Statistical Approach to the Description of Homogeneous Nucleation in the Vapor-Gas Medium: Effects of the Heat of Phase Transition

The effect of the heat release of phase transition is included in the formalism of the statistical approach in order to allow for the depletion of a substance comprising the metastable phase in the kinetics of the homogeneous nucleation of supersaturated vapor. The diffusion regime of the exchange of molecules between the vapor and the growing droplets is considered on the assumption of instantaneous creation of the initial vapor supersaturation. The time-dependent boundary condition on the surface of a sphere with a fixed radius and a center coinciding with the center of a growing droplet is used in the problem of heat conductivity that allowed us to provide the heat balance of phase transition. The main characteristics of the nucleation stage are calculated for the representative vapor-gas systems. It is shown that the allowance for the effects of the heat release of phase transition resulted in a rather notable change in the kinetics of nucleation even at a sufficiently high concentration of the passive gas.     

Diffusion of Vapor in the Presence of a Growing Droplet

As is shown, the solution to the diffusion equation for the concentration of vapor in the presence of a droplet growing in it, derived for the usual initial condition and equilibrium boundary conditions at the droplet surface, fails to ensure an equality between the numbers of molecules that have left the vapor due to diffusion by the current moment and those that have been included in the growing droplet. The difference between the total numbers of vapor molecules at the initial moment (when the vapor had a given uniform concentration) and at the current moment (when the size of the growing droplet is much larger than its initial size) differs from the total number of molecules in the droplet by a factor of 3/2. By substituting the usual boundary condition at the droplet surface by a time-dependent boundary condition at the surface of a constant-radius sphere with the center in the center of the growing droplet, a solution to the diffusion problem for the vapor concentration is derived. This solution describes the evolution of the vapor concentration field, which agrees with the rate of the vapor absorption by the growing droplet and with the law of the conservation of matter.     

Separation Capacity of an Extraction System with a Phase Transition of Mixture Components

Russian Journal of Physical Chemistry A - The relationship between the separation capacity and a change in the Gibbs energy of an extraction system with a phase transition of one mixture component...     

Ultrasound Absorption Anisotropy in the Vicinity of Smectic A-Nematic Transition

Abstract

The results of a low frequency ultrasonic study of 4-n-butyloxybenzylidene-4'-n-butylaniline (BBBA) in the vicinity of the smectic A-nematic transition are presented. The frequency and temperature dependence of the parameters describing the anisotropic ultrasound absorption are determined experimentally and compared with the predictions of fluctuation and relaxation theories of the smectic A-nematic transition. It is shown that no single theory could explain all of the experimental data.     

Ultrasound Absorption Anisotropy in the Vicinity of Smectic A-Nematic Transition

The results of a low frequency ultrasonic study of 4-n-butyloxybenzylidene-4'-n-butylaniline (BBBA) in the vicinity of the smectic A-nematic transition are presented. The frequency and temperature dependence of the parameters describing the anisotropic ultrasound absorption are determined experimentally and compared with the predictions of fluctuation and relaxation theories of the smectic A-nematic transition. It is shown that no single theory could explain all of the experimental data.     

Lamellar/Disorder Phase Transition in a Mixture of Water/2,6-Dimethylpyridine/Antagonistic Salt

The effects of adding an antagonistic salt, sodium tetraphenylborate ( \(\hbox {NaBPh}_4\) ), to a binary mixture of deuterated water and 2,6-dimethylpyridine were investigated by visual inspection, optical microscopy, and small-angle neutron scattering. With increasing salt concentration, the two-phase region shrinks. When the concentration of \(\hbox {NaBPh}_4\) is \(85\hbox { mmol}{\cdot} \hbox {L}^{-1}\) , a temperature-induced lamellar/disorder phase transition is observed at 338 K. These trends are similar to those observed for a mixture of water/3-methylpyridine/ \(\hbox {NaBPh}_4\) (Sadakane et al., Phys. Rev. Lett. 103, 167803 (2009)).     

The Full Pressure–Temperature Phase Envelope of a Mixture in 1000 Microfluidic Chambers

Knowing the thermodynamic state of complex mixtures—liquid, gas, supercritical or two‐phase—is essential to industrial chemical processes. Traditionally, phase diagrams are compiled piecemeal from individual measurements in a pressure–volume–temperature cell performed in series, where each point is subject to a long fluid equilibrium time. Herein, 1000 microfluidic chambers, each isolated by a liquid piston and set to a different pressure and temperature combination, provide the complete pressure–temperature phase diagram of a hydrocarbon mixture at once, including the thermodynamic phase envelope. Measurements closely match modeled values, with a standard deviation of 0.13 MPa between measurement and model for the dew and bubble point lines, and a difference of 0.04 MPa and 0.25 °C between measurement and model for the critical point.     

