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Cholesterol may affect the activity of microbial toxins in a direct, specific way, or it may exert indirect effects because of its role in membrane fluidity, membrane line tension, and in the stabilization of rafts in the cytoplasmic membrane. The thiol-activated toxins of gram-positive bacteria, and the cytolysin of Vibrio cholerae are presented as examples of specific toxin–cholesterol interaction. Several mechanisms of indirect effects of cholesterol are discussed using examples such as Staphylococcus aureus α-hemolysin, aerolysin, and diphtheria toxin. [Copyright &y& Elsevier]

From a thermodynamic point of view, the concept of line tension is on solid ground; it is well recognized and defined. There is a notion in the literature that there is little consensus with regards to magnitude or sign of line tension. Partly, inappropriate comparisons of line tension values may have contributed to the current uncertainty, especially some between theoretical and experimental values. A wide range of reported line tension values may not necessarily be a result of conflicting findings, but it may reflect the diversity of systems studied. However, differences among similar approaches and systems observed are sometimes caused by one or several of the following factors: difficulties in sample preparation, poor experimental techniques, non-equilibrium, or conceptual and theoretical difficulties and oversimplifications. It is important to clearly establish the magnitude and sign of line tension as it may determine its relevance to technological applications such as microfluidic systems.This review has examined a wide range of recent and past studies on the subject of line tension. The review classifies line tension studies into theoretical and experimental; it further groups the studies into liquid–liquid–vapor and solid–liquid–vapor systems for each category. The review provides a comparison between similar studies in an attempt to clarify the current status of line tension research. The majority of theoretical line tension studies (excluding the near wetting studies) have estimates for line tension of about 10-10 N; however, for special cases, values as high as 10-6 N are also reported. There is less consensus regarding the sign for the line tension as theoreticians often assert that line tension can have either a positive or a negative sign. In experimental studies of liquid–liquid–vapor systems the majority of studies reported positive values for line tension; for film studies, the magnitude of line tension reported was between 10-9 and 10-7 N, whereas for studies of liquid lens values as high as 10-6 N were also reported. The clear majority of studies for solid–liquid–vapor systems reported a positive sign for line tension. In studies involving particles, line tension values ranged from 10-9 to 10-6 N. Studies using drop size dependence of contact angles reported values mostly in the span of 10-9–10-6 N; however, a clear majority of the reported values fell in the higher end of the above range. The special topic of line tension near wetting was also studied. While the interface displacement model appears to have brought about consensus with respect to certain aspects of line tension behavior near wetting, this model maybe still too phenomenological to be satisfactory from a more fundamental standing. Experimentalists have just begun studying line tension for systems near wetting, this is encouraging, but more comprehensive studies are needed. [Copyright &y& Elsevier]

The quasi equilibrium of a liquid lens or a liquid drop on a solid substrate is considered on the basis of the thermodynamics of microscopic thin liquid films. Both contact angles, corresponding to the membrane model and to the finite thickness layer convention of the film, have been derived as a function of the disjoining pressure isotherm. The analytical expressions for the line tension terms have been obtained, and the criterion for the stability of a liquid drop on a solid substrate has been proposed. [ABSTRACT FROM AUTHOR]

The Gibbsian thermodynamics of adsorption at a line of three-phase contact is briefly recalled. The adsorptions are obtained as derivatives of the line tension with respect to the independent field variables in the system. The law with which the adsorptions diverge at a wetting transition is obtained and discussed. A possible application of the results is to three-phase equilibrium in a three-component fluid mixture, in particular, at the wetting transitions that could occur between the system’s two critical endpoints. [Copyright &y& Elsevier]

