Figure 4. The figure illustrates a crack surface inside a prototype of self-healing composite with properly mechanically aligned capsules. SEM image (left) demonstrates smooth cleavage while fluorescent optical image (right) shows presence of healing capsules. Absence of topologically outstanding capsules in the SEM image means that the crack cleaves through the capsules.
The Smart Responsive Materials Group (led by Professor Minko) is developing protective cloth and sensors. This research focuses on the synthesis and assembly of responsive nanostructured thin polymer-nanoparticle films that are capable of switching properties (wetting, permeability, volume, shape) upon exposure to external stimuli. This behavior will be used to regulate the protective properties of textiles. The group has developed a new pH and humidity sensitive polymer membrane with controlled pore size.The opening and closing of the pores depends on external conditions and can be tuned by a pH change. This behavior resembles epidermal stomatal apparatus of plants with the difference that not only humidity, but also various external stimuli can be potentially used to regulate the opening/closing cycle. Several additional principles for the protective clothing are based on wetting gradients. Transport of liquids in a porous media with wetting gradients are being investigated both theoretically and experimentally. See Figure 3.
The same principles are being explored for the development of bio/chemical sensors. The responsive composite films detect environmental changes and transform the change of the film properties into optical/electrical signals. The group uses a molecular imprinting approach to develop selective sensors based on the responsive materials. Acoustic, optical, and electrochemical devices are used in the sensor design.
The Nanocomposite Group (led by Professor Sokolov) studies self-healing materials that can be used in a variety of applications, including light and reliable protective equipment. Structural polymers, being attractive from mechanical and chemical points of view, are susceptible to deterioration in the form of cracks. This leads to degradation of their mechanical properties and a decreasing life time of such materials. The purpose of the present research is the development of special healing capsules embedded in the polymer matrix. When a crack propagates, it ruptures the capsules. Then healing glue leaks out into the crack, seals, and “cures” the crack. This repairs the crack, and to some extent recovers the mechanical integrity of the polymer.
Figure 5. Aluminum flakes prepared by milling a dispersion of spherical Al particles.
Using sol-gel self-assembly, the group has synthesized a few types of capsules suitable for the healing glue. Furthermore they are developing an electrospinning technique to make healing fibers. Using AFM and FEM simulation methods, they study the mechanical properties of porous capsules, which have to be adjusted for proper behavior inside the polymer matrix. These data will be used to model the healing process. A double-beam cantilever, needed for tests of mechanical properties of the self-healing composite material, is being developed.
See Figure 4. This figure illustrates a crack surface inside a prototype of self-healing composite with properly mechanically aligned capsules. The SEM image (left) demonstrates smooth cleavage, while the fluorescent optical image (right) shows the presence of healing capsules. An absence of topologically outstanding capsules in the SEM image means that the crack cleaves through the capsules.
CAMP Professors Pursue Obscurant Project with Support from the U.S. Army
In 2004 the U.S. Army extended an additional two years of support for an obscurant project, previously carried out by Distinguished University Professor / CAMP Director S.V. Babu, Professor Dan Goia, and Senior University Professor Richard Partch.
As part of the continuing research effort to develop IR obscurant materials for the U.S. Army, Professor Dan Goia is developing efficient physical and chemical processes capable of generating anisotropic particles (platelets and wires) of highly conductive metals (silver, copper, aluminum). To be highly effective for the intended application, the metallic particles must have at least one dimension (thickness for platelets or diameter for wires) below 40 nm and a high aspect ratio.
Figure 6. Silver nanoplatelets precipitated in aqueous solution