Measuring Interfacial Viscosity Using Macro- and Micro-rheology Público

Abstract

We measure the viscous moduli of thin films using two different methods. First, we use a magnetic needle viscometer. Our apparatus employs Helmholtz coils to control the position and orientation of the needle in the film. By driving the needle we can produce a response in the film which allows us to probe the bulk viscous properties of these film. Second, we use single particle microrheology to probe the local properties of the film. Tracking the mean-squared displacement of particles as they undergo Brownian motion probes the local viscous properties of the surface. Coupling this technique with the magnetic needle viscometer provides information on the effect local viscous properties have on the bulk properties. We begin with a general introduction to surface rheology and the techniques involved. Then we discuss the experimental techniques, including the method of building the magnetic needle viscometer, why certain decisions regarding its construction were made, the micro-rheology technique and sample preparation. The results section includes unexpected deviations in our experiments and possible reasons for these. Finally, the discussion highlights the future directions of the project.

Table of Contents

Introduction....................................................................................................... 1

Materials and Methods .................................................................................... 3

Helmholtz Coils ......................................................................................................... 3

Magnetic Needle ........................................................................................................ 8

High-Speed Camera .................................................................................................. 14

Sample Preparation .................................................................................................. 17

One Particle Mean-Squared Displacement ............................................................ 15

Tracking ..................................................................................................................... 18

Results ................................................................................................................ 19

Discussion ........................................................................................................... 23

Particle Tracking ...................................................................................................... 24

Needle ......................................................................................................................... 24

Summary ............................................................................................................ 26

Who is We? ........................................................................................................ 28

Citations ............................................................................................................. 30

About this Honors Thesis

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School	Emory College
Department	Physics
Degree	BA
Submission	Honors Thesis
Language	English
Research Field	Physics, Condensed Matter Physics, Fluid and Plasma
Palabra Clave	Microrheology Macrorheology Interfacial Needle Magnetic Rheology
Committee Chair / Thesis Advisor	Weeks, Eric, Emory University
Committee Members	Roth, Connie, Emory University Flannery, James W, Emory University Brody, Jed, Emory University

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