Contact Angles Of Methylene Iodide Research Articles

Study on properties of waterborne fluorinated polyurethane/acrylate hybrid emulsion and films

Waterborne fluorinated polyurethane acrylate (WFPUA) with the different content of HEA were successfully obtained by introducing the fluorinated monomers both in polyurethane and polyacrylate. In our study, the particles size (d), viscosity (η) and the core-shell structure of WFPUA hybrid emulsion were characterized, the films were analyzed by Fourier transform infrared spectroscopy (FT-IR), and the surface energy, thermal stability and mechanical properties of the WFPUA films was characterized. The obtained results indicated that the increase of the HEA was benefit to the thermal stability, mechanical properties and antifouling ability of the WFPUA films. When the content of HEA were increased from the 0 % to 3.28 %, the water and methylene iodide contact angles increased from 101.8° to 121.1° and from 63.1° to 81.4°, respectively. And the tensile strength of the film samples were enhanced from 20.5 MPa to 30.32 MPa. At the same time, from the analysis of the DSC curves, the Tg has been improved. However, the increasing content of HEA has some negative effect on the migration of the fluorine element to the film surface from the analysis of XPS.

Mussel-inspired fabrication of structurally stable chitosan/polyacrylonitrile composite membrane for pervaporation dehydration

The structural stability of chitosan (CS)/polyacrylonitrile (PAN) composite membrane for pervaporation dehydration was improved by the introduction of mussel-adhesive-mimetic molecule, carbopol (CP). The composite membranes were simply fabricated by layer-by-layer technique, in which CP as an intermediate layer bridging the CS active layer and the PAN support layer. The structure and morphology of composite membranes were characterized by Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscope (FESEM). The methylene iodide contact angle measurement, T-peel test and molecular dynamics (MD) simulation were employed to analyze the wetting characteristics, adhesion strength and interaction at the interface. Positron annihilation lifetime spectroscopy (PALS) was employed to probe the fractional free-volume properties of the CS active layer. The membrane pervaporation performance was investigated by varying the molecular weight (CP981, 940, 974) and concentration of CP as well as the cross-linking degree of the CS active layer. When the concentration of CP974 was 0.5 wt.%, GCCS(60)/CP(0.5)/PAN composite membrane displayed the permeation flux of 1247 g/(m 2 h) and separation factor of 256 for ethanol dehydration at 353 K. Furthermore, the enhancement of the long-term operation stability of membrane by incorporating the CP layer was also verified.

Self-Assembled Monolayers of Bisphosphonates: Influence of Side Chain Steric Hindrance

Bisphosphonates form self-assembled monolayers (SAMs) spontaneously on stainless steel, silicon, and titanium oxidized surfaces. We used contact angle measurements, atomic force microscopy, and X-ray reflectivity analysis to study the formation of SAMs on a model surface of ultraflat titanium (rms = 0.2 nm). The results were extended to standard materials (mechanically polished titanium, stainless steel, and silicon) and showed that water-soluble bisphosphonic perfluoropolyether can easily form SAMs, with 100% surface coverage and a layer thickness of less than 3 nm. Hydrophobic (water contact angle >110 degrees on stainless steel or titanium) and lipophobic (methylene iodide contact angle >105 degrees on titanium) properties are discussed in terms of industrial applications.

AFM Forces Measured between Gold Surfaces Coated with Self-Assembled Monolayers of 1-Hexadecanethiol

An atomic force microscope (AFM) was used to measure the forces between gold surfaces with and without hydrophobizing them by the self-assembly of 1-hexadecanethiol. The forces measured between bare gold surfaces were fitted to the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory with a Hamaker constant of 1.2 x 10 (-20) J, which was close to the value determined using the methylene iodide contact angle method but was lower than that calculated using the Lifshitz theory. When the surfaces were hydrophobized in a 0.01 mM thiol-in-ethanol solution for 10 min, the measured forces exhibited a long-range force with a decay length of 35 nm. Despite its high water contact angle (105 degrees ), the force curve was smooth and exhibited no steps. When the surfaces were hydrophobized in a 1 mM thiol solution for longer than 6 h, however, the force curves exhibited steps, indicating that the long-range attractions were caused by bridging bubbles. When the measurements were conducted after washing the substrates with organic solvents, the steps disappeared and long-range attractive forces appeared. In the presence of ethanol, the water contact angle decreased to below 90 degrees , the attraction became weaker, and the force curves became smooth. On the basis of the results obtained in the present work, possible mechanisms for the long-range attractions are discussed.

