Effect Of Line Tension Research Articles

Wetting dynamics on lyophilic solid surfaces patterned by lyophobic islands

A theory for wetting of structured solid surfaces is developed, based on the delta-comb periodic potential. It possesses two matching parameters: the effective line tension and the friction coefficient on the three-phase contact line at the surface. The theory is validated on the dynamics of spreading of liquid zinc droplets on morphologically patterned zinkophilic iron surface by means of square patterns of zinkophobic aluminum oxide. It is found out that the effective line tension is negative and has essential contribution to the dynamics of spreading. Thus, the theoretical analysis shows that the presence of lyophobic patterns situated on lyophilic surface makes the latter completely wettable, i.e. no equilibrium contact angle on such surface exists making the droplet spread completely in form of thin liquid layer on the patterned surface.

Rogue wave impact on a tension leg platform: The effect of wave incidence angle and mooring line tension

An understanding of the interaction between extreme ocean conditions and floating offshore platforms is required for their design and safe operation. Rogue wave impacts cannot easily be handled by traditional analytic or computational techniques. Here we use Smoothed Particle Hydrodynamics (SPH) to simulate the fully non-linear dynamics of a large breaking wave on a semi-submersible tension leg platform. We consider the effect of wave impact angle and mooring line pre-tension on the subsequent motion of the platform, and predict the maximum tension in each mooring line. The primary effect of wave impact angle is to determine the peak mooring line tension and line “slackness” during wave impact. A 45° impact results in the maximum tension on the leading line. The maximum heave, surge and pitch vary only slightly with wave angle. As mooring line pre-tension is increased, the duration of heave and pitch excursions is reduced. Peak mooring tension increases only slightly, but the incidence of mooring line “slack” decreases significantly for higher pre-tension. Properly applied, SPH has a wide application in predicting non-linear wave–structure interactions. Genuine opportunity exists for using SPH in the design of structures and mooring systems exposed to extreme ocean events such as rogue wave impact.

Gibbs energy determinants of lipoprotein insertion into lipid membranes: the case study of Ras proteins

In a combined chemical-biological and biophysical approach we explored the Gibbs (free) energy contributions to the membrane partitioning of lipidated proteins, and compared the theoretical predictions with recent experimental data on the membrane insertion of Ras proteins of various anchor systems into rationally designed model biomembrane systems. Various factors fostering or reducing the membrane partitioning properties are discussed, including hydrophobic effects, lipid chain mismatch, electrostatic interactions, membrane-mediated protein-protein interactions, and terms that account for line tension effects between coexisting lipid domains, lipid sorting, and changes in the lateral organization of the lipid bilayer system. From these data, it is apparent that two membrane anchoring motifs are needed to facilitate firm membrane binding. For heterogeneous membranes, localization and sequestration at domain boundaries as well as formation of protein clusters and collective lateral organization via an effective lipid sorting mechanism provide complementary ways of inducing membrane nanodomains that could potentially operate as effective, high fidelity signalling platforms.

Drop size dependence of soil-water contact angle in relation to the droplet geometry and line tension

The soil-water contact angle is used as a measure of the surface hydrophobicity of soils. The contact angle for particular solid–liquid combination is considered to vary with the drop size. In this paper, we focused on examining the drop size dependence of contact angle on soil surfaces compared with homogeneous solid surfaces, and determining its relation to the droplet geometry and line tension. The contact angle estimated using geometric parameters of the droplets (θ G) showed decreasing trend with increasing drop size from 5 to 50 µL irrespective of the deformations in the droplet shape in larger drops. This was considered to be a result of the corresponding deviations of the geometric parameters of the droplets. The directly measured contact angle (θ A) first decreased and then increased with increasing drop size from 5 to 50 µL. The drop size at lowest θ A for hydrophobized silica sand with 1 g kg–1 stearic acid (SA) and the acryl surfaces was 20 µL, whereas that for hydrophobized silica sand with 5 g kg–1 SA and siliconed paper was 30 µL. The decrease in θ A with increasing drop size was explained as a result of the line tension effect using the modified Young's equation. Despite the surface heterogeneity, all the surfaces tested in this study showed positive line tensions on the order of 10 µJ m–1. Irrespective of the heterogeneity of the surfaces, the θ A in this experiment agreed with the modified Young's equation for drop sizes up to about 20–30 µL, where the θ A and θ G were also in good agreement. Drop size dependence of contact angle was independent of the level of surface hydrophobicity. The θ A on all the examined surfaces started to increase with increasing drop size when the deformation index, I d, exceeded 5%, where the wetting radius, R exceeded the capillary length. The increase in θ A with increasing drop size was attributed to the deformations of water drops due to the effect of gravity.

