Surface Free Energy Materials Research Articles

Self-assembly behavior of fluorinated amphiphilic copolymer in aqueous solution and its properties in the solid film state

Owing to the high electronegativity of fluorine atoms, incorporation of fluorinated moieties in a polymer can confer unique properties such as low surface energy and self-assembling ability in solution. In this study, a series of amphiphilic copolymers were prepared by radical polymerization using three monomers: 2-((2,3,3,3- tetrafluoro- 2- (1,1,2,3,3,3- hexafluoro −2- (perfluoroethoxy) propoxy) propanoyl)oxy) ethyl acrylate (FHEMA), maleic anhydride (MAH), and acrylic acid (AA). The PFHEMA block provided low surface tension, and the MAH and AA blocks (containing carboxyl) increased solubility. The properties of the polymer (PFHEMA-co-PMAH-co-PAA) can be regulated by changing the PFHEMA length. Characterization by Fourier-transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) indicated successful polymerization (FHA01 and FHA02). When the FHEMA/MAH/AA molar ratio was 3:8:9 (FAA02), the surface tension of the hydrolyzed amphiphilic copolymers FAA02 at 300 mg·mL−1 in aqueous solution was 15.76 mN·m−1, the lowest value due to a higher fluorine content than FAA01. FAA02 self-assembled in water to form pH-sensitive micelles with diameters greater than 140 nm. For the FAA02 film, both the F/C ratio and arrangement of fluorine-containing side chains decreased with increasing film depth. Thus, this type of fluorine-containing low surface free energy material can be developed into a high performance coating material.

Synthesis of superhydrophobic FAS-EP/PTFE coating with excellent drag reduction performance and mechanical robustness

Superhydrophobic (SHP) materials have great potential for applications in self-cleaning, anti-fouling, anti-corrosion and drag reduction, but their poor mechanical robustness is a fundamental problem that hinders their practical application. In this work, we successfully and rapidly prepared SHP coating with good durability and drag reduction properties by a simple drop-coating technique after chemical modification and physical mixing. We investigated the effects of modification with 1H,1H,2H,2H-Perfluorodecyltriethoxysilane (FAS-17), a low surface free energy material, and the filling content of Poly tetra fluoroethylene (PTFE) on the hydrophobic property of the as-prepared coating. The maximum water contact angle (WCA) and the minimum sliding angle (SA) of the coating were 160.2 ± 0.4° and 5°, respectively. The coating maintained superhydrophobicity after 4.4 m of abrasion with 400 grit sandpaper and 3 h of water impact, indicating its excellent mechanical durability. In addition, it has outstanding self-cleaning and self-repairing properties. Moreover, the coating was innovatively applied to the surface of the chute, because it remarkably reduced the adhesion between the wet foam block and the chute. These findings here provide a novel insight into the design of a robust SHP coating and suggest a new potential application in express sorting industry for drag reduction.

Ionic liquid-reinforced polybenzoxazine/urethane film with robust surface for recoverable adhesive tape substrate

Surface with low energy plays an irreplaceable role in antifouling coatings, national defense and military industry. However, low-energy surface has poor surface stability, which leads to the difficulty of recovery and massive waste. Thus, it is urgent to exploit low surface free energy materials with excellent surface stability. In this work, a series of ionic liquid-reinforced polybenzoxazine/urethane (poly(DHB/PU)) films was prepared, the dihydroxybenzoxazine (DHB), stearyldiethanolamine (SDEA) and hydroxyl-terminated polydimethylsiloxane (HTPDMS) introduced into the molecular chains provide the films low-surface-energy properties. Then, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid (IL) were added into the poly(DHB/PU) system. The comprehensive properties of the modified films were further improved, including recoverability, outstanding thermal stability (10 % weight loss temperature ranged from 270.51 to 308.51 °C), solvent resistance and low surface free energy (average 20 mN/m). Besides, the dense hydrogen bonds formed between imidazolium groups in IL and carbamates are the critical factor for optimizations of compatibility and mechanical properties. The higher the content of IL, the better the compatibility, the better the mechanical properties (elastic modulus varied from 63.32 MPa to 124.57 MPa) and the lower the peel strength (<7.975 gf/in) of the films. The synthesized polymer has great potential in the application of recoverable adhesive tape substrate.

