London-van Der Waals Research Articles

Colloidal interaction and connectionist modelling of protein osmotic pressure and the effect of physicochemical properties

AbstractA proper knowledge of the osmotic pressure and thermodynamic behaviour of protein solutions is vital for designing an efficient protein separation process. It is also of great importance to develop a rapid and inexpensive technique to accurately estimate the protein osmotic pressure. A connectionist model to estimate the osmotic pressure of bovine serum albumin (BSA) in terms of pH, ionic strength and BSA concentration is proposed in this paper. Osmotic pressure of BSA is also modelled through the application of a colloidal interaction approach. Molecular interaction forces such as electrostatic, London–van der Waals and hydration along with entropy pressure are considered in the colloidal model to predict the BSA osmotic pressure. The advantages and disadvantages of both modelling approaches are discussed, and a hybrid modelling scheme is proposed for further investigations.

Determination of Hamaker constants of polymeric nanoparticles in organic solvents by asymmetrical flow field-flow fractionation

Interaction forces between all objects are either of repulsive or attractive nature. Concerning attractive interactions, the determination of dispersion forces are of special interest since they appear in all colloidal systems and have a crucial influence on the properties and processes in these systems. One possibility to link theory and experiment is the description of the London–Van der Waals forces in terms of the Hamaker constant, which leads to the challenging problem of calculating the van der Waals interaction energies between colloidal particles. Hence, the determination of a Hamaker constant for a given material is needed when interfacial phenomena such as adhesion are discussed in terms of the total potential energy between particles and substrates. In this work, the asymmetrical flow field-flow fractionation (AF-FFF) in combination with a Newton algorithm based iteration process was used for the determination of Hamaker constants of different nanoparticles in toluene.

On the molecular forces acting between macroscopic bodies

The eigenfrequencies are identified for two electromagnetically coupled semi-infinite solids with plane-parallel surfaces (two half-spaces) separated by a third, polarizable body. The corresponding van der Waals–London and Casimir forces are calculated from the zero-point energy (vacuum fluctuations) of the normal modes. It is shown how the results can be extended to bodies of any shape; in particular, the force is given for a sphere interacting with a half-space. The calculations are performed using the well-known Drude–Lorentz (plasma) model of (non-magnetic) polarizable matter. The polarization degrees of freedom are explicitly introduced. It is shown that the polarization dynamical variables for the two bodies are coupled through the electromagnetic field, very similar with two infinite sets of coupled harmonic oscillators.

A generalization of the dipolar force

The static dipolar force is generalized to time-dependent classical distributions of dipoles and electromagnetic fields. This force may exhibit a remarkable resonance character for induced dipoles, related to the pole structure of the polarizabilities. The resonance phenomenon is illustrated for two macroscopic polarizable bodies, with mutually induced polarizations, using the well-known Lorentz-Drude model for the dielectric response with optical dispersion and a characteristic (resonance) frequency. Specifically, the calculations are performed for distances much longer than the dimension of the bodies (“point-like” bodies), but shorter than the characteristic wavelength (sub-wavelength, stationary, near-field regime). The polarizations are induced via a localized external field acting upon only one body. The force is practically vanishing for distinct substances and acquires a non-vanishing value for identical substances. It falls off as the 7-th power of the distance, being reminiscent of the van der Waals-London force. The conditions of validity of this resonance phenomenon are emphasized. Particular cases corresponding to independent external fields or two isolated, interacting bodies (closed system) are also analyzed, with similar conclusions regarding the resonance character of the force.

Thermocapillary effects on steadily evaporating contact line: A perturbative local analysis

The evaporation process taking place close to the three-phase contact line is considered and studied theoretically using a linear stability analysis approach. A domain perturbation method, taking into consideration thermocapillary effects and surface forces, is used to develop the higher-order solution in terms of series expansion about lubrication condition. A closed-form solution is found for the film thickness, the pressure jump across the liquid-vapor interface and the evaporative flux in the vicinity of the contact line. The key novelty in this work is considering thermocapillary instability for very thin films (∼10 nm) accounting for surface forces. For (quasi-) flat-very-thin films, the analysis shows no instability, which is consistent with general knowledge in this field. However, for films extending from a meniscus, as encountered in wetting configurations, it is found that the competition between London–van der Waals, capillary, and thermocapillary forces leads to contact line instability and behavior revealed for the first time. According to the sign of the Marangoni number, the instability can enhance (if positive) or reduce (if negative) the evaporation rate by widening out or narrowing, respectively, the contact region and, in both cases, significantly modifies the vortical structure of the flow. If the Marangoni number is positive, the film interface close to the contact line can exhibit corrugations. The occurrence of these latter is discriminated, in addition to the Marangoni number, by the value of three operating parameters, namely the film aspect ratio, the ratio of the film diffusive thermal resistance to evaporative heat transfer resistance, and the ratio of capillary pressure to disjoining pressure. By modifying the physical and operating parameters, it is also shown that the system can be optimized in order to suppress these corrugations.

