A 3D-Simulation and Experimental Study of the Fluid Flow Around a Nano- Step Structure Formed by UV-NIL

T Ando and Y Honda and T Yanagawa and N Unno and J Taniguchi and SI Satake, JOURNAL OF PHOTOPOLYMER SCIENCE AND TECHNOLOGY, 35, 111-116 (2022).

In this work, total internal reflection fluorescence microscopy (TIRFM) was combined with the refractive index matching method to measure the three-dimensional motion of a nanoparticle on a nanosized step structure in water. A step (height = 64 nm) based on an ultraviolet (UV)-curable resin was fabricated using UV nanoimprint lithography. The step has a refractive index similar to that of water to eliminate the optical distortion due to light refraction and reflection at the interface between the nano structure and water. TIRFM could clearly capture the motion of a fluorescent nanoparticle in the vicinity of the nanostep in water. Diffusion coefficients of the particle in the vicinity of the nanostep edge were obtained from its time-lapse images, indicating that the diffusion coefficient measured along the edge of the step was 1.2 times larger than that measured across the step. Molecular dynamics simulations were also conducted to calculate the diffusion coefficients of a rigid particle close to the top of the step. The simulation results were qualitatively consistent with the experimental observations. The experimental and simulation methods presented here would help understand the nanoparticle motions and solvent flow dynamics around more complicated nanostructures.

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