Confined Assembly in Coaxially Electrospun Block Copolymer Fibers

Abstract

Electrospinning has received a lot of attention in recent years as a simple process to produce sub-micrometer-scale fibers. The process involves continuous stretching of polymer solution or melt in the presence of a strong electric field, which forms ultrathin fibers. A large amount of research is being carried out to achieve control of the diameter, morphology, and spatial alignment of electrospun nanofibers. [1,2] Unlike other 1D nanostructures, such as nanowires and nanotubes, nanofibers exhibit a wide range of unique properties, making them far more attractive for many applications, such as filtration, catalysis, sensing, protective clothing, and tissueengineering scaffolds.[3] Being a continuous process, electrospinning can produce extremely long fibers comparable to those formed via conventional mechanical drawing and spinning techniques. Nanofiber mats exhibit extremely high surface-to-mass ratios, greatly improving their efficiency for catalysis and filtration. [2] Another fascinating feature of this process is that it can be applied to a wide variety of nanostructured materials. Bognitzki et al. [4] fabricated sub-micrometerscale fibers by electrospinning ternary solutions of polylactide and poly(vinylpyrrolidone). They found that the fibers displayed an internal phase morphology, and, by selectively removing one phase, they obtained highly porous fibers. However, these morphologies were largely controlled by rapid phase separation and rapid solidification of the polymer jet, and no method for controlling these morphologies was demonstrated. In the present study, we utilize this simple process to fabricate block copolymer (BCP) nanofibers. BCP solutions and melts are known to self-assemble into a variety of nanoscale morphologies including spheres, rods, micelles, lamellae, vesicles, tubules, and cylinders, [5,6] depending on the volume fraction and interaction parameter between different blocks. We have been able to produce macroscale-length fibers with diameters of a few hundred nanometers that exhibit internal structures of only tens of nanometers in size. Such materials, we believe, can combine the unique properties of continuous nanofibers and BCP self-assembly for use in a variety of applications of nanostructured materials. BCP self-assembly has attracted increasing interest in recent years for applications in nanotechnology.[7] Precise control over the size, shape, and periodicity of these nanoscale microdomains is the key factor needed to realize nanoscale systems. Various methods, including shear and elongational deformation, compressional deformation, electric fields, and temperature gradients, have been utilized to induce orientation of the microdomains. To our knowledge, shear flow has been most extensively studied as a simple means to induce phase transitions and orient self-assembled structures in block copolymers. [8,9] The phenomenon of flow-induced alignment of lamellar BCPs is very well studied in bulk systems. [10][11][12] Three different orientations of lamellar morphology, namely, p...

Effect of elongational flow on immiscible polymer blend/nanoparticle composites: a molecular dynamics study

“…This causes the polymer solution to extend into thin, high specific surface area fibers which are attractive for modern applications in separation, filtration, and sensing. [9][10][11] The extensional strain in this process both creates the nanoscale fibers and plays a role in the placement of nanoscale additives within the fibers. 12 For complex polymer systems such as block copolymers (BCP), which are known to self-assemble into mesoscale phases like cylinders and lamellae, shear and strain also affect the morphology and alignment of the material.…”

Hierarchically Structured Electrospun Fibers

“…The water contact angle of 163° was attributed to the combined effect of surface enrichment of siloxane and increased surface roughness of the nanometer diameter fibers [122]. These internally structured polymers have a wide variety of applications from advanced filters, optical materials, and templates for nanoscale objects and to direct nanoparticle assembly [120,123].…”

Raising Nanofiber Output: The Progress, Mechanisms, Challenges, and Reasons for the Pursuit

“…Mesmerizing concentric lamellae got after annealing coaxially electrospun block‐copolymer fibers g). Reproduced with permission . Copyright 2015, RSC.…”