The coassembly of well-defined biological nanostructures relies on a delicate balance between attractive and repulsive interactions between biomolecular building blocks. Viral capsids are a prototypical example, where coat proteins exhibit not only self-interactions but also interact with the cargo they encapsulate. In nature, the balance between antagonistic and synergistic interactions has evolved to avoid kinetic trapping and polymorphism. To date, it has remained a major challenge to experimentally disentangle the complex kinetic reaction pathways that underlie successful coassembly of biomolecular building blocks in a noninvasive approach with high temporal resolution. Here we show how macromolecular force sensors, acting as a genome proxy, allow us to probe the pathways through which a viromimetic protein forms capsids. We uncover the complex multistage process of capsid assembly, which involves recruitment and complexation, followed by allosteric growth of the proteinaceous coat. Under certain conditions, the single-genome particles condense into capsids containing multiple copies of the template. Finally, we derive a theoretical model that quantitatively describes the kinetics of recruitment and growth. These results shed new light on the origins of the pathway complexity in biomolecular coassembly.

Attractive electrostatic forces between polymers can be exploited to create well-defi ned and responsive nanoscale structures. In the process of chargedriven coassembly, the polymers involved undergo subtle conformational changes. However, ascertaining these conformational transitions, and relating this to the nanostructures that are formed, has remained elusive to date. Here it is shown how the force-optical response of tailored mechanochromic polymers can be used to detect structural transitions that occur at the nanoscale during assembly. It is shown that at low-charge stoichiometry, electrostatic binding causes individual macromolecules to stretch and stiffen. Remarkably, at stoichiometries close to full charge compensation a gradual transition from single molecular complexes to multimolecular micelles is observed. Moreover, the same macromolecular sensors reveal how the assembly pathways are fully reversible as the binding strength is weakened. These results highlight how mechanochromic polymer sensors can be used to detect the molecular transitions occur during supramolecular structure formation with high precision.

The surface properties of porous carbonaceous electrodes govern the performance, durability, and ultimately the cost of redox flow batteries (RFBs). State-of-the-art carbon fiber-based electrode interfaces suffer from limited kinetic activity and incomplete wettability, fundamentally limiting the performance. Surface treatments for electrodes such as thermal and acid activation are a common practice to make them more suitable for aqueous RFBs; however, these treatments offer limited control over the desired functional properties. Here, we propose, for the first time, electrografting as a facile, rapid, and versatile technique to enable task-specific functionalization of porous carbonaceous electrodes for use in RFBs. Electrografting allows covalent attachment of organic molecules on conductive substrates upon application of an electrochemical driving force, and the vast library of available organic molecules can unlock a broad range of desired functional properties. To showcase the potential of electrografting for RFBs, we elect to investigate taurine, an amine with a highly hydrophilic sulfonic acid tail. Oxidative electrografting with cyclic voltammetry allows covalent attachment of taurine through the amine group to the fiber surface, resulting in taurine-functionalized carbon cloth electrodes. In situ polarization and impedance spectroscopy in single-electrolyte flow cells reveal that taurine-treated cloth electrodes result in 40% lower charge transfer and 25% lower mass transfer resistances than off-the-shelf cloth electrodes. We find that taurine-treated electrode interfaces promote faster Fe3+ reduction reaction kinetics as the electrochemical surface area normalized current densities are 2-fold and 4-fold higher than oxidized and untreated glassy carbon surfaces, respectively. Improved mass transfer of taurine-treated electrodes is attributed to their superior wettability, as revealed by operando neutron radiography within a flow cell setup. Through demonstrating promising results for aqueous systems with the model molecule taurine, this work aims to bring forth electrografting as a facile technique to tailor electrode surfaces for other RFB chemistries and electrochemical technologies.

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Electrode-assisted techniques are well suited for separation of ions from solutions with reduced energy and chemical consumption. This emerging platform can benefit greatly from the convection enhanced and zero-gap reactor designs unlocked by macroporous electrodes, but immobilizing ion-selective layers on such complex 3D architectures is challenging. We propose electropolymerization of conductive polymers as a coating methodology to fabricate highly conformal coatings with electrochemically-switchable ion-exchange functionality. To demonstrate this, we study the synthetic parameters, resulting morphology and ionic separation performance of poly(3,4-ethylenedioxythiophene) (PEDOT) on commercially available carbon paper electrodes. Electropolymerization of PEDOT in organic solvents results in rougher morphologies with high sensitivity to electrochemical protocols employed. When polymerized in aqueous solutions of poly(4-styrenesulfonate) (PSS-), the resulting PEDOT/PSS blend polymer forms smooth coatings with a controllable thickness down to 0.1 µm. With appropriate voltage bias, PEDOT/PSS coated electrodes can take up and release Ni2+ in the presence of excess Na+. Increasing the coating thickness decreases the adsorption capacity due to mass transfer limitations, and the maximum adsorption capacity for Ni2+ is reached for the thinnest coatings at 228 mg g-1. Through a systematic study of PEDOT/PSS coated carbon paper, we hope to establish electropolymerization as a promising avenue for porous electrode functionalization.