To study theoretically the physics of the interface between liquid ordered (“raft”) and liquid disordered domains in biological cells and bilayer lipid membranes, we approximated this complex system by considering the energetics of one planar lipid monolayer leaflet at the interface between two regions of different thickness. Because it is energetically unfavorable to expose the hydrophobic lipid tails of the thicker region to water, lipid molecules deform near the interface in order to diminish the area of the acyl chain-water contact. This deformation is used to calculate the interfacial line tension. Leaflets are treated as a continuous elastic medium and the spatial distribution of deformations and the line tension are obtained by minimizing the total (elastic and hydrophobic) energy of the monolayer. Using reasonable values of elastic and spatial parameters, we found that lipid deformation completely eliminates any hydrophobic contact with water due to thickness differences. The energy of the system is therefore determined exclusively by the elastic deformation of the monolayer. Lipid deformations occur over a narrow region of ∼2–4 nm near the interface boundary. The value of the monolayer line tension is calculated to be ∼0.5kT/nm for a ∼0.5 nm difference in monolayer thickness. This value of the line tension is sufficient to maintain the circular shape of cholesterol–sphingolipid domains observed in lipid bilayer membranes. The energy of interaction of two thick domains separated by a thinner domain is obtained: thick domains attract from a distance of 1–2 nm. [Copyright &y& Elsevier]

Contact angle measurements for three n-alkanes, heptane, octane, and nonane, on two different self-assembled surfaces (SAM) are reported as a function of drop size. These liquids all formed low contact angles (below 20°); the measurements were performed using an accurate method for systems with low contact angle, ADSA-D. The observed drop size dependence of the contact angles was interpreted using the modified Young equation. It was concluded that the observed drop size dependence of contact angles was due to line tension. The choice of systems also provided the opportunity to examine the behavior of the line tension for systems near wetting (i.e., low contact angles). It was determined that the line tension is positive and ranges from below 10−7 to just below 10−6 J/m for the systems studied; the observations suggested that the line tension decreases as the contact angle decreases and likely vanishes at complete wetting. [Copyright &y& Elsevier]

Much research has been done on line tension measurement and interpretation, and attempts have also been made to measure line tension with simple, cheap and reliable methods that do not require excessive sophistication. Of particular interest is the method of determining line tensions of solid–liquid–vapor systems from the capillary rise in a conical tube. This simple and relatively inexpensive method gives line tension values comparable to those reported in the literature obtained via highly sophisticated instruments or techniques such as the well known axisymmetric drop shape analysis technique. The absolute value of line tension obtained using the conical tube method and assuming a spherical liquid–vapor interface is larger but of the same order of magnitude (1 μJ m−1) as that reported in the literature. A theoretical analysis presented herein shows that by including the deformation of the liquid–vapor interface due to gravity in the conical capillary analysis, the line tension value inferred from the experimental data is reduced by approximately 50% and compares better with values in the literature obtained using other sophisticated methods. Thus a relatively simple, cheap, accurate and reliable method of line tension measurement has been advanced. [Copyright &y& Elsevier]

The preparation and properties of emulsions, stabilised solely by the adsorption of solid particles at the oil–water interface, are reviewed especially in the light of our own work with particles of well-controlled surface properties. Where appropriate, comparison is made with the behaviour of surfactant-stabilised emulsions. Hydrophilic particles tend to form oil-in-water (o/w) emulsions whereas hydrophobic particles form water-in-oil (w/o) emulsions. Many of the properties can be attributed to the very large free energy of adsorption for particles of intermediate wettability (contact angle at the oil–water interface, say, between 50 and 130°). This effectively irreversible adsorption leads to extreme stability for certain emulsions and is in contrast to the behaviour of surfactant molecules which are usually in rapid dynamic equilibrium between the oil–water interface and the bulk phases. There is evidence that, in some systems, weak flocculation of the particles improves the emulsion stability. Phase inversion from w/o to o/w can be brought about by increasing the volume fraction of water. Emulsions close to this inversion point tend to be the most stable, again in contrast to surfactant systems. The volume fraction needed for inversion depends on the particle wettability and the nature of the oil and these effects have been rationalised in terms of surface energy components. Stable multiple emulsions (w/o/w and o/w/o) can be made using two types of particles with slightly different wettability. Similar multiple emulsions prepared with two types of surfactant tend to be much less stable. The possibility of preparing novel solid materials by evaporating solid-stabilised emulsions is also proposed. Finally we report on some extensions to the work of Levine et al. who obtained expressions for the free energy of formation of emulsion drops covered with close-packed monolayers of monodisperse spherical particles. In particular in the light of the observations that nanoparticles can act as excellent emulsion stabilisers, we have considered potential effects on the free energy of emulsion formation of the action of small (physically realistic) positive and negative line tensions in the 3-phase contact lines skirting particles adsorbed at the droplet interfaces. We also explore the possibility that curvature properties of close-packed particle monolayers can affect emulsion properties in much the same way that surfactant monolayer properties influence emulsion type and stability. [Copyright &y& Elsevier]

