Tuning Fullerene Intercalation in a Poly (thiophene) derivative by Controlling the Polymer Degree of Self-Organisation

Controlling the nanoscale arrangement in polymer-fullerene organic solar cells is of paramount importance to boost the performance of such promising class of photovoltaic diodes. In this work, we use a pseudo-bilayer system made of poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene (PBTTT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), to acquire a more complete understanding of the diffusion and intercalation of the fullerene-derivative within the polymer layer. By exploiting morphological and structural characterisation techniques, we observe that if we increase the film solidification time the polymer develops a higher crystalline order, and, as a result, it does not allow fullerene molecules to intercalate between the polymer side-chains. Gaining insight into the detailed fullerene intercalation mechanism is important for the development of organic photovoltaic diodes (PVDs)

Profile retrieval of a buried periodic structure using spin echo grazing incidence neutron scattering

When the neutron scattering technique, Spin Echo Resolved Grazing Incidence Scattering (SERGIS) concept, was originally put forward by Rekveldt [Physica B 1135, 234–236 (1997)] and Felcher et al. [Proc. SPIE 4785, 164 (2002)], they recognized that the specular scattering and the off-specular scattering could be spatially separated due to the tight neutron beam collimation in the scattering plane, a necessity for any reflectometry experiment. In this Letter, we show that it is possible to make large area measurements of periodic grating structures using SERGIS in a number of interesting scenarios. The SERGIS data can be analyzed using a dynamical theory, which makes it possible to effectively retrieve the lateral profile of a commercial periodic diffraction grating. Interestingly, this is still the case even when that grating is buried beneath a highly deuterated poly(methyl methacrylate-D8) polymer layer. We also clearly demonstrate that the maximum sensitivity to lateral structures is achieved when the specular reflection from the grating is excluded from the data analysis, demonstrating a feature of SERGIS that was proposed over two decades ago

Magnetic Fluctuations, Precursor Phenomena and Phase Transition in MnSi under Magnetic Field

The reference chiral helimagnet MnSi is the first system where skyrmion lattice correlations have been reported. At zero magnetic field the transition at $T_C$ to the helimagnetic state is of first order. Above $T_C$, in a region dominated by precursor phenomena, neutron scattering shows the build up of strong chiral fluctuating correlations over the surface of a sphere with radius $2\pi/\ell$, where $\ell$ is the pitch of the helix. It has been suggested that these fluctuating correlations drive the helical transition to first order following a scenario proposed by Brazovskii for liquid crystals. We present a comprehensive neutron scattering study under magnetic fields, which provides evidence that this is not the case. The sharp first order transition persists for magnetic fields up to 0.4 T whereas the fluctuating correlations weaken and start to concentrate along the field direction already above 0.2 T. Our results thus disconnect the first order nature of the transition from the precursor fluctuating correlations. They also show no indication for a tricritical point, where the first order transition crosses over to second order with increasing magnetic field. In this light, the nature of the first order helical transition and the precursor phenomena above $T_C$, both of general relevance to chiral magnetism, remain an open question

Neutron reflection from the liquid helium surface.

The reflection of neutrons from a helium surface has been observed for the first time. The 4He surface is smoother in the superfluid state at 1.54 K than in the case of the normal liquid at 2.3 K. In the superfluid state we also observe a surface layer ~200 Å thick which has a subtly different neutron scattering cross-section, which may be explained by an enhanced Bose-Einstein condensate fraction close to the helium surface. The application of neutron reflectometry described in this paper creates new and exciting opportunities for the surface and interfacial study of quantum fluids

Spontaneous formation of multilamellar vesicles from aqueous micellar solutions of sodium linear alkylbenzene sulfonate (NaLAS)

We report the spontaneous formation of multilamellar vesicles (MLVs) from low concentration (<30 wt%) aqueous micellar solutions of sodium linear alkylbenezene sulfonate (NaLAS) upon cooling, employing a combination of optical microscopy (OM), Small Angle Neutron Scattering (SANS), and Cryo-TEM. Upon cooling, MLVs grow from, and coexist with, the surfactant micelles, attaining diameters ranging from hundreds of nanometers to a few micrometers depending on the cooling rate, whilst the d-spacing of internal lamellae remains unchanged, at ≃3 nm. While microscale fluid and flow properties of the mixed MLVs and micellar phase depend on rate of cooling, the corresponding nanoscale structure of the surfactant aggregates, resolved by time-resolved SANS, remains unchanged. Our data indicate that the mixed MLV and micellar phases are in thermodynamic equilibrium with a fixed relative volume fraction determined by temperature and total surfactant concentration. Under flow, MLVs aggregate and consequently migrate away from the channel walls, thus reduce the overall hydrodynamic resistance. Our findings demonstrate that the molecular and mesoscopic structure of ubiquitous, low concentration NaLAS solutions, and in turn their flow properties, are dramatically influenced by temperature variation about ambient conditions