Margaret Louise Blohm

Nonwetting of impinging droplets on textured surfaces

This paper studies the impinging droplets on superhydrophobic textured surfaces and proposes a design guideline for nonwetting surfaces under droplet impingement. A new wetting pressure, the effective water hammer pressure, is introduced in the study to clearly define wetting states for the impinging droplets. This approach establishes the design criteria for nonwetting surfaces to impinging droplets. For impingement speed higher than raindrop speed, the surfaces need to have sub-100-nm features to generate a large enough antiwetting pressure for the droplets to take a nonwetting state after impingement.

Dynamics of ice nucleation on water repellent surfaces.

Prevention of ice accretion and adhesion on surfaces is relevant to many applications, leading to improved operation safety, increased energy efficiency, and cost reduction. Development of passive nonicing coatings is highly desirable, since current antiicing strategies are energy and cost intensive. Superhydrophobicity has been proposed as a lead passive nonicing strategy, yet the exact mechanism of delayed icing on these surfaces is not clearly understood. In this work, we present an in-depth analysis of ice formation dynamics upon water droplet impact on surfaces with different wettabilities. We experimentally demonstrate that ice nucleation under low-humidity conditions can be delayed through control of surface chemistry and texture. Combining infrared (IR) thermometry and high-speed photography, we observe that the reduction of water-surface contact area on superhydrophobic surfaces plays a dual role in delaying nucleation: first by reducing heat transfer and second by reducing the probability of heterogeneous nucleation at the water-substrate interface. This work also includes an analysis (based on classical nucleation theory) to estimate various homogeneous and heterogeneous nucleation rates in icing situations. The key finding is that ice nucleation delay on superhydrophobic surfaces is more prominent at moderate degrees of supercooling, while closer to the homogeneous nucleation temperature, bulk and air-water interface nucleation effects become equally important. The study presented here offers a comprehensive perspective on the efficacy of textured surfaces for nonicing applications.

Kinetics and Initial Stages of Bismuth Telluride Electrodeposition

The kinetics and initial stages of Bi 2 Te 3 electrodeposition on gold from an aqueous electrolyte composed of bismuth and telluryl ions and nitric acid were investigated using voltammetry and chronopotentiometry. For tellurium alone, it is found that the reduction of tellurium ions to tellurium occurs with four exchanging electrons at -0.05 V vs Ag/AgCl (3 M KCl). At -0.6 V, tellurium reduces to H 2 Te under kinetic control and the following simultaneous diffusion-controlled reaction occurs with one exchange electron per tellurium atom: HTeO + 2 + H 2 Te + H + + 2e - → 2Te + 2H 2 O. Bismuth telluride deposition starts at more positive potential than bismuth and tellurium deposit individually. It is suggested that the electrodeposition of Bi 2 Te 3 proceeds via a Stransky-Krastanov mechanism. From the Bard correction to the Sand equation, the diffusion coefficients of bismuth and telluryl ions were determined to be 1.90 X 10 -5 and 1.39 X 10 -6 cm 2 /s, respectively, in the investigated solutions. Due to the low diffusivity and solubility of telluryl ions, the limiting current density for Bi 2 Te 3 deposition in the investigated solution is low; it is only 2 mA/cm 2 . Above the limiting current density, a smooth deposit cannot be obtained without agitation. A smooth deposit can be achieved when the depletion of anions is eliminated.

Poly(3,4-dibutoxythiophene vinylene): A new processable conducting polymer with unusual optical properties. Synthesis, characterization and stability

Abstract Poly(3,4-dibutoxythiophene vinylene) was prepared and investigated as a new, processable conducting polymer. Having the vinylene unit to reduce steric interactions, substitution of the thiopene in both the 3- and 4- position is possible without loss of conductivity. The dibutoxy substitution yields advantages in processing, as the high molecular weight polymer dissolves easily in common organic solvents. The polymer can be cast into tough, flexible, free-standing films. The FeCl 3 doped polymer films are nearly optically transparent and have conductivities of 1 Scm −1 . The stability of the undoped polymer to light, oxygen, ozone and water is reported.