Role of long- and short-range hydrophobic, hydrophilic and charged residues contact network in protein’s structural organization

BackgroundThe three-dimensional structure of a protein can be described as a graph where nodes represent residues and the strength of non-covalent interactions between them are edges. These protein contact networks can be separated into long and short-range interactions networks depending on the positions of amino acids in primary structure. Long-range interactions play a distinct role in determining the tertiary structure of a protein while short-range interactions could largely contribute to the secondary structure formations. In addition, physico chemical properties and the linear arrangement of amino acids of the primary structure of a protein determines its three dimensional structure. Here, we present an extensive analysis of protein contact subnetworks based on the London van der Waals interactions of amino acids at different length scales. We further subdivided those networks in hydrophobic, hydrophilic and charged residues networks and have tried to correlate their influence in the overall topology and organization of a protein.ResultsThe largest connected component (LCC) of long (LRN)-, short (SRN)- and all-range (ARN) networks within proteins exhibit a transition behaviour when plotted against different interaction strengths of edges among amino acid nodes. While short-range networks having chain like structures exhibit highly cooperative transition; long- and all-range networks, which are more similar to each other, have non-chain like structures and show less cooperativity. Further, the hydrophobic residues subnetworks in long- and all-range networks have similar transition behaviours with all residues all-range networks, but the hydrophilic and charged residues networks don’t. While the nature of transitions of LCC’s sizes is same in SRNs for thermophiles and mesophiles, there exists a clear difference in LRNs. The presence of larger size of interconnected long-range interactions in thermophiles than mesophiles, even at higher interaction strength between amino acids, give extra stability to the tertiary structure of the thermophiles. All the subnetworks at different length scales (ARNs, LRNs and SRNs) show assortativity mixing property of their participating amino acids. While there exists a significant higher percentage of hydrophobic subclusters over others in ARNs and LRNs; we do not find the assortative mixing behaviour of any the subclusters in SRNs. The clustering coefficient of hydrophobic subclusters in long-range network is the highest among types of subnetworks. There exist highly cliquish hydrophobic nodes followed by charged nodes in LRNs and ARNs; on the other hand, we observe the highest dominance of charged residues cliques in short-range networks. Studies on the perimeter of the cliques also show higher occurrences of hydrophobic and charged residues’ cliques.ConclusionsThe simple framework of protein contact networks and their subnetworks based on London van der Waals force is able to capture several known properties of protein structure as well as can unravel several new features. The thermophiles do not only have the higher number of long-range interactions; they also have larger cluster of connected residues at higher interaction strengths among amino acids, than their mesophilic counterparts. It can reestablish the significant role of long-range hydrophobic clusters in protein folding and stabilization; at the same time, it shed light on the higher communication ability of hydrophobic subnetworks over the others. The results give an indication of the controlling role of hydrophobic subclusters in determining protein’s folding rate. The occurrences of higher perimeters of hydrophobic and charged cliques imply the role of charged residues as well as hydrophobic residues in stabilizing the distant part of primary structure of a protein through London van der Waals interaction.

Análise e modelação matemática da interação entre partículas na filtração direta utilizando a teoria coloidal

Este trabalho utilizou a teoria coloidal para descrever o comportamento físico pelo balanço de forças e balanço de energia de complexos coloidais na água bruta e daqueles formados durante a filtração direta em escoamento ascendente. Nele são descritos os perfis de energia de interação entre as superfícies dos colóides para três geometrias: esférica, plana e cilíndrica; e quatro arranjos de interação entre as superfícies: dois cilindros, dois planos, duas esferas e uma esfera e um plano. Duas situações foram analisadas, antes e após a desestabilização eletrostática pela ação de sulfato de alumínio em águas de estudo contendo caulinita, utilizando-se a modelação e análise pela teoria DLVO (das iniciais de Derjarguin-Landau-Verwey-Overbeek) modificada, ou XDLVO, que inclui à abordagem tradicional das forças da dupla camada elétrica (DCE), forças de atração de superfície ou London-van der Waals (LvdW), forças estéricas, força hidrofóbica e forças de outras origens no cálculo do balanço de forças, a saber: repulsão molecular, denominada repulsão de Born, e a força oriunda das funções químicas ácido e Base (AB) de Lewis.

