ja8b03828_si_001.pdf (6.68 MB)
Mechanistic Insights into Diblock Copolymer Nanoparticle–Crystal Interactions Revealed via in Situ Atomic Force Microscopy
journal contribution
posted on 2018-06-18, 20:30 authored by Coit T. Hendley, Lee A. Fielding, Elizabeth R. Jones, Anthony J. Ryan, Steven P. Armes, Lara A. EstroffRecently, it has
become clear that a range of nanoparticles can
be occluded within single crystals to form nanocomposites. Calcite
is a much-studied model, but even in this case we have yet to fully
understand the details of the nanoscale interactions at the organic–inorganic
interface that lead to occlusion. Here, a series of diblock copolymer
nanoparticles with well-defined surface chemistries were visualized
interacting with a growing calcite surface using in situ atomic force microscopy. These nanoparticles comprise a poly(benzyl
methacrylate) (PBzMA) core-forming block and a non-ionic poly(glycerol
monomethacrylate) (Ph-PGMA), a carboxylic acid-tipped poly(glycerol
monomethacrylate) (HOOC-PGMA), or an anionic poly(methacrylic acid)
(PMAA) stabilizer block. Our results reveal three modes of interaction
between the nanoparticles and the calcite surface: (i) attachment
followed by detachment, (ii) sticking to and “hovering”
over the surface, allowing steps to pass beneath the immobilized nanoparticle,
and (iii) incorporation of the nanoparticle by the growing crystals.
By analyzing the relative contributions of these three types of interactions
as a function of nanoparticle surface chemistry, we show that ∼85%
of PMAA85-PBzMA100 nanoparticles either “hover”
or become incorporated, compared to ∼50% of the HOOC-PGMA71-PBzMA100 nanoparticles. To explain this difference,
we propose a two-state binding mechanism for the anionic PMAA85-PBzMA100 nanoparticles. The “hovering”
nanoparticles possess highly extended polyelectrolytic stabilizer
chains and such chains must adopt a more “collapsed”
conformation prior to successful nanoparticle occlusion. This study
provides a conceptual framework for understanding how sterically stabilized
nanoparticles interact with growing crystals, and suggests design
principles for improving occlusion efficiencies.