Issue 15, 2020

Liquid–liquid equilibrium in polymer–fullerene mixtures; an in situ neutron reflectivity study

Abstract

The composition profiles of a series of model polystyrene/fullerene bilayers are measured, before, during and after thermal annealing, using in situ neutron reflectometry. In combination with grazing-incidence X-ray diffraction measurements, these experiments, which quantify layer compositions as a function of molecular weight using changes in both scattering length density and layer thickness, extend and corroborate recent measurements on ex situ annealed samples and demonstrate that the composition profiles rapidly formed in these systems correspond to two co-existing liquid–liquid phases in thermodynamic equilibrium. The measurements also demonstrate a clear and systematic onset temperature for diffusion of the fullerenes into the PS layer that correlates with the known glass-transition temperatures of both the polymer (as a function of molecular weight) and the fullerene, revealing that the molecular mobility of the fullerenes in these systems is controlled by the intrinsic mobility of the fullerenes themselves and the ability of the polymer to plasticise the fullerenes at the interface. Over the temperature range investigated (up to 145 °C), measurements of equilibrated composition profiles as a function of temperature (during gradual cooling) reveal no significant changes in composition profile, other than those associated with the known thermal expansion/contraction of polystyrene thin-films.

Graphical abstract: Liquid–liquid equilibrium in polymer–fullerene mixtures; an in situ neutron reflectivity study

Supplementary files

Article information

Article type
Paper
Submitted
26 Nov 2019
Accepted
23 Jan 2020
First published
31 Mar 2020
This article is Open Access
Creative Commons BY license

Soft Matter, 2020,16, 3727-3739

Liquid–liquid equilibrium in polymer–fullerene mixtures; an in situ neutron reflectivity study

E. L. Hynes, P. Gutfreund, A. J. Parnell and A. M. Higgins, Soft Matter, 2020, 16, 3727 DOI: 10.1039/C9SM02337B

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