Block Copolymer Vitrimers.

In this report, we merge block copolymers with vitrimers in an effort to realize the prospect of higher-order, nanoscale control over associative cross-link exchange and flow. We show the use of controlled polymerization as a vital tool to understand fundamental structure-property effects through the precise control of polymer architecture and molecular weight. Vitrimers derived from self-assembling block copolymers exhibit superior resistance to macroscopic deformation in comparison to their analogs generated from statistical copolymers. Our results suggest that the enhanced creep resistance achieved by control over chain topology in block vitrimers can be used to tune viscoelastic properties. The resistance to macroscopic deformation that arises from a microphase-separated structure in this new class of materials differentiates block vitrimers from their statistical counterparts and introduces the potential of topology-control over viscoelastic flow.

Full Gamut Wall Tunability from Persistent Micelle Templates via Ex Situ Hydrolysis.

The predictive self-assembly of tunable nanostructures is of great utility for broad nanomaterial investigations and applications. The use of equilibrium-based approaches however prevents independent feature size control. Kinetic-controlled methods such as persistent micelle templates (PMTs) overcome this limitation and maintain constant pore size by imposing a large thermodynamic barrier to chain exchange. Thus, the wall thickness is independently adjusted via addition of material precursors to PMTs. Prior PMT demonstrations added water-reactive material precursors directly to aqueous micelle solutions. That approach depletes the thermodynamic barrier to chain exchange and thus limits the amount of material added under PMT-control. Here, an ex situ hydrolysis method is developed for TiO2 that mitigates this depletion of water and nearly decouples materials chemistry from micelle control. This enables the widest reported PMT range (M:T = 1.6-4.0), spanning the gamut from sparse walls to nearly isolated pores with ≈2 Å precision adjustment. This high-resolution nanomaterial series exhibits monotonic trends where PMT confinement within increasing wall-thickness leads to larger crystallites and an increasing extent of lithiation, reaching Li0.66 TiO2 . The increasing extent of lithiation with increasing anatase crystallite dimensions is attributed to the size-dependent strain mismatch of anatase and bronze polymorph mixtures.

QCM detection of molecule-nanoparticle interactions for ligand shells of varying morphology.

Nanoparticles (NP) have widespread applications from sensing to drug delivery where much behavior is determined by the nature of the surface and the resulting intermolecular interactions with the local environment. Ligand mixtures enable continuously tunable behavior where both the composition and morphology influence molecular interactions. Mixed ligand shells form multiple morphologies ranging from Janus to patchy and stripe-like with varying domain dimensions. Solvent-NP interactions are generally measured by solubility measures alone. Here we develop a quartz crystal microbalance (QCM) approach to more broadly quantify molecule-NP interactions via vapor phase uptake into solid NP-films independent from solvation constraints. The composition and morphology of mixed ligand shells were found to exhibit pronounced non-monotonic behavior that deviated from continuum thermodynamics, highlighting the influence of ligand morphology upon absorption/adsorption. Alkyl and perfluorinated thiols were used as a model case with constant core-size distribution. The ligand morphology was determined by 19F NMR. Molecule uptake into NPs was measured with five benzene derivatives with varied degree of fluorination. For the cases examined, QCM measurements revealed enhanced uptake for patchy morphologies and suppressed uptake for stripe-like morphologies. These results contrast with insights from solubility measures alone where QCM sometimes identified significant molecular uptake of poor solvents. This QCM method thus provides new insights to molecule-NP interactions independent of the solvation shell.