-
On droplets coalescence in a quasi-2D fluid
Authors:
Christoph Klopp,
Alexey Eremin
Abstract:
The coalescence of droplets plays a crucial role in nature and modern technology. Various experimental and theoretical studies explored droplet dynamics in 3D and on 2D solid or liquid substrates. In this paper, we demonstrate the coalescence of isotropic droplets confined in thin quasi-2D liquids -- overheated smectic films. We observe the merging of micrometer-sized flat droplets using high-spee…
▽ More
The coalescence of droplets plays a crucial role in nature and modern technology. Various experimental and theoretical studies explored droplet dynamics in 3D and on 2D solid or liquid substrates. In this paper, we demonstrate the coalescence of isotropic droplets confined in thin quasi-2D liquids -- overheated smectic films. We observe the merging of micrometer-sized flat droplets using high-speed-imaging and analyse the shape transformations of the droplets on the timescale of milliseconds. Our studies reveal the scaling laws of the coalescence time, which exhibits a different dependence on the droplet geometry than in case of droplets on a solid substrate. A theoretical model is proposed to explain the difference in behaviour.
△ Less
Submitted 28 March, 2020;
originally announced March 2020.
-
Self similarity of liquid droplet coalescence in a quasi-2D free-standing liquid-crystal film
Authors:
Christoph Klopp,
Torsten Trittel,
Ralf Stannarius
Abstract:
Coalescence of droplets is an ubiquitous phenomenon in chemical, physical and biolog-ical systems. The process of merging of liquid objects has been studied during the pastyears experimentally and theoretically in different geometries. We introduce a uniquesystem that allows a quasi two-dimensional description of the coalescence process,micrometer-sized flat droplets in freely suspended smectic li…
▽ More
Coalescence of droplets is an ubiquitous phenomenon in chemical, physical and biolog-ical systems. The process of merging of liquid objects has been studied during the pastyears experimentally and theoretically in different geometries. We introduce a uniquesystem that allows a quasi two-dimensional description of the coalescence process,micrometer-sized flat droplets in freely suspended smectic liquid-crystal films. We findthat the bridge connecting the droplets grows linearly in time during the initial stage ofcoalescence, both with respect to its height and lateral width. We also verify self-similardynamics of the bridge during the first stage of coalescence. We compare our resultswith a model based on the thin sheet equations.
△ Less
Submitted 12 February, 2020;
originally announced February 2020.
-
Brownian dynamics of elongated particles in a quasi-2D isotropic liquid
Authors:
Christoph Klopp,
Ralf Stannarius,
Alexey Eremin
Abstract:
We demonstrate experimentally that the long-range hydrodynamic interactions in an incompressible quasi 2D isotropic fluid result in an anisotropic viscous drag acting on elongated particles. The anisotropy of the drag is increasing with increasing ratio of the particle length to the hydrodynamic scale given by the Saffman-Delbrück length. The micro-rheology data for translational and rotational dr…
▽ More
We demonstrate experimentally that the long-range hydrodynamic interactions in an incompressible quasi 2D isotropic fluid result in an anisotropic viscous drag acting on elongated particles. The anisotropy of the drag is increasing with increasing ratio of the particle length to the hydrodynamic scale given by the Saffman-Delbrück length. The micro-rheology data for translational and rotational drags collected over three orders of magnitude of the effective particle length demonstrate the validity of the current theoretical approaches to the hydrodynamics in restricted geometry. The results also demonstrate crossovers between the hydrodynamical regimes determined by the characteristic length scales.
△ Less
Submitted 22 September, 2017; v1 submitted 21 September, 2017;
originally announced September 2017.
-
Realization of hydrodynamic experiments on quasi-2D liquid crystal films in microgravity
Authors:
Noel A. Clark,
Alexey Eremin,
Matthew A. Glaser,
Nancy Hall,
Kirsten Harth,
Christoph Klopp,
Joseph E. Maclennan,
Cheol S. Park,
Ralf Stannarius,
Padetha Tin,
William N. Thurmes,
Torsten Trittel
Abstract:
Freely suspended films of smectic liquid crystals are unique examples of quasi two-dimensional fluids. Mechanically stable and with quantized thickness of the order of only a few molecular layers, smectic films are ideal systems for studying fundamental fluid physics, such as collective molecular ordering, defect and fluctuation phenomena, hydrodynamics, and nonequilibrium behavior in two dimensio…
▽ More
Freely suspended films of smectic liquid crystals are unique examples of quasi two-dimensional fluids. Mechanically stable and with quantized thickness of the order of only a few molecular layers, smectic films are ideal systems for studying fundamental fluid physics, such as collective molecular ordering, defect and fluctuation phenomena, hydrodynamics, and nonequilibrium behavior in two dimensions (2D), including serving as models of complex biological membranes. Smectic films can be drawn across openings in planar supports resulting in thin, meniscus-bounded membranes, and can also be prepared as bubbles, either supported on an inflation tube or floating freely. The quantized layering renders smectic films uniquely useful in 2D fluid physics. The OASIS team has pursued a variety of ground-based and microgravity applications of thin liquid crystal films to fluid structure and hydrodynamic problems in 2D and quasi-2D systems. Parabolic flights and sounding rocket experiments were carried out in order to explore the shape evolution of free floating smectic bubbles, and to probe Marangoni effects in flat films. The dynamics of emulsions of smectic islands (thicker regions on thin background films) and of microdroplet inclusions in spherical films, as well as thermocapillary effects, were studied over extended periods within the OASIS (Observation and Analysis of Smectic Islands in Space) project on the International Space Station. We summarize the technical details of the OASIS hardware and give preliminary examples of key observations.
△ Less
Submitted 2 June, 2017;
originally announced June 2017.