Contact Angle Measurements In Order Research Articles

An Alternative Methodology for the Evaluation of Photocatalytic Activity of Polymeric Coatings by Monitoring Dye Degradation

This work provides an alternative method for evaluating the photodegradation behaviour of different types of dyes such as Methylene Blue, Rhodamine B, Congo Red, Metanil Yellow, and Malachite Green. In this methodology, the coating is dyed with the chosen colorant and two beams of light are combined and channelled to a spot on the dyed coating through an optical fibre, the first one from an ultraviolet (UV) source (which is the responsible of activating photocatalysis) and the second one from a Visible light source, which is employed to monitor changes in colour along the time. The photocatalytic coating selected for testing this methodology consists of a mat of electrospun poly (acrylic acid) (PAA) fibres that acts as base film, furtherly coated by using layer-by-layer (LbL) assembly technique for the immobilization of two different photocatalytic metal oxide precursors (TiO2 and Fe2O3) nanoparticles. The morphological characterization of the samples has been implemented by means of scanning electron microscopy (SEM), confocal microscopy, and water contact angle measurements in order to analyse the resultant thickness, roughness, electrospun fibre diameter, and wettability. The experimental results clearly demonstrate the validity of the methodology to measure the photocatalytic activity in all dyed coatings, although significant differences have been observed depending on the selected dye.

Wetting and adhesion evaluation of cosmetic ingredients and products: correlation of in vitro-in vivo contact angle measurements.

The aim of this work was to use the contact angle measurement in order to predict the behaviour of ingredients and finished cosmetic products on skin to improve skin feel and product texture. Different classes of cosmetic ingredients and formulations were evaluated. The contact angle measurements were carried out by the sessile drop method using an apparatus, designed and set up in laboratory. Glass, Teflon and human skin were the reference substrates. In a preliminary phase, TEWL parameter, sebum content and hydration of human skin were measured to set up method. Data demonstrated that glass substrate may be used as replacement of the skin:critical surface tension of skin and glass were about of 27 and 31 dyne cm-1 , respectively. Non-ionic surfactant with increasing HLB was evaluated: a correlation between contact angle measured and HLB was not observed because of different and complex molecular structure. In detail, ethylhexyl hydroxystearate (θglass = 17.1°) showed lower contact angle value with respect to Polysorbate 20 (θglass = 28.1°). Sodium laureth sulphate and stearalkonium chloride were also evaluated: anionic molecule showed more affinity for glass with respect to Teflon (θglass = 21.7° and θTeflon = 52.3°). Lipids and silicones showed different affinity for substrate according to hydrophilic groups and hydrocarbon chain: contact angles of silicones remained unchanged independently from substrate. Finished cosmetic products (O/W, W/O emulsions, cleansing oil, dry skin oil) showed different profiles according to surfactant and its affinity for continuous phase of the formulation. Comparing the values of the contact angle on skin of non-ionic surfactants, as ethylhexyl hydroxystearate and Polysorbate 20, they showed values lower (near to zero) than ones of sodium laureth sulphate and Stearalkonium Chloride (21.7° and 66.8°, respectively). Finally, finished cosmetic products tested on human skin showed different profile: corresponded contact angle values were less than 20°. The product tended to be quickly adsorbed on human skin. Systematic study carried out by evaluating the wettability of single cosmetic ingredients on different substrates allowed to find correlations between the use of certain ingredients and the final performance of a cosmetic product.

Wettability and Surface Morphology Investigation of RGP Eye Contact Lens Irradiated by 193 nm Excimer Laser

In this work, Rigid gas permeable (RGP) contact lenses based on Fluoro Silicone Acrylate, were ir- radiated by using 193 nm ArFexcimer laser, at 1 Hz pulse repetition rate with 75 mJ/pulse energy to improve surface wettability. We investigated the morphology of the ablated area by imaging the surface modification with Atomic force microscopy (AFM) with roughness analysis and Scanning electron microscopy (SEM). Characterization techniques were performed too via contact angle measurement in order to determine the surface wettability and Fourier transform infra-red spec- troscopy (FTIR). The morphological appearance of samples reveals the effect of a photochemical and photothermal ablation mechanism. The laser irradiation without changing the chemical bonds has modified the lens surface properties and increased the surface hydrophilicity. Morphological surface changes with laser exposure and the water contact angle decreases as the surface of the fluorosilicone acrylate material is modified.

