Flow-Dependent Polarization Anisotropy of Phosphorescent Nanoparticles
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Date
2018-07-19
Publication Type
Conference Paper
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yes
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Abstract
The direct measurement of vorticity is an ongoing challenge in experimental fluid dynamics. The effect of polarized luminescence has been applied for the measurements of various properties in physics, biology and biological engineering, e.g. the measurement of Brownian rotational motion or the size of molecules.
In the present work, a theory for the measurement of Brownian motion and deterministic rotations of spherical nanoparticles is outlined. In addition, the applicability of time-gated measurements is shown under certain assumptions, supporting the theoretical feasibility of "single shot" measurements of rotation for time resolved measurements.
In a second part, the production of suitable nanoparticles is discussed. The material of the particles is poly(methyl methacrylate) (PMMA), stained with the xanthenic dye Eosin Y and produced with emulsion polymerization. For a sample of such phosphorescent nanoparticles, the determination of luminescent lifetimes and anisotropy in aqueous suspension is demonstrated. The setup is realized with an intensified CCD camera and a polarizing splitting device, enabling the acquisition of parallel and perpendicular polarization images at the same time. A pulsed laser light sheet is used for the excitation of the suspension in a cuvette.
The lifetimes are shown to follow the shape of a two-exponential decay, indicating the presence of delayed fluorescence and phosphorescence in the sample. Moreover, the comparatively short lifetime of the phosphorescence indicates quenching present in the sample.
The anisotropy of the suspension can be measured with an exposure significantly shorted than the correlation time of the Brownian motion, showing the possibility to neglect the Brownian motion in future fluid flow measurements. The anisotropy is in the order of the fundamental anisotropy of Eosin Y in the area of excitation, indicating the correct choice of seeding density to avoid depolarization from secondary scattering.
The work demonstrates the potential applicability of phosphorescence anisotropy for the measurement of nanoparticle rotations in a fluid matrix.
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published
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Book title
Proceedings of the 19th International Symposium on Application of Laser and Imaging Techniques to Fluid Mechanics
Journal / series
Volume
Pages / Article No.
1175 - 1186
Publisher
Istituo Superior Técnico
Event
19th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics (LXLASER 2018)
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Methods
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Date collected
Date created
Subject
Phosphorescence Lifetime Imaging; PLIM; Anisotropy
Organisational unit
03479 - Rösgen, Thomas (emeritus) / Rösgen, Thomas (emeritus)
02628 - Institut für Fluiddynamik / Institute of Fluid Dynamics