Simulation Study of Hydrophobically Modified Chitosan as an Oil Dispersant Additive

Hydrophobically modified chitosan (HMC) is being considered as a possible oil dispersant additive to reduce the volume of dispersant required in oil spill remediation. We present the results of discontinuous molecular dynamics (DMD) simulations intended to determine how the HMC architecture affects its ability to prevent oil aggregation. The HMCs have a comb copolymer architecture with hydrophobic side chains (modification chains) of various lengths (5-15 spheres) to represent alkane chains that are attached to the chitosan backbone. We calculated the oil's solvent accessible surface area (SASA), aggregate size distribution, and aggregate asymmetry at various values of the HMC modification chain length, modification density, and concentration to determine HMC efficacy. HMCs with long modification chains result in larger oil SASA than HMCs with short modification chains. For long modification chains, there is no increase in oil SASA with increasing modification density above a saturation value. The size distribution of the oil aggregates depends on the modification chain length; systems with long modification chains lead to large aspherical aggregates, while systems with short modification chains lead to small tightly packed aggregates. A parametric analysis reveals that the most important factor in determining the ability of HMCs to prevent oil aggregation is the interaction between the HMC's modification chains and the oil molecules, even when using short modification chains. We conclude that HMCs with long modification chains are likely to be more effective at preventing oil aggregation than HMCs with short modification chains, and that long modification chains impede spherical oil droplet formation.