ma9b01809_si_001.pdf (1.33 MB)
Molecular Parameters Governing the Elastic Properties of Brush Particle Films
journal contribution
posted on 2020-02-03, 20:41 authored by Jaejun Lee, Zongyu Wang, Jianan Zhang, Jiajun Yan, Tingwei Deng, Yuqi Zhao, Krzysztof Matyjaszewski, Michael R. BockstallerElucidation of the mutual influence
of composition and architecture
of polymer canopies on the
assembly and mechanical properties of brush particle-based materials
holds the promise of advancing the understanding of the governing
parameters controlling interactions in hybrid materials and the development
of novel functional materials. In this work, the elastic properties
of three series of brush particle systems were investigated, differentiated
by grafting density as dense, intermediate, and sparse brush systems.
Dense and intermediate systems displayed uniform microstructures;
the degree of order (measured using Voronoi cell area analysis) increased
with grafting density. For dense and intermediate brush particle systems,
instrumented indentation analysis revealed an increase of the elastic
modulus with the degree of polymerization of tethered chains, in contrast
to effective medium predictions. Furthermore, the contribution of
ligands to particle interactions increased with decreasing grafting
density. The results indicated that the response behavior of particle
brush films in tensile-type deformations depends on dispersion interactions
between ligands of adjacent brush particles. The more pronounced brush
interdigitation in the case of intermediate graft densities enhanced
the dispersion interactions between brush particles and hence the
modulus of films. A reversed trend in modulus was observed in films
of sparse brush particles that also featured the formation of string-like
superstructures. Here, the elastic modulus was substantially increased
for low-molecular ligands and continuously decreased with increasing
degree of polymerization of tethered chains along with a transition
from string-like to uniform morphologies. Independent of grafting
density, the elastic modulus of the pristine polymer was recovered
in the limit of a high degree of polymerization of polymer ligands.