Allison Victoria Cordova-Huaman

Amphiphilic monolayers composed of end groups with distinct polar and nonpolar functional groups offer rapid and reversible interfacial adaptation in response to environmental stimuli such as a change in interfacial medium polarity. We have synthesized and characterized a suite of monolayers with functional groups of competing polarity designed to reconfigure their interfacial chemical composition in response to solvent polarity. In these films, the end group is designed to be able to reorient and expose the functional groups that minimize the interfacial free energy between the film and the environment. Using a combination of spectroscopic, computational, and wettability studies, we have investigated the responsive interfacial behavior of different end groups upon exposure to environments with varying polarities. Contact angle measurements across a series of polar and dispersive probe liquids reveal trends that reflect the underlying molecular flexibility and composition. Vibrational sum frequency generation (SFG) spectroscopy and atomistic molecular dynamics (MD) simulations confirm solvent-driven reorientation of the end groups, with restructuring observed at the interface. To quantify these effects, we have developed a surface energy calculation model that incorporates solvent-induced surface rearrangements into the estimations. Our findings reveal a strong dependence of surface energy and switching behavior on the length and flexibility of the functionalities in the end group, which affects the exposure of certain interfacial compositions under different solvents. These results offer new insights into the design of adaptive monolayers and provide a framework for evaluating solvent-responsive surfaces.

Functionalized alkylsilane films exhibit switching interfacial behavior in response to different solvents. Image shows exposed oxygen (red) and carbon atoms (green). Hydroxyl films switch more favorably than carboxyl counterparts.

The trans-membrane protein photosystem I is incorporated with the semiconducting polymer poly(p-anisidine) for the fabrication of biohybrid photoactive films.

Graphite is the most commercialized electrode active compound for lithium-ion batteries (LIB). However, its limited theoretical capacity (372 mAh/g) and relatively poor rate performance make it unsuitable for LIB with higher energy density and fast charge ability. Therefore, alternative carbon-based materials, like graphene, have also been explored due to their attractive electrochemical properties.¹ Despite having these properties, the low density and the high specific surface area of graphenic materials result in a low coulombic efficiency when it is used in LIB. To solve this, the physical and electrochemical properties of graphenic materials can be modified during the process of obtention of this material. This work presents a methodology with unique advantages in terms of low cost, stability, scalability, and non-use of hazardous conditions for obtaining an N-doped graphene-like graphite material. This procedure consists of the electrochemical oxidation of graphite rods and a subsequent hydrothermal reduction of the oxidated graphene. First, the electrochemical exfoliation of graphite rods was carried out under constant potential in a basic solution. Due to the exfoliation process, this graphenic material was characterized by having oxygenated functional groups and a graphite-like structure. The structural properties of this material were investigated at room temperature using X-ray diffraction (XRD), infrared spectroscopy (FTIR), and Raman spectroscopy. To reduce the oxygenated functional groups on the graphenic material, a hydrothermal method was used. Simultaneously to the reduction, heteroatom doping was carried out to enhance the electrochemical properties of the obtained reduced graphenic material. To further control the doping process of the rGO and the final properties of the material, a pre-reduction treatment was also introduced. This low-cost, pre-reduction process allowed the controlled introduction of defects in the material to enhance the doping percentage of the N-rGO. Besides the structural characterization techniques previously indicated, electrochemical impedance spectroscopy (EIS) and voltammetric methods were used to characterize the final N-doped electrochemical properties fully. The observed features of the samples indicate that the graphenic material possesses a graphite-like graphene structure, which allows the material to act like independent graphene layers that maintain a highly regulated orientation between the sheets, which can increase the charge/discharge capacity if used in LIB.² Furthermore, it was shown that the pre-reduction treatment allowed an increase in the doping percentage of the graphenic material. This increased doping led to an increased charge-transfer conductivity, as indicated by the electrochemical characterization methods. Overall, this low-cost, scalable procedure allows the obtention of graphenic materials with properties suitable for their applications in LIB. Al Hassan, M. R., Sen, A., Zaman, T. & Mostari, M. S. Emergence of graphene as a promising anode material for rechargeable batteries: a review. Mater. Today Chem. 11, 225–243 (2019). Matsuo, Y. et al. Electrochemical Intercalation Behaviors of Lithium Ions into Graphene-Like Graphite. J. Electrochem. Soc. 165, A2409 (2018).