关于表面张力和表面自由能的讨论

简要地回顾了表面物理化学中表面张力和表面吉布斯自由能(以下简称为表面自由能)两个基本概念的发展历史,讨论了表面张力和表面自由能形成的机制,以及键能与表面张力的关系,最后指出了尽管表面相可以在理论上抽象为几何面,但它是真实存在的独立相,而且由于表面自由能的原因它始终处于亚稳定状态.     

Sandwich教学法在药学专业物理化学教学中的应用（Ⅰ）——表面张力教学实例

物理化学教学内容繁杂且抽象、枯燥乏味,学生容易产生厌学情绪。采用传统教学法往往不能达到较好的教学效果。将Sandwich教学法引入药学专业物理化学的教学实践中,以表面张力的教学为实施例具体阐述了教学设计和实施过程。该教学方法以学生自我学习为主,教师引导为辅,在教学实施的各个环节充分调动学生学习的主动性和积极性,同时培养了学生表达和沟通能力、分析问题和解决问题的能力。     

Wilhelmy吊片法测定磷脂溶液的表面张力等温线

表面活性物质的表面张力等温线测定是大学物理化学实验的重要内容。随着磷脂类表面活性剂的广泛应用，有必要在大学化学中更新经典表面张力等温线测定的实验内容，并使学生掌握先进的测量方法。以二硬脂酰基磷脂酰胆碱(DSPC)和二棕榈酰基磷脂酰胆碱(DPPC)为研究对象，应用界面张力仪测定了两种溶液表面张力等温线，计算了其表面超量和分子横截面积，并设计了拓展性实验内容，对于培养学生分析问题和解决问题的能力具有积极的意义。     

Sandwich教学法在物理化学教学中的应用——以化学势表达式的推导为例

以化学势表达式的推导为例,探究了Sandwich教学法在物理化学教学中的应用。详细介绍了Sandwich教学法实施过程中教师如何提出问题以呈现教学目标,学生如何通过自主学习与全班交流来探究与解决问题,以及最后又如何通过总结与反馈回归教学目标。通过以学生为主体的Sandwich教学过程的实施,学生对化学势概念、热力学基本方程及状态函数法等重要的物理化学基本概念、公式及方法有了更深入的理解和掌握。Sandwich教学方法相较于传统教学模式更能激发学生学习的主动性和积极性,从而提高学生学习物理化学的兴趣与效果。     

关于一些热力学公式使用条件的讨论

物理化学中的热力学公式在不同条件下有不同的衍变形式,极易诱导学生产生错误理解。通过实例分析,对热力学能和焓变化计算公式、赫姆霍兹自由能和吉布斯自由能判据、热力学基本方程等的使用和理解中存在的一些问题予以讨论。     

表面张力与溶液浓度函数关系的拟合

在表面活性剂溶液物理化学性质的研究中,经常涉及到溶液表面张力γ与溶液中表面活性剂浓度 C 的对应函数关系问题。比如,在利用 Gibbs 吸附公式:     

关于Gibbs吸附等温式的推导

Gibbs吸附等温式■是表面化学的一个重要公式,主要用于溶液的表面吸附,也用于两个溶剂互不相溶的溶液之间。但它是用热力学原理推出的,故原则上能用于任何两个平衡相之间,是具有普遍意义的吸附公式。通过Γ_i和Γ_i~1可以定量地说明什么是正吸附和负吸附。Gibbs公式表示组分i的吸附量与表面张力σ随体相中i的浓度的变化     

关于一种开尔文方程推导方法的讨论

不同版次物理化学教材对开尔文方程推导的方法不同。本文通过对吉布斯界面热力学基本方程中球状液滴压强的分析,并依据对于弯曲液滴,附加压力本质上就是由弯曲液面表面张力引起的,得出某物理化学教材中,对小液滴的气液两相平衡过程,其吉布斯自由能的变化为零。对于恒温下,把处于外压为p0的平面液滴分割为处于外压为p_r的小液滴的过程,其吉布斯自由能的变化为2σM/ρr。     

关于等温循环方法推导开尔文公式的讨论

等温循环方法是物理化学教材中推导开尔文公式的一个经典方法。本文从热力学基本原理出发,明确指出其中小液滴可逆相变为气体的吉布斯自由能变化值应由吉布斯自由能判据求解,并对温度恒定、两相压强分别恒定时的判据进行了重新推导。同时,本文还提出了一种对推导开尔文公式的等温循环法的新理解方式,该方式在建立的"箱管模型"辅助下,意义明确,便于理解,更适宜教学使用。     

