Ionic gels - Physical Gels from Biological and Synthetic Polymers - page 132

10 − 1

5 0.4

0.2

0

4

− 0.2

− 0.4

0.1 mW

(a)

(b)

10 − 2

− 0.6
− 20

3

− 20 0 0 40 60 80 0 20 40 60 80

Temperature ( ° C)

(a) Temperature dependence of storage Young ' s modulus E 0 ( ● ), loss Young ' s modulus E 00 ( ○ ) and
mechanical loss tangent (

Figure 5.4

). (b) Heating differential scanning calorimetry (DSC) curve (solid
curve) and temperature dependence of the speci

□

) of a 1.6%w/w gellan gel
on heating at 0.5°C min − 1 . Reprinted from Nitta et al.( 2001 ) with permission from the Materials
Research Society of Japan.

c ellipticity at 202 nm (

♦

T c

0.1 M Nal 0.1 M Csl

Cooling

T h T c

Heating

T h

30 40 50 60 70

Temperature ( ° C)

Two typical DSC thermograms for κ -carrageenan. The cooling and heating curves for both molar
fractions X Cs = 0 (0.1 M NaI) and X Cs = 1 (0.1 M CsI) are displayed. Reprinted with permission
from Viebke et al.( 1998 ) © 1998 American Chemical Society.

Figure 5.5

5.4.1 Effects of ions on structure formation

Viebke et al.( 1998 ) examined further the dependence of the coil - helix-aggregate

transition of -carrageenan on salt composition. The transition enthalpy on cooling

was measured by differential scanning calorimetry (DSC; see Chapter 2 ), and the salt
composition was varied systematically using mixtures of the four salts NaCl, NaI, CsI
and CsCl, which includes those generating both aggregating and non-aggregating con-
ditions. In this work, either the anion or cation was exchanged for another, but with the
total salt concentration kept constant ( Figure 5.5 ).

κ