Imaginary contact angles underlying hyperhydrophilicity and the Inverse Lotus Effect introduce a fundamental new development in the area of contact angles and wettability. Just as the Lotus Effect expanded hydrophobicity beyond the maximal contact angle of 119° on a smooth surface, the Inverse Lotus Effect expands hydrophilicity beyond the minimal contact angle of 0° on a smooth surface. Imaginary dynamic contact angles thus offer an exciting enhancement in tools and methodology for measuring the wettability on rough, highly hydrophilic surfaces. Contrary to current thinking, full or perfect wetting of rough surfaces is only little understood and cannot be predicted by classical equations. Therefore also the exact physical basis of imaginary dynamic contact angles remains to be elucidated. In this short treatise some aspects of the new field will be treated with examples derived from rough titanium surfaces employed in the medical field.

Dipodal silanes possess two silicon atoms that can covalently bond to a surface. They offer a distinctive advantage over conventional silanes in terms of maintaining the integrity of surface coatings, adhesive primers and composites in aqueous and aggressive environments. The improved durability of such dipodal silanes is associated with an increased crosslink density of the interphase and the inherent resistance to hydrolysis, as they can form six, rather than three, Si-O bonds to the substrate. This study examines dipodal silanes with hydrophobic alkyl functionality and compares them with similar functionality on conventional silane coupling agents. It also introduces new structural dipodal silanes containing “pendant” and “bridged” functionality and then examines their stability in aqueous environments. In strongly acidic and brine environments, dipodal silanes clearly demonstrate improved resistance to hydrolysis compared to conventional silane coupling agents.

This work demonstrates wafer bonding using initiated chemical vapor deposition (iCVD) poly(glycidylmethacrylate) (PGMA) thin films, and studies the impact of surface treatment to manipulate adhesion energy between polymer film and silicon substrate. Substrates were modified with organosilanes or nitrogen plasma prior to iCVD and bonding. Adhesion was characterized by measuring critical energy release rate (Gc) using a 4-point bend technique. Results demonstrate a correlation between substrate surface energy and polymer-substrate adhesion energy where, depending on the functional group, close to an order of magnitude variation in adhesion energy was observed. These results point to minimal covalent interaction between polymer and substrate for these samples. Exposing the bonded wafers to a thermal anneal step led to an improved grafting of PGMA to substrate. For grafted films, the sample failure mode shifted from adhesive to cohesive, with drastic increase in Gc. These findings demonstrate that the adhesion energy and failure mode of iCVD-PGMA bonded wafers can be manipulated through surface functionalization and thermal treatment, which enable both temporary and permanent chip-bonding applications using iCVD polymer films as adhesives.

We report a study on the wetting and spreading of hydrazine-CZTS solution on a series of solid surfaces. The work of adhesion between a hydrazine solution and soda-lime glass, Si, graphite, ITO, SnO2, ZnO, CdS, In2S3, Cu, Au, Ag, Al, Ni, Mo, and carbon single-walled nanotubes was calculated using observed contact angles and the areas of the interface. The surface roughness of drop-casted CZTS precursor films was lower on surfaces with better hydrazine wettability. This suggests that the surface roughness of solution-processed films can be controlled by altering the wetting behavior of the solution on the substrate.

Remora fish are capable of fast, reversible and reliable adhesion to a wide variety of both natural and artificial marine hosts through a uniquely evolved dorsal pad. This adhesion is partially attributed to suction, which requires a robust seal between the pad interior and the ambient environment. Understanding the behavior of remora adhesion based on measurable surface parameters and material properties is a critical step when creating artificial, bio-inspired devices. In this work, structural and fluid finite element models (FEM) based on a simplified “unit cell” geometry were developed to predict the behavior of the seal with respect to host/remora surface topology and tissue material properties.

Three types of 316L stainless steel surface with different topography were prepared by a Fine Particle Peening (FPP) treatment using titania, silica and alumina shot particles and analyzed the cell proliferation and cell-scaffold interaction. FPP-treated surface with titania and silica particles had micro asperities at low frequency. On the other hand, the alumina treated surface had micro asperities at high frequency. L929 fibroblasts were seeded on these specimens and then the number of cells was counted after 72 hours of culturing. The FPP-treated surfaces showed good cell proliferation comparing to polished surface. This indicates that micro asperities formed on the surface encourage cell adhesion. Cell adhesion behavior was evaluated by a scanning electron microscope (SEM) and a fluorescence microscope. Dense filopodia were observed when cells cultured on the FPP-treated surface. This means that FPP treatment enhances cell adhesion and proliferation. The number of cells observed on the FPP-treated surface depended on the shape of asperities formed by FPP treatment; the highest cell counts were obtained on alumina treated surface. This is because cell migration was not inhibited by the shape of alumina treated surface asperities.

Ordered arrays of polymeric nanostructures with different shapes were generated using laser interference lithography and plasma etching. Surface energy anisotropy was produced in each nanostructure in the array through oblique angle deposition of a hydrophilic metal. When a water droplet was placed on such a surface, it was found to wet preferentially in the direction of the hydrophilic face. Depending on the shape of the nanostructure and the deposition direction, wetting can be made uni-, bi- or tri-directional. Insights obtained in this study contribute to the understanding of wetting on rough, chemically heterogeneous surfaces and provide new methods to engineer functional surfaces for the control of wetting directions.

We will present a simplified approximate model showing how even small changes in the dielectric response result in substantial variations in the Hamaker coefficient of the van der Waals interactions. Since all the terms in the Matsubara summation depends on the variation of the dielectric response spectra at one particular frequency, the total change in the Hamaker coefficient depends on the spectral changes not only at that frequency but also at the rest of the spectrum properly weighted. The Matsubara terms most affected by the addition of a single peak are not those close to the position of the added peak, but are distributed over the entire range of frequencies. We comment on the possibility of eliminating van der Waals interactions and/or drastically reducing them by spectral variation in a narrow regime of frequencies.