I. Organic-Inorganic Hybrids: Mother Nature's Secrets
Mother Nature has demonstrated amazing hybrid materials, which are strong, light-weight, and multifunctional, constructed from the intimate integration of organic and inorganic components. For example, organic-inorganic hybrid materials such as nacre and bone are well known for their hardness, strength, and resilience. These natural materials consist of brittle minerals connected by small amounts of biopolymer and have highly complex hierarchical structures whose properties far exceed what is obtained from simply mixing these two components together. I have aimed to unravel Mother Nature’s secrets in order to design and tailor-make multifunctional organic-inorganic hybrids. The areas of interest include flexible/structural batteries, surface-agnostic conductive coatings, and sensor devices.
(1) Flexible/structural batteries
Flexible batteries are essential for wearable devices and flexible electronics to become more widely available but, most currently available batteries are bulky and rigid and their components are often brittle. We solved that problem by hybridizing vanadium pentoxide (V2O5) with a conductive block copolymer, poly(3-hexylthiophene)-block-poly(ethylene oxide) (P3HT-b-PEO), in order to fabricate a highly flexible battery cathode. The V2O5 layers were arranged in parallel and held together by the block copolymer binder in a brick-and mortar-like fashion resulting in an organic-inorganic hybrid that mimics materials found in nature. This unique structure significantly enhances mechanical flexibility and toughness without sacrificing battery capacity.
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(2) Surface-agonistic highly stretchable conductive coatings
MXenes are a new and exciting class of materials that show great promise for use in the fields of conductive coatings, however, they are lacking in mechanical performance. Using nature as inspiration, I replicated the brick-and-mortar structure of tough and resilient nacre shells using layer-by-layer assembly. This hybridization combined high conductivity, mechanical robustness, and mechanical flexibility. This addresses one of the main obstacles in functional MXene materials and composites: failure and loss of functionality at low strains (4% strain). Furthermore, these MXene multilayer coatings can be deposited on to nearly any surface, regardless of chemistry, topography, or softness. This opens up a range of applications such as human motion sensing, topographic sensors, humidity sensors, and human health monitoring devices.
II. Advanced Soft Material Characterization
To complete the foundation for my own research program, I cultivated an electron microscopy tomography–quantitative morphometry skill set during my postdoctoral work that I will couple with my hybridization engineering tool kit. Specifically, I developed low-dose electron microscope tomography that enables investigations of beam-sensitive soft materials with heterogenous nanoscale morphologies. As a model soft material, I studied polyamide membranes which are used in water desalination, purification of chemicals and pharmaceuticals, and recycling of catalysts. Polyamide membranes has been used in separation industries for over 30 years, however, it is challenging to develop the predictive design of nanometer thin polyamide membranes for two major reasons: it is difficult (i) to investigate the nonperiodic heterogenous nanostructures that emerge from synthesis and (ii) to characterize the 3D soft material structure at the nanoscale. Thus, quantitative understanding of their synthesis–structure–functionality relationship has been limited.
To address these issues, I developed a 3D electron microscopy imaging-quantitative morphometry platform. More specifically, I took over 60 projections at various tilt angles from −60° to +60° and reconstructed a full 3D view with nanometer resolution (i.e., one 3D pixel is 6.8 Å). I quantified various structural parameters governing film transport properties, such as void volume, local curvature, thickness mapping in 3D, and surface-to-volume ratio from the 3D reconstructed image as single data set. I also demonstrated that reaction conditions (i.e., reactant concentrations, reaction time) can serve as a handle on structure parameters like pore structure, local curvature, film thickness, and interconnectivity. 3D imaging and quantitative characterization of soft matter will bridge the structural organization in space and the functionality of materials.