Dynamic Simulation of Polymer Adsorption in Flowing Fluids for Design of Polymer Thin-film Materials

1132083Kumar，SatishProject技术总结。由于其独特的电学性质，AB叠层石墨烯在下一代光电子学和微处理器应用中显示出了非凡的潜力。然而，这些有希望的材料需要新的合成方法来通过石墨剥离和先进的加工技术来有效地控制AB堆叠层的数量。溶液石墨烯分散体是制造可印刷电子器件和纳米复合材料的很有前途的原材料，最重要的是，这种方法是目前批量生产AB堆叠的双层和三层石墨烯的唯一可能途径。然而，自2008年报道第一个石墨烯解决方案以来，仍有许多悬而未决的问题和技术瓶颈阻碍了该领域的进展。虽然实验表明石墨烯层数的分布高度依赖于所使用的溶剂或表面活性剂的选择，但关于石墨烯与溶剂/表面活性剂分子之间相互作用的分子起源，包括这些相互作用与石墨烯溶液的胶体稳定性之间的关联，人们知之甚少。此外，无论采用哪种方法生产溶液相石墨烯，其大小、形状和堆积层数都是多分散的。必须开发工程方法来直接控制剥离的石墨烯薄片的尺寸和堆积几何形状(通过缩小它们的分布)。智力优势：这个项目试图通过大规模的分子动力学模拟来理解悬浮石墨烯与周围的溶剂/表面活性剂分子之间相互作用的起源。这些相互作用将通过计算溶剂或表面活性剂水溶液中石墨烯之间的平均作用力势来量化，以建立分散石墨烯的热力学性质库。一个结合分子动力学模拟和胶体聚集动力学理论的理论框架将被用来进一步设计能够有效稳定石墨烯分散的最佳溶剂/表面活性剂分子。在实验中，将使用离子石墨层间化合物(GIC)来制备层控石墨烯分散体。通过仔细控制插层动力学，将合成高质量的第二阶段和第三阶段石墨烯，有望成为制备两层和三层石墨烯分散体的优良前驱体。将对石墨烯分散体进行系统的表征，以优化剥离过程，以使产生的分散体足够集中，并且石墨烯薄片足够大，用于传统的光刻，在传统光刻中，它们将被沉积在目标衬底上。先进的分离技术也将被开发出来，以生产单分散的双层和三层石墨烯溶液。从所提出的建模和实验中获得的新的基本和实用的见解将被用于指导电子器件的制造。这两家PI在胶体科学、工程纳米技术、计算机模拟和分子建模方面的专业知识相结合，将使设备制造的石墨烯工程解决方案取得快速进展。更广泛的影响和影响：开发一种在液体中剥离石墨烯的新先进技术，将极大地提高生产AB堆叠的双层和三层石墨烯的能力，用于实际应用，如制造电子设备。此外，对石墨烯与其他分子相互作用的新的基本见解将有助于从整体上从理论和实践上理解石墨烯在液体中的动力学行为。最终，这些知识可以导致更好的石墨烯分散介质的合理设计。所取得的建模和实验进展将被纳入麻省理工学院的课程(麻省理工学院Blankschtein教授的课程10.55-胶体和表面活性剂科学，以及斯特拉诺教授的10.585-工程纳米技术)和研讨会，这些课程将向更多的科学受众展示石墨烯在液体中分散和稳定的基础，以及在分子水平上对这些现象进行建模。值得注意的是，用于生产石墨烯分散体的原材料是石墨，这种材料很容易大量获得。以石墨为基础的新材料/装置是现有技术的一种可行和经济的替代方案。这里提出的高导电性二维分散体的生产将潜在地用于生产导电油墨、可打印电子产品和生物传感器。技术对社会的影响从可滚动显示器的开发延伸到为糖尿病患者创造新的血糖检测器。参与拟议研究的本科生和研究生都将从这里提出的综合实验/建模研究中获得智力和专业上的收益。参与的PI和学生将参加麻省理工学院的周六工程浓缩和发现(SEED)学院，以及少数族裔工程和科学入门(METES)计划，这两个项目都针对高中生，并影响少数族裔的招募。

1132083Kumar, SatishProject Technical Summary. Due to their distinct electronic properties, AB-stacked bilayer and trilayer graphene have shown extraordinary potential for next-generation optoelectronic and microprocessor applications. These promising materials, nevertheless, require new synthesis methods to effectively control the number of AB-stacked layers through graphite exfoliation and advanced processing techniques. Solution graphene dispersions are promising raw materials for printable electronics and nanocomposites, and most importantly, this approach represents the only possible route at this time for the mass-production of AB stacked bi- and tri-layer graphene. However, since the first graphene solution was reported in 2008, there are still many unanswered questions and technical bottlenecks that hinder the progress of this field. Although experiments have shown that the distribution of graphene layer numbers highly depends on the choice of solvents or surfactants used, very little is known about the molecular origin of the interactions between graphene and solvent/surfactant molecules, including correlating these interactions with the colloidal stability of the graphene solution. In addition, regardless of the methods used to produce solution-phase graphene, its size, shape, and number of stacked layers are all poly-disperse. Engineering approaches that can directly control the size and the stacking geometry (by narrowing their distributions) of the exfoliated graphene flakes have to be developed.Intellectual Merit:This project seeks to understand the origin of the interactions between suspended graphene with surrounding solvent/surfactant molecules via large-scale molecular dynamics simulations. These interactions will be quantified by calculating the potential of mean force between graphene sheets in solvents or aqueous surfactant solutions to establish a library of thermodynamic properties for