We previously established that compression of monolayers containing the lipids in pulmonary surfactant, with or without the surfactant proteins, initially leads to phase separation. On further compression, however, phase coexistence terminates at a critical point that requires the presence of cholesterol. The studies reported here address the changes in the phospholipid phase diagram produced by cholesterol. We used the two systems of the lipids from calf surfactant with and without the surfactant proteins. For both systems, we began with the postulate that cholesterol had no effect on the composition of other constituents in the two phases, and then used the known behavior of interfacial tension at a critical point to test the two extreme cases in which the cholesterol partitions exclusively into condensed domains or into the surrounding film. Measurements of surface potential along with the fraction of the nonfluorescent area and the radius of the domains, both obtained by fluorescence microscopy, for films with and without cholesterol allowed calculation of the interfacial tension between the two phases. Only the model that assumes the presence of cholesterol within the domains accurately predicts a decreasing line tension during film compression toward the critical point. That model, however, also predicts an unlikely decrease during compression of the dipole moment density for the condensed phase. Our results are best explained in terms of cholesterol partitioning predominantly into the condensed domains, with a resulting partial redistribution of the phospholipids between the two phases. [Copyright &y& Elsevier]

We investigate the thermodynamics of inhomogeneous polymer melts in the framework of a coarse grained off-lattice model. Properties of the liquid–vapour interface and the packing of the melt in contact with an attractive wall are considered. We employ Monte Carlo simulations in the grand canonical ensemble to determine excess free energies, the wetting temperature and the pre-wetting line, as well as the pre-wetting critical point. Having determined the wetting properties and the phase diagram of the model polymer, we perform canonical Monte Carlo simulations of small droplets on a surface. This allows us to study the dependence of droplet size on the wetting properties. It is found that the contact angles of small droplets may be very much larger than those observed for macroscopic drops. [Copyright &y& Elsevier]

A first-order phase transition has been studied by Brewster angle microscopy in mixed monolayers of 2-hydroxyethyl laurate (2-HEL) and two anionic surfactants, sodium 3,6,9,12-tetraoxa-octacosanoate (TOOCNa) and sodium 3,6,9,12-tetraoxa-triacontanoate (TOTCNa) at the air–water interface. Condensed phase domains are observed on the surface of a mixed solution containing 1.0×10−5 M each of 2-HEL and of TOOCNa or TOTCNa up to 20 °C. This concentration of 2-HEL is much lower than that required for the phase transition in the pure system at the studied temperatures. The phase transition pressures (πt) of all the systems increase with increasing temperature. The πt of 2-HEL-TOOCNa system almost corresponds to that of pure 2-HEL at a definite temperature. In contrast, the πt of 2-HEL-TOTCNa system is lower than the corresponding value of 2-HEL. The shapes and the textures of the domains formed in the mixed system are different to those formed in the pure system. The formed domains in the mixed system have a circular shape with internal segments whereas those of 2-HEL have a fingering pattern with an optical isotropy at the same temperature. A large variety of defects are found in the domains formed in the mixed system. Furthermore, these domains undergo fusion while touching each other. [Copyright &y& Elsevier]

Ordinary dislocations in γ-TiAl frequently cross-slip onto various non-primary slip planes at high temperatures. The anomalous hardening in γ-TiAl was believed to be linked to cross-slip behavior. Therefore, the stability of ordinary dislocations and the interaction energy of kink pairs or jog pairs in these cross-slip planes were examined to understand the cross-slip behavior. The energy factors and line tension for 1/2〈110] screw dislocations in γ-TiAl were calculated on the basis of the Sextic formalism. Inverse Wulff plots were applied to determine the instability of dislocations on (111), (110) and (001) glide planes. The dislocations are stable due to the convexity of the plots and always have positive line tension. The interaction energy in kink pairs on the cross-slip planes were calculated. The results show that the interaction energy was highly anisotropic in the cross-slip planes and was found to be the minimum on the (110) plane, which is consistent with the transmission electron microscopy (TEM) observations in the literature. The temperature effects on the stability and interaction energy were also investigated using six independent elastic constants at different temperatures. [Copyright &y& Elsevier]

