Dynamics Study and Analysis of Laser-Induced Transport of Nanoferrofluid in Water Using Fluorescein Isothiocyanate (FITC) as Fluorescence Marker

摘要

FITC-conjugated nanoferrofluid (FNFF) was synthesized and characterized to study the dynamic of laser-induced transport of NPs in water. The results confirmed a definite laser-induced enhanced velocity of NPs (100 μm⋅s−1) almost twice as much the without laser (i.e. Brownian motion). The diffusion coefficients of 17 × 10−6 m2⋅s−1 and 55 × 10−6 m2⋅s−1 were found for the cases without and with laser action respectively. The act of laser when switched on after NPs had reached the steady state was very prominent. The laser-induced heat and power generated by NPs were calculated 0.2μW⋅cm−3 and 0.4 pW⋅cm−2 respectively. Our experiment condition was non-adiabatic and that the heat generated was diffused into the surrounding. We considered the Maxwell’s criteria (Kp/Kw −1⋅K−1. Based on the Brownian diffusion and DLVO theory, at earlier times where the NPs are more dispersed within the medium are displaced faster. However, at later stages they become less mobile as they are agglomerated. The mechanisms for the enhanced mobility and laser transport of NPs are thought to be due to e.m.w induced force (i.e. an oscillatory motion) and laser absorptive force (i.e., photothermophoresis). A beam divergence of about 5.24°(or 91 mrad) was determined. A non-linear behaviour of laser beam was observed as a trajectory path within the water due to thermal heating hence causing the change of refractive index of medium and redistribution of NPs concentration.