dispersed graphene sheets. A theoretical framework that combines molecular dynamics simulations and kinetic theories of colloid aggregation will be developed to further design optimal solvent/surfactant molecules that can stabilize graphene dispersions efficiently. Experimentally, layer-controlled graphene dispersions will be produced using ionic graphite intercalation compounds (GICs). By carefully controlling the intercalation kinetics, high-quality Stage-2 and Stage-3 GICs will be synthesized, which are expected to be excellent precursors for bilayer and trilayer graphene dispersions. Systematic characterizations of graphene dispersions will be carried out to optimize the exfoliation process such that the produced dispersions are sufficiently concentrated, and that the graphene flakes are large enough, for conventional photolithography in which they will be deposited on a target substrate. Advanced separation techniques will also be developed to produce monodisperse bilayer and trilayer graphene solutions. The novel fundamental and practical insights gained from the proposed modeling and experiments will be used to guide the fabrication of electronic devices. The combined expertise of the two PIs across colloid science, engineering nanotechnology, computer simulations, and molecular modeling will enable rapid progress towards engineering graphene solutions for device manufacturing. Broader Impact and Outreach:The development of a novel advanced technique to exfoliate graphene in liquid phases will greatly increase the capability to produce AB-stacked bilayer and trilayer graphene for practical applications, such as fabricating electronic devices. In addition, novel fundamental insights into the interactions between graphene and other molecules will contribute to the overall theoretical and practical understanding of the kinetic behavior of graphene in the liquid phase. Ultimately, such knowledge can lead to the rational design of better media for graphene dispersions.The modeling and experimental advances made will be incorporated into courses (MIT course 10.55 - Colloid and Surfactant Science by Professor Blankschtein and 10.585 - Engineering Nanotechnology by Professor Strano) and workshops at MIT that will expose a larger scientific audience to the fundamentals of graphene dispersion and stabilization in liquid phases, as well as to modeling these phenomena at the molecular level. It is noteworthy that the raw material used to produce the graphene dispersions is graphite, which is readily available in large quantities. New materials/devices based on graphite represent a viable and economical alternative to existing technologies. The production of the highly-conductive, two-dimensional dispersions proposed here will be potentially useful for the production of conducting inks, printable electronics, and biological sensors. The technological impact to society extends from the development of rollable displays to the creation of novel glucose detectors for diabetics. The students involved in the proposed research at both the graduate an undergraduate level will gain intellectually and professionally from the integrated experimental/modeling research proposed here. The PIs and students involved will participate in the Saturday Engineering Enrichment and Discovery (SEED) Academy at MIT, as well as in the Minority Introduction to Engineering and Science (MITES) program, both of which target high school age students and influence minority recruitment.