Application of polymer nanoparticle coating for tuning the hydrophobicity of cellulosic substrates

Nanoparticles of partially imidized poly(styrene–maleic anhydride) were applied from an aqueous dispersion as a one- or two-layer coating onto paper substrates, for controlling the paper surface hydrophobicity and improving the water barrier resistance. The effect of deposition conditions and thermal treatments on the topography and properties of the coating was studied by scanning electron microscopy, atomic force microscopy (AFM), contact angle measurements, and friction measurements. The wettability of paper surfaces with adsorbed nanoparticles can be controlled by tuning the chemical and topographical surface parameters: the water contact angles were found to increase at higher imide content as determined by Raman spectroscopy (depending on synthesis and thermal treatment), and higher average surface roughness determined by AFM (depending on the deposition method). The present technique may serve as a unique replacement for chemical treatments hydrophobizing fibrous substrates.     

Effect of roughness as determined by atomic force microscopy on the wetting properties of PTFE thin films

The influence of film roughness on the wetting properties of vacuum-deposited polytetrafluorethylene (PTFE) thin films has been investigated using atomic force microscopy (AFM) and contact angle goniometry. Surface roughness has been characterized by atomic force microscopy in terms of RMS roughness (R_q) and fractal dimensions. A contact angle correlation with surface roughness, as determined by AFM, is evident from these results, which are discussed on the basis of wetting theory. The results also confirm that the high water contact angles (as high as 150°) recently observed at the surface of a new water repulsive coating material (mixture of PTFE and binder) are because of surface roughness. Such measurements clarify the effect of nanometer-size surface asperities on the wetting properties of hydrophobic coating.     

Surface and mechanical properties of an organic-inorganic super- hydrophobic coating using modified nano-SiO2 and mixing polyurethane emulsion as raw materials

A series of organic-inorganic super-hydrophobic coatings were prepared using nano-SiO₂ particles modified by fluorine and silicone coupling agents, and a mixing polyurethane emulsion as main raw materials. The mixing polyurethane emulsion was consisted of the polyurethane emulsion end-terminated by double bond (WPUD) and polyurethane emulsion modified by silicone (WPUS). The influence of content of modified nano-SiO₂ particles and the weight ratio of WPUS to WPUD on microstructure and hydrophobicity of the coating surface were studied. The morphologies of coating surface were examined using SEM and AFM, hydrophobicity of the coating was researched by examining static water contact angle and so on. It was found that modified nano-SiO₂ particle was an indispensable factor during the preparation of super-hydrophobic coating. The roughness and hydrophobicity of the coating surface were enhanced obviously with an increase of the content of the modified nano-SiO₂ particles. When the content of the modified nano-SiO₂ particles increased up to 1.5%, the surface of coating possessed good super-hydrophobicity, and static water contact angle reached 169.1°. It was also noticed that the weight ratio of WPUS to WPUD in the base layer has also an important influence on the hydrophobicity and mechanical property of coating surface. With an increase of the ratio of WPUS to WPUD the hydrophobicity of the coating was enhanced, the tensile strength and peel strength reduced, but the elongation at break increased. When the weight ratio of WPUS to WPUD reaches up to 9/100, the static water contact angle reaches the maximum value of 169.1°.     

Comparison of drag characteristics of self-polishing co-polymers and silicone foul release coatings: A study of wettability and surface roughness

An experimental study has been carried out to evaluate the drag characteristics of different self-polishing co-polymers (SPC) (tin based and tin-free) and a silicone foul release (FR) coating. Drag measurements have been performed on a smooth aluminum cylinder connected to a rotor device. Various coatings on cylinders were examined and differential length technique was also used to avoid the end effects during rotation. Surface energy of the coated samples was determined using static contact angle measurement. Characteristic roughness measurements of the coated surfaces were evaluated with atomic force microscopy (AFM) technique.Drag measurements showed that the frictional resistance of the FR coated cylinders was lower than that of SPC coated samples.Contact angle results showed that the critical surface tension and its polar component for silicone FR coating are less than SPC coatings. This prevents firm adhesion of fouling organisms on underwater hulls.AFM studies revealed a lower surface roughness for silicone FR coating as compared to SPC coatings. Also, its surface texture is considerably different from SPC coatings.It can be concluded that the drag characteristics of a surface are affected by its free energy and roughness parameters.     

