Posted: Mar 29, 2010 | |
Electrospinning self-healing polymer coating systems |
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(Nanowerk Spotlight) The concept of self-healing has become a popular theme in the field of material science. The whole concept of 'smart' materials that react on external impact – pH, humidity changes, or distortion of the coating integrity – and repair themselves has experienced a tremendous boost with the advent of nanotechnology. The nanoscale multilayer structure of a coating, in which the components are integrated and mutually reactive, is a main point in sophisticated and strong corrosion protection (Nanowerk has reported on several recent activities in this area in previous Spotlights: Nanomaterial, heal thyself, Self-healing nanotechnology anticorrosion coatings as alternative to toxic chromium or Self-healing protection for plastic electronics). | |
a) The coaxial electrospinneret and fiber spinning process. b) Healing agent release from mechanically ruptured capsules which consequently passivates the substrate from the environment. c) Photographs of control and self-healing coating samples that were stored under ambient conditions for 2 months. (Reprinted with permission from Wiley-VCH Verlag) | |
Researchers at the Beckman Institute at the University of Illinois at Urbana-Champaign have now proposed a new approach to self-healing polymer coating systems based on an electrospun coaxial healing agent. In a recent paper in Advanced Materials ("Coaxial Electrospinning of Self-Healing Coatings") they describe the effectiveness of such an approach to add autonomic functionality to polymer coatings. | |
"We have demonstrated the concept of a coaxial electrospun self-healing polymer coating system for polysiloxane-based healing agents and an acrylate matrix," Paul Braun, a a professor of materials science and engineering, explains. "Electrospinning offers a number of unique opportunities. Perhaps most significantly, the location and concentration of the healing component can be spatially varied; this is in contrast to a capsule-based system, where the capsules are mixed into the matrix precursors before it is applied to the substrate." | |
Braun, together with Jeong-Ho Park, the paper's first author, point out that the fibers are electrospun before the matrix is applied, thereby reducing a number of issues with chemical incompatibilities between various matrices and healing agents that are present when capsules are dispersed in the matrix precursors. | |
"In a typical procedure, two viscous liquids are simultaneously fed through the inner and outer capillaries, respectively. If the proper combination of liquids and operation conditions are satisfied, a layered Taylor cone can be developed and a coaxial jet can be formed when a high voltage is applied to the outer metallic capillary. The electro-hydro-dynamic forces smoothly stretch the fluid interface to generate coaxial fibers due to the electrostatic repulsion between the accumulated surface charges." | |
For this technique, the electrospun polymer nanofibers are randomly oriented on a surface with the liquid healing agent completely encapsulated in beads that are randomly distributed along the nanofibers. The capsules have to be quite susceptible to mechanical damage because successful self-healing requires the capsules to rupture upon a damage event. | |
SEM images of as-spun bean-on-string capsules as a function of feed rate. At a fixed volumetric flow rate of the sheath PVP polymer solution of 5.0 µL/min, the feed rate of the core polysiloxane, was (a) FSi = 0.5, (b) 1.5, (c) 2.5, and (d) 3.5 µL/min. (Reprinted with permission from Wiley-VCH Verlag) | |
This being a two-part healing system, the beads contain one of two liquid polysiloxane precursors. Upon a damage event, for instance a crack, the beads rupture and the two precursor liquids are released into the damage area and mix in the vicinity of the existing coating where they polymerize, thereby filling the crack. | |
By Michael Berger – Michael is author of three books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology, Nanotechnology: The Future is Tiny, and Nanoengineering: The Skills and Tools Making Technology Invisible Copyright © Nanowerk LLC | |
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