The Thermo-Mechanical and Dielectric Properties of Superhydrophobic Pbz/TiO2 Composites

Polymer composites display the synergistic property of the polymer (matrix) and inorganic particles (filler material), when their combination is properly utilized. In the present work, polymer composites possessing a superhydrophobic property are fabricated by imposing the combination of both surface free energy and surface roughness. Polybenzoxazine (Pbz) is a choice of low surface free energy material and TiO2 particles contribute to create surface roughness. Thus, Pbz/TiO2 composites were fabricated by varying TiO2 contents to produce superhydrophobicity. The hydrophobicity increased from 94° for Pbz to 140° for Pbz/T5. The advantage of molecular design flexibility is also utilized to synthesize benzoxazine monomer (Bzo), which then undergoes thermally induced self-polymerization with different contents of TiO2 to produce Pbz-TiO2 composites. The structure analysis and curing behavior of the Bzo monomer was examined using FT-IR, NMR and DSC techniques. Whereas the properties of the Pbz/TiO2 composites were analyzed by WCA, SEM, DMA, TGA, and dielectric techniques.

Fiber-based photothermal, UV-resistant, and self-cleaning coatings fabricated by silicon grafted copolymers of chitosan derivatives and gallic acid

Superhydrophobic and hydrophobic properties are generally created by adopting low surface free energy materials. Therefore, most studies have focused on creating surface hydrophobicity by using hydrophobic or fluorinated materials. However, few studies are reported on realizing surface hydrophobicity by directly introducing hydrophilic molecules, which is also a challenge. Herein, with platinum nanozyme as the catalyst, the novel hydrophobic coatings have been rapidly gained via anchoring the polymer of hydrophilic gallic acid and chitosan or chitosan quaternary ammonium salt onto cotton fabric surface. Notably, the novel hydrophobic coatings exhibit significant advances compared with conventional hydrophobic ones created by utilizing fluorinated or hydrophobic materials, which breaks the limitation of employing low surface energy materials for gaining surface hydrophobicity. Subsequently, the sodium methyl silicate was grafted on the polymer's coatings to strengthen surface hydrophobicity and the abrasion resistance of hydrophobicity. Interestingly, the heating could induce the hydrophilicity of cotton fabric to recover to hydrophobicity. Moreover, the hydrophobic coatings also possess good photothermal conversion, UV resistance, and anti-oxidation activity for self-cleaning application and oil water separation. Briefly, the present work may open a new direction for preparing novel hydrophobic coatings by combining gallic acid and chitosan-based macromolecular carbohydrates.

Engineering construction of robust superhydrophobic two-tier composite membrane with interlocked structure for membrane distillation

The major challenge in membrane distillation for seawater desalination and/or wastewater purification is the development of high-efficiency membrane distillation (MD) membranes with high porosity, hydrophobicity, and adequate mechanical strength for long-term operation. Herein, a superhydrophobic two-tier interlocked composite membrane based on a hierarchically structured isotactic polypropylene (iPP) coating and an electrospun poly(vinylidene fluoride) (PVDF) nanofibrous support was engineering constructed. The obtained coating layer possessed a deformed micro/nanostructured microsphere surface with robust superhydrophobicity and further glorious anti-fouling property, which was owed to the synergistic effect of the low surface free energy material and hierarchical roughness. Specially, the middle transitional interlocking zone between the crystalline iPP microsphere coating and PVDF nanofibers endowed the resultant composite membrane with excellent structural integrity including the remarkable enhancement in mechanical performance compared with PVDF flat sheet or nanofibrous membranes, and also resulted in the iPP/PVDF composite membranes with robust durability against ultrasonication in isopropanol and strong acid/base attacks. Moreover, for the simulated high salinity sunset yellow (SY) wastewater, the optimized superhydrophobic composite membrane exhibited a competitive permeate flux of 53.9 kg/(m2·h) and complete rejection over 50 h operation (ΔT = 40 °C) because of its highly porous nanofibrous support and firmly sustainable liquid repellency.

Morphology-controllable gold hierarchically micro/nanostructured arrays prepared by electrodeposition on colloidal monolayer and their structurally related wettability

In this paper, we demonstrated a clean fabrication of the morphology-controllable gold hierarchically micro/nanostructured arrays (HMNAs) by electrochemical deposition on polystyrene monolayer colloidal crystal template. Through varying cathodic current density and deposition time to adjust electrocrystallization process, the HMNAs can be controlled from the one with microspheres and nanoparticles to the one with microbowls and nanorods. Further adjusting the nucleating sites via ion-sputtering deposition of gold film over the polystyrene spheres, we designed and prepared a new kind of HMNA with microspheres and nanowimbles. Interestingly, these Au HMNAs exhibited structurally related wettability. Correlated with their different hierarchical micro/nano-structures, they all showed superhydrophobicity after surface modification of low surface free energy material while with different surface adhesions. A water droplet can pine on the surface of the concave Au HMNA with microbowls and nanorods even turned upside down, showing ultrahigh liquid-solid adhesion. However, the convex Au HMNA with microspheres and nanowimbles shows very low surface adhesion with a sliding angle close to zero. These surface adhesion-controlled superhydrophobic surfaces can be found many potential applications, such as self-cleaning surfaces, liquid transportation, and multifunctional microfluidic devices.

