Magnetically-Driven Orientation of Multiphase Polymer Systems: A Ligand-Functionalized, Magnetic Nanoparticle Approach

提案号：0967559pi。当前位置Richard spontako将无机纳米颗粒（NPs）分散到聚合物基质中，作为一种可行且简便的方法，可以增强有机聚合物的机械、光学、电学和磁性能，这一研究兴趣不断增加。虽然许多研究都集中在使用（co）聚合物基质来空间调节NPs，但本研究的总体目标是证明使用场定向表面功能化磁性纳米颗粒（NPs）来指导相取向的可行性，从而产生具有潜在新各向异性特性的新多相聚合物形态。在两种体系中：聚合物共混体系和由聚苯乙烯和聚甲基丙烯酸甲酯（PS/PMMA）组成的嵌段共聚物中，通过外部施加均匀磁场形成的磁性NP链对（微）相分离过程中纳米/微观结构的影响将被探索。我们假设，由于沿场方向形成NP链，共混物将形成高度拉长的相域或可能形成层，而不是传统的球形畴，而共聚物中的片层将与NP对齐，形成大晶粒尺寸（缺陷数量减少）。具有天然长链脂肪官能团的NP表面有望在两种系统的界面处聚集，从而作为稳定位点。这一预测将通过在高达20 kOe的磁场下使用磁性（Co和Fe3O4） NP来诱导线性NP链的形成来验证。这些NP链负责观察到的铁磁流体行为，通过它们的钉住行为预测界面的模板形成。为了探索不同的热力学行为，NPs将被低聚苯乙烯（OS）或低聚甲基丙烯酸甲酯（OMMA）功能化，以赋予其中一种聚合物的选择性溶解度。将比较磁场排列的纳米/微结构在界面上与在一个（微）域内形成的磁性NP链。同时还制备了Au/Fe3O4二元核NPs。由于Au和Fe3O4的表面化学性质不同，每一半都将独立地官能化，一半是OPS，另一半是OMMA，形成Janus NPs。将探索定向Au/Fe3O4 NPs改变界面的可能性。将进行多尺度分子动力学模拟来补充实验，以(i)提供NP链形成动力学的理论框架，（ii）通过建立操作阈值来指导实验设计。智力优势：提出的研究将大大提高目前对NPs在非均相聚合物体系中用于固定或排列相边界的作用的理解。由于在多相聚合物体系中需要实现对形态取向的更大控制，因此利用磁场排列的NP链来形成定向片层相边界的模板将是进一步研究和应用的兴趣所在。更广泛的影响：拟议研究的结果将被纳入NCSU的两门课程。除了通过学生参与丰富本科和研究生课程外，我们还计划通过NCSU的凯南研究员计划向当地K-12年级的学生推广项目。pi将努力吸引来自北卡罗来纳州立大学RISE（即将入学的新生）和Pack Promise（提供学费减免、研究职位和学术支持的低收入学生）项目的代表性不足和少数民族学生。私立学校有从这些学生群体中招募优秀学生的成功经验。

Proposal Number: 0967559P.I.: Richard SpontakInterest in dispersing inorganic nanoparticles (NPs) in polymeric matrices continues to increase as a viable and facile means by which to enhance the mechanical, optical, electrical, and magnetic properties of organic polymers. While many studies have focused on using the (co)polymer matrix to spatially modulate the NPs, the overarching objective of the present proposal is to demonstrate the feasibility of using field aligned surface functionalized magnetic nanoparticles (NPs) to direct phase orientation and therefore generate new multiphase polymer morphologies with potentially new anisotropic properties. The effects of magnetic NP chains formed in homogeneous polymer mixtures by externally applied, uniform magnetic fields, on the nano/microstructure during (micro)phase separation will be explored in two systems: polymer blends and block copolymers composed of polystyrene and poly(methyl methacrylate) (PS/PMMA). We hypothesize that, due to the formation of NP chains along the field direction, the blends will form highly elongated phase domains or possibly layers instead of conventional spheroidal domains, whereas the lamellae in the copolymer will align with the NPs to form large grain sizes (with a reduced number of defects). The NP surfaces with native long chained aliphatic functional groups are expected to agglomerate at the interface in both systems and thus serve as stabilizing sites. This prediction will be verified using magnetic (Co and Fe3O4) NPs under magnetic fields of up to 20 kOe to induce formation of linear NP chains. These NP chains, responsible for observed ferrofluid behavior, are predicted to template formation of the interface through their pinning behavior. To explore a different regime of thermodynamic behavior, NPs will be functionalized with oligostyrene (OS) or oligo(methyl methacrylate) (OMMA) to impart selective solubility in one of the polymer species. The field aligned nano/microstructures will be compared for magnetic NP chain formation at the interface versus within one of the (micro)domains. Binary core Au/Fe3O4 NPs will also be prepared. Owing to the distinct Au and Fe3O4 surface chemistries, each half will be independently functionalized one half with OPS, and the other with OMMA, to form Janus NPs. The possibility of altering interfaces with oriented Au/Fe3O4 NPs will be explored. Multiscale molecular dynamics simulations complementing experiments will be performed to (i) provide a theoretical framework of the dynamics of NP chain formation and (ii) guide experimental design by establishing operational thresholds.Intellectual Merit: The proposed research will significantly enhance the current understanding of the role that NPs can serve to pin or align phase boundaries in heterogeneous polymer systems. Use of magnetic-field aligned NP chains to template formation of oriented lamellar phase boundaries will be of interest for further studies and applications, since there exists a great need to achieve greater control over morphological orientation in multiphase polymer systems.Broader Impact: The results from the proposed research will be incorporated into two courses at NCSU. In addition to enriching the undergraduate and graduate curriculum through student participation, we plan outreach programs to local students at the K-12 levels through the Kenan Fellows Program at NCSU. The PIs will endeavor to attract underrepresented and minority students from the RISE (incoming freshman students) and Pack Promise (low income students provided with tuition wavers, research positions, and academic support) programs at NC State. The PIs have successful experience recruiting exemplary students from such student groups.