Delta-Comb Potential in Modeling Three-Phase Contact Line (TPCL) on Periodically Patterned Surfaces

This work is a study of wetting of small water droplets on smooth glass surfaces with periodic patterns in the form of imprinted net with hydrophilic cells and hydrophobic bars. Microcover slides consisted of soda lime glass were used. The imprinted images of the net were with cell sizes in the range 40-200 μm, which corresponds to a quite narrow scope of hydrophilic surface fractions f(1)(30-36%) due to the relative increase in the size of the hydrophobic bars. The receding contact angles θ(R) of small water droplets, positioned on the patterned surfaces, were measured. The experiment showed significantly lower receding contact angles as compared to the theoretical expectations by the Cassie formula, which accounts for the contribution to the contact angle of the surface fraction of the imprinted hydrophobic/hydrophilic net. For this reason, we developed new theory accounting for the periodicity of the surface and the contribution of the three-phase contact line on the contact angle. This new theory considered delta-comb potential energy Δ(x,y) of the surface, effective line tension κ, and the lattice parameter a. The restriction of theory was discussed as well. It was pointed out that the theory is not valid for very small and very large lattice parameters.

Nanoporous Surface Wetting Behavior: The Line Tension Influence

The aim of this work is to develop a physical model to describe the evolution of the apparent contact angle for four different liquids on nanotextured alumina surfaces with different pore radius. The nanoporous alumina templates were fabricated by anodization of Al foil in a 0.3 M oxalic acid solution. Scanning electron microscopy was used to characterize the morphology of the surfaces. The templates are approximately 400 nm in thickness and consist of a well-ordered hexagonal array of uniform radius pores spaced 105 nm apart with pore radii from 12 to 42 nm. The wettability of nanoporous alumina templates was investigated using contact-angle measurements. We measured the contact angles using four liquids: water, ethylene glycol, aniline, and a mixture of ethylene glycol and aniline. We developed a new theoretical model for the contact angle on nanoporous surfaces as a function of the pore radius. This model is based on energy considerations and involves liquid penetration into the nanopores driven by the capillarity (Laplace's law). Because the air is compressed inside the pores, this model also includes the effect of the line tension. This is important because the three-phase line length is greatly enhanced in our nanoporous structures. For example: for a millimeter-sized droplet, the three-phase line around the perimeter of the droplet is a few millimeters long, whereas the total three-phase line within the pores can reach several tens of meters. Using our model, the line-tension value for our nanopore samples is positive and ranges from 4 to 13 × 10(-9) N, which falls within the wide interval from 10(-11) to 10(-5) N quoted in the literature. Nanoporous surfaces may allow the effect of line tension to be visible for micro- to macrodroplets.

Physics of shell assembly: Line tension, hole implosion, and closure catastrophe

The self-assembly of perfectly ordered closed shells is a challenging process involved in many biological and nanoscale systems. However, most of the aspects that determine their formation are still unknown. Here we investigate the growth of shells by simulating the assembly of spherical structures made of N identical subunits. Remarkably, we show that the formation and energetics of partially assembled shells are dominated by an effective line-tension that can be described in simple thermodynamic terms. In addition, we unveil two mechanisms that can prevent the correct formation of defect-free structures: "hole implosion," which leads to a premature closure of the shell; and "closure catastrophe," which causes a dramatic production of structural disorder during the later stages of the growth of big shells.

