Superhydrophobic Polymer Surfaces Research Articles

Development of superhydrophobic fractal surfaces using Silica nanoparticles based on polylactic acid through molding technique

This research introduces a novel approach to creating superhydrophobic surfaces on polymer substrates. The objective is to develop a general method for producing various types of superhydrophobic polymer surfaces using modified nanoparticles, as well as making Unplasticized PolyVinyl Chloride(UPVC) and polylactic acid hydrophobic. To achieve this goal, we investigate the circulation of a rotating cover, pressure, and pressure time. We embed modified silica nanoparticles onto UPVC boards, which confirms surface hydrophobicity with a contact angle of 155° and a sliding angle of 6–7° for water droplets. Under specific conditions, including a suspension concentration of 10 g/L, coating time of 5 seconds, temperature of 155°C, rotation speed of 400 rpm, and pressure of 2 MPa with a pressure time of 4 minutes, we achieve superhydrophobicity on PVC boards, resulting in contact angles of 150–160°. Additionally, we find that the sliding angle of water droplets is less than 10°.

Microtopographic superhydrophobic polymer surface to prevent urinary tract infections causing nosocomial drug-resistant bacterial adhesion

Catheter-associated urinary tract infections (CAUTIs) are one of the most prevalent forms of healthcare-associated infections worldwide. Recurrent episodes of infections and development of antibiotic resistance/tolerance among biofilm-forming bacteria are well documented. We developed a simple method of making superhydrophobic micro-structured antibacterial polymer surfaces for coating-free catheters. A two-step fabrication approach was used to turn the hydrophobic polydimethylsiloxane (PDMS) into superhydrophobic surfaces. The nanosecond pulsed Nd:YAG laser was used to fabricate two types of structures (holes and grooves) on a steel mold. The soft-molding technique was adopted to replicate these structures on PDMS films. The pillar structured PDMS surface exhibited a water droplet contact angle (WDCA) of 169○ ± 3° with a low sliding angle of 12○, whereas the grooved surface had 142○ ± 5° contact angle. Moreover, the Luria Broth which is media for bacterial growth shows contact angle of 141○ ± 2° and 120○ ± 3°, respectively. Theoretically, the micro-pillar structures with selected dimensions could sustain the Cassie–Baxter state. The crystal violet binding assay was used to assess the anti-biofilm activity of structured surfaces (grooved and pillared) against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), as well as clinical isolates of Klebsiella pneumonia (K. pneumoniae), E. coli, and S. aureus. Furthermore, the attachment and interaction of bacteria with surfaces were investigated through filed emission scanning electronic microscope (FE-SEM) and confocal microscopy. Overall, the pillar-structured surface reduces the average bacterial attachment more efficiently than a grooved surface (>80% vs. >50% reduction) compared to a plain PDMS surface due to its higher water-repellent property. This work will give new insights into the development of coating-free, long-lasting antibacterial surfaces for polymeric medical devices.

What if designing superhydrophobic polymer surfaces turned out to be very simple?

Various natural or artificial surface topographies or textures lead to slippery superhydrophobicity, but have little in common. Thus, simple questions need to be asked: what are the key parameters required for reaching slippery superhydrophobicity, i.e. forming a Cassie-Baxter's interface instead of a Wenzel's one? Is the double texturing scale, i.e. nano and micro, imperative to reach this superhydrophobicity regime as usually agreed upon the literature? In this paper, a simple model of the wetting of a textured surface based on the balance between the liquid pressure and the surface tension for a Cassie-Baxter's interface is described. The textured surface is supposed to be slippery superhydrophobic as long as a pure Cassie-Baxter's interface with a contact angle larger than 150° is established. The stability limits of such an interface upon pressure are studied depending on simple parameters such as asperities shape, size, or spacing distance. Then, this model is applied on simple theoretical surfaces and its conclusions are challenged with surface wetting situations described in the literature, showing great accordance. The proposed model offers a simple understanding of the relationship between surface texture and superhydrophobicity. Such an understanding guides the design of stable superhydrophobic surfaces using simple parameters. An ideal surface texture for superhydrophobicity can be described: An intrinsically hydrophobic surface with as small as possible re-entrant asperities that are spaced by more than their own width, and at least as high as their spacing distance.

