(382b) Examining Hydration and Mineralization in Polyelectrolyte Brushes

Layers of end-grafted polymer chains immersed in good solvents – often referred to as “polymer brushes” – are useful for tailoring interfacial properties and are often viewed as archetypical systems for teasing apart the inherent links between organization, structure, and properties of confined, soft materials. Polyelectrolyte brushes are of particular interest due to their relevance to biology and the possibilities they offer as constructs for lubricious biomaterial coatings or scaffolds, electro-actuators (synthetic muscles), biosensors, or high affinity separation agents. Despite this potential, polyelectrolytes remain perhaps the least understood form of soft matter due to their complex connections between charge and conformation. In this presentation, we describe recent efforts aimed at understanding how responsive polyelectrolyte brushes regulate their nanoscale structure as a function of their design and environmental conditions. We have synthesized homopolymer and copolymer brushes based on methacrylic acid using controlled (free) radical polymerization methods, and characterized their surface organization and structure using in situ ellipsometry and neutron reflectometry. In addition to useful insights into how polymer design impacts the swelling behavior of the brush, we find impactful consequences in terms of how we think about these systems: In short, our studies reveal a general misunderstanding in terms of the thickness and areal density of water-soluble brush systems, and we find that structural transitions are shifted or stretched compared to behaviors expected for unconfined systems because of how the chains regulate their structure. In addition, we describe the use of neutron reflectivity measurements to understand the in situ growth of calcium carbonate mineral phases in these ionotropic matrices. These findings underscore not only the complexity of these materials, but also how sophisticated characterization methods such as neutron reflectometry facilitate decoding synthesis-structure-property relationships.