Comparative Sessile Drop and Dip Pen Nanolithography Investigation for Various Hydrophilic Ink/Surface Systems

We present a dip pen nanolithography study of various hydrophilic ink/surface systems with application in the field of biosensors and novel nano-materials. The inking process was investigated by studying a number of inks, such as Deoxyribonucleic acid (DNA), Bovine serum albumin (BSA), Streptavidin, 16-mercaptohexadecanoic acid (MHA) and a 20 nm nanosphere (NS) polystyrene solution onto a range of substrates, namely glass, silicon, gold and tetrahedral amorphous carbon (taC). In the majority of cases, this resulted in patterns with sub-100 nm line widths and dot diameters. Importantly, contact angle measurements in the microl range showed a decrease of contact angle with drop volume, interpreted as a line tension effect. The significance of this to the nanoscale wetting behaviour is discussed. The effect of dwell time and writing speed indicates that the inking process is not solely defined by surface diffusion but also influenced by the ink dissolution rate from the tip.

Electrowetting on curved surfaces

In this work, we explore the influence of the surface curvature on the contact angle in electrowetting (EW). By using the method of energy minimization, an extended EW equation for EW on curved surfaces is obtained. A curvature-modified EW number is introduced to describe the surface curvature effect. It is found that the variation of the contact angle will be curvature dependent; especially, with decreasing of the system size, the surface curvature effect would be even more significant. Comparing with the planar situation, the contact angle variation decreases on convex surfaces but increases on concave surfaces. Then considering the line tension effect, an extended expression for EW on curved surfaces is proposed. Since curved surfaces are more common, both natural and synthetic, our findings will have important implications for the miniaturization of future electronic products.

Buckling of multicomponent elastic shells with line tension

We explore the effects of line tension on the shape of two component elastic shells. Segregation between components with different elastic properties combined with the subtleties related to the spherical topology leads to a rich variety of shapes. They range from irregular polyhedra at weak segregation to Janus-like morphologies with spherical and buckled regions coexisting on the same shell for large values of the line tension. We use Monte Carlo simulations to map a detailed phase diagram as a function of the relative fraction of the two components, the ratio of their bending rigidities, and the strength of the line tension.

Effect of Pore Size on the Condensation/Evaporation Transition of Confined Water in Equilibrium with Saturated Bulk Water

The effect of pore size on the condensation/evaporation transition of confined water upon varying the strength of the water-surface interaction is studied under conditions of equilibrium with saturated bulk. Monte Carlo simulations in the grand canonical ensemble were used to determine water density in spherical pores of radius R(p) = 9, 12, 15, 20, and 25 Å in the temperature range from T = 270 K to the bulk critical temperature. The critical values of the well depth of the water-surface interaction potential, which mark the limits of the metastability of vapor and liquid phases in pores (U(0)(cond) and U(0)(evap), respectively), were determined. U(0)(cond) strongly depends on temperature, practically does not depend on the pore size, and corresponds to some particular density of water vapor near a surface. In contrast, U(0)(evap) only slightly depends on temperature, depends strongly on pore size, and corresponds to the density in the pore interior by about 2% below the bulk value. The critical water-pore interaction U(0)(c), which separates regimes of capillary condensation and capillary evaporation, is found to be changed from -1.75 to -0.94 kcal/mol when the pore radius R(p) increases from 9 to 25 Å. The size dependence of U(0)(c) is attributed to the change of the contact angle due to the line tension effect. Extrapolation of the dependence U(0)(c)(R(p)) to the flat surface gives the critical value U(0)(c)(∞) ≈ -0.61 kcal/mol.

