Wetting characteristics of a water droplet on solid surfaces with various pillar surface fractions under different conditions

A numerical study was carried out using a molecular dynamics program to examine the wetting characteristics of nano-sized water droplets on surfaces with various pillar surface fractions under different conditions. Square-shaped pillars had surface fractions that increased from 11.1 % to 69.4 %. The pillars had 4 different heights and 3 different surface energies. When the pillar surface fraction changed, the contact angle of a water droplet also changed due to the attraction between the droplet and the pillar surface or the inner attraction of the water molecules. The pillar height also has different effects on the water droplet depending on the magnitude of surface energy.     

Dynamic hydrophobicity on flat and pillared graphite surfaces with different pillar surface fractions

The motion of a droplet on a surface is of importance to many fields. While many things are known at the macro-scale still a complete understanding of fluid flow at the nano-scale is far from being known. This study focuses on the dynamic hydrophobicity of a pillar surface with different pillar surface fractions at the nano-scale using molecular dynamics simulations. Five pillar heights and four pillar surface fractions were modeled using a graphite surface which has anisotropic characteristics due to its spaced layers. A nano-sized water droplet with 5124 molecules was run to equilibrium on each surface. Then a body force was applied and the dynamic contact angles were calculated for 5 ns. These contact angles were used to calculate the surface’s effective hydrophobicity. The droplets were categorized into one of three groups as different phenomena were identified depending on the pillar surface fraction, applied force, and pillar height. It was found that at the nano-scale smooth, flat surfaces are dynamically more hydrophobic than any of the cases with pillars. Larger pillar surface fractions tended to be more hydrophobic and the pillar surface fraction of 36% was least affected by pillar height and applied body force.     

A study of a nano-sized water droplet’s transition from a flat surface to a pillared surface

The ability to control the hydrophobicity of a surface is of importance to many industries. The dynamic behavior of nano-sized water droplets moving from a flat surface to a pillared surface using molecular dynamics simulations was investigated. Simulations were carried out in two steps. In the first computational step, the initial group of water molecules reached equilibrium on a flat graphite surface. In the second computational step, a constant force was applied to the water droplet and the motion of the water droplet was evaluated as it moved from the flat surface to the pillar-type surface. The movement of the water droplet could be grouped into three different categories and depended on the pillar height and the magnitude of the applied force. The results showed the strongest body force with a pillar height of 6 graphite layers allowed most of the water molecules to move along the top of the pillars. In conclusion, a strong force and pillar height approximately half of the droplet height displayed the best transition from a flat surface to a pillared surface.

     

Analysis of Forest Structure Using Thematic Mapper Simulator Data

Remotely sensed data from forested landscapes contain information on both cover type and structure. Structural properties include crown closure, basal area, leaf area index, and tree size. Cover type and structure together are useful variables for designing forest volume inventories. The potential of Thematic Mapper Simulator (TMS) data for sensing forest structure has been explored by principal components and feature selection techniques. Improved discrimination over multispectral scanner (MSS) data proved possible in a mixed conifer forest in Idaho for estimating crown closure and tree size (saplings/seedlings, pole, sawtimber). Classification accuracy increased monotonically with the addition of new channels up to seven; the four optimum channels were 4, 7, 5, and 3. The analysis of TMS data for 123 field sites in Sequoia National Park indicated that canopy closure could be well estimated by a variety of bands or band ratios (r = 0.62-0.69) without reference to forest type. Estimation of basal area was less successful ( r = 0.51 or less) on average, but improved for certain forest types when data were stratified by floristic composition. To achieve such a stratification, sites were ordinated by a detrended correspondence analysis (DECORANA) based on the canopy of dominant species. Within forest types, canopy closure continued to be the best predictor of spectral variation. Total basal area could be predicted in certain forest types with improved or moderate reliability using various linear ratios of TMS bands (e. g., red fir, 5/4, r = 0.76; lodgepole pine, 4/3, r = 0.82).