Resonant Soft X-Ray Scattering Reveals Chromophore Domains in Polymer Doped with Disperse Orange 11 Dye

Chromophore domains were proposed in a previous work as the mediators of self-healing of optical properties in dye-doped polymers. A statistical mechanical model based on domains matches all observed self-healing dynamics as a function of dye concentration, temperature and light intensity. This suggests that domains are responsible. However, there is no direct observation of domains, nor has their physical morphology been determined. This work reports the first observation of domains in a self-healing polymer using resonant soft X-ray scattering (RSoXS), which gives a domain size in the range of 39.3 Å to 62.8 Å. This range includes the domain model’s prediction of an average domain size of roughly 30 molecules, which is about 56 Å, if the molecules form a loosely packed ball. X-ray scattering of samples of concentration spanning from neat polymer to the saturation limit of disperse orange 11 (DO11) dye in poly(methyl methacrylate) (PMMA) polymer shows domains in the expected size scales, with the mode of the effective scattering width varying little with concentration. However, for constant domain shape, the mode peak would decrease in q with increasing concentration, according to the domain model. This work suggests that the domain shape might change with concentration, which warrants further investigations of domain topology and geometry. The important evidence presented in this work is the direct experimental observation of domains, which is central to self-healing models.