FFATA: CAREER: Internal Structure and Properties of Confined Layer-by-Layer Films and Nanotubes
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TECHNICAL SUMMARY: Layer-by-layer (LbL) assemblies represent a novel and revolutionary class of materials with potential applications ranging from biological and energy systems to smart surfaces and sensors. However, their internal structure and materials properties are challenging to discern because they are often ultra thin or confined to their substrate. As shown for many neutral polymers, the materials properties (such as the glass transition temperature) significantly depart from bulk behavior as the film thickness deceases. The aim of this work is (i) to discern physical and structural differences within LbL assemblies of varying thickness, curvature (in the form of polymer nanotubes), and components using calorimetry, ellipsometry, and electrochemistry and (ii) to relate that information to how LbL films grow and perform. Bulk free-standing LbL films will be compared to LbL-coated porous templates. LbL thickness and pore diameter will be varied to isolate the influence of confinement and curvature, respectively. The assembly and adsorption of polyelectrolytes within small pores will also be explored for polyelectrolyte solutions of varying pH and ionic strength. Layer-structure and properties of composite LbL films containing nanoparticles will be compared to those without to determine the influence of hard inorganic materials within some of the layers. Calorimetry will access thermal fluctuations and ellipsometry will access density fluctuations related to phase transitions within the film. Electrochemical permeability measurements will qualitatively determine structure and free volume within the films using redox-active probes. Together, these techniques will give new knowledge regarding layer mixing, polyelectrolyte complexation, and confinement for LbL assemblies. NON-TECHNICAL SUMMARY: Layer-by-layer (LbL) assemblies represent an exciting new class of polymer coatings and films. Made from the alternating layers of oppositely charged molecules, LbL films have applications in energy storage and production, biomaterials, self-cleaning surfaces, and more. However, little is known regarding whether these films melt, soften, or crosslink at a given temperature; such knowledge is important to discern if LbL assemblies are to be commercialized. In this program, the thermal properties of LbL films and LbL nanotubes will be determined. The aim is to understand how thickness, curvature, and components influence film structure and properties. If successful, acquired knowledge could be used to manipulate and design thin films for organic energy storage and other applications. The major impact of this program would be in the acquisition of new knowledge and mentoring of individuals in STEM disciplines. Participants will learn state-of-the-art characterization and processing techniques as well as valuable professional skills. One graduate student will be supported. Community outreach is planned via online video demonstrations, Texas A&M University?s E3 program for high school teachers, Texas A&M University?s Women Explore Engineering program for young women, and other outlets.