Search

Dielectric elastomers, such as thermoplastic polyurethanes (TPUs), are widely used as the dielectric layer, encapsulation layer, and substrate of flexible and stretchable devices. To construct capacitors and actuators that work stably upon deformation, it has become urgent to investigate the evolution of dielectricity under stress and strain. However, the lack of effective methods for estimating the dielectric constant of elastomers under strain poses a big challenge. This study reports a device for the in situ measurement of the dielectric constant of TPU under strain. It is found that upon stretching TPU to a strain of 400%, its dielectric constant decreases from 8.02 ± 0.01 to 2.88 ± 0.25 (at 1 MHz). In addition, combined Fourier-transform infrared spectroscopy, the X-ray scattering technique, and atomic force microscopy were utilized to characterize the evolution of the microstructure under strain. The investigation under tensile strain reveals a decreased density and average size of polarized hard domains, along with a tendency of the molecular chains to align in parallel with the tensile stress. The evolution of the microstructures results in a reduction in the measured dielectric constant in TPU. [ABSTRACT FROM AUTHOR]

We present a report on the nanopatterning of an epitaxial ultrathin film of Fe3O4 with room-temperature (ferri)magnetism using atomic force microscopy (AFM). Fe3O4 thin films with atomically flat surfaces were grown using laser molecular-beam epitaxy on a MgAl2O4(111) single-crystal substrate. (Nanowire) were constructed on Fe3O4 thin film by applying an electric field between an AFM conductive tip and the surface of the film. The minimum width and height in the resulting nanowire are 48 nm and 2 nm, respectively. The patterned region of the Fe3O4 film surface possesses a resistance which is 105 times higher than the unpatterned region. Furthermore, magnetic force microscopy measurements also revealed that magnetization of the patterned region is strongly suppressed. [ABSTRACT FROM AUTHOR]

Bacterial adhesion and transport in the geological formation are controlled by their mutual complex interactions, which have been quantified by the traditional and extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory as well as direct atomic force microscopy (AFM) measurements. In this research, the DLVO forces calculated based on the independently determined bacterial and porous media surface thermodynamic properties were compared with those of AFM measurements. Although differences in the order of several magnitudes existed, forces obtained from both ways could explain the observations of E. coli attachment to alumino-silica clays evaluated in laboratory columns under saturated and steady-state flow conditions. E. coli deposition in alumino-silica clays was simulated using a two-site convection-dispersion transport model against E. coli transport breakthrough curves, which was then linked to the interactions forces. By exploring the differences of the two force measurements, it was concluded that the thermodynamic calculations could complement the direct force measurements in describing bacterial interactions with the surrounding environment and the subsequent transport in the porous media. [ABSTRACT FROM AUTHOR]