Flotation de-inking studies using model hydrophobic particles and non-ionic dispersants

A series of non-ionic alcohol ethoxylated surfactants (with HLB within the range of 11.1–12.5) were used as dispersants during flotation of mondisperse hydrophobised silica particles (representing ink particles) in de-inking formulations. Laboratory scale flotation experiments, contact angle, dynamic surface tension and thin film drainage experiments were carried out. The reduction in dynamic surface tension at the air/solution interface (which is dependent on the adsorption kinetics) followed the order C₁₀E₆>C₁₂E₈≈C₁₂E₆>C₁₄E₆ and these values were lower than sodium oleate, which is commonly used in de-inking systems. In addition the non-ionics adsorbed on the hydrophobised silica particles reducing the contact angle. These results indicated that the non-ionic surfactant with the highest CMC (C₁₀E₆) gave (a) the highest rate of adsorption at the air/solution interface (b) the froth with the greatest water content and higher froth volume (c) the lowest reduction in contact angle and (d) the highest flotation efficiency at concentrations above the CMC. It was also observed that flotation occurred, in spite of the fact that thin-film measurements indicated that the adsorption of non-ionic at the air/solution and silica/solution interfaces reduced the hydrophobicity of the particles, as indicated by an increase in stability of the aqueous thin film between the particle and air-bubble. This result suggests that the bubble-ink particle captures mechanism (occurring through rupture of the thin aqueous film separating the interfaces) is not the only mechanism controlling the flotation efficiency and that other parameters (such as the kinetics of surfactant adsorption, foaming characteristics, and bubble size) need to be taken into account. The kinetics is important with respect to the rate of adsorption of surfactant to both interfaces. Under equilibrium conditions, this may give rise to repulsive steric forces between the air-bubble and the particles (stable aqueous thin-films). However, a lower amount of surfactant adsorbed at a freshly formed air bubble or inkparticle (caused by slow adsorption rates) will produce a lower steric repulsive force allowing effective collection of particles by the bubble. Also, it was suggested that the influence of alcohol ethoxylates on bubble-size could effect the particle capture rate and mechanical entrainment of particles in an excessively buoyant froth, which will also play an important role in the flotation recovery.     

Design of molecular architectures for polymeric mesophase formation

Based on the tendency of low molar mass liquid crystals composed of extended mesogens symmetrically disubstituted with long n-alkoxy substituents to exhibit smectic C mesophases, we have proposed that SCLCPs with laterally attached (vs. terminally attached) mesogens offer an ideal architecture for obtaining s_C* mesophases. In particular, mesogens that typically form the desirable s_C*-n phase sequence can be laterally attached to the polymer backbone through a chiral spacer, which should result in high values of spontaneous polarization. Not only are we using mesogens which exhibit s_C*-n phase sequences, we are also attempting to induce smectic layering into systems which typically form nematic mesophases by using immiscible hydrocarbon/fluorocarbon components and electron-donor-acceptor interactions. Thus far, the thermotropic behavior of poly{5-[[[2', 5'-bis[(3″-fluoro-4″-dimethoxyphenyl)ethynyl]benzyl]oxy]carbonyl[2.2.1]hept-2-ene]s and poly(5-[[[2',5'-bis[(3″-fIuoro-4″-methoxybenzoyl)oxy]benzyl]oxy]carbonyl]-bicyclo[2.2.1]hept-2-ene)s correspond to that of their low molar mass analogs. Preliminary results demonstrate that smectic layering is successfully induced in 2,5-bis[(4'-n-alkoxybenzoyl)oxy]toluenes and polynorbornenes with laterally attached 2,5-bis[(4'-n-alkoxybenzoyl)oxy]benzyl mesogens by terminating the n-alkoxy substituents with perfluorinated segments.     

Comparison of living polymerization mechanisms. Acrylates and carbocationic polymerization

The concept of a living polymerization is critically discussed. A system ranking various classes of “livingness” is proposed, and the importance of determining the real values of k_tr/k_p and k_t/k_p ratios is expounded. New living systems, including carbocationic polymerization and group transfer polymerization of acrylates are compared with classic ionic systems. The mechanism of propagation and the nature of the true active species are similar in both new and classic polymerizations. The role of various components which improve the “livingness” of the polymerizations is discussed and explained by dynamic equilibration between dormant and active species and suppression of side reactions.     

