Piezoresistive and electrical properties of a catecholic amino acid-polyacrylamide single-walled carbon nanotube hydrogel hybrid network

We have developed a functional hydrogel combining the advantages of single-walled carbon nanotube (SWCNT) hydrogels and 3,4-dihydroxy-l-phenylalanine (l-DOPA) that would be expected to lead to a material with elevated piezoresistive ability. SWCNT hydrogel precursors were thus embedded into the catecholic amino acid 3,4-dihydroxy-l-phenylalanine-polyacrylamide (l-DOPA-PAM) hydrogel to form a l-DOPA-PAM-SWCNT hydrogel hybrid network. This hybrid network as formed was soft but became a hard gel at room temperature. An advantage of this material design is the prevention of overoxidation of l-DOPA to maintain enough free catechol groups to endow the desired properties. Several characterization techniques, including optical microscopy, field-emission scanning electron microscopy, Raman spectroscopy, and dynamic mechanical analysis, were utilized to characterize the l-DOPA-PAM-SWCNT hydrogel hybrid network. The negative piezoresistive effect and electrical properties of the l-DOPA-PAM hydrogel and the l-DOPA-PAM-SWCNT hydrogel hybrid network were measured under different pressures and at different times after the application of pressure started, demonstrating the potential for pressure-sensing applications.</p

Determination of vibrational modes of ʟ-alanine single crystals by a combination of terahertz spectroscopy measurements and density functional calculations

Density-functional theory may be used to predict both the frequency and the dipole moment of the fundamental oscillations of molecular crystals. Suitably polarized photons at those frequencies excite such oscillations. Thus, in principle, terahertz spectroscopy may confirm the calculated fundamental modes of amino acids. However, reports to date have multiple shortcomings: (a) material of uncertain purity and morphology and diluted in a binder material is employed; (b) consequently, vibrations along all crystal axes are excited simultaneously; (c) data are restricted to room temperature, where resonances are broad and the background dominant; and (d) comparison with theory has been unsatisfactory (in part because the theory assumes zero temperature). Here, we overcome all four obstacles, in reporting detailed low-temperature polarized THz spectra of single-crystal l-alanine, assigning vibrational modes using density-functional theory, and comparing the calculated dipole moment vector direction to the electric field polarization of the measured spectra. Our direct and detailed comparison of theory with experiment corrects previous mode assignments for l-alanine, and reveals unreported modes, previously obscured by closely spaced spectral absorptions. The fundamental modes are thereby determined.</p

Anomalous magnetization peak effect in spiral-grown Bi2Sr2CaCu2Oy crystals

Magnetic hysteresis loops were measured on spiral-grown Bi2Sr2CaCu2Oy (Bi-2212) crystals. An anomalous peak effect at a magnetic field of 1000–2000 Oe was observed both in high-Tc (86 K) and oxygen underdoped (Tc=76 K) spiral-grown crystals between 20 and 40 K. The peak effect was observed to be stronger than that induced by oxygen vacancies, defect dislocation networks reported in Bi-2212 crystals. Further, the anomalous peak almost completely disappeared after removing growth spiral patterns from the crystal surface. Edge barriers associated with the growth spirals are suggested to be responsible for the strong peak effect for the spiral-grown Bi-2212 crystals and not oxygen vacancies or screw dislocations