Techniques for the characterization of physical gels - Physical Gels from Biological and Synthetic Polymers - page 27

y illustrate
the various techniques by examples which help to illustrate the applicability of each
approach to gelation studies. More details are given in the relevant systems chapters.

We shall introduce the experimental methods in this section, and then brie

2.3.1 Basic concepts

DSC is a differential method in which the measured quantity is proportional to the
heat

flow rate. DSC can be operated in isothermal conditions, under a preset rate of
temperature change (heating or cooling) or even in a modulated way (temperature-
modulated DSC or TMDSC) where a modulation is superimposed on a constant rate of
temperature change (Hatakeyama and Quinn, 1999 ;Brown, 2001 ;Höhneet al., 2003 ;
Matsuo, 2004 ).

2.3.2 Differential scanning calorimetry (DSC)

A typical DSC apparatus is shown in Figure 2.6 . The device has a disc-like measuring
system made of a good thermal conducting material and two sample containers posi-
tioned symmetrically to the centre of the disc. One of the containers is

filled with the

-

sample and the other is a reference generally an empty pan, identical to the sample

container. In gel studies the reference is often

filled by approximately the same amount of
solvent to balance the heat capacity of the sample and the reference, and achieve a good
baseline.
The main heat

flow passes from the furnace through the disc to the two containers.
Temperature sensors (for example, thermocouples or resistance thermometers) are
attached to the base of the sample and reference holders. A second set of thermocouples
measures the temperature of the furnace and of the heat-sensitive plate. If the sample
contains volatile components the pans must be sealed hermetically with a sealing press.
Typical DSC pans contain approximately 10mg of sample by weight.

Lid

Sample crucible Reference crucible

Disc

Temperature
control

Thermocouples

Furnace

Calibration Computer

Δ T

Schematic view of a differential scanning calorimetry (DSC) set-up with disc type measuring
system.

Figure 2.6