Antibacterial activity and biodegradability assessment of chemically grafted nanofibrillated cellulose

Nanofibrillated cellulose (NFC) and their derivatives were prepared using three chemical surface modification strategies. All grafting was characterized by FTIR and contact angle measurements in order to evaluate the efficiency of grafting. Antibacterial activities of neat and grafted samples were investigated against two kinds of bacteria (i.e. Gram+ (Staphylococcus aureus) and Gram− (Klebsiella pneumoniae)). All the grafted samples displayed promising results with at least bacteriostatic effect or bactericidal properties. They also strongly enhanced the photo-catalytic antimicrobial effect of TiO2. This study proves that it is better to use grafted NFC either alone or for functionalization with TiO2 if anti-bacterial properties are desired. The cellulose backbone is known to be easily biodegradable in different biodegradation conditions and environments. The chemical surface modifications applied on NFC in the present work did not negatively influence this valuable property of cellulose but help for monitoring this property, which could be very useful for paper, packaging and composites.

Improving cell adhesion: development of a biosensor for cell behaviour monitoring by surface grafting of sulfonic groups onto a thermoplastic polyurethane.

The surface properties of a material in combination with the mechanical properties are responsible for the material performance in a biological environment as well as the behaviour of the cells which contact with the material. Surface properties such as chemical, physical, biological play an important role in the biomaterials filed. In this work, the surface of a thermoplastic polyurethane film (Elastollan(®)1180A50) was tailored with sulfonic groups by grafting [2-(methacryloxyl)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide (SB) after a previous surface activation either by Argon plasma or by ultra-violet irradiation. This surface modification had the purpose of improving cell adhesion in order to develop a biosensor able to monitor cell behaviour. The surfaces were characterized by X-ray photoelectron spectroscopy, by atomic force microscopy and by contact angle measurements in order to evaluate the efficiency of the modification. Additionally, blood compatibility studies and cell adhesion tests with human bone marrow cells were performed. These methods allowed the grafting of SB and the results indicate that a higher density of grafting was achieved with previous surface plasma treatment than with UV irradiation. However, for both techniques, the presence of SB functional groups led to a decrease of hydrophobicity and roughness of the surface, together with an improvement of the materials biological performance.

Modification of a Nafion membrane by n-dodecyltrimethylammonium cation inclusion for potential application in DMFC

Changes in a protonated Nafion-112 membrane as a result of the incorporation of the cation n-dodecyltrimethylammonium (DTA+) by proton exchange mechanism are studied. Membrane surface modifications were analysed by AFM, XPS and contact angle measurements in order to obtain information about changes in the membrane surface roughness, chemical nature and hydrophobic character, while electrochemical impedance spectroscopy (EIS) and methanol permeation measurements were carried out to establish changes in the bulk membrane. The reduction obtained for the surface roughness and the hydrophobic character of Nafion-112/DTA+ equilibrated membrane as well as for the fluorine atomic concentration percentage and the increase in nitrogen percentage indicates modification of Nafion-112 membrane surface, while the increase of electrical resistance and the decrease of methanol permeability give information on bulk membrane changes. The higher thermal stability and lower water loss of the Nafion-112/DTA+ membrane are points of interest for applications such as PEMFC or DMFCs, respectively.

Adlayers of Dimannoside Thiols on Gold: Surface Chemical Analysis

Carbohydrate films on gold based on dimannoside thiols (DMT) were prepared, and a complementary surface chemical analysis was performed in detail by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), near-edge X-ray absorption fine structure (NEXAFS), FT-IR, and contact angle measurements in order to verify formation of ω-carbohydrate-functionalized alkylthiol films. XPS (C 1s, O 1s, and S 2p) reveals information on carbohydrate specific alkoxy (C-O) and acetal moieties (O-C-O) as well as thiolate species attached to gold. Angle-resolved synchrotron XPS was used for chemical speciation at ultimate surface sensitivity. Angle-resolved XPS analysis suggests the presence of an excess top layer composed of unbound sulfur components combined with alkyl moieties. Further support for DMT attachment on Au is given by ToF-SIMS and FT-IR analysis. Carbon and oxygen K-edge NEXAFS spectra were interpreted by applying the building block model supported by comparison to data of 1-undecanethiol, poly(vinyl alcohol), and polyoxymethylene. No linear dichroism effect was observed in the angle-resolved C K-edge NEXAFS.

Modification of Food-Contacting Surfaces by Plasma Polymerization Technique: Reducing the Biofouling of Microorganisms on Stainless Steel Surface

In this study, the prevention of the attachment of test microorganism Enterobacter sakazakii onto stainless steel (SS 316) surfaces by radio frequency (RF) plasma polymerization (PlzP) technique using several hydrophilic monomers as precursors was reported. Different plasma conditions (RF discharge power of 20–80 W with exposure time of 10 min) were employed during the modifications. PlzP-modified surfaces were characterized in detail by static contact angle measurements in order to state the change of surface hydrophilicity. The surface topology of unmodified and PlzP [ethylenediamine (EDA)]-modified SS 316 plates was characterized by atomic force microscopy. The attachment of the model microorganism on the SS 316 surface modified by plasma using EDA at 45 W and 10 min was reduced by 99.74% in comparison to the unmodified control surface. For equilibrium adsorption behavior, Freundlich and Langmuir models were attempted and model parameters for Freundlich (KF and 1/n) and for Langmuir (a and b) were obtained. The values of the KF and 1/n were 5.6 and 0.58 and 0.9 and 0.39, respectively; the values of a and b were 25 × 104 and 1.82 × 10−8 and 0.3 × 104 and 7.96 × 10-8, for bare and PlzP-EDA-modified SS 316 surfaces, respectively. As a result, PlzP technique was found to be an alternative simple method to decrease the microbial attachment and create bacterial anti-fouling surfaces.

