Millimeter wave rheometry: theory and experiment

A novel millimeter wave (MMW) rheometry is developed to determine the viscosity of fluids based on an unsteady film flow on an inclined plane. The method measures fringes due to MMW interference between the front and back surfaces of a fluid flowing across the field of view of a ceramic wave guide coupled to a MMW receiver operating at 137 GHz. With knowledge of the dielectric constant, the interference fringe spacing is used to calculate the thickness of the fluid layer. This thickness is then transformed into the viscosity by means of a simple hydrodynamic theory. Our results show that the MMW rheometry can practically distinguish between the 30, 100, and 200 Pa·s silicone oils. The geometry of the method allows for potential industrial applications such as measuring viscosity of the flowing slag down the walls of coal gasifiers. The MMW rheometry with simple modifications can be easily extended to measure important non-Newtonian fluid characteristics such as yield stress.     

A general approach to controlling the surface composition of poly(ethylene oxide)-based block copolymers for antifouling coatings

To control the surface properties of a polystyrene-block-poly(ethylene oxide) diblock copolymer, perfluorinated chemical moieties were specifically incorporated into the block copolymer backbone. A polystyrene-block-poly[(ethylene oxide)-stat-(allyl glycidyl ether)] [PS-b-P(EO-stat-AGE)] statistical diblock terpolymer was synthesized with varying incorporations of allyl glycidyl ether (AGE) in the poly(ethylene oxide) block from 0 to 17 mol %. The pendant alkenes of the AGE repeat units were subsequently functionalized by thiol-ene chemistry with 1H,1H,2H,2H-perfluorooctanethiol, yielding fluorocarbon-functionalized AGE (fAGE) repeat units. (1)H NMR spectroscopy and size-exclusion chromatography indicated well-defined structures with complete functionalization of the pendant alkenes. The surfaces of the polymer films were characterized after spray coating by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS), showing that the P(EO-stat-fAGE) block starts to compete with polystyrene to populate the surface after only 1 mol % incorporation of fAGE. Increasing the incorporation of fAGE led to an increased amount of perfluorocarbons on the surface and a decrease in the concentration of PS. At a fAGE incorporation of 8 mol %, PS was not detected at the surface, as measured by NEXAFS spectroscopy. Water contact angles measured by the captive-air-bubble technique showed the underwater surfaces to be dynamic, with advancing and receding contact angles varying by >20°. Protein adsorption studies demonstrated that the fluorinated surfaces effectively prevent nonspecific binding of proteins relative to an unmodified PS-b-PEO diblock copolymer. In biological systems, settlement of spores of the green macroalga Ulva was significantly lower for the fAGE-incorporated polymers compared to the unmodified diblock and a polydimethylsiloxane elastomer standard. Furthermore, the attachment strength of sporelings (young plants) of Ulva was also reduced for the fAGE-containing polymers, affirming their potential as fouling-release coatings.     

Preparation of Co/Pd alloy particles dispersed multiwalled carbon nanotube supported nanocatalysts via gamma irradiation

New multiwalled carbon nanotube/silica supported cobalt-palladium bimetallic nanocatalysts (MWNT@silica/Co–Pd NPs) were prepared by a simple one step gamma irradiation method. The method involves the in-situ surface modification of MWNT with silica (MWNT@silica) and simultaneous formation of Co–Pd bimetallic NPs using gamma irradiation. The bimetallic NPs were stabilized by silica particles formed over the surface of MWNT. Extensive characterization studies have been performed on structural, morphological, and electrochemical, aspects of MWNT@silica/Co–Pd NPs. MWNT@silica/Co–Pd NPs were characterized by field emission scanning microscopy (FESEM), UV–visible spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Raman spectroscopy. The influence of irradiation dosage levels on the stabilizing effect of silica particles has been studied. The electrolytic activities of the MWNT@silica/Co–Pd NPs were investigated by cyclic voltammetry.     

Is the (hfac)Cu(I)–(tmvs) bond intrinsically weak?

Density functional theory studies were performed to study the structure and bonding of (hexafluoroacetylacetonate)-copper(I)-(trimethylvinylsilane) [Cu(hfac)(tmvs)], an ideal and important Cu(I)-CVD compound. A popular three-parameter hybrid density functional (B3LYP) with 6-311+G(d,p) and an effective core potential included LanL2DZ basis set was utilized for this purpose. The (hfac)Cu–(tmvs) bond energy of approximately 30?kcal?mol^?1 obtained at the B3LYP/6-311+G(d,p) level of theory reveals that the Cu–olefin bond in Cu(hfac)(tmvs) is not as weak as previously estimated/assumed and, hence, that the substrate plays a vital role in copper film formation from Cu(hfac)(tmvs). Bonding analysis reveals that fairly strong (hfac)Cu–(tmvs) bonding is the result of DCD-model σ-donation and π-back-bonding between the copper and tmvs in Cu(hfac)(tmvs).     

