Low-rate Dynamic Contact Angles on Poly(methyl methacrylate/n-butyl methacrylate) and the Determination of Solid Surface Tensions

Low-rate dynamic contact angles of 12 liquids on a poly(methyl methacrylate/n-butyl methacrylate) P(MMA/nBMA) copolymer are measured by an automated axisymmetric drop shape analysis-profile (ADSA-P). It is found that 6 liquids yield non-constant contact angles, and/or dissolve the polymer on contact. From the experimental contact angles of the remaining 6 liquids, it is found that the liquid- vapour surface tension times the cosine of the contact angle changes smoothly with the liquid-vapour surface tension, i.e., γ_iv cos θ depends only on γ_iv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and noninert (polar and non-polar) surfaces [34-42, 51 -53]. The solid-vapour surface tension calculated from the equation-of-state approach for solid -liquid interfacial tensions [14] is found to be 34.4 mJ/m², with a 95% confidence limit of \pm 0.8mJ/m², from the experimental contact angles of the 6 liquids.     

Atmospheric Plasma Surface Activation of Poly(Ethylene Terephthalate) Film for Roll-To-Roll Application of Transparent Conductive Coating

An effective surface activation is crucial for high-speed roll-to-roll coating of functional films for printed electronics applications. In this article, we report a study of surface treatment of three types of poly(ethylene terephthalate) (PET) films by an argon/oxygen atmospheric pressure plasma and an ambient air atmospheric pressure plasma to obtain the required wettability for subsequent slot die coating of transparent conductive polymer layer using a poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) ink. Prior to plasma treatment, the PET surfaces, which differ in manufacturing process of their preparation, were characterized by X-ray photoelectron spectroscopy. The surface changes after the plasma treatments were characterized by water contact angle measurement and atomic force microscopy. We found that the water contact angles of the three types of untreated PET surfaces were 80.9°, 75.9°, and 66.3°, respectively, and the water contact angles after argon/oxygen plasma treatment at treatment speed of 1 m · min^?1 decreased to 36.2°, 31.9°, and 40.9°, respectively. These conditions were stable from 1 up to 4 days, which are longer than reported values of 15–60 min and sufficient for roll-to-roll coating processes.     

Contact angle measurements and interpretation: wetting behavior and solid surface tensions for poly(alkyl methacrylate) polymers

Low-rate dynamic contact angles of a large number of liquids were measured on a poly(ethyl methacrylate) (PEMA) polymer using an automated axisymmetric drop shape analysis profile (ADSA-P). The results suggested that not all experimental contact angles can be used for the interpretation in terms of solid surface tensions: eight liquids yielded non-constant contact angles and/or dissolved the polymer on contact. From the experimental contact angles of the remaining four liquids, we found that the liquid-vapor surface tension times the cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. γlv cos ζ depends only on γlv for a given solid surface (or solid surface tension). This contact angle pattern is again in harmony with those from other methacrylate polymer surfaces of different compositions and side-chains. The solid-vapor surface tension of PEMA calculated from the equation-of-state approach for solid-liquid interfacial tensions was found to be 33.6 ± 0.5 mJ/m2 from the experimental contact angles of the four liquids. The experimental results also suggested that surface tension component approaches do not reflect physical reality. In particular, experimental contact angles of polar and nonpolar liquids on polar methacrylate polymers were employed to determine solid surface tension and solid surface tension components. Contrary to the results obtained from the equation-of-state approach, we obtained inconsistent values from the Lifshitz-van der Waals/acid-base (van Oss and Good) approach using the same sets of experimental contact angles.     

Effect on wettability of the topography and oxidation state of biaxially oriented poly(propylene) film

Surface topography and surface chemistry heterogeneity are widely accepted as causes of contact angle hysteresis. Contact angle hysteresis occurs on essentially all industrial polymer films. Four unmodified and flame-treated biaxially oriented poly(propylene) (BOPP) films produced from the same poly(propylene) base resin, but differing in surface topography and orientation, were characterized by measurement of the advancing and receding contact angles of water and diiodomethane, by atomic force microscopy (AFM) and by x-ray photoelectron spectroscopy (XPS). Contact angle hysteresis was much larger on flame-treated samples than on untreated samples even though some of the untreated films have significantly different topography at the nanoscale.     

