Conformation of Arborescent Polymers in Solution by Small-Angle Neutron Scattering: Segment Density and Core−Shell Morphology

Ultra-/Small Angle X-ray Scattering (USAXS/SAXS) and Static Light Scattering (SLS) Modeling as a Tool to Determine Structural Changes and Effect on Growth in S. epidermidis

Usually, to characterize bacterial cells' susceptibility to antimicrobials, basic microbiology techniques such as serial dilutions or disk assays are used. In this work, we present an approach focused on combining static light scattering (SLS) and ultra-/small angle X-ray scattering (USAXS/SAXS). This approach was used to support microbiology techniques, with the aim of understanding the structural changes caused to bacteria when they are exposed to different stresses like pH, oxidation, and surfactants. Using USAXS/SAXS and SLS data, we developed a detailed multiscale model for a Gram-positive bacterium, S. epidermidis, and we extracted information regarding changes in the overall size and cell thickness induced by different stresses (i.e., pH and hydrogen peroxide). Increasing the concentration of hydrogen peroxide leads to a progressive reduction in cell wall thickness. Moreover, the concomitant use of pH and hydrogen peroxide provides evidence for a synergy in inhibiting the S. epidermidis growth. These promising results will be used as a starting base to further investigate more complex formulations and improve/refine the data modeling of bacteria in the small angle scattering regime.

High shear vortex fluidic morphologically controlled polysulfone formed under anhydrous conditions

Polysulfone (PSF) was prepared under anhydrous conditions in DMSO, under high shear in a vortex fluidic device (VFD) operating under confined mode thereby avoiding the use of chlorinated solvents, unlike in conventional batch processing.

Structural and magnetic properties of multi-core nanoparticles analysed using a generalised numerical inversion method

The structural and magnetic properties of magnetic multi-core particles were determined by numerical inversion of small angle scattering and isothermal magnetisation data. The investigated particles consist of iron oxide nanoparticle cores (9 nm) embedded in poly(styrene) spheres (160 nm). A thorough physical characterisation of the particles included transmission electron microscopy, X-ray diffraction and asymmetrical flow field-flow fractionation. Their structure was ultimately disclosed by an indirect Fourier transform of static light scattering, small angle X-ray scattering and small angle neutron scattering data of the colloidal dispersion. The extracted pair distance distribution functions clearly indicated that the cores were mostly accumulated in the outer surface layers of the poly(styrene) spheres. To investigate the magnetic properties, the isothermal magnetisation curves of the multi-core particles (immobilised and dispersed in water) were analysed. The study stands out by applying the same numerical approach to extract the apparent moment distributions of the particles as for the indirect Fourier transform. It could be shown that the main peak of the apparent moment distributions correlated to the expected intrinsic moment distribution of the cores. Additional peaks were observed which signaled deviations of the isothermal magnetisation behavior from the non-interacting case, indicating weak dipolar interactions.

Aggregation behavior of polyisoprene-pluronic graft copolymers in selective solvents

Novel amphiphilic graft copolymers composed of a polyisoprene (PIP) backbone with Pluronic side chains, polyisoprene-g-Pluronic, have been synthesized using a "graft onto" technique. Small-angle neutron scattering (SANS) has been used to characterize the conformation of the P123 and P103 Pluronic graft copolymers in selective solvents such as ethanol and hexane and in a nonselective solvent, tetrahydrofuran (THF). The results indicated that, in a selective solvent for the side chain Pluronics (e.g., ethanol), "crew-cut" micelles were formed with a large core of radius ∼ 120 Å; data were fitted with a core-shell model. In a good solvent for the backbone (e.g., hexane), "flowerlike" micelles were formed with a small inner radius of ∼64 Å. In the nonselective solvent, a swollen polymer coil was found, which was described using the Guinier-Debye model. As THF/ethanol and THF/hexane can be prepared in any ratio, it was possible to vary the solvent composition gradually in order to study the transition from swollen coil to micelle. When going from 100% THF to 100% ethanol, the transition to micellar behavior was observed at a ratio of 20:80 (v/v %) THF/ethanol for both grafted copolymers and 40:60 (v/v %) THF/hexane for grafted P123 copolymers.