Hydrophobic recovery of repeatedly plasma-treated silicone rubber. Part 2. A comparison of the hydrophobic recovery in air,water, or liquid nitrogen

Surfaces of medical grade silicone rubber (Q7-4750, Dow Corning) were modified by repeated (six times) RF plasma treatments using various discharge gases: oxygen, argon, carbon dioxide, and ammonia. The treated samples were stored for a period of 3 months in ambient air, water, or liquid nitrogen. Subsequently, the temporal behavior of the effects of the plasma treatment on the physicochemical surface properties of the silicone rubber was investigated using water contact angle measurements and X-ray photoelectron spectroscopy (XPS). Hydrophobic recovery during 3 months storage in ambient air was considerable and nearly complete for all four plasmas used. Hydrophobic recovery was almost completely suppressed during storage in liquid nitrogen, and only a minor increase of around 10° in advancing water contact angle was observed for all four plasma treatments. Also during storage of treated samples in water, hydrophobic recovery was minimal and initiated again by returning the treated samples to ambient air. XPS analyses showed that argon, carbon dioxide, and ammonia plasma-treated silicone rubber all had increased carbon percentages at the expense of oxygen and silicon after storage in water, or in liquid nitrogen, compared with after storage in ambient air. Interestingly, the carbon content of oxygen plasma-treated silicone rubber decreased during storage in water, or in liquid nitrogen, compared with storage in ambient air, while its oxygen and silicon percentages increased.     

Aging effects of repeatedly glow-discharged polyethylene: influence on contact angle,infrared absorption,elemental surface composition,and surface topography

Aging effects of repeatedly oxygen glow-discharged polyethylene surfaces were determined by water contact angle measurements, infrared (IR) spectroscopy, X-ray photoelectron (XPS) spectroscopy, and surface topography determination. Glow-discharged surfaces were stored at room temperature and in liquid nitrogen for 8 days prior to the next glow-discharge (Gld) treatment. This cycle was repeated up to 13 times. Hydrophobic recovery of the polyethylene surface, as determined by contact angle measurements, became less when the number of glow-discharge treatments increased. Hydrophobic recovery was suppressed when the samples were stored in liquid nitrogen. After five glow-discharge treatments it was possible to detect the incorporation of hydroxy groups by IR spectroscopy, while XPS spectroscopy showed that repeated glow-discharge gives rise to a higher oxygen to carbon ratio and a broadening of the C_Is peak, suggesting the incorporation of C-O and C=O bonds in the surface layer of polyethylene. The surface roughness of repeatedly glow-discharge-treated polyethylene remained almost unaltered in the submicrometer range (0.30-0.35 μm), although scanning electron microscopy revealed fine-grained structures for samples after a large number of Gld treatments. It can be concluded from this study that repeated oxygen glow-discharge treatments of polyethylene create more stable, hydrophilic surfaces than can be obtained with only one treatment. However, even after repeated glow-discharge treatments, polymer surface dynamics cause a small hydrophobic recovery.     

Surface modification of nylon 6 films treated with an He/O2 atmospheric pressure plasma jet

To investigate the effect of the gas composition of the plasma treatment on the surface modification of an atmospheric pressure plasma jet (APPJ), nylon 6 films were treated with APPJ with pure helium (He), He + 1% oxygen (O₂), and He + 2% O₂, respectively. Atomic force microscopy showed increased surface roughness, whereas X‐ray photoelectron spectroscopy revealed increased oxygen contents after the plasma treatments. The plasma‐treated samples had lower water contact angles and higher T‐peel strengths than the control. The addition of a small amount of O₂ to the He plasma increased the effectiveness of the plasma treatment in the polymer surface modification in terms of surface roughness, surface oxygen content, etching rate, water contact angle, and bonding strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Hydrophobic recovery of femtosecond laser processed silicone rubber insulator surfaces

This article demonstrates the loss and recovery in hydrophobicity of silicone rubber insulator surface processed by a femtosecond laser. The two stages of the wettability conversion were investigated. First, a rough micro/nano structure was formed on the original hydrophobic sample surface processed by the femtosecond laser, and the water contact angle on the surface was reduced from ~ 110° to a minimum of ~ 35°. This hydrophilicity loss was due to the increase in the hydrophilic  OH groups and the reduction of the hydrophobic  CH₃ groups on the surfaces. Second, the roughened samples were stored in a natural ambient environment. Over a certain storage time, the surface hydrophobicity recovered gradually and evolved into a superhydrophobic state. It was found that the migration of low molecular weight cycle and/or linear siloxane oligomers resulted in the recovery of the hydrophobicity property. Coupled with the increase of surface roughness caused by laser irradiation, the further evolution of the hydrophobicity was promoted. Moreover, the higher temperature accelerates the recovery of the surface hydrophobicity. The research on the conversion mechanism of the wettability on the silicone rubber insulator surface processed by femtosecond laser is of great significance for improving its reliability in practical applications.     

