Abstract
Controlling environmental humidity level and thus moisture interaction with an electrospinning solution jet has led to a fascinating range of polymer fibre morphological features; these include surface wrinkles, creases and surface/internal porosity at the individual fibre level. Here, by cross-correlating literature data of far-field electrospinning (FFES), together with our experimental data from near-field electrospinning (NFES), we propose a theoretical model, which can account, phenomenologically, for the onset of fibre microstructures formation from electrospinning solutions made of a hydrophobic polymer dissolved in a water-miscible or polar solvent. This empirical model provides a quantitative evaluation on how the evaporating solvent vapour could prevent or disrupt water vapor condensation onto the electrospinning jet; thus, on the condition where vapor condensation does occur, morphological features will form on the surface, or bulk of the fibre. A wide range of polymer systems, including polystyrene, poly(methyl methacrylate), poly-l-lactic acid, polycaprolactone were tested and validated. Our analysis points to the different operation regimes associated FFES versus NFES, when it comes to the system’s sensitivity towards environmental moisture. Our proposed model may further be used to guide the process in creating desirable fibre microstructure.
Highlights
Controlling environmental humidity level and moisture interaction with an electrospinning solution jet has led to a fascinating range of polymer fibre morphological features; these include surface wrinkles, creases and surface/internal porosity at the individual fibre level
We proposed a generic model which accounts for the formation of surface and internal fibre microstructures as a result of moisture interaction during electrospinning
This model was evaluated against a number of polymer systems based on PS, PCL, PLLA, and PMMA with their respective electrospinning solutions
Summary
We proposed a generic model which accounts for the formation of surface and internal fibre microstructures as a result of moisture interaction during electrospinning. This model was evaluated against a number of polymer systems based on PS, PCL, PLLA, and PMMA with their respective electrospinning solutions. The fabrication of electrospinning fibres could vary significantly across different laboratory settings, our model successfully integrated the varied experimental factors into one ensemble, free fitting parameter f, to predict the onset of water condensation interaction with solvent-rich fibres. The notable difference in f values between the two methods may be a result of the difference in mechanical stretching experienced, where the FFES fibres would be subjected to greater mechanical stretching leading to higher probabilities for moisture condensation. The fitted parameter f could provide a calibration factor for a particular electrospinning setup, which can be used to predict, for example, the feasibility in forming surface porous fibre structures via VIPS for new polymer–solvent systems
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