We have used atomic force microscopy (AFM) to image liquid droplets on solid substrates. The technique is applied to determine the contact line tension. Compared to conventional optical contact angle measurements, the AFM extends the range of accessible drop sizes by three orders of magnitude. We analyze the global shape of the droplets and the local profiles in the vicinity of the contact line. These two approaches show that the optical measurement overestimates the line tension by approximately four orders of magnitude. [ABSTRACT FROM AUTHOR]

The solvation of a wedge can be related to that of planar pores by employing an interface displacement or Derjaguin analysis. This approach implies that the line tension and solvation force for a wedge are proportional to an amplitude defined from averaging the planar pore solvation potential over all possible pore widths, times simple monotonic functions of the wedge angle θ. At small values of θ all sensible choices lead to the same angular dependence. The amplitude is a well known quantity in colloidal science, linked directly to the barrier for flocculation by the depletion effect. [Copyright &y& Elsevier]

The possibility of determining the topography of liquid profiles by scanning force microscopy (SFM) in tapping mode is discussed in detail as to its possible mechanism and accuracy. Applications of this technique to the investigation of contact line tensions and effective interface potentials are presented. Two complementary methods, both based on SFM of the liquid topography, are demonstrated for determining contact line tensions. The values obtained are within the theoretically expected range. [ABSTRACT FROM AUTHOR]

Advancing and receding contact angles on individual hydrophobic microspheres at the air-water and liquid-liquid, namely hexadecane-water, interfaces were determined. For this purpose, spherical silanated silica particles(R = 2.35 μm) and polystyrene particles of different radii (R = 1.80-4.38 μm) were attached to atomic force microscope (AFM) cantilevers. Polystyrene particles were sintered onto the AFM cantilevers to provide stability in organic solvent. Then the equilibrium position of the microsphere at the air-water interface of a drop or an air bubble was measured with an AFM-related set-up. From the equilibrium position the contact angles were calculated. Advancing and receding contact angles determined with silanated silica particles (Θa = 97° and Θr = 81°) agreed roughly with contact angles measured on similarly prepared planar surfaces (Θa = 95° and Θr = 83°). The apparent contact angles measured on polystyrene particles decreased with increasing particle size. This can be interpreted by assuming a negative line tension of the order of -0.3 μN. [ABSTRACT FROM AUTHOR]

[Display omitted] • High [Ca2+] increases the thickness difference and line tension between phases. • Speed of domain shape relaxation produces line tension in the 0.1−1 pN range. • Line tension and thickness mismatch between phases are related. • Surface behavior in multilayers and monolayers of myelin show a good correlation. Purified myelin membranes (PMM) were spread as monomolecular films at the air/aqueous solution interface, and visualized by Brewster Angle Microscopy (BAM) at different lateral pressures (π) on three specific aqueous solutions: absence of salts, physiological conditions and presence of calcium. Coexistence of Liquid-Expanded (LE) and Liquid Ordered (LO) phases persisted up to collapse in the presence of salts, whereas monolayers became homogeneous at π ≥ 35−40 mN/m when salts are absent. This PMM phase-mixing behavior in monolayers is similar to the previously reported behavior of PMM multilamellar vesicles. Reflectivities (R p) of p-polarized light from both phases were assessed throughout the whole π -range, and film thicknesses (t) were calculated from the R p values and measured film refractive indices (n). The LO phase was found to be more reflective and thicker than the LE phase at π ≤ 15 mN/m, but less reflective and thinner at higher π. We also determined the line tension (λ) of PMM monolayers at the domain boundaries from the rate of domain shape relaxation, which turned out to be of the order of picoNewtons (pN) and decreased as π increased. A correlation between λ and thickness differences (Δ t) was found, suggesting that Δ t is a molecular determinant for λ in PMM monolayers. Both λ and Δ t were found to increase markedly when calcium was present in the subphase. This result corroborates the concept of divalent cations as a stabilizing factor for phase separation, in line with earlier studies on this mixture forming multilamellar membrane arrangements. [ABSTRACT FROM AUTHOR]