Preparation of transparent ultrahydrophobic silica film by sol�Cgel process

Transparent ultrahydrophobic films were synthesized by sol–gel process with organic silicones modified into silica sol and cured under UV irradiation. The effects of hydrolysis temperature, hydrolysis time, molar ratio of organic silicone to silica sol, and surface morphology on the hydrophobicity of the films were discussed in detail using FTIR spectroscopy, scanning electron microscopy (SEM), AFM, optical transmission, and contact angle measurement, respectively. The AFM and SEM images indicated that the surface roughness enhanced the hydrophobicity of the films. The results revealed that methyl-trimethoxysilane (MTMS)-modified silica film prepared at 50°C for 2 h with an MTMS/silica sol molar ratio of 1:10 had a very high contact angle (130°). However, the higher hydrolysis temperature and longer reaction time might have accelerated the self-condensation of silanol and decreased the contact angle of the films.     

表面沉积化镁合金基底上超疏水聚偏氟乙烯微孔膜的制备与性能

用一步浸泡法制得表面沉积化镁合金板,再以此镁合金板为制膜基底,以聚偏氟乙烯（PVDF）/N,N-二甲基乙酰胺（DMAc）/辛醇/水为制膜体系,采用干-湿相转化法制备了超疏水PVDF膜,该膜的水接触角可达160°。用粗糙度仪、扫描电镜、能谱仪、红外光谱仪等对镁合金表面和PVDF膜底面的微观结构、化学组成进行表征和分析。研究表明,一步浸泡处理过的镁合金表面生成了均匀的十四酸铁沉积物,该沉积物可在膜制备中部分嵌入膜底面,增加了膜底面的粗糙度,从而使PVDF膜的疏水性大幅提高。对PVDF膜的磨损试验表明,所制备的超疏水膜表面具备良好的机械稳定性。真空膜蒸馏实验表明,所制备的PVDF膜具有较高的通量和截留率,在运行中保持了更好的操作稳定性。     

Antibacterial polymeric coating based on polypyrrole and polyethylene glycol on a new alloy TiAlZr

In order to enhance properties of the polymer composite films, composite coatings based on polypyrrole (PPy) and polyethylene glycol (PEG), using various percentages of PEG (0.5%, 2%, 4%), were electrodeposited on a new titanium alloy electrode as insulating material. The structure of the coatings was investigated via infrared (FTIR) analysis, and the surface features were studied using contact angle determination, atomic force microscopy (AFM) and scanning electronic microscopy (SEM). When testing the antibacterial properties of the coatings, the best effect was found for the coating with 2% PEG concentration, which has hydrophilic character and small roughness. Such results are in concordance with mechanism of biomaterial–bacteria interaction which involves as factors affecting bacterial adhesion and growth an initial physicochemical interaction stage, where roughness and wettabilitty are factors promoting bacterial adhesion and biofilm deposition.     

Formulation and properties of a model two-component nanocomposite coating from organophilic nanoclays

Polyurethane bicomponent coatings have been modified by formulation with different amount (2–6% by weight) of organophilic nanoclays according to a solution blending procedure. The clays (indicated as 72T and 30B) differ each other in the nature and polarity of the organic quaternary ammonium salt. After application and curing the coatings were characterized by X-rays diffraction (XRD), contact angle measurements, atomic force microscopy (AFM), dynamic-mechanical analysis, tensile tests. The presence of clay additives enhances both modulus and strength of coating materials, and shows some effect also on surface hydrophobicity. The more polar 30B clay seems to form more homogeneous and smoother surfaces, and also a higher coating toughness is retained. Solvent swelling measurements were carried out in toluene allowing the estimate of the extent of clay exfoliation in the material. These measurements along with XRD result suggest that only a partial delamination was achieved.     

Comparison of drag characteristics of self-polishing co-polymers and silicone foul release coatings: A study of wettability and surface roughness

An experimental study has been carried out to evaluate the drag characteristics of different self-polishing co-polymers (SPC) (tin based and tin-free) and a silicone foul release (FR) coating. Drag measurements have been performed on a smooth aluminum cylinder connected to a rotor device. Various coatings on cylinders were examined and differential length technique was also used to avoid the end effects during rotation. Surface energy of the coated samples was determined using static contact angle measurement. Characteristic roughness measurements of the coated surfaces were evaluated with atomic force microscopy (AFM) technique.

Drag measurements showed that the frictional resistance of the FR coated cylinders was lower than that of SPC coated samples.

Contact angle results showed that the critical surface tension and its polar component for silicone FR coating are less than SPC coatings. This prevents firm adhesion of fouling organisms on underwater hulls.

AFM studies revealed a lower surface roughness for silicone FR coating as compared to SPC coatings. Also, its surface texture is considerably different from SPC coatings.

