Significantly more carbon is stored in the world's soils--including peatlands, wetlands and permafrost--than is present in the atmosphere. Disagreement exists, however, regarding the effects of climate change on global soil carbon stocks. If carbon stored belowground is transferred to the atmosphere by a warming-induced acceleration of its decomposition, a positive feedback to climate change would occur. Conversely, if increases of plant-derived carbon inputs to soils exceed increases in decomposition, the feedback would be negative. Despite much research, a consensus has not yet emerged on the temperature sensitivity of soil carbon decomposition. Unravelling the feedback effect is particularly difficult, because the diverse soil organic compounds exhibit a wide range of kinetic properties, which determine the intrinsic temperature sensitivity of their decomposition. Moreover, several environmental constraints obscure the intrinsic temperature sensitivity of substrate decomposition, causing lower observed 'apparent' temperature sensitivity, and these constraints may, themselves, be sensitive to climate.

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Temperature sensitivity of soil carbon decomposition and feedbacks to climate change

Wetting phenomena are ubiquitous in nature and technology. A solid substrate exposed to the environment is almost invariably covered by a layer of fluid material. In this review, the surface forces that lead to wetting are considered, and the equilibrium surface coverage of a substrate in contact with a drop of liquid. Depending on the nature of the surface forces involved, different scenarios for wetting phase transitions are possible; recent progress allows us to relate the critical exponents directly to the nature of the surface forces which lead to the different wetting scenarios. Thermal fluctuation effects, which can be greatly enhanced for wetting of geometrically or chemically structured substrates, and are much stronger in colloidal suspensions, modify the adsorption singularities. Macroscopic descriptions and microscopic theories have been developed to understand and predict wetting behavior relevant to microfluidics and nanofluidics applications. Then the dynamics of wetting is examined. A drop, placed on a substrate which it wets, spreads out to form a film. Conversely, a nonwetted substrate previously covered by a film dewets upon an appropriate change of system parameters. The hydrodynamics of both wetting and dewetting is influenced by the presence of the three-phase contact line separating "wet" regions from those that are either dry or covered by a microscopic film only. Recent theoretical, experimental, and numerical progress in the description of moving contact line dynamics are reviewed, and its relation to the thermodynamics of wetting is explored. In addition, recent progress on rough surfaces is surveyed. The anchoring of contact lines and contact angle hysteresis are explored resulting from surface inhomogeneities. Further, new ways to mold wetting characteristics according to technological constraints are discussed, for example, the use of patterned surfaces, surfactants, or complex fluids.

/pdf/wetting-and-spreading-56ditqbfmj.pdf

Wetting and Spreading

The science of the total environment

We discuss in this review how the roughness of a solid impacts its wettability. We see in particular that both the apparent contact angle and the contact angle hysteresis can be dramatically affected by the presence of roughness. Owing to the development of refined methods for setting very well-controlled micro- or nanotextures on a solid, these effects are being exploited to induce novel wetting properties, such as spontaneous filmification, superhydrophobicity, superoleophobicity, and interfacial slip, that could not be achieved without roughness.

Wetting and Roughness

In the 19th century, Oscar Wilde stated “We live, I regret to say, in an age of surfaces”. Today, we do so even more, and we do not regret it: key advances in the understanding and fabrication of surfaces with controlled wetting properties are about to make the dream of a contamination-free (or 'no-clean') surface come true. Two routes to self-cleaning are emerging, which work by the removal of dirt by either film or droplet flow. Although a detailed understanding of the mechanisms underlying the behaviour of liquids on such surfaces is still a basic research topic, the first commercial products in the household-commodity sector and for applications in biotechnology are coming within reach of the marketplace. This progress report describes the current status of understanding of the underlying mechanisms, the concepts for making such surfaces, and some of their first applications.

Self-cleaning surfaces - virtual realities

Research into extreme water-repellent surfaces began many decades ago, although it was only relatively recently that the term superhydrophobicity appeared in literature Here we review the work on the preparation of superhydrophobic surfaces, with focus on the different techniques used and how they have developed over the years, with particular focus on the last two years We discuss the origins of water-repellent surfaces, examining how size and shape of surface features are used to control surface characteristics, in particular how techniques have progressed to form multi-scaled roughness to mimic the lotus leaf effect There are notable differences in the terminology used to describe the varying properties of water-repellent surfaces, so we suggest some key definitions

Progess in superhydrophobic surface development.

https://northumbria-test.eprints-hosting.org/id/document/264686

An introduction to superhydrophobicity

Super-hydrophobicity can be achieved on relatively smooth surfaces. Short, wide pillars on slightly rough surfaces are shown to produce super-hydrophobic surfaces (see Figure) where neither the pillars nor the slight roughness suffice alone. This use of two length scales to create super-hydrophobic surfaces directly mimics the mechanism used by some plants including the lotus.

/pdf/dual-scale-roughness-produces-unusually-water-repellent-1q9ztul4nx.pdf

Dual‐Scale Roughness Produces Unusually Water‐Repellent Surfaces

Intrinsically superhydrophobic foams with contact angles greater than 150° were prepared using a sol−gel phase-separation process. Hydrophobicity was built in by using organofunctionalized inorganic monomers and setting the conditions so that they were retained in the product. The materials were characterized by advancing and receding water contact angle measurements, scanning electron microscopy, and infrared spectroscopy. The sol−gel phase-separation preparation method used was simple and produced roughness and hydrophobicity in the same material, thus obviating the need for a hydrophobic coating to achieve superhydrophobicity. Superhydrophobicity was retained when the materials were cut or abraded. On heating, a rapid hydrophobic to hydrophilic transition was present at around 400 °C, generating a material that absorbed water rapidly. “Flat” sol−gel materials prepared without phase separation treated in the same manner showed a more gradual contact angle change, but the switch from hydrophobicity to hy...

Intrinsically Superhydrophobic Organosilica Sol−Gel Foams

The evaporation process for small, 1−2-mm-diameter droplets of water from patterned polymer surfaces is followed and characterized. The surfaces consist of circular pillars (5−15 μm diameter) of SU-8 photoresist arranged in square lattice patterns such that the center-to-center separation between pillars is 20−30 μm. These types of surface provide superhydrophobic systems with theoretical initial Cassie−Baxter contact angles for water droplets of up to 140−167°, which are significantly larger than can be achieved by smooth hydrophobic surfaces. Experiments show that on these SU-8 textured surfaces water droplets initially evaporate in a pinned contact line mode, before the contact line recedes in a stepwise fashion jumping from pillar to pillar. Provided the droplets of water are deposited without too much pressure from the needle, the initial state appears to correspond to a Cassie−Baxter one with the droplet sitting upon the tops of the pillars. In some cases, but not all, a collapse of the droplet into...

Michael I. Newton

Papers

Progess in superhydrophobic surface development.

An introduction to superhydrophobicity

Dual‐Scale Roughness Produces Unusually Water‐Repellent Surfaces

Intrinsically Superhydrophobic Organosilica Sol−Gel Foams

Analysis of droplet evaporation on a superhydrophobic surface.