Andrew P. Nowak

Hierarchical carbon foams with independently tunable mesopore and macropore size distributions.

Hierarchical carbon foams with independently tunable mesopore and macropore size distributions were formed in a high internal phase emulsion (HIPE) template. The HIPE consists of an internal oil phase that controls the macropore dimensions and an aqueous resorcinol-formaldehyde precursor solution external phase that directs the mesopore size distribution. Once the emulsion is formed, the precursor solution is cured, fluid elements are extracted from the monolith via solvent exchange, and then the sample is pyrolyzed to create a hierarchical open-cell foam consisting of macropores with mesoporous carbon xerogel walls. Both mesopore and macropore size distributions may be independently tuned by changing the synthesis parameters. These samples have a peak in the mesopore size distribution that may be tuned to between 5 and 8 nm and macropore average diameters that may be tuned to between 0.7 and 2.1 microm. Furthermore, the 0.7 and 2.1 microm average diameter macropores have 0.18 and 0.53 microm diameter macropore windows between adjacent pores, respectively. Pore volumes up to 5.26 cm(3)/g and electrical conductivities as high as 0.34 S/cm are observed after 1200 degrees C carbonization of the framework. These foams may have potential applications as 3-D current collectors in batteries and as fuel cell catalyst supports.

Insect Abatement on Lubricious, Low Adhesion Polymer Coatings Measured with an Insect Impact Testing System

Insect debris disrupts laminar flow, obstructs operator vision, and degrades vehicle aesthetics. To protect vehicle surfaces, anti-contamination coatings have been under development for 70 years, but no known homogeneous coating both adequately reduces debris and survives on vehicle surfaces. Coatings with synergistic combinations of physical properties and materials, however, may enable improved anti-fouling and maintain long-term durability. Transparent, spray-on coatings were developed that contain a combination of fluorinated and hygroscopic chemistries in which the fluorinated component reduces wetting of insect debris while the hygroscopic component produces a lubricating layer of absorbed water that interferes with debris adhesion. Debris area after insect impact was approximately twice as low on these coatings as compared to homogeneous control materials. Furthermore, the sensitivity of debris accumulation to hygroscopic content, and thus lubricity, was measured. At least 13 wt% hygroscopic content in the developed coatings was required for decreased debris accumulation compared to a pure fluorinated surface. Lastly, resistance to common vehicle fluids and scribe-tape adhesion was measured on fluorinated-hygroscopic coatings as initial demonstrations of durability.

Enhanced light scattering in coatings templated with interfacially stabilized colloids

Controlling inter-pore distances enables tuning the color or whiteness of microvoid coatings. While pore spacings have been modified in limited area inverse opal films, little work has occurred studying the feasibility of controlling pore spacings and thus the appearance of scalable, spray-on, microvoid inorganic coatings. In this work we investigated using interfacially stabilized colloidal templates to increase pore spacing and thus enhance Mie scattering in porous silica films. Coatings were fabricated by forming monodisperse colloids with or without a polyvinylpyrrolidone (PVP) interfacial stabilizing layer, dispersing them in a silica precursor solution, and spraying this suspension on a substrate. The films were cured and the colloids subsequently solution extracted at mild temperatures to create porous surfaces. Coatings made with PVP coated colloids had thicker pore walls and scattered light approximately 3× more efficiently than coatings made with bare colloids. Furthermore, a viewing angle dependent color shift was observed in the PVP colloid templated coatings. Side illumination of the samples with white light causes an orange appearance under angles of specular reflection, while a light blue appearance is observed out of these angles because of strong Mie scattering of short-wavelength radiation in both situations. Lastly, modeling based on Mie scattering confirms that it is the dominant optical effect in these coatings and explains the appearance of these coatings. The approach of using interfacially stabilized colloids to improve pore separation applies to many porous films and should be considered when increased light scattering is desired.