Macroporous Polyimide Aerogels: A Comparison between Powder Microparticles Synthesized via Wet Gel Grinding and Emulsion Processes.

It is noteworthy to mention that synthesizing the polyimide aerogel powder, which is carried out in this study, benefits from two advantages: (i) the powder particles can be used for some specific applications where the monolith is not suitable and (ii) there is a possibility to investigate how a polyimide aerogel monolith can be made through the polyimide powder to reduce its cost and cycle time. In this study, two straightforward methods, wet gel grinding and emulsion, are introduced to prepare polyimide aerogel powders using ambient pressure drying. The microscopic properties of interest, including skeletal and porous structures, microparticle size and assembly, combined with macroscopic properties such as thermal stabilities and conductivities (0.039 W/m·K), confirm that the fabricated microparticles with a size in the range of 7-20 µm and porosity in the range of 65-85% are thermally stable up to 500 °C.

Effect of the Chloride Anions on the Formation of Self-Assembled Diphenylalanine Peptide Nanotubes.

Self-assembled peptide nanostructures are being intensively investigated due to their potential applications such as biosensors, piezotransducers, and microactuators. It was predicted that their formation and hence piezoelectric property strongly depend on the water content and acidity of the stock solution. In this paper, simple diphenylalanine (FF) tubular structures were fabricated from the solutions with added hydrochloric acid in order to understand the influence of chloride ions on the self-assembly process and resulting piezoelectricity. Low-frequency Raman scattering, atomic, and piezoresponse force microscopies were used to characterize both the morphology and piezoelectric properties of the grown samples. The mechanism of chloride anions' effect on the formation of self-assembled peptide nanostructures is discussed based on the acquired Raman data and quantum-chemical modeling. It is shown that the addition of chloride anions causes a significant reduction of the dipole moments of FF tubes accompanied with the concomitant decrease of tube dimensions and apparent shear piezoelectric coefficients.