展示了 5-烷氧基-2-(4-壬氧基苯基)嘧啶(PhP)液晶化合物第二和第七同族系列二元混合物比热容随温度变化的系统实验数据集。这些二元混合物在 xPhP1 = 0 至 0.45 的浓度范围内呈现出向列、共晶-A 和共晶-C 相。我们使用同步辐射 X 射线衍射法对液晶相进行了结构表征。我们确定了向列相的表观分子长度、共晶层间距、分子长轴之间的平均距离、相关长度以及取向阶参数( 和 )与温度的函数关系。根据层间距数据推断出 SmC 相的倾斜角。为了研究向列相到共晶 A(NA)相和共晶 A 相到共晶 C(AC)相转变附近的临界行为,我们评估了临界指数:α 来自比热容,β 来自与温度相关的倾斜角拟合,ν‖、ν⊥ 来自与温度相关的纵向(ξ‖)和横向(ξ⊥)相关长度。调制差示扫描量热法(MDSC)测量结果表明,不存在相移、潜热和虚比热容,这表明所有二元混合物的交流转变都是二阶的。热容量的测量结果表明,AC 和 NA 转变均表现出非均相行为,其有效指数介于三临界值和 3D-XY 值之间,并随着 Sm-A 和 N 相宽度的减小而遵循几乎相同的曲线。约瑟夫森超尺度关系在不同混合物的 NA 和 AC 转变中都得到了验证。此外,知道了热容量临界指数α和阶次参数临界指数β,就可以根据拉什布鲁克等式α+2β+γ=2估算出交流跃迁的易感性临界指数γ,γ值在 1.015 至 1.313 之间,这表明系统具有交叉特性,显然验证了拉什布鲁克等式。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Thermal and structural analysis of binary mixtures of pyrimidine liquid crystals using Modulated Differential Calorimetry and Synchrotron X-ray Diffraction measurements.

We present a systematic experimental dataset on the temperature dependence of specific heat capacity in a binary mixture of the second and seventh homologous series of 5-alkyloxy-2-(4-nonyloxy-phenyl) pyrimidine(PhP) liquid crystal compound. These binary mixtures exhibit nematic, smectic-A, and smectic-C phases within a concentration range of xPhP1 = 0 to 0.45. The liquid crystalline phases are structurally characterized using synchrotron X-ray diffraction. We determine the apparent molecular length in the nematic phase, smectic layer spacing, average distance between the long axes of molecules, correlation length, and orientational order parameters ( and ) as functions of temperature. The tilt angle in the SmC phase is inferred from the layer spacing data. To examine the critical behavior near the nematic to smectic A(NA) and smectic A to the smectic C (AC) phase transitions, we evaluate the critical exponents: α from specific heat capacity, β from the fitting of the temperature-dependent tilt angle, and ν, νfrom the temperature-dependent longitudinal (ξ) and transverse (ξ) correlation lengths. Modulated Differential Scanning Calorimetry (MDSC) measurements indicate the absence of phase shift, latent heat and imaginary specific heat capacity, suggesting that the AC transitions are second-order for all binary mixtures. The results obtained from heat capacity reveal that both the AC and NA transitions exhibit non-universal behaviours with effective exponents lying between the tricritical and 3D-XY values and follow nearly identical curve with decreasing width of the Sm-A and N phases. The Josephson hyperscaling relation is verified for both the NA and AC transitions in different mixtures. Moreover, knowing the heat capacity critical exponent α and the order parameter critical exponent β, the susceptibility critical exponent γ for the AC transition can be estimated from Rushbrooke equality α+2β+γ=2, with γ values ranging from 1.015 to 1.313, indicating the system's crossover character and apparently validating the Rushbrooke equality.

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来源期刊
Journal of Physics: Condensed Matter
Journal of Physics: Condensed Matter 物理-物理:凝聚态物理
CiteScore
5.30
自引率
7.40%
发文量
1288
审稿时长
2.1 months
期刊介绍: Journal of Physics: Condensed Matter covers the whole of condensed matter physics including soft condensed matter and nanostructures. Papers may report experimental, theoretical and simulation studies. Note that papers must contain fundamental condensed matter science: papers reporting methods of materials preparation or properties of materials without novel condensed matter content will not be accepted.
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