Innovative optical techniques based on nano-biophotonics such as surface plasmon resonance (SPR) imaging and R-G-B natural fringe mapping techniques are developed to characterize the transport and optical properties of nanofluids in situ, real-time, and full field manner. Recent results regarding the characterization of nanofluids are summarized and future research directions are presented.
47 nm Al2O3 nanoparticles are dispersed in water with various concentrations. Al2O3 nanofluids droplets are placed on substrates and evaporated in room temperature. In-situ visualization of evaporation-induced self-assembly is conducted to detect concentration, effective refractive index, and different self-assembled pattern including cavity with various nanofluids concentrations and surface hydrophobbicities with SPR and fringe mapping.
During the evaporation, time-dependent and near-field nanoparticle concentrations are determined by correlating the SPR reflectance intensities with the effective refractive index (ERI) of the nanofluids.
With increasing the concentrations of nanofluids, the existence of hidden complex cavities inside a self-assembled nanocrystalline structure or final dryout pattern is discovered in real-time. R-G-B natural fringe mapping allowed the reconstruction of the 3D cavity formation and crystallization processes quantitatively. The formation of the complex inner structure was found to be attributable to multiple cavity inceptions and their competing growth during the aquatic evaporation.
Furthermore, the effect of surface hydrophobicity is examined in the formation of hidden complex cavities, taking place on three different substrates bearing different levels of hydrophobicity; namely, cover glass (CG), gold thin film (Au), and polystyrene dish (PS).
These surface plamson resonance imaging and natural fringe mapping techniques are expected to provide a breakthrough in micro-nanoscale thermal fluids phenomena and nano-biochemical sensing when coupled with localized surface Plasmon and metamaterials techniques.