Activated Poly(hydromethylsiloxane)s as Novel Adhesion Promoters for Metallic Surfaces

A poly(hydromethylsiloxane) (PHMS) was bound to aluminum, copper and steel surfaces via activation with cis-[PtCl₂(PhCH = CH₂)₂] in solution at room temperature. The attached polymer promotes the adhesion to two-component silicone resins where the curing process is based on catalytic hydrosilylation of olefins. In lap-shear or peel tests, cohesive failure was always observed. An example shows that the adhesive joint withstood boiling water for 200 h without considerable loss of adhesive strength. It is suggested that a small fraction of the olefinic component of the resin, e.g., a poly(dimethylsiloxane) containing some olefinic groups, is also connected with the attached PHMS via catalytic hydrosilylation, thus binding the silicone resin to the surface via the PHMS layer.     

Improved Hydrophilicity from Poly(ethylene glycol) in Amphiphilic Conetworks with Poly(dimethylsiloxane)

This paper focuses on the improvement of hydrophicility and water content of poly(dimethylsiloxane) (PDMS) by bonding a hydrophilic macromer, hydroxyl-terminated linear poly(ethylene glycol) (PEG), into a highly hydrophobic macromer, hydroxyl-terminated linear PDMS to prepare amphiphilic conetworks (APCNs) with the crosslinkers, tetraethoxysilane (TEOS) and bis[(3-methyldimethoxysilyl)propyl]-polypropylene oxide (BMPPO), which also functioned as a compatibilizer. Fourier transform infrared results clearly demonstrated the occurrence of the hydrolysis reactions between the terminal hydroxyl groups on the terminal of the two polymer chains and the alkoxy groups in TEOS and BMPPO. Differential scanning calorimetry results and X-ray diffraction obviously showed the presence of the two phases in the conetworks. The contact angle (CA) indicated the wettability of the conetworks increased in the surfaces, that is, CA values decreased significantly from 105° in PDMS to 55° in the PEG/PDMS APCN (10/1 mol ratio), and the swelling degrees of the APCNs increased from ca. 0 to 60 % when the PEG/PDMS mol ratio was larger than 4/1. The APCNs with such high hydrophilicity and the good mechanical properties should be useful as biomaterials.     

Surface Molecular Mobility for Copolymers Having Both Hydrophobic and Hydrophilic Side Chains Via Dynamic Contact Angle Measurement

The reorganization of a surface structure in response to a change in environmental media was investigated for copolymers having both hydrophobic polydimethylsiloxane (PDMS) and hydrophilic methoxypoly-ethyleneglycol (MPEG) side chains via dynamic contact angle (DCA). These copolymers showed a large contact angle hysteresis and a dependency of the advancing and receding contact angle on dipping velocity (DV). Composition dependency of DCA for these copolymers is also discussed. In addition to this, adhesion tension relaxation, F(t), for MMA/MPEGMA/PDMSMA was determined. F(t) in the advancing process increased with elapsed time and decreased in the receding process. These phenomena were explained by the adsorption and reorientation of hydrophilic segments to the water/copolymer interface in water. In XPS analysis, more oxygen atoms were detected on the surfaces of MMA/MPEGMA after immersion in water than before. For MMA/MPEGMA/PDMSMA, the atomic ratio of Si to C increased with an increase in PDMSMA content.     

Grafting of Epoxy Resin on Surface-modified Poly(tetrafluoroethylene) Films

An epoxy/PTFE composite was prepared by curing the epoxy resin on the surface-modified PTFE film. Surface modification of PTFE films was carried out via argon plasma pretreatment, followed by UV-induced graft copolymerization with glycidyl methacrylate (GMA). The film composite achieved a 90°-peel adhesion strength above 15 N/cm. The strong adhesion of the epoxy resin to PTFE arose from the fact that the epoxide groups of the grafted GMA chains were cured into the epoxy resin matrix to give rise to a highly crosslinked interphase, as well as the fact that the GMA chains were covalently tethered on the PTFE film surface. Delamination of the composite resulted in cohesive failure inside the PTFE film and gave rise to an epoxy resin surface with a covalently-adhered fluoropolymer layer. The surface composition and microstructures of the GMA graft-copolymerized PTFE (GMA-g-PTFE) films and those of the delaminated epoxy resin and PTFE film surfaces were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle and scanning electron microscope (SEM) measurements. The delaminated epoxy resin surfaces were highly hydrophobic, having water contact angles of about 140°C. The value is higher than that of the pristine PTFE film surface of about 110°. The epoxy resin samples obtained from delamination of the epoxy/GMA-g-PTFE composites showed a lower rate of moisture sorption. All the fluorinated epoxy resin surfaces exhibited rather good stability when subjected to the Level 1 hydrothermal reliability tests.     

