MWN: Thermal Transitions in Polyelectrolyte Multilayers and Complexes

技术综述：聚电解质络合物和多层膜(分别为聚乙二烯和聚乙二烯)都是由带相反电荷的聚合物形成的，它们在结构和性能上有许多相似之处。对于从水下粘合剂到药物输送和生物材料的应用，PECS和PEMS都变得越来越重要。Lutkenhaus小组最近的研究发现，质子交换膜在有水存在的情况下加热时，会经历类似玻璃转变的二级热转变。尽管卢肯豪斯观测到的热转变具有玻璃化转变的所有经典特征，但它的确切性质仍然难以捉摸。质子交换膜通常被近似为PECs，并与之相比，因为它们都使用离子配对和熵相互作用来控制它们的形成。合理地说，PECS可以作为实验和模拟的平台来近似水化作用、离子强度和温度在PEMS中的作用。因此，PI建议使用水化作用、离子强度和离子物种以及温度作为调节参数来研究PECS作为PEMS的近似值。在国家科学基金会材料研究部和芬兰科学院自然科学与工程研究部的财政支持下，这个材料世界网络项目将通过实验和模拟两种方法进行研究，美国和芬兰的团队在这方面分别拥有专业知识。团队将举行学生和教师交流，以促进国际合作。非技术摘要：由相反电荷的聚合物之间相互作用形成的聚电解质复合体，在从水下粘合剂到药物输送和生物材料的应用中变得越来越重要。是否形成络合物取决于几个参数：聚电解质类型、盐类型、浓度、水化和温度。最近，Lutkenhaus小组观察到，被认为类似于络合物的聚电解质多层膜在高温下经历了一种独特的热转变。这种转变的本质还完全不为人所知，但这样做对复合体和多层膜未来的创新至关重要。因此，材料世界网络项目将研究上述参数对聚电解质复合体的形成和热转变的影响。美国队和芬兰队计划进行学生交流。聚电解质络合演示计划在德克萨斯农工大学的化学开放日上进行，这是一年一度的向公众开放的活动。计划对本科生和研究生进行研究指导，并对中学教师进行指导。

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.