Combinatorial and High-Throughput Screening of the Effect of Siloxane Composition on the Surface Properties of Crosslinked Siloxane−Polyurethane Coatings

Libraries of siloxane-polyurethane coatings were designed, formulated, and screened using high-throughput experimentation. Four independent variables that were analyzed were the molecular weight of poly(dimethylsiloxane) (PDMS), presence or absence of poly(epsilon-caprolactone) (PCL) blocks attached to the PDMS backbone, the length of the PCL blocks, and the siloxane polymer level in the coating formulations. In addition to the siloxane libraries (3-aminopropyl-terminated PDMS and poly(epsilon-caprolactone)-poly(dimethylsiloxane)-poly(epsilon-caprolactone) (PCL-PDMS-PCL) triblock copolymers), the coating formulation included a trifunctional isocyanate crosslinker, trifunctional poly(epsilon-caprolactone) polyol, 2,4-pentanedione (pot-life extender), dibutyltin diacetate (catalyst), and a blend of solvents. The resulting coatings were analyzed for their surface energy and pseudobarnacle adhesion both before and after aging the coatings for 30 days in water. The water and methylene iodide contact angle averages increase with increasing molecular weight of PDMS. Coatings prepared from PCL-PDMS-PCL triblock copolymers have lower surface energies than coatings prepared from 3-aminopropyl-terminated PDMS; however, lower pseudobarnacle adhesion results were obtained for the coatings prepared from 3-aminopropyl-terminated PDMS than coatings prepared from PCL-PDMS-PCL triblock copolymers. The siloxane polymer level in the coating formulations does not have a significant effect on the surface energy of the coatings, but it resulted in higher pseudobarnacle adhesion.

The physicochemical characteristics of modified carbon fibers by Fluorination

The surface of PAN-based carbon fiber was directly modified with fluorine-oxygen mixtures at room temperature. The surface characteristics of the modified fiber were determined by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and dynamic contact angle analyzer. The surface free energy was also calculated with the Owens-Wendt geometric mean method using water and methylene iodide contact angle. The surface of carbon fiber was changed into hydrophilicity by the formation of semicovalent C-F bond and C-O bond depending on reaction conditions and the surface free energy of oxyfluorinated fiber was significantly increased.

Trialkylsilane Monolayers Covalently Attached to Silicon Surfaces: Wettability Studies Indicating that Molecular Topography Contributes to Contact Angle Hysteresis

Chemically grafted monolayers of trialkylsilanes were prepared by reaction of (primarily) alkyldimethylchlorosilanes with silicon wafers under three conditions: in the vapor phase at elevated temperature (60−70 °C), in toluene in the presence of ethyldiisopropylamine (EDIPA) at room temperature, in toluene/EDIPA at 60−70 °C. It was determined that reactions at the solution−solid interface are very slow in the later stages of the reaction and that long reaction times are necessary to achieve maximum bonding density. The bonding density is determined and can be controlled by the reaction conditions. The highest carbon content on the surface (assessed by X-ray photoelectron spectroscopy) as well as the highest contact angles were obtained using vapor phase reactions. A series of nine H(CH2)nMe2Si− surfaces was prepared with n = 1, 2, 3, 4, 8, 10, 12, 18, and 22. Water contact angles (θA/θR = ∼105°/∼94°) are independent of chain length, indicating that these surfaces project disordered methyl groups toward the probe fluid and that water does not penetrate the monolayers. Hydrophobization is achieved topologically: the monolayers prevent water from penetrating and interacting with residual silanols. n-Hexadecane and methylene iodide contact angles decrease with increasing chain length for this series, indicating that these probe fluids penetrate the monolayers and interact with methylene groups. These chemically grafted monolayers differ in structure from those prepared by self-assembly in that the distance between molecules is significantly greater and that all molecules are covalently attached to the substrate. The contact angle hysteresis for these surfaces is a function of alkyl group structure and bonding density: mobile surfaces with flexible chains or rotational mobility and rigid surfaces that pack well exhibit low hysteresis, whereas rigid surfaces that cannot pack well exhibit high hysteresis. We argue that molecular level topography (roughness and rigidity) is responsible for the observed hysteresis.