Solid-Liquid-Liquid Wettability of Surfactant-Oil-Water Systems and Its Prediction around the Phase Inversion Point.

Surfactant-oil-water (SOW) systems are important for numerous applications, including hard surface cleaning, detergency, and enhanced oil-recovery applications. There is limited literature on the wettability of solid-liquid-liquid (SLL) systems around the surfactant phase inversion point (PIP), and the few references that exist point to wettability inversion accompanying the microemulsion (μE) phase inversion. Despite the significance of this phenomenon and the extreme changes in contact angles, there are no models to predict SLL wettability as a function of proximity to the PIP. Recent works on SLL wettability in surfactant-free systems suggest that SLL contact angles can be predicted with an extension of Neumann's equation of state (e-EQS) if the interfacial tension (IFT or γo-w) is known and if there is a good estimate for the interfacial energy between the wetting phase and the surface (γS-wettingliquid). In this work, IFT predictions for SOW systems around the PIP were obtained via the combined hydrophilic-lipophilic difference (HLD) and net-average-curvature (NAC) framework. To test the hypothesis that the combined HLD-NAC + e-EQS can predict wettability inversion around the PIP, with a given γS-μE, the contact angles (measured through the light oil phase, θO) for the μE of sodium dihexyl sulfosuccinate-toluene-saline water system were measured on high surface free energy (SFE) materials (glass, stainless steel, and mica) and on polytetrafluoroethylene (low SFE) around the PIP. Considering that at the PIP, most systems have a contact angle of 90°, an estimated γS-μE = 1/4γo-w@PIP was found to be suitable for the systems considered in this work and for systems presented in the literature. The largest deviations between the predictions and the experimental values were found in the positive HLD range (surfactant in the light oil phase). Although there is room for improvement, this framework can estimate the wetting behavior of SOW systems starting solely from formulation parameters.

Effect of groups at α-position and side-chain structure of comonomers on surface free energy and surface reorganization of fluorinated methacrylate copolymer

Surface free energy and surface reorganization, two essential properties for low surface free energy materials, have been researched by studying the effects of the groups (H or CH3) at α-position and the side-chain structures (flexible or rigid) of alkyl (meth)acrylate on a series of fluorinated copolymers poly (perfluorohexylethyl methacrylate)-co-poly [alkyl (meth)acrylate]. The static contact angle, X-ray photoelectron spectroscopy (XPS), and surface tension studies indicate that both the groups at α-position and the side-chain structures of alkyl (meth)acrylate can significantly influence the arrangement of perfluoroalkyl chains at the interface, resulting in different fluorine-enriched concentrations on the interface, which will finally affect the surface free energy of the copolymer. The dynamic contact angle measurement shows that the surface reorganization of the fluorinated chains are directly associated with the Tg of these copolymers, and decrease with the increasing Tg. All these results show that the copolymers containing H at the α-position and flexible side-chain in comonomer have lower surface free energy and higher surface reorganization, while the steric hindrance effects of α-methyl groups and/or rigid side-chain in comonomer allow the copolymers having higher surface free energy and lower surface reorganization.

Super-Hydrophobic Surface Prepared by Lanthanide Oxide Ceramic Deposition Through PS-PVD Process

Super-hydrophobic surface has received widespread attention in recent years. Both the surface morphology and chemical composition have significant impact on hydrophobic performance. A novel super-hydrophobic surface based on plasma spray-vapor deposition was introduced in the present paper. Samaria-doped ceria, which has been proved as an intrinsic hydrophobic material, was used as feedstock material. Additionally, in order to investigate the influence of surface free energy on the hydrophobicity, chemical modification by low surface free energy materials including stearic acid and 1,1,2,2-tetrahydroperfluorodecyltrimethoxysilane (FAS) was used on coating surface. Scanning electron microscopy and Fourier transform infrared spectroscopy were employed to characterize the coating surface. The results show that the obtained surface has a hierarchical structure composed by island-like structures agglomerated with angular-like sub-micrometer-sized particles. Moreover, with the surface free energy decreases, the hydrophobic property of the surface improves gradually. The water contact angle of the as-sprayed coating surface increases from 110° to 148° after modification by stearic acid and up to 154° by FAS. Furthermore, the resultant surface with super-hydrophobicity exhibits an excellent stability.

