(420k) Experimental Characterization and Multiphysics Modeling of Surface Tethered, Environmentally Responsive Poly(acrylic acid) Brushes on Thin Film Au and Cellulose Substrates

In this study, surface-tethered poly(acrylic acid) (PAA) brushes grown from gold and cellulose substrates were created and characterized for surface morphology, chemical composition and adsorptive behavior.  PAA brushes are of interest in the design of environmentally responsive ion exchange (IEX) materials; brush morphology and adsorptive properties can be controlled in large part by environmental variables such as salt concentration, ionic strength, and pH.  PAA brushes have been utilized in biosensing applications as a three dimensional precursor layer with high loading capacity for subsequent biomolecular functionalization.  In bioseparations, grafted polymer brushes can be used for protein separation and purification applications.  This study aimed to characterize PAA brushes tethered to two types of substrates, a thin film of gold (for biosensing applications) and regenerated cellulose (for bioseparations applications).  Scanning electron microscopy (SEM) and Fourier Transform Infared Spectroscopy (FTIR) were used to characterize sample morphology and chemical composition of the grafted materials.  Surface Plasmon Resonance (SPR) was used to characterize layer thickness and adsorption of common proteins for the PAA brushes attached to a gold substrate while batch adsorption studies were used study adsorption on the modified cellulose materials. Using results from these characterization studies, multiphysics models were developed using Comsol Multiphysics to probe the adsorptive behavior of lysozyme (PI~11) and bovine serum albumin (BSA) (PI~4.8) to these complex tethered polymer materials for a variety of environmental conditions and brush geometries.  Initial models were based on experimental investigations; hence the brush geometry, protein fluid samples, environmental parameters, and operating conditions corresponded with experimental studies.  Further models were developed to investigate how different flow conditions, brush densities, grafted layer thicknesses, and brush conformations affected protein binding and elution, with the overall goal of improving adsorptive behavior of these materials.