Low Contact Angle Hysteresis Research Articles

Sequential Evaporation–Induced Formation of Polymeric Surface Microdents via Ouzo Effect

AbstractMicrodents fabricated on solid substrates have numerous applications, such as containers for cell growth, reactors for chemical reactions, and nucleation sites for growing photonic crystals. In this study, a new method is developed to fabricate microdents on polystyrene (PS) film deposited on a solid surface. The process relied on Ouzo effect in a ternary solution consisting of three solvents exhibiting different volatilities. In the ternary solution, precursor water droplets are first nucleated when a good solvent of water evaporated. The nucleated water droplets then act as templates for microdent formation during PS film deposition. After water droplets eventually evaporates, microdents are generated on the PS film. The detailed process of microdent formation is experimentally revealed. By controlling the nucleation of water droplets and PS concentration, the lateral size and the depth of microdents are systematically tuned. Moreover, it is demonstrated that the microdent decorated films obtained with the proposed method can be used to fabricate lubricating surfaces, which exhibit a low contact angle hysteresis of 2°.

Electrowetting on liquid-infused membrane for flexible and reliable digital droplet manipulation and application

Droplet manipulation is a critical step for microfluidic applications. We present digital microfluidic devices based on electrowetting-on-dielectric (EWOD) for reliable and repeatable droplet manipulation. The EWOD device consists of two flexible conductive films as top and bottom electrodes, and one flexible liquid-infused membrane (LIM) as the hydrophobic insulating layer. LIMs made by infusing various fluids (air, fluorocarbon, silicone and hydrocarbon oils) into polytetrafluoroethylene (PTFE) membranes are evaluated by electrowetting performance of a sessile water droplet. Silicone oil is selected as the filling insulating oil according to its excellent electrowetting performance in good reversibility, low contact angle hysteresis, and negligible volatility. Fast (85 mm⋅s−1), repeatable (>5000 times without obvious decay) and continuous droplet (designed routes) moving, merging, mixing and positioning have been demonstrated. The factors affecting droplet transport velocity are investigated, including the infused oil viscosity, the conductive volume and the top-to-bottom gap distance. Both the conductive film and LIM are replaceable and robust, showing reliable and long-term stability. Quantitative chromogenic reactions and a flexible EWOD device are demonstrated. These devices are easy-to-fabricate, replaceable-in-material and robust-in-performance, showing high potential for applications in sample preparation, and flexible sensing and display devices.

Colloidal Transfer Printing–Mediated Fabrication of Zinc Oxide Nanorods for Self‐Cleaning Applications

AbstractFabrication of superhydrophobic surfaces with extremely low contact angle hysteresis (θCAH < 4°), which exhibits excellent self‐cleaning behavior by colloidal template–guided hydrothermal growth of zinc oxide nanorods (ZnO NRs), is reported. A hexagonal close packed monolayer of polystyrene (PS) colloids is first deposited by spin coating on a thin poly(methyl methacrylate) (PMMA) film. Subsequently, the colloidal array is transferred to a substrate precoated with sputtered zinc oxide seed layer by UV‐Ozone (UVO) mediated colloidal transfer printing. ZnO NRs are grown with colloids of different diameter (dD) varying between 300 and 800 nm, and for each dD the growth time (tG) is optimized to obtain maximum level of hydrophobicity. These experiments show that best self‐cleaning property is achieved with colloids having dD = 600 nm and tG = 4 h, which do not require any subsequent low surface energy coating. Using transfer printing allows uniform coverage of the monolayer colloidal array over the sputtered seed layer spanning over large areas, irrespective of the roughness or curvature of the target substrate.

Fabrication of fluorine-free ZnO/CuO nanocomposite superantiwetting surfaces with reversible wettability tuning