三乙酸甘油酯玻璃化转变的焓弛豫与介电弛豫研究

脆性较高的玻璃形成分子液体通常在焓弛豫和介电弛豫动力学上表现出明显的差异性, 为了深入理解这一问题, 本文针对具有较高液体脆性的三乙酸甘油酯对比研究了焓弛豫与介电弛豫行为. 利用这两个技术分别研究了结构弛豫动力学过程的非Arrhenius 与非指数特征, 液体脆性因子与非指数性因子的对比显示很好的一致性. 分析表明分子的柔性有可能对这两种弛豫过程中分子运动的相关性产生明显的影响. 讨论了玻璃形成液体的分子结构与动力学参数之间的关联.     

可控相转变温度热敏高分子的制备及其在免疫分析中的应用

合成了一种新型的快速响应热敏高分子聚N－异丙基丙烯酰胺－丙烯酰胺[P(NIP-co-AA)]，通过改变丙烯酰胺的含量可以改变高分子的临界溶解温度（LCST），使之用于不同用途。其中，将相转变温度（Ttr)在37℃的热敏高分子用于免疫分析的载体，建立了夹心型荧光免疫分析兔IgG的新方法。与聚N－异丙基丙烯酰胺（PNIP）作载体相比，两灵敏度相当，但由于相转变温度的提高，使得免疫反应的温度更接近于生物体的生理环境，并使免疫反应速率得到提高。该方法线性范围为0-1000μg/L；检出限为10μg/L。用于兔血清中兔IgG的测量，结果令人满意。     

Pressure and Temperature Dependence of the Ferroelectric-Paraelectric Phase Transition in PbTiO3

Synchrotron X-ray powder diffraction patterns were collected at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) on powder samples of PbTiO₃ (tetragonal, Z=1 P4mma=3.9036(1) Å and c=4.1440(2) Å at room conditions) applying external pressure using a diamond anvil cell. Data were collected at four different temperatures (room temperature, 462, 538 and 623 K) up to the phase transition to the cubic phase (Z=1, Pm3ma=3.8647(4) Å at RT and 11.6 GPa). Analyzing the behavior of the cell parameters obtained by the Rietveld refinement, we were able to extract the dependence of the critical temperature on external pressure. The bulk moduli of the lead titanate were calculated for the first time. The progressive decrease of the distortion of the Pb and Ti coordination polyhedra with pressure allows to propose a structural explanation of the first-/second-order cross-over in the ferroelectric-paralectric phase transition on applying pressure.     

化学修饰1，4，7，10-四氮杂环十二烷提高铼酸化合物的相变温度

通过碘甲烷对1,4,7,10-四氮杂环十二烷（cyclen）进行化学修饰得到甲基取代的N-甲基-1,4,7,10-四氮杂环十二烷（Me-cyclen）。将cyclen和Me-cyclen与HReO₄以1∶2的比例进行反应,分别获得化合物（cyclen）（ReO₄）₂（1）和（Me-cyclen）（ReO₄）₂（2）。差示扫描量热法和介电研究发现化合物1和2具有可逆的相变,相变温度为324 K （1）和384 K （2）。以上研究表明：通过对环状有机胺进行化学改性,在降低分子对称性同时可以显著提高该有机-无机杂化材料的相变温度。     

A Study on the Adsorption Isotherms in the Vicinity of the Critical Temperature

Adsorption data of nitrogen and methane on micro-porous activated carbon and on meso-porous silica gel were measured near the critical temperature. It was found that the values of the compressibility factor (z) exerted a significant effect on the behavior of isotherms. Selection of reliable z-values is very important for the analysis of experimental results obtained near the critical temperature. The isotherms on activated carbon always show type-I features at sub- and supercritical temperatures, but those on silica gel remarkably show a change from type-II at sub-critical temperatures to type-I at supercritical temperatures. The critical temperature appears to be shifted up in some case.     

