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Physical aspects - Gel - Mixed gels and filled gels

4 important questions on Physical aspects - Gel - Mixed gels and filled gels

What is a Type I gel?

Only one of the components forms a gel. The component that does not gel, has a concentration below the gelling concentration. The polymers should not have any attractive interactions.

What is a filled gel?

Polymer gels incorporating particles.

The strength of the network of a filled gel depends on:

Size of the particles vs network pore size
Volume fraction of particles
Interaction between particles and network polymers (depletion, H-bonding, hydrophobic interactions,...)

How do we measure the strength of a gel (yogurt in this case)?

Change in pH

Addition of cultures (circles) --> slow drop in pH
Addition of GDL (glucone-delta-lactone), (squares), has the ability to decrease the pH fast

Drop in pH --> casein micelles aggregate --> network formed

Network formation measured as increase in storage modulus G'. Measure increase G' is the pH where the aggregation starts. Culture has a slow drop in pH, aggregation slower, network formed later.

Developed of network over time, tan delta. Tan delta is ratio between liquid and solid behaviour. Decrease in tan delta, network becomes stronger over time and more solid and elastic like.