Search

The continued advancement of complex materials often requires a deeper understanding of the structure–function relationship across many length scales, which quickly becomes an arduous task when multiple measurements are required to characterize hierarchical and inherently heterogeneous materials. Therefore, there are benefits in the simultaneous characterization of multiple length scales. At the National Institute of Standards and Technology, a new neutron far‐field interferometer is under development that aims to enable a multi‐scale measurement combining the best of small‐angle neutron scattering (SANS) and neutron imaging and tomography. Spatially resolved structural information on the same length scales as SANS (0.001–1 µm) and ultra‐small‐angle neutron scattering (USANS, 0.1–10 µm) will be collected via dark‐field imaging simultaneously with regular attenuation radiography (>10 µm). The dark field is analogous to the polarization loss measured in spin‐echo SANS (SESANS) and is related to isotropic SANS through a Hankel transform. Therefore, we use this close relationship and analyze results from SANS, USANS, SESANS and dark‐field imaging of monodisperse spheres as a validation metric for the interferometry measurements. The results also highlight the strengths and weaknesses of these neutron techniques for both steady‐state and pulsed neutron sources. Finally, we present an example of the value added by the spatial resolution enabled by dark‐field imaging in the study of more complex heterogeneous materials. This information would otherwise be lost in other small‐angle scattering measurements averaged over the sample. [ABSTRACT FROM AUTHOR]

pH dependence on water soluble aggregates is well‐known in the field of low molecular weight gelators (LMWGs), with different aggregates sometimes having very different properties depending on their final pH. This aggregation determines their applications and performance. Here, we investigate the pH dependence of perylene bisimide gels; initially solutions are formed at a high pH and gels form as the pH is decreased. We find it is not only the final pH but also the starting pH that can impact the resulting gel. We use small angle neutron scattering (SANS), rheology, 1H NMR spectroscopy and absorption spectroscopy to examine the effect of starting pH on gelation kinetics and final gel properties. Adjusting the solution from pH 9 (where there are few or no aggregates) to pH 6 results in the formation of different worm‐like micelles than the ones directly formed at pH 6, leading to again gels with different mechanical properties. This work highlights the importance of controlling the pH of solutions before gelation, but also opens up more possible morphologies and therefore more properties from the same molecule. [ABSTRACT FROM AUTHOR]

The modulated intensity by zero effort small‐angle neutron scattering (MI‐SANS) technique is used to measure scattering with a high energy resolution on samples normally ill‐suited for neutron resonance spin echo. The self‐diffusion constant of water is measured over a q–t range of 0.01–0.2 Å−1 and 70–500 ps. In addition to demonstrating the methodology of using time‐of‐flight MI‐SANS instruments to observe diffusion in liquids, the results support previous measurements on water performed with different methods. This polarized neutron technique simultaneously measures the intermediate scattering function for a wide range of time and length scales. Two radio frequency flippers were used in a spin‐echo setup with a 100 kHz frequency difference in order to create a high‐resolution time measurement. The results are compared with self‐diffusion measurements made by other techniques and the general applicability of MI‐SANS at a pulsed source is assessed. [ABSTRACT FROM AUTHOR]

ABSTRACT We show that [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) at the surface of thin film blends of poly(3-hexylthiophene) (P3HT):PC61BM can be patterned by water. Using a series of heating and cooling steps, water droplets condense onto the blend film surface. This is possible due to the liquid-like, water swollen layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Breath pattern water deformation and subsequent drying on the film surface results in isolated PC61BM structures, showing that migration of PC61BM takes place. This was confirmed by selective wavelength illumination to spatially map the photoluminescence from the P3HT and PC61BM. Within a device, redistribution of the surface PC61BM into aggregates would be catastrophic, as it would markedly alter device performance. We also postulate that repeated volume change of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate layer by water swelling may be, in part, responsible for the delamination failure mechanism in thin film solar cells devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 141-146 [ABSTRACT FROM AUTHOR]