Sung-Chul Bae

Confocal Raman spectroscopy has been implemented within the molecularly thin films of a surface forces apparatus. Applying this technique to an initial system, we investigate the confinement and shear-induced changes in the Raman spectra of poly(dimethylsiloxane) (PDMS) liquids confined between atomically smooth mica surfaces at thicknesses less than the unperturbed radius of gyration of the polymer. We focus on stretch vibrations of the PDMS methyl group, whose net orientation is perpendicular

Spatially resolved and time-resolved understanding of complex fluid situations compose a new frontier in physical chemistry. Here we draw attention to the significance of spatially resolving systems whose ensemble average differs fundamentally from the spatially resolved individual elements. We take examples from the field of fluid phospholipid bilayers, to which macromolecules adsorb; the field of polymer physics, when flexible chains adsorb to the solid-liquid interface; and from the field of

Within a surface forces apparatus newly equipped for spectroscopic measurements, the photoluminescence and absorption spectra were studied of conjugated polymer films confined to less than the random coil dimension. A dilute solution of MEH-PPV, poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene), was exposed to atomically smooth surfaces of muscovite mica and allowed to adsorb from toluene, and then the surface spacing was reduced to ≈2 nm, which is less than the unperturbed radius of gyr

Several instrumental developments to examine the spectroscopic response of molecularly thin fluids confined between mica sheets are described. They are predicated on using a redesigned surface forces apparatus where dielectric coatings, transparent to light at needed optical wavelengths, retain the ability to measure interferometric thickness at other optical wavelengths. Examples of recent measurements are presented using confocal laser Raman spectroscopy to evaluate how molecules orient as wel

Bioreporters, microbial species genetically engineered to provide measurable signals in response to specific chemicals, have been widely investigated as sensors for biomedical and environmental monitoring. More specifically, the bioreporter encapsulated within a biocompatible material, such as a hydrogel that can provide a suitable microenvironment for its prolonged activity as well as efficient scalable production, has been viewed as a more broadly applicable mode of biosensors. In this study,

The vibrational relaxation rate constants of the four low-lying vibrational levels in the 3B1 state of the SO2 molecule have been investigated by a laser induced phosphorescence method in pure SO2. The relaxation rate constants for the 3B1(0,1,0) level have also been studied in Ar, O2, N2, and CO2. The low-lying vibrational levels of the 3B1 state are populated from ground state SO2(X 1A1) by direct pumping, and the phosphorescence emissions from the laser excited as well as the collisional prod

Collision-induced intersystem crossing rate constants from the (0,4,1) and (1,2,1) levels of the à 1A2 to ã 3B1 state and rovibronic relaxation rate constants in the à 1A2 state of SO2 have been studied. The laser wavelength was set at 335.86 and 334.09 nm for the (0,4,1) and (1,2,1) excitation, respectively. When a few rotational levels belonging to the (0,4,1) and (1,2,1) vibrational levels were populated by a narrow bandwidth laser, both the fluorescence from the à 1A2 state and the phosphore

Vibronic relaxation among the Clements bands of SO 2 molecule has been studied from time-resolved fluorescence spectra in the 300−350 nm region. The K ‘ = 6, J ‘ = 7 level of the Clements E-band was populated at 32 812.8 cm -1, and detailed time-resolved fluorescence spectra for the period 0−160 ns were obtained. Following the fast decay of the laser excited level, weak emissions from Clements A−F bands appeared almost simultaneously. The simultaneous appearance of many Clements bands was attrib

The pressure saturation effect on the phosphorescence decay rates of the B-3(1) State of SO2 has been reinvestigated by the laser induced phosphorescence method in pure SO2. We have attempted to fit the pressure dependence of the phosphorescence decay rates using the radiationless transition model by introducing different coupling constants for each vibrational level of the B-3(1) state. The experimental decay rates can be fitted well, when the coupling constants for the (0,0,0), (0,1,0) and (0,

A simple interferometric method is described to measure the time-dependent deformation of piezoelectric bimorphs driven by ac voltage. Applying this method to a bimorph assembly used to measure viscoelastic forces in a surface forces apparatus, we find that a sinusoidal-shaped harmonic drive voltage generates sinusoidal deformation but that a triangular-shaped harmonic drive voltage fails to produce triangular-shaped deformation if the drive frequency exceeds 1/100 of the resonance frequency. Si

In this paper, we present a <TEX>$C^3$</TEX> quartic B-spline approximation of circular arcs. The Hausdorff distance between the <TEX>$C^3$</TEX> quartic B-spline curve and the circular arc is obtained in closed form. Using this error analysis, we show that the approximation order of our approximation method is six. For a given circular arc and error tolerance we find the <TEX>$C^3$</TEX> quartic B-spline curve having the minimum number of control points within the tolerance. The algorithm yield