A Review of Recent Advances in the Development of Superhydrophobicity over Various Substrate Surfaces Using Polymers

AbstractOwing to its hydrophobic nature, polymers are more commonly employed to impart superhydrophobicity over different surfaces. This review gives a brief account on the theories behind superhydrophobicity and techniques employed to develop superhydrophobic coatings over metal, fabrics, papers, sponges, foam, glass, wood, mesh, concrete and ceramic surfaces. Fine‐tuning of superhydrophobic polymeric surfaces is much required to enhance corrosion control, oil‐water separation, self‐cleaning, drag reduction, anti‐microbial, anti‐bio‐fouling, anti‐icing and desalination properties. Methodology and current developments in the designing such superhydrophobic polymeric surfaces are highlighted. To conclude, the challenges to be addressed by the scientific world to solve the problems associated with mass production, stability and durability of the coatings, development of hierarchical micro‐nanostructures are detailed.

Icing behavior of supercooled droplets on superhydrophobic polymercoatings between lotus effect and petal effect

Abstract This paper investigated anti-icing behavior and wettability of droplets on superhydrophobic polymercoatings between lotus effect and petal effect, which were prepared on surfaces of 2021 aluminum alloy with 1H, 1H, 2H, 2H-heptafluorodecyl (FAS-17). The prepared surfaces displayed excellent hydrophobicity with contact angles of 154.9° ± 1.5°and 139.8° ± 1.3°, while rolling angles are 4° ± 1.0° (lotus effect) and 30° ± 1.5° (petal effect). Thus, the present study focused on the different characterizations and the anti-icing potential of the superhydrophobic polymersurfaces were analyzed based on three parameters including the icing delay time, the crystallization temperature of water droplets, and contact time of impinging droplets on the cold superhydrophobic polymer coatings (−15 °C). Furthermore, the anti-icing of superhydrophobic coatings between lotus effect and petal effect with freezing time and crystallization temperature experimental phenomena were consistent with the thermodynamic analysis. It is also proved that the droplets have different bounce behavior on different polymercoating surfaces by droplet impact experiment. The study offers a comprehensive perspective on polymercoatings of different wetttablility for anti-icing behavior applications.

Real‐Time Monitoring and Quantification of Underwater Superhydrophobicity

AbstractLong‐lasting underwater superhydrophobicity involves stable‐in‐time air layer trapped and retained between a submersed surface and the overlying liquid. Due to its underwater nature, it is rather difficult to accurately observe this air layer in submerged systems, let alone to measure it. Here, white light reflectance spectroscopy is used for real‐time monitoring (acquisition speed 50–200 ms) of underwater superhydrophobicity as well as for the calculation of the entrapped air layer thickness on “everlasting” underwater polymeric superhydrophobic surfaces fabricated by plasma micro‐nanotexturing. The proposed method enables real‐time monitoring and accurate calculation of air layers with thicknesses ranging from a few nanometers to several tens of micrometers involving small underwater bubbles. In addition, different scale topographies of superhydrophobic plasma micro‐nanotextured surfaces are tested and found to retain underwater superhydrophobicity for at least 60 days. As a demonstration, the air layer thickness is also monitored in real time when titrating water with low surface tension liquids. Among several topographies tested, a superhydrophobic surface exhibiting hierarchical topography and a high roughness ratio is able to retain a stable air layer when submersed in liquids with surface tension down to 44 mN m−1.

Carbon black-based NIR-responsive superhydrophobic shape memory microplate array with switchable adhesion for droplets and bubbles manipulation

Superhydrophobic stimuli-responsive shape memory polymer (SMP) surfaces with tunable wettability have been extensively explored, but in situ reversibly switching ability as well as selectively capturing and releasing different liquids or bubbles, unfortunately, is still a blockage. Here, we fabricated a kind of light-responsive superhydrophobic SMP microplate array by utilizing femtosecond laser ablation and replica-mold method to achieve in situ switchable adhesion. By combining the photothermal effect of carbon black with the shape memory effect of SMP, the reversible switching between the upright state and temporary bending state of the microplate array can be readily realized. Simultaneously, the apparent force for the microplate array can be reversibly switched between low and high adhesion. More significantly, the current surface is competent for the amphibious manipulator, that is, the microplate array is adaptive for the selective capture and release of droplets as well as underwater bubbles. The current superhydrophobic SMP microplate array will have potential applications in intelligent droplet and bubble operation.