Ultrahydrophobic and Ultralyophobic Surfaces: Some Comments and Examples

The preparation of ultrahydrophobic and ultralyophobic surfaces using several techniques is described. Plasma polymerization of 2,2,3,3,4,4,4-heptafluorobutyl acrylate on poly(ethylene terephthalate) yields surfaces with water contact angles of θA/θR = 174°/173°. Argon plasma etching of polypropylene in the presence of poly(tetrafluoroethylene) renders surfaces with water contact angles as high as θA/θR = 172°/169°. Surfaces of compressed pellets of submicrometer, variable-diameter spherical particles of PTFE oligomers exhibit water contact angles of θA/θR = 177°/177°, methylene iodide contact angles of θA/θR = 140°/138°, and hexadecane contact angles of θA/θR = 140°/125°. We emphasize that contact angle hysteresis is more important in characterizing lyophobicity than is the maximum achievable contact angle. These surfaces are rough at the micrometer and submicrometer scales, and water drops roll easily on all of them. We make an intuitive argument that the topology of the roughness is important and contr...

A comparative study of the effects of ammonia and hydrogen plasma downstream treatment on the surface modification of polytetrafluoroethylene

Abstract Polytetrafluoroethylene (PTFE) was treated with hydrogen and ammonia microwave plasmas and the effects of treatment were evaluated by means of advancing and receding contact angle measurements, X-ray photoelectron spectroscopy, secondary-ion mass spectroscopy and atomic force microscopy analysis. Hydrogen plasma downstream treatment principally leads to defluorination and creation of CC and CH groups. This surface modification results in a slight decrease of the water contact angle and a large decrease of the methylene iodide contact angle. No evolution of the surface properties occurs over a period of at least two months following treatment. Ammonia plasma downstream treatment leads to defluorination and creation of CC and CH groups, as already observed with the H2 plasma, but also to the introduction of nitrogen-containing groups. The modification produces a decrease of both water and methylene iodide contact angles. A large hysteresis is found with water contact angles due to the reorientation of the polar groups when the surface is in contact with a polar liquid. The surface modifications that result after a NH3 plasma treatment are less stable than after a H2 treatment. Nevertheless, after two days of ageing the water contact angle reaches a constant value, which is largely inferior to that of the untreated PTFE.

Protein adsorption on a copolymer having pendant monosaccharide groups. Relationship between surface free energy and protein adsorption

AbstractProtein adsorption on copolymer films having pendant monosaccharide groups was investigated from the viewpoint of surface chemistry. The copolymers were synthesized by the copolymerization of a monomer having a pendant monosaccharide (GEMA) and methyl methacrylate (MMA). The contact angles of methylene iodide and air bubble on the GEMA‐MMA copolymer films were measured in water, and the surface free energy of the copolymer films in water was calculated from the contact angles. With increasing GEMA content, the amount of protein adsorbed on the GEMA‐MMA copolymer films decreased gradually. The relationship between protein adsorption and the surface free energy of the copolymer films in water is discussed. The differences between surface free energy before and after protein adsorption on the copolymer surface is closely related to the amount of adsorbed protein.

698 PB 306 WETTABILITY AND SURFACE TENSION OF FRUIT SURFACES

Nettability is an important factor to be considered in postharvest treatments such as washing, aqueous dippings, coatings, etc. Pome fruits (ten apple and four pear cultivars) and stone fruits (nectarine and plums) were evaluated for wetting behavior and surface tension at room temperature. Nettability was assessed by measuring contact angles of water. Surface tension was calculated by measuring contact angles of methylene iodide and water or by a series of pure surfactants using Zisman's method. Wetting behavior on apple fruits depended on cultivar, with water contact angles ranging from 75° to 131°. For pear fruits, wetting also depended on cultivar. Calculated surface tensions of pear fruits were in general higher than most apple cultivars tested. In stone fruits, plums presented a high water-repellency with a contact angle of 137°. The wetting of fruit surfaces seems to be governed by the nature of the chemical groups exposed on the surface of the cuticle and also by the surface roughness, as evidenced by tire high values of some contact angles.

