Fig. 10
From: Self-assembled nematic colloidal motors powered by light
Experimental characterization of platelets with azobenzene monolayers. a An integrated imaging and excitation setup. White light from a mercury lamp is filtered to provide blue excitation light while red light is used for transmission-mode polarizing optical microscopy. Pe is a rotatable polarizer used to define linear polarization direction of the blue excitation light; NDs are neutral density filters used to control excitation power. DM is a dichroic mirror reflecting the blue excitation light but transmitting the red imaging light. P and A are polarizer and analyzer of the polarizing microscope, respectively. λ/4 is a broadband quarter-wave plate used for polarimetric imaging. Inset shows a schematic of a cell with a particle. b Optical micrograph of a platelet on a substrate obtained without polarizers. c Scanning electron microscopy image showing that the silica platelets used for probing rotational dynamics is about 0.5 μm in thickness. d, e Three-photon excitation fluorescence microscopy37 images of a cell with a platelet in its midplane obtained d, for the cross-sectional plane passing through the platelet’s middle and e, for the vertical plane orthogonal to the plane of cell and platelet’s large area faces, passing through the platelet’s center of mass. f Chemical structure of the used derivative methyl red molecule containing azobenzene moiety. g Normalized spectra of the red and white imaging light and blue excitation incident light used in experiments. Scale bars are 1 µm. h Absorbance spectrum of the used photosensitive molecules of derivative methyl red in toluene at concentration of 5 × 10−5 M. The spectrum was obtained using a 1-cm-thick cuvette and a spectrometer Cary 500 (from Varian). i A histogram quantifying the angular diffusion of a platelet in a plane containing n0. Experimental data are fitted to Gaussian distribution (black line) to obtain an angular diffusion constant of Dφ = 1.2 (°)2 s−1 = 3.8 × 10−4 rad2 s−1. j Translational diffusion of a platelet in a sample plane containing n0. Gaussian fitting yields the diffusion constants measured for the translations normal to and along n0: D⊥ = 0.88 × 10−3 µm2 s−1, D|| = 1.5 × 10−3 µm2 s−1
