Contrast variation by dynamic nuclear polarization and time-of-flight small-angle neutron scattering. I. Application to industrial multi-component nanocomposites

Yohei Noda; Satoshi Koizumi; Tomomi Masui; Ryo Mashita; Hiroyuki Kishimoto; Daisuke Yamaguchi; Takayuki Kumada; Shin-Ichi Takata; Kazuki Ohishi; Jun-Ichi Suzuki

doi:10.1107/S1600576716016472

Contrast variation by dynamic nuclear polarization and time-of-flight small-angle neutron scattering. I. Application to industrial multi-component nanocomposites

J Appl Crystallogr. 2016 Nov 8;49(Pt 6):2036-2045. doi: 10.1107/S1600576716016472. eCollection 2016 Dec 1.

Authors

Affiliations

¹ Institute of Quantum Beam Science, Ibaraki University, Ibaraki, 316-8511, Japan.
² Sumitomo Rubber Industries Ltd, Kobe, 651-0072, Japan.
³ Materials Science Research Center, Japan Atomic Energy Agency, Ibaraki, 319-1195, Japan.
⁴ J-PARC Center, Japan Atomic Energy Agency, Ibaraki, 319-1195, Japan.
⁵ Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), Ibaraki, 319-1106, Japan.

Abstract

Dynamic nuclear polarization (DNP) at low temperature (1.2 K) and high magnetic field (3.3 T) was applied to a contrast variation study in small-angle neutron scattering (SANS) focusing on industrial rubber materials. By varying the scattering contrast by DNP, time-of-flight SANS profiles were obtained at the pulsed neutron source of the Japan Proton Accelerator Research Complex (J-PARC). The concentration of a small organic molecule, (2,2,6,6-tetramethylpiperidine-1-yl)oxy (TEMPO), was carefully controlled by a doping method using vapour sorption into the rubber specimens. With the assistance of microwave irradiation (94 GHz), almost full polarization of the paramagnetic electronic spin of TEMPO was transferred to the spin state of hydrogen (protons) in the rubber materials to obtain a high proton spin polarization (P_H). The following samples were prepared: (i) a binary mixture of styrene-butadiene random copolymer (SBR) with silica particles (SBR/SP); and (ii) a ternary mixture of SBR with silica and carbon black particles (SBR/SP/CP). For the binary mixture (SBR/SP), the intensity of SANS significantly increased or decreased while keeping its q dependence for P_H = -35% or P_H = 40%, respectively. The q behaviour of SANS for the SBR/SP mixture can be reproduced using the form factor of a spherical particle. The intensity at low q (∼0.01 Å^-1) varied as a quadratic function of P_H and indicated a minimum value at P_H = 30%, which can be explained by the scattering contrast between SP and SBR. The scattering intensity at high q (∼0.3 Å^-1) decreased with increasing P_H, which is attributed to the incoherent scattering from hydrogen. For the ternary mixture (SBR/SP/CP), the q behaviour of SANS was varied by changing P_H. At P_H = -35%, the scattering maxima originating from the form factor of SP prevailed, whereas at P_H = 29% and P_H = 38%, the scattering maxima disappeared. After decomposition of the total SANS according to inverse matrix calculations, the partial scattering functions were obtained. The partial scattering function obtained for SP was well reproduced by a spherical form factor and matched the SANS profile for the SBR/SP mixture. The partial scattering function for CP exhibited surface fractal behaviour according to q^-3.6, which is consistent with the results for the SBR/CP mixture.

Keywords: contrast variation; dynamic nuclear polarization; nanocomposites; small-angle neutron scattering (SANS); ternary mixtures.