Living ring opening metathesis polymerization of mesogenic norbornene derivatives

A new class of SCLCPs was prepared by polymerizing mesogenic norbornene derivatives using Mo(CHCMe₂R)(N-2,6-C₆H₃-i-Pr₂)(O-t-Bu)₂ (R = CH₃ or Ph). Monomers based on norbornene ring systems were chosen because the rings are highly strained and therefore yield irreversible polymerizations. The Mo-alkylidene initiators were chosen because they initiate norbornene derivatives relatively fast and quantitatively, and provide stable chain ends which have low reactivity to both the internal double bonds of the polymer backbone and the functional groups present in the monomers. The apparent absence of termination and transfer reactions in ROMP results in polymerizations which appear to be living, and the fast initiation and irreversible chain growth leads to polymers with narrow molecular weight distributions in which the degree of polymerization is controlled by the ratio of monomer to initiator used. The resulting well-defined polymers were used to determine the most basic structure-property relationships of this new class of SCLCPs. The thermotropic behavior of both terminally attached and laterally attached SCLCPs based on polynorbornene backbones becomes independent of molecular weight at approximately 25 repeat units. In addition, polydispersity was found to have no effect on the breadth of nematic phase transitions in the terminally attached polymers, with the transition temperature determined simply by the number average degree of polymerization.     

Synthesis and crosslinking of hyperbranched poly(n‐nonyl acrylate) to form organogels

(2‐Bromo‐n‐nonan‐1‐oxycarbonyl)ethyl acrylate was synthesized as an inimer for self‐condensing vinyl polymerization (SCVP) to produce hyperbranched poly(n‐nonyl acrylate), either as a homopolymer or as a copolymer with n‐nonyl acrylate. The inimer was homopolymerized and copolymerized by atom transfer radical polymerization (ATRP) and activator generated by electron transfer ATRP to produce soluble polymers with broad polydispersities (up to ? = 9.91), which is characteristic of hyperbranched polymers produced by SCVP. The resulting hyperbranched (co)polymers were crosslinked by atom transfer radical coupling in both one‐pot and two‐step procedures. The radical–radical crosslinking reaction is extremely efficient, resulting in hard plastic particles from the homopolymer of (2‐bromo‐n‐nonan‐1‐oxycarbonyl)ethyl acrylate synthesized in bulk. Crosslinked organogels that swell in tetrahydrofuran were formed when the rate of crosslinking decreased using acetonitrile solutions. Dynamic shear and stress relaxation experiments demonstrated that the dry network behaves as a covalently crosslinked soft gel, with a glass transition at ?50 °C according to differential scanning calorimetry. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2399–2410     

The electronic states in diamond

An account of a method of performing a priori tight-binding calculations on a crystal lattice of the diamond type is given. The method is a generalization of that of Cohan et al. [8]. Certain possible extensions of the method are discussed. New results for the electronic energy bands in diamond are presented in which the variation of the bands with the hybridization parameter of the initial bonding orbitals and the orbital exponent of the basic atomic orbitals is investigated.     

Halometallate Complexes of Germanium(II) and (IV): Probing the Role of Cation,Oxidation State and Halide on the Structural and Electrochemical Properties

The Ge^IV chlorometallate complexes, [EMIM]₂[GeCl₆], [EDMIM]₂[GeCl₆] and [PYRR]₂[GeCl₆] (EMIM=1‐ethyl‐3‐methylimidazolium; EDMIM=2,3‐dimethyl‐1‐ethylimidazolium; PYRR=N‐butyl‐N‐methylpyrrolidinium) have been synthesised and fully characterised; the first two also by single‐crystal X‐ray diffraction. The imidazolium chlorometallates exhibited significant C?H???Cl hydrogen bonds, resulting in extended supramolecular assemblies in the solid state. Solution ¹H NMR data also showed cation–anion association. The synthesis and characterisation of Ge^II halometallate salts [EMIM][GeX₃] (X=Cl, Br, I) and [PYRR][GeCl₃], including single‐crystal X‐ray analyses for the homologous series of imidazolium salts, are reported. In these complexes, the intermolecular interactions are much weaker in the solid state and they appear not to be significantly associated in solution. Cyclic‐voltammetry experiments on the Ge^IV species in CH₂Cl₂ solution showed two distinct, irreversible reduction waves attributed to Ge^IV–Ge^II and Ge^II–Ge⁰, whereas the Ge^II species exhibited one irreversible reduction wave. The potential for the Ge^II–Ge⁰ reduction was unaffected by changing the cation, although altering the oxidation state of the precursor from Ge^IV to Ge^II does have an effect; for a given cation, reduction from the [GeCl₃]^? salts occurred at a less cathodic potential. The nature of the halide co‐ligand also has a marked influence on the reduction potential for the Ge^II–Ge⁰ couple, such that the reduction potentials for the [GeX₃]^? salts become significantly less cathodic when the halide (X) is changed Cl→Br→I.     

Linear Stability of Steady States for Thin Film and Cahn-Hilliard Type Equations

We study the linear stability of smooth steady states of the evolution equation