Four-component phase diagrams reveal that Liquid-disordered + liquid-ordered (Ld + Lo) nanodomains are exclusively found adjacent to a three-phase region, and so cannot be a one-phase microemulsion. Of importance for understanding biological membranes, a small change in lipid bilayer composition can change the size of these coexisting phase domains hundreds of fold, between tens of nanometers and microns. Nanodomain diameter, measured from small angle neutron scattering, is in the range 15–35 nm, consistent with stabilization by repulsive dipole fields. Ld/Lo line tension controls the Ld + Lo domain size transition. Other than size, chemical and physical properties of the phase domains do not seem to change during the transition. Unfavorable lipid-lipid pairwise interactions, rather than phase thickness mismatch, seem to be the main reason for Ld + Lo immiscibility. Pairwise interactions of cholesterol-phospholipid seem to be favorable, whereas pairwise interactions of high-melting phospholipid with low-melting phospholipid are unfavorable. Measured Ld/Lo line tension, like the phase separation, is created mainly by unfavorable lipid-lipid pairwise interactions. Lipid dipole-dipole repulsion opposes these unfavorable lipid-lipid pairwise interactions and thus, in a sense, is the reason that nanodomains form. Bilayer physical and chemical properties measured from macroscopic domains of coexisting Ld + Lo phases should be good approximations for the properties of coexisting nanoscopic domains. [Display omitted] • Unfavorable lipid-lipid pairwise interactions explain liquid-disordered/liquid-ordered line tension • Ld + Lo phase nanodomains result from lipid dipolar repulsion that opposes unfavorable lipid-lipid pairwise interactions • Physical and chemical properties of macroscopic Ld + Lo domains are good approximations for those properties of nanodomains [ABSTRACT FROM AUTHOR]

A mechanical model description is presented of the transition zone between a thin soap (emulsion) film and its adjacent meniscus. The mechanical state of the system is described by introducing three surfaces of tension - two of them are at the surfaces of the film and the transition zone and constant surface tensions are attributed there; the central surface of tension divides the distance between the other two surfaces of tension in inverse ratio of their surface tensions. The disjoining pressure like the capillary pressure acts always normal to the phase surfaces of tension. This model is applied for calculating the line tension of the contact line film/meniscus. Thus a new way of deriving the formula of de Feijter and Vrij for line tension at thin liquid films is presented. The asymmetric case of emulsion films is also considered. [ABSTRACT FROM AUTHOR]

The reverse Wilson chamber method (RWC), developed for heterogencous nucleation investigation is applied to critical supersaturation measurements and determination of the surface concentration of nuclei (droplets) vs. supersaturation dependence in the case of nucleation from supersaturated water vapors on n-dodecane substrate. The experimental results obtained are interpreted in terms of the classical (Volmer) theory of heterogeneous nucleation as well as in the framework of the theory of barrierless nucleation. The several times lower critical supersaturations measured at four different temperatures, covering the range between 20° and 35° C, are explained by taking into account the effect of the negative line tension of three-phase contact. The temperature dependence of line tension for the three-phase system n-dodecane/water/water vapor is extracted from the data to fir the theory. The results obtained are in complete disagreement with those ones obtained by Wu and Maa for the same system using jet-tensimeter technique, however, in another temperature interval. This discrepancy is discussed in detail in the text. [ABSTRACT FROM AUTHOR]

The pressure in the Reverse Wilson Chamber (RWC) was directly measured at different rates of compression of the gas mixture. It was shown that at compression time Τ in the range from 0.06 to 0.3 s an intermediate, between adiabatic and isothermal, process took place in the chamber. To obtain the relative pressure increase δ P/ P from the values of the relative gas compression δ V/V, a calibration of the experimental set-up was carried out. The calibration showed that the values of critical supersaturation Sc for water condensation on hexadecane, estimated for intermediate regime of the gas compression, were reduced with respect to the values calculated when the adiabatic regime was assumed. This fact confirmed the conclusions made earlier [1-3] that the classical theory was not applicable in this case of heterogeneous phase formation and that the line tension κ < 0 should be taken into account. Moreover, in an atmosphere of very pure argon (instead of room air [1-3]) the critical supersaturation turned out to be independent of the initial state of undersaturation S. The more accurate values obtained for condensation of water on hexadecane were: ln S=0.204 (instead of the maximum value obtained earlier: ln S=0.26) and κ=−1.9×10 dyne (instead of κ=−1.5×10 dyne). [ABSTRACT FROM AUTHOR]

