Fast Processing Affects the Relaxation of Polymers: The Slow Arrhenius Process Can Probe Stress at the Molecular Level.

Polymer materials are commonly processed at rates higher than those at which their molecules spontaneously reach equilibrium conditions. The resulting nonequilibrium conformations might significantly affect the mechanical behavior and the shelf time of the final products. To understand how processing-properties relations work, we investigated the impact of spin coating, an archetypical method to fabricate thin polymer layers. By using a geometry in which nonequilibrium conformations are frozen over sufficiently long experimental times, we could identify how molecular relaxation is affected by fast preparation methods. We find that while the (α-)segmental relaxation is not affected by the rate at which films are processed, the intensity of the slow Arrhenius process (SAP), a relaxation mechanism active both above and below the glass transition, can be used as a probe of the degree of mechanical stress experienced by the material.