Browsing by Author "Ujihara, Toni"

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Plasmonic Heating-Assisted Laser-Induced Crystallization from a NaCIO3 Unsaturated Mother Solution
(2017-02)
Niinomi, Hiromasa
;
Sugiyama, Teruki
;
Tagawa, Miho
;
Maruyama, Mihoko
;
Ujihara, Toni
We provide a novel laser-induced crystallization mechanism which explains crystallization induced by visible laser trapping of silver nanoparticles (AgNPs) at the air/unsaturated mother solution interface from the focal spot [Niinomi et al.CrystEngComm 2016, 18, 7441-7448]. Simultaneous in situ microscopic observation of Raman scattering and polarized-light image revealed that the optical trapping of nanoparticles that exhibit surface-enhanced Raman scattering (SERS) triggers the crystallization, showing the excitation of localized surface plasmon resonance (LSPR) significantly promotes the crystallization. Numerical analysis of temperature distribution based on the combination of finite-difference time-domain electromagnetic and finite-difference heat transfer calculations shows that temperature reaches 390 degrees C at the focal spot because of plasmonic heating, the energy dissipation of the plasmon-enhanced electromagnetic field as heat. A conceivable mechanism of the crystallization is local increment of supersaturation caused by local solvent evaporation via the Plasmonic heating. This plasmonic heating assisted laser-induced nucleation process has the possibility to provide not only a novel approach for spatiotemporal control of crystallization but also a novel nucleation field based on nonlinear light matter interaction originating from the plasmon-enhanced electromagnetic near field through heterogeneous nucleation on the surface of plasmonic particles.
Plasmonic Trapping-Induced Crystallization of Acetaminophen
(2019-02-01)
Niinomi, Hiromasa
;
Sugiyama, Teruki
;
Uda, Satoshi
;
Tagawa, Miho
;
Ujihara, Toni
We demonstrate that plasmonic trapping can control crystallization of acetaminophen from its aqueous solution. Irradiation of a focused continuous-wave near-infrared laser to a plasmonic Au nanolattice supporting a thin film of a saturated solution allowed acetaminophen molecules to crystallize in annular distribution with the center of the focal spot. The annularly distributed crystals can be spatially manipulated by changing the position of the laser focal spot. The annular pattern is rationalized by competition between electrical field gradient force as an attractive force to the focal spot and thermophoretic force as a repulsive force. It is also found that, upon stopping the laser irradiation, the crystals first transformed to highly concentrated droplets rather than directly dissolving to the solution. Relaxation of the droplets by self-diffusion to the solution followed to the crystal/droplet transformation. These two-step dissociation dynamics indicate that not only plasmonic trapping of the molecules but also the enhanced electrical field by surface plasmon contributes to drive the crystallization, and it has a possibility to show the reverse process of the two-step nucleation model. Our demonstration highlights the possibility that plasmonic trapping by designed near-field and temperature distribution can manipulate not only molecular assembly but also creation of functional crystalline materials in nanoscale.