Aggregation and elastic properties of poly(ethylene oxide)-block-poly(butylene oxide) polymersomes

In this research work, the effect of salts and the membrane toughness of polymersomes made with the block copolymer poly(ethylene oxide)16-poly(butylene oxide)22 (E16B22) were studied, where the subscript correspond to the average degree of polymerisation. Also, a new methodology to form vesicles was implemented in order to be used in conjunction with a micropipette aspiration (MPA) equipment. The effect of salts on nano- and giant vesicles was analysed using dynamic light scattering (DLS), transmission electron microscopy (TEM) and light microscopy. Aggregation was observed only for NaH2PO4 at high molar concentrations (3 M), which agrees with the Hofmeister series. Halide and sulphate sodium salts, at relative high (~1 M) and low concentrations (0.3 M), did not affect nanovesicles. Similarly, the presence of 0.2 M K2SO4 in a giant vesicle solution was determined not to induce aggregation. In addition, polymersomes were made by hydrating micro-size polymer droplets, on a glass surface, created using an inkjet printer. Modifying the contact angle by surface treatment; the addition of different substances such as sugars and salt on the hydration process was studied. Polymersome unbinding from the polymer substrate can be obtained by doping the polymer substrate with sugar or salts in a molar ratio of at least 1:10 (polymer/additive). Addition of 0.1 M or 0.01 M salt solutions to doped polymer layers prevents vesicle formation. However, samples pre-hydrated with water, allowing vesicles to grow, and then additionally hydrating with a salt solution can permit vesicles to grow in a salt environment however only at low salt concentrations (≥ 10 mM). The area expansion modulus (KA) was measured using the MPA technique and the inkjet printing technique. A modulus of 61.4 (±23.1) mN/m was found. The relative low value of E16B22 polymersomes compared with other polymer vesicles is attributable to a liquid-crystal like behaviour of EB block copolymers and the apparently longer times to reach equilibrium in the projection length.