Single-Camera 3D PTV Methods for Evaporation-Driven Liquid Flows in Sessile Droplets

The experimental characterization of liquid flows in sessile evaporating droplets is an important task for the fundamental understanding of the complex phenomena occurring in these apparently simple systems. The liquid flow induced by the droplet evaporation has a strong three-dimensional character and conventional visualization methods are typically difficult to apply. A more effective approach is to look inside the droplets from the substrate where the droplet lies and use single-camera 3D particle tracking velocimetry (PTV) methods to reconstruct the whole flow field. This paper discusses the implementation of an experimental setup for the quantitative characterization of the flow inside sessile evaporating droplets based on two single-camera 3D PTV methods: the Astigmatic Particle Tracking Velocimetry (APTV) and the General Defocusing Particle Tracking (GDPT). Exemplary results on different types of sessile evaporating droplets are reported and discussed. The presented approach is easy to implement, does not require special or costly equipment, and has the potential to become a standard tool for this type of experiments.</p

Migration of droplets driven by thermocapillary effects

Se estudia el desplazamiento de gotas, en dos dimensiones y bajo condiciones de mojabilidad parcial, ubicadas sobre un sustrato calentado en forma no uniforme. Se resuelve la ecuación que gobierna el perfil de altura de la gota, bajo las hipótesis de lubricación. El modelado incluye el efecto de la mojabilidad parcial (ángulo de contacto no nulo) mediante un termino que representa las fuerzas intermoleculares entre el sustrato y el líquido. En vez de asumir una forma fija para la forma de la gota, como en trabajos previos, aquí se resuelve la evolución temporal del perfil de altura. Hemos identificado dos regímenes de flujo y una zona de transición.We study the thermocapillary migration of two dimensional droplets of partially wetting liquids on a nonuniform heated substrate. An equation for the thickness profile of the droplet is solved under the hypothesis of the lubrication theory. The model includes the effect of a non-zero contact angle introduced through a disjoiningconjoining pressure term. Instead of assuming a fixed shape for the droplet, as in previous works, here we allow the droplet to change its profile with time. We identify and describe two different regimes and a transition zone.Fil: Gomba, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física Arroyo Seco; ArgentinaFil: Homsy, G. M.. University of California; Estados Unido

Morphology selection of nanoparticle dispersions by polymer media

A systematic theory of ultrathin polymer films as organizing media to achieve 2D nanoparticle arrangements was developed. The key physical variables to achieve nanoparticle dispersions and control morphology were determined.open727

TRANSITION METAL OXIDES AS MATERIALS FOR ADDITIVE LASER MARKING ON STAINLESS STEEL

The product information plays an important role in the improvement of the manufacturing, allowing the tracking of the part through the full life cycle. Laser marking is one of the most versatile techniques for this purpose. In this paper, a modification of the powder bed selective laser melting for additive laser marking of stainless steel parts is presented. This modification is based on the use of only one transition metal oxide chemically bonded to the stainless steel substrate, without using any additional materials and cleaning substances. The resulting additive coatings, produced from initial MoO3 and WO3 powders, show strong adhesion, high hardness, long durability and a high optical contrast. For estimation of the chemical and structural properties, the Raman and X-Ray Diffraction (XRD) spectroscopy have been implemented. A computer model of the process of the laser melting and re-solidification has been developed as well. A comparative analysis of the properties of both (MoO3 and WO3) additive coatings has been performed. An attempt for a qualitative explanation of the thermo-chemical phenomena during the marking process has been undertaken

Computational Image Analysis of Guided Acoustic Waves Enables Rheological Assessment of Sub-nanoliter Volumes