吉布斯自由能的多功能性质探讨

在物理化学常用的热力学函数中,吉布斯自由能是一个用途最为广泛、最具有明确意义的热力学函数,它除了在特定条件下可作为过程与方向的判据外,还具有狭义化学势、最大非膨胀功和狭义表面自由能等功能。本文就吉布斯自由能的多功能特性展开讨论,并通过两个实例说明实际体系中ΔG的计算方法及用途,以帮助学生在物理化学学习过程中深入理解吉布斯自由能。     

醋酸离子液体[C2mim][OAc]水溶液的摩尔表面Gibbs自由能

在288.15-318.15 K温度范围内测定了不同浓度离子液体1-乙基-3-甲基咪唑醋酸盐([C₂mim][OAc])水溶液的表面张力和密度;在改进李以圭等人的溶液表面张力模型基础上,提出摩尔表面Gibbs自由能新概念,建立了摩尔表面Gibbs自由能随溶液浓度变化的线性经验方程,利用这个经验方程估算了[C₂mim][OAc]水溶液的摩尔表面Gibbs自由能,并进一步预测了该溶液的表面张力,其预测值与相应的表面张力实验值高度相关并非常相似。由此可见,摩尔表面Gibbs自由能与等张比容极其类似,可能成为预测离子液体及其溶液性质的一种新的半经验方法。在指定溶液浓度下,根据溶液的摩尔表面Gibbs自由能随温度呈线性变化的规律,得到了新的Eötvös方程,与传统的Eötvös方程相比,新Eötvös方程的每一个参数都有明确的物理意义:斜率的负值是摩尔表面熵,截距是摩尔表面焓,在指定浓度的溶液中摩尔表面焓几乎不随温度变化。     

Numerical approaches to determine the interface tension of curved interfaces from free energy calculations

A recently proposed method to obtain the surface free energy σ(R) of spherical droplets and bubbles of fluids, using a thermodynamic analysis of two-phase coexistence in finite boxes at fixed total density, is reconsidered and extended. Building on a comprehensive review of the basic thermodynamic theory, it is shown that from this analysis one can extract both the equimolar radius R(e) as well as the radius R(s) of the surface of tension. Hence the free energy barrier that needs to be overcome in nucleation events where critical droplets and bubbles are formed can be reliably estimated for the range of radii that is of physical interest. It is found that the conventional theory of nucleation, where the interface tension of planar liquid-vapor interfaces is used to predict nucleation barriers, leads to a significant overestimation, and this failure is particularly large for bubbles. Furthermore, different routes to estimate the effective radius-dependent Tolman length δ(R(s)) from simulations in the canonical ensemble are discussed. Thus we obtain an instructive exemplification of the basic quantities and relations of the thermodynamic theory of metastable droplets/bubbles using simulations. However, the simulation results for δ(R(s)) employing a truncated Lennard-Jones system suffer to some extent from unexplained finite size effects, while no such finite size effects are found in corresponding density functional calculations. The numerical results are compatible with the expectation that δ(R(s) → ∞) is slightly negative and of the order of one tenth of a Lennard-Jones diameter, but much larger systems need to be simulated to allow more precise estimates of δ(R(s) → ∞).     

Viscosity,refractive index,and surface tension of multicomponent systems: Mathematical representation and estimation from data for binary systems

An equation previously developed for estimation of the excess thermodynamic properties of multicomponent systems from binary mixing data has been applied to other physical properties through extrathermodynamic properties such as the excess Gibbs free energy of activation for viscous flow, molar refractivity, and exess surface free energy. This equation provides reasonably accurate predictions for viscosity, refractive index and surface tension of ternary and quaternary systems, given the properties of the various binary combinations of the components. The equation also serves quite well as a point-of-departure for mathematical representation of experimental data, in that all of the data considered could be represented within experimental uncertainty with the aid of no more than one adjustable parameter for each multicomponent system.     

