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Identifier

000421999

Title

Light scattering techniques for probing near-wall dynamics and flow of complex fluids

Alternative Title

Τεχνικές σκέδασης φωτός για τη μελέτη δυναμικής κοντά σε επιφάνεια και ροής πολύπλοκων ρευστών

Author

Giuliani, Antonio

Thesis advisor

Loppinet, Benoit

Reviewer

Βλασσόπουλος, Δημήτριος
Πετεκίδης, Γεώργιος
Παπάζογλου, Δημήτριος
Βαμβακάκη, Μαρία
Fischer, Peter
Lang, Peter

Abstract

In this thesis, we reported advances in internal reflection techniques applied to the study of interfaces between a hard solid (glass substrate) and various soft material. Such developments might be valuable to the soft matter community as the techniques to study such interfacial processes are scarce. We present the principle and implementation of a novel in situ near wall dynamic light scattering velocimetry on a commercial rheometer. The method was tested on a variety of materials where different boundary conditions were observed, from stick to plug flow behavior. Furthermore we investigate the effect of multiple scattering on EW-DLS measurements. The localized scattering and the point of entrance detection of the EW geometry yield a sizable single scattering component that made it possible to recover quasi single scattering dynamics in strongly turbid media. Moreover studies under shear reveal strong temporal decoupling of the near wall single scattering dynamics and useful DWS like bulk shear rate information so that both the near wall velocimetry and DWS like velocimetry can be performed in the same experiment. We looked into the application and validity of effective medium models for turbid media in internal reflection variable angle spectroscopic ellipsometry (VASE). The proper description of the clear-turbid interface is not fully established. The reflectivity between a transparent substrate and a turbid medium is of interest as it could be used to characterize the turbid medium and provide a way to estimate size, refractive index and composition. Here we report on internal VASE to characterize turbid medium using an effective medium approximation. In particular we show the value of the wavelength dependence for determining the scattering losses. The merit of effective medium approximation based models is evaluated. We investigate the dynamics and pH induced swelling kinetics of high Mw polyelectrolyte brushes (PEB) after they have undergone strong degrafting. The results presented are preliminary. Measurements of internal dynamics of PEB’s are not intensely pursued in literature, due to lack of experimental techniques. Internal reflection VASE was used to determine wet thicknesses and measure its pH time response.

Language

English

Subject

dynamic light scattering

evanescent wave

multiple scattering

near wall dynamics

soft matter

total internal reflection

velocimetry

Δυναμική σκέδαση φωτός

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