Ionic gels - Physical Gels from Biological and Synthetic Polymers - page 143

(a) (b)

1.0%
2.0%

3.0%
3.2%
3.5%

3.6%
3.8%
3.9%

4.2%

0.1 mW

0 20 40 60 80 100 0 20 40 60 80 100

Temperature ( ° C)

(b)

(a)

1.0%
2.0%
3.0%
3.5%
3.8%
4.0%

4.5%
4.8%
5.0%
5.5%

0.1 mW

0 0 0 60 80 100 0 20 40 60 80 100

Temperature ( ° C)

Cooling (a) and heating (b) μDSC curves for Na gellan solutions of various concentrations
(indicated on the right-hand axis). Scan rate: 0.5°C min − 1 . Upper: reprinted with permission from
Miyoshi et al.( 1996a ) © 1996 Elsevier. Lower: reprinted with permission from Miyoshi et al.
( 1999 ) © 1999 Springer.

Figure 5.15

distributions could not be produced, common samples of a sodium type gellan were
distributed among the group.
Figure 5.15 shows DSC heating and cooling curves for sodium type gellan samples
used in the Japanese collaborative programme. An exothermic peak at 29°C in the
cooling DSC curve and an endothermic peak at 30.5°C in the heating DSC curve for a
1% gellan gum solution shifted to higher temperatures with increasing gellan concen-
tration. The effect of gel-promoting cations K + ,Ca 2+ and Mg 2+ was much reduced in the
latter (1999) work compared to the effect reported in the earlier 1996 publication, as
shown in these DSC curves.
Consequently, before de nitive conclusions can be drawn, still further - ideally

cooperative - work using pure sodium type gellan with a narrow molecular mass