Surface rheology and foaming properties of sodium oleate and C12(EO)6 aqueous solutions

The dynamic surface tension (DST) and the surface viscoelastic modulus of sodium oleate aqueous solutions at different concentrations were measured using an image analysis tensiometer based on the oscillating bubble technique. The diffusion coefficient of oleate moieties was calculated from DST measurements and the surface viscoelastic modulus using the Langmuir-Szyszkowski and the diffusion-controlled adsorption models. The viscoelastic moduli obtained from model calculations were compared with the corresponding experimental values. The diffusion coefficient of C(12)(EO)(6) in water and the parameters of the Langmuir-Szyszkowski adsorption isotherm were taken from the literature and used to calculate the surface viscoelastic modulus of its aqueous solutions at different concentrations. The foaming properties of both C(12)(EO)(6) and sodium oleate solutions, viz., the foam conductance and the water volume fraction in the foam, were measured using a commercial Foamscan device. Foaming experiments with C(12)(EO)(6) and sodium oleate solutions were carried out either under static conditions; i.e., the foam conductance and the water volume fraction were measured as a function of time after the generation of a fixed volume of foam, or under dynamic conditions; i.e., the foam conductance and the water volume fraction were measured during foam formation. The variations in the foam permeability as a function of surfactant concentration were related to the viscoelastic properties of the air/water interface and to the presence of micelles in the foam films. With foams in which the water volume fraction was higher than 0.05, the foam electrical conduction could be described using a simple parallel resistor model and their conductance measurements were related to the foam water volume fraction. The results related to water drainage under static conditions were used to interpret water drainage under dynamic conditions. Preliminary conjectures on the influence of foam permeability and water volume fraction on the yield of the flotation deinking process were drawn from these results.     

Design and Synthesis of Aviram–Ratner‐Type Dyads and Rectification Studies in Langmuir–Blodgett (LB) Films

The design and synthesis of Aviram–Ratner‐type molecular rectifiers, featuring an anilino‐substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ‐spacer bicyclo[2.2.2]octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X‐ray analysis. The photophysical properties of the TTF‐BCO‐exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir–Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current–voltage (I–V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I–V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor.     

Four bromo‐substituted pyrazoline and isoxazolinone spiro derivatives

Conformational analyses and a structural comparison of the four spiro compounds 3‐bromo‐1,9‐di­phenyl‐4‐p‐tolyl‐7‐oxa‐1,2,8‐tri­aza­spiro­[4.4]­nona‐2,8‐dien‐6‐one, (I), C₂₄H₁₈BrN₃O₂, 3‐bromo‐4‐(4‐methoxy­phenyl)‐1,9‐di­phenyl‐7‐oxa‐1,2,8‐tri­aza­spiro­[4.4]­nona‐2,8‐dien‐6‐one, (II), C₂₄H₁₈BrN₃O₃, 3‐bromo‐4‐(4‐chloro­phenyl)‐1,7,9‐tri­phenyl‐1,2,7,8‐tetra­aza­spiro­[4.4]­nona‐2,8‐dien‐6‐one, (III), C₂₉H₂₀BrClN₄O, and 3‐bromo‐1,7,9‐tri­phenyl‐4‐p‐tolyl‐1,2,7,8‐tetra­aza­spiro­[4.4]­nona‐2,8‐di­en‐6‐one, (IV), C₃₀H_22.89Br_1.11N₄O, are presented. The mol­ecular structures are rather similar, which is as expected since the compounds are all products of concerted 1,3‐dipolar attack on (Z)‐4‐aryl­idene oxazolone and pyrazolone derivatives. The observed conformations tend to favour extended π conjugation of the benzene rings and other π systems, as shown by a comparison of selected geometric parameters of the four structures.     

Attitude dynamic singularities in 3D free-flying manipulators for improved path planning

This paper extends the solution, already presented to the trajectory planning problem of 2D free-flying manipulators, to 3D manipulators. It demonstrates it is possible to design a robotic arm with a special dynamic singularity (attitude singular configuration), thus permitting to determine and execute its trajectory without affecting the attitude of the spacecraft carrying it. This methodology provides an exact solution to trajectory planning problems that are usually dealt with by approximate algorithms based on the concept of Disturbance Map. After a theoretical introduction, some educational design examples are presented.     

Gold nanoparticles stabilized by modified halloysite nanotubes for catalytic applications

A highly sustainable prototype of a flow system based on gold nanoparticles (4.2 nm) supported on thiol‐functionalized halloysite nanotubes (HNTs) was developed for catalytic applications. The catalytic performances were evaluated using the reduction of 4‐nitrophenol to 4‐aminophenol as a model system. Under the best experimental conditions (0.0001 mol%, 1.97 × 10^?8 mg of Au nanoparticles), an impressive apparent turnover frequency value up to 2 204 530 h^?1 was achieved and the halloysite‐based catalyst showed full recyclability even after ten cycles. The high catalytic activity confirms the importance of the use of HNTs as support for Au nanoparticles that can exert a synergistic effect both as medium for transfer of electrons from borohydride ions to 4‐nitrophenol and by modulating interfacial electron transfer dynamics. With the application of flow technology, the obtained heterogeneous HNT@Au catalyst was fully recovered and reused for at least one month.     

Synthesis and X-ray crystal structures of some isothiosemicarbazone complexes

Transition Metal Chemistry - Four complexes of a new isothiosemicarbazone ligand have been prepared and characterized as μ2-pip-(NiL)2 (1), MnL2 (2), UO2L(BrSal)BuOH (3) and (μ2-MoO2L)2...