Advances in the Fabrication of Superhydrophobic Polymeric Surfaces by Polymer Molding Processes

Superhydrophobic materials are found in a suite of scientific and industrial applications, and given their broad potential use, there is great interest in facilitating their mass production. Although numerous methods have been used to produce superhydrophobic materials, only a few are capable of fabricating superhydrophobic surfaces and materials at an industrial scale. Techniques such as injection molding, compression molding, hot embossing, and polymer casting play an important role in the mass production of superhydrophobic polymer surfaces. This technical literature review summarizes recent advances in the polymer molding processes used to fabricate superhydrophobic materials. Here, we review replication methods and the materials that can be used by these approaches. We also evaluate the advantages and disadvantages of these methods and discuss the challenges of molding and demolding single-level structures (e.g., microstructures and nanostructures) and multilevel structures (e.g., micro-nanostructures, micro-microstructures, and micromicro-nanostructures), with a focus on superhydrophobic surfaces. We evaluate the relationship between structure geometry and the wettability of a surface, highlighting the effect of structure type and size in achieving the desired wettability. We then offer perspectives, discuss current limitations, and suggest required studies. This review aims to assist researchers in understanding the fundamentals related to the fabrication of patterned surfaces via polymer molding processes and offer avenues for the successful creation of superhydrophobic polymeric surfaces.

Mimicking flower petals to fabricate self-cleaning and antireflective polymer surfaces

This work explored a facile way to fabricate superhydrophobic and antireflective polymer surfaces using Canna indica flower petals. A simple, inexpensive two-step soft-lithography technique was employed to replicate the surface structures of C. indica flower petals onto two different polymer surfaces namely, polydimethylsiloxane (PDMS) — a hydrophobic polymer and resorcinol–formaldehyde (RF) xerogel — a hydrophilic polymer. First, a negative replica was prepared in PDMS using the flower petal as a template. Second, the negative PDMS replica was later used as a stamp to prepare a positive replica in both PDMS and RF xerogel. These replicated structured surfaces greatly influenced the wettability properties. The contact angle of the replicated PDMS surfaces increased to the nearly superhydrophobic values of 145° (negative PDMS replica) and 144° (positive PDMS replica) compared with that of the plain surface, which is 101°. Interestingly, the contact angle of the replicated RF surface significantly increased to 151° (superhydrophobic) compared with that of the planar RF surface, which is hydrophilic (68°). Furthermore, the replicated polymer surfaces exhibited not only excellent superhydrophobic properties but also antireflective properties. These multifunctional surfaces with superhydrophobicity as well as an omnidirectional antireflective property may find a wide range of applications, such as solar energy harvesting, optical displays and marine applications.

Creating Superhydrophobic Polymer Surfaces with Superstrong Resistance to Harsh Cleaning and Mechanical Abrasion Fabricated by Scalable One‐Step Thermal‐Imprinting

AbstractIn this work, a scalable thermal imprinting method that allows to directly fabricate superhydrophobic polymer surfaces with superstrong resistance to harsh cleaning and mechanical abrasion is reported. A titanium (Ti) mold is produced by femtosecond laser processing to possess a hierarchical micro‐ and nanoscale pattern. Through thermal imprinting, this hierarchical pattern onto poly(propylene) sheets is able to be accurately reproduced, rending the polymer surface superhydrophobic. The imprinting method employed uses an aqueous ethanol solution of stearic acid to assist demolding, and periodically uses xylene to limit mold contamination and restore the mold to excellent condition for further imprinting. These strategies allow to repeatedly use the mold over 50 times without degradation. A range of durability tests are further performed, and showed that the produced suprehydrophobility on the poly(propylene) sheets exhibit excellent durability, withstanding brush washing, ultrasound cleaning, and sandpaper abrasion. The reported method can also be used to fabricate superhydrophobic surfaces of various thermoplastics that are broadly utilized in daily life.

