Mechanical Characterization of Hybrid Vesicles Based on Linear Poly(Dimethylsiloxane-b-Ethylene Oxide) and Poly(Butadiene-b-Ethylene Oxide) Block Copolymers

Poly(dimethylsiloxane-ethylene oxide) (PDMS-PEO) and poly(butadiene-b-ethylene oxide) (PBd-PEO) are two block copolymers which separately form vesicles with disparate membrane permeabilities and fluidities. Thus, hybrid vesicles formed from both PDMS-PEO and PBd-PEO may ultimately allow for systematic, application-specific tuning of vesicle membrane fluidity and permeability. However, given the relatively low strength previously noted for comb-type PDMS-PEO vesicles, the mechanical robustness of the resulting hybrid vesicles must first be confirmed. Toward this end, we have characterized the mechanical behavior of vesicles formed from mixtures of linear PDMS-PEO and linear PBd-PEO using micropipette aspiration. Tension versus strain plots of pure PDMS(12)-PEO(46) vesicles revealed a non-linear response in the high tension regime, in contrast to the approximately linear response of pure PBd(33)-PEO(20) vesicles. Remarkably, the area expansion modulus, critical tension, and cohesive energy density of PDMS(12)-PEO(46) vesicles were each significantly greater than for PBd(33)-PEO(20) vesicles, although critical strain was not significantly different between these vesicle types. PDMS(12)-PEO(46)/PBd(33)-PEO(20) hybrid vesicles generally displayed graded responses in between that of the pure component vesicles. Thus, the PDMS(12)-PEO(46)/PBd(33)-PEO(20) hybrid vesicles retained or exceeded the strength and toughness characteristic of pure PBd-PEO vesicles, indicating that future assessment of the membrane permeability and fluidity of these hybrid vesicles may be warranted.