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This paper examines different binary mixtures of anionic/nonionic surfactants using a new technique known as solvent-free extrusion emulsification (SFEE) to control the surface charge in resulting ...

A new continuous emulsification technique known as solvent-free extrusion emulsification (SFEE) was recently introduced to prepare submicron particles (100–500 nm) from high viscosity polymers (100–1000 Pa·s) with a twin screw extruder. The present study examined the influence of matrix viscosity on its dispersion mechanism using cross-linked polyester as a viscosity modifier. The investigation used an inline rheometer for transient and steady state viscosity measurements, and offline characterizations including Soxhlet extraction, colorimetric titration, and particle size analysis. Though it remained possible to produce particles close to their target size of 100–200 nm, particle size was notably increased by varying the matrix viscosity from 250 Pa·s for the neat polyester up to 630 Pa·s with the added modifier. The results point to thicker striated lamellae from less effective mixing prior to phase inversion when the matrix viscosity was increased without a corresponding increase in surface active spec...

Solvent-free extrusion emulsification (SFEE) is a complex process using twin-screw extrusion to prepare solid-liquid dispersions of high viscosity polymers and has received little study to date on its inherent mechanisms. To gain rheological insights into the earliest stage of SFEE as the interfacial boundary between water and polymer grows, prior to phase inversion, an inline orifice-plate type viscometer is introduced to monitor transient behavior over a wide range of viscosities. The presented work examines rheological changes of a polyester-water system produced by varying two factors thought to significantly control the final state of the dispersion, specifically polar group contributions to surface energy and viscosity. A processing modifier was combined with the polyester to study the influence of these two factors. The inline viscometer revealed an abrupt transition in viscosity occurred with the developed state of water dispersion, confirming observations of a prior batch study. Analysis of the rheological response indicated that a higher polar surface energy contribution had the greatest influence on the state of this transition, and that a steeper transition was related to greater incorporation of water within the polyester matrix. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Solvent-free extrusion emulsification (SFEE) is a new continuous approach for producing nanoparticles from high viscosity molten polymers using a twin-screw extruder. In a previous study, the influence of melt viscosity on lamellae development in the phase inversion mechanism was investigated for an otherwise fixed system of variables including temperature, mixing intensity and surfactant content. Varying system temperature in the current study to produce the same melt viscosities as those previously examined, did not produce the same linear effect on particle size. The investigation to understand the influence of system temperature on the SFEE mechanism was done by using an inline rheometer and different screw/barrel configurations to simulate different zones of SFEE. Characterizations of the emulsified polyester included colorimetric titrations, particle size analysis, parallel plate rheometry, and gel permeation chromatography (GPC). Raising system temperature has a negative effect on the mechanism for producing smaller particles, countering the positively affected parameters, namely lower melt viscosity and a higher content of surface active species based on a contributing neutralization reaction. The findings show good fit to published studies of an osmotic pressure driven emulsification mechanism, which is beneficial in clarifying the role of surfactants in the process. Overall, the results show system temperature to be a complex variable in SFEE, deeming it undesirable in optimizing the process. NSERC

Rheological analysis of a complex fluid system like an aqueous polymer dispersion can be challenging but can reveal mechanistic information as the viscous melt is emulsified. A pressurized vessel was used as a rheometer, based on the Metzner–Otto approach, to evaluate formulation variables where the developed morphology of a polyester/water mixture was shear-dependent. The parameters of the study were resin-to-water ratio (R/W), surfactant (type and concentration), and process variables of impeller speed and temperature. Transient in situ information on the system during the mixing of water into the molten polymer showed that a rapid, near-instantaneous decrease in the torque on the impeller occurred consistently around 2% water addition, related to the onset of the developed morphological state. It was observed to only demonstrate a drop in the torque for high shear rates and only with the appropriate content of surface-active species, revealing the chemical and physical parameters necessary to emulsify ...

