Van der Waals forces in oil–water systems from the study of thin lipid films - I. Measurement of the contact angle and the estimation of the van der Waals free energy of thinning of a film

1975 ◽  
Vol 347 (1649) ◽  
pp. 141-159 ◽  
Keyword(s):  
Free Energy ◽  
Van Der Waals ◽  
Monochromatic Light ◽  
Van Der Waals Forces ◽  
Contact Angles ◽  
Steric Interaction ◽  
Isotropic Layer ◽  
Free Energies ◽  
Lipid Film ◽  
Lipid Films

Free energies of formation of ‘black’ lipid films have been determined from measurements of their contact angles. The contact angles were calculated from the interference fringes formed in monochromatic light reflected from either the Plateau–Gibbs border or from lenses of bulk lipid solution trapped in the films. It is concluded that the electrostatic repulsion between the two surfaces of a film is negligibly small and that the ‘ steric’ interaction between the adsorbed monolayers of lipid molecules is of such short range that the free energy change during film formation originates almost entirely from work done by the van der Waals forces. The free energies determined for a range of different films all agree to within a factor of three with the free energy calculated from Lifshitz theory for water phases interacting across an isotropic layer of liquid hydrocarbon. Nevertheless, a systematic trend in the experimental data suggests that this picture of the lipid film is too simple and that either the polar groups of the lipid or the structure of the hydrocarbon region (or both) of the film have a significant influence on the results.

Contact Angles for Thin Lipid Films and the Determination of London-van der Waals Forces

Nature ◽  
1968 ◽  
Vol 217 (5130) ◽  
pp. 739-740 ◽  
Author(s):  
D. A. HAYDON ◽  
J. L. TAYLOR
Keyword(s):  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Contact Angles ◽  
Lipid Films

On the free energy of nematic wetting layers

1988 ◽  
Vol 66 (4) ◽  
pp. 553-556 ◽  
Author(s):  
Donald E. Sullivan ◽  
Reinhard Lipowsky
Keyword(s):  
Free Energy ◽  
Layer Thickness ◽  
Order Parameter ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Wetting Layer ◽  
Nematic Director ◽  
The Mean ◽  
Wetting Layers

The contributions to the free energy of a nematic wetting layer as a function of its thickness l are analyzed. The longest-range contribution is due to distortion of the nematic director across the film, resulting from different preferred molecular orientations at the two interfaces bounding the film. Van der Waals forces as well as the decaying tails of the interfacial order-parameter profiles yield contributions to the free energy of successively shorter range. These effects lead to crossovers between different scaling régimes for variation of the mean wetting-layer thickness with temperature. Experimental implications of the results are described.

scholarly journals Drops on soft solids: free energy and double transition of contact angles

2014 ◽  
Vol 747 ◽  
Author(s):  
L. A. Lubbers ◽  
J. H. Weijs ◽  
L. Botto ◽  
S. Das ◽  
B. Andreotti ◽  
...  
Keyword(s):  
Free Energy ◽  
Equilibrium Shape ◽  
Molecular Size ◽  
Contact Angles ◽  
Free Energies ◽  
Elastic Deformations ◽  
Liquid Drops ◽  
Soft Solids ◽  
Double Transition ◽  
Elastic Substrates

AbstractThe equilibrium shape of liquid drops on elastic substrates is determined by minimizing elastic and capillary free energies, focusing on thick incompressible substrates. The problem is governed by three length scales: the size of the drop $R$, the molecular size $a$ and the ratio of surface tension to elastic modulus $\gamma /E$. We show that the contact angles undergo two transitions upon changing the substrate from rigid to soft. The microscopic wetting angles deviate from Young’s law when $\gamma /(Ea)\gg 1$, while the apparent macroscopic angle only changes in the very soft limit $\gamma /(ER)\gg 1$. The elastic deformations are worked out for the simplifying case where the solid surface energy is assumed to be constant. The total free energy turns out to be lower on softer substrates, consistent with recent experiments.