Liquid Chromatography Study on Atenolol--Cyclodextrin Inclusion Complex

Inclusion complex formation of atenolol with -cyclodextrin (-CD) has been investigated by HPLC on different stationary phases, by varying pH and concentration of -CD added as an additive in the mobile phase over a wide range of column temperature. Stationary phases of different polarity and hydrophobicity were evaluated to find the best conditions for complex formation. The optimum conditions for inclusion complexation were achieved on YMC ODS-AQ C18 ( mm, 5 μ) analytical column. The apparent formation constant () of the complex as evaluated by liquid chromatography using retention factors () was M−1 at 25°C. The stoichiometry of the complex was 1 : 1 as is evident from the straight line plot of 1/ versus -CD concentration. The formation of inclusion complex was essentially enthalpy (−42.12 kJ/mol) driven and the binding forces included hydrophobic, van der Waals-London dispersion interactions. The enthalpy-entropy compensation criterion was used to prove the inclusion phenomena.

Stability of a Liquid Film on a Surface with Periodic Array of Gas-filled Grooves

We develop a linear stability theory for a thin liquid film on a structured solid surface with periodic grooves filled by a gas. The main mechanism driving the instability is due to the London-van der Waals disjoining pressure. The grooves are shown to have a destabilizing effect on the film. The results of linear stability analysis are compared with numerical simulations based on the strongly nonlinear equation for film thickness.

Interfacial thin films rupture and self-similarity

Two superposed thin layers of fluids are prone to interfacial instabilities due to London-van der Waals forces. Evolution equations for the film thicknesses are derived using lubrication theory. Using the intrinsic scales, for a single layer, results in a system with parametric dependence of four ratios of the two layers: surface tension, Hamaker constant, viscosity, and film thickness. In contrast to the single layer case, the bilayer system has two unstable eigenmodes: squeezing and bending. For some particular parameter regimes, the system exhibits the avoided crossing behavior, where the two eigenmodes are interchanged. Based on numerical analysis, the system evolves into four different rupture states: basal layer rupture, upper layer rupture, double layer rupture, and mixed layer rupture. The ratio of Hamaker constants and the relative film thickness of the two layers control the system dynamics. Remarkably, the line of avoided crossing demarks the transition region of mode mixing and energy transfer, affecting the scaling of the dynamical regime map consequentially. Asymptotic and numerical analyses are used to examine the self-similar ruptures and to extract the power law scalings for both the basal layer rupture and the upper layer rupture. The scaling laws for the basal layer rupture are the same as those of the single layer on top of a substrate. The scaling laws for the upper layer rupture are different: the lateral length scale decreases according to (tr-t)1/3 and the film thickness decreases according to (tr-t)1/6.

Toner Charge and Environmental Interactions with Toner Adhesion

Understanding charged particle adhesion forces is a critical step in the understanding and modeling of electrophotographic printing processes. Electrostatic and mechanical (Van der Waals) forces are both significant contributors to toner adhesion to substrates, and previous work has shown these to have roughly equivalent magnitudes in modern printer designs. Measuring distributions of toner adhesion as a function of multiple parameters including environmental and toner charge variation has revealed that there are additional interactions beyond Coulombic Attraction and dipole induced London-Van der Waals' forces which are significant contributors to system performance. A model for toner adhesion is presented, including a term which describes the increased adhesion resulting from particle deformation at higher temperatures. Experimental results show good correlation to the model.

ELECTROMAGNETIC EIGENMODES IN MATTER. VAN DER WAALS-LONDON AND CASIMIR FORCES

We derive van der Waals-London and Casimir forces by calculating the eigenmodes of the electromagnetic fleld interacting with two semi-inflnite bodies (two halves of space) with parallel separated by distance d. We adopt simple models for metals and dielectrics, well-known in the elementary theory of dispersion. In the non-retarded (Coulomb) limit we get a d i3 -force (van der Waals-London force), arising from the zero-point energy (vacuum ∞uctuations) of the surface plasmon modes. When retardation is included we obtain a d i4 -(Casimir) force, arising from the zero- point energy of the surface plasmon-polariton modes (evanescent modes) for metals, and from propagating (polaritonic) modes for identical dielectrics. The same Casimir force is also obtained for \flxed surfaces boundary conditions, irrespective of the pair of bodies. The approach is based on the equation of motion of the polarization and the electromagnetic potentials, which lead to coupled integral equations. These equations are solved, and their relevant eigenfrequencies branches are identifled.