The interpretation of the critical supersaturation at water condensation on hexadecane, put forward in [3], is now completed with the treatment of the barrier mechanism of a new phase formation in the case of negative line tension ( κ<0). Instead of κ=−1.50×10 dynes, estimated in [3], a value of κ=−1.16×10 dynes is obtained here. However, the analysis of the extrapolation, through which the critical supersaturation is determined in [3], indicates that the sensitivity of detecting the initiation of the process of condensation used there corresponds most probably to the outset of barrierless phase formation. Therefore, the value of κ=−1.50×10 dynes obtained in [3] is accurate. [ABSTRACT FROM AUTHOR]

The impulse-adiabatic method of measuring the critical supersaturation (ln S) at water condensation on hexadecane is improved; the experiments are conducted with purer hexadecane than in previous work [2]. The dependence of In Son -ln S (undersaturation in the initial state) obtained earlier has been confirmed and the asymptotic value of ln S at sufficiently low humidity is established with better accuracy: In S=0.255≧0.26. With this value of ln S, the line tension κ is estimated to be −1.50×10 dyn, assuming that the established critical supersaturation refers to the onset of barrierless phase formation. [ABSTRACT FROM AUTHOR]

CO 2 has been considered as an effective fluid to replace CH 4 in shale rock. Wetting behavior of water in CO 2 /CH 4 mixtures in organic nanopores is a key parameter influencing CO 2 based enhanced gas recovery processes in shale. However, there is lack of fundamental understanding of water wetting in such systems. We perform Molecular Dynamics (MD) simulations of nanoscopic liquid water drops on a graphite substrate mimicking an organic-rich shale pore in the presence of CH 4 /CO 2 mixtures at temperatures in the range 300 K–400 K. The equilibrium contact angle of the water droplets on graphite is a pronounced function of CH 4 as well as CO 2 pressure with the water droplet lifting-off, that is reaching a 180° contact angle, at a threshold pressure of 12 MPa for CO 2 and 78 MPa for CH 4. The contact angles recovered from simulations match well with experimental literature via the modified Young's equation. The line tension in our studied systems does not show a specific dependence on temperature. As compared to methane, CO 2 exhibits a stronger interaction with organic-rich surfaces, which has strong impact on wettability. For CH 4 /CO 2 mixtures, this translates in an approximately linear increase of the contact angle with the CO 2 mole fraction. Image 1 • Microscopic equilibrium water contact angle on graphite and immersed in CH 4 or CO 2 is a pronounced function of pressure. • Line tension does exhibit a decrease with increasing contact angle. • Water contact angle in organic-rich nanopores immersed in CH 4 /CO 2 mixture increases linearly with the CO 2 mole fraction. • CO 2 exhibits stronger interaction with organic-rich surface and thus could replace adsorbed methane on organic rich shale. [ABSTRACT FROM AUTHOR]

Abstract: The problem of wetting is discussed in the framework of the variational approach. Derivation of the general equation describing the wetting of rough chemically homogenous surfaces is presented. The equation considers effects related to the line tension at the perimeter of the drop and at the details of the relief. The equation comprises as particular cases the Cassie and Wenzel equations and the equation proposed recently by Wong and Ho. [Copyright &y& Elsevier]