It can be concluded that the drag characteristics of a surface are affected by its free energy and roughness parameters.     

Tuning of polypropylene wettability by plasma and polyhedral oligomeric silsesquioxane modifications

In this work, we have exposed polypropylene (PP) to plasma treatment and then reactively coated with polyhedral oligomeric silsesquioxane-isothiocyanate (POSS-NCS) in order to modify both of its surface characteristics: chemical composition and roughness. The results of scanning electron microscopy (SEM), atomic force microscopy (AFM), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) showed a strong relation between plasma exposure time and PP roughness, as expected. On the other hand, the POSS-coating promoted the reduction of surface roughness, but induced a substantial increase in the water contact angle (WCA), probably due to the modification of the surface chemical nature. Besides, the surface tuning method discussed here is a fast, industrial-suitable procedure which can be applied to different polymers.     

Surface energy of metal containing amorphous carbon films deposited by filtered cathodic vacuum arc

Metal containing amorphous carbon (a-C:Me) films including a-C:Al, a-C:Ti, a-C:Ni, a-C:Si were prepared by the filtered cathodic vacuum arc (FCVA) technique with metal-carbon (5 at.% metal) composite targets. The substrate bias ranging from floating to 1000 V was applied. The wettability of the films was examined using the VCA Optima system from AST Products, Inc. Three types of liquid with different polarities were used to study the surface energy changes of the films. X-ray photoelectron spectroscopy (XPS) was used to analyze the composition and chemical state of the films. Atomic force microscopy (AFM) was employed to characterize the morphology and roughness of the films. The contact angle of the a-C:Me films remains relatively constant with different substrate bias. The Al containing films show the highest contact angle with water, which reaches as high as 101°. The Si containing films show the lowest contact angle approximately 64°. The contact angles of Ni and Ti containing films are approximately 80°, 97°, respectively. The harmonic-mean method was used to calculate the polar and depressive component of the surface energy. The absorption of oxygen on the surface plays an important role on the polar component of the a-C:Me films. The formation of AlO and TiO bonds is responsible for their lower polar component. The metal state Ni results in higher polar component. However, the SiO bond is contributed to the high polar component of a-C:Si films. As all films are atomic scale smooth, the RMS roughness is below 0.5 nm, the roughness does not have obvious effect on the surface energy.     

Effect of surface pre-treatment on surface characteristics and adhesive bond strength of aluminium alloy

In this work aluminium alloy surfaces have been subjected to three different methods of surface pre-treatments such as solvent degreasing, FPL (Forest Products Laboratory) etching and priming using an epoxy based primer. The treated surfaces were evaluated for surface energy, contact angle, surface topography, surface roughness and adhesive strength characteristics. The influence of surface pre-treatments on the variation of polar, dispersive and total surface energy of the surfaces is addressed. A wettability test was performed on the surfaces using an epoxy adhesive in order to assess the influence of the pre-treatment techniques on substrate/adhesive interaction. Theoretical work of adhesion values for the various pre-treated surfaces were calculated using the contact angle data and further tested experimentally by adhesive bond strength evaluation by tensile testing of a single lap aluminium-epoxy-aluminium assembly. The method of surface pre-treatment showed a profound effect on the surface topography and roughness by AFM. This study reveals that a combination of high surface energy and high surface roughness of the substrate along with good wettability of the adhesive contributed to the highest joint strength for the aluminium alloy through the FPL etching pre-treatment.     

AFM measurements of hydrophobic forces between a polyethylene sphere and silanated silica plates- the significance of surface roughness

Recently, substantial research effort has been devoted to the study of non-DLVO forces between hydrophobic surfaces. However, the significance of surface roughness in the analysis of these hydrophobic attractive forces has not been given sufficient consideration and research is now in progress to attend to this issue. Fused silica plates covered with adsorbed octadecyltrichlorosilane (OTS) were characterized by water contact angle measurements and atomic force microscopy (AFM). Surfaces with different surface coverages and different contact angles were obtained by variation of the adsorption time. OTS formed patches on the silica surfaces, the lateral size and height of which depended on the adsorption time. Such surfaces exhibit differences in roughness at the sub-nanometer level. Using the AFM colloidal probe technique, forces between a polyethylene sphere and silanated silica surfaces were measured in water. Long-range attractive forces were found, usually referred to as hydrophobic forces. The resulting force vs. distance curves were fitted with a double exponential function. The magnitude of the short-range part of the force curves seems to correlate with water contact angles at silanated silica surfaces. On the other hand, the range of the long-range force correlates with the roughness of the silanated silica surface. These results with silanated silica surfaces were compared with the AFM results for polyethylene and graphite surfaces and on the basis of these experimental efforts, it appears that the nature of these hydrophobic attractive forces is related to surface roughness.     