Tunable dual-responsive superantiwetting hierarchical ZnO/CuO nanocomposite surfaces were prepared with mixing different starting molar ratios of copper and zinc nitrates solutions by the chemical bath deposition method. The fluorine-free composite surfaces indicated excellent superhydrophobic properties. The morphology and structure of the samples were analyzed by SEM, XRD, EDS and Raman analyses. Moreover, the abrasion resistance and underwater stability were evaluated. The SEM results exhibited the formation of dual-scale ZnO/CuO nanostructures combined nanorods, flower-like and urchin-like features on the stainless steel meshes. Compared to the ZnO surface with water contact angle (CA) of 149° ±1.4° and contact angle hysteresis (CAH) of 2.5° ± 0.6°, the ZnO/CuO nanocomposite with Zn2+:Cu2+ initial molar ratio of 4:1 displayed higher CA (161.4° ± 2.1°) and lower CAH (1.5° ± 0.5°) values. However, the amounts of CAs decreased dramatically after post-annealing treatment at 300 °C (~0°) or UV irradiation (27° ± 2°) while the water droplets were completely pinned on the surface. The surface again became superhydrophobic by further annealing at 150 °C for 30 min. Results revealed that the photo-induced hydrophilic properties of the ZnO/CuO nanocomposites were much better than that of the ZnO surface. Additionally, Raman assessments confirmed that the surface defective sites play key roles in the wettability alteration of the fabricated surfaces.

Ultrastable Underwater Anti-Oil Fouling Coatings from Spray Assemblies of Polyelectrolyte Grafted Silica Nanochains.

Surfaces that have superhydrophilic characteristics are known to exhibit extreme oil repellency under water, which is attractive for applications including anti-fogging, water-oil separations, and self-cleaning. However, superhydrophilic surfaces can also be easily fouled and lose their extreme oil repellency, which limits their usage in practical applications. In this work, we create an anti-oil fouling coating by spray coating poly(acrylic acid) (PAA)-grafted SiO2 nanochains (approximately 45 nm wide and 300 nm long) onto solid surfaces, forming a nanoporous film exhibiting superhydrophilicity (water contact angle in air ≈ 0°) and underwater superoleophobicity (dichloroethane contact angle ≥ 165°). The polymer-grafted nanochain assemblies exhibit extremely low contact angle hysteresis (<1°) and small adhesion hysteresis (-0.05 mN m-1), and thus, oil can readily roll off from the surface when the coating is immersed in water. Compared to other superhydrophilic surfaces, we show that both the unique structure of spray-assembled nanochains and the hygroscopic nature of PAA are essential to enable ultrastable anti-oil fouling. Even after the PAA-grafted nanochain coating is purposely fouled by oil, oil can be readily and completely expelled and lifted-off from the coating within 10 s when placed under water. Further, we show that our coating retains underwater superoleophobicity even after being subjected to shearing under water for more than 168 h. Our approach offers a simple yet versatile method to create an ultrastable superhydrophilic and anti-oil fouling coating via a scalable manufacturing method.

P(VDF-TrFE)/PMMA Blended Films with Enhanced Electrowetting Responses and Superior Energy Storage Performance.

P(VDF-TrFE) (vinylidene fluoride-co-trifluoroethylene)/PMMA (PVT/PMMA) blended films synthesized through a facile solution-blending method show outstanding performance for practical electrowetting and energy storage applications. The van der Waals forces and dipolar interactions in neighboring P(VDF-TrFE) and PMMA chains, together with the suppressed free volume (or defect) are critical to the significantly-enhanced electrical properties. Typical, Teflon-covered P(VDF-TrFE)/PMMA blended film exhibits a high dielectric constant of 13 with low dielectric loss (~0.05) at 100 Hz and a large initial contact angle of 122°. Its electrowetting response with a contact angle modulation of 50° in air and low contact angle hysteresis demonstrate that it is promising for low-voltage electrowetting applications. Furthermore, with an energy density of 11.8 J/cm3, approximately double that of pure P(VDF-TrFE), PVT/PMMA blended films containing 20 wt % PMMA turn out to be superior materials for energy storage applications, due to their significantly-enhanced polarization and reduced remnant polarization.

Uniform generation of water slugs in air flowing through superhydrophobic microchannels with T-junction

This article describes an approach to render all walls of a rectangular microchannel superhydrophobic by coating them with hydrophobically modified silica nanoparticles. Differences between the coated nanoparticles in terms of feature size and structure resulted in different contact angle hysteresis (CAH) on the channel walls. The generation of water slugs in a continuous air flow was experimentally studied in the superhydrophobic microchannels with T-junction. The breakup mechanism of water slugs was proved to accord with the squeezing regime by analyzing the data collected from pressure sensor and high-speed camera at the T-junction. A home-made optical measurement system was employed to investigate the uniformity of the water slugs, which was characterized by the standard deviation and coefficient of variation of slug length. The results showed that superhydrophobic microchannels with CAH lower than 15° could produce uniform water slugs in a slug flow pattern, whereas those with CAH of nearly 30° led to unstable flow. Lower CAH and higher gas flow rate were preferred to reduce slug length and improve slug uniformity. An empirical scaling law was established to predict the slug length and was based on the finding that the total length and number of water slugs in the microchannel were controlled by the volumetric flow ratio of water to air and water flow rate, respectively. This work provides a novel microfluidic platform to generate uniform liquid-in-gas slugs under moderate ranges of air flow rate from 5 mL min−1 to 30 mL min−1 (6 < ReG < 40) and volumetric flow ratio of water to air from 1/300 to 1/2, and this performance benefits from superhydrophobic coatings with low CAH.