Superhydrophobic Polymer Surface with Hierarchical Patterns Fabricated in Hot Imprinting Process

Superhydrophobic surfaces have been widely applied to solve environmental issues using their many functions such as drag reduction, oil–water separation and self-cleaning. It is well known that superhydrophobicity of materials can be enhanced by imparting micro/nano hierarchical patterns on its surface. Although several techniques, such as MEMS, coating, and laser ablation, have been suggested to improve superhydrophobicity, they are unsuitable for mass production. To overcome this limitation, a facile fabrication method using hot imprinting process was developed in this study. Hierarchical patterns including micro sinusoidal patterns with discharge craters were formed on the die surface obtained using wire electrical discharge machining. Thermoplastic PTFE and PC polymer surfaces with hierarchical patterns were successfully replicated from the die surface after hot imprinting. In addition, an entangled micro fibril network was observed on the PTFE surface, whereas torn shapes were developed on the PC polymer surface. As a result, the polymer surfaces were found to exhibit superhydrophobicity with a water contact angle > 150°.

Simple and Affordable Way To Achieve Polymeric Superhydrophobic Surfaces with Biomimetic Hierarchical Roughness.

A water contact angle greater than 150° together with a sliding angle less than 10° is a special surface phenomenon that appears on superhydrophobic surfaces. In this paper, a brief introduction of the development history and present research on superhydrophobic surfaces was given. Polymeric superhydrophobic surfaces with biomimetic hierarchical roughness were fabricated by a simple method of hot embossing without any chemical treatments. Stainless steel meshes with different mesh numbers were used as template. Moreover, the influences of processing parameters, including mesh number, mold temperature, and pressure, were deeply investigated. Hierarchical microplatforms, microfibers, and oriented arrayed nanowrinkles structure on them, which were resembled with the nanowrinkles structure and hierarchical roughness on a red rose petal, were observed by a scanning electron microscope. A water contact angle of 154° can be achieved after parameter optimization. The method proposed in this study offered a fine and affordable choice for the fabrication of polymeric superhydrophobic surfaces. With the rapid development of functional applications in micro- and nanodevices, this method will show greater superiority in large-area and large-scale production due to its advantages of low cost, high efficiency, and high reliability.

Effect of Structure Hierarchy for Superhydrophobic Polymer Surfaces Studied by Droplet Evaporation.

Super-hydrophobic natural surfaces usually have multiple levels of structure hierarchy. Here, we report on the effect of surface structure hierarchy for droplet evaporation. The two-level hierarchical structures studied comprise micro-pillars superimposed with nanograss. The surface design is fully scalable as structures used in this study are replicated in polypropylene by a fast roll-to-roll extrusion coating method, which allows effective thermoforming of the surface structures on flexible substrates. As one of the main results, we show that the hierarchical structures can withstand pinning of sessile droplets and remain super-hydrophobic for a longer time than their non-hierarchical counterparts. The effect is documented by recording the water contact angles of sessile droplets during their evaporation from the surfaces. The surface morphology is mapped by atomic force microscopy (AFM) and used together with the theory of Miwa et al. to estimate the degree of water impregnation into the surface structures. Finally, the different behavior during the droplet evaporation is discussed in the light of the obtained water impregnation levels.

Petal-effect superhydrophobic surface self-assembled from poly(p-phenylene)s

In the nonsolvent vapor atmospheres, the petal-effect superhydrophobic surface was self-assembled from conjugated poly(2,5-dibutoxy-p-phenylene). During the dissolution of the nonsolvent vapor and the evaporation of the solution, the side-chain interactions and the π–π interactions between conjugated backbones induced the formation of polymer particles, which further agglomerated and formed the network structures and radiate spherical-like hierarchical microstructures. The increase in the distribution of microspheres improved the roughness of the surface and increased the contact angles more than 150°. The network of agglomerated polymer particles were easier to be formed and induced a relatively important penetration of the water inside the pores. Therefore, the network of agglomerated polymer particles and radiate spherical-like hierarchical microstructures can form a Cassie-impregnating regime to display the petal-effect. This provides a new strategy for preparing petal-effect superhydrophobic polymer surfaces, which show significant potential for future application in the control of microdroplet and micro-fluidics.

