Simulations polyimide films

Figure 7.42. Experimental setup and eastic recoil detection (ERD) spectra for multiwalled nanotubes, and a Kapton polyimide film. A computer program, SIMRA, is useful to simulate ERD as well as other non-RBS data. Reproduced with permission from Naab, F. U. Holland, O. W. Duggan, J. L. McDaniel, F. D. J. Phys. Chem. B 2005,109, 1415. Copyright 2005 American Chemical Society.

Intense excimer laser excitation of poly(methyl methacrylate) (PMMA) and polyimide films gives the transient expansion and the following contraction, which was directly measured as a function of nanosecond delay time during and after excitation. Depending on laser excitation condition, very rapid decay component and oscillatory behavior were observed in contraction and also phase transition is confirmed for PMMA. The behaviors are well interpreted by photothermal mechanism. In case of pol3dmide the expansion behavior is inconsistent with the simulation based on photothermal mechanism, on which we consider photochemical processes. New aspects of nonlinear polymer dynamics are presented and summarized. 

Simulation of Surface Temperature Elevation of Polyimide Film... 

Figure 6, Expansion and contraction dynamics of polyimide film at the fiuence of 20 mJ/cm below the ablation. The solid and dashed curves represent the time profiles of the excimer laser pulse and time-integration of the laser pulse, respectively, while the dotted and dash-dotted curves are simulated surface temperature rise at the fiuence of 20 mJ/crn and 30 mJ/cm, respectively. Excitation wavelength is 248 nm. An error bar is included.

Figure 8. TEM and optical absorption of the sample implanted with 5 x 10 Au /cm (a) TEM cross-sectional micrograph (dashed lines represent the free surface and film-substrate interface) (b) nanoparticles size distribution (c) simulated optical spectra (1) Au cluster in a non-absorbing medium with n = 1.6 (2) Au cluster in polyimide (absorbing) (3) Au(core)-C(shell) cluster in a nonabsorbing medium with n = 1.6 (4) the experimental spectrum of Au-implanted polyimide sample, (d) X-ray diffraction patterns as a function of the implantation fiuence.

Fujiwara et al [51] have used molecular dynamics simulations to interpret the images obtained from STM experiments. The combined use of these two techniques is proving to be a very powerful tool for understanding the conformation of polymer films on surfaces. They showed that the individual polyimide strands observed were aligned parallel to the deposition direction of the Langmuir-Blodgett film. 

First we consider that the different expansion behavior at 248 nm aiul 351 nm excitation is due to the different etching mechanism discussed above. In the case of 351 nm excitation, multiphoton photochemical and photothermal processes are involved and the latter may be more important at lower fluence. The contraction behavior at 80 mJ/cm may reflect slow heat dissipation in polyimide, which behavior is actually consistent with photothermal expansion and contraction dynamics of PMMA film (21). On the other hand, toe thin surface layer is excited at 248 nm, so that heat dissipation to quartz substrate should be slower than that at 351 nm. More quantitative analysis of cooling processes by the simulation was conducted to understand the expansion and contraction dynamics. 

Polyimides are of great interest because of their display application and simulations of large film areas have been carried out [88]. Furthermore, analysis of different combination of surface molecules and liquid crystal molecules has been carried out [89-92]. 

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