Pinning-Free Evaporation of Sessile Droplets of Water from Solid Surfaces.

Contact-line pinning is a fundamental limitation to the motion of contact lines of liquids on solid surfaces. When a sessile droplet evaporates, contact-line pinning typically results in either a stick-slip evaporation mode, where the contact line pins and depins from the surface in an uncontrolled manner, or a constant contact-area mode with a pinned contact line. Pinning prevents the observation of the quasi-equilibrium constant contact-angle mode of evaporation, which has never been observed for sessile droplets of water directly resting on a smooth, nontextured, solid surface. Here, we report the evaporation of a sessile droplet from a flat glass substrate treated with a smooth, slippery, omni-phobic covalently attached liquid-like coating. Our characterization of the surfaces shows high contact line mobility with an extremely low contact-angle hysteresis of ∼1° and reveals a step change in the value of the contact angle from 101° to 105° between a relative humidity (RH) of 30 and 40%, in a manner reminiscent of the transition observed in a type V adsorption isotherm. We observe the evaporation of small sessile droplets in a chamber held at a constant temperature, T = (25.0 ± 0.1) °C and at constant RH across the range RH = 10-70%. In all cases, a constant contact-angle mode of evaporation is observed for most of the evaporation time. Furthermore, we analyze the evaporation sequences using the Picknett and Bexon ideal constant contact-angle mode for diffusion-limited evaporation. The resulting estimate for the diffusion coefficient, DE, of water vapor in air of DE = (2.44 ± 0.48) × 10-5 m2 s-1 is accurate to within 2% of the value reported in the literature, thus validating the constant contact-angle mode of the diffusion-limited evaporation model.

Highly Durable Superhydrophobic Polymer Foams Fabricated by Extrusion and Supercritical CO2 Foaming for Selective Oil Absorption.

The severe water contamination caused by oil leakage is calling for low-cost and high-performance absorbent materials for selective oil removal. In this study, a scalable green method was proposed to produce polypropylene (PP)/poly(tetrafluoroethylene) (PTFE) composite foams via conventional processing techniques including twin-screw extrusion and supercritical carbon dioxide foaming. To produce the superhydrophobic foam, micro- and nanosized PTFE particles were melt blended with PP and subsequently foamed. Ascribed to the nanofibrillation of microsized PTFE during processing, the fabricated foam exhibited a special highly porous structure with PTFE nanofibrils and nanoparticles uniformly distributed on the pore surfaces within the PP matrix, which resulted in a remarkably high water contact angle of 156.8° and a low contact angle hysteresis of 1.9°. Unlike traditional surface-modified superhydrophobic absorbers, the foams prepared are entirely superhydrophobic, which means that they remain superhydrophobic when being fractured or cut. Moreover, they are highly durable and maintained the superhydrophobicity when subjected to ultrasonication and mechanical sanding. When used in selective oil absorption, the durable foams exhibited excellent absorption efficiency and high stability in repetitive and long-term use. These advantages make the PP/PTFE foam a promising superabsorbent material for water remediation.

Characterization of microfibril development on PTFE surface during hot imprinting process and its application for oil–water separation

The importance of oil–water separator has increased due to environmental pollution caused by marine accidents. Many studies related to fabrication method of superhydrophobic surface have been conducted because those functional surfaces are an important component used in oil and water separators. However, processes that can be applied to large area and mass production still exist as limitations. In this paper, superhydrophobic surfaces were fabricated on polytetrafluoroethylene (PTFE) surface by hot imprinting. To impart rough surface morphology to PTFE surface, hot imprinting process using an electrical discharge textured (EDT) mold was conducted. It was found that undercut of a discharge crater on the EDT surface induced tensile deformation of PTFE surface during the hot imprinting process resulting in microfibril development. As a result, PTFE surface had rough morphology consisting of replicated EDT surface and microfibril network. Imprinted PTFE sheets showed high water contact angles about 154.3° with low contact angle hysteresis about 1.4°. Additionally, the effects of process temperature and roughness of the EDT mold on microfibril formation were investigated. It was found that microfibril formation is activated when the process temperature reaches glass transition temperature (115 °C) of PTFE. The PTFE sheets for oil–water separation were prepared by hot imprinting and followed by additional drilling process. The optimal hole diameter with respect to efficiency of oil–water separation was determined through experiments and separation of oil and water was effectively conducted.

