NSRRC Activity Report 2022

Neutron Science 077 cold neutron triple axis spectrometer SIKA has high-energy resolution and allows researchers to probe this small difference in the location of the spin dynamics. The chopper spectrometer 4SEASONS at J-PARC was used to observe high-energy modes of the itinerant electron model. These inelastic neutron scattering experiments provided valuable insight into the fundamental physics of magnetism. (Reported by Shinichiro Yano) This report features the work of Song Bao and his collaborators published in Phys. Rev. X 12 , 011022 (2022). ANSTO SIKA – Cold Neutron Triple-axis Spectrometer • Neutron Inelastic Scattering • Materials Science, Condensed-matter Physics Reference 1. S. Bao, W. Wang, Y. Shangguan, Z. Cai, Z.-Y. Dong, Z. Huang, W. Si, Z. Ma, R. Kajimoto, K. Ikeuchi, S.-I. Yano, S.-L. Yu, X. Wan, J.-X. Li, J. Wen, Phys. Rev. X 12 , 011022 (2022). Determining the Structures of Photoresponsive Polymers Using Small-Angle Neutron Scattering An azobenzene-containing polymer provides tunable structures and a unique performance under an external stimulus, which enables it to be used as a light-controllable nanocarrier for drug delivery. C hieh-Tsung Lo’s group in National Cheng Kung University, Taiwan, prepared an azobenzene-containing triblock copolymer, poly(6-[4-(4 ' -ethoxyphenylazo)phenoxy]hexyl methacrylate)-block-poly(ethylene glycol)-block-poly(6-[4- (4 ' -ethoxyphenylazo)phenoxy]hexyl methacrylate) (PMMAzo-b-PEG-b-PMMAzo), and developed a relation between its structures and its photoresponsive properties. The morphology of PMMAzo-b-PEG-b-PMMAzo in solvents was manipulated through the variation of the solvency and salt addition. Chun-Ming Wu (NSRRC) determined the detailed structures of PMMAzo-b-PEG-b-PMMAzo in selective solvents through small-angle neutron scattering (SANS). In their experiments, PMMAzo-b-PEG-b-PMMAzo was dissolved in mixed d -DMF/D 2 O solvents of concentration 3.9 × 10 −6 M and then sealed in quartz cells. In the mixed solvents, d -DMF is a neutral solvent for the PEG and PMMAzo blocks, whereas D 2 O is a PEG-selective solvent. The solvency thus altered when the solvent composition was varied. A SANS measurement was conducted at the QUOKKA beamline of Australian Centre for Neutron Scattering, Australia's Nuclear Science and Technology Organisation (ACNS, ANSTO). Figure 1 1 shows SANS profiles of PMMAzo-b-PEG- b-PMMAzo in various mixed d -DMF/D 2 O solvents. In the regions with large Q values, the SANS curves were approximated according to the spherical micelle form factor. By contrast, the increasing trend of intensity in regions with small Q values was attributed to the formation of micellar aggregates. The scattering curves of fractal aggregates were approximated with a simple power-law expression for the structure factor. Using a power-law expression for the regions with small Q values and the spherical micelle form factor for the regions with large Q values, they successfully predicted the morphologies that were formed by PMMAzo-b- PEG-b-PMMAzo in various mixed solvents ( Table 1 ). 1 Fig. 1 : SANS profiles of PMMAzo-b-PEG-b-PMMAzo in various mixed d -DMF/D 2 O solvents measured at Quokka . [Reproduced from Ref. 1]