We present a method for the computational image analysis of high frequency guided sound waves based upon the measurement of optical interference fringes, produced at the air interface of a thin film of liquid. These acoustic actuations induce an affine deformation of the liquid, creating a lensing effect that can be readily observed using a simple imaging system. We exploit this effect to measure and analyze the spatiotemporal behavior of the thin liquid film as the acoustic wave interacts with it. We also show that, by investigating the dynamics of the relaxation processes of these deformations when actuation ceases, we are able to determine the liquid’s viscosity using just a lens-free imaging system and a simple disposable biochip. Contrary to all other acoustic-based techniques in rheology, our measurements do not require monitoring of the wave parameters to obtain quantitative values for fluid viscosities, for sample volumes as low as 200 pL. We envisage that the proposed methods could enable high throughput, chip-based, reagent-free rheological studies within very small samples

Capillary forces exerted by a water bridge on cellulose nanocrystals: the effect of an external electric field

Capillary forces play an important role during the dewatering and drying of nanocellulosic materials. Traditional moisture removal techniques, such as heating, have been proved to be deterimental to the properties of these materials and hence, there is a need to develop novel dewatering techniques without affecting the desired properties of materials. It is, therefore, important to explore novel methods for dewatering these high-added-value materials without negatively influencing their properties. In this context, we explore the effect of electric field on the capillary forces developed by a liquid-water bridge between two cellulosic surfaces, which may be formed during the water removal process following its displacement from the interfibrillar spaces. All-atom molecular dynamics (MD) simulations have been used to study the influence of an externally applied electric field on the capillary force exerted by a water bridge. Our results suggest that the equilibrium contact angle of water and the capillary force exerted by the water bridge between two nanocellulosic surfaces depend on the magnitude and direction of the externally applied electric fields. Hence, an external electric field can be applied to manipulate the capillary forces between two particles. The close agreement between the capillary forces measured through MD simulations and those calculated through classical equations indicates that, within the range of the electric field applied in this study, Young-Laplace equations can be safely employed to predict the capillary forces between two particles. The present study provides insights into the use of electric fields for drying of nanocellulosic materials

A frequency-response-based method of sound velocity measurement in an impedance tube

A stable and accurate new method for the measurement of the velocity of sound is proposed. The method is based on the characteristics of the frequency response measured at different positions in an impedance tube and it eliminates adverse effects caused by reflections from the transmitting transducer at the bottom of the impedance tube. A series of experiments is conducted, at different water temperatures, different positions in the impedance tube and under constant pressure, to validate the feasibility and stability of the new method. The new technique is also extended to hydrostatic pressure conditions with stable sound velocity. Our method generates an accurate measurement result in comparison to the estimated or average value obtained with currently existing methods. The novel method is suitable to be widely used in underwater acoustics

Heliconical smectic phases formed by achiral molecules

M.S. acknowledges the support of the US National Science Foundation I2CAM International Materials Institute Award, Grant DMR-1411344 and NSF grant DMR-1307674. D.P., E.G. acknowledges the support of the National Science Centre (Poland) under the grant no. 2016/22/A/ST5/00319. R.W. gratefully acknowledges the Carnegie Trust for the Universities of Scotland for the award of a PhD studentship. The beamline 11.0.1.2 at the Advanced Light Source at the Lawrence Berkeley National Laboratory is supported by the Director of the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02- 05CH11231. Addendum: Heliconical smectic phases formed by achiral molecules Published: 17 July 2018, https://doi.org/10.1038/s41467-018-05334-x "We would like to make our readers aware of the related publications by S.P. Sreenilayam et al. (Nat. Commun. 7, 11369 (2016) and Phys. Rev. Mat. 1, 035604 (2017)), which report the spontaneous helix formation in a polar smectic liquid crystal phase made of achiral bent-core mesogens."Peer reviewedPublisher PD

Simulation of surfactant transport during the rheological relaxation of two-dimensional dry foams

We describe a numerical model to predict the rheology of two-dimensional dry foams. The model accurately describes soap film curvature, viscous friction with the walls, and includes the transport of surfactant within the films and across the vertices where films meet. It accommodates the changes in foam topology that occur when a foam flows and, in particular, accurately represents the relaxation of the foam following a topological change. The model is validated against experimental data, allowing the prediction of elastic and viscous parameters associated with different surfactant solutions