Molecular Ionic Composites (MICs)

Our group has discovered and is pursuing a new class of materials with an unprecedented combination of properties, which we now term Molecular Ionic composites (MICs). A MIC (a form of ion gel) molecularly self assembles as the combination of a rigid-rod polyanion and an ionic liquid. This material overcomes the usual compromise between ionic conductivity and modulus in solid-polymer electrolytes, which may demonstrate its potential to resolve current limitations and enable safe and high energy density Li metal batteries, as well as new technologies such as sodium batteries. While these materials display impressive properties, we are still exploring the detailed origins of these behaviors. If we can understand the fundamental origin of this effect, then we can enhance and design new MICs to meet desired requirements for battery electrolytes or other molecular conduction or chemical separations applications.

Block copolymer micelles

Block copolymer micelles (BCMs) have been favored for a multiple of applications such as tailored nanoreactors, tissue engineering, and advanced coatings. In particular, BCMs have been used as a novel carrier in targeted drug delivery, due to their controllable sizes and structures, prolonged circulation time, low critical micelle concentration and in vivo degradability. Biodegradable BCMs can aid in controlled delivery of poorly water-soluble anticancer drugs, e.g., doxorubicin (DOX) and paclitaxel (PTX).

We are studying a diblock poly(ethylene oxide)-b-(caprolactone) (PEO–PCL) that forms spherical micelles at 1% (wt/vol) in the mixed solvents (D2O/THF-d8) (see Figure 1). We are using NMR spectroscopy and diffusometry to quantify both the populations and diffusion coefficients of coexisting micelles and free unimers over a range of temperatures and solvent compositions.  Surprising results on the populations of free unimers are pointing the way to new insights in BCM behaviors and exchange processes. 

Transport in polymer membranes

Our group has been study various kinds of polymer membranes including cation exchange membranes (CEMs), anion exchange membranes (AEMs) and various reverse osmosis membranes. Polymer membrane technology is crucial in applications such as fuel cells,  water purification, and a host of other chemical separations. While polymer membranes emerged more than half a century ago, we still lack sufficient knowledge to make quantitative predictions of how structure and composition of the membrane may influence transport properties, which limits the development of efficient membrane technology. 

For example, Nafion is still among the membranes having the highest proton conductivity. A common feature for this membrane is the formation of water channels from the phase separation between the hydrophobic backbone and hydrophilic side chain (as shown in the figure below). The size of the water channels is believed to be on the length scale of nanometers. The effects of the structure of Nafion on the transport of water molecules and ions through its water channels are still not well understood. Our group is exploring two aspects of an ionic polymer membrane, morphology and local environment, to understand how transport is regulated in such membranes. Both NMR spectroscopy and molecular dynamics (MD) simulations have been utilized in this study.

We are also studying membranes such as ammonium-based anion exchange membranes and reverse osmosis membranes. Such studies will not only improve fundamental understanding of polymer membranes but also inform the design of better polymer membranes.