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.

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.

[3-(4-Chlorophenyl)isoxazol-5-yl]methanol

2006 ◽  
Vol 62 (4) ◽  
pp. o1298-o1299 ◽  
Author(s):  
Li-Da Tang ◽  
Da-Tong Zhang ◽  
Fang-Gang Sun ◽  
Gui-Yun Duan ◽  
Jian-Wu Wang
Keyword(s):  
Hydrogen Bonds ◽  
Dihedral Angle ◽  
Normal Values ◽  
Crystal Packing ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Bond Lengths ◽  
Isoxazole Ring ◽  
The Mean ◽  
Title Molecule

In the title molecule, C10H8ClNO2, the isoxazole ring shows normal values of bond lengths and angles. The mean planes of the benzene and isoxazole rings make a dihedral angle of 16.3 (2)°. Intermolecular O—H...N hydrogen bonds link the molecules into chains extended along the b axis. The crystal packing is further stablized by weak C—H...O interactions and van der Waals forces.

Difluoro[1-(1-naphthyliminomethyl)-2-naphtholato-N,O]boron

2006 ◽  
Vol 62 (7) ◽  
pp. o2625-o2626 ◽  
Author(s):  
Min Xia ◽  
Shao-Qin Ge ◽  
Xiang-Sheng Li
Keyword(s):  
Dihedral Angle ◽  
Title Compound ◽  
Boron Trifluoride ◽  
Crystal Packing ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Boron Trifluoride Etherate ◽  
Stacking Interactions ◽  
Compound C ◽  
The Mean

The title compound, C21H14BF2NO, was synthesized by the reaction of 3-[(E)-(naphthalen-1-ylimino)methyl]naphthalen-2-ol, diisopropylethylamine and boron trifluoride etherate. The mean planes of the two naphthalene systems make a dihedral angle of 71.97 (4)°. The crystal packing is stabilized by π–π stacking interactions and van der Waals forces.

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.

Crystal and Molecular Structure of cis-2,2',3',2"-Tetraacetoxy-1,1':4',1"-ternaphthyl

1996 ◽  
Vol 61 (5) ◽  
pp. 726-732
Author(s):  
Jaroslav Podlaha ◽  
Ivana Císařová ◽  
Martin Bělohradský ◽  
Jiří Závada
Keyword(s):  
Molecular Structure ◽  
Single Crystal ◽  
Title Compound ◽  
Crystal And Molecular Structure ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Mean ◽  
Configuration And Conformation

The configuration and conformation of the title compound as a representative of conformationally locked ternaphthyls was determined by single-crystal X-ray diffraction. The arrangement of the mean planes of naphthyl and acetoxy groups results from intramolecular van der Waals forces.

scholarly journals Crystal structure of 4-(4-methoxyphenyl)-4′,4′-dimethyl-3-p-tolyl-3′,4′-dihydro-1′H,3H-spiro[isoxazole-5,2′-naphthalen]-1′-one

2015 ◽  
Vol 71 (12) ◽  
pp. o981-o981
Author(s):  
Mohamed Akhazzane ◽  
Ghali Al Houari ◽  
Mohamed El Yazidi ◽  
Mohamed Saadi ◽  
Lahcen El Ammari
Keyword(s):  
Crystal Structure ◽  
Dihedral Angle ◽  
Title Compound ◽  
Crystal Packing ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Dihedral Angles ◽  
Isoxazole Ring ◽  
Compound C ◽  
The Mean

In the title compound, C28H27NO3, the cyclohexanone and isoxazole rings have envelope conformations, with the methylene and spiro C atoms as the flaps, respectively. The mean plane of the isoxazole ring is inclined slightly to thep-tolyl ring, making a dihedral angle of 14.20 (9)°, and is nearly perpendicular to the mean plane through the tetralone moiety and to the methoxyphenyl ring [dihedral angles = 83.41 (8) and 72.12 (9)°, respectively]. The crystal packing is stabilized mainly by van der Waals forces.

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.

Self-Assembly of a Chiral Cubic Three-Connected Net from the High Symmetry Molecules C60 and SnI4

2020 ◽  
Author(s):  
Daniel B. Straus ◽  
Robert J. Cava
Keyword(s):  
Organic Synthesis ◽  
Self Assembly ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
High Symmetry ◽  
Molecular Chirality ◽  
Chiral Materials ◽  
Self Assembled ◽  
Chiral Centers

The design of new chiral materials usually requires stereoselective organic synthesis to create molecules with chiral centers. Less commonly, achiral molecules can self-assemble into chiral materials, despite the absence of intrinsic molecular chirality. Here, we demonstrate the assembly of high-symmetry molecules into a chiral van der Waals structure by synthesizing crystals of C<sub>60</sub>(SnI<sub>4</sub>)<sub>2</sub> from icosahedral buckminsterfullerene (C<sub>60</sub>) and tetrahedral SnI4 molecules through spontaneous self-assembly. The SnI<sub>4</sub> tetrahedra template the Sn atoms into a chiral cubic three-connected net of the SrSi<sub>2</sub> type that is held together by van der Waals forces. Our results represent the remarkable emergence of a self-assembled chiral material from two of the most highly symmetric molecules, demonstrating that almost any molecular, nanocrystalline, or engineered precursor can be considered when designing chiral assemblies.

scholarly journals Nanotube‐Based 1D Heterostructures Coupled by van der Waals Forces

Small ◽  
2021 ◽  
pp. 2102585
Author(s):  
Sofie Cambré ◽  
Ming Liu ◽  
Dmitry Levshov ◽  
Keigo Otsuka ◽  
Shigeo Maruyama ◽  
...  
Keyword(s):  
Van Der Waals ◽  
Van Der Waals Forces

scholarly journals Tuning adlayer-substrate interactions of graphene/h-BN heterostructures on Cu(111)–Ni and Ni(111)–Cu surface alloys

RSC Advances ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 1916-1927
Author(s):  
Jianmei Huang ◽  
Qiang Wang ◽  
Pengfei Liu ◽  
Guang-hui Chen ◽  
Yanhui Yang
Keyword(s):  
Long Range ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Alloy Surface ◽  
Surface Alloys ◽  
Substrate Interactions

The evolution of the interface and interaction of h-BN and graphene/h-BN (Gr/h-BN) on Cu(111)–Ni and Ni(111)–Cu surface alloys versus the Ni/Cu atomic percentage on the alloy surface were comparatively studied by DFT-D2, including critical long-range van der Waals forces.

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