Lynden A. Archer
Fellow, Elected 2020
Research in the Archer group uses experiment and theoretical analysis to investigate structure, dynamics, surface migration, and transport phenomena at liquid-solid interfaces.
The Archer group’s contributions to rheology lie at the intersection of three large fields: polymer science, colloid science, and electrochemistry. These contributions range
from basic science studies of how microscopic condensed phases (e.g. polymers, nanoparticles, ions) in liquids move and partition near interfaces; to work centered on design
of nanoparticle-polymer hybrid materials that allow interfacial fluid behaviors to be isolated and studied; and ultimately to research aimed at understanding how hydrodynamics
in liquid electrolytes at electrolyte-electrode interfaces impact stability of metal electrodes in rechargeable batteries.
In one class of problems results from the Archer group
have shed light on how and why slower motions of polymers at interfaces alter classical assumptions about slippage and adhesion of liquids at liquid-solid interfaces. Insights
from these studies led to the conclusion that occurrences of interfacial slip at entangled polymer/solid interfaces are as fundamental to these materials as the presence of
entanglements themselves. The slip in fact originates from a mismatch in dynamics between chains adsorbed to the substrate and those that are not. Strategies that break the mismatch
(e.g., small-scale surface roughness or polydispersity of the anchored chains), blur the interfacial zone and as a result provide the most effective approaches for suppressing
wall slip in entangled polymers. In search for high signal-to-noise methods for quantifying surface-induced slow-down of polymer chains adsorbed at solid substrates, the Archer group
discovered a family of starbranched molecules, termed nanoscale organic hybrid materials (NOHMs), in which the core of the star is an inorganic nanostructure. At high polymer
coverages/grafting densities the materials exist as solvent-free self-suspended fluids in which the quiescent structure and bulk rheological properties are determined by space filling
constraints of the tethered polymer chains.
A large body of work by the Archer group has shown that rheological behaviors ranging from temperature-induced jamming, soft glassy dynamics,
and hyperdiffusive dynamics on timescales well outside those associated with the ballistic regime in Brownian motion can be explained — and tuned — by manipulating these constraints.
Variables such as the polymer grafting density, molecular weight of the tethered chains, and Fluory-Huggins χ parameter between tethered chains (e.g., in
SiO2-PEO/SiO2-PMMA NOHMs/NOHMs blends), have been shown by the group to provide the most straightforward way to manipulate particle-particle correlations in the
fluids and thereby rheology. The Archer group has also shown how one might leverage the tunable rheology of NOHMs to suppress hydrodynamic and morphological instabilities at metal
battery anodes that limit reversibility of rechargeable batteries that utilize such anodes for achieving energy-dense and low-cost portable storage of electrical energy.