Effect of submicron particles on electrowetting on dielectrics (EWOD) of sessile droplets

The present study elucidates the effects of included submicron-sized particles on the wetting behavior of sessile droplets under the influence of applied electric field in an electro-wetting-on-dielectric (EWOD) configuration. A thermodynamic description using an energy minimization approach is used to analyze the experimental results related to the effects of the included particles on the EWOD phenomenon, considering the effects of line tension as well. The effects of particle size and concentration on interfacial areas are included in the model to analyze the wetting characteristics. Experiments are also conducted with submicron-sizes latex beads, in an effort to elucidate the related phenomena. It is further postulated that these beads act as suspended dielectrics in the droplet, thereby mimicking a system of two capacitors in series. An effective electrical permittivity of the composite medium is used to study the experimental results related to contact angle changes at different concentrations and diameters of submicron particles in the droplet.

Relating domain size distribution to line tension and molecular dipole density in model cytoplasmic myelin lipid monolayers

We fit the size distribution of liquid-ordered (L(o)) domains measured from fluorescence images of model cytoplasmic myelin monolayers with an equilibrium thermodynamic expression that includes the competing effects of line tension, λ, dipole density difference, Δm, and the mixing entropy. From these fits, we extract the line tension, λ, and dipole density difference, Δm, between the L(o) and liquid-disordered (L(d)) phases. Both λ and Δm decrease with increasing surface pressure, , although λ/Δm(2) remains roughly constant as the monolayer approaches the miscibility surface pressure. As a result, the mean domain size changed little with surface pressure, although the polydispersity increased significantly. The most probable domain radius was significantly smaller than that predicted by the energy alone, showing that the mixing entropy promotes a greater number of smaller domains. Our results also explain why domain shapes are stable; at equilibrium, only a small fraction of the domains are large enough to undergo theoretically predicted shape fluctuations. Monolayers based on the composition of myelin from animals with experimental allergic encephalomyelitis had slightly lower values of λ and Δm, and a higher area fraction of domains, than control monolayers at all . While it is premature to generalize these results to myelin bilayers, our results show that the domain distribution in myelin may be an equilibrium effect and that subtle changes in surface pressure and composition can alter the distribution of material in the monolayer, which will likely also alter the interactions between monolayers important to the adhesion of the myelin sheath.

Triple junction effects in solids

The grain boundary–free surface triple line tension and grain boundary triple line tension were investigated in copper using a recently introduced novel approach. The effect of triple line tension on grain growth, Zener drag and Gibbs–Thompson relation was studied. The results showed that the triple line tension has a considerable effect on grain growth, particle–boundary interactions and void shape, especially for nanocrystalline materials.

Effective line tension and contact angles between membrane domains in biphasic vesicles

Inhomogeneities in membranes give rise to localized interactions at the interface between domains in two-component vesicles. The corresponding energy is expressed as a line tension between the two phases. In this paper we study the implications of the thickness mismatch between domains which has been experimentally reported to be of order 20-30% and the conditions under which the induced line tension can destabilize the domains in inhomogeneous vesicles. For asymmetric lipidic membranes we prove an increase of the line tension and the existence of a contact angle. Adsorption of impurities is also examined, our scope being the extension of the Canham-Helfrich model to describe elastic deformations and chemical interactions arising at microscopic scales. This mismatch effect may have important consequences for the stability of very small domains.

Electrostatic-driven pattern formation in fibers, nanotubes and pores

The physical properties of interfaces between media with different dielectric permittivities are modified by the adsorption of charged particles. The adsorbed charges can be arranged into self-assembled nanostructures with properties that can be controlled by, for example, varying the ionic abundance of charged species in the media separated by the interface. The presence of inhomogeneous charge distributions at interfaces between media with different dielectric permittivity is a crucial feature of many interesting physical systems including clay, biological ion channels, and DNA-carbon nanotubes complexes. We describe here a general formalism using the electrostatic Green's function to compute the optimal arrangement of charges in cylindrical geometry. This geometry serves as model for a porous medium or a fiber. We study, in particular, the electrostatic energy of charged lamellar structures that cover the cylinder. We demonstrate that, under a variety of conditions, chiral helices are the preferred structure adopted by the lamellar system. These helices are more prominent in systems with higher permittivity in the interior of a tube separating two media, such as in porous media and ion channels, than in fibers with low dielectric interiors in aqueous media. We also analyze the effect of line tension on the surface pattern that competes with the charge-accumulation penalty upon the adsorption of polyions with hydrophobic groups.

