Within the instrument is a component called a digital correlator. A correlator
basically measures the degree of similarity between two signals over a period of
time.
If we compared the intensity signal of a particular part of the speckle pattern at
one point in time (say time = t) to the intensity signal a very short time later
(t+
d
t) we would see that the two signals are very similar - or strongly correlated.
If we then compared the original signal a little further ahead in time (t+2
d
t),
there would still be a relatively good comparison between the two signals, but it
will not be as good as at t+
d
t. The correlation is therefore reducing with time.
Now consider the intensity of the signal at ‘t’, with the intensity at a much later
time - the two signals will have no relation to each other as the particles are
moving in random directions (due to Brownian motion). In this situation it is said
that there is no correlation between the two signals.
With DLS we are dealing with very small time scales. In a typical speckle pattern
the length of time it takes for the correlation to reduce to zero is in the order of 1
to 10's of milliseconds. The "short time later" (
d
t) will be in the order of
nanoseconds or microseconds!
If we compare the signal intensity at (t) with itself then we would have perfect
correlation as the signals are identical. Perfect correlation is reported as 1 and no
correlation is reported as 0.
If we continue to measure the correlation at (t+3
d
t), (t+4
d
t), (t+5
d
t), (t+6
d
t),
etc, the correlation will eventually reach zero. A typical correlation function of
correlation against time is shown below.
Using the correlation function to get size information
How does the correlation function relate to the particle size? We mentioned
earlier that the speed of particles that are being moved by Brownian motion is
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 . 3
Correlation
1.00
0
t=0
Time
t=
¥
ILL
4022
Summary of Contents for Zetasizer Nano Series
Page 7: ...Part 1 Operators guide Part 1 Operators guide...
Page 8: ......
Page 9: ...Introduction to this manual Introduction to this manual C H A P T E R 1...
Page 10: ......
Page 16: ...C H A P T E R 1 Z e t a s i z e r N a n o S e r i e s Page 1 6 M A N 0 3 1 7...
Page 17: ...What is the Zetasizer Nano What is the Zetasizer Nano C H A P T E R 2...
Page 18: ......
Page 26: ...C H A P T E R 2 Z e t a s i z e r N a n o S e r i e s Page 2 8 M A N 0 3 1 7...
Page 27: ...How does the Zetasizer Nano work How does the Zetasizer Nano work C H A P T E R 3...
Page 28: ......
Page 51: ...Making measurements A tutorial Making measurements A tutorial C H A P T E R 4...
Page 52: ......
Page 78: ......
Page 90: ...C H A P T E R 5 Z e t a s i z e r N a n o S e r i e s Page 5 12 M A N 0 3 1 7...
Page 91: ...Sample Preparation Sample Preparation C H A P T E R 6...
Page 92: ......
Page 100: ...C H A P T E R 6 Z e t a s i z e r N a n o S e r i e s Page 6 8 M A N 0 3 1 7...
Page 101: ...Maintenance Maintenance C H A P T E R 7...
Page 102: ......
Page 107: ...Part 2 Supervisors guide Part 2 Supervisors guide...
Page 108: ......
Page 109: ...Security Security C H A P T E R 8...
Page 110: ......
Page 118: ...C H A P T E R 8 Z e t a s i z e r N a n o S e r i e s Page 8 8 M A N 0 3 1 7...
Page 119: ...Using SOPs Using SOPs C H A P T E R 9...
Page 120: ......
Page 152: ......
Page 161: ...Exporting results Exporting results C H A P T E R 1 1...
Page 162: ......
Page 168: ...C H A P T E R 1 1 Z e t a s i z e r N a n o S e r i e s Page 11 6 M A N 0 3 1 7...
Page 169: ...Creating custom reports Creating custom reports C H A P T E R 1 2...
Page 170: ......
Page 183: ...Size theory Size theory C H A P T E R 1 3...
Page 184: ......
Page 193: ...Molecular Weight theory Molecular Weight theory C H A P T E R 1 4...
Page 194: ......
Page 200: ...C H A P T E R 1 4 Z e t a s i z e r N a n o S e r i e s Page 14 6 M A N 0 3 1 7...
Page 201: ...Zeta Potential theory Zeta Potential theory C H A P T E R 1 5...
Page 202: ......
Page 215: ...Part 3 Appendices Part 3 Appendices...
Page 216: ......
Page 217: ...Health and Safety Health and Safety A P P E N D I X A...
Page 218: ......
Page 223: ...Specification Specification A P P E N D I X B...
Page 224: ......
Page 227: ...Site requirements f r o m M A N 0 3 1 7 I s s u e 1 0 Site requirements A P P E N D I X C...
Page 237: ...Installation Installation A P P E N D I X E...
Page 238: ......
Page 241: ...Regulatory Statements Regulatory Statements A P P E N D I X F...
Page 242: ......
Page 246: ...A P P E N D I X F Z e t a s i z e r N a n o S e r i e s Page F 4 M A N 0 3 1 7...
Page 247: ...Index Index...
Page 248: ......