Novel neutron reflectometer SOFIA at J-PARC/MLF for in-situ soft-interface characterization

Structural characterization of interfaces composed of soft materials (soft interfaces) helps in understanding their physical behavior. Neutron reflectometry is one of the most powerful tools to characterize interfacial structures with spatial resolution in nanometers. We have installed a novel horizontal-type time-of-flight neutron reflectometer SOFIA (SOFt Interface Analyzer) at the Japan Proton Accelerator Research Complex. The instrument is capable of accepting two downward neutron beams, at 2.2° and 5.7° to horizontal, which dedicate neutron reflectivity (NR) measurements over a wide range of neutron momentum transfer q ( q =(4π/ λ )sin θ , where λ and θ are wavelength and incident angle, respectively). The accuracy of NR up to q =6 nm −1 was confirmed by measuring deuterated polystyrene (d-PS) thin films on a silicon (Si) wafer and multilayers of cadmium stearate prepared by the Langmuir–Blodgett method. NR at the deuterium oxide (D 2 O)/Si disk showed specular reflection down to 10 −6 –10 −7 and q up to 2.0 nm −1 along the perpendicular to the sample surface, which improved the precise analysis of swollen polyelectrolyte brush structure at the D 2 O interface. Then, time-resolved in-situ NR measurements were carried out at 1-min intervals to observe interfacial mixing of d-PS on the PS brush surface during 398 K annealing, demonstrating that nonequilibrium behavior at the interfaces can be analyzed on the order of minutes. Novel horizontal-type time-of-flight neutron reflectometer SOFIA (SOFt Interface Analyzer) was installed in BL 16 of Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex (J-PARC). The design and performance of SOFIA reflectometer was described based on the preliminary results of the neutron reflectivity (NR) measurements of deuterated polystyrene (d-PS) thin films, Langmuir–Blodgett film and at deuterium oxide/ polymer brush interfaces. Time-resolved in-situ NR measurement at 1-min intervals was also demonstrated to observe interfacial mixing of d-PS on the PS brush surface during annealing.