The viscoelastic properties of the cytoplasm of living yeast cells were investigated by studying the motion of lipid granules naturally occurring in the cytoplasm. A large frequency range of observation was obtained by a combination of video-based and laser-based tracking methods. At time scales from 10(-4) to 10(2) s, the granules typically perform subdiffusive motion with characteristics different from previous measurements in living cells. This subdiffusive behavior is thought to be due to the presence of polymer networks and membranous structures in the cytoplasm. Consistent with this hypothesis, we observe that the motion becomes less subdiffusive upon actin disruption.

Anomalous diffusion in living yeast cells

Remarkable advances have been achieved in modern material technology, especially in device fabrication, and these have facilitated the use of diverse materials in various applications. Carbon nanotubes (CNTs) are being successfully implemented in drug delivery, sensing, water purification, composite materials, and bone scaffolds. Thus, CNTs must meet a wide range of criteria such as surface modification, high aspect ratio, desired conductivity, high porosity and loading, non-toxicity, specificity, and selectivity, and compatibility for device fabrication. The main focus of this review is to explore the maximum applications of CNTs for human health, and we particularly focus on nanocarrier and biomedical applications. The scope of this review initially covers the basic aspects of CNTs and is also extended further to describe their synthesis strategies as well as various challenges encountered in their functionalization, dispersion, and toxicity. Our discussion also emphasizes future directions for these emerging fields of research.

Carbon nanotubes: a novel material for multifaceted applications in human healthcare

Contemporary methods for dispersion of carbon nanotubes in water and non-aqueous media are discussed. Most attention is paid to ultrasonic and plasma techniques and other physical techniques, as well as to the use of surfactants, functionalizing and debundling agents of distinct nature (elemental substances, metal and organic salts, mineral and organic acids, oxides, inorganic and organic peroxides, organic sulfonates, polymers, dyes, natural products, biomolecules, and coordination compounds). Special studies on CNTs solubilization are examined.

Dispersion of carbon nanotubes in water and non-aqueous solvents

In this study, we investigate the adsorption capability of molybdenum sulfide (MoS2)/thiol-functionalized multiwalled carbon nanotube (SH-MWCNT) nanocomposite for rapid and efficient removal of hea...

Efficient Removal of Pb(II) and Cd(II) from Industrial Mine Water by a Hierarchical MoS2/SH-MWCNT Nanocomposite.

Crystallization of concentrated colloidal suspensions was studied in real space with laser scanning confocal microscopy. Direct imaging in three dimensions allowed identification and observation of both nucleation and growth of crystalline regions, providing an experimental measure of properties of the nucleating crystallites. By following their evolution, we identified critical nuclei, determined nucleation rates, and measured the average surface tension of the crystal-liquid interface. The structure of the nuclei was the same as the bulk solid phase, random hexagonal close-packed, and their average shape was rather nonspherical, with rough rather than faceted surfaces.

Real Space Imaging of Nucleation and Growth in Colloidal Crystallization

Surface oxidation and effect of electric field on dispersion and colloids stability of multiwalled carbon nanotubes

Polyaniline (PANI) was synthesized and doped with 0, 2, 4 and 16 wt.% of pure and functionalized multiwall carbon nanotubes (MWCNTs) by “in-situ” polymerization. Measurement of temperature dependence of electrical resistivity showed a reduction in the resistivity of the composites at all temperatures. The reduction was increased by increasing the wt.% of MWCNTs. This decrease was more for the composites containing functionalized MWCNTs and was more prominent for temperatures below 150 K. The glass transition temperature (T g ) of the pure and doped PANI was measured using electrical resistivity measurements. It was observed that by increasing the amount of functionalized MWCNTs in PANI, its T g increases. Temperature dependence of resistivity of pressed pure PANI showed that by increasing the pelletization pressure, the bulk electrical resistivity decreased but the T g increased.

Electrical properties and glass transition temperature of multiwalled carbon nanotube/polyaniline composites

We demonstrate that strong elastic pump wave pulses soften sandstone more in humidified conditions than they do in dry conditions and that this effect is repeatable and reversible. We assess these changes via the non-linear interactions of a strong pump wave with a weaker probe wave. We find that there is an exponential time constant ( τ ≈ 13 days) associated with this process that is independent of the amplitudes of the pump and the probe, the phase delay between the two waves (the time between transmission of the pump and probe waves), the sampling rate, and whether the sample is being dried or humidified. We demonstrate that the humidity-dependent differences in the amount of softening are induced by only a very small amount of absorbed water vapor and argue that this water is intercalated within clay particles. We also show that our pump–probe experiments detect these humidity-dependent differences in the amount of softening easily and repeatably using an experimental design that does not rely on resonance conditions. This means that, in principle, our experiments could be more easily generalized to other experimental geometries to investigate non-linear elastic properties in complex or irregular sample geometries. Our method and findings have potential relevance in oil and gas exploration, civil engineering, and understanding of the mechanism of earthquakes.

A non-linear elastic approach to study the effect of ambient humidity on sandstone

A two-fluid emulsion (silicone oil drops in the “leaky dielectric”, castor oil) with electrohydrodynamically driven flows can serve as a model system for tunable studies of hydrodynamic interactions [Varshney et al., Sci. Rep., 2012, 2, 738]. Flows on multiple length- and time-scales have been observed but the underlying mechanism for these chaotic, multi-scale flows is not understood. In this work, we conducted experiments varying the thickness of the test cell to examine the role of substrate interactions on size distribution, mean square displacement and velocity of the drops as a function of the electric field strength. We find that the electric capillary number, CaE, at the threshold of drop breakup is of order unity for cell thicknesses of 100 μm or thicker, but much larger for thinner cells. Above this threshold, there is a clear transition to super-diffusive droplet motions. In addition, we observe that there is a convective instability prior to the onset of chaotic flows, with the lengthscale associated with the convection rolls increasing linearly with an increase in the cell thickness. The fact that the convective instability appears to occur in the leaky dielectric castor oil regardless of whether the second component is liquid drops, solid particles, or dissolved dye has implications on the underlying mechanism for the unsteady flows.

The effect of confinement on the electrohydrodynamic behavior of droplets in a microfluidic oil-in-oil emulsion

We demonstrate a simple and robust method to produce large 2-dimensional and quasi-3-dimensional arrays of tunable liquid microlenses using a time varying external electric field as the only control parameter. With increasing frequency, the shape of the individual lensing elements (~40 μm in diameter) evolves from an oblate (lentil shaped) to a prolate (egg shaped) spheroid, thereby making the focal length a tunable quantity. Moreover, such microlenses can be spatially localized in desired configurations by patterning the electrode. This system has the advantage that it provides a large dynamic range of shape deformation (with a response time of ~30 ms for the whole range of deformation), which is useful in designing adaptive optics.

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Somayeh Khajehpour Tadavani

Papers

Surface oxidation and effect of electric field on dispersion and colloids stability of multiwalled carbon nanotubes

Electrical properties and glass transition temperature of multiwalled carbon nanotube/polyaniline composites

A non-linear elastic approach to study the effect of ambient humidity on sandstone

The effect of confinement on the electrohydrodynamic behavior of droplets in a microfluidic oil-in-oil emulsion

Large scale arrays of tunable microlenses