Designing Viruses for Studies of Liquid-Crystals and Self-Assembly

该项目的长期目标是了解部分或全部由液晶形成分子组成的大分子悬浮液的相行为。物质的性质，即两个粒子不能同时处于同一位置，导致了排除体积的概念，排除体积是一个分子阻止另一个分子进入的空间区域，是粒子形状、相互取向和分离的函数。减少被排除的体积给了分子更多的运动自由，从而增加了熵。因此，分子被驱动经历相变，这些相变具有使排除体积最小化的分子构型。为了揭示熵在相变中的作用，将合成由两部分组成的分子，这两部分分别有相分离的倾向，但它们结合在一起形成嵌段共聚。这些块将是丝状病毒，一种长而薄的半柔性聚合物，可以形成液晶和DNA，这种柔性聚合物太长，不能形成液晶。将研究该体系的相行为，以及形状两亲性化合物与单个组分的混合物的相行为。熵是控制这些电荷稳定胶体相行为的主要特征，可以高精度地对该体系进行理论建模。本研究中的熵表面活性剂与表面活性剂、嵌段共聚物和液晶这三类重要的材料具有相同的特征，它们自组装成复杂的结构。了解这些材料的自组织是纳米技术和软物质研究的基本目标。这项工作将为微相分离的理论、模拟和实验研究奠定基础。参与该项目的学生将接受理论和实验两方面的培训，这将为他们在生物物理学和纳米技术方面的富有成效的职业生涯做好准备。热力学第二定律(熵增加)是如此成熟，以至于美国专利局不接受违反其原则的申请。熵经常与无序联系在一起，因此，结构相的出现是最大化熵的结果，这是违反直觉的。这项与韦尔斯利学院合作的项目的目标是创造分子，被称为“熵表面活性剂”，由熵驱动自组装成复杂的结构。了解这些材料的自组织是纳米技术和复杂流体研究的基本目标。研究生和本科生将接受合成生物纳米粒子的培训，并将构建由两个部分组成的分子，这两个部分分别有相分离的趋势，但它们结合在一起形成嵌段共聚物。这些块将是丝状病毒，一种长而薄的半柔性聚合物，可以形成液晶和DNA，这种柔性聚合物太长，不能形成液晶。将研究这一体系的相行为，以及熵表面活性剂与各组分的混合物的相行为。熵是控制这些带电分子相行为的主要特征，由于粒子间相互作用的大小、形状和简单性，这个系统可以在理论上得到高精度的模拟。这种理论和实验方面的培训将为学生在生物物理学和纳米技术领域从事富有成效的职业生涯做好准备。这项工作将作为相分离的理论、模拟和实验研究的基础，该相分离适用于包括纳米技术、表面活性剂和聚合物在内的许多领域。

The long term goals of this project are to understand the phase behavior of macromolecular suspensions that are either partially or totally composed of liquid crystalline forming molecules. The property of matter that two particles cannot be in the same place at the same time leads to the concept of excluded volume, a region of space that one molecule prevents the other from entering and is a function of the particles' shape, mutual orientation, and separation. Reducing excluded volume gives molecules more freedom of motion and thus increases entropy. Consequently molecules are driven to undergo phase transitions that have molecular configurations which minimize excluded volume. In order to reveal the role of entropy in phase transitions "entropic surfactants" will be synthesized consisting of molecules composed of two parts that separately have a tendency to phase separate, but which are bound together forming a block co-polymer. The blocks will be filamentous virus, a long, thin, semi-flexible polymer that forms liquid crystals and DNA, a flexible polymer too long to form liquid crystals. The phase behavior of this system will be studied, as well as the phase behavior of mixtures of the shape amphiphiles with the individual components. Entropy is the dominant feature controlling the phase behavior of these charge stabilized colloids and this system can be theoretically modeled with high precision. The entropic surfactants in this study share features with three important classes of materials, surfactants, block co-polymers and liquid crystals, which self-assemble into complex structures. Understanding the self-organization of these materials is a basic goal of nanotechnology and soft matter research. This work will serve as a foundation for theory, simulation, and experimental study of microphase separation in general. The students involved with this project will receive training in both theory and experiment, which will prepare them for productive careers in biophysics and nanotechnology.%%%The second law of thermodynamics (entropy increases) is so well established that the US patent office does not accept applications that violate its principles. Entropy is often associated with disorder, and consequently it is counter-intuitive that structured phases occur as a result of maximizing entropy. The objectives of this project, involving a collaboration with Wellesley College, are to create molecules, denoted "entropic surfactants", that self-assemble into complex structures driven by entropy. Understanding the self-organization of these materials is a basic goal of nanotechnology and complex fluids research. Graduate and undergraduate students will receive training in the synthesis of bionanoparticles and will build molecules composed of two parts that separately have a tendency to phase separate, but which are bound together forming a block co-polymer. The blocks will be filamentous virus, a long, thin, semi-flexible polymer that forms liquid crystals and DNA, a flexible polymer too long to form liquid crystals. The phase behavior of this system will be studied, as well as the phase behavior of mixtures of the entropic surfactants with the individual components. Entropy is the dominant feature controlling the phase behavior of these charged molecules and because of the size, shape, and simplicity of the interparticle interactions this system can be theoretically modeled with high precision. This training in both theory and experiment will prepare students for productive careers in biophysics and nanotechnology. This work will serve as a foundation for theory, simulation, and experimental study of phase separation that is applicable to a wide number of fields including nanotechnology, surfactants, and polymers.