DLS setup for in-situ measurements of photo-induced size changes of microgel-based hybrid particles

Photoinduced size changes in microgel particles loaded with gold nanoparticles (AuNPs) were investigated with an extended multiangle dynamic light scattering (DLS) setup. The DLS setup was equipped with a conventional laser (λ = 633 nm) to determine the microgel particle size. Additionally, a laser (λ = 532 nm) is installed to study the photoresponsive behavior of the AuNP–microgel hybrids. The wavelength of 532 nm is close to the absorption maximum of the plasmon resonance of the AuNPs used in the present study (i.e. spherical AuNPs with a diameter of 14 nm). The extended DLS setup enables us to follow in situ the change in microgel size during irradiation. The light stimulus is directly correlated with the size changes of the hybrid particles and the photothermal effect depends on the intensity of the excitation laser. The increase in excitation laser intensity results in a size reduction of hybrid particles because of the ability of AuNPs to partially transform the absorbed photon energy into heat which is emitted into the surrounding microgel network

Grazing incidence neutron spin echo spectroscopy: instrumentation aspects and scientific opportunities

Grazing Incidence Neutron Spin Echo Spectroscopy (GINSES) opens new possibilities for observing the thermally driven dynamics of macromolecules close to a rigid interface. The information about the dynamics can be retrieved as a function of scattering depth of the evanescent neutron wave, on the length scale in the range of some 10-100 nm. Using a classical neutron spin echo spectrometer with a laterally collimated beam, dynamics can be measured in grazing incidence geometry. We show examples of how the interface modifies the dynamics of microemulsions, membranes and microgels. Instrumental details and possible improvements for this technique will be presented. The key issue is the low intensity for dynamics measurements with an evanescent neutron wave. Conceptual questions how a specialised instrument could improve the experimental technique will be discussed