Fabrication of an Anisotropic Superhydrophobic Polymer Surface Using Compression Molding and Dip Coating

Many studies of anisotropic wetting surfaces with directional structures inspired from rice leaves, bamboo leaves, and butterfly wings have been carried out because of their unique liquid shape control and transportation. In this study, a precision mechanical cutting process, ultra-precision machining using a single crystal diamond tool, was used to fabricate a mold with microscale directional patterns of triangular cross-sectional shape for good moldability, and the patterns were duplicated on a flat thermoplastic polymer plate by compression molding for the mass production of an anisotropic wetting polymer surface. Anisotropic wetting was observed only with microscale patterns, but the sliding of water could not be achieved because of the pinning effect of the micro-structure. Therefore, an additional dip coating process with 1H, 1H, 2H, 2H-perfluorodecythricholosilanes, and TiO2 nanoparticles was applied for a small sliding angle with nanoscale patterns and a low surface energy. The anisotropic superhydrophobic surface was fabricated and the surface morphology and anisotropic wetting behaviors were investigated. The suggested fabrication method can be used to mass produce an anisotropic superhydrophobic polymer surface, demonstrating the feasibility of liquid shape control and transportation.

Bioinspired Design of Three-Dimensional Ordered Tribrachia-Post Arrays with Re-entrant Geometry for Omniphobic and Slippery Surfaces.

Hydro- and oleophobic (namely, omniphobic) coatings or surfaces have many important applications, but tremendous challenges in fabrication aspects still remain. Herein, we report a bioinspired design and nanofabrication of three-dimensional (3D) tribrachia-post arrays with re-entrant geometry (3D TPARG) for superhydrophobic and oleophobic polymer films or surfaces. By simply controlling the temperatures and time to treat silica colloidal templates, we can readily fabricate 3D ordered polymer arrays of tribrachia-posts or hexagonal tribrachia-posts with re-entrant geometries that resemble the skin of a springtail insect after the template is removed. These polymer surfaces exhibit excellent and self-healing superhydrophobicity and oleophobicity even against temperature, acids, alkalis, and mechanical damage. Moreover, their liquid-infused nanostructured surfaces still display very good liquid-sliding ability for water and oils. Our 3D TPARG design strategy may help the development of omniphobic polymer coatings or surfaces for practical applications in self-cleaning surfaces, liquid transport, antifouling materials, and many other important fields.

Physical Texturing for Superhydrophobic Polymeric Surfaces: A Design Perspective

Surface wetting on the textured surface is classically explained by the theories of Cassie-Baxter or Wenzel. However, in recent years, an increasing number of complex surface topographies with superhydrophobic properties have been achieved without prediction or simulation using these theories. One example is biomimetic surfaces. In many instances, theories were used to explain surface properties found in nature but have not led to or predicted the complex topographies. Although new wetting theories continue to emerge, there is not yet a set of design rules to guide the selection of surface topographies to achieve superhydrophobicity. By grouping known surface topographies into common geometrical descriptions and length scale, this paper suggests a set of surface topography classifications to provide selection guidelines for engineering superhydrophobic surfaces. Two key outcomes emerged from the design analysis: first, categorization of frequently reported surface patterns shows that there exists a set of commonly used descriptions among diverse designs; second, the degree of hydrophobicity improvement within a class of topography design can be used to predict the limit of improvement in superhydrophobicity for a given material. The presentation of topography descriptors by categories of design and performance may serve as a prologue to an eventually complete set of design guidelines for superhydrophobic performance.

