| Abstract: | Photoirradiation of polymer films at constant length induced a fast tension reduction (time scale: seconds) followed by slow tension buildup (time scale: minutes). Immediately after irradiation, fast tension buildup was followed by slow tension decay. Cycles were repeatable without significant hysteresis loss. The amplitude of both phenomena are intensity-dependent in the ultraviolet–visible spectral regions; both phenomena are thermal rather than photochemical effects. Light-absorbing chromophores in the polymer structure, or in additives such as dyes, lead to absorption of light and internal conversion into heat. The classical, rapid thermal expansion (or contraction) on heating (or cooling) leads to the fast relaxation (or buildup) of tension. The elastic, entropic response of the sample with its longer relasation time leads to slow buildup (or decay) of tension. Fast and slow responses are observed sequentially with film of extensively crosslinked Riston photopolymer resist or with Kapton polymide film, whereas, in experiments with latex rubber, the rubbery behavior dominates. |
