Abstract
In the protoplanetary disks, different organic matters can be generated via various chemical processes, including photohcemical reactions on the disk surface and hydrothermal reactions in the parent body of asteroids. These organic materials may play a pivotal role for promoting the collisional growth of dust in the disk due to their high stickiness. In this study, several organic analog materials were produced by simulating different chemical processes in the disks. Their chemical structures were investigated via mass spectroscopy, infrared/visible/ultraviolet spectroscopy, raman spectroscopy, and elemental analysis. The surface energy and elasticity, which control the sticking properties of these organic analog materials, were determined by using atomic force microscope and analysis of IXS spectra, respectively. Based on the results of the chemical analysis and the measurement of the physical properties, chemical structure and temperature dependence of these physico-chemical properties were revealed. Our results suggest that the organic materials with a variety of functional groups show higher surface energy and lower elasticity compared with aromatic-rich organic materials. The temperature dependence of the surface energy and elasticity followed the Arrhenius equation, with indicating that the surface energy decreases and the elasticity increases at lower temperatures. Our results also suggest that the sticking properties of organic materials increase at higher temperatures, although the dependence of chemical structure is under debate. Our results imply that organic matter may have promoted collisional growth of dusts in high-temperature regions inside the H2O snow line in the protoplanetary disks.
