Effect of environmental conditions on gel strength

Question 1

Effect of pH :

Answer 1

1. Low concentration of polymer (liquid form, no gel).
   * Increase in pH: electrostatic internal repulsion between the same molecule, increase the size. When the size increases also the volume fraction increases, and the viscosity also increases. Repulsion limits mobility, may form network.
2. High concentration network , junction zones (gel formation). More junction zones, higher the network strength. If the chains are flexible, more movement, weak gel. Chains are stiff: less movement, stronger gel. If we change the pH, charge of the groups increases: * more repulsion in junction zones–> weaker network. * Repulsion between chains limits their movements, straight chains, tight –>stronger gel .

Question 2

What happen if we have a high concentration of polymer but instead of junctions zones we have a helix formation such as gelatin?

Answer 2

*Change in pH: polymer negative charge, lead to increase in the charges, increase in electrostatic repulsion. Repulsion is too high, helices are more difficult to form–>network weaker. 1 more repulsion between the chain os the helices, less flexible, more space –>stronger network.

Question 3

Effect of salt addition on the gel strength:

Answer 3

Will screen the charges and reduce the amount of electrostatic repulsion. This makes easier again for the chains to approach each other–>increase in the gel strength. On the other hand, less repulsion between chains also reduces the distance and increases the flexibility–>weaker network, lower gel strength.

Question 4

Combination of particles: EXAMPLE. Assume that the polymer is negatively charged.

Answer 4

1. Particles (oil droplets or casein micelles ) are negative charge. Particles will be in the system and requiere space. More repulsive interaction, less mobile–>stronger network.
2. Particles are positive charge: attractive interaction through electrostatic interactions, if there is more attraction between polymers and particles, prevent of helix formation–>weaker network .

Question 5

Type of network and gel strength depends on:

Answer 5

• Type of network (particle, polymer, mixed, filled)
• Combination of different polysaccharides and/or proteins
• pH
• Concentration
• Salt concentration
• **determine the strength of interactions