Understanding the Role of Crystalline Junctions in Associative Polymer Gels

点击翻译按钮获取中文摘要

PART 1: NON-TECHNICAL SUMMARYNew strategies are needed to create polymers with mechanical and structural properties that more closely mimic natural materials. In this project, the Bhatia and Grubbs groups at Stony Brook University will explore how including very small rigid domains, or nanoscale crystallites, into soft polymer gels impacts their structure, flow properties, and elasticity. These crystalline domains represent a novel method for controlling the structural and mechanical properties of polymer gels. Thus, the work will impact design of improved materials for applications that contribute to national health and prosperity, including soft tissue engineering and drug delivery. The project will also contribute to the development of new experimental techniques to characterize polymeric materials that contain both ordered and disordered domains such as biopolymer gels, conductive polymer films, and thermoplastic elastomers. The PI and Co-PI will train graduate and undergraduate students in a wide range of techniques for modern polymer materials research, including synthesis, chemical characterization, scattering studies, and mechanical characterization; and they will aim to recruit under-represented student populations for this project, benefiting STEM workforce development and inclusion of diverse students in STEM fields. Finally, examples from the research will be incorporated into video lectures on macromolecules and nanomaterials that can be used to update the core chemistry curricula at the college level and into demonstrations for K-6 students. PART 2: TECHNICAL SUMMARYThis work is focused on control of hydrogel nanostructure and microstructure while maintaining desired rheological and transport properties. In this project, the Bhatia and Grubbs groups at Stony Brook University will explore the impact of stereochemistry and crystallinity on the rheology and nano- to micro-scale structure of associative block copolymer gels. Although crystallinity has long been used as a means of controlling polymer properties in the solid state, studies of solutions and gels with crystalline domains have been limited. A major challenge in understanding the physics of these systems is quantifying ordering in multiphase systems that contain both amorphous and ordered domains, where the ordered domains are too small to easily discern through conventional diffraction methods. The researchers will overcome this by utilizing X-ray pair distribution analysis (PDF) to quantify chain ordering in these materials. The project will focus on ABA triblock copolymers in a selective solvent, where the midblock is poly(ethylene oxide) (PEO) and the endblocks are poly(lactic acid) (PLA). The overall goal is to build fundamental, comprehensive structure-property relationships for block copolymers with crystallizable blocks in selective solvents. Specific objectives are to: (1) Synthesize a series of PLA-PEO-PLA triblock polymers with varying PLA and PEO block length and L/D ratio; (2) Characterize the structure, assembly, and crystallinity of these polymers using DLS, SAXS/SANS, PDF, USANS, and confocal microscopy; (3) Measure the rheological properties of the gels and compare these to existing models of polymer networks; and (4) Integrate examples from the research into undergraduate and graduate core courses in chemistry and demonstrations for K-6 audiences..This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.