Equilibrium Parameters of Polyelectrolyte Complex Coacervates

PART 1: NON-TECHNICAL SUMMARY

Polymers having electrically charged chemical groups, called polyelectrolytes, are seen throughout nature and technology. Because they are charged, these polymers dissolve in water, substantially increasing viscosity. When polyelectrolytes of opposite charge are mixed, they associate to give new materials, polyelectrolyte complexes or PECs, with potential applications as membranes for purification, biomedical materials, antifouling coatings, and waterproof adhesives.

Salt helps to loosen the attractions between oppositely charged polymers, allowing the material to be processed into desired shapes. All of these valuable applications depend on how the properties of these PECs can be designed by choice of materials and processing conditions. This research will shed light on three parameters essential to understanding the response and performance of PECs.

First, the size of polymer coils, known to be entangled within the amorphous PEC, will be measured inside the material by labeling polymer chains with heavy atoms. Second, the efficiency of salt in actively breaking interactions between polymer charges, as opposed to passively sitting near the charges, will be investigated. Finally, the influence of salt on water, salt and polymer content of PECs will be measured with ultraprecise analytical techniques.

In addition to serving as a training vehicle for domestic students, this project will reach out across continents, engaging colleagues and students in France and in Nigeria in seminars on polyelectrolytes and other aspects of modern polymer science and technology. PART 2: TECHNICAL SUMMARY

Polyelectrolyte coacervation/complexation, PECs, a subset of liquid/liquid phase separation, occurs when two polyelectrolytes of opposite charge are mixed. The system represents a hydrated blend of charged polymers with characteristics overlapping both a hydrogel and a classical blend of neutral polymers. This morphology offers novel applications in the areas of separations/purification, biomedical materials, antifouling coatings, energy conversion, and waterproof adhesives.

The materials and their properties also lie at the intersection of intense interest in liquid/liquid phase separation from the physics, chemistry, biology and materials fields. A deep understanding of the properties of PECs requires knowledge of many parameters both fundamental to polymer science and unique to PECs. The proposed research will accurately measure three important parameters.

First, the scaling of the polymer coil size as a function of molecular weight will be determined using a series of narrow molecular-weight-distribution deuterated polyelectrolytes. The second area addresses the central uncertainty of what happens to salt ions when they enter a PEC to break pairing between positive and negative repeat units: whether each ion breaks a pair or whether some of the ions are simply present to balance the osmotic pressure between PEC and solution.

In the final subproject, a series of short-chain-length polyelectrolytes, radiolabeled with C-14, will be prepared and employed in highly precise and accurate radioanalytical methods to determine a PEC phase diagram as a function of molecular weight. All of these parameters are needed to supply the burgeoning theoretical treatments with reliable data.

In addition to serving as a training vehicle for domestic students, this project will reach out across continents, engaging colleagues and students in France and in Nigeria in seminars on polyelectrolytes and other aspects of modern polymer science and technology. .

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.