Stabilization and characterization of carboxylated medium-chain-length poly(3-hydroxyalkanoate) nanosuspensions

The effects of carboxylation (via mercaptoundecanoic acid) on colloidal properties of medium-chain-length poly(3-hydroxyalkanoate) (mcl-PHA) latexes were studied. Non-ionic surfactants tested at 0.4% solids of 11 mol% carboxylated mcl-PHA produced similar particle sizes and particle size distribution (PdI) with Triton X-100 giving the smallest size. When Triton X-100 was combined with an ionic surfactant, smaller nanoparticles (97.1±1.1 to 121.7±5.7nm) with narrower PdIs (0.21±0.001 to 0.25±0.003) were obtained. The combination of SDS and Triton X-100 gave the smallest particle size (97.1±1.1nm) and narrowest PdI (0.21±0.001). At higher solids content (10%), a mixture of 5mM SDS and 20mM Triton X-100 produced stable (zeta potential=-39.6± 0.9) 170.3±4.6nm nanoparticles. As carboxylation increased, particle size and hydrophobicity decreased while stability increased. When comparing nanoparticles of similar size and stability, carboxylated mcl-PHA needed ∼50% less surfactant to make stable nanoparticles compared to aliphatic mcl-PHAs, with the amount of surfactant required decreasing as carboxylation increased. This is the first study to show that stable nanoparticle suspensions of a range of carboxylated mcl-PHAs above 0.4% solids can be made using a mixture of ionic and nonionic surfactants.