Vesicles of double hydrophilic pullulan and poly(acrylamide) block copolymers : a combination of synthetic- and bio-derived blocks

The formation of vesicular structures with average diameters from 200 to 300 nm consisting of double hydrophilic diblock copolymers pullulan-b-poly(N,N-dimethylacrylamide) (Pull-b-PDMA) and pullulan-b-poly(N-ethylacrylamide) (Pull-b-PEA) in aqueous solution is described. Bio-derived pullulan was depolymerized and functionalized with alkyne endgroups. Furthermore, azide end functionalized acrylamide blocks PDMA and PEA were synthesized via RAFT polymerization. Individual blocks were conjugated via copper catalyzed azide alkyne cycloaddition (CuAAC) to afford defined double hydrophilic block copolymers. Aqueous solutions of the synthesized block copolymers showed formation of completely hydrophilic vesicles that were observed via various techniques including dynamic light scattering (DLS), static light scattering (SLS), laser scanning confocal microscopy (LSCM), and cryogenic scanning electron microscopy (SEM)

Electrochemical kinetics as a function of transition metal dichalcogenide thickness

Two-dimensional transition metal dichalcogenides are used as electroactive materials for electrochemical and electrocatalytic applications. However, it remains unclear how transition metal dichalcogenide thickness influences the electrochemical response measured at its surface. We use scanning electrochemical cell microscopy to assess the electrochemical response of different thicknesses of bottom-contacted MoS2, MoSe2, WS2, and WSe2 towards the simple outer-sphere redox couple [Ru(NH3)6]3+/2+ with submicron spatial resolution. A detailed analysis, coupling mass transport and electrochemical kinetics, reveals that the electrochemical response can be described using an electron tunneling barrier, which scales with the band gap of the two-dimensional transition metal dichalcogenide. Our results suggest that interpretation of the electrochemical and electrocatalytic responses on transition metal dichalcogenide-covered electrodes should account for the through-layer electron transport kinetics