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Molecular dynamics simulations for calculation of the contact angle of surface nanodroplets and solid–liquid surface tension γ sl of linear triocontane (C 30 , left image) and four of its branched isomers (centre image is for 2,6,13,17, tetrapropyloctadecane (C 18 (C 3) 4)) are used to calculate line tension τ. The results reveal (left plots) that γ sl and line tension τ depend on surface oleophilicity/oleophobicity and molecular degree of branching (DB*). [Display omitted] • Developed a novel MD calculation method of surface nanodroplet line tension (τ). • Calculated Solid-liquid surface tension γ sl of linear and branched liquid alkanes, showed deviation from Young equation. • γ sl and τ signs depend on surface wettability, and their magnitude reduce with increased branching. • On the oleophilic surface, positive line tensions in the order of 10-10 for all alkanes. • On the oleophobic surface, τ is two orders of magnitude lower for branched alkanes. Surface nanodroplets have important technological applications. Previous experiments and simulations have shown that their contact angle deviates from Young's equation. A modified version of Young's equation considering the three-phase line tension (τ) has been widely used in literature, and a wide range of values for τ are reported. We have recently shown that molecular branching affects the liquid–vapour surface tension γ lv of liquid alkanes. Therefore, the wetting behaviour of surface nanodroplets should be affected by molecular branching. This study conducted molecular dynamics (MD) simulations to gain insight into the wetting behaviour of linear and branched alkane nanodroplets on oleophilic and oleophobic surfaces. We aim to examine the Young equation's validity and branching's effect on fundamental properties, including solid–liquid surface tension γ sl and line tension τ. The simulations were performed on a linear alkane, triacontane (C 30 H 62), as well as four of its branched isomers: 2,6,13,17-tetrapropyloctadecane,2,6,9,10,13,17-hexaethyloctadecane, 2,5,7,8,11,12,15-heptaethylhexadecane and 2,3,6,7,10,11-hexapropyldodecane. Nanodroplets with a diameter of approximately 15 nm were released onto the surfaces, and their contact angles were measured. Additionally, using a novel approach, the solid–liquid surface tension (γ sl), the validity of Young's equation and line tension for all alkane and surface combinations are determined. It was discovered that the calculated γ sl , deviated from the theoretical γ sl , Young predicted from Young's equation for all alkanes on oleophilic surfaces. However, this deviation was minimal for branched alkanes on the oleophobic surfaces but more significant for the linear alkane. The findings indicated that γ sl < 0 for oleophilic surfaces and γ sl > 0 for oleophobic surfaces. Moreover, it was observed that | γ sl | was lower for branched molecules and decreased as branching increased. Line tension values were then determined through a novel method, showing τ was positive for oleophilic surfaces ranging from 1.30 × 10-10 to 6.27 × 10-11N. On an oleophobic surface, linear alkane shows a negative line tension of −1.15 × 10-10N and branched alkanes up to two orders of magnitude lower values ranging from −2.09 × 10-12 to 2.43 × 10-11N. Line tension values between −1.15 × 10-10 and + 1.1 × 10-10N are calculated for various linear alkane and surface combinations. These findings show the dependence of line tension on the contact angle and branching, demonstrating that for linear alkanes, τ is significant, whereas, for branched alkanes, line tension is smaller or negligible for large contact angles. [ABSTRACT FROM AUTHOR]

Nucleation and growth is a technique widely used to prepare colloids, in which droplets are adsorbed onto substrate particles. Changing the contact angle of the substrates can greatly alter the morphology of the product particles. Here, we investigate the nucleation and growth of 3-methacryloxypropyltrimethoxysilane (MPTMS) both onto Stöber spheres and onto (cross-linked) MPTMS* spheres. The former results in 'snowman' particles with a cap-shaped MPTMS* compartment, and we show that their morphology is highly controllable via the MPTMS content in the reaction mixture. The contact angle of the MPTMS* compartment decreases with droplet diameter, suggesting that this wetting process is affected not only by surface tension but also by line tension. In contrast to Stöber spheres, MPTMS* substrate particles yield highly reproducible and tuneable 'engulfed-sphere' colloids with an internal reference axis (but a homogeneous mass distribution). These engulfed-sphere particles can be fully index-matched for confocal microscopy on account of their homogeneous refractive index. Suitable index-matching mixtures of polar and of low-polar media are presented, where cyclohexyl iodide (CHI) is introduced as a new medium for colloids of high refractive index. Finally, the index-matched engulfed-sphere colloids are self-assembled into (close-packed and long-range) plastic phases, and the particles' rotational diffusion inside the crystal phases is tracked via confocal microscopy. [ABSTRACT FROM AUTHOR]

