Scientists showed how to manage motion of liquid in crystals with a help of heating
Scientists from Immanuel Kant Baltic Federal University made a numerical description how microscopic flows of substance in liquid crystals move under the influence of temperature change. It turned out that direction and velocity of motion of liquid crystals' components depend on the side of the material that heats. Obtained information will be useful for elaboration of microfluidic devices that can be used in systems of drug delivery and biomedical sensors. Results of the research are published in journal Crystals.
Liquid crystals are materials that combine characteristics of liquids and solid bodies. They are fluid, like liquids, but have uneven texture, like solid bodies. Liquid crystals are widely used for displays and temperature detectors due to their ability to change color depending on changes of the environment (for example, temperature, tension of magnetic or electronic fields). However, it is not yet clear how you can effectively manage properties of liquid crystals that lie in micro-or nanochannels—elements of microfluidic devices. Such constructions are perspective for medicine: on their base you can create systems of drug delivery and biosensors. In that case it is not always possible to use electric fields for management, because they can damage biological samples. As alternative you can use temperature gradients—gradual changes of temperature in liquid—that enable to manage the motion of molecules very softly.
Scientists from Immanuel Kant Baltic Federal University (Kaliningrad), Institute of Problems of Mechanical Engineering, Russian Academy of Sciences (St. Petersburg) and Poznan University of Economics (Poland) mathematically described the behavior of 10 micrometers width liquid crystal's layer, that is sandwiched between two surfaces with different temperatures.
Calculations showed that direction of heating greatly influences the direction and velocity of liquid. Thus, if you heat surface, that is situated over the liquid crystal, substance begins to "run" from the hot zone downwards, thus creating flow along the bottom cold surface. If you heat bottom surface, liquid, on the contrary, begins to move upwards, but slower, and the main flow appears in the center of liquid crystal's layer.
By this, authors mathematically proved that flows of liquid in microscopic channel are greatly influenced by compressibility of liquid crystal—its ability to change its density under external action. Thus, in contrast to incompressible (or practically incompressible) liquids, for example, water, liquid crystals form complex three-dimensional flows. They must be taken into account during designing of microfluidic systems, where it's important to control the movement of matter.
"We mathematically showed how with the help of temperature gradients it is possible to control microscopic flows in liquid-crystal systems. This knowledge will be useful in microfluidics, material engineering and electronics. Thus, for example, management of liquid's movement with the help of temperature can be used in systems of drug delivery and microchips for blood tests, where different zones of heating direct drops with samples in target places,"—tells Pavel Maslennikov, Ph.D. Biology, member of Laboratory of Natural Antioxidants, associate professor of Institute of Medicine and Life sciences.
In future authors are planning to pass from theoretical description to experiments, widen model for more complex conditions and create prototypes of microfluidic devices. This enables not only to understand thermomechanical effects in liquid crystals better, but to widen their application in real technologies—from biomedical sensors to "smart" materials of new generation.
More information:
doi.org/10.3390/cryst15030235
Provided by Immanuel Kant Baltic Federal University
