Computer Simulation of the Pre-Heating, Gelation, and Rheology of Acid Skim Milk Systems - Food Colloids: Self-Assembly and Material Science - page 283

180

160

high pH

140

120

reference sample

100

80

medium pH

60

40

low pH

20

0

0 20 40 60 80 100 120 140

Time

Figure 12 Average number of particles (small and large) per cluster during the gelation
phase as a function of time. All systems consist of rather large clusters, even if
the largest one is not percolating. The low pH system has smaller clusters than
the medium pH one, even though the largest cluster is larger. These differences
are probably within the statistical scatter of the simulations

contradiction relates to the fact that the size of the largest cluster cannot be
expected to be a very reproducible sample parameter, even though the overall
shape of the curves in Figure 11 is indicative of a gel transition.

18.5 The Deformation Phase
All interaction parameters were set to zero in the deformation phase, apart
from the bond and overlap potentials. Bonds could be broken when stretched
to beyond a length of 0.3. It was decided to diminish the Brownian motion of
the particles by lowering the diffusion coefficients by a factor of 10. In practice,
particle gels of this type are mainly enthalpic in character, in contrast to
polymer gels that have a large entropic character. Lowering the temperature
greatly reduces the stress fluctuations in the system and avoids bonds being
broken by the fluctuations. Again the same values are used for all the four
systems. Parameters are kept constant during each phase; and between the
gelation phase and the deformation phase, a short equilibration period (1000
steps) is included during which no bonds are formed and all interactions but the
bonds and overlap potentials are set to zero. The samples are strained at a low
constant rate, allowing individual bonds to relax relatively rapidly. Relaxation
of all bonds within the larger clusters is a much slower process, and so we may
expect to see stresses build up in all samples. If the stresses become large, the
clusters will break up. In the percolating strands the stresses can never relax
without the breaking of bonds.