Treatment with Ar–O2 low-pressure plasma of vulcanized rubber sole containing noticeable amount of processing oils for improving adhesion to upper in shoe industry

Vulcanized rubber (L3 rubber) containing intentionally noticeable excess of processing oils in its formulation was treated with Argon–Oxygen (Ar–O₂) (2:1, vol/vol) low-pressure (LP) plasma for achieving a satisfactory level of adhesion to waterborne polyurethane adhesive. The effectiveness of the Ar–O₂ LP plasma treatment of L3 rubber depended on both the configuration of the plasma chamber shelves and the treatment time. Surface modifications were assessed by attenuated total reflectance-IR and X-ray photoelectron spectroscopy, contact angle measurements, and scanning electron microscopy. Ar–O₂ LP plasma treatment in direct configuration provided the most effective surface modification of the L3 rubber, and the increase in the treatment time improved the extent of the surface modifications. However, even important surface modifications were produced by Ar–O₂ LP plasma treatment, adhesion of treated L3 rubber was not improved due to the creation of weak boundary layer at the polyurethane–rubber interface after joint formation. Heating at 80 °C for 12 h of the as-received L3 rubber prior to Ar–O₂ LP plasma treatment enhanced the extent of the surface modifications, and improved adhesion was obtained for Ar–O₂ LP plasma treatment times higher than 600 s.     

SURFACE MODIFICATIONS AND ADHESION OF VULCANIZED SBR RUBBER TREATED WITH RF PLASMAS OF DIFFERENT GASES

The surface modifications produced by treatment of a synthetic vulcanized styrene-butadiene rubber (R1) with oxidizing (oxygen, air, carbon dioxide) and nonoxidizing (nitrogen, argon) RF plasmas have been assessed by ATR-IR and XPS spectroscopy, SEM, and contact angle measurements. The effectiveness of the treatment depended on the gas atmosphere used to generate the RF plasma. In general, acceptable adhesion values of treated R1 rubber were obtained for all plasmas, except for the nitrogen plasma treatment during 15 min, due to the creation of weak layers of low molecular weight moieties on the outermost R1 rubber layer. A toluene wiping of the 15 min N₂-plasma-treated R1 rubber surface removed those moieties, and increased adhesion was obtained. On the other hand, the air, carbon dioxide, and oxygen plasmas produced ablation of the R1 rubber surface, whereas mechanical degradation was not produced by treatment with the Ar plasma.     

Improvement of adhesion strength of self-adhesive silicone rubber on thermoplastic substrates – Comparison of an atmospheric pressure plasma jet (APPJ) and a Pyrosil® flame

Polymeric hard/soft combinations consisting of a rigid, thermoplastic substrate and an elastomeric component offer many advantages for plastic parts in industry. Manufactured in one step by multi-component injection moulding, the strength of the thermoplastics can be combined with sealing, damping or haptic properties of an elastomer. Bonds of self-adhesive liquid silicone rubber (LSR) on high performance thermoplastics such as polyetheretherketone (PEEK) or polyphenylene sulphide (PPS) are especially interesting e.g. for medical applications due to their outstanding resistance properties. To ensure good adhesion between the two components, surface treatments from an atmospheric pressure plasma jet (APPJ) and a Pyrosil® flame are applied. Chemical changes on the thermoplastic surfaces are verified by water contact angle measurement (CA) and X-ray photoelectron spectroscopy (XPS). Plasma treatment causes a decline in water contact angle, indicating the formation of functional groups, especially –OH, on the surface. XPS measurements confirm the increase of oxygen on the surface. Thus, the number of functional groups on the thermoplastic surface is enlarged by plasma treatment, leading to stronger bonding to the organofunctional silanes of the self-adhesive silicone rubber. A thin layer of silanol groups is created by the Pyrosil® flame on the thermoplastic substrates, which could be verified by XPS. A hydrophilic behaviour of the coated surface is noticed. Both surface modification methods lead to enhanced adhesion properties of self-adhesive LSR on thermoplastic surfaces. This is confirmed by 90°- peel tests of the injection-moulded composites leading to an increase in peel force by the applied surface modification techniques.     

