People

Sharon Wang

Sharon Sharick

PhD Candidate
B.S. Materials Science and Engineering, Carnegie Mellon University, 2010

LRSM 231
215-898-2700
sharick@seas.upenn.edu

 

 

Morphology of Polymerized Ionic Liquids

Polymerized ionic liquids (PILs) contain ionic liquid (molten salt) molecules where either the anion or cation is covalently bound to each polymer repeat unit. Potential applications for these materials include batteries, fuel cells, solar cells, and capacitors, due to the thermal and chemical stability, wide electrochemical window, and high ionic conductivity of PILs. Notably, these materials can be made into solid polymer electrolytes to replace liquid electrolytes. In addition, these materials are single-ion conductors with only one mobile ion, which eliminates the phenomenon of electrode polarization.

Chemical structure of PIL block copolymer, PMMA-b-PMEBIm-Br or -OH.

Figure 1. Chemical structure of PIL block copolymer, PMMA-b-PMEBIm-Br or -OH.

 

My research aims to understand the relationship between the structure and properties of PIL materials, in particular PIL block copolymers. PIL block copolymers self-assemble into microphase separated structures, creating alternating domains of conductive polymer and mechanically robust polymer. We recently observed that the ionic conductivity of a lamellar PIL block copolymer (chemical structure shown in Figure 1) exceeded that of its analog PIL homopolymer at 80°C, 90% relative humidity, despite the block copolymer having lower PIL content (fewer ions) and lower water content (see Figure 2). One possible explanation for this finding is that the spatial restriction of anion transport in the block copolymer, due to the confinement of PIL in layers, results in accelerated ion transport. In comparison, in a homopolymer PIL there is no such limitation on the pathway of the anion, which can sample all three dimensions of space with equal probability. It is also possible that the glass transition temperature of the hydrated PIL is locally lower in the block copolymer than in the homopolymer, or the local concentration of water may enhance ion transport. This observation of PIL block copolymer ionic conductivity exceeding PIL homopolymer conductivity is a significant finding and further validates the use of PIL block copolymers as nanostructured single ion conductor solid electrolytes.

Figure 2. Hydroxide conductivity as a function of temperature at 90% RH for the PIL block copolymer PMMA-b-PMEBIm-OH (37 vol% PIL), random copolymer PMMA-r-PMEBIm-OH (37 vol% PIL), and homopolymer PMEBIm-OH.

 

Figure 3. In situ SAXS profiles of the PIL block copolymer PMMA-b-PMEBIm-Br (39 vol% PIL) as a function of humidity at 30 °C (left) and temperature at 90% RH (right). SAXS data were collected in an environmental chamber and data are offset vertically for clarity.

 

Currently I am investigating the alignment of PIL block copolymers by electric field to better understand the mechanism of ion conduction in block copolymers. There are two primary mechanisms: ions moving through ion-containing polymer domains or through grain boundaries that separate regions of oriented, microphase separated sample. Aligning the block copolymer morphology by electric field increases the formation of large, uniformly oriented, nanostructured grains and removes grain boundaries. The corresponding change in ionic conductivity of aligned samples will give insight into how ions conduct.


Publications


1. “High Hydroxide Conductivity in Polymerized Ionic Liquid Block Copolymers.”
Y. Ye, S. Sharick, E. M. Davis, K. I. Winey*, Y. A. Elabd*, ACS Macro Letters, 2, 575-580, 2013.

2. “Hydroxyalkyl-Containing Imidazolium Homopolymers: Correlation of Structure with Conductivity.”
M. H. Allen, Jr., S. Wang, S. T. Hemp, K. I. Winey, T. E. Long*, Macromolecules, 46, 3037-3045, 2013.

3. “Ionic conduction and dielectric response of poly(imidazolium acrylate) ionomers.”
U. H. Choi, M. Lee, S. Wang, W. Liu, K. I. Winey, R. H. Colby*, Macromolecules 45, 3974-3985, 2012.