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 2.21 and 5.71 to horizontal, which dedicate neutron reflectivity (NR) measurements over a wide range of neutron momentum transfer q (q ¼ (4p/k)sinh, where k and h are wavelength and incident angle, respectively). The accuracy of NR up to q ¼ 6 nm À1 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 À6-10 À7 and q up to 2.0 nm À1 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.

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Abstract. The chain dimensions of free and immobilized polysulfobetaine in aqueous solution at various salt concentrations were investigated by size-exclusion chromatography with multiangle light scattering and neutron reflectivity measurement, respectively. The dependence of the z-average mean square radius of gyration ( z 1/2 ) on the weight-average molecular weight (M w ) of free poly(3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate) (MAPS) in aqueous solution at salt concentrations of 74, 100, 200, and 500 mM was described by the perturbed wormlike chain model using the chain stiffness parameter λ -1 , the molar mass per unit contour length M L , and the excluded volume effect B. B increased from 0 to 1.8 nm with increasing salt concentration to 500 mM due to the screening of attractive electrostatic interaction between ammonium cations and sulfonyl anions by salt ions. The swollen structure of the poly(MAPS) brush in D 2 O changed from a shrunken state to a relatively extended state with increasing salt concentration from 0 to 500 mM NaCl/D 2 O solution. The thickness of the swollen poly(MAPS) brush in 500 mM NaCl/D 2 O was 9.0 times greater than 2 z 1/2 of free poly(MAPS) due to high osmotic pressure generated by the excluded volume effect of densely grafted polymer chains.