Self-Cleaning of Hydrophobic Rough Surfaces by Coalescence-Induced Wetting Transition.

The superhydrophobic leaves of a lotus plant and other natural surfaces with self-cleaning function have been studied intensively for the development of artificial biomimetic surfaces. The surface roughness generated by hierarchical structures is a crucial property required for superhydrophobicity and self-cleaning. Here, we demonstrate a novel self-cleaning mechanism of textured surfaces attributed to a spontaneous coalescence-induced wetting transition. We focus on the wetting transition as it represents a new mechanism, which can explain why droplets on rough surfaces are able to change from the highly adhesive Wenzel state to the low adhesion Cassie-Baxter state and achieve self-cleaning. In particular, we perform many-body dissipative particle dynamics simulations of liquid droplets (with a diameter of 89 μm) sitting on mechanically textured substrates. We quantitatively investigate the wetting behavior of an isolated droplet as well as coalescence of droplets for both Cassie-Baxter and Wenzel states. Our simulation results reveal that droplets in the Cassie-Baxter state have much lower contact angle hysteresis and smaller hydrodynamic resistance than droplets in the Wenzel state. When small neighboring droplets coalesce into bigger ones on textured hydrophobic substrates, we observe a spontaneous wetting transition from the Wenzel state to the Cassie-Baxter state, which is powered by the surface energy released upon coalescence of the droplets. For superhydrophobic surfaces, the released surface energy may be sufficient to cause a jumping motion of droplets off the surface, in which case adding one more droplet to the coalescence may increase the jumping velocity by one order of magnitude. When multiple droplets are involved, we found that the spatial distribution of liquid components in the coalesced droplet can be controlled by properly designing the overall arrangement of droplets and the distance between them. These findings offer new insights for designing effective biomimetic self-cleaning surfaces by enhancing spontaneous Wenzel-to-Cassie wetting transitions, and additionally, for developing new noncontact methods to manipulate liquids inside the small droplets via multiple-droplet coalescence.

Prototyping of Superhydrophobic Surfaces from Structure‐Tunable Micropillar Arrays Using Visible Light Photocuring

A new approach is reported to fabricate micropillar arrays on transparent surfaces by employing the light‐induced self‐writing technique. A periodic array of microscale optical beams is transmitted through a thin film of photo‐crosslinking acrylate resin. Each beam undergoes self‐lensing associated to photopolymerization‐induced changes in the refractive index of the medium, which counters the beam's natural tendency to diverge over space. As a result, a microscale pillar grows along each beam's propagation path. Concurrent, parallel self‐writing of micropillars leads to the prototyping of micropillar‐based arrays, with the capability to precisely vary the pillar diameter and inter‐spacing. The arrays are spray coated with a thin layer of polytetrafluoroethylene (PTFE) nanoparticles to create large‐area superhydrophobic surfaces with water contact angles greater than 150° and low contact angle hysteresis. High transparency is achieved over the entire range of micropillar arrays explored. The arrays are also mechanically durable and robust against abrasion. This is a scalable, straightforward approach toward structure‐tunable micropillar arrays for functional surfaces and anti‐wetting applications.

Tailoring the hydrophobicity of copper surface with ion beam irradiation

ABSTRACTDropwise condensation of water vapor present in moist air on copper surface is of significant scientific interest worldwide, for developing an efficient condensing unit of water harvesting via dewing devices. However, it does not prolong for a long duration on these surfaces because of the highly reactive nature of copper. In this work, simple and economically viable methods are described for altering the morphology of copper surfaces which exhibit dropwise condensation for long duration. The durable hydrophobic copper surfaces are fabricated by electrochemical deposition and solution immersion methods on chemically etched copper samples, followed by ion beam irradiation of 15 keV Ne ions at a fluence of 1017 ions/cm2. The roughness of tailored samples is measured using atomic force microscope and contact angle measurements are performed for measuring the static contact angle of deionized water droplets on these modified surfaces. The results show that the irradiated surfaces have low contact angle hysteresis and prolonged dropwise condensation of water vapor present in moist air.

