Use laser to manipulate micro droplets directional motion to draw a panda pattern and convert music signals into droplet motion... This series of phenomena sounds a bit incredible.
Figure | Professor Jiang Lingxiang of South China University of Technology (Source: Jiang Lingxiang)
Recently, Professor Jiang Lingxiang's team from the School of Frontier Soft Mathematics of South China University of Technology and the team of Jinan University's Nanophoton Research Institute Associate Professor Li Yuchao collaborated with the light-thermal-powered physics coupled to successfully achieve high-temporal and spatial accuracy manipulation of phase separation micro droplets.
talked about the basic principles of the experiment, Jiang Lingxiang mentioned: "Some specific molecules have the characteristics of liquid-liquid phase separation caused by heat. The two phases formed are liquids and contain a lot of water. One phase contains more solutes, and the other phase contains less solutes." During the experiment, the researchers focused the laser on the gold film, thereby generating a local solution temperature and responding to the solution hot spots, thereby generating a single photothermal droplet.
The stable thermal field ensures that the spatial accuracy can reach 1μm, and the fast heating and response speed ensures that the time accuracy is maintained at 0.1 seconds.
Use laser focusing technology to determine the formation, dissolution, positioning, forming and dynamic reconstruction of phase separation liquids according to needs. The researchers further programmed laser-focused micro droplets, arranged micro droplet patterns in a time-continuous manner, and created a high-fidelity micro-scale liquid animation.
(Source: Advanced Materials)
related papers are titled "Optothermally programmable liquids with spatiotemporal precision and functional complexity" (Optothermally programmable liquids with spatiotemporal precision and functional complexity), and are published in the journal Advanced Materials Advanced Materials
Laser-induced liquid liquid phase separation
Figure | Principle of photothermal phase separation (Source: Advanced Materials)
The most critical step in the entire study is to separate the liquid liquid phase with temperature-induced liquid phase, and heat it by irradiating the laser on the gold film. During the irradiation process, the plasma effect will be generated, and the micro droplets will be heated at a fixed point, resulting in a local temperature difference, and inducing the molecules to liquid-liquid phase separation.
Figure | Experimental device for generating photothermal droplets (Source: Advanced Materials)
The device used in the experiment includes an inverted fluorescence microscope and a scanning light system. The laser is modulated by an acousto-optical deflector (AOD) and expanded by a beam expander, focusing on the imaging plane of a 60× water-immersion objective.
According to reports, the key to achieving photothermal liquid-phase separation is optical technology. This technology can deflect a single high-frequency laser beam (up to 100kHz) in a 100×100μm2 workplace, producing up to 2500 focal points, fluorescent excitation with a white LED light source.
fluorescent images were taken using green fluorescent filters or red fluorescent filters, and recorded with high-speed camera and color cameras.
Select a representative low critical solution temperature (LCST) system to carry out experiments
Figure | UCST and LCST system schematic diagram (Source: Advanced Materials)
Liquid-liquid phase separation process will reach high critical solution temperature (UCST, upper critical solution temperature) and low critical solution temperature (LCST, lower critical solution temperature).
At lower temperatures, strong intermolecular interactions (such as hydrogen bond ) lead to negative enthalpy of mixing and a mixed phase formed between the two components. The interactions between these molecules are often highly directed and require a certain entropy cost.
When heated above the critical temperature, the entropy term mainly drives phase separation by breaking the directional intermolecular interaction releases degrees of freedom.
Figure | Low critical solution system selected in the experiment (Source: Advanced Materials)
Figure | Component structure of low critical solution temperature system (Source: Advanced Materials)
Low critical solution temperature has been observed in various polymer or small molecule systems.
This photothermal experiment was used to select 7 representative LCST systems, consisting of small molecules, synthetic polyelectrolytes, and proteins, and liquid-liquid phase separation is achieved at different laser beam temperatures and time.
Use a laser beam to control the arrangement of micro droplets to convert light energy into thermal energy
Figure | The "Panda hugs bamboo" pattern achieved by photothermal phase separation micro droplets (Source: Advanced Materials)
Liquid has surface tension , which maintains its own shape, so it is difficult to control. The arrangement of laser spots can make the liquid produce different shapes and patterns, such as dots, linear, circular, triangle and square droplets.
Specifically, the researchers convert light energy into thermal energy by controlling the distribution and power of the laser, so as to control the photothermal phase separation liquid to produce corresponding patterns.
droplets are arranged into different complex patterns as the heat field is distributed. Taking the formed "panda hugs bamboo" pattern as an example, the spatial resolution of the image reaches about 1μm. The panda presented is clear outline and highly mimics the original panda graphics.
Figure | "Change cocoon into butterfly" liquid animation produced by photothermal phase separation micro droplets (Source: Advanced Materials)
research team used the force of the droplets and their own shaping properties to make the micro droplets move and reorganize at the same time under the moving trajectory of the laser, successfully achieving the purpose of dynamic reconstruction and achieving programmable and precise manipulation.
Under the dynamic and precise control of the laser, the droplets are arranged in an orderly manner, drawing a liquid animation of the whole process of "turning into a butterfly" (from caterpillars to insect cocoons and butterflies).
Figure | Micro droplets present music visualization effect and construct bionic micro reactors (Source: Advanced Materials)
Based on the above application, the research team digs deep into other application scenarios of programmable micro droplets. The audio information is successfully converted into the motion behavior pattern of micro droplets, displaying the visual dynamic effects of the music to the audience.
Finally, the team achieved microliquid titration point enrichment and transportation in various microscopic samples such as proteins and dye molecules. They also used microliquid droplets to recombinate the simulated biological microscopic reaction biological system that can be controlled by time and space, strengthened the cascade enzymatic reaction and played the role of a catalyst.
is used in microelectronics and cell biology fields
liquid-liquid phase separation technology will be able to have an impact in the fields of microelectronics, unbalanced physics and cell biology.
For example, liquid painting can be cured by introducing crosslinked monomers, thereby separating the liquid-liquid phase to produce a permanent structure. The liquid type containing concentrated electrolytes in
can be used as a reconfigurable wire leading to the liquid circuit, creating an inherent unbalanced system. The continuous input energy of the laser irradiation can drive the internal and external convection of the droplets, potentially guiding the flow of fluid over a larger range.
This photothermal conversion strategy can enable living cells to achieve subcellular accuracy, express heat-sensitive proteins by engineering cells, and culture them on a medium substrate with a gold coating.
" Although laser focus technology has been conventionally used to manipulate solid particles or micro-process solid materials, it has functional complexity in information encryption, load transfer and reaction positioning.We expect it to be further applied to scenarios such as subcellular tissues of biomolecular aggregation and programmable modulation of unbalanced systems. "Jiang Lingxiang said.
Reference materials:
Xixi Chen, Tianli Wu, Danmin Huang, Jiajia Zhou, Fengxiang Zhou, Mei Tu, Yao Zhang, Baojun Li, Yuchao Li, Lingxiang Jiang (2022).Optothermally Programmable Liquids with Spatiotemporal Precision and Functional Complexity.Advanced Materials
