Dynamics of amphiphilic PEG-PDMS-PEG triblock copolymer assemblies

The size and stability of micelles and vesicles determine the uptake capacity of guest molecules, thereby influencing potential applications in drug/gene delivery, bioreactors, and templates for nanoparticle synthesis. Polyethylene glycol (PEG) and polydimethylsiloxane (PDMS) are commonly used in these applications. We discovered that PEG-PDMS-PEG triblock copolymers can assemble into micelles and vesicles, making them valuable for dynamic studies to derive the bending elasticity,κη, which governs the stability these objects. We analyzed the structure using cryogenic transmission electron microscopy and small-angle neutron scattering. We investigated the dynamics through dynamic light scattering and neutron spin echo spectroscopy. By varying the number of repeating units in the hydrophilic block, we created micellar (PEG₂₈-PDMS₁₅-PEG₂₈) and vesicular systems (PEG₁₄-PDMS₁₅-PEG₁₄). For the vesicle, membrane rigidity was determined from experiments to beκη=(16±2)kBT, wherekBTis the thermal energy (kBBoltzmann's constant andTis the temperature). According to Zilman and Granek's concept, membrane rigidity reflects height-height fluctuations within the membrane layer. Compared to polymers at the oil-water interface of a microemulsion, the membrane rigidity in polymersomes is over an order of magnitude higher, indicatingsignificantly enhanced stability. This value closely aligns with that of liposomes, suggesting similar stability between polymersomes and liposomes.