Coupling of Rotational Motion with Shape Fluctuations of Core-shell Microgels Having Tunable Softness

The influence of shape fluctuations on deformable thermosensitive microgels in aqueous solution is investigated by dynamic light scattering (DLS) and depolarized dynamic light scattering (DDLS). The systems under study consist of a solid core of polystyrene and a thermosensitive shell of cross-linked poly(N-isopropylacrylamide) (PNIPA) without and with embedded palladium nanoparticles. PNIPA is soluble in water, but has a lower critical solution temperature at 32 C (LCST). Below the LCST the PNIPA shell is swollen. Here we find that besides translational and rotational diffusion, the particles exhibit additional dynamics resulting from shape fluctuations. This leads to a pronounced apparent increase of the rotational diffusion coefficient. Above the transition temperature the shell collapses and provides a rather tight envelope of the core. In this state the dynamics of the shell is frozen and the core-shell particles behave like hard spheres. A simple physical model is presented to capture and explain the essentials of the coupling of rotational motion and shape fluctuations.Comment: 9 pages, 7 figure

Polypeptide hybrid copolymers as selective micellar nanocarriers in nonaqueous media

Gil GO, Prevost S, Losik M, Hermes F, Schlaad H, Hellweg T. Polypeptide hybrid copolymers as selective micellar nanocarriers in nonaqueous media. Colloid & Polymer Science. 2009;287(11):1295-1304.The self-assembly of polystyrene-block-poly(l-lysine) (PS-PLLys center dot HCl) copolymers with different block lengths has been studied in toluene. The obtained spherical micelles exhibit size variations upon addition of acids or bases, as indicated by light and neutron scattering studies. It is shown that pyridine induces a shrinking of the polystyrene chains in the corona region of the micelles, decreasing the aggregate solvent interface. The addition of benzoic acid, on the other hand, leads to a swelling of the copolymer micelles proportional to the molar fraction of polypeptide. This behavior suggests a selective permeability of the PS-PLLys micelles and the possibility to encapsulate organic compounds in toluene depending on their chemical nature

Establishing a Diagnosis: Inventorying, Monitoring and Assessing

International audienceImproving air quality is a major challenge for public health and the environment. Assessing the contribution of agricultural activity to air pollution and the resulting impacts is a prerequisite for recommending mitigation practices. More important, their long-term adoption can only be justified by performing a real-time assessment of their effectiveness. Since the 1990s, using emission indicators, air contamination levels and environmental impacts has indeed become a widespread means of supporting decision-making at different levels, risk management and public policy assessment. However, this assessment is made difficult owing to the complex network of processes involved and the variability in pollutant emission and deposition. This chapter first details the methodologies implemented for emission inventories, used to better target the largest contributing sources, to check whether national commitments have been met, and to assess the trends. It also presents observation networks established to monitor background air pollution, deposition as precipitation, gases and particles in rural and forest areas, and impacts on terrestrial ecosystems. Finally, it outlines the indicators used to assess the impacts of agricultural practices on human and ecosystem health via the atmospheric compartment and it gives examples of their practical use to manage pollution risks, evaluate agricultural practices or compare agricultural products