Continuum model for dislocation dynamics in a slip plane

In this paper, we present a continuum model for dislocation dynamics in a slip plane, which accurately incorporates both the long-range interaction and the local line tension effect of dislocations. Unlike the continuum models in the literature using dislocation densities, we use the disregistry across the slip plane to represent the continuous distribution of dislocations in the slip plane, which has the advantage of including the orientation dependence of dislocations in a very simple way. The continuum dislocation dynamics model is validated by linear instability analysis of a uniform dislocation array to small perturbations and comparisons of the results with those of the discrete dislocation dynamics model. Numerical examples for the evolution of distributions of dislocations and plastic slips in a slip plane are presented.

Phase-Field Crystal Modeling of Compositional Domain Formation in Ultrathin Films

Bulk-immiscible binary systems often form stress-induced miscible alloy phases when deposited on a substrate. Both alloying and surface dislocation formation lead to the decrease of the elastic strain energy, and the competition between these two strain-relaxation mechanisms gives rise to the emergence of pseudomorphic compositional nanoscale domains, often coexisting with a partially coherent single phase. In this work, we develop a phase-field crystal model for compositional patterning in monolayer aggregates of binary metallic systems. We first demonstrate that the model naturally incorporates the competition between alloying and misfit dislocations, and quantify the effects of misfit and line tension on equilibrium domain size. Then, we quantitatively relate the parameters of the phase-field crystal model to a specific system, CoAg/Ru(0001), and demonstrate that the simulations capture experimentally observed morphologies.

Stabilizing force on perturbed grain boundaries using a dislocation model

In this paper, we study the glide force due to stress on the constituent dislocations of slightly perturbed symmetric low-angle tilt boundaries. We show that the stabilizing force comes from both the long-range interaction of the constituent dislocations and their local line tension effect. We also present a continuum model for this glide force. The obtained results and continuum model provide a basis for further understanding of the stress-driven migration of distorted grain boundaries.

Comparison of the liquid-ordered bilayer phases containing cholesterol or 7-dehydrocholesterol in modeling Smith-Lemli-Opitz syndrome

The phase behavior of egg sphingomyelin (ESM) mixtures with cholesterol or 7-dehydrocholesterol (7-DHC) has been investigated by independent methods: fluorescence microscopy, X-ray diffraction, and electron spin resonance spectroscopy. In giant vesicles, cholesterol-enriched domains appeared as large and clearly delineated domains assigned to a liquid-ordered (Lo) phase. The domains containing 7-DHC were smaller and had more diffuse boundaries. Separation of a gel phase assigned by X-ray examination to pure sphingomyelin domains coexisting with sterol-enriched domains was observed at temperatures less than 38 degrees C in binary mixtures containing 10-mol% sterol. At higher sterol concentrations, the coexistence of liquid-ordered and liquid-disordered phases was evidenced in the temperature range 20 degrees -50 degrees C. Calculated electron density profiles indicated the location of 7-DHC was more loosely defined than cholesterol, which is localized precisely at a particular depth along the bilayer normal. ESR spectra of spin-labeled fatty acid partitioned in the liquid-ordered component showed a similar, high degree of order for both sterols in the center of the bilayer, but it was higher in the coexisting disordered phase for 7-DHC. The differences detected in the models of the lipid membrane matrix are said to initiate the deleterious consequences of the Smith-Lemli-Opitz syndrome.