Equilibrium Drop Shapes on a Tilted Substrate with a Chemical Step.

We calculate the equilibrium shape of a droplet sitting on a tilted substrate with a "chemical step", that is, different lypophilicity at the two sides of the step. This problem can be generalized to that of a droplet experiencing a body force, pushing it from the lyophilic part to the lyophobic part of the substrate. We present phase diagrams, in which we show for which droplet sizes there are dynamically inaccessible equilibrium shapes. We also identify what determines the threshold volume. While this given system was studied previously in the literature using contact angle hysteresis laws, we present the full static thermodynamical solution of the interfacial energy including the contact energy, while omitting the hysteresis effects from the contact line.

Morphology of Evaporating Sessile Microdroplets on Lyophilic Elliptical Patches.

The evaporation of droplets occurs in a large variety of natural and technological processes such as medical diagnostics, agriculture, food industry, printing, and catalytic reactions. We study the different droplet morphologies adopted by an evaporating droplet on a surface with an elliptical patch with a different contact angle. We perform experiments to observe these morphologies and use numerical calculations to predict the effects of the patched surfaces. We observe that tuning the geometry of the patches offers control over the shape of the droplet. In the experiments, the drops of various volumes are placed on elliptical chemical patches of different aspect ratios and imaged in 3D using laser scanning confocal microscopy, extracting the droplet's shape. In the corresponding numerical simulations, we minimize the interfacial free energy of the droplet, by employing Surface Evolver. The numerical results are in good qualitative agreement with our experimental data and can be used for the design of micropatterned structures, potentially suggesting or excluding certain morphologies for particular applications. However, the experimental results show the effects of pinning and contact angle hysteresis, which are obviously absent in the numerical energy minimization. The work culminates with a morphology diagram in the aspect ratio vs relative volume parameter space, comparing the predictions with the measurements.

Cloninger's temperament and character dimensions and dopaminergic genes: DAT1 VNTR and COMT Val158Met polymorphisms.

BACKGROUND: the objective of this study was to examine the associations between Cloninger temperament and character dimensions with the DAT1 VNTR and COMT Val158Met polymorphisms. SUBJECTS AND METHODS: The study was conducted on 101 subjects, consisting of students of the Police College in Zagreb and staff of the Sestre Milosrdnice University Hospital in Zagreb. The Cloninger Temperament and Character Inventory (TCI) was used to test personality traits. RESULTS: A main effect of the DAT1 VNTR polymorphism was found on the subscale self-directedness - SD2 (F=5.18, df=1, p<0.05), where a higher result was detected in carriers of the 9/9 genotype (M=7.33, SD=0.51) than those carrying the 10-repeat allele (M=6.02, SD=1.36). Also for the COMT Val158Met polymorphism, main effects were found on the subscales: NS3 (novelty seeking) (F=5.18, df=1, p<0.05), where a higher result was found in carriers of the Val allele (M=5.03, SD=2.22) than in carriers of the Met/Met genotype (MD=4.76, SD=2.37), SD3 (self-directedness) (F=5.18, df=1, p<0.05) where a higher result was found in carriers of the Val/Val genotype (M=4.50, SD=0.78) than in those carrying the Met allele (M=3.80, SD=1.31); C3 (cooperativeness) (F=5.18, df=1, p<0.05), where a high result was found in carriers of the Val allele (M=5.68, SD=1.25) than those carrying the Met/Met genotype (M=5.08, SD=1.11); and ST3 (self-transcendence) (F=5.18, df=1, p<0.05), where a higher result was found in carriers of the Met/Met genotype (M=3.46, SD=2.37) than carriers of the Val allele (M=2.69, SD=1.84). Two significant interactions were detected, on the subscale NS3 (novelty seeking) (F=5.18, df=1, p<0.05), and on the subscale C2 (cooperativeness) (F=5.18, df=1, p<0.05). CONCLUSIONS: Cloninger's (1987) hypothesis about negative relationship between novelty seeking and dopamine was confirmed on allele level, because higher novelty seeking was found in Val allele carriers comparing to Met/Met genotype carriers.

Sessile Nanodroplets on Elliptical Patches of Enhanced Lyophilicity.

We theoretically investigate the shape of a nanodroplet on a lyophilic elliptical patch in lyophobic surroundings on a flat substrate. To compute the droplet equilibrium shape, we minimize its interfacial free energy using both Surface Evolver and Monte Carlo calculations, finding good agreement between the two methods. We observe different droplet shapes, which are controlled by the droplet volume and the aspect ratio of the ellipse. In particular, we study the behavior of the nanodroplet contact angle along the three-phase contact line, explaining the different droplet shapes. Although the nanodroplet contact angle is constant and fixed by Young's law inside and outside the elliptical patch, its value varies along the rim of the elliptical patch. We find that because of the pinning of the nanodroplet contact line at the rim of the elliptical patch, which has a nonconstant curvature, there is a regime of aspect ratios of the elliptical patch in which the nanodroplet starts expanding to the lyophobic part of the substrate, although there is still a finite area of the lyophilic patch free to be wetted.

How a Surface Nanodroplet Sits on the Rim of a Microcap.

The location and morphology of femtoliter nanodroplets that nucleate and grow on a microcap-decorated substrate in contact with a liquid phase were investigated. We experimentally examined four different wetting combinations of the flat area and the microcaps. The results show that depending on the relative wettability, the droplets sit either on the plain surface or on the top of the microcap or on the rim of the microcap. The contact angle and, for the last case, the radial positions of the nanodroplets relative to the microcap center were characterized, in reasonable agreement with our theoretical analysis, which is based on an interfacial energy minimization argument. However, the experimental data show considerable scatter around the theoretical equilibrium curves, reflecting pinning and thus nonequilibrium effects. We also provide the theoretical phase diagram in parameter space of the contact angles, revealing under which conditions the nanodroplet will nucleate on the rim of the microcap.

Effect of Disjoining Pressure on Surface Nanobubbles.

In gas-oversaturated solutions, stable surface nanobubbles can exist thanks to a balance between the Laplace pressure and the gas overpressure, provided the contact line of the bubble is pinned. In this article, we analyze how the disjoining pressure originating from the van der Waals interactions of the liquid and the gas with the surface affects the properties of the surface nanobubbles. From a functional minimization of the Gibbs free energy in the sharp-interface approximation, we find the bubble shape that takes into account the attracting van der Waals potential and gas compressibility effects. Although the bubble shape slightly deviates from the classical one (defined by the Young contact angle), it preserves a nearly spherical-cap shape. We also find that the disjoining pressure restricts the aspect ratio (size/height) of the bubble and derive the maximal possible aspect ratio, which is expressed via the Young angle.