Molecularly Oriented Films for Space Applications

Abstract

Because of their inherent toughness and flexibility, low density, thermal stability, radiation resistance and mechanical strength, aromatic polyimides have excellent potential for use as advanced materials on large space structures. Polyimides were uniaxially and biaxially oriented to further enhance their dimensional stability, stiffness, elongation and strength. Both unoriented and oriented polymeric thin films were also cryogenically treated to temperatures below −184 • C to show their stability in cold environments. Successful stretching depended on film quality, film thickness, soak time, grip pressure, stretching rate and stretching temperature. In-plane birefringence increased with increased stretch ratios as expected. Coefficients of thermal expansion (CTEs) decreased with increased stretch ratio by as much as 31%. Tensile strengths increased by up to 85% with increasing stretch ratio. Elongations increased by as much as 95% with stretching. Significant improvements in elongation were obtained with only a 2× uniaxial orientation. Moduli did not change significantly with stretching. Mechanical properties increased more with uniaxial stretching than biaxial stretching. Cryogenic treatment increased the tensile strength of some stretched samples by a maximum of 10-20%. Properties such as modulus and CTE did not change significantly after the films had been slow cooled to cryogenic temperatures.

Nonlinear Dynamics of Cantilever Tip-Sample Surface Interactions in Atomic Force Microscopy

“…Using the value 1.5 degrees, we obtain from the model that the variation in the Young modulus ΔE/E ≈ 18%. This value is consistent with the value ΔE/E ≈ 21%obtained from independent mechanical stretching experiments on pure LaRC TM -CP2 polymer sheets (Fay et al, 1999). An RDF-AFUM phase image of the same scan area as that of Fig.…”

“…A commercial cantilever having a stiffness constant of 14 N m -1 , a lowest-mode resonance frequency of 302 kHz, and a cantilever damping coefficient of roughly 10 -8 kg s -1 is driven at 2.1 MHz to obtain the micrograph of Fig.5a (Cantrell et al, 2007). The values of the relevant model parameters for LaRC TM -CP2 polyimide polymer are 1.4 x 10 3 kg m -3 for the mass density ρ, 2.4 GPa for the Young modulus E, 0.37 for the Poisson ratio υ, k s = 96.1 N m -1 , and γ s = 4.8 x 10 -5 kg s -1 (Park et al, 2002;Fay et al, 1999;Cantrell et al 2007). Since no bulk ultrasonic wave is involved, the image contrast results only from variations in the specimen near-surface sample stiffness constant k s .…”

Flexible all‐aromatic polyesterimide films with high glass transition temperatures

“…Their elastic modulus increased from 2.9 GPa to 3.9 GPa and from 2.0 GPa to 5.4 GPa, respectively. Typically, when polymer fibers or films are stretched, the tensile strength increases and the elongation at break decreases, because the polymer chains become highly extended. However, the elongation at break of our thermally stretched films showed a moderate increase from 2.3% to 3.0%, which is most likely related to an increase in molecular weight.…”

Evaluation of microbolometer-based thermography for gossamer space structures

“…10 However, sailcraft intended for future missions are intended to operate for greater than 10, perhaps even as long as 30 years. Thus, material property changes that occur during operation may result in unpredicted sailcraft performance.…”