Jung-Dae Cho

Optimization and characterization of UV-curable adhesives for optical communications by response surface methodology

Novel organic UV-curable material (UCM) containing fluorine and methoxy-silane has been specifically developed for the fabrication of optical-communications systems devices. Response surface methodology (RSM) was used to evaluate the effect of UCM and colloidal silica content in UV-curable adhesive formulations on the refractive index, curing, adhesion strength (dry and wet) and coefficient of thermal expansion (CTE). A central composite design for two variables at five levels was chosen as the experimental design. UCM for all six responses was highly significant and colloidal silica was significant for conversion and adhesion strength (dry and wet). UCM and colloidal silica had significant interactive effects on adhesion strength and CTE. Based on the fitted model, in order to get the optimal conditions for the application of optical adhesives in high-performance optical components, UCM should be set over 20 wt% and colloidal silica be set below 10 wt%.

Dual curing of cationic UV-curable clear and pigmented coating systems photosensitized by thioxanthone and anthracene

Abstract We investigated the effects of photosensitizers (2,4-diethylthioxanthone (DETX) and anthracene) and dual curing on the kinetic and physical properties of cationic photocurable clear and pigmented coatings based on cycloaliphatic diepoxide/ϵ-caprolactone polyol. The cationic photopolymerizations were investigated by Fourier-transform infrared spectroscopy with attenuated total internal reflection (FTIR-ATR), real-time infrared spectroscopy (RTIR), and differential scanning photocalorimetry (photo-DSC). The coatings were shown to polymerize in the dark due to the “living” character of cationic polymerization. Measurements of the yellowness index revealed that the yellowing of the coatings containing the blend of DETX with anthracene photosensitizer was less than that of the coatings containing DETX only. Depth-profile analyses of FTIR-ATR spectroscopy data showed that the dual curing significantly increased both surface and interior curing of the coating films. The RTIR and Photo-DSC analyses showed that the polymerization reactivity and the ultimate percentage conversion for the cationic clear and pigmented formulations containing photosensitizers were higher than the corresponding values for the formulation without photosensitizer.

An investigation of the surface properties and curing behavior of photocurable cationic films photosensitized by anthracene

We investigated differences in the curing behavior of cationic photopolymerizations photosensitized by anthracene by preparing various epoxy/vinyl-ether-based formulation systems with and without anthracene photosensitizer. Cationic photopolymerizations of formulations with different ratios of diglycidyl ether of bisphenol A epoxide (DGEBA), 1,4-cyclohexane dimethanol divinyl ether (CHVE), and anthracene were investigated using differential photocalorimetry (photo-DSC) and Fourier-transform infrared spectroscopy with attenuated total internal reflection (FTIR-ATR). In photo-DSC experiments, the formulations containing more than 5% (by weight) anthracene exhibited a two-stage exothermic reaction. As the concentration of anthracene photosensitizer was increased, the first exotherm decreased and the second one increased. Photo-DSC and real-time infrared spectroscopy analyses showed that the reaction rate increased as the anthracene photosensitizer concentration was increased. Depth profile analyses using FTIR-ATR spectroscopy showed that the films containing more than 0.5% anthracene exhibited significantly improved surface properties and more thorough curing for film thicknesses up to 100 μm.

Photocure kinetics and control of LC microdroplets for acrylate-based polymer dispersed liquid crystal with different methacrylate contents

AbstractThis paper reports on the relationship between the photocure kinetics and the morphological properties of UV-curable acrylate-based polymer dispersed liquid crystal (PDLC) systems with the various 2-ethylhexylacrylate (2-EHA) and 2-ethylhexylmethacrylate (2-EHMA) contents using photo-differential scanning calorimetry (photo-DSC), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). Photo-DSC analysis using an autocatalytic kinetics model demonstrated that the cure extent and cure rate gradually decreased and then leveled off as the concentration of 2-EHMA increased up to 25 wt%, which was well confirmed by using FTIR spectroscopy. The morphological observations revealed that increasing the 2-EHMA content increased the size of the LC droplets within the acrylate-based polymer matrix. Notably, there was a marked increase in the number of LC droplets larger than 10 μm in PDLC composites containing more than 20 wt% 2-EHMA, suggesting that the addition of more than 20 wt% 2-EHMA to the acrylate-based PDLC compounds is not desirable. The presence of 2-EHMA clearly affected the photocure behaviors of acrylate-based PDLC compounds, which interestingly means that the slow reactivity of methacrylate monomer could be simply used to control the phase separation rate and the microstructures of LC droplets of acrylate-based PDLC systems.