We are working on large area magnetic field alignment of PEO containing block copolymers which is an attractive polymer electrolyte for battery applications. High defect density and lack of long range order prevent continuous pathways for the ionic conduction and the subsequent utility of these materials as membranes for ion transport. We utilize strong magnetic fields to impose long range order in these soft materials.

We have accomplished large area domain alignment of poly(ethylene oxide-b-6-(4’-cyanobiphenyl-4-yloxy) hexyl methacrylate) (EO-MA/LC) block copolymer in high magnetic field (5T) while cooling from elevated temperatures through ODT of the system. The diamagnetic anisotropy provided by the LC ordering of the mesogens permit facile control of the alignment of the block copolymer superstructure over large length scales (>1 mm) by the application of magnetic fields. The orientation order is characterized by small angle X-ray scattering and polarized optical microscopy. The thermal behavior of the system is studied by DSC and impedance spectroscopy is utilized to measure the anisotropic thermal conductivity of the system. Small angle X-ray scattering demonstrated that lamellar and cylindrical PEO microdomains aligned with their interfaces along the applied field while the smectic layers of the liquid crystalline mesophase are perpendicular to the field in agreement with the positive diamagnetic anisotropy of the cyano-biphenyl mesogen and a homogeneous anchoring condition at the inter-material dividing surface (IMDS) between the two blocks. Doping with Li salt improves the microphase separation and orientation order in the system. We believe that facile control of PEO microdomains by magnetic fields will spur new developments in this area.

We continue to work on obtaining anisotropic Li conducting membranes from cylindrical material where the magnetic alignment is unique unlike the degeneracy associated with lamellar systems.

Reversible hydrogen bonding between a surfactant and a polymer having complementary sites for the surfactant can lead to phase separation and block copolymer-like morphology. Our studies are focused on the structure and dynamics of polymer-surfactant complexes, with efforts paid to explicitly address the effect of the strength of the interaction between the polymer and surfactant. Above a critical stoichiometry, i.e. the ratio of ligand concentration to that of binding sites, these polymers may display liquid crystalline behavior in the melt state. The weak interaction between the ligands means that the binding equilibrium is dynamic, and so ligands are thought to change their sequence distribution along the polymer chain in response to changes in temperature, stoichiometry and the chemistry of the ligand. Characterizing this behavior is the central theme in our research. We study the thermal properties of the mesophases via DSC, and correlate this with polarized optical microscopy and small angle X-ray scattering studies in solution and in the melt. Figure2 depicts temperature dependent SAXS measurements on a melt sample showing the emergence of a bilayer liquid crystalline structure at elevated temperatures. The structure transitions back to a monolayer at lower temperatures.

The surfactant is designed such that specific environmental stimuli such as temperature induces changes in the polymer chain-level structure by modifying the interaction strength. We use a combination of FTIR and Isothermal Calorimetry (ITC) measurements to carefully quantify the weak, reversible hydrogen bonding interactions between hydrophilic materials such as poly(acrylic acid) or poly(vinyl alcohol) and conjugate small molecular ligands.

In addtion to engineering novel polymer-surfactant systems through hydrogen bond interactions, our current work also encompasses utilizing simple non covalent interactions to obtain long range order in block copolymers by magnetic fields. We have succesfully obtained large area magnetic alignment of PS-b-AA polymer bearing mesogenic side chains interacting with AA backbone through intermolecular hydrogen bonding. We are also working on improving microphase separation and large area alignment of phase mixed block copolymers using simple non covalent interactions as well.