Application of a Low Transition Temperature Mixture for the Dispersive Liquid–Liquid Microextraction of Illicit Drugs from Urine Samples

The use of psychoactive substances is a serious problem in today’s society and reliable methods of analysis are necessary to confirm their occurrence in biological matrices. In this work, a green sample preparation technique prior to HPLC-MS analysis was successfully applied to the extraction of 14 illicit drugs from urine samples. The isolation procedure was a dispersive liquid–liquid microextraction based on the use of a low transition temperature mixture (LTTM), composed of choline chloride and sesamol in a molar ratio 1:3 as the extracting solvent. This mixture was classified as LTTM after a thorough investigation carried out by FTIR and DSC, which recorded a glass transition temperature at −71 °C. The extraction procedure was optimized and validated according to the main Food and Drug Administration (FDA) guidelines for bioanalytical methods, obtaining good figures of merit for all parameters: the estimated lower limit of quantitation (LLOQ) values were between 0.01 µg L⁻¹ (bk-MMBDB) and 0.37 µg L⁻¹ (PMA); recoveries, evaluated at very low spike levels (in the ng-µg L⁻¹ range), spanned from 55% (MBDB) to 100% (bk-MMBDB and MDPV); finally, both within-run and between-run precisions were lower than 20% (LLOQ) and 15% (10xLLOQ).     

差热分析求可逆相变焓的模拟研究

就样品的比热在相变前后均是温度函数的一般情况 ,通过动态地模拟DTA测量样品所经历的整个相变过程 ,验证了DTA中该相变潜热公式及相应的面积方法的正确性。证明对于可逆相变 ,采用文章所建议的面积法 ,把升降温过程中测得的相变潜热取一算术平均值 ,可最大限度地减少由于样品内温度梯度及样品比热是温度函数所带来的测量误差     

用Diamond TG/DTA热重/差热综合热分析仪在外加磁场下研究磁性材料相转变

介绍综合热分析仪Diamond TG/DTA在磁性材料研究中的应用.提出在外加磁场作用下,得到样品的热重曲线(TG),由TG曲线分析样品磁性相变及样品居里温度变化的原因,看到稀土铁基金属间化合物样品替代的Co元素的站位和元素之间相互作用对居里温度有很大影响.作为一种测量居里温度的方法,拓展Diamond TG/DTA热分析仪应用研究领域.     

New Approach to Determine the Phase Transition Temperature,Cloud Point,of Thermoresponsive Polymers

In this study, a novel method to determine the cloud point temperature variation in aqueous solutions of thermoresponsive homo- and copolymers was developed. Poly(N-vinylcaprolactam) (PVCL) and triblock copolymers of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-vinylcaprolactam)-b-(t-butyl acrylate-co-acrylic acid) (P[(tBA-co-AA)-b-PVCL-b-P(tBA-co-AA)] were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and used as models. The incorporation of AA units (hydrophilic segments) into the polymeric chain of PVCL influenced the phase transition, increasing the cloud point temperature of the final copolymer. The cloud point temperatures of the PVCL and the triblock copolymer P(tBA-co-AA)-b-PVCL-b-P(tBA-co-AA) were determined by measuring the transmittance of aqueous solutions of the polymers in a Turbiscan Lab instrument in the range of 29 to 40 C. This is the first study in which Turbiscan Lab is used to determine the cloud point temperature.     

D-和L-丙氨酸的低温磁相变——磁场变化下的比热和直流磁化率(英文)

为了解D-和L-丙氨酸单晶晶格在极低温下是否存在磁手性相变,在2-20 K下改变磁场强度(0,1,3,5T)测定其比热.实验结果表明比热和温度之间的函数关系很好地符合C(T)=aT3+b/T2方程,其中aT3项为晶格声子的贡献,可由公式CV=(12/5)π4R(T/ΘD)3来描述(ΘD为德拜温度),b/T2项为磁场对比热的贡献.实验发现,在2-20 K范围内D-和L-丙氨酸单晶在不同磁场强度下均存在Boson峰(在Cp/T3-T曲线中表现为一个最大值).磁的贡献导致D-和L-丙氨酸单晶的四条Cp/T3-T曲线在2-12 K时不重合,且在12-20 K时消失,此即Schottky反常.零磁场下,D-和L-丙氨酸的Boson峰分别为9.44和10.86 K;德拜温度分别为151.5和152.7 K.结合磁场强度1 T下的直流磁化率测定,发现在温度低于5 K时,D-和L-丙氨酸单晶有相反的磁化率行为,反映了核自旋和电子自旋弱相互作用的手性表现.     

HCN→HNC异构化反应过渡态附近的拓扑特性

电荷密度拓扑分析方法(topological analysis of charge distribution)已经被广泛应用于研究化合物的各种静态性质及反应特性.对IRC反应途径上过渡态附近构型的拓扑性质研究报导较少.本工作是用电荷密度分布的拓扑分析方法对HCN→HNC异构化反应IRC过渡态附近的性质进行了研究.对电荷密度分布拓扑分析和IRC途径确定选用相同的基组,得到了一些新的结论。