Laser Induced Propulsion in Toluene Diisocyanate Based Polyurethane Polymers: Effect of Molecular Weight

Abstract

The dependence of laser ablation propulsion parameters on both the laser fluence and the molecular weight of toluence diisocyanate based polyurethane polymer is reported in this work. As recoil momentum depends upon the laser supported shockwaves and the mass of ejected particles.A (Q-switched) Nd-YAG laser ( 5ns pulse duration and max energy 400 mJ) operating at 1064 nm was used to irradiate in the polymer samples for recoil momentum generation at different laser fluence. A contact free method named optical triangulation method was employed for measurement of laser ablation momentum in the samples. The results have shown that the critical propulsion parameters i.e. momentum coupling coefficient and specific impulse vary inversely with molecular weight for each value of fluence. The measurements and calculations depicted that Toluene diisocyanate polymer exhibiting low molecular weight shows better results in terms of performance of critical propulsion parameters at a specific value of fluence. Also, the laser ablation propulsion parameters decrease with decreasing laser fluence. The highest value of Cm (momentum coupling coefficient) is found to be 0.14 mN-s/J at laser fluence 5.79×106 J/m2 for sample with lowest molecular weight i.e. 75 kg/mol. Similarly, Isp (specific impulse) for this sample is found to be 13500 sec.

Keywords: Laser Ablation Propulsion, Toluene diisocyanate Polymers, Momentum coupling coefficient, Specific impulse