Gel - Decision tree gel

8 important questions on Gel - Decision tree gel

What happens with the gel strength of a polymer gel (helices) when the charge is increased?

The gel strength can

  • Decrease: more electrostatic repulsion, so helix formation is more difficult --> less strong network
  • Increase: more repulsion, so the strength in between the contact points can become stiffer --> increasing gel strength

What happens with the gel strength of a polymer gel that gelates due to salt-bridges when salt/calcium is added?

The gel strength can
  • Decrease: too much calcium creates too many contact points --> no formation of 3-dimensional network
  • Increase: more charged, more contact points/stronger interactions for the polymer to form a gel --> can show syneresis when unstable

How is a stable particle gel formed?

Particles have attractive interactions. To increase the gel strength, the amount of interactions should be increased. For example by decreasing the charge. Note: too many interactions can create syneresis.
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You have a gel (mixed system) of polymers + large particles, the gel strength decreases due to electrostatic attraction, how come?

  • Particle withdraws polymer from network --> creaming/sedimentation (depending on kinetics). Phase separation and partly gelation can occur
  • With large particles, network formation is more difficult. Particles are disrupting network formation. Take space and only small networks can be formed.

You have a gel (mixed system) of different polymers, the gel strength decreases due to electrostatic attraction, how come?

  • Salt bridges: the two polymers form a complex with the help of a salt. This can precipitate. Depending on the kinetics a turbid gel can be observed.
  • Oppositely charged polymers: the two polymers form a complex with strong interactions. Precipitation occurs. Depending on the kinetics a turbid gel can be observed.

You have a gel (mixed system) of different polymers, the gel strength decreases due to electrostatic repulsion, how come?

The added polymer prevented gel (helix) formation and decreasing the gel strength.

You have a gel (mixed system) of different polymers, the gel strength increases due to electrostatic repulsion, how come?

  • Single network: 1 polymer gels and the other fills the space and interacts with water. The concentration of the network polymer increases and a stronger network is created.
  • Interpenetrating network: both polymers formed a network. A stronger gel was formed

You have a gel (mixed system) of different polymers, the gel strength increases due to electrostatic attraction, how come?

Attractive interactions with salt or oppositely charged polymers --> Coupled network: polymers form a network together

Concentrations too high: depletion interactions --> Phase separated network

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