Surface characterization of low‐temperature cascade arc plasma–treated low‐density polyethylene using contact angle measurements

AbstractLow‐density polyethylene (LDPE) was treated with a low‐temperature cascade arc plasma torch (LTCAT) of argon with or without adding a reactive gas of oxygen or water vapor. The static sessile droplet method and the dynamic Wilhelmy balance method were employed to perform surface contact angle measurement in order to investigate and characterize the effects of LTCAT treatment on LDPE surfaces. These treatment effects included changes in surface wettability and surface stability and possible surface damage that would create low‐molecular‐weight oligomers on the treated surface. Experimental results indicated that the combination of static and dynamic surface contact angle measurements enabled a comprehensive investigation of these effects of plasma treatment on a polymer surface. Without the addition of a reactive gas, a 2‐s argon LTCAT treatment of LDPE resulted in a stable hydrophilic surface (with a water contact angle of 40°) and little surface damage. The addition of oxygen into argon LTCAT produced a less stable LDPE surface and showed more surface damage. Adding H2O vapor into argon LTCAT produced an extremely hydrophilic surface (with a water contact angle < 20°) of LDPE but with pronounced surface damage. When compared with conventional radio frequency (13.56 MHz) plasmas, LTCAT treatment provides a much more rapid, effective, and efficient method of surface modification of LDPE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2528–2541, 2006

Preparation of poly(vinylidene fluoride)(pvdf) ultrafiltration membrane modified by nano-sized alumina (Al 2O 3) and its antifouling research

Organic–inorganic composite membranes are formed by nano-sized alumina particles uniformly dispersed in the poly(vinylidene fluoride) solution (19% polymer weight). Membranes were prepared by phase inversion process and were characterized by ultrafiltration (UF) experiments in terms of water flux, molecular weight cut-off for the wet membranes. Contact angle between water and the membrane surface were measured by contact angle measurement in order to characterize the hydrophilicity changing of the membrane surface. The cross-sectional structures, porous dispersion in membranes surface and nanometer particles distribution in the membrane were examined by scanning electron microscopy (SEM) and transmission microscopy (TEM), respectively. The effect of nanometer Al 2O 3 particles concentration in the polymer dope on the permeation properties, membrane structures and antifouling performances were examined. The experimental results indicate that Al 2O 3–PVDF composite membranes exhibit significant differences in surface and intrinsic properties due to nanometer particles addition.

Chemical and Thermal Stability of Surface‐Modified Porous Polyethylene Membranes

In this paper, we describe the surface modification of porous polyethylene by the adsorption of polyelectrolyte mutilayers on plasma‐activated polyethylene surfaces. We use the migration rates of deionized water as an effective alternative to contact angle measurements in order to probe the interfacial energy of the modified surface. The newly acquired surface properties that result from the surface modification are monitored with respect to several key chemical and environmental variables. These variables were chosen so that they will reflect some of the common handling procedures in a laboratory or health care environments, such as exposure to solvents of different pH and polarities, and fluctuations of ambient temperature over an extended period, i.e., “shelf‐life” duration. The stability of these surface properties of the modified membranes is a fundamental requirement for their potential use in a variety of applications involving lateral flow and binding media for bio‐assays. In this paper, we show that a membrane modified by a polyelectrolyte monolayer is more stable than a membrane that has undergone plasma activation alone, while a membrane modified by a polyelectrolyte bilayer exhibits retention of the enhanced surface hydrophilic properties under various conditions and over a long period of time.

Influencia del proceso de esterilización en la mojabilidad del titanio modificado superficialmente

