Collaborative Research: Locking Nanoparticles

CBET-0756457 Luzinov智力优点拟议研究的目标是合成和研究由无机超顺磁性核和混合聚合物刷壳构成的直径为10-100 nm的混合纳米颗粒。混合聚合物刷是指两种不同聚合物末端接枝到同一固体基底上的单层。PI成功地使用接枝到纳米颗粒上的混合刷来设计改变其性质的响应性胶体系统（例如，界面能和组成、粘附、吸附、聚集、稳定性等）根据外部信号，如溶剂质量、pH和温度。这种开关/响应行为的机制被证明是源于不同的聚合物在壳中的微相分离，其中外部条件可能会强烈影响相分离。在这项提案中，我们建议进一步发展响应性粒子方法，以实现具有挑战性的新系统-由于纳米粒子的特殊定制的核-壳结构而具有双重响应的混合纳米粒子。超顺磁性纳米粒子的核将被由水溶性聚合物和疏水性弱磁性聚合物组成的混合刷壳包覆。后一种聚合物在水溶液中的溶解度可以通过pH、离子强度和温度来调节。例如，在室温和pH 7下，该聚合物分离到颗粒核，并且混合刷形成径向分离的壳。具有分层混合刷壳的颗粒将表现出非粘性特性，并在宽范围的pH值和离子强度的水溶液中形成稳定的悬浮液。由于空间排斥机制，它们将被由水溶性聚合物制备的聚合物刷（形成外壳）稳定。这种情况可以通过施加外部磁场而发生戏剧性的变化。磁力将克服空间排斥力，并且颗粒将通过内刷壳相互作用。因此，该外部磁场可以开启颗粒本身之间或颗粒与目标基底之间的相互作用。由于内壳层之间的强相互作用，即使在去除外部磁场后，相互作用也保持不变。该机构在此被称为“锁定机构”。内壳之间的相互作用可以通过宿主环境中的pH和温度来调节和切换。因此，可以通过施加外部刺激来解锁粒子。这里提出的纳米颗粒将响应外部磁场，同时，它们将响应pH值，离子强度和温度的变化。颗粒的胶体分散体的性质将通过磁场和化学/物理刺激的组合来调谐/切换。在拟议的研究中，我们的目标是：（1）开发具有双重响应的纳米颗粒的合成;（2）研究颗粒的响应行为，以及（3）在粘合剂和非粘合剂颗粒壳之间切换，以打开和关闭颗粒在各种表面上的吸附及其聚集。更广泛的影响所获得的结果预计将大大影响纳米科学和纳米技术领域，涉及纳米粒子技术和复杂的功能材料和设备的设计。磁响应颗粒将用于一系列重要的技术，生物和医学应用，其中特异性与非特异性颗粒相互作用可以在外部磁场中打开。拟议项目的另一个优先事项是让最聪明的高中生、本科生和研究生参与现代纳米结构材料研究。该项目将在纳米科学、纳米技术、颗粒科学和表面科学方面对这些学生进行培训。学生将从这个项目的跨学科性质中受益匪浅。将作出重大努力，增加攻读科学和工程学高级学位的学生人数，特别是少数民族和妇女的人数。

CBET-0756457LuzinovIntellectual Merit The goal of the proposed research is to synthesize and study hybrid nanoparticles 10-100 nm in diameter constituted of an inorganic superparamgnetic core and a mixed polymer brush shell. Mixed polymer brushes refer to monolayers of two unlike polymers end-grafted to the same solid substrate. Mixed brushes grafted onto nanoparticles were successfully used by the PIs to design responsive colloidal systems which change their properties (e.g., interfacial energy and composition, adhesion, adsorption, aggregation, stability, etc.) according to external signals such as solvent quality, pH and temperature. The mechanism of this switching/responsive behavior was shown to originate from the microphase segregation of unlike polymers in the shell, where outside conditions may strongly affect the phase segregation. In this proposal, we suggest the further development of the responsive particle approach to a challenging new system - hybrid nanoparticles with dual responses due to the nanoparticles' specially tailored core-shell structure. The superparamgnetic nanoparticle's core will be coated by the mixed brush shell composed of a water soluble polymer and a hydrophobic weak polyelectrolyte. Solubility of the latter polymer in aqueous solutions can be tuned by pH, ionic strength, and temperature. For example, at room temperature and at pH 7 this polymer segregates to the particle core and the mixed brush forms radially segregated shell. The particles with a stratified mixed brush shell will demonstrate non-sticky properties and form stable suspensions in aqueous solutions in a broad range of pH values and ionic strengths. They will be stabilized due to the steric repulsion mechanism by the polymer brush (forming the outer shell) prepared from a water soluble polymer. The situation can be dramatically changed by applying an external magnetic field. The magnetic forces will overcome the steric repulsion and the particles will interact via the inner brush shells. Thus, this external magnetic field can turn on interactions between particles themselves, or between particles and the targeted substrate. The interaction remains unchanged even after removal of the external magnetic field due to the strong interactions between the inner shells. This mechanism is termed here the "locking mechanism". The interaction between the inner shells can be tuned and switched by the pH and temperature in their host environment. Thus, the particles can be unlocked by applying external stimuli. The nanoparticles proposed here will respond to an external magnetic field and, at the same time, they will respond to changes in pH, ionic strength and temperature. Properties of the particles' colloidal dispersion will be tuned/switched by a combination of a magnetic field and chemical/physical stimuli. In the proposed research we will aim: (1) developing the synthesis of the nanoparticles with the dual response; (2) studying the responsive behavior of the particles, and (3) switching between an adhesive and a non-adhesive particle shell to turn the adsorption of particles on various surfaces and their aggregation on and off. Broader Impact The obtained results are expected to substantially impact nanoscience and nanotechnology fields involving nanoparticle technologies and the design of complex functional materials and devices. The magnetically responsive particles will be used for a range of important technical, biological and medical applications where the specific versus nonspecific particle interactions can be switched on in an external magnetic field. Another priority of the proposed project is the involvement of the brightest high school, undergraduate and graduate students in modern nanostructured materials research. The project will train these students in nanoscience, nanotechnology, particulate science and surface science. Students will benefit greatly from this project's interdisciplinary nature. Significant effort will be directed to increasing the number of students, especially minorities and women, who pursue advanced degrees in science and engineering.