Thermal Transitions in Polyelectrolyte Multilayers and Complexes
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TECHNICAL SUMMARY: Polyelectrolyte complexes and multilayers (PECs and PEMs, respectively) are both formed from oppositely charged polymers, and share many similarities in structure and properties. Both PECs and PEMs are increasingly important for applications ranging from underwater adhesives to drug delivery and biomaterials. Recent work by the Lutkenhaus group has discovered that PEMs undergo a second-order, glass transition-like thermal transition upon heating in the presence of water. Even though the thermal transition observed by Lutkenhaus has all the classic features of a glass transition, its exact nature remains elusive. PEMs are often approximated as, and compared to, PECs because they both use ion-pairing and entropic interactions to control their formation. Rationally, PECs can be used as a platform for both experiments and simulations to approximate the role of hydration, ionic strength, and temperature in PEMs. Therefore, the PIs propose to study PECs as an approximation of PEMs using hydration, ionic strength and ionic species, and temperature as tuning parameters. With financial support from the Division of Materials Research at the National Science Foundation and the Natural Sciences and Engineering Research Unit at the Academy of Finland, this Materials World Network project will approach the study through both experimental and simulational approaches, in which the U.S. and Finnish teams have expertise, respectively. Teams will hold student and faculty exchanges to foster the international collaboration. NON-TECHNICAL SUMMARY: Polyelectrolyte complexes, which are formed from the interactions between oppositely charged polymers, are increasingly important for applications ranging from underwater adhesives to drug delivery and biomaterials. Whether or not the complex forms depends on several parameters: polyelectrolyte type, salt type, concentration, hydration and temperature. Recently, the Lutkenhaus group has observed that polyelectrolyte multilayers, which have been proposed to be similar to complexes, undergo a unique thermal transition at elevated temperatures. The nature of this transition is not at all understood, but it is critically important to the future innovation of complexes and multilayers to do so. Therefore, this Materials World Network project will study the effects of the aforementioned parameters on the formation in and thermal transitions of polyelectrolyte complexes. Student exchanges are planned between U.S. and Finnish teams. Polyelectrolyte complexation demonstrations are planned for Texas A&M University''s Chemistry Open House, an annual event open to the public. Undergraduate and graduate research mentoring, as well of mentoring of secondary school teachers is planned.