Abstract
Despite the need for sophisticated instrumentation, breath figure assembly (BFA) methods are restricted to produce macroporous films on a tiny scale so far. The current study narrates the fabrication of macroporous films in hollow fiber geometry which extends to adopt the method for continuous production of isoporous surfaces from commercially available low-priced polymer materials. The fabrication of the films in the hollow fiber geometry is carried out by a co-centric quadruple orifice spinneret through which four different liquids are co-extruded simultaneously: bore fluid (to fill the lumen of the fiber), support layer solution, glycerol, and an isoporous film forming solution through the outer most orifice. The extruded entities plunge into a coagulation bath after passing a definite air gap. The implementation of the concept of diffuse-in, droplet formation, and then condense-out behavior of glycerol in a co-extrusion method of hollow fiber spinning makes macroporous film formation possible in an interminable way sidestepping the use of breath figure assembly method. Moreover, the continuous film formation by the proposed mechanism is also authenticated in flat sheet geometry by employing two casting blades in a casting machine. The structure of the films is analyzed by scanning electron microscopy (SEM).
Highlights
Porous polymeric films have earned an enormous attention in research because of their significant potential in many fields
Along with the flat sheet geometry porous films need to be framed on substrates with cylindrical, spherical, or concave surfaces for many applications, too
In this study we report on the formation of macroporous films in hollow fiber geometry from commercially available polymers in a continuous process
Summary
The pore formation with the residing time of the fiber in the air might be explained as 1,4-dioxane of boiling point 101 °C has slow rate of evaporation and evaporation of 1,4-dioxane promotes condensing out of the glycerol droplets at the cooled surface. The larger difference of surface tension between glycerol and THF compared to glycerol and 1,4-dioxane (Supplementary Table S2) leads to a smaller size of the droplets If they do not coalesce, they will form pores by stacking in multiple layers through the film thickness. In our study we have presented that the pore formation by glycerol droplets welded with the equipment of hollow fiber spinning or flat sheet casting makes possible macroporous film formation in a non-intermittent manner. Analyzing different solutions and spinning parameters (for hollow fiber geometry) or casting parameters (for flat sheet geometry) may lead to uniform pore sizes with their ordered arrangement on the film surface by the described approach in large scale in a single step. The method is expected to offer a continuous process to create micropatterned surfaces which may find their way to applications in catalysis, sensing, templating, cell culture or in microelectronics
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