Timo Rager

Micelle formation of poly(acrylic acid)-block-poly(methyl methacrylate) block copolymers in mixtures of water with organic solvents

The micelle formation of poly(acrylic acid)-block-poly(methyl methacrylate) (AA-MMA) block copolymers in mixtures of water with organic solvents was investigated by non-radiative energy transfer (NRET). In the case of block copolymers with 70 hydrophobic MMA units, which form strongly aggregated micelles in pure water, the addition of a non-selective organic solvent (methanol or 1,4-dioxane) induces a micelle-unimer transition within a relatively small range of solvent composition without significantly increasing the rate of chain exchange between micelles close to this transition region. The addition of 2 vol.-% dimethyl adipate (a solvent with chemical similarity to the PMMA block and only limited solubility in water) does not speed up the chain exchange in this system either. In contrast, this solvent promotes the aggregation of smaller block copolymers (20 or 40 MMA units) which are mainly present as single chains in pure water. In the case of the block copolymer with 40 MMA units the so formed micelles show a very slow chain exchange extending over many days. These observations prompt us to assume that the rate of the micelle-unimer exchange equilibrium is not kinetically hindered (i.e., determined by the T g of the core material of the micelle) but controlled by a strong thermodynamic preference for the aggregated state.

Block copolymer micelles as seed in emulsion polymerization

The size of aggregates formed by poly(acrylic acid)-block-poly(methyl methacrylate) block copolymers was determined and the applicability of these block copolymers as stabilizers in emulsion polymerization was investigated. The analytical methods included transmission electron microscopy, light scattering, and analytical ultracentrifugation. Polymers with a hydrophilic poly(acrylic acid) block of equal or larger size than the hydrophobic poly(methyl methacrylate) block are efficient as stabilizers down to block copolymer-to-monomer ratios of less than 1 wt.-%. From the influence of the block copolymer-to-monomer ratio on the latex particle size, from the relation between the number of block copolymer molecules per latex particle and the aggregation number of the block copolymer micelles, and from fluorescence studies we conclude that micelles consisting of block copolymers with 35 or more hydrophobic MMA units act as a seed in the emulsion polymerization of acrylic and methacrylic monomers.

Stability Domains of Multi-Component Crystals in Ternary Phase Diagrams

Abstract The topology of ternary phase diagrams of systems that are forming salts, cocrystals, solvates, or hydrates is discussed based on a simple mathematical model. The considerations include the thermodynamic stability of the multi-component crystal relative to the individual components, the character of the interactions in solution, the effect of relative solubility of the components, the consequences of using liquid components, the formation of multi-component crystals with different stoichiometry, and the competition between cocrystals or salts and solvates. Based on the characteristics of the phase diagrams, recommendations are provided as to an efficient design of salt formation and cocrystallization experiments.

Solar-thermal zinc oxide reduction assisted by a second redox pair

Abstract Thermochemical cycles have been investigated for quite some time as a means to convert heat into storable chemical energy. A particularly attractive reaction is the solar-thermal decomposition of zinc oxide into zinc and oxygen, but the efficiency of this process is impaired by the fast recombination of zinc and oxygen upon cooling of the gas phase. The combination with a second, nickel/nickel oxide redox cycle is presented as a possibility to avoid the simultaneous presence of metal and oxygen in the gas phase.

Chapter 12:Application of Phase Diagrams in Co-crystal Search and Preparation

Typical selection criteria for co-crystal formers include toxicological considerations, physico-chemical properties such as water solubility, and the functional groups that are available for interaction with the substance to be co-crystallized (e.g., a drug substance). Some degree of predictability for the formation of a crystalline multi-component compound is often claimed for certain combinations of functional groups. The expression crystal engineering has been coined for this strategy and combined with the concept of synthons from organic chemistry. Computer modeling may further improve the predictive potential based on interaction energies and steric aspects.Thermodynamic considerations offer a complementary approach for targeted co-crystal search and development. They can provide selection criteria for suitable co-crystal formers and can also help to predict the most promising preparation conditions. This includes the potential to reduce experimental effort in co-crystal search and crystallization optimization significantly. Phase diagrams are the method of choice for visualizing the thermodynamic relationships and simplifying their application. Phase diagrams are thus a powerful and intuitive tool for planning co-crystal screenings and crystallization optimizations.