Reversible transition between superhydrophobicity and superhydrophilicity of a silver surface

Abstract In the present work, superhydrophobic silver surface was prepared by immersing a copper plate in an aqueous solution of AgNO 3 for 20 min. The sample exhibits superhydrophilicity after dried at 150 °C for 30 min in an oven. The as-prepared silver surfaces exhibit contact angle (CA) larger than 160° and sliding angle (SA) lower than 5°. Neither low surface free energy (SFE) materials nor organic compounds were used during the producing process. It was suggested that the spontaneously adsorbed carbon contaminant with low SFE was very critical for the superhydrophobicity of silver surface during heat treatment. Additionally, the silver surface could be switched between superhydrophobicity and superhydrophilicity by alternating UV irradiation and heat treatment for many times. Our findings in this work might provide a simple route to rational control the spontaneously adsorbed carbon contaminant on solid surface to endow the metal or other solid surfaces with superhydrophobicity or superhydrophilicity.

Polybenzoxazine a non-fluorinated polymer for anti-adhesion surface treatment of moulds

Polybenzoxazine (PBZ), a new class of low surface free energy material, is successfully used for anti-adhesion treatment on the patterned nickel mould surface. Bis (3-allyl-3, 4-dihydro-2H-1, 3-benzoxazinyl) isopropane (B-ala) type benzoxazine is prepared and characterisation of its thermosets are also described in this article. In addition, liquid phase deposition method is used for forming B-ala PBZ anti-adhesion layer with about 60 μm trench microstructures. However, the thickness affects the trench structures seriously, which involves the pattern of translating film. Apart from this, the process of depositing PBZ is investigated by utilising different solvent and concentrations. In the meanwhile the contact angles before and after B-ala PBZ deposition are analysed to confirm the performance of anti-adhesion. The morphologies of translating films after hundreds of imprints remain nearly unchanged. The experiment results show the lifetime of the nickel mould can be improved by depositing B-ala PBZ to the surface.

Synthesis and characterization of a novel siloxane‐imide‐containing polybenzoxazine

AbstractA novel siloxane‐imide‐containing polybenzoxazine based on N,N′‐bis(N‐phenyl‐3,4‐dihydro‐2H‐benzo[1,3]oxazine)‐5, 5′‐bis(1,1′,3,3′‐tetramethyldisiloxane‐1,3‐diyl)‐bis(norborane‐2,3‐dicarboximide) (BZ‐A1) was successfully synthesized. The thermal properties of BZ‐A1 are superior to those of conventional polybenzoxazines lacking siloxane groups. Polymerized BZ‐A1 possesses extremely low surface free energy (γs = 15.1 mJ m−2) after curing at 230 °C for 1 h. Moreover, the surface free energy of polymerized BZ‐A1 is more stable than conventional bisphenol A‐type polybenzoxazine during thermal curing and annealing processes, indicating that polymerized BZ‐A1 is more suitable for applications requiring low surface free energy materials for high temperatures over long periods of time. Copyright © 2010 Society of Chemical Industry

Adhesion Loss of Syrups in a Metering Glass Which Consists of a Low Surface Free Energy Material

We previously reported a strong positive correlation between syrup viscosity and the rate of syrup loss due to adhesion to a glass metering device. In this study, we examined differences in the surface free energies of metering devices made of different polymeric materials, since reducing adhesion loss to metering devices could improve the efficiency of drug preparation involving highly viscous syrups. Among metering devices made of glass only, glass with a silicone coating (SLC), polypropylene (PP), and polymethylpentene (PMP) the surface free energy of the glass-only metering device was the highest (49.2 mN/m). The adhesion loss obtained for highly viscous syrups in the PP and PMP metering devices was significantly lower than that of the glass metering device. Measurements of syrup contact angles suggested that in metering devices made of PP and PMP, which have low surface free energies, a decrease in the spreading wetting of syrups was a factor in reducing the rate of adhesion loss. Thus irrespective of the syrup viscosity being measured, metering devices produced from materials with low surface free energies can reduce the time required to prepare prescriptions without compromising the accuracy of drug preparation.