Superhydrophobic hierarchical three-level structures on 3D polypropylene surfaces

Hierarchical micro–micro–nanostructures were fabricated on planar and curved polypropylene surfaces by injection molding. The metal mold insert was microstructured with a microworking robot and nanostructured with an anodization process. 3D surface curvature was based on the simple bending of the mold insert into convex and concave dome-shaped formations. Three-level structural hierarchy was demonstrated to enhance superhydrophobicity compared to two-level structures. The third structural level on top of two lower structural levels decreased the contact area between the water droplet and polymer surface, which resulted in the high contact angle (CA) of 170°, low CA hysteresis of 5° and easily sliding droplets. Microstructures can be considered to protect other hierarchical levels, and the three-level-structured surface is less susceptible to lose its superhydrophobicity compared to two-level-structured surfaces. Structuration of four length scales was realized on the curved surfaces when the curvature in millimeter scale was combined with the surface structures in two microscales and nanoscale.

Wettability of zinc oxide nanorod surfaces.

In this work, we have studied the wettability of zinc oxide (ZnO) nanorods grown on fluorine-doped tin oxide (FTO) by highlighting the effect of polar and non-polar ZnO facets on contact angle (CA) results. The variation in the wettability behaviors of the synthesized surfaces is mainly related to physical and chemical surface texturing which influenced the liquid drop penetration. Indeed, three main penetration states can be deduced: total, partial, and null-penetration. Where, low CA (100.9°) with high contact angle hysteresis (CAH) (13°) is observed for total penetration of the liquid drop. While, high CA (139.6°) with low CAH (7°) is observed for null-penetration. Moreover, we have found that the chemical texturing of ZnO, especially the hydrophilicity of ZnO tips, responsible for liquid drop sticking, prevents the liquid slipping over the surface. In order to promote the liquid rolling on the ZnO surface, we reported the physical modification of the ZnO structures. Therefore, the rolling of the liquid drop on the inclined surface of ZnO is achieved by using a new structure based on double scale roughness. This surface exhibits superhydrophobic behavior with a CA of 153° and CAH of 3°.

Superhydrophobic and Highly Oleophilic Polystyrene Fibers (PS) with Delayed Freezing Time and Effective Oil Adsorption

We present an efficient and simple approach for preparing superhydrophobic-superoleophilic polystyrene (PS) fibers via electrospinning. Bead-on-string fibers from a 5% PS solution and micro-sized fibers from a 20% PS solution were combined to achieve a surface having very high contact angle (about 160°) and low contact angle hysteresis. The presence of bead-on-string fibers increases the superhydrophobicity of the sorbent. The micro-sized PS fibers improve the mechanical properties of the electrospun mat through their elastic and flexible behavior. An evaluation of wettability at a low temperature (-10 oC) showed a delayed freezing time for water droplets on the superhydrophobic surface. Water droplets on a polished aluminum surface froze more quickly (about 6 seconds) than droplets on the fabricated superhydrophobic surface (about 500 seconds). Finally, the oil adsorption capacity of the developed superhydrophobic PS fibers, which have a porous surface structure, showed values of 69.1, 69.3 and 61.2 g/g for canola oil, olive oil and motor oil, respectively.

Tuning the structure and wetting properties of organic-inorganic nanocomposite coatings prepared by aerosol-assisted atmospheric pressure cold plasma deposition

Dispersions of oleate-capped ZnO nanoparticles (NPs) in binary n-octane/1,7-octadiene solvent mixtures are injected, in aerosol form, in a dielectric barrier discharge to deposit hydrocarbon polymer/ZnO nanoparticles nanocomposite (NC) thin films at atmospheric pressure and room temperature. The chemical composition of the coatings, and in turn their morphology and wettability, can be tuned by simply changing the composition of the starting dispersion. Specifically, the increase of the NPs concentration in the dispersion (0.5–5 wt%) results in a continuous increase of both the ZnO content and deposition rate of the coatings. Moreover, when the concentration of 1,7-octadiene in the solvent mixture is very low (0.5–2 vol%), the incorporation of NPs is further promoted, while at concentrations >2 vol% the growth of the organic component starts to be favored. Overall, results reveal a considerable increase of the root-mean-square (RMS) roughness of the coatings with the ZnO loading. In addition, once the threshold ZnO loading and RMS roughness of 60 wt% and 350 nm are reached, respectively, the coatings are superhydrophobic and exhibit very low water contact angle hysteresis, due to the coexistence of the low surface energy conferred by the hydrocarbon polymer and the hierarchical multiscale surface texture induced by NPs incorporation.

