Simulations-based Design of a Hydrophobicallymodified Chitosan Dispersant
PI: Carol Hall
Student: Steven Benner
Collaborations: Jan Genzer & Vijay John
Collaborating with Vijay John on
developing a biocompatible oil
dispersant/stabilizer to prevent
oil coalescence.
Research Goal:
Design a biocompatible oil dispersant using hydrophobically-modified chitosan and
study its behavior using discontinuous molecular dynamics (DMD) simulations
System Species:
HMC molecules
Oil molecules
Hydrophobic
modification
chains (red)
Chitosan backbone (blue)
Three types of simulations:
Short HMC at interface
Short HMC in bulk
Long HMC in bulk
Short HMC’s at oil interface
System specifications:
• 6 HMC chains
• 450 oil chains
• Modification: 5 – 33%
• Modification chain length:
5, 10, or 15 spheres
Oil only
HMC’s modification
chains penetrate
into a previously
formed oil interface
8% modified HMC
33% modified HMC
As modification density is
increased, the width of the oil
interface increases
No HMC
8% modified
33% modified
0
5
10
15
Distance from center of box
Number of oil spheres
Number of oil spheres
5-sphere mod chains
400
350
300
250
200
150
100
50
0
20
15-sphere mod chains
400
350
300
250
200
150
100
50
0
No HMC
8% modified
33% modified
As modification chain length is
increased, the width of the oil
interface increases
0
5
10
15
Distance from center of box
20
System specifications:
• 5 HMC chains
• 250 oil chains
• Modification: 5 – 33%
• Modification chain length:
5, 10, or 15 spheres
Short HMC’s in bulk oil
Oil only
Adding HMC to the bulk
oil system slows down oil
aggregation
HMC and oil
Mod chain length = 5 spheres
Mod chains = 15 spheres
3500
Solvent accessible surface area (Å)
Solvent accessible surface area (Å)
3500
No HMC
17% modified
33% modified
3000
2500
2000
1500
1000
500
0
1000
2000
Time (collisions)
3000
4000
No HMC
17% modified
33% modified
3000
Increasing both
modification chain
length and percent
modification leads
to an increase in oil
solvent accessible
surface area
2500
2000
1500
1000
500
0
1000
2000
3000
Time (collisions)
4000
Single long HMC chain in bulk oil
System specifications:
• 1 HMC chain (400 chitosan backbone)
• 400 oil chains
• Modification: 10%
• Modification chain length: 4 spheres
•
Long HMC chain
wraps around oil
molecules and
stabilizes them
•
Aggregation is slowed
by the chitosan
backbone blocking
interaction between
oil chains
Single long HMC chain in bulk oil with varying interaction energies
ε mod-mod = εmod-oil
ε mod-mod > εmod-oil
ε mod-mod < εmod-oil
4- sphere
modification chains
12 -sphere
modification chains
Good wrapping in
both cases
Less effective
wrapping, less oil
captured
4 bead case: oil
aggregates
12 bead case: good
wrapping
Slides End
Long HMC with short range interactions: networks begin
to form holding oil aggregates apart, no wrapping occurs
ε mod-mod = εmod-oil
Increasing
modification
chain length
ε mod-mod > εmod-oil
ε mod-mod < εmod-oil
100 million collisions
200 million collisions
300 million collisions
500 million collisions
1 billion collisions
1.5 billion collisions