Evaluation of Ni‐Mo and Ni‐Mo‐P Electroplated Coatings on Stainless Steel for PEM Fuel Cells Bipolar Plates

Stainless steel bipolar plates (BPPs) are the preferred choice for proton exchange membrane fuel cells (PEMFCs); however, a surface coating is needed to minimize contact resistance and corrosion. In this paper, Ni–Mo and Ni–Mo–P coatings were electroplated on stainless steel BPPs and investigated by XRD, SEM/EDX, AFM and contact angle measurements. The performance of the BPPs was studied by corrosion and conduction tests and by measuring their interfacial contact resistances (ICRs) ex situ in a PEMFC set‐up at varying clamping pressure, applied current and temperature. The results revealed that the applied coatings significantly reduce the ICR and corrosion rate of stainless steel BPP. All the coatings presented stable performance and the coatings electroplated at 100 mA cm⁻² showed even lower ICR than graphite. The excellent properties of the coatings compared to native oxide film of the bare stainless steel are due to their higher contact angle, crystallinity and roughness, improving hydrophobicity and electrical conductivity. Hence, the electroplated coatings investigated in this study have promising properties for stainless steel BPPs and are potentially good alternatives for the graphite BPP in PEMFC.     

Photocatalytic activity of thin TiO2 films deposited using sol–gel and plasma enhanced chemical vapor deposition methods

Thin titanium dioxide films, deposited using RF PECVD and sol–gel techniques, were studied comparatively with respect to their bactericidal as well as self-cleaning properties. The effect of the deposition process on film morphology, chemical and crystalline structure, bactericidal activity and hydrophilic properties was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), surface profilometry, optical microscopy and contact angle measurements. It was found that the bactericidal activity of amorphous TiO₂ films, produced using the RF PECVD method, as either comparable to or better than those of crystalline (anatase) films deposited by means of the sol–gel technique. One reason for such advantageous behavior of plasma deposited materials is thought to be their substantially higher surface roughness, as revealed by AFM measurements. The hydrophilic effect, induced with UV irradiation, was strongest in the case of sol–gel films, but the RF PECVD synthesized coatings were found to be only slightly less hydrophilic. The conclusion follows that both sol–gel and RF PECVD techniques are equally capable of producing titanium dioxide films of high photocatalytic quality.     

Surface properties and moisture behaviour of pine and heat-treated spruce modified with alkoxysilanes by sol–gel process

The surface morphology and moisture behaviour of pine (Pinus sylvestris) sapwood and heat-treated spruce (Picea abies) deposited with two types of silane-based sol–gel coatings were studied by atomic force microscopy (AFM) and water contact angle measurement. The chemical composition and distribution of sol–gel coatings on wood surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The AFM images revealed that the sol–gel coatings applied by spreading covered the fine structure of the wood substrates. The surface roughness analysis of the AFM topographical images indicated that the sol–gel coatings, especially the one with short aliphatic chain, had a tendency to smooth the wood surface. The XPS results confirmed that the sol–gel coatings had successfully deposited onto pine sapwood and heat-treated spruce changing their surface chemistries. ToF-SIMS images showing Si ion distribution on treated surfaces revealed that the coatings fully covered pine sapwood surfaces. The thin coating layers formed on heat-treated spruce surfaces followed the original wood surface structure. The contact angle measurements indicated that the water repellent properties of both pine and heat-treated spruce were improved to certain extent by the sol–gel coatings.     

Fabrication of superhydrophobic unplasticized poly(vinyl chloride)/nanosilica sheets using Taguchi design methodology

This study introduces a relatively simple technique for the manufacture of superhydrophobic coatings on polymeric surfaces. Plastics such as unplasticized poly(vinyl chloride) (UPVC ) do not have a strong hydrophobic nature that is characterized by their low contact angles. Techniques of both increasing surface roughness and lowering surface energy are required to change their hydrophilicity to superhydrophobicity. In the present study, a coating of a low‐surface‐energy thermoplastic polyurethane (TPU ) was spin‐coated with chemically treated nanosilica to reduce the surface energy of UPVC . Nanosilica particles were embedded on the surface using a hot‐press. Taguchi design was used to optimize multiple processing parameters. Samples spin‐coated with 10 g L^?1 nanosilica suspension in ethanol at a rate of 400 rpm for 5 s and then hot‐pressed at 155 °C under 2 atm (203 kPa ) for 4 min had a contact angle of ca 157° and sliding angle of ca 6°, which are characteristic of superhydrophobic surfaces. Atomic force microscopy (AFM) and scanning electron microscopy (SEM ) imaging showed that these superhydrophobic surfaces were highly rough with nanoscale features. Peel test and SEM analysis showed that silica nanoparticles embedded in the TPU coating were more stable than particles immobilized on UPVC sheet without TPU coating, proving that a layer of more flexible coating can improve the longevity of superhydrophobic surfaces manufactured using this facile method. © 2016 Society of Chemical Industry     

