Search NASA⌕ Search

Engineering topics

Li, Lengwan

Publications and source records attributed to Li, Lengwan.

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Ultrastrong Ionotronic Films Showing Electrochemical Osmotic Actuation

Abstract A multifunctional soft material with high ionic and electrical conductivity, combined with high mechanical properties and the ability to change shape can enable bioinspired responsive devices and systems. The incorporation of all these characteristics in a single material is very challenging, as the improvement of one property tends to reduce other properties. Here, a nanocomposite film based on charged, high‐aspect‐ratio 1D flexible nanocellulose fibrils, and 2D Ti 3 C 2 T x MXene is presented. The self‐assembly process results in a stratified structure with the nanoparticles aligned in‐plane, providing high ionotronic conductivity and mechanical strength, as well as large water uptake. In hydrogel form with 20 wt% liquid, the electrical conductivity is over 200 S cm −1 and the in‐plane tensile strength is close to 100 MPa. This multifunctional performance results from the uniquely layered composite structure at nano‐ and mesoscales. A new type of electrical soft actuator is assembled where voltage as low as ±1 V resulted in osmotic effects and giant reversible out‐of‐plane swelling, reaching 85% strain.

Chemistry↗
DOE OSTI2023

Residual Strain and Nanostructural Effects during Drying of Nanocellulose/Clay Nanosheet Hybrids: Synchrotron X-ray Scattering Results

Cellulose nanofibrils (CNF) with 2D silicate nanoplatelet reinforcement readily form multifunctional composites by vacuum-assisted self-assembly from hydrocolloidal mixtures. The final nanostructure is formed during drying. The crystalline nature of CNF and montmorillonite (MTM) made it possible to use synchrotron X-ray scattering (WAXS, SAXS) to monitor structural development during drying from water and from ethanol. Nanostructural changes in the CNF and MTM crystals were investigated. Changes in the out-of-plane orientation of CNF and MTM were determined. Residual drying strains previously predicted from theory were confirmed in both cellulose and MTM platelets due to capillary forces. The formation of tactoid platelet stacks could be followed. We propose that after filtration, the constituent nanoparticles in the swollen, solid gel already have a “fixed” location, although self-assembly and ordering processes take place during drying.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Deuteration and Polymers: Rich History with Great Potential

Deuterium, a stable hydrogen isotope, has been playing important roles in many scientific areas, including polymer science. The developments of deuteration science and polymer science have been interwoven for the past 60 years. The unique characteristics of the scattering lengths for hydrogen isotopes (protium and deuterium) result in the dramatic differences of scattering length densities for protiated and deuterated compounds omnipresent in polymers, rendering neutron scattering a powerful tool for the investigation of polymeric structures and dynamics that are inaccessible to other tools. While the role of deuteration in neutron scattering of polymeric materials can hardly be overstated, it has also enabled the addressing of many questions using other approaches, such as NMR and vibrational spectra. In this Perspective, we provide a brief account of deuterium in the synthesis, properties, and application of various polymers. We also offer an outlook of the potentials in this ever-evolving and exciting area.

36 MATERIALS SCIENCE↗