Polydimethylsiloxane (PDMS) has been widely used in a variety of biomedical applications: microfluidic device, implant, and biomedical phantom due to its unique physiochemical and mechanical properties. To use PDMS properly, in-depth study for properties of PDMS is needed. Many studies for analysis of PDMS properties are suggested, however, there are shortages of systematic analysis and study on the origin of PDMS properties.
Typically, PDMS is produced by mixing and curing pre-polymer and curing agent with catalyst and thermal energy. The recommended mixing ratio (pre-polymer: curing agent) is typically 10:1 by raw materials suppliers. However, the reason why the mixing ratio 10:1 is considered proper than other mixing ratios has not been known clearly.
In this research, we presented the change of physicochemical properties of PDMS according to the mixing ratio and figured out the origin to change PDMS physiochemical properties by Raman spectroscopy and absorption spectroscopy.
We produced PDMS samples with various mixing ratios(1:1, 1.5:1, 2:1, 3:1, 5:1, 7:1, 9:1, 10:1, 12:1, 20:1, 30:1) and analyzed mechanical, optical, and surface properties of PDMS by measuring Young’s modulus, OCT, hydrophobicity, and surface profiles according to the mixing ratio of PDMS. Also, we demonstrated the chemical composition of PDMS is changed when the mixing ratio of PDMS is changed by measuring Raman spectra and absorption spectra.
As a result, when the mixing ratio is about 9:1, the mechanical, optical, and surface properties of PDMS had extreme points and the reason was explained quantitatively with the data of Raman spectra and absorption spectra.
Yield stress of 80 μm thick glass wafer chip diced with fs-laser μ-processing was investigated with varying the repetition
rate of laser pulse and scanning speed under constant number of shot. By using constant laser fluence, the yield stress is
almost invariant at lower repetition rate less than 20 kHz, but abruptly drops to the half of initial yield stress. Based on
the effect of the ambient gas on the transition point of yield stress changes, we propose an empirical relation between the
yield stress and cumulative stress caused by temperature increment with changing the laser repetition rate.
The temporal coupling of femtosecond and nanosecond laser induces a remarkable increase in the processing efficiency
12 times more than that with an independent laser exposure. When femtosecond laser arrives before nanosecond laser,
the dependence of the ablation efficiency on the time delay between the femtosecond and nanosecond laser pulses is very
resemble to nanosecond laser traces. When femtosecond laser arrives after nanosecond laser, however, we observed an
apparent delayed decaying component with a time constant of several hundreds of nanosecond in the ablation efficiency
curve. Based on the current observation, we have explained the rather large enhancement in femtosecond laser ablation
efficiency with synchronization between femtosecond and nanosecond laser in terms of silicon surface metallization due
to the proceeding nanosecond laser. Such a progress in femtosecond laser micro processing makes it possible to
maximize the processing speed and reduce the processing threshold energy. The current findings prominently reduce a
various high order nonlinear effects which are frequently confronted when we focus high-power femtosecond laser
pulses on the target under atmospheric conditions.
Terahertz transmission filters have been manufactured by perforating metal surface structures with various geometric shapes which all support near-unity transmission at specific frequencies determined by geometric shape, symmetry, polarization, and lattice constant. Our results show that the structures specifically designed by the shape resonance are extremely versatile, dependable, easy to control and easy to make the multifunctional filters.
We present that size of Ge nanoparticle can be controlled by changing the angle between ultrafast laser polarization and crystal axis using ultrafast laser irradiation. The nanoparticle size dependence on the laser polarization with respect to the Ge crystal axis exhibits a sinusoidal function with a minimum size at (100) axis. Moreover, the measurement of transient reflection reveals the presence of large anisotropies in both its amplitude and its relaxation dynamics with a minimum at (100) crystal axis. This implies that the observed anisotropic dependence of nanostructure size of Ge is followed by a different carrier density as well as its relaxation process depending on the orientation of Ge crystal axis only at near and above threshold fluence.