Role of Water Solidification Concepts in Designing Nano-Textured Anti-Icing Surfaces.

Creating anti-icing surfaces has proven to be a challenging task. With such a wide range of impacting parameters it is important to quantify ones with a large effect. Water solidification mechanisms play a fundamental role in designing anti-icing surfaces. In this Review Article, we will consider the effects of surface roughening on the mechanisms of nucleation and ice growth to show how surface roughening can be an alternative to overcome the limitations of icing of superhydrophobic coatings and surfaces. The results from various studies of anti-icing properties of superhydrophobic surfaces are reviewed and expanded to incorporate water solidification mechanisms to provide a more comprehensive approach to the design of anti-icing surfaces. The literature within this review shows that by applying the necessary roughness to either hydrophilic or hydrophobic surfaces and adjusting the surface topography, we can significantly suppress ice nucleation on various surfaces.

Microwave Heating of Functionalized Graphene Nanoribbons in Thermoset Polymers for Wellbore Reinforcement.

Here, we introduce a systematic strategy to prepare composite materials for wellbore reinforcement using graphene nanoribbons (GNRs) in a thermoset polymer irradiated by microwaves. We show that microwave absorption by GNRs functionalized with poly(propylene oxide) (PPO-GNRs) cured the composite by reaching 200 °C under 30 W of microwave power. Nanoscale PPO-GNRs diffuse deep inside porous sandstone and dramatically enhance the mechanics of the entire structure via effective reinforcement. The bulk and the local mechanical properties measured by compression and nanoindentation mechanical tests, respectively, reveal that microwave heating of PPO-GNRs and direct polymeric curing are major reasons for this significant reinforcement effect.

Beyond Wenzel and Cassie-Baxter: second-order effects on the wetting of rough surfaces.

The Wenzel and Cassie-Baxter models are almost exclusively used to explain the contact angle dependence of the structure of rough and patterned solid surfaces. However, these two classical models do not always accurately predict the wetting properties of surfaces since they fail to capture the effect of many interactions occurring during wetting, including, for example, the effect of the disjoining pressure and of crystal microstructure, grains, and defects. We call such effects the second-order effects and present here a model showing how the disjoining pressure isotherm can affect wettability due to the formation of thin liquid films. We measure water contact angles on pairs of metallic surfaces with nominally the same Wenzel roughness obtained by abrasion and by chemical etching. These two methods of surface roughening result in different rough surface structure, thus leading to different values of the contact angle, which cannot be captured by the Wenzel- and Cassie-type models. The chemical and physical changes that occur on the stainless steel and aluminum alloy surfaces as a result of intergranular corrosion, along with selective intermetallic dissolution, lead to a surface roughness generated on the nano- and microscales.

Self-assembling particle-siloxane coatings for superhydrophobic concrete.

We report here, for the first time in the literature, a method to synthesize hydrophobic and superhydrophobic concrete. Concrete is normally a hydrophilic material, which significantly reduces the durability of concrete structures and pavements. To synthesize water-repellent concrete, hydrophobic emulsions were fabricated and applied on portland cement mortar tiles. The emulsion was enriched with the polymethyl-hydrogen siloxane oil hydrophobic agent as well as metakaolin (MK) or silica fume (SF) to induce the microroughness and polyvinyl alcohol (PVA) fibers to create hierarchical surfaces. Various emulsion types were investigated by using different mixing procedures, and single- and double-layer hydrophobic coatings were applied. The emulsions and coatings were characterized with optical microscope and scanning electron microscope (SEM), and their wetting properties, including the water contact angle (CA) and roll-off angle, were measured. A theoretical model for coated and non-coated concrete, which can be generalized for other types of materials, was developed to predict the effect of surface roughness and composition on the CA. An optimized distance between the aggregates was found where the CA has the highest value. The maximal CA measured was 156° for the specimen with PVA fibers treated with MK based emulsion. Since water penetration is the main factor leading to concrete deterioration, hydrophobic water-repellent concretes have much longer durability then regular concretes and can have a broad range of applications in civil and materials engineering.

From superhydrophobicity to icephobicity: forces and interaction analysis.

