Magnetic Nanorobots: Rainbow through Intelligent Liquid in Laboratory




The article describes magnetic nanorobots' adventure journey focused on seeing a rainbow in the laboratory through the intelligent liquid. It explains the connexion between magnetic nanorobots and optics. I dissected the storyline into small parts to keep it straightforward and less complicated. I attempted to overcome the technical words into comprehensible sentences. Here, the tour starts.

Inspiration's Origin

Optics is a fascinating field of physics that explores how light originates and spreads, how it evolves, and what results in its causes. Another related phenomena, i.e., Optics, is the geometry of light. The only source of energy that the human eye can see is light. Sir Isaac Newton, an English physicist and mathematician, experimented with clear white light and understood geometry in the 1660s and considered it to consist of seven visible colours (the colors we see in the rainbow). When white light encounters an obstruction (grating), known as diffraction, it bends and spreads. —the entity divides the white color into a rainbow known as a diffraction grating. In the 17th century, John Wolfgang Von Goethe – a German writer, said, colors are light's joy and suffering. There are numerous diffraction grating available in our daily life, such as water, cloud, spider web, comb, grater, masher, and shower. The distance between successive gratings remains fixed, which is why they are hard gratings. Therefore, using the same hard grating, we cannot achieve the desired color from white light. Soft grating is the solution to overcome this limitation, which can vary the successive distance between gratings per the requirement. Hence, soft grating can get every shade of color from white light.

Magnetic Fluid Family

Smart materials are essential to preparing soft grating. These are solid objects with characteristics such as shape and color that change in response to external stimuli, such as temperature, light, pressure, electric, and magnetic fields. One of the smart materials made up of coated magnetic nanoparticles suspended in a liquid is the magnetic fluid (ferrofluid). Steve Papell's National Aeronautics and Space Administration (NASA) first prepared magnetic fluid in 1963 to produce liquid rocket fuel, which could be drawn to pump injection with magnetic field application in a weightless environment. At the same time, R. V. Mehta, a research scholar from Gujarat University, Gujarat, India, started working on magnetic fluid. Subsequently, he developed the field the glory. Hence, Prof. R. V. Mehta is India's father of magnetic fluid. The magnetic nanoparticles are made up of using ferrous chloride (FeCl2) and ferries chloride (FeCl3) solutions in any alkaline chemicals like ammonium hydroxide (NH4OH) and ammonia (NH3). This process gives magnetic nanoparticles the form of black color precipitates, which collect using a magnet. The magnetic nanoparticles separate from each other by coating surfactants such as lauric acid (C12H24O2), oleic acid (C18H34O2), and capric acid (C10H20O2) at 80 oC. The surfactant coating behaves like a spring surrounding magnetic nanoparticles (figure 1 (a) & (b)). The coated magnetic nanoparticles are suspended in a liquid such as water and kerosene. Prof. R. V. Mehta and Prof. R. V. Upadhyay have contributed a wet chemical synthesis route during the '90s to synthesize ferrite nanoparticles and magnetic fluid. The coated magnetic nanoparticles can control using an external magnetic field. Hence, the intelligent fluid which contains magnetic nanorobots behaves like a liquid (figure 1 (c)) and a solid (figure 1 (d)) with a split personality.

There are numerous potential applications of magnetic fluid. However, few applications, like a magnetic fluid seal, are very well developed. Magnetic fluid in a rotary machine may act as an airtight seal. Indeed, the first industrial use of magnetic fluid was a pressure seal for rotating shafts. Magnetic fluid has friction-reducing capabilities as well as semi-active dampers. It also has applications in the medical industry as targeted drug delivery. Scientists have worked on hyperthermia treatment using magnetic fluid for the last decade. Optics is also a potential area in which using magnetic fluid can prepare an adaptive liquid lens, tunable mirror, and tunable diffraction grating.

The Pursuit of the Struggle

The magnetic nanorobots are randomly oriented without a magnetic field inside the intelligent liquid. The magnetic nanorobots begin to align in the field direction immediately when applying a homogeneous magnetic field and create a fascinating micron-size structure like chains and columns (figure 2 (a)). These microstructures look the same as the national patriotic parade's top view on Rajpath every year on 26th January. The light (polychromatic and monochromatic) diffracts when it passes through the magnetic fluid due to the different microstructures shape of magnetic nanorobots (figure 2 (b), (c), and (d)).

Hence, magnetic chain formation is crucial to preparing magnetic fluid-based diffraction grating. However, the magnetic nanorobots are running spontaneously towards the magnetic field direction. So, controlling the magnetic nanorobots is possible by changing the magnetic fluid composition and field intensity. Hence, the magnetic fluid-based grating is known as a tunable diffraction grating.

In our research published last year in the journal Material Research Express,' we found, that better control on magnetic nanorobots is possible by incorporating different kinds of non-magnetic materials such as silica, polymer, and graphene oxide inside the magnetic fluid. The non-magnetic materials are stubborn to the magnetic field. Hence, they become an obstacle for the magnetic nanorobots while aligning with the magnetic field direction in magnetic fluid. The mixture of magnetic and non-magnetic material increases the number density of magnetic chains and columns in the magnetic fluid under the external magnetic field's influence. Hence, the blend can help to develop and increase the efficiency of the magnetic fluid-based tunable diffraction grating.

Conclusion

The diffraction phenomenon happens when white light meets grating (parallel lines or obstruction). Now, we create parallel lines using controlling magnetic nanorobots in magnetic fluid. The number of parallel lines is high due to diffraction phenomena occurring at a small angle. Hence, we can get a rainbow from white light using a magnetic fluid-based tunable diffraction grating. The magnetic fluid-based tunable diffraction grating has various applications in spectroscopy, which separates white light into a rainbow and in-camera to enhance the lens's efficiency. Apart from that, it can also behave as a monochromator. Soon, we hope to fabricate magneto-optical devices such as magnetic fluid-based tunable diffraction grating.

Acknowledgments

The author would like to thank Dr. Rucha Desai, associate professor and head of the department of physical science division, PDPIAS, CHARUSAT, Gujarat, India, for embracing my adventures and misadventures with the same smile.