Steric stabilising properties of hydrophobically modified starch: Amylose vs. amylopectin

• Self Consistent Field (SCF) calculations are extended to highly branched polymers.
• Adsorption behaviour of hydrophobically modified amylose and amylopectin are compared.
• Modified amylopectin forms denser but thinner surface layers than amylose.
• Amylose layers induce longer range repulsion, but are also more prone to bridging.
• Best stabilisation is seen for layers containing mixtures of amylose and amylopectin.

Self-Consistent Field Theory of Scheutjens and Fleer is extended to deal with highly branched polymer chains. Using the method, the surface adsorption and the steric stabilising properties of hydrophobically modified amylose and amylopectin were compared. For unmodified starch, both biopolymers induce attractive depletion interactions between emulsion droplets. However, for chains of comparable molecular weight, the forces are stronger and longer ranged for amylose. Upon hydrophobic modification, amylopectin has a higher level of surface adsorption, but forms thinner and denser interfacial layers. While both starch molecules provide a sufficient degree of steric repulsion to keep fine emulsions stable, those induced by amylose layers are longer ranged and decay more slowly with inter-droplet separation distances. This desirable property is partially offset by the greater propensity of linear chains to cause bridging. It is found that mixed layers of amylose and amylopectin lead to superior steric stabilising properties, as compared to either component alone.

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