Mixed gels - Physical Gels from Biological and Synthetic Polymers - page 301

a b c

L(t)

25 μ m

f

d e

100 μ m

CLSM micrographs for a ternary solution of 4.2% gelatin, 7.9% maltodextrin and water quenched
to T = 20°C: (a) 47.3 s after quench start; (b) 52.9 s; (c) 58.5 s; (d) 64.1 s; (e) 69.7 s; (f) 40 min. The
bright phase is maltodextrin-rich and the dark phase is gelatin-rich. The corresponding two-
dimensional fast Fourier transform (2D-FFT) is shown as an inset for each micrograph. After Lorén
et al.( 2002 ) © 2002 American Institute of Physics.

Figure 10.6

the centres of the maltodextrin bicontinuous microstructure grows with time. The differ-
ence in intensity between the phases increases and the interfacial width decreases with
time. However, since the end temperature is below the gelation temperature of this
gelatin, phase separation is pinned. The arrested microstructure is shown in micrograph
(f ), where the size of maltodextrin domains is about 100 μm. Secondary phase separation
appears in micrograph (f ) as dark gelatin inclusions in the maltodextrin phase. The
formation of small, bright maltodextrin inclusions in the dark gelatin phase during
secondary phase separation is perturbed by gelation.
The two-dimensional fast Fourier transforms (2D-FFT) corresponding to the CLSM
micrographs are included as insets in Figure 10.6 . The rings re ect the strong correlations

in the local maltodextrin concentration that are directly visible in the micrographs. The
rings intensify and collapse towards the centre, which indicates that the correlated
maltodextrin domains grow larger with time, in agreement with the results of Tromp
et al.( 1995 ), and the characteristic wavelength derived from FFT increases with time
following power-law behaviour. On the other hand, the experimental values of the
exponent reported by Lorén et al.( 2002 ) in the gelling system depart from theoretical
predictions; in particular, the exponent is temperature-dependent and increases with the
quench depth. The reason for this is not clear: it could be related to the rate of helix
formation in gelatin gels, which could accelerate the phase separation. It is also important
to mention that maltodextrins have a complex chemical structure and this may interfere
with the observations and interpretations.

10.4.1.3 Gelatin agarose

Both components here are the subject of Chapter 7 . The gelatin

-

-

agar(ose) mixed-gel
system has been studied by Watase and Nishinari ( 1980 ) and by Clark et al.( 1983 ).