Why is surface tension a force parallel to the interface
26 Sep 2011-American Journal of Physics (American Association of Physics Teachers)-Vol. 79, Iss: 10, pp 999-1008
TL;DR: In this paper, the authors address several conceptual questions that are often encountered when teaching capillarity and provide a perspective that reconciles the macroscopic viewpoints from thermodynamics and fluid mechanics and the microscopic perspective from statistical physics.
Abstract: A paperclip can float on water. Drops of mercury do not spread on a surface. These capillary phenomena are macroscopic manifestations of molecular interactions and can be explained in terms of surface tension. We address several conceptual questions that are often encountered when teaching capillarity and provide a perspective that reconciles the macroscopic viewpoints from thermodynamics and fluid mechanics and the microscopic perspective from statistical physics
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TL;DR: This work proposes an untethered jellyfish-inspired soft millirobot that could realize multiple functionalities in moderate Reynolds number by producing diverse controlled fluidic flows around its body using its magnetic composite elastomer lappets, which are actuated by an external oscillating magnetic field.
Abstract: The functionalities of the untethered miniature swimming robots significantly decrease as the robot size becomes smaller, due to limitations of feasible miniaturized on-board components. Here we propose an untethered jellyfish-inspired soft millirobot that could realize multiple functionalities in moderate Reynolds number by producing diverse controlled fluidic flows around its body using its magnetic composite elastomer lappets, which are actuated by an external oscillating magnetic field. We particularly investigate the interaction between the robot's soft body and incurred fluidic flows due to the robot's body motion, and utilize such physical interaction to achieve different predation-inspired object manipulation tasks. The proposed lappet kinematics can inspire other existing jellyfish-like robots to achieve similar functionalities at the same length and time scale. Moreover, the robotic platform could be used to study the impacts of the morphology and kinematics changing in ephyra jellyfish.
314 citations
TL;DR: A review of the published articles on contact angles and summarizes the views of the both sides can be found in this article, where the weak and strong sides of both three-phase contact line and contact area approaches are discussed in detail and some practical conclusions are drawn.
229 citations
Journal Article•
TL;DR: In this paper, the authors compute the shape of Lennard-Jones nanodrops using molecular dynamics and compare them to density functional theory in the approximation of the sharp kink interface, and show that the deviation from Young's law is very small and would correspond to a typical line tension length scale (defined as line tension divided by surface tension) similar to the molecular size and decreasing with Young's angle.
Abstract: The existence and origin of line tension has remained controversial in literature. To address this issue, we compute the shape of Lennard-Jones nanodrops using molecular dynamics and compare them to density functional theory in the approximation of the sharp kink interface. We show that the deviation from Young’s law is very small and would correspond to a typical line tension length scale (defined as line tension divided by surface tension) similar to the molecular size and decreasing with Young’s angle. We propose an alternative interpretation based on the geometry of the interface at the molecular scale
183 citations
TL;DR: This paper aims to provide a comprehensive review of omniphobic interfaces and illustrate their fundamental working principles, innovative design approaches and novel applications on membrane distillation to provide insights in designing stable solid-liquid-vapor interfaces and serve as a guidance for the development of robust anti-wetting membranes for industrial wastewater reclamation via membranes distillation.
179 citations
TL;DR: This review presents the state of the art in molecular simulations of interfacial systems and of the calculation of the surface tension from the underlying intermolecular potential and considers the challenging problems of reproducing the interfacial tension of salt solutions as a function of the salt molality.
Abstract: This review presents the state of the art in molecular simulations of interfacial systems and of the calculation of the surface tension from the underlying intermolecular potential. We provide a short account of different methodological factors (size-effects, truncation procedures, long-range corrections and potential models) that can affect the results of the simulations. Accurate calculations are presented for the calculation of the surface tension as a function of the temperature, pressure and composition by considering the planar gas-liquid interface of a range of molecular fluids. In particular, we consider the challenging problems of reproducing the interfacial tension of salt solutions as a function of the salt molality; the simulations of spherical interfaces including the calculation of the sign and size of the Tolman length for a spherical droplet; the use of coarse-grained models in the calculation of the interfacial tension of liquid-liquid surfaces and the mesoscopic simulations of oil-water-surfactant interfacial systems.
155 citations
References
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Book•
01 Jan 1985
TL;DR: The forces between atoms and molecules are discussed in detail in this article, including the van der Waals forces between surfaces, and the forces between particles and surfaces, as well as their interactions with other forces.