Superhydrophobic Fabrics with Mechanical Durability Prepared by a Two-Step Plasma Processing Method

Most studies on superhydrophobic fabrics focus on their realization using additive manufacturing (bottom-up) techniques. Here we present the direct modification of three different fabrics using a plasma-based method to obtain anti-adhesive and self-cleaning properties. A two-step plasma processing method is used: (a) for the creation of micro-nanoscale features on the fabric surface (plasma texturing step) and (b) the minimization of the fabric surface energy (by a short plasma deposition step of a very thin, low surface energy layer). The entire process takes only 14 min and all fabrics after processing exhibit high water static contact angles (WSCA &gt; 150°), low contact angle hysteresis (CAH &lt; 7°) and advantageous mechanical durability against hand-rumpling. The method is simple and generic, and it can be therefore expanded to other polymeric fabrics (i.e., acrylic) in addition to polyester, without any limitation rising from the weaving characteristics of the fabric or the starting nature of the material (i.e., hydrophobic or hydrophilic).

Transparent, fluorine-free, heat-resistant, water repellent coating by infusing slippery silicone oil on polysiloxane nanofilament layers prepared by gas phase reaction of n-propyltrichlorosilane and methyltrichlorosilane

The subject of slippery liquid-infused porous surfaces (SLIPS) have attracted many researchers due to their excellent liquid repellent properties and widespread usage in many fields such as anti-wetting, anti-icing, omniphobic, self-cleaning and anti-biofouling surfaces. Choosing an environmentally friendly, durable lubricant and easy-clean preparation method is very important when designing SLIPS. In this work, fluorine-free, transparent, water and oil repellent slippery liquid-infused porous surfaces (SLIPS) were successfully obtained via infusing silicone oil, which is a fluorine free and durable liquid, onto superhydrophobic polysiloxane nanofilament surfaces. Polysiloxane nanofilaments were prepared on activated glass slides by an easy, clean and environmentally friendly gas phase reactions of n-propyltrichlorosilane (n-PTCS) for the first time and also methyltrichlorosilane (MTCS) and the results were compared. Advancing contact angles of the n-PTCS based polysiloxane nanofilament layers were between 143 and 172° and contact angle hysteresis as low as 7° was obtained on these surfaces by altering the relative humidity and reaction time during filament growth. Then, transparent SLIPS were obtained by infusing silicone oil into polysiloxane filament layers of MTCS and n-PTCS. The obtained SLIPS shows excellent liquid repellency, very low contact angle hysteresis for long durations and maintains its water repellency after heating up to 80 °C for 6 days and also after exposure to continuous water droplet flow up to 2 h.

Forming nanostructured surfaces through Janus colloidal silica particles with nanowrinkles: A new strategy to superhydrophobicity

Proper nano-structuring coupled with low surface energy properties is exploited to obtain super-hydrophobic surfaces. A biomimicking hierarchically structured coating upon a material surface is obtained by depositing Janus nano-structured wrinkled colloidal particles. The morphology of the surface is thus ruled by different scales: the size of the wrinkles (few tens of nanometer), particle radius (several hundreds of nanometer) and interparticle distance. Janus wrinkled silica particles have one side exposing hydroxyl groups while the other side is partially silanized with dichlorodimethylsilane. To obtain these Janus particles, wax colloidosomes with surface covered by starting rough particles were successfully prepared. The exposed surface of rough wrinkled silica particles was then silanized, thus obtaining a Janus structure. The Janus character was prooved in different manners: the simple so called “visual test”, through Energy Filtered Transmission Electron Microscopy (was proven in different EFTEM) and by further functionalization with polypropylene grafted maleic anhydride (PPgMA).A glass microscope slide was covered by drop casting the particles obtaining super-hydrophobic features of the surface characterized by a high water contact angle (149°) and, more interestingly, by a very low water contact angle hysteresis (CAH = 2°) and roll-off angle (ROA = 1.8°). Superhydrophobicity is confirmed by the very low values of apparent surface free energy estimated with the OWRK (Owens-Wendt-Rabel e Kaelble) method. SEM and AFM analyses prove the multiple scale hierarchical roughness, from nano to micro size, that resembles the one present at the surface of the lotus leaves.