Ternary thallinm lanthanide dichalcogenides TILnX2 (X = S, Se, or Te; Ln = lanthanide, except Ce and Pr) crystallize in the rhombohedral structure of α-NaFeO 2 type (R3m). Their crystal lattice consists of the layers of Ln 3 + ions separated by three layers of the non-magnetic ions (-Ln-X-Tl-X-Ln-). The magnetization was measured in the field range 0-14 T. The molecular field constants λm were estimated by fitting the Brillouin function to the experimental magnetization plots. The difference between the λ m values for the thallium gadolinium sulphide and the selenide corresponds to the different character of Gd-S and Gd—Se bonds and gives rise to the different J 1 and J2 exchange integrals.

The magnetic properties of the lanthanide chalcogenides are much less explored than the monopnictides. The main reasons are probably difficulties in syntheses and the crystals growth. In particular, the properties of monotellurides are almost completely unknown. The dysprosium tellurides: DyTe and Dy2Τe3, crystallize in the structures related to the rock salt type. The first compound is metallic, while the second — semiconducting. Dysprosium sesquitelluride behaves like a simple antiferromagnet with the Neel temperature equal to 4.1 K [1]. We synthesized and investigated the dysprosium monnotelluride in order to examine a change of exchange interactions after transition to the metallic state.

Thallium lanthanide diselenides TlLnSe2 (Ln  Nd, Gd to Er and Yb) crystallize in the α-NaFeO2 structure type (R 3 m). It is an NaCl-related ordered structure with the thallium and lanthanide layers separated by the anion layers. The TlSe6 octahedra are strongly elongated and the LnSe6 octahedra are slightly shrunk along the threefold axis. The deformation of the LnSe6 polyhedra decreases on going from light to heavy lanthanides. The parameters of the crystal field Hamiltonian were estimated from the high field magnetization. The second-order crystal field parameters were found to correlate with the deformation of the environments of the lanthanide ions.

FeSc2S4, MnSc2S4 and MnSc2Se4 crystallize in the normal spinel structure. None of them orders magnetically above 4.2 K contrary to FeLu2S4, which orders at 8 K. This difference is discussed as being strongly dependent on the transfer of divalent iron to the octahedral sites and not on the interionic distances.

Results of the susceptibility, specific heat and thermal expansion are reported for the compounds CeM 2 Ge 2 (M: Ag, Au, Ru), which order antiferromagnetically below T N = 5 K (Ag) and 15 K (Au) and ferromagnetically below T c = 7.5 K (Ru). Distinct maxima in the electronic specific heat coefficient γ( T ) at 0.3 K for the Ag- and Au-based compounds hint at a coexistence of coherent electronic quasiparticles of “medium”-heavy mass with magnetic order.

The magnetic properties of the heavier lanthanide sesquiselenides were studied as early as 1937 by Klemm and Koczy 1 and later in the 1970’s by a group of Soviet investigators2,3. The measurements were carried out down to liquid nitrogen temperature, and they gave linear plots of the temperature dependence of the reciprocal magnetic susceptibility. The widening of the measurement range down to helium temperatures makes a more detailed interpretation of magnetic properties possible, relating magnetic susceptibility to crystal field effects. Such an analysis becomes simplest in the case of compounds with a high symmetry of the magnetic ion environment. This is the reason for our interest in sesquiselenides with the Sc2S3 crystal structure, since they are the ones which demonstrate an octahedral environment of metal ions. The orthorhombic Sc2S3 structure arises from the NaCl structure by removing 1/3 of the cations in an ordered manner. The first coordination sphere of each metal ion contains six selenide ions forming a slightly distorted octahedron. The deviations of the lattice constant ratios a/b and c/b from their ideal values, being equal to $\sqrt{2}$ and 3 respectively, can be taken as a measure of that distortion.

Crystal field parameters of Ce 3+ in tetragonal TlCeSe 2 and TlCeTe 2 were determined from the magnetic susceptibility measurements down to 4.2 K: B 0 2 = -14.7 K and -6.9 K, B 0 4 = -0.38 K and -0.39 K, B 4 4 = 3.8 K and 9.8 K for selenide and telluride, respectively.

The magnetic susceptibility and the high field magnetization of MgYb 2 S 4 and MgYb 2 Se 4 have been measured. A weakly deformed octahedral crystal field was found with x = -0.959, W = 22.4 K, B 0 2 = -0.30 K for the sulphide and x = -0.977, W = 22.6 K, B 0 2 = -0.082 K for the selenide.