Van der Waals-London dispersion interaction framework for experimentally realistic carbon nanotube systems

Abstract A system's van der Waals–London dispersion interactions are often ignored, poorly understood, or crudely approximated, despite their importance in determining the intrinsic properties and intermolecular forces present in a given system. There are several key barriers that contribute to this issue: 1) lack of the required full spectral optical properties, 2) lack of the proper geometrical formulation to give meaningful results, and 3) a perception that a full van der Waals–London dispersion calculation is somehow unwieldy or difficult to understand conceptually. However, the physical origin of the fundamental interactions for carbon nanotube systems can now be readily understood due to recent developments which have filled in the missing pieces and provided a complete conceptual framework. Specifically, our understanding is enhanced through a combination of a robust, ab-initio method to obtain optically anisotropic properties out to 30 electron Volts, proper extensions to the Lifshitz's formulations to include optical anisotropy with increasingly complex geometries, and a proper methodology for employing optical mixing rules to address multi-body and multi-component structures. Here we review this new framework to help end-users understand these interactions, with the goal of better system design and experimental prediction. Numerous examples are provided to show the impact of a material's intrinsic geometry, including optical anisotropy as a function of that geometry, and the effect of the size of the nanotube core and surfactant material present on its surface. We'll also introduce some new examples of how known trends in optical properties as a function of [n, m] can result in van der Waals interactions as a function of nanotube classification, radius, and other parameters. The concepts and framework presented are not limited to the nanotube community, and can be equally applied to other nanoscale or even biological systems.

Amendment to published paper: "Turbulent coagulation model considering effects of London-van der Waals force and wettability"

This paper is to correct a mistake in the authors' previous paper (Nakaoka et al., Progress in Computational Fluid Dynamics, 2008, 8(5), 270-275), which originated in the solution procedure of the population-balance (PB) equation.

A program concerning intermolecular forces and tissue-specific cell contacts

The intermolecular forces responsible for the highly specific cell-to-cell attachment in normal and abnormal tissues are studied. It is often taken for granted that before any physical study of a mechanism of high biological specificity is made, the biochemical nature of the participating molecular species should be determined. While such detailed knowledge of the chemistry of the mechanism is most important and, for an ultimate clarification of the situation, absolutely necessary, a great many detours and wrong preconceptions may be avoided if there is a clear understanding of the possible types of intermolecular forces and structural relationships which may be responsible for the specificity in question. Since there are only a quite limited number of physical types of intermolecular forces and mechanisms to choose from, it may not be too presumptuous to take advantage of that limitation of choice to infer and study model systems for highly specific biological interactions. In particular, the significance of van der Waals forces and of related charge fluctuation forces for the issue of specific cell-to-cell attachment is to be determined. Charge fluctuation forces of the London-van der Waals type (dispersion forces), forces due to permanent dipoles (Keesom forces), and also charge fluctuation forces due to mobile H + ions are investigated.

Effective pair potentials for spherical nanoparticles

An effective description for rigid spherical nanoparticles in a fluid of point particles ispresented. The points inside the nanoparticles and the point particles are assumed tointeract via spherically symmetric additive pair potentials, while the distribution of pointsinside the nanoparticles is taken to be spherically symmetric and smooth. The resultingeffective pair interactions between a nanoparticle and a point particle, as well as betweentwo nanoparticles, are then given by spherically symmetric potentials. If overlap betweenparticles is allowed, as can occur for some forms of the pair potentials, the effectivepotential generally has non-analytic points. It is shown that for each effective potential theexpressions for different overlapping cases can be written in terms of one analytic auxiliarypotential. Even when only non-overlapping situations are possible, the auxiliary potentialsfacilitate the formulation of the effective potentials. Effective potentials for hollownanoparticles (appropriate e.g. for buckyballs) are also considered and shown to berelated to those for solid nanoparticles. For hollow nanoparticles overlap is morephysical, since this covers the case of a smaller particle embedded in a larger, hollownanoparticle. Finally, explicit expressions are given for the effective potentials derivedfrom basic pair potentials of power law and exponential form, as well as from thecommonly used London–van der Waals, Morse, Buckingham, and Lennard-Jonespotentials. The applicability of the latter is demonstrated by comparison with anatomic description of nanoparticles with an internal face centered cubic structure.