Surface Modification of Epoxy Resin with Silicone-containing Block Copolymers

In order to improve oil and water repellency, silicone-containing block copolymers, composed of methylmethacrylate (MMA), glycidylmethacrylate (GMA), and polydimethylsiloxanemethacrylate (SMA), were blended in an epoxy resin. It was expected that the low surface energy dimethylsiloxane segments would adsorb and orient at the exterior of the resin to make a thin surface phase and the glycidyl groups would mesh with the epoxy resin by primary bonding. The techniques of X-ray photoelectron spectroscopy (ESCA), dynamic contact angle (DCA) and peel strength measurements of pressure sensitive adhesives were used to characterize the modified epoxy resin surface phases. The amount of Si_2p obtained via angular dependent ESCA investigation in the near surface region of the modified resin increased with decreasing sampling depth. With an increase in modifier content, both the amount of Si_2p and O_1s also increased. Both advancing and receding contact angles for an aluminum plate coated with modified resin, measured by dipping into and out of water, increased with the addition of these modifiers. The peel strength of a pressure sensitive adhesive tape affixed to the modified epoxy resin decreased dramatically with increasing modifier content. It was found that these copolymers were good surface modifiers to improve oil and water repellency and that they acted as release agents.     

Synthesis, characterization, and properties of a novel acrylic terpolymer with pendant perfluoropolyether segments

A novel acrylic terpolymer with pendant perfluoropolyether (PFPE) segments has been synthesized and fully characterized. By hexamethylene diisocyanate functional groups PFPE monofunctional macromonomers have been grafted on a poly(butyl methacrylate-co-hydroxyethyl acrylate-co-ethyl acrylate) random terpolymer. Such grafted copolymer behaves like an interface-active material, since the perfluoropolyether segments in solvent cast films rearrange themselves at the air-polymer interface by surface segregation. In addition, blends of the above graft copolymer with acrylic base polymers (either the terpolymer itself or a commercial copolymer) have been examined in terms of surface segregation and fluorine enrichment of the external layers.The critical surface tension, γ_c, of solid films made of the neat graft copolymer as well as of the polymer blend has been evaluated by contact angle measurements and Zisman plots. Even a small addition (5 wt%) of the fluorinated copolymer to the acrylic component has been found very effective in lowering the surface tension. The outermost surface composition has been investigated by XPS technique, confirming the strong fluorine enrichment. Furthermore, SEM and EDX analyses have been performed on cross-sectioned films, showing that in the above polymer blends macrophase surface segregation has originated a thick layer made of fluorinated copolymer close to the air-polymer interface.     

聚硅氧烷-聚氨酯表面改性剂

采用聚硅氧烷 -聚氨酯共聚物作为表面改性添加剂对热塑性聚氨酯进行共混改性。接触角和ESCA测定结果表明 :聚硅氧烷向共混物表面迁移 ,富集在共混物表面 ,使其接触角增大 ,具有憎水性。     

Preparation and morphology of transparent poly(methyl methacrylate)–poly(dimethylsiloxane) hybrid materials using multifunctional silicone macromonomer

In this study, transparent poly(methylmethacrylate) (PMMA)‐silicone hybrid materials, P(MMA‐co‐SigUMAx), were prepared with methylmethacrylate (MMA) and multifunctional silicone macromonomer introduced methacryl groups. The transmittance of hybrid materials improved with increase of methacryl groups of silicone macromonomer and reached around 90% T. Atomic force microscopic analysis, scanning electron microscope examinations, and copolymerization kinetics estimation by proton nuclear magnetic resonance revealed that the silicone macromonomer randomly incorporated in the copolymer with MMA by the increase of methacryl groups and suppresses the aggregation of the silicone segment. The hybrid materials introduced over 10 wt % of silicone component had water‐shedding surface and the water contact angle was elevated from 65 to 95°. Though the mechanical properties of hybrid materials were lowered by introduction of flexible silicone component, thermal property such as 5 wt % weight loss temperature were improved. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation and characterization of superhydrophobic surface based on polydimethylsiloxane (PDMS)