Biomimetic polymeric superhydrophobic surfaces and nanostructures: from fabrication to applications

Numerous research studies have contributed to the development of mature superhydrophobic systems. The fabrication and applications of polymeric superhydrophobic surfaces have been discussed and these have attracted tremendous attention over the past few years due to their excellent properties. In general, roughness and chemical composition, the two most crucial factors with respect to surface wetting, provide the basic criteria for yielding polymeric superhydrophobic materials. Furthermore, with their unique properties and flexible configurations, polymers have been one of the most efficient materials for fabricating superhydrophobic materials. This review aims to summarize the most recent progress in polymeric superhydrophobic surfaces. Significantly, the fundamental theories for designing these materials will be presented, and the original methods will be introduced, followed by a summary of multifunctional superhydrophobic polymers and their applications. The principles of these methods can be divided into two categories: the first involves adding nanoparticles to a low surface energy polymer, and the other involves combining a low surface energy material with a textured surface, followed by chemical modification. Notably, surface-initiated radical polymerization is a versatile method for a variety of vinyl monomers, resulting in controlled molecular weights and low polydispersities. The surfaces produced by these methods not only possess superhydrophobicity but also have many applications, such as self-cleaning, self-healing, anti-icing, anti-bioadhesion, oil-water separation, and even superamphiphobic surfaces. Interestingly, the combination of responsive materials and roughness enhances the responsiveness, which allows the achievement of intelligent transformation between superhydrophobicity and superhydrophilicity. Nevertheless, surfaces with poor physical and chemical properties are generally unable to withstand the severe conditions of the outside world; thus, it is necessary to optimize the performances of such materials to yield durable superhydrophobic surfaces. To sum up, some challenges and perspectives regarding the future research and development of polymeric superhydrophobic surfaces are presented.

UV-induced switchable wettability between superhydrophobic and superhydrophilic polypropylene surfaces with an improvement of adhesion properties

Polypropylene (PP) surfaces with reversible switching between superhydrophobicity and superhydrophilicity were fabricated by a simple dip-coating method. The reversibility was obtained using a combination of UV and thermal treatment cycles. Superhydrophobic polymeric surfaces were prepared by dipping PP substrates in a hot suspension of xylene containing TiO2 nanoparticles (NPs) functionalized with trimethoxypropyl silane (TMPSi). This resulted in superhydrophobic PP surfaces with water contact angles (WCA) of 158° that were converted to superhydrophilic (WCA ~0°) by UV irradiation. However, the superhydrophobic state can be easily recovered using a soft thermal treatment (100 °C for 2 h). A continuous switch in the extreme wettability properties of the surfaces was achieved using cycles of UV irradiation and thermal treatments. Additionally, the hydrophilicity obtained by UV illumination improved the weak adhesion that existed between the nanocoating and the PP surface before the UV treatment by about 90 %. Detailed high-resolution X-ray photoelectron spectroscopy data showed that the relative concentration of the hydrophilic component, Ti–OH, in the O 1s signal increased from 32 % to more than 50 % when the surface was irradiated. Simultaneously, the Ti 2p signal showed a reduction of Ti(IV) to Ti(III) after the photochemical treatment leading to a surface hydroxylation and the superhydrophilicity found after UV irradiation. This paper reports the preparation of PP surfaces with excellent controllable wettability with important applications where improvement in the coating adhesion is necessary.

Simple processes for the preparation of superhydrophobic polymer surfaces

Abstract Two simple processes; (i) spin-coating, and (ii) doctor blade coating of silica/polymer dispersions are described for the preparation of superhydrophobic polymer surfaces. To demonstrate the versatility and broad applicability of the processes, polymeric surfaces modified included a thermoplastic resin, polystyrene (PS) and a thermoset, crosslinked epoxy resin (ER). Micro/nano hierarchical nature of the surface topographies obtained were demonstrated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and white light interferometry (WLI) studies. Roughness factor (r) and average surface roughness (Ra) values, which are critical in obtaining superhydrophobic surfaces were determined for each polymeric system. It was clearly demonstrated that increased (r) and (Ra) values resulted in superhydrophobic behavior with very high static, advancing and receding water contact angles, well above 150° and contact angle hysteresis values of less than 10°. Incorporation of small amounts (1.0% by weight) of a silicone copolymer or a perfluoroether glycol oligomer reduced the contact angle hysteresis in the epoxy resin system well below 10° and produced truly superhydrophobic surfaces.