Atomic force microscopy visualization of hard segment alignment in stretched polyurethane nanofibers prepared by electrospinning

Abstract

Molecular-level orientation within nanofibers has been attracting attention as a tool for controlling and designing highly functional nanofibers. In this study, we used atomic force microscopy to visualize the phase separation between soft and hard segments on a polyurethane (PU) nanofiber surface prepared by electrospinning. Furthermore, the stretched nanofibers prepared with a high-speed rotating collector were found to have a different phase distribution in the phase-separated structure, with the hard segment domains aligned to the fiber axis. In contrast, unstretched PU nanofibers prepared without rotation were observed to have nonuniformly distributed segments. These results indicate that the application of an intense elongation force along the nanofiber axis with a rotating mandrel collector changed the distribution of segment alignments.

A multiscale investigation on controlling bovine serum albumin adsorption onto polyurethane films

“…The structure of microphase‐separated PUs can be easily investigated by AFM and usually, bright and dark regions in a phase‐contrast image are an indicator of changing surface properties . Hard segments generally appear as bright areas, while soft segments are anticipated to give dark contrast in the phase imaging . Phase‐contrast in AFM images for dry samples are given in Figure .…”

Ultrasoft polycarbonate polyurethane nanofibers made by electrospinning: Fabrication and characterization

“…Lee et al reported that the crystalline structure in fibers can be developed in ductile polymers. Polymers that have low T g values such as our novel PCPU ( T g = −22.9°C) take a longer time to crystallize . Overall, the sharper reflections in electrospun samples indicate that crystallization occurs during the electrospinning process when the polymer fibers are elongating and possibly after the fibers have dried and solidified.…”

“…The authors proposed that the strength and elastic modulus of the fibers are influenced by the crystal lamellar and amorphous fractions of the chains within the polymer fibers. Additionally, they proposed that structural formation changes taking place in the fibers during electrospinning, specifically crystallinity and molecular orientation impart physical uniqueness to the material and play an important role in the deformation behavior of the fibers . Strain to break values in the electrospun samples is somewhat lower than that of neat PCPU.…”

“…In addition, PCPU also has properties similar to segmented PUs, which consists of hard and soft segments. It exhibits microphase separation due to a high degree of mixing of hard and soft segments because of hydrogen bonding between the hard segment urethane groups and the soft segment carbonate groups . The ability to electrospin our novel PU to fabricate nanofibers and nanomembranes has broadened its applications in the medical and industrial fields for sensor fabrications, drug delivery systems, and scaffolds for tissue engineering where lightweight material with larger surface area is needed.…”

Polyurethane rheology modifiers for organic compositions

“…Polyurethanes are known to exhibit microphase separation of their flexible soft segments and rigid hard segments . The Oil‐Thickener PU microstructure alteration in the presence of hydrophobic SFO molecules was studied using AFM, anticipating a correlation to the network formation of Oil‐Thickener PU in SFO.…”