Malvern Zetasizer Nano Series, Руководство пользователя

Страница: 185 / 256

Introduction
The aim of this chapter is to describe the basic Size principles behind the
Zetasizer Nano series. This will help in understanding the meaning of the results
achieved.
The chapter is divided into two major sections. What is Dynamic light
scattering? and Operation of the Zetasizer Nano - Size measurements .
The first section describes the theory, while the second describes the physical
operation of how a size measurement is performed.
What is Dynamic Light Scattering?
The Zetasizer Nano series performs size measurements using a process called
D ynamic L ight S cattering ( DLS )
Dynamic Light Scattering (also known as PCS - P hoton C orrelation
S pectroscopy) measures Brownian motion and relates this to the size of the
particles. It does this by illuminating the particles with a laser and analysing the
intensity fluctuations in the scattered light.
Scattering intensity fluctuations
If a small particle is illuminated by a light source such as a laser, the particle will
scatter the light in all directions.
If a screen is held close to the particle, the screen will be illuminated by the
scattered light. Now consider replacing the single particle with thousands of
stationary particles. The screen would now show a speckle pattern as shown
below.
The speckle pattern will consist of areas of bright light and dark areas where no
light is detected.
C H A P T E R 1 3
Z e t a s i z e r N a n o S e r i e s
P a g e 1 3 . 1
ILL
4022