5 years ago

Nanomechanical Imaging of the Diffusion of Fullerene into Conjugated Polymer

Nanomechanical Imaging of the Diffusion of Fullerene into Conjugated Polymer
Shaowei Shi, Feng Liu, Thomas P. Russell, Dong Wang, Ken Nakajima
The large Young’s modulus difference between chemically modified fullerene (PCBM) and a conjugated polymer was used to nanomechanically map the diffusion of PCBM into PTB7, a high-efficiency low-band-gap conjugated polymer. The sharp tip in nanomechanical atomic force microscopy ensures a high-resolution nanomechanical characterization of the diffusion front, with the intrinsic benefits of revealing the mechanical properties of the mixtures. Localized structure changes induced by diffusion were investigated by grazing incidence X-ray diffraction methods. We found a most unusual diffusion behavior that shows Case II characteristics, where a front of PTB7 saturated with PCBM moves into the pure PTB7 with a linear time dependence. This diffusion is due mainly to a majority fraction of the disordered PTB7 that has continuous paths for PCBM diffusion without obvious energetic barriers, and as diffusion proceeds, the paths for diffusion gets larger, leading to a step in the concentration profile. The donor/acceptor-dependent diffusion constants may also contribute to the observed Case-II-like diffusion front.

Publisher URL: http://dx.doi.org/10.1021/acsnano.6b08456

DOI: 10.1021/acsnano.6b08456

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