Mechanism Research Of Rotation Of Carbon Nanotube Paper Driven By Pulsed Laser

As a brand-new driving method which can realize long-distance and non-contact driving,light-driven macroscopic object motion is now gradually used in aerospace engineering,biomedicine,military engineering and other fields.The current main driving mechanisms of light driving technology include light pressure,light-induced electron jet and air convection.Carbon Nanotube Paper(CNTP)is a paper-like thin layer structure composed of entangled carbon nanotubes(CNTs)through Van der Waals Force between the tubes,which can be driven under the action of pulsed lasers.The laboratory initially observed that CNTP would rotate under the action of pulsed laser and accompanied by material loss.COMSOL multiphysics simulation software(COMSOL)was used to analyze the temperature distribution of CNTP after laser action.However,the specific mechanism of action of the nanosecond pulsed laser and the relationship between the driving effect and the material properties have not been analyzed.In this paper,we simulate and analyze the experimental process of nanosecond pulsed laser driving CNTP rotation,and propose a driving mechanism of equal body heating.COMSOL software is used to simulate the dynamic distribution of temperature and heat of CNTP after the action of nanosecond pulsed laser,and explore the impact of pulsed laser and CNTP parameters on the experiment.Finally,the experimental device and measuring device are redesigned.The main research work and results of this paper are as follows:(1)Analysis of the rotation dynamics of CNTP driven by pulsed laser:the driving effect of nanosecond pulsed laser acting on CNTP can be equivalent to the linear superposition of the driving effect after a single pulsed laser.In the previous experiment,the CNTP rotates with a uniform angular velocity,so as to estimate the driving force of the CNTP during the rotation(?14.7 N).It is calculated that the maximum light pressure produced by the pulsed laser(2.25×10^-4 N,0.27 m J)is more than 4 orders of magnitude smaller than 14.7 N,so the light pressure produced by the laser cannot drive CNTP.The experiment observed that CNTP was irradiated by laser to produce CNTs ejection process.Starting from the quality loss caused by this process,the driven mechanism of equal body temperature rise is proposed:the laser irradiates the CNTP and the temperature rises sharply,which triggers a rapid increase in the pressure in the micro-cavity formed by CNTs intertwined;while the CNTs are connected by a weak van der Waals force,and the increase in the air pressure of the micro-cavity leads to CNTs ejection,CNTP is obtained from this Backward driving force.According to the calculation results,the driving force obtained by CNTP(9 N)is close to the experimental estimate(14.7 N).The driving force is mainly related to the sharp increase in the temperature of the micro-cavity.(2)Conditions for pulsed laser driving CNTP:using COMSOL to simulate the dynamic changes and distribution of temperature and heat after a single pulse irradiates the porous medium CNTP,so as to explore the driving conditions.According to the simulation results,after the pulsed laser is applied to the CNTP,the temperature in the central area of the surface rises rapidly(within 15 ns)to a maximum of 10~4 K,and then rapidly decays.When the light frequency is less than 20 MHz,the driving effect of the nanosecond pulsed laser(pulse width 10 ns)is equivalent to the linear superposition of the driving effect after a single pulsed laser is applied.The higher the emissivity?(0.05-1),the smaller the constant pressure heat capacity C_p(200-2000 J/kg*K)and the density?(500-3000 kg/m~3),and the higher the central area?T of the CNTP within a short period of time(15 ns)after the pulse laser is applied.When the porosity?of CNTP is 0.4,the thermal conductivity?of CNTs is large but the overall effective thermal conductivity?_effof CNTP is small,the surface temperature of the material is higher after the pulse laser is applied,and the temperature decays fster during the cooling process.It can be obtained from the simulation results that the porous structure of CNTPs and the thermal conductivity properties of CNTs cause heat to accumulate in the center area of the material surface after the pulsed laser,which makes the temperature rise rapidly.The simulation results provide a strong basis for the driving mechanism proposed in this paper.(3)Selection of optically driven lasers and improvement of experimental equipment:a laser that can output larger energy(pulse power?10~5 W)in a short period of time is chosen to provide a larger driving force.However,if the laser energy is too large,the CNTP will be broken down and the driving effect will be poor.The carbon nanotube paper is placed with a windmill device instead of the filament suspension to reduce the drag effect;the windmill blade is redesigned,and the test device is improved to precisely measure the rotation angle and the driving force.