El objetivo de este trabajo es estudiar el cambio en las propiedades energéticas de muestras de
 titanio comercialmente puro debido a distintos tratamientos superficiales y a distintos métodos de
 esterilización; con la finalidad de entender cómo afectan estos cambios a los procesos biológicos de
 los implantes de titanio.
 Los distintos tratamientos superficiales utilizados fueron: la formación de rugosidad mediante la
 proyección de partículas abrasivas, el granallado, y la esterilización mediante autoclave, óxido de
 etileno o radiación gamma.
 Tanto el nivel de rugosidad generada como la naturaleza de las partículas del granallado influyen
 en el carácter energético de las muestras; incrementando el carácter hidrofóbico con el aumento de la
 rugosidad y con la utilización de alúmina. Los contaminantes debidos al proceso de autoclave
 hidrofobizan las superficies; contrariamente a la esterilización por óxido de etileno que disminuye el
 valor del ángulo de contacto.
 La modificación de las superficies tratadas fue examinada con una serie de técnicas analíticas
 superficiales que incluyen el microscopio electrónico de barrido (SEM), la interferometría óptica y la
 medición del ángulo de contacto para poder realizar una caracterización topográfica, cualitativa y
 cuantitiva, y una caracterización energética, respectivamente. The aim of this work is to study the energetic properties of commercially pure titanium samples due
 to different surface treatments and different sterilization methods; with the purpose to understand
 how these changes affect to the biological processes of titanium implants.
 The different surface treatments were: roughness obtained by shot blasting, and sterilization by
 steam autoclaving, ethylene oxide or gamma radiation.
 Roughness level and the nature of the abrasive particles of shot blasting influence energetically
 the samples; increasing the hydrophobic behaviour with the increase of the surface roughness and
 the alumina use. The contamination due to steam autoclaving hydrophobizes the surface; contrary to
 sterilization by ethylene oxide, which reduces the contact angle value.
 The modification of treated surfaces was examined with a series of surface analytical techniques
 that include the scanning electron microscopy (SEM), the white light interferometer microscopy and
 the static contact angle measurement in order to determine a qualitative and quantitative topographic
 characterization and an energetic characterization.

Comparison of model monomeric and polymeric alkyl stationary phases on silica using sum-frequency spectroscopy

Model monomeric and polymeric stationary phases were examined using sum-frequency spectroscopy and contact angle measurements in order to determine structural differences between the two stationary phases. Octadecyldimethylchlorosiloxane (ODMS) monolayers and ODMS/methyl siloxane (MS) mixed monolayers in contact with water and acetonitrile solvent were examined. The results showed that the alkyl chains in the ODMS and the ODMS/TMS monolayer are highly disordered and are weakly sensitive to the change in solvent environment. In order to determine whether the observed disorder in ODMS is due to steric effects of the silicon bonded methyl groups or the lack of crosslinking, “surface-bonded” ODS and “highly crosslinked” ODS were studied and compared with ODMS. Calculations using contact angle data on ODMS monolayers showed that water interacts 70% with methyl groups and 30% with methylene groups.

Stability and ageing of plasma treated poly(tetrafluoroethylene) surfaces

In this study CO 2, H 2/H 2O and H 2O low pressure plasma treatment of poly(tetrafluoroethylene) (PTFE) foils and of thin plasma deposited fluorocarbon polymer (PDFP) films with a structure close to PTFE was investigated. The properties of the plasma were analyzed by mass spectroscopy (MS) and optical emission spectroscopy (OES). The modified fluorocarbon surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), fourier transform infrared (FTIR) spectroscopy, spectroscopic ellipsometry, electrokinetic measurements and dynamic contact angle measurements in order to find optimized treatment conditions. The results of the surface modification were compared with respect to the efficiency of the plasma treatment and the stability of the modification effect at different ambient conditions. It was shown that the H 2O plasma treatment is the most effective process for the intended modification. The hydrophobic PTFE surface was converted into a more hydrophilic one. The introduced radicals after the H 2O plasma treatment can be utilized subsequently for post plasma reactions such as grafting processes.

Poly(vinylidene fluoride) with improved functionalization for membrane production

Poly(vinylidene fluoride) (PVDF) was modified by chemical treatments in order to obtain a functionalized polymer suitable for the preparation of ultrafiltration membranes with improved hydrophilicity and fouling resistance. Membranes obtained from the modified polymer as well as from the unmodified one were characterized through pure water permeability measurements and ultrafiltration tests with a dilute solution of skim milk. The fouling tendency of the membranes was measured from the relative reduction in water permeability before and after ultrafiltration. Dense films were also prepared and characterized through contact angle measurement in order to obtain a preliminary evaluation of the hydrophobicity. Vibrational spectroscopy (FT-IR and FT-Raman) techniques were effectively used to investigate the functionalities introduced by the chemical treatments.

Dispersion and Polar Force Components of Surface Tension of Some Polymer Films

The surface tension and the dispersion and polar components of the surface tension for solids and liquids were estimated by contact angle measurement in order to apply these concepts to a detergency study. Two approximation methods, the extended Fowkes' equation and Wu's equation, were adopted for the calculations. Among the twelve experimental liquid pairs, methylene iodide/water and tricresyl phosphate/water gave values for paraffin, polyethylene, and polystyrene close to the average for the twelve pairs. Values for cellulost acetate and cellophane were there fore obtained using these two pairs. The results showed that the dispersion force component becomes larger with increasing degree of acetylation, while the polar force component becomes smaller.