Abstract: It is shown that the force exerted by a monolayer bubble cluster on a confining plate, in the absence of gravity, equals one half of the cluster surface energy per unit length along the bubbles including the surface energy of the Plateau borders (PBs). The contribution of the PBs to the force can be accounted for in terms of their (negative) line tensions which oppose but never overcome the contractile film tensions. The PB line tension τ can be related to its excess energy ɛ defined as the energy of the PB surfaces minus the energy of the film prolongations into the PB, leading to τ = ɛ/2 in fairly dry foams, as found for other triple lines studied in the literature. At constant volume of gas in the bubbles, the force decreases as the liquid fraction ϕ L increases from zero, but may go through a minimum at intermediate ϕ L. For a honeycomb foam this minimum occurs for ϕ L ≅0.05. When the height, h, of the cluster is changed at constant volumes of gas and liquid, the force F decreases linearly with h −1/2. The effect of gravity on the force exerted on a transverse horizontal plate is briefly discussed. [Copyright &y& Elsevier]

A triangular lattice model for pattern formation by core-shell particles at fluid interfaces is introduced and studied for the particle to core diameter ratio equal to 3. Repulsion for overlapping shells and attraction at larger distances due to capillary forces are assumed. Ground states and thermodynamic properties are determined analytically and by Monte Carlo simulations for soft outer- and stiffer inner shells, with different decay rates of the interparticle repulsion. We find that thermodynamic properties are qualitatively the same for slow and for fast decay of the repulsive potential, but the ordered phases are stable for temperature ranges, depending strongly on the shape of the repulsive potential. More importantly, there are two types of patterns formed for fixed chemical potential—one for a slow and another one for a fast decay of the repulsion at small distances. In the first case, two different patterns—for example clusters or stripes—occur with the same probability for some range of the chemical potential. For a fixed concentration, an interface is formed between two ordered phases with the closest concentration, and the surface tension takes the same value for all stable interfaces. In the case of degeneracy, a stable interface cannot be formed for one out of four combinations of the coexisting phases, because of a larger surface tension. Our results show that by tuning the architecture of a thick polymeric shell, many different patterns can be obtained for a sufficiently low temperature. [ABSTRACT FROM AUTHOR]

We use phase contrast microscopy of red blood cells to observe the transition between the initial discocyte shape and a spiculated echinocyte form. During the early stages of this change, spicules can move across the surface of the cell; individual spicules can also split apart into pairs. One possible explanation of this behaviour is that the membrane forms large scale domains in association with the spicules. The spicules are formed initially at the rim of the cell and then move at speeds of up to 3 μm/min towards the centre of the disc. Spicule formation that was reversed and then allowed to proceed a second time resulted in spicules at reproducible places, a shape memory effect that implies that the cytoskeleton contributes towards stopping the spicule movement. The splitting of the spicules produces a well-defined shape change with an increase in membrane curvature associated with formation of the daughter pair of spicules; the total boundary length around the spicules also increases. Following the model in which the spicules are associated with lipid domains, these observations suggest an experimental procedure that could potentially be applied to the calculation of the line tension of lipid domains in living cells. Unlabelled Image • Spicules can move across the erythrocyte surface and can split spontaneously. • After spicule formation is reversed, spicules re-form at the same places. • Spicules behave like lipid domains with end positions determined by the cytoskeleton. • Well-defined shape changes provide a means for line tension calculation in cells. [ABSTRACT FROM AUTHOR]

An analysis of equilibrium size distributions of circular liquid-condensed (LC) domains in amphiphilic monolayers at the air/water interface, gleaned from microscopic images, is presented in terms of Gaussians fitted to a theoretical expression derived previously. It is demonstrated how, in principle, important properties of the monolayer, such as molecular dipole moments of surfactant head groups and line tension of the liquid-condensed/liquid-expanded phase boundary, can be obtained by combining the results of this simplified analysis with information from X-ray diffraction or surface pressure measurements. [Copyright &y& Elsevier]

Recent experiments have shown that certain molecular agents can selectively penetrate and aggregate in bacterial lipid membranes, leading to their permeability and rupture. To help reveal and understand the underlying mechanisms, here we establish a theory to show that the deformation energy of the membrane tends to limit the growth of molecular domains on a lipid membrane, resulting in a characteristic domain size, and that the domain aggregation significantly reduces the energy barrier to pore growth. Coarse-grained molecular dynamics simulations are performed to validate such domain aggregation and associated pore formation. This study sheds light on how lipid membranes can be damaged through molecular domain aggregation and contributes to establish a theoretical foundation for the next-generation membrane-targeting nanomedicine.