Photo-differential Scanning Calorimetry Study on Photopolymerization of Polyacrylate/E7 Liquid Crystal Blends

Abstract

Photo-differential scanning calorimetry (photo-DSC) was used to investigate the cure kinetics of a photo-initiated polymerization of tripropylene glycol diacrylate (TPGDA) monomers mixed with a eutectic liquid crystal mixture, E7, chosen due to its significant optical properties. The thermal photo-polymerization reactions were performed in isothermal mode in order to identify and evaluate the different thermal effects occurring during the photo-polymerization reaction under UV light. The results obtained help to better understand the curing mechanisms as well as the kinetics of the curing reactions. The isothermal photo-DSC provided complex thermograms showing the presence of two thermal effects: an exothermic heat (positive activation energy) generated during the conversion of monomers and an endothermic heat produced by the UV lamp. The latter phenomenon was observed in our previous work and was associated to the heating of the polymer dispersed liquid crystals (PDLC) material by the UV irradiation lamp. The dependence of photopolymerization on the time and intensities of the curing UV light were investigated. The results showed that the high intensity UV light heats the material and slows the process of phase separation which, in turn, affects the electro-optical properties of the material under study. The photo DSC results also revealed that the heating of the system was insignificant and can, therefore, be neglected, for materials exposed to UV radiation with an irradiation time of 5 seconds and a low intensity of 13.80 mW/cm 2 .

Curing Kinetic Analysis of Acrylate Photopolymer for Additive Manufacturing by Photo-DSC

“…During the polymerization, under UV irradiation, exothermic heat flow from the polymerization reaction induced by a UV lamp heats the sample. Calorimetric measurements were carried out by photo-DSC as a function of the intensity and exposure time of the UV lamp for the various samples [ 10 , 11 ].…”

“…Hong discovered the curing kinetics of a cationic polymerization system and discovered that the higher isothermal temperature leads to a significantly higher reaction rate constant and the higher concentration of photoinitiator will reduce the activation energy for the reaction [ 10 ]. Belaid found that the composite composed of TPGDA and eutectic liquid crystal that the exothermic reaction was nearly independent of the dose and intensity of the UV radiation [ 11 ]. Michaud focused on photopolymerization kinetics and structure formation.…”

Thermal Behaviour in the Stereolithography Process for Al₂O₃ Ceramic Suspension

“…The polymerization of the light-activated ceramic suspension results in a temperature increase, caused by both the exothermic reaction process and the energy absorbed during irradiation [5][6][7]. PhotoDSC has been used to characterize the real-time conversion rate change process based on the exotherm of this process [8][9]. However, few attempts have been made to visualize the DLP fullformat photocuring process with the associated temperature changes, which play an important role in photopolymerization.…”