The term "icephobicity" has emerged in the literature recently. An extensive discussion took place on whether the icephobicity is related to the superhydrophobicity, and the consensus is that there is no direct correlation. Besides the parallel between the icephobicity and superhydrophobicity for water/ice repellency, there are similarities on other levels including the hydrophobic effect/hydrophobic interactions, mechanisms of protein folding and ice crystal formation. In this paper, we report how ice adhesion is different from water using force balance analysis, and why superhydrophobic surfaces are not necessary icephobic. We also present experimental data on anti-icing of various surfaces and suggest a definition of icephobicity, which is broad enough to cover a variety of situations relevant to de-icing including low adhesion strength and delayed ice crystallization and bouncing.

Efficacy of 10% sucralfate ointment in the reduction of acute postoperative pain after open hemorrhoidectomy: a prospective, double-blind, randomized, placebo-controlled trial.

BACKGROUND: The aim of the present study was to evaluate the efficacy of 10 % sucralfate ointment in the reduction of acute postoperative pain after open hemorrhoidectomy. METHODS: A total of 48 patients (24 men and 24 women) between 20 and 70 years of age who underwent open hemorrhoidectomy were included in this prospective, double-blind, randomized, controlled trial and were randomly divided into two groups (24 in each group), receiving either sucralfate ointment or placebo immediately after surgery and then every 12 h for 14 days. The primary outcome measure was pain intensity measured by a visual analogue scale at different time points after hemorrhoidectomy. RESULTS: The sucralfate group had significantly less pain than the placebo group at 24th h and the 48th h after hemorrhoidectomy (4 ± 1.14 vs 5.08 ± 0.97; P = 0.001 and 3 ± 0.72 vs 4.41 ± 0.8; P < 0.001, respectively), and they consumed lower amounts of analgesics at the same time intervals (12.50 ± 16.48 vs 21.87 ± 15.30 mg of pethidine; P = 0.047 and 152 ± 23 vs 172 ± 29 mg of diclofenac; P = 0.009, respectively). The same trend continued until the end of the trial. CONCLUSIONS: Sucralfate ointment reduced the acute postoperative pain after hemorrhoidectomy.

Why superhydrophobic surfaces are not always icephobic.

We discuss mechanical forces that act upon a water droplet and a piece of ice on a rough solid surface and the difference between dewetting and ice fracture. The force needed to detach a water droplet depends on contact angle (CA) hysteresis and can be reduced significantly in the case of a superhydrophobic surface. The force needed to detach a piece of ice depends on the receding CA and the initial size of interfacial cracks. Therefore, even surfaces with very high receding CA may have strong adhesion to ice if the size of the cracks is small.

Wetting transitions in underwater oleophobic surface of brass.

An oil droplet in water can be in the Cassie state (with water and/or air trapped between the solid and oil) with a high contact angle (top left) or in the Wenzel state (top right). Depending on the roughness of the brass substrate, both states with high (bottom left) and low (bottom right) contact angle are observed.

Wetting transitions in two-, three-, and four-phase systems.

We discuss wetting of rough surfaces with two-phase (solid-liquid), three-phase (solid-water-air and solid-oil-water), and four-phase (solid-oil-water-air) interfaces mimicking fish scales. We extend the traditional Wenzel and Cassie-Baxter models to these cases. We further present experimental observations of two-, three-, and four-phase systems in the case of metal-matrix composite solid surfaces immersed in water and in contact with oil. Experimental observations show that wetting transitions can occur in underwater oleophobic systems. We also discuss wetting transitions as phase transitions using the phase-field approach and show that a phenomenological gradient coefficient is responsible for wetting transition, energy barriers, and wetting/dewetting asymmetry (hysteresis).

Metal matrix composites for sustainable lotus-effect surfaces.

The lotus effect involving roughness-induced superhydrophobicity is a way to design nonwetting, self-cleaning, omniphobic, icephobic, and antifouling surfaces. However, such surfaces require micropatterning, which is extremely vulnerable to even small wear rates. This limits the applicability of the lotus effects to situations when wear is practically absent. To design sustainable superhydrophobic surfaces, we suggest using metal matrix composites (MMCs) with hydrophobic reinforcement in the bulk of the material, rather than only at its surface. Such surfaces, if properly designed, provide roughness and heterogeneity needed for superhydrophobicity. In addition, they are sustainable, since when the surface layer is deteriorated and removed due to wear, hydrophobic reinforcement and roughness remains. We present a model and experimental data on wetting of MMCs. We also conducted selected experiments with graphite-reinforced MMCs and showed that the contact angle can be determined from the model. In order to decouple the effects of reinforcement and roughness, the experiments were conducted for initially smooth and etched matrix and composite materials.