Surface biomedical effects of plasma on polyetherurethane

Surface biomedical effects of plasma treatment and plasma polymerization on medical-grade polyetherurethane were studied. N₂ and Ar plasma treatments and hexamethyldisiloxane (HMDS) plasma polymerization were performed at a power of 100 W with exposure times ranging from 1 to 15 min. The results showed that the contact angle of water was decreased from 79° to 62° by N₂ and Ar plasma treatments, and N₂ plasma treatment caused a slight enhancement in anti-coagulability and anti-calcific behavior. HMDS polymerization resulted in a decrease from 79° to 43° in the contact angle and an increase from 30.5 to 37.4 s in the recalcification time. At the same time, the anti-coagulability of polymerized samples for the exposure time of 2-5 min was 2.5 times that of the untreated sample. Results of XPS and ESR analyses showed that HMDS deposited onto the polyetherurethane surface and formed new Si-N bonds, and increased the number of radicals in the sample. XPS analysis also showed that N₂ and Ar plasma treatments broke some of the C-O and C=O bonds at the surface and resulted in oxidation of the surface.     

Stretchable Gold Tracks on Flat Polydimethylsiloxane (PDMS) Rubber Substrate

A process to fabricate stretchable gold tracks on silicone rubber substrates is studied by XPS, static water contact angle measurement, AFM, and SEM. The process involves several steps: removing uncured oligomers by hexane Soxhlet extraction; pre-stretching the substrate; activating the strained silicone surface by an oxygen plasma treatment; coating the strained substrate with 5 nm titanium and 80 nm gold layers; and finally releasing the sample. The plasma treatment creates a thin brittle silica-like layer that temporarily increases the substrate's surface energy. Indeed, the plasma treatment is followed by a hydrophobic recovery. As a consequence, the delay between plasma treatment and metal deposition has to be reduced as much as possible. The silica-like layer can be nicely observed after release. The entire process allows us to obtain stretchable metallized samples that remain conductive even after an excessive deformation leading to electrical failure.     

Tailoring the Surface Properties of Silicone Elastomers to Improve Adhesion of Epoxy Topcoat

Two modification routes have been applied to control the surface properties of spin-coated and screen-printed poly(dimethylsiloxane) (PDMS) layers and to improve their adhesion to a photopatternable epoxy resin topcoat. The first route is based on the optimization of low-pressure oxygen and ammonia plasma treatments to generate acidic or basic reactive surface groups capable of forming covalent bonds with the epoxy groups of the topcoat. The main disadvantage of these fast and practicable processes is the instability of the modification effects. Therefore, the plasma-activated PDMS surfaces were used for subsequent 'grafting to' procedures with reactive polymers. The functional surface groups generated by oxygen or ammonia plasma treatments of PDMS (SiOH, OH, COOH and NH₂) were used as anchors to graft epoxy group containing homopolymers and copolymers as well as maleic anhydride copolymers. All of grafted materials provided thin barrier layers that prevented the hydrophobic recovery of the modified PDMS surface. A very promising concept to tailor the surface properties of PDMS is the grafting of epoxy group containing methacrylate copolymers. Depending on the molar ratio of the monomers used the epoxy groups will act mainly as anchor groups. The surface properties of the grafted layer will, then, be controlled by the functionality of the second comonomer. In order to study the effect of the surface modifications on the surface properties of the silicone elastomer layers we used a combination of various surface-sensitive characterization techniques, namely, X-ray photoelectron spectroscopy (XPS), contact angle and electrokinetic measurements as well as roughness analysis. Additionally, pull-off tests were carried out to quantify the effect of the surface modification on the adhesion between an epoxy resin and PDMS.     

Controlling the surface wettability of poly(sulfone) films by UV‐assisted treatment: benefits in relation to plasma treatment

Hydrophilic and superhydrophilic surfaces of poly(sulfone) (PSU) thin films were prepared by UV irradiation in the presence of O₂ or acrylic acid (AA) vapor. Treated surfaces were then investigated by water contact angle measurements, Fourier transformed IR spectroscopy in attenuated total reflectance mode (FTIR‐ATR), X‐ray photoelectron spectroscopy (XPS), near‐edge X‐ray absorption fine structure (NEXAFS) and AFM. Water contact angle values of treated PSU films using either O₂ or AA vapor as the reactive atmosphere reached about 6° after more than 120 min of irradiation. FTIR‐ATR, XPS and NEXAFS analysis showed incorporation of oxygenated groups onto the surface that led to its hydrophilic characteristics. In addition, when AA vapor was used as the reactive atmosphere, a photopolymerization process of poly(acrylic acid) onto the surface of the PSU was observed. AFM analysis showed a very low level of roughness after the treatments. A comparison of UV‐assisted surface modifications of PSU films with traditional plasma treatments showed excellent qualitative agreement between the two techniques. Our results show that UV‐assisted treatments in the presence of AA vapor or O₂ are efficient ways of controlling the surface wettability and functionalities grafted on the surface of PSU films. This treatment can be considered as a permanent dry grafting method that resists aging and uses a simple experimental setup. © 2012 Society of Chemical Industry     