Biomimetic superhydrophobic surfaces exhibit excellent self-cleaning properties due to their special micro/nano-scale binary structures. In order to prepare the superhydrophobic surface of the polydimethylsiloxane (PDMS), a facile fabrication method for replicating micro/nano-scale binary aluminium structures into PDMS is presented. The microscopic morphology, composition, surface roughness (Ra) and wettability of the sample surface were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, roughness measurement equipment and contact angle meter respectively. Based on the measurements of the contact angles of deionized water (DI water) and ethanediol, surface free energies of the coatings were estimated according to the Owens two-liquid method. The superhydrophobic PDMS exhibited lower surface free energy than flat PDMS with a DI water contact angle (WCA) of 165°. The surface roughness (Ra) increased with the increasing of etching time in the range 0–80?min, and then decreased with the change of etching time, similar to the variation of contact angle with etching time. Moreover, the prepared surface had different micro-morphologies and its wettability was changed by regulating the chemical etching time. In addition, the superhydrophobic PDMS also showed good self-cleaning properties and the bouncing effect of the water droplets.     

Surface modification of poly(tetrafluoroethylene) and poly(ethylene terephthalate) films via environmental crazing

This work addresses the phenomenon of the development of a patterned surface relief on polymer films via different modes of environmental crazing. Commercial films of semicrystalline poly(tetrafluoroethylene) (PTFE) and amorphous glassy poly(ethylene terephthalate) (PET) were subjected to tensile drawing in the presence of physically active liquid environments (carbon tetrachloride or aliphatic alcohols). The structure parameters and wettability of the modified films were studied by AFM, SEM, profilometer measurements and contact angle measurements. Environmental intercrystallite crazing of PTFE is accompanied by the development of an unstable structure with a high free surface, which experiences marked strain recovery upon unloading. As a result of the relief formation, PTFE hydrophobicity is enhanced (the water contact angle increases by 25°). Classical environmental crazing of PET films is accompanied by the formation of an anisotropic surface relief which is an assembly of crazes oriented perpendicular to the direction of tensile drawing, thus leading to the phenomenon of anisotropic wetting. The proposed approach for structural surface modification makes it possible to use the advantages of surface instability and spontaneous self‐organization of the polymer towards the development of a unique surface microrelief. © 2020 Society of Chemical Industry     

Synthesis and Characterization of Poly(ethylene glycol) grafted Poly(ε-Caprolactone)

Summary A new graft copolymer, poly(ε-caprolactone) (PCL) grafted with poly(ethylene glycol) (PEG), was prepared by one-pot synthesis of ε-caprolactone and modified PEG. Aluminium isopropoxide or potassium tert-butoxide was used as a catalyst for the ring-opening polymerization. Polymerization using potassium tert-butoxide as a catalyst showed very effective graft reaction of PEG onto poly(ε-caprolactone). A slight decrease in the melting temperature was observed with the increase of the PEG graft frequency. Interestingly, considerable changes were observed on the surface property by the introducing PEG side chains compared to that of PCL homopolymer. Measurements of water contact angle showed that the hydrophilic surface of the polymer could be obtained even at a low graft frequency of PEG.     

Alteration of the Surface Energy of Wood Using Lignin-(1-Phenylethene) Graft Copolymers

Graft copolymers of lignin, made by free radical graft copolymerization of 1-phenylethene on lignin, increased the contact angle of water on birch wood (Betula papyrifera) and decreased the critical surface tension of the wood when coated onto the wood surface from an N, N-dimethylformamide solution. The coating of copolymer changed the wood from hydrophilic (～50°) to hydrophobic (110°).

The most pronounced change in contact angle was produced by benzene-soluble extracts of the reaction product. These extracts contained lignin with long poly(1-phenylethylene) sidechains and pure poly(1-phenylethylene). They produced surfaces with the numerically highest contact angles with water and changed the wetting behavior of the surface more than physical mixtures of lignin and poly(1-phenylethylene) or either of the pure polymers.

Despite coating weights of less than 100 mg/cm, the critical surface tension of the birch wood coated with the various lignin-(1-phenylethylene) graft copolymers ranged from 26.9 to 44.9 dynes/cm while the uncoated birch had a critical surface tension of 49.6 dynes/cm.     

