19 research outputs found
Laser Trapping and Crystallization Dynamics of lâPhenylalanine at Solution Surface
We present laser trapping behavior of l-phenylalanine
(l-Phe) at a surface of its unsaturated aqueous solution
by a focused continuous-wave (CW) near-infrared (NIR) laser beam.
Upon the irradiation into the solution surface, laser trapping of
the liquid-like clusters is induced concurrently with local laser
heating, forming an anhydrous plate-like crystal at the focal spot.
The following laser irradiation into a central part of the plate-like
crystal leads to laser trapping at the crystal surface not only for l-Phe molecules/clusters but also for polystyrene (PS) particles.
The particles are closely packed at crystal edges despite that the
crystal surface is not illuminated by the laser directly. The molecules/clusters
are also gathered and adsorbed to the crystal surface, leading to
crystal growth. The trapping dynamics and mechanism are discussed
in view of optical potential formed at the crystal surface by light
propagation inside the crystal
Millimeter-Scale Dense Liquid Droplet Formation and Crystallization in Glycine Solution Induced by Photon Pressure
A millimeter-scale dense liquid droplet of glycine is prepared by focusing a CW near-infrared laser beam at the glass/solution interface of a thin film of its supersaturated heavy water solution. The formation process is investigated by direct observation with CCD and by measuring temporal change of the surface height with a displacement meter. The droplet becomes much larger than a focal spot size, a few mm width and âŒ150 ÎŒm height, and observable with the naked eye. Interestingly, the droplet remains for a few tens of seconds even after switching off the laser beam. Whereas the droplet is kept during laser irradiation, the crystallization is immediately attained by shifting the laser beam to the air/droplet surface. It is considered that the droplet is possibly the early stage of the multistep crystallization process and plays an important role in photon pressure-induced crystallization of glycine
Formation, Dissolution, and Transfer Dynamics of a Millimeter-Scale Thin Liquid Droplet in Glycine Solution by Laser Trapping
The formation, dissolution, and transfer of a millimeter-scale
dense liquid droplet are demonstrated by focusing a CW near-infrared
laser beam into a thin film of glycine solution in heavy water. The
entire process is investigated by directly monitoring the temporal
change in the two-dimensional surface profile using a laser displacement
meter. Upon laser irradiation, the surface depression is initially
induced by laser heating, followed by the formation of the shallow
convex-shaped droplet around the focal spot, in which the droplet
is always in contact with the surrounding solution through the ultrathin
solution layer. After the laser is switched off, the dissolution occurs
through the recovery from the ultrathin layer toward the original
solution film. When the laser is set to the outside of the droplet,
the solution depression is similarly induced, and subsequently the
droplet starts moving toward the focal spot. These processes are summarized
and discussed in view of laser-induced effects of concentration increase
and temperature elevation
âFreezingâ of NaClO<sub>3</sub> Metastable Crystalline State by Optical Trapping in Unsaturated Microdroplet
We
reversibly controlled phase conversion between a microdroplet
of a NaClO<sub>3</sub> unsaturated aqueous solution and a metastable
single crystal, which is usually a short-lived phase in spontaneous
crystallization, simply by irradiating a tightly focused visible continuous-wave
(CW) laser to the microdroplet. The laser irradiation allowed the
metastable crystal to generate and stably grow without a polymorphic
transformation. This successful metastable phase control is attributed
to the combination of the advantage of optical trapping-induced nucleation
that nucleation takes place from unsaturated mother solution and the
advantage of microdroplet method, which suppresses additional nucleation
leading to the transformation. In situ observation shows the crystal
dissolves when the laser irradiation is stopped, whereas the laser
irradiation stabilizes the crystal even if the size of the crystal
becomes larger than that of focal spot. These observations indicate
that a change in the relative magnitudes of chemical potentials between
solution/crystalline phases. This change is possibly promoted via
crystal growth by trapping of crystalline clusters in optical potential
well formed on a crystal surfaces originating from âlight propagationâ
through the crystal. Our results shed a light not only on polymorph
control but also on a method to prepare a longer-lived achiral precursor
for analysis on achiralâchiral transition by âfreezingâ
a kinetic pathway of chiral crystallizatio
Formation, Dissolution, and Transfer Dynamics of a Millimeter-Scale Thin Liquid Droplet in Glycine Solution by Laser Trapping
The formation, dissolution, and transfer of a millimeter-scale
dense liquid droplet are demonstrated by focusing a CW near-infrared
laser beam into a thin film of glycine solution in heavy water. The
entire process is investigated by directly monitoring the temporal
change in the two-dimensional surface profile using a laser displacement
meter. Upon laser irradiation, the surface depression is initially
induced by laser heating, followed by the formation of the shallow
convex-shaped droplet around the focal spot, in which the droplet
is always in contact with the surrounding solution through the ultrathin
solution layer. After the laser is switched off, the dissolution occurs
through the recovery from the ultrathin layer toward the original
solution film. When the laser is set to the outside of the droplet,
the solution depression is similarly induced, and subsequently the
droplet starts moving toward the focal spot. These processes are summarized
and discussed in view of laser-induced effects of concentration increase
and temperature elevation
Dynamics and Mechanism of Laser Trapping-Induced Crystal Growth of Hen Egg White Lysozyme
We propose the dynamics and mechanism
of laser trapping-induced
crystal growth of hen egg-white lysozyme (HEWL). A continuous-wave
near-infrared laser beam is used as a trapping light source and focused
at a point 10 ÎŒm away from a target tetragonal HEWL crystal
that is spontaneously generated in solution. Laser trapping of HEWL
liquid-like clusters in solution increases local concentration in
the focus, where the free motion and orientation of the clusters are
strongly restricted, and the clusters show high rigidity and ordering.