Abstract: The Forces between Atoms and Molecules. Principles and Concepts. Historical Perspective. Some Thermodynamic Aspects of Intermolecular Forces. Strong Intermolecular Forces: Covalent and Coulomb Interactions. Interactions Involving Polar Molecules. Interactions Involving the Polarization of Molecules. van der Waals Forces. Repulsive Forces, Total Intermolecular Pair Potentials, and Liquid Structure. Special Interactions. Hydrogen-Bonding, Hydrophobic, and Hydrophilic Interactions. The Forces between Particles and Surfaces. Some Unifying Concepts in Intermolecular and Interparticle Forces. Contrasts between Intermolecular, Interparticle, and Intersurface Forces. van der Waals Forces between Surfaces. Electrostatic Forces between Surfaces in Liquids. Solvation, Structural and Hydration Forces. Steric and Fluctuation Forces. Adhesion. Fluid-Like Structures and Self-Assembling Systems. Micelles, Bilayers, and Biological Membranes. Thermodynamic Principles of Self-Assembly. Aggregation of Amphiphilic Molecules into Micelles, Bilayers, Vesicles, and Biological Membranes. The Interactions between Lipid Bilayers and Biological Membranes. References. Index.
18,048 citations
Book•
01 Jan 1976
TL;DR: In this article, the authors present a mathematical model for time-dependent correlation functions and response functions in liquid solvers, based on statistical mechanics and molecular distribution functions, and show that these functions are related to time correlation functions in Ionic and Ionic liquids.
Abstract: Introduction. Statistical Mechanics and Molecular Distribution Functions. Computer "Experiments" on Liquids. Diagrammatic Expansions. Distribution Function Theories. Perturbation Theories. Time-dependent Correlation Functions and Response Functions. Hydrodynamics And Transport Coefficients. Microscopic Theories of Time-Correlation Functions. Ionic Liquids. Simple Liquid Metals. Molecular Liquids. Appendices. References. Index.
9,144 citations
TL;DR: In this paper, the authors present an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.
Abstract: The wetting of solids by liquids is connected to physical chemistry (wettability), to statistical physics (pinning of the contact line, wetting transitions, etc.), to long-range forces (van der Waals, double layers), and to fluid dynamics. The present review represents an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.
6,042 citations
TL;DR: In this article, it has been shown that for each combination of a solid and a fluid, there is an appropriate angle of contact between the surfaces of the fluid, exposed to the air, and to the solid.
Abstract: It has already been asserted, by Mr. Monge and others, that the phenomena of capillary tubes are referable to the cohesive attraction of the superficial particles only of the fluids employed, and that the surfaces must consequently be formed into curves of the nature of lintearias, which are supposed to be the results of a uniform tension of a surface, resisting the pressure of a fluid, either uniform, or varying according to a given law. Segner, who appears to have been the first that maintained a similar opinion, has shown in what manner the principle may be deduced from the doctrine of attraction, but his demonstration is complicated, and not perfectly satisfactory; and in applying the law to the forms of drops, he has neglected to consider the very material effects of the double curvature, which is evidently the cause of the want of a perfect coincidence of some of his experiments with his theory. Since the time of Segner, little has been done in investigating accurately and in detail the various consequences of the principle. It will perhaps be most agreeable to the experimental philosopher, although less consistent with the strict course of logical argument, to proceed in the first place to the comparison of this theory with the phenomena, and to inquire afterwards for its foundation in the ultimate properties of matter. But it is necessary to premise one observation, which appears to be new, and which is equally consistent with theory and with experiment; that is, that for each combination of a solid and a fluid, there is an appropriate angle of contact between the surfaces of the fluid, exposed to the air, and to the solid. This angle, for glass and water, and in all cases where a solid is perfectly wetted by a fluid, is evanescent: for glass and mercury, it is about 140°, in common temperatures, and when the mercury is moderately clean.
5,149 citations
Book•
01 Jan 1982
TL;DR: The theory of Van Der Waals statistical mechanics of the liquid-gas surface model fluids in the mean-field approximation computer simulation of the calculation of the density profile three-phase equilibrium interfaces near critical points as mentioned in this paper.
Abstract: Mechanical molecular models thermodynamics the theory of Van Der Waals statistical mechanics of the liquid-gas surface model fluids in the mean-field approximation computer simulation of the liquid-gas surface calculation of the density profile three-phase equilibrium interfaces near critical points. Appendices: thermodynamics Dirac's delta-function.
3,403 citations