Mechanism of Short-Pulse-Induced Solute Migration in Comparison to Continuous-Light-Driven Thermal Diffusion
Po-Yuan Huang1*, Tai-Huei Wei1, Yu-Ting Kuo1, Yi-Ci Li2
1Physics, National Chung Cheng University, Chia-Yi, Taiwan
2Physics, Academia Sinica, Taipei, Taiwan
* Presenter:Po-Yuan Huang
The aim of this work is to clarify the mechanism of photo-absorption-caused solute migration at the microscopic level. Experimentally, we respectively measured the short-pulse-induced and continuous-light-driven migrations of chloroaluminum phthalocyanine molecules dissolved in ethanol at two concentrations, 4.2*10¹⁷/cm³ and 1.2*10¹⁷/cm³. Theoretically, by verifying that individual solute molecules in the concentrated solution, compared to those in the dilute solution, absorb more photo energy collectively but less photo energy individually, we consider solute migration as net movement of individual solute molecules and then sequentially analyze how individual solute molecules absorb photo energy, convert the absorbed photo energy into translational excess energy intra-molecularly and carry out movement. Subsequently, by summing up movement of individual solute molecules in a unit of volume, we deduce the solute migration behaviors which coincide with the experimental results: for short pulse excitation, solute migration is more/less in the concentrated solution depending on the pulse energy; for continuous light irradiation, solute migration is more in the concentrated solution. Note that, in our theoretical deduction, the short-pulse-induced and continuous-light-driven solute migrations differ in that the former proceeds before inter-molecular relaxation becomes apparent and the latter carries on with inter-molecular relaxation practiced sufficiently. Accordingly, the former is non-quasistatic and the latter is quasistatic and thus referred to as thermal diffusion.

Keywords: short pulse induced solute migration, continuous-light-driven solute migrations, thermal diffusion , photo absorption