Hydrophobic surface modification of ramie fibers by plasma-induced addition polymerization of propylene

The low affinity between hydrophilic cellulose fibers and hydrophobic matrices leads to poor interfacial bonding, reducing the mechanical performances of natural cellulose fiber-reinforced composites. This study illustrates plasma-induced addition polymerization of propylene to create a hydrophobic surface on ramie fibers for enhancing their bonding with polypropylene (PP). Plasma treatment with propane is applied for comparison. The advancing contact angles of the plasma-treated ramie fibers are raised from 66.3° to 106.1° and the interfacial shear strengths with PP are enhanced up to 36.4%, likely resulted from the increase in fiber surface roughness observed under a scanning electron microscope and the introduction of plasma-grafted PP and alkyl groups on fibers surfaces proven by X-ray photoelectron spectroscopy. It is also revealed that plasma treatment with propylene is highly effective in increasing surface carbon content (from 68.3% to 82.4% in 0.5 min) and more efficient than the treatment with propane, though both plasma treatments show substantial modification efficacies to the fiber surfaces. The treatment duration affects surface roughness more than surface chemical composition, and the optimized treatment time is around 1 min. The modification method developed in this research has the potential to be used for surface modification of fibers for many applications.     

Enhanced wave-absorbing performances of silicone rubber composites by incorporating C-SnO2-MWCNT absorbent with ternary heterostructure

SnO₂ and amorphous carbon were simultaneously introduced onto the surface of multi-walled carbon nanotube (MWCNT) by a simple and green hydrothermal process followed by heat treatment, finally to obtain the C-SnO₂-MWCNT absorbent with ternary heterostructure. Subsequently, the C-SnO₂-MWCNT/silicone rubber wave-absorbing composites were prepared. XRD, Raman, XPS, SEM, TEM and TGA indicated the C-SnO₂-MWCNT absorbent with ternary heterostructure was fabricated successfully. When the mass fraction of C-SnO₂-MWCNT was 30 wt% and the thickness was 2.65 mm, the minimum reflection loss (RL_min) and effective absorption bandwidth (EAB) of the C-SnO₂-MWCNT/silicone rubber wave-absorbing composites could reach −53.5 dB and 3.16 GHz, respectively. Excellent wave-absorbing performance was due to the synergistic effect of multiple interface & dipole polarization and conduction loss. Furthermore, the corresponding heat resistance index (T_HRI) of the C-SnO₂-MWCNT/silicone rubber wave-absorbing composites with 30 wt% C-SnO₂-MWCNT reached 209.9 °C, higher than that of neat silicone rubber (187.4 °C).     

Preparation and characterization of superhydrophobic FEP-Teflon surfaces

Abstraet-Supcrhydrophohic FEP-Teflon was prepared by argon ion etching followed by oxygen glow discharge treatment of commercially available FEP-Teflon sheet material. This combined treatment yielded an increase in water contact angle from 109° to > 140°. Ion etching alone caused a small increase in surface roughness and a loss of fluorine from the surface, but the water contact angles increased only to 120°. Scanning electron micrographs of ion-etched surfaces showed stalky protrusions with a diameter of approximatcly 40 nm. Glow discharge treatment of ion-etched surfaces reduced the length of these protrusions and therewith the microscopic surface roughness. However, in all cases the macroscopic surface roughness was less than 1 um (R_A value). X-Ray photoelectron spectroscopy indicated major changes in elemental surface composition as a result of the treatments. These modifications did not influence the infrared absorption spectra (attenuated total reflection) of the modified surfaces, indicating that the chemical changes brought about are really superficial. It is concluded that the superhydrophobicity created is mainly due to changes in the specific, microscopic surface topography resulting from ion etching, but also partly due to the role of the glow discharge treatment, restoring a high surface concentration of fluorine after ion etching.     

Surface modification of aramid fibers via ammonia‐plasma treatment

In this article, aramid fibers III were surface modified using an ammonia‐plasma treatment to improve the adhesive performance and surface wettability. The surface properties of fibers before and after plasma treatment were investigated by X‐ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and water contact angle measurements. The interfacial shear strength of each aramid fibers III‐reinforced epoxy composites was studied by micro‐debonding test. The ammonia‐plasma treatment caused the significant chemical changes of aramid fibers III, introducing nitrogen‐containing polar functional groups, such as ? C? N? and ? CONH? , and improving their surface roughness, which contributed to the improvement of adhesive performance and surface wettability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40250.     

