Biopolymer and synthetic polymer nanocomposite reinforcement via interfacial assembly
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Protein biopolymer composites bring together the tunability and flexibility of protein matrices and functionality of filler components. Graphene-based biocomposites are particularly popular for design of aqueously processible and strong flexible electronics for sensing, nanowires, and semiconductors. However, a lot of trial and error is required to determine biopolymer and co-constituent chemistry as well as the assembly process needed to capitalize on their synergistic properties. This dissertation identifies non-covalent methods to control interfacial interactions that drive and stabilize assembly of silk fibroin from Bombyx mori silkworm cocoons in order to induce mechanical reinforcement. This work, then shows the cross-applicability of assembly triggers for silk with other semi-crystalline, amphiphilic biopolymers using Humbolt squid sucker ring teeth protein suckerin. And, lastly, synthetic copolymers are used to clarify the role of biopolymer and surface properties on interfacial assembly without post-processing treatments. The main drivers of assembly and interfacial binding studied here include temperature, shear force, hydropathy, and pH. Surface topography and polymer chemistry/conformation were studied concurrently via atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). This data was supported by simulation to better define assembly mechanisms at the interface of biopolymers and inorganic 2D fillers and their timescales. Then, mechanical characterization via bulging tests and scanning probe microscopy methods (SPM), force distance spectroscopy (FDS) and quantitative nanomechanical mapping (QNM). Mechanical performance is evaluated at the macro and nanoscales using quantitative nanomechanical mapping, FDS, and buckling tests. Overall, this dissertation shows how interfacial assembly driven by the hydrophobic effect can be manipulated using non-covalent means to study to tune mechanical performance. Thus, this work a roadmap for further optimization of biopolymer-based nanocomposites through interface-minded design.