Two-dimensional photopolymerization at adsorbed monolayers on gold

Disulfide-bearing ammonium amphiphiles with different counter-anions, Cl–(1Cl) styrene-p-sulfonate (1SS), and poly(styrene-p-sulfonate)(1PSS), and a photoinitiator bearing a dithiocarbonate group (2) have been prepared. They formed monolayers on gold by spontaneous adsorption from organic solutions. Surface properties of these monolayers have been estimated by contact-angle and electrochemical measurements. Both techniques showed that there are distinct differences in surface propertias among counter-anions. The surface free energy calculated from the results of water and methylene iodide contact angle decreased in the order: 1Cl > 1SS > 1PSS, dependent upon the hydrophobicity of the counter-anions. Reverse trends (1Cl < 1SS < 1PSS) were observed in the electrochemical barrier capability of the monolayers toward Fe(CN)64–. Photopolymerizations of 1SS monolayers have been studied by cyclic voltammetry using Fe(CN)64– as an electroactive species. The polymerization process could be traced on the basis of reduction of the redox peak currents. For the 1SS–2([2]:[1SS]= 0.5%) monolayer, polymerization proceeded smoothly upon uv irradiation, with completion of the polymerization after ca. 3 h. The pure 1SS monolayer (without 2) showed only a slight decrease in the redox peak current, indicating that effective polymerization did not occur.Binary monolayers composed of 1SS and a fluoroalkanethiol (3) could also be formed on gold from solution, and their photopolymerization behaviour has also been studied. With decreasing 1SS content in the mixture, the redox peak currents increased with UV irradiation, in contrast to the results of the single-component (1SS) monolayer, suggesting formation of a boundary void between phase-separated domains of polymerized 1SS and 3.

Surface tension of polytrifluoropropylmethylsiloxane

AbstractSurface 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.

Stearic-1- 14C acid adsorption on metals and the contact angle as a function of surface coverage

Stearic-1- 14C acid was adsorbed as close-packed monomolecular layers on metallographically polished iron, nickel, chromium, and AISI types 304 and 416 stainless steels. Measurements of the adsorbed radioactivity allowed the determination of the number of adsorbed molecules per unit area and the effective area per molecule on each of the metals. Desorption and exchange experiments indicated two types of adsorption bonding in these systems; the relative amounts of each bonded type were determined for each metal. Methylene iodide contact angles were measured on both freshly prepared, completely intact monolayers and on monolayers which had been partially depleted during the desorption process. These measurements have allowed the determination of the variation in the magnitude of the contact angle as a function of surface coverage.

Ultra-high vacuum techniques in the measurement of contact angles: Methylene iodide on glass

The surface of a smooth fused silica disk was dehydrated by heating in an ultrahigh-vacuum system. Contact angles of methylene iodide on the disk were measured in situ by a vapor-phase transfer method. Values were obtained which were lower than any previously reported for methylene iodide on siliceous glass. Included among them was the value of zero degrees, which was obtainable under certain conditions. The contact angles were interpreted in terms of the types of glass surface obtainable in ultra-high vacuum.

The adsorption of C 14-labeled stearic acid on iron

Stearic-1-C 14 acid was adsorbed as a close-packed monomolecular layer on mechanically polished iron and fire-polished glass by the method of solution retraction. Measurements of the adsorbed radioactivity were made which allowed the determination of the number of adsorbed molecules per apparent unit area. Measurements of the methylene iodide contact angle on these two kinds of monolayer-covered surfaces showed that the surface-packing density of stearic acid molecules was the same in both cases. This conclusion, together with the assumption that the fire-polished glass surface had a roughness factor of unity, allowed the calculation of the area occupied per stearic acid molecule and the roughness factor of the iron surface. Desorption and exchange experiments indicated that about 60% of a complete monolayer was rather weakly adsorbed on iron while the remainder was probably chemically adsorbed. A rectilinear relationship was found between the measured contact angle and the extent of surface coverage. Surface-active impurities, which may occur in radioactive stearic acid solutions as a result of radiation damage, can be eliminated by treatment with activated adsorption alumina.