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Scientists discover how to track the tiny movements of clay particles in soft clay colloids using optical tweezers

Scientists have found a way to track the tiny movements of clay particles in soft clay colloids using optical tweezers the application of which in biological systems won the 2018 Nobel Prize in Physics. This new way of tracking particles and manipulating them as needed can be used in areas such as targeted drug delivery.

Using optical tweezers, scientists at the Raman Research Institute (RRI), an autonomous institute funded by the Ministry of Science and Technology, Govt. from India, attempted to study the dynamics and hidden structural details of Laponite, a synthetic clay.

As these clay particles are uniform in size (monodisperse) and transparent, they are best suited for performing advanced studies under light. Laponite is a widely used raw material in the pharmaceutical and cosmetic industry. This clay contains disc-shaped particles 25 to 30 nanometers (nm) in size and 1 nm thick.

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Tiny movements of clay particles in soft clay colloids

Polystyrene balls dispersed in a Laponite clay suspension were used for the experimental arrangement. Over time, microstructures were noted to develop due to electrostatic interactions between clay particles. These microstructures grew stronger over time, with their mesh size depending on the concentration of Laponite particles.

“These structures are responsible for the elasticity of the material and allow elasticity to be adjusted by tuning the microstructures. These microstructures also form connections with micron-sized polystyrene particles that are used to probe these suspensions in such studies,” said Anson G. Thambi, a third-year Ph.D. student at RRI.

In a study published in the journal Soft Matter, Ranjini Bandyopadhyay, faculty, RRI, and her team used optical tweezers to measure probe movements at the nanometer scale, where the properties of the medium evolve over time.

Optical tweezers are a popular tool in the optical laboratory, used to measure minute forces and manipulate tiny dielectric beads caught in the tight focus of an intense laser beam up to a few nanometers in length. It allows motion to be induced in the trapped probe particle and its response is analyzed to extract previously unavailable local viscoelastic properties of the underlying medium.

“These connections between the probe (PS) and the Laponite clay particles are essential to understanding the suspension properties if the internal networks are larger than the probe itself,” said Bandyopadhyay.

In addition, the team used cryogenic field emission scanning electron microscopy (cryo-FESEM) to investigate the average pore areas formed by the Laponite microstructures.

“Interestingly, the collective observations obtained with optical tweezers and cryo-FESEM experiments revealed an interesting and previously unknown correlation. We found that beads captured by optical tweezers moved much more slowly in denser network structures,” added Bandyopadhyay.

The RRI team thus concluded that a direct relationship prevails between the morphologies of the clay suspension structures and the dynamics of the probe particles at micrometer lengths.

Edited by: Vaishali verma

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