PdCl2 anchorage onto the surface of polystyrene films via oxygen and ammonia plasma treatment

The surface properties of polystyrene as a possible catalytic support for active coordinative species were investigated. To improve the surface properties, discharge treatments in the presence of oxygen and ammonia were carried out. The polymer surface was studied before and after the plasma treatments. Contact angles for the polymer surface were measured in order to determine the surface free energy. Polymer‐bound complex catalysts were prepared by anchoring PdCl₂ on the surface of the polystyrene samples. The chemical compositions were studied by X‐ray Photoelectron Spectroscopy (XPS). Plasma treatments in the presence of oxygen or ammonia caused an increase in the surface free energy of polystyrene, as a consequence of the higher concentration of oxygenated or nitrogenated functional groups, respectively, on the polymer surface. Contact angle measurements are in agreement with the corresponding values obtained by XPS. After treatment with PdCl₂, the amount of palladium anchored to the polymer surface treated with ammonia is greater than in the case of the oxygen plasma treatments; this may be explained on the basis of the higher nucleophilic character of the amine groups. No palladium was detected in the untreated polystyrene surface. © 2000 Society of Chemical Industry     

硅橡胶膜滴状冷凝强化传热管的制备

实验采用涂覆-热处理法制备了4种硅橡胶膜滴状冷凝强化传热管。其中白炭黑-硅橡胶强化传热管的表面水接触角为137.19°,其冷凝传热系数比相应的膜状冷凝提高了3.1～3.3倍,表面温差大约是相应膜状冷凝的1.3～1.4倍。     

Improvement of the adsorption properties of carbon black granules by means of plasma enhanced-chemical vapour deposition with acrylic acid vapours

Carbon black granules were coated by thin polymers in radio frequency glow discharges fed with acrylic acid/argon mixtures at different input powers, in order to improve the adsorption ability of basic compounds in the liquid and gas phases.The treated surfaces were characterized by X-ray photoelectron spectroscopy analyses and water contact angle measurements, performed immediately after the plasma treatment, after ageing in water and in air, and after heating up to 150 °C.The adsorption ability of basic compounds in the liquid and gas phases was evaluated with Boehm titrations and ammonia adsorption, respectively.Scanning electron microscopy observations and Brunauer, Emmett, Teller specific surface area measurements were performed to evaluate the morphological changes induced by the plasma treatments on the carbon black granule surface.The results show that the plasma treatments significantly improve the absorption ability of carbon black mainly for grafting of carboxylic groups and not for surface morphological modifications.     

Optical Emission Spectroscopy Study and 3-D Surface Characterization of Silicone Rubber Exposed to Different Argon RF Plasma Powers

Abstract

The present study was undertaken to investigate the effect of argon plasma treatment on the extent of Foley catheter surface modification. Foley catheter (flexible tube made of silicone rubber, used for urinary catheterization) surface was treated at different argon (Ar) RF plasma powers. The surface modification was assessed by measurement of contact angle. Contact angle study shows decrease in contact angle and increase in surface free energy shows more polar group incorporation at low power plasma treatment. Atomic force microscopy (AFM) revealed an increased average surface roughness proportional to plasma power. Optical emission spectroscopy (OES) shows various states of argon causing surface modification.     

Direct laser etching of hierarchical nanospheres on silicon rubber surface with robust dynamic superhydrophobic stability

Silicone rubbers with high dynamic superhydrophobic stability have an extensive application prospect. Applying direct laser etching technology, a fast and efficient method is proposed for the preparation of silicone rubber surfaces with hierarchical nanospheres and robust dynamic superhydrophobicity. A 4 μl water droplet on the laser modified silicone rubber surface exhibits a contact angle (CA) of 154 ± 3° and a roll-off angle (RA) of 5 ± 1°, there is a 65.6% increase in CA compared with the pristine silicon rubber. Moreover, the modified surface can stabilize its superhydrophobic state under a dynamic pressure of 1960.2 Pa. Interestingly, no significant change in the contacting time for the droplets with different impacting speed is found, which means that the stabilized contact time and robust dynamic superhydrophobicity are induced on the modified silicone rubber surface. The self-cleaning and anti-icing properties on the modified surface can effectively reduce the damage caused by surface pollution, ice formation, and other natural factors when applied to power lines, sealing elements, and automotive.