The cluster association and reorientation at the micrometer-sized
focus is evolved to a large highly concentrated domain of the clusters,
where the specific target crystal is grown. Initially, the high rigidity
and ordering of the clusters strongly suppress the crystal grow rate
compared to spontaneous crystal growth. Continuous laser trapping
at the focus of the initially formed domain, however, leads to the
transition to another domain with different concentration, rigidity,
and ordering of the clusters, which surprisingly enhances the crystal
growth rate. More interestingly, the clusters in both domains have
anisotropic features reflecting the laser polarization direction,
which also contributes to the crystal growth
Reflection Microspectroscopic Study of Laser Trapping Assembling of Polystyrene Nanoparticles at Air/Solution Interface
We present the formation of a single
nanoparticle assembly with
periodic array structure induced by laser trapping of 200 nm polystyrene
nanoparticles at air/solution interface of the colloidal heavy water
solution. Their trapping and assembling behavior is observed by monitoring
transmission and backscattering images and measuring reflection spectra
under a microscope. Upon the laser irradiation into the solution surface
layer, nanoparticles are gathered at and around the focal spot, and
eventually a nanoparticle assembly with the size much larger than
the focal volume is formed. The assembly gives structural color in
visible range under halogen lamp illumination, indicating that constituent
nanoparticles are periodically arrayed. Reflection spectra of the
assembly show a reflection band, and its peak position is gradually
shifted to short wavelength and the bandwidth becomes narrow with
time, depending on the distance from the focal spot. After the laser
is switched off, red-shift is observed in the reflection band. These
results indicate that nanoparticles are rearranged into a densely
packed periodic array during laser irradiation and diffused out to
the surrounding solution after turning off the laser. These dynamics
are discussed from the viewpoints of the attractive optical trapping
force and the electrostatic repulsive force among nanoparticles
Reflection Microspectroscopic Study of Laser Trapping Assembling of Polystyrene Nanoparticles at Air/Solution Interface
We present the formation of a single
nanoparticle assembly with
periodic array structure induced by laser trapping of 200 nm polystyrene
nanoparticles at air/solution interface of the colloidal heavy water
solution. Their trapping and assembling behavior is observed by monitoring
transmission and backscattering images and measuring reflection spectra
under a microscope. Upon the laser irradiation into the solution surface
layer, nanoparticles are gathered at and around the focal spot, and
eventually a nanoparticle assembly with the size much larger than
the focal volume is formed. The assembly gives structural color in
visible range under halogen lamp illumination, indicating that constituent
nanoparticles are periodically arrayed. Reflection spectra of the
assembly show a reflection band, and its peak position is gradually
shifted to short wavelength and the bandwidth becomes narrow with
time, depending on the distance from the focal spot. After the laser
is switched off, red-shift is observed in the reflection band. These
results indicate that nanoparticles are rearranged into a densely
packed periodic array during laser irradiation and diffused out to
the surrounding solution after turning off the laser. These dynamics
are discussed from the viewpoints of the attractive optical trapping
force and the electrostatic repulsive force among nanoparticles
Femtosecond Laser Trapping Dynamics of Nanoparticles: A Single Transient Assembly Formation Leading to Their Directional Ejection
We
investigated femtosecond laser trapping dynamics of silica nanoparticles
with different hydrophobic surface properties. We demonstrated that
the hydrophobic surface on the silica nanoparticles facilitates mutual
association of the nanoparticles in the optical trapping site. Such
association of optically trapped nanoparticles is a prerequisite to
induce their directional ejection away from the trapping site. The
directional ejection of the optically trapped nanoparticles is most
probably due to asymmetric three-dimensional ejecting forces generated
by the electromagnetic interaction between transient assembly in the
focal spot and the incident pulses. These findings provide important
insights into the directional ejection of nanoparticles from the trapping
site in the femtosecond laser trapping, and this physicochemical phenomenon
is controlled by both the trapping laser and material properties
Optically Evolved Assembly Formation in Laser Trapping of Polystyrene Nanoparticles at Solution Surface
Assembling
dynamics of polystyrene nanoparticles by optical trapping
is studied with utilizing transmission/reflection microscopy and reflection
microspectroscopy. A single nanoparticle assembly with periodic structure
is formed upon the focused laser irradiation at solution surface layer
and continuously grows up to a steady state within few minutes. By
controlling nanoparticle and salt concentrations in the colloidal
solution, the assembling behavior is obviously changed. In the high
concentration of nanoparticles, the assembly formation exhibits fast
growth, gives large saturation size, and leads to dense packing structure.
In the presence of salt, one assembly with the elongated aggregates
was generated from the focal spot and 1064 nm trapping light was scattered
outwardly with directions, while a small circular assembly and symmetrical
expansion of the 1064 nm light were found without salt. The present
nanoparticle assembling in optical trapping is driven through multiple
scattering in gathered nanoparticles and directional scattering along
the elongated aggregates derived from optical association of nanoparticles,
which dynamic phenomenon is called optically evolved assembling. Repetitive
trapping and release processes of nanoparticles between the assembly
and the surrounding solution always proceed, and the steady state
at the circular assembly formed by laser trapping is determined under
optical and chemical equilibrium