ABSTRACT:The visibility of graphene sheets on different types of substrates has been investigated both theoretically and experimentally. Although single layer graphene is observable on various types of dielectrics under an optical microscope, it is invisible when it is placed directly on most of the semiconductor and metallic substrates. We show that coating of a resist layer with optimum thickness is an effective way to enhance the contrast of graphene on various types of substrates and makes single layer graphene visible on most semiconductor and metallic substrates.Experiments have been performed to verify the results on quartz and NiFe-coated Si substrates.The results obtained will be useful for fabricating graphene-based devices on various types of substrates for electronics, spintronics and optoelectronics applications.
Self-propelling micromotors are emerging as a promising microscale and nanoscale tool for singlecell analysis. We have recently shown that the field gradients necessary to manipulate matter via dielectrophoresis can be induced at the surface of a polarizable active ("self-propelling") metallodielectric Janus particle (JP) under an externally applied electric field, acting essentially as a mobile floating microelectrode. Here, we successfully demonstrated for the first time, that the application of an external electric field can singularly trap and transport bacteria and can selectively electroporate the trapped bacteria. Selective electroporation, enabled by the local intensification of the electric field induced by the JP, was obtained under both continuous alternating current and pulsed signal conditions. This approach is generic and is applicable to bacteria and JP, as well as a wide range of cell types and micromotor designs. Hence, it constitutes an important and novel experimental tool for single-cell analysis and targeted delivery.
One Sentence Summary:This work presents the application of active particles as mobile microelectrodes, where selective bacteria trapping and releasing, transport and electroporation are singularly controlled using an external electric field.
Dynamic rheology and steady shear viscosity of an aqueous salt solution of 2 wt% viscoelastic gemini surfactant 1,2-N,N′-bis (dimethyloctadecyl) ethene ammonium bromide and its mixture with low molecular weight hydrophobically modified polyacrylamide (HMPAM) were investigated. The solution of surfactant in the presence of potassium chloride exhibited typical Maxwellian fluid behavior with a single stress relaxation time, indicating the formation of transient networks of entangled wormlike micelles (WLMs). Polymer profoundly affected the rheological properties of WLMs.The WLMs/HMPAM system demonstrated higher plateau modulus and zero-shear viscosity than the single WLMs system by self-assembling into common networks which was identified by scanning electron microscopy morphology. In contrast to the WLMs system, the WLMs/ HMPAM system exhibited better temperature and shear resistance while retaining complete responsiveness to hydrocarbons. Based on the fracturing fluid application evaluation, the WLMs/HMPAM system had an applicable temperature, which was 30°C higher than the WLMs system, and the core damage rate showed that the WLMs/HMPAM system was very promising in clean fracturing fluid application.
The use of active colloids for cargo transport offers unique potential for applications ranging from targeted drug delivery to lab-on-a-chip systems. Previously, Janus particles (JPs), acting as mobile microelectrodes have been shown to transport cargo which is trapped by a dielectrophoretic mechanism [Boymelgreen et al. (2018)]. Herein, we aim to characterize the cargo loading properties of mobile Janus carriers, across a broad range of frequencies and voltages. In expanding the frequency range of the carrier, we are able to compare the influence of different modes of carrier transport on the loading capacity as well as highlight the differences between cargo trapped by positive and negative dielectrophoresis. Specifically it is shown that cargo trapping results in a reduction in carrier velocities with this effect more pronounced at low frequencies where cargo is trapped close to the substrate. Interestingly, we observe the existence of a maximum cargo loading capacity which decreases at large voltages suggesting a strong interplay between trapping and hydrodynamic shear. Finally, we demonstrate that control of the frequency can enable different assemblies of binary colloidal solutions on the JP. The resultant findings enable the optimization of electrokinetic cargo transport and its selective application to a broad range of targets.
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