EQUILIBRIUM AND KINETIC STUDIES OF PHENOL SORPTION BY CHITOSAN COATED MONTMORILLONITE

ABSTRACT In order to provide physical support for chitosan and increase the accessibility of the binding sites for sorption process applications, chitosan was coated on the surface of montmorillonite. For the optimization of the sorption of phenol on chitosan coated montmorillonite (CCM), effects of pH, initial concentration and temperature on the sorption of phenol by CCM were investigated. In order to find the sorption characteristics, the isothermal data were applied to Langmuir and Freundlich linear isotherm equation, and the thermodynamic parameters (ΔH, ΔG and ΔS) were also calculated according to the values of binding Langmuir constant K L . The L type sorption isotherm between phenol and CCM suggests a relatively high affinity between the adsorbate and adsorbent, and the mechanism involved in the association of phenol with CCM were proton transfer, hydrogen bonding, London-Van der Waals forces because of lots of the OH and NH 2 groups in the chitosan chain. The negative ΔH constant confirmed that the more phenol was adsorbed by CCM at lower temperature and the driving force for sorption process is an enthalpy effect. The kinetics of the sorption process of phenol on CCM were also investigated using the pseudo-first order and pseudo-second order kinetics, results showed that the second order equation model provided the best correlation with the experimental results. It was reached that modification of chitosan with montmorillonite increased the possibility of utilization of chitosan for phenol remove from aqueous solution.

Spreading of thin liquid droplets on rotating disks

AbstractIn many industrial processes solids are coated to obtain specific surface properties, as e.g. corrosion resistance, mechanical, optical, or electrical properties. Even today many of such coating processes are not fully understood and the choice of parameters is mainly based on experience. Hence, a prediction of the complete hydrodynamic process in its dependency on the parameters appears highly desirable. This would e.g. allow for a precise prediction of the (liquid) layer thickness and shape and help to optimize the quality of the coating. A common coating technique is the so–called spin coating. The coating agent is dissolved or suspended in a liquid, brought onto the solid, spread by rotation, and the carrier liquid is finally removed by evaporation or by chemical reactions. In this article an evolution equation is derived from lubrication theory, valid for thin liquid layers. The model involves a dynamic contact angle, centrifugal, capillary, gravitational, and molecular (London–van–der–Waals) forces. The evolution equation without molecular forces can even be solved analytically, provided the capillary number is small. Otherwise a numerical integration of the governing equations is engaged. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Cutoff variation induces different topological properties: A new discovery of amino acid network within protein

An increasing attention has been dedicated to the characterization of complex networks within the protein world. Before now most investigations about protein structures were only considered where the interactive cutoff distance R c =5 or 7 Å. It is noteworthy that the length of peptide bond is about 1.5 Å, the length of hydrogen bond is about 3 Å, the range of London-van der Waals force is about 5 Å and the range of hydrophobic effect can reach to 12 Å in protein molecule. Present work reports a study on the topological properties of the amino acid network constructed by different interactions above. The results indicate that the small-world property of amino acid network constructed by the peptide and hydrogen bond, London-van der Waals force and the hydrophobic effect is strong, very strong and relatively weak, respectively. Besides, there exists a precise exponential relation C∝ k −0.5 at R c =12 Å. It means that the amino acid network constructed by the hydrophobic effect tend to be hierarchical. Functional modules could be the cause for hierarchical modularity architecture in protein structures. This study on amino acid interactive network for different interactions facilitates the identification of binding sites which is strongly linked with protein function, and furthermore provides reasonable understanding of the underlying laws of evolution in genomics and proteomics.

Spectral mixing formulations for van der Waals-London dispersion interactions between multicomponent carbon nanotubes.

Recognition of spatially varying optical properties is a necessity when studying the van der Waals-London dispersion (vdW-Ld) interactions of carbon nanotubes (CNTs) that have surfactant coatings, tubes within tubes, andor substantial core sizes. The ideal way to address these radially dependent optical properties would be to have an analytical add-a-layer solution in cylindrical coordinates similar to the one readily available for the plane-plane geometry. However, such a formulation does not exist nor does it appear trivial to be obtained exactly. The best and most pragmatic alternative for end-users is to take the optical spectra of the many components and to use a spectral mixing formulation so as to create effective solid-cylinder spectra for use in the far-limit regime. The near-limit regime at "contact" is dominated by the optical properties of the outermost layer, and thus no spectral mixing is required. Specifically we use a combination of a parallel capacitor in the axial direction and the Bruggeman effective medium in the radial direction. We then analyze the impact of using this mixing formulation upon the effective vdW-Ld spectra and the resulting Hamaker coefficients for small and large diameter single walled CNTs (SWCNTs) in both the near- and far-limit regions. We also test the spectra of a [16,0,s+7,0,s] multiwalled CNT (MWCNT) with an effective MWCNT spectrum created by mixing its [16,0,s] and [7,0,s] SWCNT components to demonstrate nonlinear coupling effects that exist between neighboring layers. Although this paper is primarily on nanotubes, the strategies, implementation, and analysis presented are applicable and likely necessary to any system where one needs to resolve spatially varying optical properties in a particular Lifshitz formulation.