Study of out-of-plane elastic properties of PMDA-ODA and BPDA-PDA polyimide thin films

Prism coupling technique investigation of elasto-optical properties of thin polymer films

“…For example, Liou et al measured out-of-plane elastic properties for thin polyimide films as a function of thickness using precision capacitance dilatometer. 12,26 They have found that the out-of-plane elastic moduli of the thin polymer films decrease with decreasing film thickness. For polyimide films, Liou et al obtained one order of magnitude decrease from about 2.8ϫ 10 9 N/m 2 down to 0.3 ϫ 10 9 N/m 2 in the out-of-plane modulus as the film thickness decreased from ϳ15 m to ϳ4 m and verified that the in-plane modulus has a larger value.…”

“…The observed anisotropy is mainly due to effects such as in-plane orientation of the polymeric chains during the spinning process and solvent evaporation and may depend on the specific type of polymer itself. 12,30 Due to the spinning process, the expected anisotropy of the layers is of uniaxial type and one of the principal axis of symmetry is parallel to the incident polarization. The measured birefringence in this case is Ͻ 0.002 and in this regime the isotropic assumption for mode equations remains as a reasonable approximation.…”

“…Therefore, all measurements of out-of-plane modulus and refractive index were performed during the unloading process. 12 …”

“…9 Other approaches include use of nanoindentor, 10 atomic force microscopy, 11 and precision capacitance dilatometry. 12 While all of these methods measure the out-of-plane mechanical properties of the polymer films, they do not measure optical properties simultaneously. Therefore, the relation between the stress and the optical properties can only be established indirectly for thin polymer films.…”

Stress effects in prism coupling measurements of thin polymer films

“…Polymers are typically spin coated onto substrates where the spin-coating and curing processes may introduce u Fax: +90-312/266-45-79, E-mail: aydinli@fen.bilkent.edu.tr in-plane orientation of polymeric chains. It is proposed that this is due to a biaxial tensile stress caused by substrate confinement when the solvent evaporates [9]. This leads to a molecular ordering, resulting in in-plane and out-of-plane optical anisotropy for the thin polymer films, as was confirmed by several investigations analyzing optical anisotropy for films with thicknesses in the few-micrometers range [10,11].…”