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Gel - Effect of environmental conditions on gel strength

6 important questions on Gel - Effect of environmental conditions on gel strength

What happens if you increase the pH of a low concentration of polymer (liquid form, no gel)?

Increase in charges --> electrostatic repulsion --> increase in size (radius) --> volume fraction increases --> viscosity increases (also by less mobility of the particles due to the repulsion)

larger size --> closer to each other --> network formation

What happens if you increase the pH of a high concentration of polymer (gel formation)?

Network of junction zones (hydrogen bonds, salt bridges, hydrophobic bonds)

Charges lead to repulsion between chains --> chains cannot approach each other easily --> less junction zones --> weaker network --> weaker gel
Repulsion limits movement --> chains become straight --> stiff chain --> network more tight --> stronger network

Helix formation (gelatin) --> negatively charged --> increase in electrostatic repulsion

Repulsion too high --> helices difficult to form --> network weaker
More repulsion between the loose chains between helices --> less flexible, require more space --> network stronger

What is the effect of salt addition on the gel network strength?

Start with situation that chains are charged because of pH. Adding salt will screen the charges and reduces amount of electrostatic repulsion.

Easier for chains to approach each other --> helices formed easier --> network stronger
Less repulsion between loose chains --> reduces distance and increases flexibility --> weaker network

What happens if you combine negatively charged particles and negatively charged polymers?

There is a lot of repulsive interaction --> less space available --> less mobile --> stronger network

What happens if you combine positively charged particles and negatively charged polymers?

Attractive interaction --> interactions between polymers and particles are stronger than between polymers --> polymers don't interact with each other anymore --> network formation is decreased --> weaker gel network

The type of gel network and gel strength depends on:

Type of network (particle, polymer, mixed, filled)
Combination of different polysaccharides and/or proteins (how they create junction zones)
pH --> determine strength of interactions
Concentration --> determine strength of interactions
Salt concentration --> determine strength of interactions