Nanooptics and photonics

Dynamic light scattering at the aggregation processes of spherical nanoparticles in millimeter- and micrometer-sized droplets
Derkachov G.1, Jakubczyk D.1, Kolwas K.1, Shopa Y.2, Wozniak M.1
1 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, Warsaw 02-668, Poland. 
2 Cardinal Stefan Wyszyński University in Warsaw. Faculty of Mathematics and Natural Sciences, Wóycickiego 1/3, 01-938 Warsaw, Poland
E-mail: i.shopa@uksw.edu.pl

The dynamic light scattering (DLS) technique [1] were used for studying various solutions and suspensions of SiO2 and TiO2 nanoparticles as well as single droplets levitated in an electrodynamic quadrupole trap [2,3]. The intensity fluctuations of the scattered light were interpreted in terms of an autocorrelation function (ACF) and processed in real time with a digital correlator.
The suspended and levitated droplets were illuminated with blue-green (497, 515 nm) polarized Ar+ laser and violet (405 nm) semiconductor laser. Silica and titanium dioxide nanoparticles were dispersed in different base liquids (water, diethylene and tetraethylene glycol). The sensitivity of the DLS setup is enough for detection of the light scattered at 90 deg by a single micron sized droplet. However, the structural resonances (Whispering Gallery Modes) substantially deform the ACF at the initial stage of the droplets evolution.
Characteristic times, obtained from the ACF, allow tracing of the changes of the suspension in the droplet. Using the results of the DLS experiment we follow the agregatization process and found influence of the initial conditions (size of nanoparticles, concentration, viscosity of the base fluids etc.) on ACF in final stage of the droplets evolution.

1.	Berne B.J., Pecora R. Dynamic Light Scattering: With Applications to Chemistry, Biology, and Physics. Courier Corporation, 2000 – 376.
2.	Derkachov G., Jakubczyk D., Kolwas K., Shopa Y., Woźniak M. Dynamic Light Scattering with Nanoparticles: Setup and Preliminary Results // Springer Proceedings in Physics. Springer, Cham. -2017. -195. -P. 275-282.
3.	Derkachov G., Jakubczyk D., Kolwas K., Shopa Y., Woźniak M., Wojciechowski T. Application of dynamic light scattering for studying the evolution of micro- and nano-droplets // Proc. SPIE -2018. 10612, 106120U.