Surface tension of polytrifluoropropylmethylsiloxane

Surface tension studies of the most common fluorosilicone, poly(3,3,3-trifluoropropylmethylsiloxane) (PTFPMS), give unexpected results. Compared to polydimethylsiloxane (PDMS), the liquid surface tension is higher, the critical surface tension of wetting similar, and the solid surface tension, determined by water and methylene iodide contact angles and the method of Owens and Wendt, considerably lower. As the outermost surface of the lowest energy materials are comprised of close-packed perfluoromethyl groups and as a flexible polymer backbone should aid in the adoption of the lowest surface energy configuration, fluorosilicones could in principle be the lowest surface energy polymers. In practice, other groups such as the ethylene link between the perfluoromethyl group and the siloxane backbone in PTFPMS are required to produce a stable material. This introduces factors such as bulkiness of side chains, unresolved fluorocarbon/hydrocarbon dipoles, and fluorine/silicon coordination effects. The results are discussed in these terms and compared with PDMS and two fluoropolymers, polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE). PTFE shows similar trends to PTFPMS whereas PCTFE behaves rather like PDMS.     

Wetting properties of homopolymers and copolymers of pentafluorostyrene and methylacrylate and homopolymer blends

Polypentafluorostyrene (PPFS), polymethylacrylate (PMA), and poly(pentafluorostyrene-co-methylacrylate), poly(PFS-co-MA) were prepared and the wetting characteristics of polymer blends of PPFS and PMA were compared with that of poly(PFS-co-MA) via contact angle measurements. The critical surface tension of polypentafluorostyrene was found to be 22.6 dyne/cm, which is comparable to the value reported for polytrifluoroethylene (22 dyne/cm). The critical surface tension of poly(PFS-co-MA) is not linearly related to its composition. The polymer blends of PPFS and PMA exhibit significant surface enrichment of the fluoropolymer. The harmonic-mean method¹ was employed to determine surface tensions of these polymers and many known polymers. It is found that the method produces useful surface tension data provided the contact angle values are derived from testing liquids of dissimilar polarity.     

Contact Angle Hysteresis on Polymer Surfaces: An Experimental Study

In order to characterize a solid surface, the commonly used approach is to measure the advancing and receding contact angles, i.e., the contact angle hysteresis. However, often an estimate of the average wettability of the solid–liquid system is required, which involves both the dry and wetted states of the surface. In this work, we measured advancing and receding contact angles on six polymer surfaces (polystyrene, poly(ethylene terephthalate), poly(methyl methacrylate), polycarbonate, unplasticized poly(vinyl chloride), and poly(tetrafluoroethylene)) with water, ethylene glycol and formamide using the sessile drop and captive bubble methods. We observed a general disagreement between these two methods in the advancing and receding contact angles values and the average contact angle determined separately by each method, although the contact angle hysteresis range mostly agreed. Surface mobility, swelling or liquid penetration might explain this behaviour. However, we found that the 'cross' averages of the advancing and receding angles coincided. This finding suggests that the cross-averaged angle might be a meaningful contact angle for polymer–liquid systems. Hence, we recommend using both the sessile drop and captive bubble methods.     

Above 170° water contact angle and oleophobicity of fluorinated graphene oxide based transparent polymeric films

Understanding and tuning the wettability of the surfaces are highly intriguing for various applications. The development of stable and transparent coatings over aluminium alloys and glass substrates for making them superhydrophobic and extended oleophobic (lower to the surface tension of 33.4 mN/m (coconut oil)) using a scalable and simple spray painting technique is demonstrated. Fluorinated graphene oxide (FGO, fluorine content of 34.4 atomic weight %), an atomically layered material, modified Polydimethylsiloxane (PDMS) polymer composite is used as the paint for the coatings. The coated films were studied for their surface and compositional features. A water contact angle (CA) of 173.7° (close to the highest ever reported water CA, 175°) is achieved with 60 wt% FGO in PDMS, and the same showing a CA of 94.9° with coconut oil, in conjunction with a low contact angle hysteresis (4°). The work of adhesion with the amount of FGO is studied and the surface energy of FGO containing paints is calculated and compared with the bare paints using Zisman plot analysis.