Hierarchically structured PMMA fibers fabricated by electrospinning

The role of solvents is pivotal for determining the primary and hierarchical structures of electrospun fibers. The preparation of beads-on-string structures or uniform poly methyl methacrylate (PMMA) fibers with circular and collapsed ribbon-like cross sections from six solvents with different properties was described in this work. The formation of a fiber cross section can be explained by buckling instability. Moreover, all of the resultant fiber surfaces are porous or wrinkled when electrospun with these solvents. It was concluded that vapor-induced phase separation (VIPS) by high relative humidity is the mechanism responsible for the formation of hierarchical structures. The nucleation growth (NG) mechanism during phase separation accounted for the round nanopores with radii of 60-150 nm and elliptical nanopores with long axis of 60-140 nm, short axis of 20-40 nm on the electrospun PMMA fibers from dichloromethane (DCM), chloroform, and ethyl acetate, whereas the formation of the wrinkled fiber surface of the PMMA/acetone, PMMA/tetrahydrofuran (THF), and PMMA/N,N-dimethyl formamide (DMF) systems resulted from spinodal decomposition (SD) mechanism. Furthermore, the fibers with round cross sections and highly porous interiors and surfaces were observed due to the VIPS and phase separation caused by the different evaporation rates of DCM and DMF.