Durable and scalable icephobic surfaces: similarities and distinctions from superhydrophobic surfaces

Formation, adhesion, and accumulation of ice, snow, frost, glaze, rime, or their mixtures can cause severe problems for solar panels, wind turbines, aircrafts, heat pumps, power lines, telecommunication equipment, and submarines. These problems can decrease efficiency in power generation, increase energy consumption, result in mechanical and/or electrical failure, and generate safety hazards. To address these issues, the fundamentals of interfaces between liquids and surfaces at low temperatures have been extensively studied. This has lead to development of so called "icephobic" surfaces, which possess a number of overlapping, yet distinctive, characteristics from superhydrophobic surfaces. Less attention has been given to distinguishing differences between formation and adhesion of ice, snow, glaze, rime, and frost or to developing a clear definition for icephobic, or more correctly pagophobic, surfaces. In this review, we strive to clarify these differences and distinctions, while providing a comprehensive definition of icephobicity. We classify different canonical families of icephobic (pagophobic) surfaces providing a review of those with potential for scalable and robust development.

Stable biopassive insulation synthesized by initiated chemical vapor deposition of poly(1,3,5-trivinyltrimethylcyclotrisiloxane)

The permanent implantation of electronic probes capable of recording neural activity patterns requires long-term electrical insulation of these devices by biopassive coatings. In this work, the material properties and neural cell compatibility of a novel polymeric material, poly(trivinyltrimethylcyclotrisiloxane) (poly(V3D3)), are demonstrated to be suitable for application as permanently bioimplanted electrically insulating films. The poly(V3D3) polymeric films are synthesized by initiated chemical vapor deposition (iCVD), allowing for conformal and flexible encapsulation of fine wires. The poly(V3D3) also exhibits high adhesive strength to silicon substrates, a common material of manufacture for neural probes. The poly(V3D3) films were found to be insoluble in both polar and nonpolar solvents, consistent with their highly cross-linked structure. The films are pinhole-free and extremely smooth, having a root-mean-square (rms) roughness of 0.4 nm. The material possesses a bulk resistivity of 4 x 1015 Ohm-cm exceeding that of Parylene-C, the material currently used to insulate neurally implanted devices. The iCVD poly(V3D3) films are hydrolytically stable and are demonstrated to maintain their electrical properties under physiological soak conditions, and constant electrical bias, for more than 2 years. In addition, biocompatibility studies with PC12 neurons demonstrate that this material is noncytotoxic and does not influence cell proliferation.

Initiated chemical vapor deposition of antimicrobial polymer coatings

The vapor phase deposition of polymeric antimicrobial coatings is reported. Initiated chemical vapor deposition (iCVD), a solventless low-temperature process, is used to form thin films of polymers on fragile substrates. For this work, finished nylon fabric is coated by iCVD with no affect on the color or feel of the fabric. Infrared characterization confirms the polymer structure. Coatings of poly(dimethylaminomethyl styrene) of up to 540 microg/cm2 were deposited on the fabric. The antimicrobial properties were tested using standard method ASTM E2149-01. A coating of 40 microg/cm2 of fabric was found to be very effective against gram-negative Escherichia coli, with over a 99.99%, or 4 log, kill in just 2 min continuing to over a 99.9999%, or 6 log, reduction in viable bacteria in 60 min. A coating of 120 microg/cm2 was most effective against the gram-positive Bacillus subtilis. Further tests confirmed that the iCVD polymer did not leach off the fabric.

Chain mobility in the amorphous region of nylon 6 observed under active uniaxial deformation

A specially designed solid-state deuterium nuclear magnetic resonance probe was used to examine the effect of uniaxial elongation on the chain mobility in the amorphous region of semicrystalline nylon 6. In measurements conducted near the glass transition temperature, there was measurable deformation-induced enhancement of the mobility of the amorphous chains up to the yield point. This enhanced mobility decayed once deformation was stopped. Enhanced mobility was not observed in deformation at room temperature. The mechanics of deformation can be explained by the Robertson model for glassy polymers near the glass transition temperature, which states that applied stress induces liquid-like behavior in the polymer chains.