Phase-Field Modelling in Extractive Metallurgy

The phase-field method has already proven its usefulness to simulate microstructural evolution for several applications, e.g., during solidification, solid-state phase transformations, fracture, etc. This wide variety of applications follows from its diffuse-interface approach. Moreover, it is straightforward to take different driving forces into account. The purpose of this paper is to give an introduction to the phase-field modelling technique with particular attention for models describing phenomena important in extractive metallurgy. The concept of diffuse interfaces, the phase-field variables, the thermodynamic driving force for microstructure evolution and the phase-field equations are discussed. Some of the possibilities to solve the equations describing microstructural evolution are also described, followed by possibilities to make the phase-field models quantitative and the phase-field modelling of the microstructural phenomena important in extractive metallurgy, i.e., multiphase field models. Finally, this paper illustrates how the phase-field method can be applied to simulate several processes taking place in extractive metallurgy and how the models can contribute to the further development or improvement of these processes.     

Preparation and Cytotoxicity of Poly(Methyl Methacrylate) Nanoparticles for Drug Encapsulation

Summary: This work aimed to produce poly(methyl methacrylate) nanoparticles for use in drug encapsulation. The polymer nanoparticles were produced using miniemulsion polymerization technique. Monomer miniemulsion showed moderate stability and polymer average particle size was about 90 nm. PMMA nanoparticles were tested for toxicity in human leukemic cell strain K562 and they did not show any adverse effect on cell viability. Therefore, poly(methyl methacrylate) nanoparticles are suitable to encapsulate antitumor agents.     

Stimuli-Responsive Particle-Based Amphiphiles as Active Colloids Prepared by Anisotropic Click Chemistry

Amphiphiles alter the energy of surfaces, but the extent of this feature is typically constant. Smart systems with amphiphilicity as a function of an external, physical trigger are desirable. As a trigger, the exposure to a magnetic field, in particular, is attractive because it is not shielded in water. Amphiphiles like surfactants are well known, but the magnetic response of molecules is typically weak. Vice-versa, magnetic particles with strong response to magnetic triggers are fully established in nanoscience, but they are not amphiphilic. In this work colloids with Janus architecture and ultra-small dimensions (25 nm) have been prepared by spatial control over the thiol-yne click modification of organosilica-magnetite core–shell nanoparticles. The amphiphilic properties of these anisotropically modified particles are proven. Finally, a pronounced and reversible change in interfacial stabilization results from the application of a weak (<1 T) magnetic field.     

N,N'-dialkyl- and N-alkyl-N-mesityl-substituted N-heterocyclic carbenes as ligands in Grubbs catalysts

Various symmetrically and asymmetrically substituted N-heterocyclic carbene (NHC) ligands bearing aliphatic nitrogen-containing side groups have been synthesised. In our attempts to isolate the corresponding second-generation Grubbs catalysts, we were unsuccessful when using the symmetrical aliphatic NHC ligands. For the asymmetrical ligands bearing an aliphatic moiety on one side and an aromatic mesityl group on the other side, substitution of a phosphine ligand was achieved. The performance of a so-formed series of Ru-based metathesis initiators has been evaluated for the ring-opening metathesis polymerisation (ROMP) of cycloocta-1,5-diene and the ring-closing metathesis (RCM) of diethyl diallylmalonate.     

Computation of molecular weight distributions by polynomial approximation with complete adaptation procedures

The choice of appropriate reference functions is still the major drawback for collocation techniques to be used during the computation of molecular weight distributions (MWDs) in polymerization reactions and other problems constituted by systems of differential‐difference equations. Complete adaptation procedures provide significant improvement of numerical approximations obtained, but convergence to the real solution is not assured and oscillatory numerical approximations may be obtained when the actual solution experiences large variations during time integration. An alternative method to compute the reference function in an adaptative manner, called here the integration of the reference function procedure, is presented. The technique is used to allow the computation of MWDs in two polymerization problems: the metallocene‐based propene polymerization and the methyl methacrylate/butyl acrylate emulsion polymerization. The integration of the reference function procedure allowed the proper computation of broad, bimodal and fast changing distributions with polynomials of very low order (below 4), where other approximation techniques failed. The method may be easily implemented and does not require any pre‐processing before implementation.