Chemistry Reference
In-Depth Information
21.5 Results and Discussion
The gelatin solution was filled into a 5-mm path length cuvette (Hellma,
Germany). Before the measurement the sample was heated to
601C, i.e.,
well above the melting point, and subsequently kept at (20
0.1)1C during the
actual experiment. Rapid quenching was ensured by immersing the sample in a
temperature-controlled water bath for 60 s before transferring it to the sample
cell holder (kept in air). We define this instant as time zero.
Figure 2 shows the time evolution of the ICF in transmission geometry. Just
after the quench the ICF fully decays to zero, as expected for freely diffusing
particles in a purely viscous fluid. As gelation proceeds the recorded ICF shows
an increasing slowing down of its characteristic decay time reflecting the
growing viscoelastic response felt by the tracers. Once the gel is formed, tracers
are trapped in the elastic cage formed by the surrounding biopolymer matrix
B
(a)
1.0
0.8
0.6
0.4
0.2
0.0
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
τ[s]
(b)
10
0
10
-1
g
2
(τ=0.2s)-1
10
-2
10
-3
0
60
120
180
240
time, minutes
Figure 2 Time evolution of the recorded intensity correlation function g
2
(
t
). Data sets
were recorded for 60 s at a rate of one experiment every 75 s. (a) Correlation
functions at waiting times of 0, 12, and 24 min and 1, 2, and 4 h. (b) Correlation
function for a lag time of
t
¼
0.2 s. The noise level was found to be well below
1%, despite the short measurement time of only 1 min
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