Inhomogeneous dynamic nuclear polarization of protons in a lamella-forming diblock copolymer investigated by a small-angle neutron scattering method

Abstract

By combining two methods of selective doping of paramagnetic species into a microdomain and small‐angle neutron scattering (SANS), the spatially inhomogeneous proton polarization created by dynamic nuclear polarization (DNP) has been precisely evaluated. A lamella‐forming diblock copolymer composed of polystyrene (PS) and polyisoprene (PI) block chains (PS‐b‐PI) was employed, the SANS profile of which clearly shows scattering peaks up to the third order due to interlamellar interference. As a source of electron spin for DNP, 2,2,6,6‐tetramethylpiperidine 1‐oxyl (TEMPO) was doped into one or other of the microdomains; samples with PS or PI microdomains selectively doped with TEMPO are designated PS.‐b‐PI and PS‐b‐PI., respectively. The SANS intensity at the first‐ and third‐order peaks is well reproduced by assuming that the proton polarization is homogeneous throughout the sample, but that at the second‐order peak cannot be explained by this assumption. This anomaly regarding the second‐order peak was successfully explained by a model postulating that proton polarization in a doped microdomain decreases with increasing distance from the interface with a neighbouring doped microdomain. The decrease in proton polarization at the centre of a doped microdomain was estimated to be 0.07 (2) for PS‐b‐PI. and 0.05 (1) for PS.‐b‐PI, relative to constant proton polarization in a doped microdomain. The inhomogeneous proton polarization results from two competing dynamic processes, i.e. spin diffusion from doped to undoped microdomains, and spin lattice relaxation occurring on the pathway of proton spin diffusion.

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

“…After that pioneering work, several papers reported the utilization of proton spin polarization in neutron scattering experiments (Kohgi et al, 1987;Knop et al, 1992;Fermon et al, 1992;Grinten et al, 1995;Brandt et al, 2006Brandt et al, , 2007Noda et al, 2009Noda et al, , 2011Noda et al, , 2013Kumada et al, 2010;Stuhrmann, 2015). Bunyatova (2004) originally developed the vapour sorption technique of TEMPO [(2,2,6,6-tetramethylpiperidine-1-yl) Figure 2 Chemical structure formulae of (a) TEMPO and (b) styrene-butadiene random copolymer, SBR.…”

“…On the basis of this technique, we prepared polymer systems for SANS studies after the construction of a DNP cryostat (Kumada et al, 2009a,b) and polarized neutron ultra-small-angle scattering spectrometer (SANS-J-II) (Koizumi et al, 2007) at research reactor JRR-3, Tokai, Japan. We investigated a polyethylene film (Noda et al, 2009) and a di-block copolymer to evaluate precisely the inhomogeneity of the proton polarization around the doped TEMPO molecules (Noda et al, 2011). Subsequently, the vapour sorption technique was successfully applied to silica-filled rubber, which is used for fuel-efficient tyres (Noda et al, 2013).…”

Fuel Cell Electrode Characterization Using Neutron Scattering

“…This is especially useful for such heterogeneous systems as electrode layers. As a future plan, experiments using dynamic nuclear polarization combined with SANS[21,22] are planned, where contrast variation is achieved in industrial type heterogeneous samples by polarizing the proton spin in the sample.Author Contributions: conceptualization, O.H.. and H.F., W.L. ; methodology, O.H., H.F., M.C.…”

Development of closed -cycle dynamic nuclear polarization system for small -angle neutron scattering and neutron reflectometry

“…van den Brandt et al [3] developed a compact DNP system for SANS, which enables changing the sample within 2 hours by omitting the dilution refrigerator. Following their basic design, we have developed a DNP system for the SANS-J diffractometer at Japan Research Reactor (JRR-3) and TAIKAN (BL15) at the Materials and Life Science Experimental Facility (MLF) in Japan Proton Accelerator Research Complex (J-PARC), and then carried out SCV-SANS measurements [4][5][6][7]. However, our first-made cryogen-filled DNP system is still large and tough to operate for the people who do not have a special skill of cryogenics.…”