Zhenyu Di

Drug-Induced Morphology Switch in Drug Delivery Systems Based on Poly(2-oxazoline)s

Defined aggregates of polymers such as polymeric micelles are of great importance in the development of pharmaceutical formulations. The amount of drug that can be formulated by a drug delivery system is an important issue, and most drug delivery systems suffer from their relatively low drug-loading capacity. However, as the loading capacities increase, i.e., promoted by good drug–polymer interactions, the drug may affect the morphology and stability of the micellar system. We investigated this effect in a prominent system with very high capacity for hydrophobic drugs and found extraordinary stability as well as a profound morphology change upon incorporation of paclitaxel into micelles of amphiphilic ABA poly(2-oxazoline) triblock copolymers. The hydrophilic blocks A comprised poly(2-methyl-2-oxazoline), while the middle blocks B were either just barely hydrophobic poly(2-n-butyl-2-oxazoline) or highly hydrophobic poly(2-n-nonyl-2-oxazoline). The aggregation behavior of both polymers and their formulations with varying paclitaxel contents were investigated by means of dynamic light scattering, atomic force microscopy, (cryogenic) transmission electron microscopy, and small-angle neutron scattering. While without drug, wormlike micelles were present, after incorporation of small amounts of drugs only spherical morphologies remained. Furthermore, the much more hydrophobic poly(2-n-nonyl-2-oxazoline)-containing triblock copolymer exhibited only half the capacity for paclitaxel than the poly(2-n-butyl-2-oxazoline)-containing copolymer along with a lower stability. In the latter, contents of paclitaxel of 8 wt % or higher resulted in a raspberry-like micellar core.

Structural Instabilities in Lamellar Diblock Copolymer Thin Films During Solvent Vapor Uptake

We have studied the structural rearrangements in a lamellae-forming poly(styrene-b-butadiene) film during exposure to toluene vapor. Real-time, in situ grazing-incidence small-angle X-ray scattering allowed us to identify distinct kinetic regimes: First, the lamellae swell linearly, and the blocks stretch uniaxially. Then, the blocks relax to a more globular molecular conformation, and the lamellar thickness abruptly shrinks again. The increased interfacial area culminates in a dramatic instability causing a major rearrangement of the lamellar stack and the formation of new lamellae. Finally, the lamellar thickness levels off, and the interfaces flatten again.

KWS-1 high-resolution small-angle neutron scattering instrument at JCNS: current state

The KWS-1 small-angle neutron scattering (SANS) instrument operated by the Julich Centre for Neutron Science (JCNS) at the research reactor FRM II of the Heinz Maier-Leibnitz Zentrum in Garching near Munich has been recently upgraded. The KWS-1 instrument was updated, from its active collimation apertures to the detector cabling. Most of the parts of the instrument were installed for the first time, including a broadband polarizer, a large-cross-section radio-frequency spin flipper, a chopper and neutron lenses. A custom-designed hexapod in the sample position allows heavy loads and precise sample positioning in the beam for conventional SANS experiments as well as for grazing-incidence SANS under applied magnetic field. With the foreseen in situ polarization analysis the main scientific topic of the instrument tends towards magnetism. The performance of the polarizer and flipper was checked with a polarized 3He cell at the sample position. The results of these checks and a comparison of test measurements on a ferrofluid in a magnetic field with polarized and nonpolarized neutrons are presented.

Observational evidence confirms modelling of the long-term integrity of CO2-reservoir caprocks

Storage of anthropogenic CO2 in geological formations relies on a caprock as the primary seal preventing buoyant super-critical CO2 escaping. Although natural CO2 reservoirs demonstrate that CO2 may be stored safely for millions of years, uncertainty remains in predicting how caprocks will react with CO2-bearing brines. This uncertainty poses a significant challenge to the risk assessment of geological carbon storage. Here we describe mineral reaction fronts in a CO2 reservoir-caprock system exposed to CO2 over a timescale comparable with that needed for geological carbon storage. The propagation of the reaction front is retarded by redox-sensitive mineral dissolution reactions and carbonate precipitation, which reduces its penetration into the caprock to ∼7 cm in ∼105 years. This distance is an order-of-magnitude smaller than previous predictions. The results attest to the significance of transport-limited reactions to the long-term integrity of sealing behaviour in caprocks exposed to CO2.

Novel thermoresponsive block copolymers having different architectures—structural, rheological, thermal, and dielectric investigations

Thermoresponsive block copolymers comprising long, hydrophilic, nonionic poly(methoxy diethylene glycol acrylate) (PMDEGA) blocks and short hydrophobic polystyrene (PS) blocks are investigated in aqueous solution. Various architectures, namely diblock, triblock, and starblock copolymers are studied as well as a PMDEGA homopolymer as reference, over a wide concentration range. For specific characterization methods, polymers were labeled, either by partial deuteration (for neutron scattering studies) or by fluorophores. Using fluorescence correlation spectroscopy, critical micellization concentrations are identified and the hydrodynamic radii of the micelles, rhmic, are determined. Using dynamic light scattering, the behavior of rhmic in dependence on temperature and the cloud points are measured. Small-angle neutron scattering enabled the detailed structural investigation of the micelles and their aggregates below and above the cloud point. Viscosity measurements are carried out to determine the activation energies in dependence on the molecular architecture. Differential scanning calorimetry at high polymer concentration reveals the glass transition of the polymers, the fraction of uncrystallized water and effects of the phase transition at the cloud point. Dielectric relaxation spectroscopy shows that the polarization changes reversibly at the cloud point, which reflects the formation of large aggregates upon heating through the cloud point and their redissolution upon cooling.

Probing the Self-Organization Kinetics in Block Copolymer Thin Films

Solvent annealing [1-3] has recently emerged as a powerful alternative to thermal annealing of block copolymer (BCP) thin films and nanocomposites. Taking a more general point of view, solvent treatment procedures, employing the selectivity of the solvents towards the different blocks, can produce new structures [4], and provide fascinating insights into the swelling kinetics and instabilities in such self-assembled and oriented thin films [5]. Taking a lamellar polystyrene-polybutadiene (PS-b-PB) film right from the spin coater into an in-situ vapor cell provided an intriguing trip through configuration space, with various lamellar re-orientations encountered during swelling.

Inducing hetero‐aggregation of different azo dyes through electrostatic self‐assembly

Combining chemically different building blocks in supramolecular nanoparticles is a promising key to tailored structures and functionalities. π-π heterostacks of dye molecules form upon electrostatic self-assembly with a polyelectrolyte, resulting in stable ternary nano-assemblies in aqueous solution. Core-shell spheres, cylinders, and flexible cylinders result, which exhibit new shapes different from the binary systems. Particle shapes can be tuned through the dye composition.