Electro-assisted preparation of dodecyltrimethoxysilane/TiO2 composite films for corrosion protection of AA2024-T3 (aluminum alloy)

Thin films of organosilanes have been successfully used as the alternative to toxic chromate coatings for surface pretreatment of metals and alloys. To further improve their corrosion performance, in the present work nano-scaled TiO₂ particles were added to the dodecyltrimethoxysilane (DTMS) films coated onto AA2024-T3 substrates, by using either the dip-coating or the cathodically electro-assisted deposition process. The obtained composite films were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle measurements, Fourier transform reflection-absorption IR (FTRA-IR) and electrochemical impedance spectroscopy (EIS). The results show that these two techniques (nanoparticles incorporation and the electro-assisted deposition) both facilitate the deposition process of silane films, giving thicker deposit and higher coverage surface along with higher roughness and hydrophobicity, and thereby improve their corrosion resistance. Moreover, the corrosion performance of silane films is further improved by the combined use of nanoparticles modification and electro-assisted deposition.     

Evaluation of CrAlN multilayered coatings deposited by PVD magnetron sputtering

The purpose of this experimental work is to evaluate the mechanical and tribological properties of chromium aluminum nitride (CrAlN) coating deposited on hypereutectic Al–Si-alloy. The microstructural, topographical analysis, and composition of CrAlN-coated substrates were examined by using scanning electron microscopy and energy-dispersive spectroscopy, whereas phase formation was analyzed by X-ray Diffractometer (XRD). Atomic force microscopy (AFM) images were taken from the substrate surface before and after the coating. The scratch adhesion of film-to-substrate was measured by using scratch machine. In an effort to understand the critical point, loads were identified by Scratch track in terms of load vs. depth as a function of scan distance. Moreover, the critical load as the beginning of chipping or spallation of the coating was studied. The tribological properties of CrAlN coating were evaluated by pin on disc tribometer at room temperature. XRD analysis showed that CrAlN successfully deposited with a preferential orientation along the (1?1?1), (2?0?0) and (2?2?0) peaks. The AFM images of coated sample confirmed that the surface roughness was lower(R_a = 14 nm) as compared to uncoated sample (R_a = 46 nm). The hardness of coated hypereutectic Al–Si-alloy was increased about 5.8 times as compared to uncoated sample. The coefficient of friction and wear rate of coated specimen were found to be improved. The coating adhesion strength of 2341 mN was obtained with coating parameters for deposition of DC power (350 W), RF power (200 W), temperature (175 °C), and nitrogen flow rate (5%).     

HMMM cured corrosion resistance waterborne ormosil coating for aluminum alloy

Due to the exceptional advantages of sol–gel process, organically modified silane (ormosil) coating has been applied to study the corrosion protection of aluminum alloy. In the present work, GPTMS/MTMS sol–gel solution was prepared by hydrolysis and condensation of 3-glycidoxypropyltrimetoxysilane (GPTMS) and methyltrimethoxysilane (MTMS) in aqueous solution of 0.05 M acetic acid in molar ratios 3:1. To prepare the ormosil coating solutions, a crosslinking agent hexamethoxymethylmelamine (HMMM) and a blocked acid catalyst p-toluenesulphonic (p-TSA) were combined with the sol–gel solution. Aluminum substrates were dip coated and cured at 130 °C for 45 min. Effectiveness of HMMM as a crosslinking agent was analyzed by evaluating corrosion resistance, chemical resistance and hydrophobicity of coating using potentiodynamic polarization method, immersion test and water contact angle, respectively. UV stability of sol–gel solution, ormosil coating formulation and coated substrate was also studied using UV–vis spectroscopy and UV-weatherometer to see performance of coating in outdoor application. Thermal behavior of ormosil was characterized using TGA and DSC. Surface morphology and structural characteristics were also characterized using SEM, AFM and FT-IR-RAS (reflection absorption spectroscopy). Pencil hardness, impact test and bend test were carried out to determine the adhesion, hardness and flexibility of coating.