Abstract: We examined the phase-separated structures of the mixed Langmuir–Blodgett (LB) films of C k H2 k +1COOH (HkA: k =17, 21) and C m F2 m +1C10H20COOH (FmH10A: m =6, 8) fabricated isothermally or after isobaric thermal treatments. Under isothermal fabrication conditions, disks and wire-type domains formed in the H17A/F6H10A LB films at high and low fabrication temperatures, respectively, because the line tension and dipole–dipole interaction were comparable with each other. The thermodynamically stable phases of H21A/F6H10A LB films at high and low fabrication temperatures were disks and polygonal domains, respectively. Isobaric thermal treatments of the Langmuir films affected the domain size and not the domain shape when the transfer temperature was the same. Isobaric thermal treatments were effective in controlling the domain size. The thermodynamically stable phases of both H17A/F8H10A LB films and H21A/F8H10A LB films were nanowires in the range of the fabrication temperatures studied. Isobaric thermal treatments of the Langmuir films did not affect the domain shape significantly and affected the domain size in both the LB films studied. The change in the value m of FmH10A was more effective in controlling the phase-separated structures of the mixed LB films than the value of k of HkA. [Copyright &y& Elsevier]

Abstract: We report a useful technique for the deposition of dyes in the form of J-aggregates using directed self-assembly on the micro- and nanopatterned templates fabricated from the phase-separated mixed Langmuir–Blodgett (LB) films. The patterns of the mixed LB films can be tuned by adjusting the intermolecular interactions between the film-forming molecules. We used the mixed LB films containing silane coupling agent for the fabrication of micro- and nanopatterned templates, taking advantage of the difference between the surface free energy of the patterned regions and that of the self-assembled monolayers of the silane coupling agent. Atomic force microscopy showed that dyes were deposited by casting, spin-coating and the LB technique in accordance with the patterns of the original mixed LB films. Emission spectroscopy revealed that J-aggregates were formed in the patterned films. We succeeded in obtaining nanopatterns of a cyanine dye in the form of J-aggregates on the templates. [Copyright &y& Elsevier]

Abstract: As-placed contact angle is the contact angle a drop adapts as a result of its placement on a surface. As expected, the as-placed contact angle, , of a sessile drop on a horizontal surface decreases with the drop size due to the increase in hydrostatic pressure. We present a theoretical prediction for which shows that it is a unique function of the advancing contact angle, , drop size, and material properties (surface tensions and densities). We test our prediction with published and new data. The theory agrees with the experiments. From the relation of the as-placed contact angle to drop size the thermodynamic equilibrium contact angle is also calculated. [Copyright &y& Elsevier]

Abstract: Contact angle measurements are of great importance in surface characterization but the practical use has often been limited to macroscopic dimensions (millimeters). Therefore, we have developed a confocal microscopy method that allows non-destructive measurements of both low (<30°) and high (30°–90°) contact angles. Low contact angles were measured by reconstructing the drop profile from the interference patterns in droplets condensed from atmospheric humidity. At higher contact angles water droplets with a small amount of fluorescein were sprayed onto the surfaces and 3D-image stacks were recorded and used to extract the contact angle. Suitable drop sizes were between a few up to about 50 μm radius, using a 40× magnification objective. Using drops >10 micrometers radius for microcontact angle measurements a good correlation was obtained between measured micro- and macrocontact angles. After microcontact angle measurements the surfaces were rinsed and heavy meromyosin motor fragments were adsorbed to the surface. Importantly, the sensitive actin propelling function of these motor proteins was not affected by the previous contact angle measurements using fluorescent droplets. This suggests that the methodology should be suitable for non-destructive characterization of different parts of micropatterned surfaces being developed for biological assays. [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]

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]

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]