KRÜSS Surface Science Hub
interfacial Science and Surface Engineering Lab
Droplet dynamics relates to the study of the behaviour of droplets, especially during the time in which the droplet is being manipulated by an external force.
Microfluidics is the science and technology of systems that process or manipulate small (10 -9 to 10 -18 liters) amounts of fluids using channels with dimensions of tens to hundreds of micrometres. With this range of small dimensions, surface forces, inertial forces, and viscous forces are dominate over gravitational forces. It has numerous applications in biomedical research, food and chemical industries to achieve high-throughput separation of purified plasma or purification of drinking water from water-borne pathogens.
Relating to our studies, this category is the collection of how droplets effect the transfer of heat in a system. This includes the evaporative cooling of an object as the liquid changes states into a gas, as well as the use of the liquids themselves to carry heat from one location to another as the bulk liquid flows (utilising the thermal capacity of the liquid).
The preparation of surfaces with different types of wettability profiles for varying applications. A frequent approach is growth of nano- and micro-structures on metal surfaces through chemical etching, which is then followed by surface modification with low surface energy materials to endow the surfaces with water repellency. Besides the wet chemical method, solvent-less methods have been developed to create contrasting patterns of wettability on a substrate. Surfaces with wettability contrast can be used for fog harvesting and guided fluid transport.
The knowledge of droplet adhesion and shedding is paramount in the development of anti-icing coatings, which will increase the efficiency of windmills in a cold region, agricultural industry and many more. If the adhesion force of a droplet is overcome by the external aerodynamic or other body forces on the drop, then the shedding of droplet takes place. The droplet adhesion or shedding can be also be quantified by the characterisation of substrate.
Electrohydrodynamics (EHD) is related with the study of the dynamic response of fluids that are under the application of electric fields. It has already been proven that a sessile drop on a dielectric will spread when a potential difference is applied, and this phenomenon is usually referred as Electrowetting. Electrowetting is described by the Young-Lippmann’s equation, which predicts the change in the contact angle of the drop as a function of the applied voltage. The better understanding of the transient dynamic of Electrowetting can allow to improve the performance of devices based on this phenomenon as liquid lenses, labs on a chip, and electronic paper.
The competition between capillary forces and gravitational forces is crucial in many field of sciences ranging from microfluidics to 3D printing. It has already been proven that, if the characteristic length of a droplet is smaller than the capillary length (Bond number << 1 ), the behaviour of a droplet is unaffected by gravity. However, a flawless drop deposition technique in microgravity is yet to be discovered. Moreover, understanding the effect of gravitational forces on physical phenomena governed by the interfacial or surface tension driven forces has led us to explore a new area of research: 3D printing in on board space vehicles.
Magnetohydrodynamics (MHD) is the field of science which involves the study of the interaction between a magnetic field and electrically conducting fluids. We are focusing on the effect of the magnetic field on the spreading, impact, freezing and coalescing of droplets. There is a significant influence of magnetic field on the impact of a ferrofluid droplet. The maximum spreading diameter of a droplet, upon impact, can be manipulated by the magnetic field. By applying the magnetic field, the parameter related to solidification or freezing of a droplet can
be also be varied. The knowledge of MHD can be utilised in 3D metal printing, manufacturing, anti-cancer drug delivery.
High Pressure/High Temp
The behaviour of droplets under atmospheric/ambient conditions varies with the behaviour under high pressures and/or high temperatures. Super-critical fluids can interact differently with the substrates; additionally, by changing the temperature or pressure of the environment, the time-scale of the process may change, which may effect the dynamic interactions inside the system if one time-scale now dominates the other.
Projects in this category either do not fit within the typical areas of research that have been listed previously or the number of such projects do not warrant the creation of another category (for brevity purposes).