Computational analysis of fouling by low energy surfaces

Fouling is a cost increasing problem for a variety of industries including aerospace, chemical, petroleum, and food. There have been studies on mitigation of fouling some of which recommend use of lower surface free energy materials, manufactured by different techniques, as an alternative to conventional materials. Although modeling of fouling for a given surface has been an area of interest; there is a lack in the models about correlating the surface free energy with deposit amount computationally. In this study, computational model, including the effect of surface energy and operational parameters, was proposed and validated to estimate amount of foulants deposits and rate of deposition. Towards this purpose, four coated surfaces (Microlube/PTFE, TM117P, AMC148, and CNT) were compared with stainless steel (SS316 as control) for flow rates of 3 and 10 g/s and inlet milk temperatures of 40 and 60 °C. The percent error for the decrease in outlet milk temperatures between the experimental data and computed results was between 2% and 18% except for CNT (29.2%). The calculations of deposit amount for each test case and the surfaces tested were in good agreement with the experiments, i.e., average percent difference values between measured and calculated values were from 11.1% to 38.1% (except CNT) with overall average of 21.5%.

Effect of an Organically Modified Nanoclay on Low‐Surface‐Energy Materials of Polybenzoxazine

AbstractNovel low surface free energy materials of polybenzoxazine/organically modified silicate nanocomposites have been prepared and characterized. The CPC (cetylpyridinium chloride)/clay10%/poly(3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine) (PP‐a) material possesses an extremely low surface free energy (12.7 mJ · m−2) after 4 h curing at 200 °C, which is even lower than that of poly(tetrafluoroethylene) (22.0 mJ · m−2) calculated on the basis of the three‐liquid geometric method. X‐Ray photoelectron spectroscopy (XPS) shows a higher silicon content on the surface of the nanocomposites than for an average composition, which implies that the clay is more preferentially enriched on the outermost layer. In addition, the glass transition temperature (Tg) of the polybenzoxazine (PP‐a) in the nanocomposite is 22.6 °C higher and its thermal decomposition temperature is also 31.5 °C higher than the pure PP‐a. This finding provides a simple way to prepare low surface energy and high thermal stability materials.magnified image

Synthesis of Superhydrophobic Surface of Polyethylene via in Situ Ziegler-Natta Polymerization

Abstract A new strategy for fabricating superhydrophobic polyethylene (PE) surface by utilizing the feature of “morphology duplicating effect” of Ziegler-Natta catalysts was investigated. The Ziegler-Natta catalyst components (MgCl2 and TiCl4) were first intercalated in between the montmorillonite (MMT) gallery and then the PE/MMT nanocomposite was prepared by in situ Ziegler-Natta polymerization. The surface morphology of PE/MMT was highly rough with a petal-like microstructure. The film made from such a nanocomposite has the superhydrophobic performance with a water contact angle of (152.2 ± 0.8)° without any modification by the low surface free energy material.

Modification of Polymer Substrates with Low Surface Free Energy Material by Low‐Temperature Cured Polybenzoxazine

AbstractThe B‐ala/AIBN PBZ system has a high extent of ring‐opening of oxazine because phenol‐containing oligomers are formed at the early stage of the curing process. As a result, the B‐ala/AIBN PBZ system possesses a relatively stronger intramolecular hydrogen bonding and lower surface energy than the pure B‐ala system at low temperature curing. In this context, poly(4‐vinyl pyridine), poly(4‐vinyl phenol) thin films and polycarbonate substrates, which lack liquid resistance, possess low surface free energy after modification with B‐ala/AIBN = 5/1 PBZ.magnified image

Controllable superhydrophobic and lipophobic properties of ordered pore indium oxide array films

Using the polystyrene (PS) colloidal monolayers as templates, ordered indium oxide pore array films with different morphologies were prepared by sol-dipping method. These porous films took on hydrophilicity, however, after chemical modification, such pore array films displayed both superhydrophobicity and lipophobicity due to rough surface and low surface free energy materials on their surfaces. Interestingly, with increase of the pore size in the films, the superhydrophobicity could be controlled and was gradually enhanced due to the corresponding increase of roughness caused by nanogaps produced by the thermal stress in the annealing process with increase of film thickness.

Polybenzoxazine as a Mold-Release Agent for Nanoimprint Lithography

One of the most important tasks remaining to be resolved in nanoimprint lithography is the elimination of the resist sticking to the mold during demolding. Previously, the main approach was to apply a thin layer of fluorinated alkyl silane mold-release agent on the surface on the mold; however, this involves complicated steps and high costs. The low surface free energy material polybenzoxazine provides an efficient mold-release agent for silicon molds that is easier to process, costs less, and has no side reactions.