Search

The structural characterization of microgels at interfaces is fundamental to understand both their 2D phase behavior and their role as stabilizers that enable emulsions to be broken on demand. However, this characterization is usually limited by available experimental techniques, which do not allow a direct investigation at interfaces. To overcome this difficulty, here we employ neutron reflectometry, which allows us to probe the structure and responsiveness of the microgels in-situ at the air-water interface. We investigate two types of microgels with different cross-link density, thus having different softness and deformability, both below and above their volume phase transition temperature, by combining experiments with computer simulations of in silico synthesized microgels. We find that temperature only affects the portion of microgels in water, while the strongest effect of the microgels softness is observed in their ability to protrude into the air. In particular, standard microgels have an apparent contact angle of few degrees, while ultra-low cross-linked microgels form a flat polymeric layer with zero contact angle. Altogether, this study provides an in-depth microscopic description of how different microgel architectures affect their arrangements at interfaces, and will be the foundation for a better understanding of their phase behavior and assembly.

We investigate the cononsolvency effect of poly(N-isopropyl acrylamide) (PNIPAM) in mixtures of water and methanol. Two systems are studied: micellar solutions of polystyrene-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) diblock copolymers and, as a reference, solutions of PNIPAM homopolymers, both at a concentration of 20 mg/mL in D2O. Using a stopped-flow instrument, fully deuterated methanol was rapidly added to these solutions at volume fractions between 10 and 20%. Time-resolved turbidimetry revealed aggregate formation within 10 100 s. The structural changes on mesoscopic length scales were followed by time-resolved small-angle neutron scattering (TR-SANS) with a time resolution of 0.1 s. In both systems, the pathway of the aggregation depends on the content of deuterated methanol; however, it is fundamentally different for homopolymer and diblock copolymer solutions: In the former, very large aggregates (>150 nm) are formed within the dead time of the setup, and a concentration gradient appears at their surface in the late stages. In contrast, the growth of the aggregates in the latter system features different regimes, and the final aggregate size is∼50 nm, thus much smaller than for the homopolymer. For the diblock copolymer, the time dependence of the aggregate radius can be described by two models: In the initial stage, the diffusion-limited coalescence model describes the data well; however, the resulting coalescence time is unreasonably high. In the late stage, a logarithmic coalescence model based on an energy barrier which is proportional to the aggregate radius is successfully applied.

Damit Metallschichten auf Kunststoffoberflächen dauerhaft haften, müssen diese vorbehandelt werden. Bisher gängige Methoden sind entweder unter Umwelt- oder Arbeitsschutzaspekten bedenklich, oder sie sind durch ihre speziellen Eigenschaften auf bestimmte Einsatzbereiche beschränkt. Als neue Vorbehandlungsmethode wird vorgeschlagen, Emissionen im Vakuum-Ultraviolett (VUV)-Bereich, erzeugt von Excimer-Strahlern, zur Verbesserung der Metallhaftung zu nutzen.

A new treatment method is proposed where excimer lamps are used to emit in the vacuum ultraviolet (VUV) region to improve adhesion of the metal. It is possible for irradiation in the VUV range to be used for targeted and selective surface treatment. he emitter in an excimer lamp consists of tubes and the intensity profile transverse to the lamps on one plane is inhomogeneous, as the intensity of radiation decreases with distance from the source. The process can be made more efficient by purging the space between the lamps and materials at atmospheric pressure with gases to produce the desired treatment atmosphere. It is necessary to keep control over the atmosphere as different gases absorb in the wavelength emission range of the xenon excimer. One of the advantages is that oxygen atoms can be generated for reactions at the surface.