Physical aspects of wear of the piston-ring—cylinder set of combustion engines

2008 ◽  
Vol 222 (11) ◽  
pp. 2103-2119 ◽  
Author(s):  
A Kazmierczak
Keyword(s):  
Free Energy ◽  
Surface Free Energy ◽  
Piston Ring ◽  
Van Der Waals ◽  
Cylinder Liner ◽  
Van Der Waals Forces ◽  
Real Object ◽  
Lubricating Oil ◽  
Combustion Engines ◽  
The Real

The research presented in this paper has shown that the physical aspects of interfacial phenomena, described by the total value of surface free energy and the values of its components, make it possible to select more suitable materials for sliding pairs. The total value of surface free energy depends on the molecular structure and the bonds characteristic of a given material, and determines its hardness. In order to reduce friction losses in a sliding pair that is being designed, it is proposed to match such materials for the pair in such a way that the surface of one of them has a high sum of surface free energy components originating from van der Waals interactions, while the other material's surface has a possibly low value of the sum. Furthermore, proper values of the components of surface free energy ensure proper wettability with lubricating oil. In order to minimize friction in a sliding contact, the element with the larger surface area (e.g. a cylinder sleeve) should have larger dispersion and van der Waals forces compared with those of the oil, while the element with the smaller area (e.g. a piston ring) has to have smaller (as low as possible) dispersion and van der Waals forces compared with those of the lubricating oil. Thus a basis for reducing friction losses, particularly during mixed friction and boundary friction, has been created. Pursuing the practical goal of this research, a new cylinder liner sliding pair of a piston-ring—cylinder (PRC) set (in which the ring has a titanium nitride (TiN) coating and the cylinder liner has a surface layer with varying properties, applied by vacuum nitriding) of a piston packing ring—combustion engine was designed and made. The sliding pair can be used in self-ignition combustion engines and in spark-ignition engines. The sliding pair is the result of the research carried out as part of this paper, including tests in a tribotester and three-stage testing embracing numerical simulations, preliminary tests on the real object, and tests proper on the real object.

Van der Waals forces in oil—water systems from the study of thin lipid films - II. The dependence of the van der Waals free energy of thinning on film composition and structure

1975 ◽  
Vol 347 (1649) ◽  
pp. 161-177 ◽  
Keyword(s):  
Free Energy ◽  
Layer Structure ◽  
Van Der Waals ◽  
Dielectric Permeability ◽  
Water Systems ◽  
Water Model ◽  
Polar Groups ◽  
Composition And Structure ◽  
Lipid Films ◽  
Oil Water

The van der Waals contribution to the free energy of thinning of lipid films has been determined for a variety of lipids, solvents and polar phases, and Hamaker coefficients have been calculated from this free energy, using the equation for a simple three layer (water–hydrocarbon–water) model. The results confirm and extend the findings presented in part I (Requena, Billett & Haydon 1975) i. e. that, for systems of comparable composition, the Hamaker coefficient approaches a constant value as the film thickness increases but that, towards smaller thicknesses, the coeffi­cient tends to rise rapidly. This latter observation is not readily accounted for in terms of the three layer structure, and experiments have been carried out in order to pinpoint the shortcomings of the model. Inter­action between the layers of lipid polar groups is shown to have been justifiably neglected, but it is inferred that small variations across the films of the dielectric permeability of the hydrocarbon may play a con­siderable part in determining the Hamaker coefficient.

Non-linear statics and dynamics of nanoelectromechanical systems based on nanoplates and nanowires

2005 ◽  
Vol 219 (1) ◽  
pp. 29-40 ◽  
Author(s):  
N Pugno
Keyword(s):  
Free Energy ◽  
Van Der Waals ◽  
Hessian Matrix ◽  
Three Dimensional ◽  
Van Der Waals Forces ◽  
Structural Instability ◽  
Nanoelectromechanical Systems ◽  
Statics And Dynamics ◽  
Dimensional Element ◽  
Thermal Vibrations

An analysis of the three-dimensional nanoelectromechanical systems (NEMS) is presented. Nanotubes could be a key one-dimensional element in future NEMS device; but they would be inadequate when two- or three-dimensional structures are required. A general free-energy-based formulation to treat statics and dynamics of three-dimensional NEMS, according to classical or quantum mechanics, is derved and presenteed; the method is then applied to nanoplates and nanowires. The equilibrium and stability of an elastic (e.g., graphene sheet) nanoplate-based NEMS under an electrical field and van der Waals forces (pauli's repulsion and large displacements are also discussed) are evaluated by minimizing the free energy and by the sign of the determinant of its Hessian matrix. The structural instability, arising at ythre so-called pull-in voltage, would correspond to the switch of the device. The amplitude and frequency of the thermal vibrations of the nanoplate are evaluated as a function of the applied voltage. The effect of the van der Waals forces on the NEMS dynamics is also presented. The amplitude and frequency of the oscillations at O K, from the uncertainty principle, are estimated.

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