Biologists and physicists from Tyumen State University and National Research Nuclear University MEPhI are exploring the possibility of manipulating particles not only by heating the carrier medium, but also by reducing its temperature. This opens up broad prospects for the application of the proposed method in biological research and medicine, with the important being the absence of destruction of hot living objects.
Article by physicists at Tyumen State University's Photonics and Microfluidics Research Laboratory, Mohamed Al-Muzaiker, Natalia Ivanova, Viktor Flyagin and the National Nuclear Research University MEPhI Petr, "Transportation and Assembly of Particles through Marangoni Streams in Heating and Cooling Modes" Lebedev-Stepanov published in the journal Colloids and Surfaces A: Physical Chemistry and Technology. The operation of microparticles suspended in liquid media (including solid particles, polymers, cells, micelles, and proteins) and self-assembly of the formation of the desired structure and morphology on the surface for chemical and biomedical research, manufacturing of new electronic and optical industries, coatings and purification.
In most cases, the self-assembly or aggregation of particles is determined by the action of capillary flow, which brings particles to strong evaporation areas in the spontaneously evaporated liquid. A prominent example of the self-organization of particles in evaporated droplets is the coffee ring effect, i.e., the coffee particles form an annular structure after the droplets are dried.
Today, the method of forming the required particle collection form (pattern) in the evaporated colloid liquid can be divided into passive and active. For example, creating relief on a surface by etching or lithography, or by implementing a passive method by using an evaporation mask (so-called evaporation lithography) in an open system. However, the disadvantage of these methods is that the particles cannot be manipulated by adjusting the control parameters in real time.
Active method is the influence of external stimulation on the system, such as sound waves, inertia fields, and electromagnetic fields. Sound effects produce periodic pressure fields (stayed sound waves), resulting in corresponding distribution of large-scale particle sets. Recently, precise acoustic tweezers are needed to capture individual particles.
The applicability of the method based on magnetic and dielophoretic effects is limited by the specific properties of particles and media (polarization rate, magnetization rate, conductivity ). The use of optical tweezers provides high-precision operation of individual particles, but to control many particles requires complex optical settings and expensive optical tools to convert the beam time and space, which cannot be achieved by compact devices.
This paper proposes a method of manipulating particles in a layer of volatile liquids that are hundreds of microns thick, based on the symbol of changing the temperature gradient in the liquid through the local action of the heat source and the radiator to control Marangoni flow.
Scientists have clearly demonstrated that this method can be used to perform a wide range of operations on particle collections: assemble particles into circular patterns on substrates when heated, and transfer particles from the radiator when the substrate cools, by changing the symbol of temperature gradient during particle assembly.
research results show that in the heating mode, the particles gather in the heating zone in the form of a circular pattern, and the final area increases with the increase of the number of particles and decreases with the increase of the number of particles. Layer thickness. The latter is due to the dense multi-layered collection of particles lifted by upflow in the thick layer. A distinctive feature of the proposed method in
is that the reversible control and mode conversion can be performed by changing the symbol of the temperature gradient according to any requirement. In this case, a ring configuration can be created in addition to the circular assembly of the particles or surface cleaning.
Scientists also pointed out that setting the thickness of the carrier layer allows you to control the structure of the final pattern by creating a single or multi-layer structure. The ability to manipulate particles not only by heating the carrier medium, but also by reducing its temperature, opens up broad prospects for the proposed method used in biological research and medicine, where important is not to destroy hot living objects. Further research by physicists aims to develop a method for creating the desired morphological structure consisting of biological objects such as living cells and bacteria in nutrient medium.Scientists expect this approach to be a powerful tool to create artificial biological tissues of organs or as a tool to study bacteria. This work was funded by the Russian Foundation for Basic Research.