Cellulose acetate nanocomposite ultrafiltration membranes tailored with hydrous manganese dioxide nanoparticles for water treatment applications

Hydrous manganese dioxide (HMO) nanoparticles incorporated cellulose acetate (CA) composite ultrafiltration (UF) membranes are prepared with the aim of improving the water permeation and BSA contaminant removal. The HMO nanoparticles are synthesized from manganese ion and characterized by FT‐IR, XRD, and FESEM. The effect of variation of HMO on CA membranes is probed using FT‐IR, EDAX, contact angle, SEM, and AFM analysis to demonstrate their chemical functionality, hydrophilicity, and morphology. CA/HMO membranes are showing the enhancement in pure water flux (PWF), water uptake, porosity, hydrophilicity, fouling resistance, BSA rejection, and flux recovery ratio (FRR). CA‐1 membrane displayed higher PWF (143.6 Lm²h^?1), BSA rejection (95.9%), irreversible fouling (93.3%), and FRR (93.3%). Overall results confirmed that the CA/HMO nanocomposite UF membranes overcome the bottlenecks and shows potential for water treatment applications.     

Mechanical characterization of HIV‐1 with a solid‐state nanopore sensor

Enveloped viruses fuse with cells to transfer their genetic materials and infect the host cell. Fusion requires deformation of both viral and cellular membranes. Since the rigidity of viral membrane is a key factor in their infectivity, studying the rigidity of viral particles is of great significance in understating viral infection. In this paper, a nanopore is used as a single molecule sensor to characterize the deformation of pseudo‐type human immunodeficiency virus type 1 at sub‐micron scale. Non‐infective immature viruses were found to be more rigid than infective mature viruses. In addition, the effects of cholesterol and membrane proteins on the mechanical properties of mature viruses were investigated by chemically modifying the membranes. Furthermore, the deformability of single virus particles was analyzed through a recapturing technique, where the same virus was analyzed twice. The findings demonstrate the ability of nanopore resistive pulse sensing to characterize the deformation of a single virus as opposed to average ensemble measurements.     

Field-induced phases of an orientable charged particle in a dilute background of point charges

We report numerical simulations of a two-dimensional dynamical model comprised of a rodlike particle surrounded by a cloud of smaller particles of the same charge, in the presence of an alternating electric field inside a box. We show that this system displays a remarkable dynamical effect; at low forcing frequencies the rod tends to align perpendicularly to the external field, whereas for higher field frequencies the standard orientation (parallel to the field) prevails. Interestingly, the transition between orientations is abrupt enough to resemble a phase transition. The fact that the "anomalous" orientation (perpendicular to the field) takes place is also interesting in the light of some recent laboratory experiments on colloidal solutions, where anomalous orientation at low frequencies was observed. Our toy model suggests that future physically realistic simulations of these systems should explore whether the anomalous orientation may be due to the collective dynamics of the colloidal particles, without necessarily involving more sophisticated electro-osmotic effects.     

Bulk-stress effects in double contacts of similar elastic materials

The effects of a remote applied stress on double contacts of similar elastic materials are examined using a numerical method based on Cauchy singular integral equations (SIE). In contrast to single contacts, the space of possible shear configurations is very rich. In many cases, the partial slip problem does not have a contact equivalent. An equation based on displacement continuity is derived to relate the stick-zone extents for any shear configuration; this equation is essential for the solution of general partial slip problems involving two stick-zones. A shear configuration map that shows the types of partial slip solution that occur for various shear load-remote bulk-stress combinations is obtained for biquadratic indenters. Lastly, it is shown that it is possible to predict the shear configuration in some cases for double cylindrical indenters.     

Viscous flow and temperature distribution in rotating annulus with suction and injection

Part A.—Steady viscous incompressible flow in a rotating coaxial cylindrical annulus with suction and injection is studied. The unsteady flow is also considered. Part B.—An exact solution for temperature distribution at different constant wall temperatures is obtained. It is assumed that the rate of injection at the inner wall equals the rate of suction at the outer wall.     

ESCA determination of the electronic structure of PtCu alloys

A systematic series of ESCA measurements in Pt_1?xCu_x manifest observable shifts for only the Cu core levels. These shifts are linearly related to the corresponding centroids of the valence band spectra. Physical arguments permit extraction of electronic valence structure changes induced by alloying from the measured quantities. Changes in Fermi energy are not related to differences in work function. The Pt valence structure appears unchanged and the Cu structure exhibits dehybridization. There is little charge transfer.