Effects of solid-liquid interface on the interfacial tension measured by micropipet technique

Measurement of interfacial tension (IFT) using the micropipet technique involves the solid-liquid interface. At equilibrium, oil-water interfacial tension is determined from the interface curvature and the critical pressure, according to the Young-Laplace equation. This paper aims to examine the possible contribution of the solid-liquid interface on IFT measurement. Three different experimental configurations are used to examine the sought effect. The three configurations are straight, concentric, and tapered pipets with diameters ranging from 2.5 to 30 microm. For all three configurations, the critical pressure is found to depend only on the pipet diameter. However, when the Young-Laplace equation is applied to determine the IFT, a significant error was noticed at small pipet diameters. The IFT error was described by an exponential function whose asymptote approached the independently determined IFT value with a sufficiently large pipet diameter. The IFT error is anticipated to arise from the layerlike effect of an "ultrastructured" liquid near the solid surface. The solid-induced error in oil-water IFT is noted to fade away at lowered IFT by the addition of surfactant.     

Observing capillarity in hydrophobic silica nanotubes

The development of template-synthesized silica nanotubes has created a unique opportunity for studying confined fluids by providing nanometer-scale containers in which the inner diameter (i.d.) and surface chemistry can be systematically and independently varied. An interesting question to be answered is the following: do solvents wet nanometer-scale tubes in the same way they wet ordinary capillaries? To answer this question, we have conducted studies to explore the wettability of the hydrophobic interiors of individual nanotubes. In these studies, single nanotubes with i.d.'s of either 30 or 170 nm were investigated over a range of water/methanol mixtures. These studies provide a direct route for comparing wetting phenomena in nanotubes with conventional macroscopic theories of capillarity. Our observations reveal four important aspects of capillary wetting in the 30-170 nm regime, a size range where the application of the Young-Laplace theory has not been experimentally investigated for hydrophobic pores. They are (i) a sharp transition between wetting and nonwetting conditions induced by addition of a cosolvent, (ii) invariance of this transition between nanotubes of 30 and 170 nm pore diameter, (iii) failure of the Young-Laplace equation to accurately predict the cosolvent's (methanol) mol fraction where the transition occurs, and (iv) reversibility of the observed wetting. The first two aspects conform to conventional capillarity (Young-Laplace), but the latter two do not. These measurements were complemented with ensemble experiments. The difference between theory and experiment is likely due to reliance on macroscopic values of contact angles or to liquid-phase instability within the hydrophobic pore.     

A Membrane Tension-Responsive Mechanosensitive DNA Nanomachine

Membrane curvature reflects physical forces operating on the lipid membrane, which plays important roles in cellular processes. Here, we design a mechanosensitive DNA (MSD) nanomachine that mimics natural mechanosensitive PIEZO channels to convert the membrane tension changes of lipid vesicles with different sizes into fluorescence signals in real time. The MSD nanomachine consists of an archetypical six-helix-bundle DNA nanopore, cholesterol-based membrane anchors, and a solvatochromic fluorophore, spiropyran (SP). We find that the DNA nanopore effectively amplifies subtle variations of the membrane tension, which effectively induces the isomerization of weakly emissive SP into highly emissive merocyanine isomers for visualizing membrane tension changes. By measuring the membrane tension via the fluorescence of MSD nanomachine, we establish the correlation between the membrane tension and the curvature that follows the Young-Laplace equation. This DNA nanotechnology-enabled strategy opens new routes to studying membrane mechanics in physiological and pathological settings.     

物理化学理论与实验教学内容更新与教学模式改革——物理化学教学研究会第五次会议纪要

物理化学教学研究会第五次会议以物理化学及物理化学实验"金课"建设的思路与举措为主题,围绕物理化学教学内容更新、物理化学课程思政建设和学科思维教育、物理化学实验创新设计三个方面展开研讨。相关讨论对今后物理化学课程和实验教学内容更新和教学模式改革具有一定的指导意义。     

The Calculation of Interfacial Tension and Electrostatic Free Energy of Spherical Ionic Micelles with High Surface Potentials

Based on extended Langmuir's method on the dressed micelles, approximate expressions for the calculation of interfacial tension and electrostatic free energy of spherical ionic micelles with high surface potentials have been presented. These expressions are derived from nonlinear Poisson‐Boltzmann equation. The present formulae for the calculation of interfacial tension and electrostatic free energy of spherical ionic micelles are in quite good agreement with Hayter's results.     

Surface tension and surface free energy of polymers

The curent state of problems connected with the definition and experimental determination of surface free energy and surface tension of polymers is discussed. An analysis of the application of some equations based on classical and modern thermodynamics of polymer solutions shows that present theories need an essential improvement to fit experimental data. The Zisman concept of critical surface tension and Fowkers' hypothesis of additivity in the contribution of polar and dispersion forces to surface tension are criticized and a new approach to the problem is proposed.