Confined and Directed Polymer Crystallization at Curved Liquid/Liquid Interface

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NON-TECHNICAL SUMMARY:The intriguing geometrical shapes of familiar crystals such as snowflakes and diamond are dictated by regular molecular packing. The smallest unit of the crystal, the unit cell, repeats itself in straight lines across three dimensions to grow these stunning objects. But what if the available space for the crystals to form is non-flat, i.e. curved? How could the unit cells be accommodated and how will the structure be distorted? The molecules have to make turns as they pack into the crystalline lattice, and the shape and properties of the resultant crystals will vary. This project is concerned with such a scenario, and aims to understand the fundamentals on how polymer crystals are formed in a very small and curved space. The PI has recently shown that hollow crystal capsules can be formed by crystallizing polymers on the surface of liquid droplets. These unique capsules are termed "crystalsomes". In this project, crystallization from solution will be conducted in small liquid droplets. Crystallization conditions and the molecular structure of the polymers will be systematically varied to control the shape and size of the crystalsomes, whose structure will be studied using a number of advanced instrumental techniques. It is anticipated that well-controlled crystalsomes may find applications in the fields of nanomotors, drug delivery and gene therapeutics. The educational component of the proposal includes: (1) Developing two class modules which will be used in an Advanced Polymer Characterization course; (2) Mentoring graduate and undergraduate students; (3) Involving high school students and teachers, particularly from under-represented populations, in the proposed research activities; and (4) Engaging in local outreach activities to enhance broader interest in science and technology. TECHNICAL SUMMARY: Crystallization is a ubiquitous self-assembly process in nature. By definition, crystallization implies that a unit cell self-repeats in a three-dimensional (3D) lattice following translational symmetry. A curved space, on the other hand, is intrinsically incommensurate with 3D translational symmetry. Recently, the PI's group observed a unique type of crystalline morphology in a miniemulsion system. Polymer crystallization was found to be confined within and directed by the curved liquid/liquid interface. Polymer single crystal-like capsules were obtained and the structure mimics the familiar polymersomes. The term "crystalsome" was coined to describe this unique structure, and the goal of the proposed work is to systematically investigate the structure and crystallization behavior of these peculiar crystalsomes. The specific aims of the proposal are to understand 1) the single-crystal growth mechanism in miniemulsion-solution crystallization systems, and 2) the crystal structure and chain packing in these curved crystalsomes. In this project, a variety of tailor-designed crystalsomes will be fabricated using the novel miniemulsion solution crystallization method. The crystalline morphology and structure of these crystalsomes will be systematically investigated using X-ray scattering, differential scanning calorimetry, electron microscopy, and scanning probe microscopy. It is anticipated that this project will lead to clearer understanding of the mechanism of polymer crystallization at nanosized and curved liquid/liquid interfaces.