Urine Advancing Contact Angle on Several Surfaces

Urine wetting properties may influence the design and performance of catheters, urinalysis instruments, and lab-on-a-chip technologies. In this study the advancing contact angle _adv of urine on several materials is characterized. Material type and surface tension have a significant effect on _adv, while pretreatment and aging do not. Mean urine _adv are between ≈78° and ≈89° on hydrophilic surfaces, and up to over ≈105° on hydrophobic surfaces. Expected urine contact angles will decrease from the DI water contact angles by on average 10°, and up to 20°, while urine surface tension will be lower than DI water by 12.12 mN/m and 18.53 mN/m. A unit change (mN/m) in surface tension results in a 0.75° change in _adv. These results indicate that systems attempting to exploit urine wetting must account for highly variable conditions.     

Effects in Surface Free Energy of Sputter-Deposited VNx Films

Vanadium nitride (VN _x ) thin films have attracted much attention for semiconductor integrated circuit (IC) packaging molding dies, and forming tools due to their excellent hardness and, thermal stability. VN _x thin films with VN_0.45, VN_0.83, VN_1.22, VN_1.73, VN_2.06 were prepared using a radio frequency (RF) sputter technique. The experimental results showed that the contact angle at 20°C increases with increasing nitrogen content of the VN _x films, to 101.4° corresponding to VN_1.73 and then decreased. In addition, the contact angles decreased with increasing surface temperature, because an increase of the surface temperature disrupts the hydrogen bonds between water and the films and the water gradually vaporizes. The total surface fee energy (SFE) at 20°C decreased with nitrogen content of the VN _x films to 29.8 mN/m (VN_1.73) and then increased. This is because a larger contact angle means weaker hydrogen bonding which results in a lower SFE. The polar SFE component had the same trend as the total SFE, but the dispersive SFE component had the opposite trend. The polar SFE component is also lower than the dispersive SFE component. This is because hydrogen bonds are polar. The total SFE, dispersive SFE and polar SFE of the VN _x films all decrease with increasing surface temperature. This is because with increasing temperature, water evaporates from the surface, disrupting hydrogen bonds and hence increasing surface entropy. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. As a result the SFE and surface roughness can be expressed in terms of a simple ratio function.     

Adhesion and Wettability Characteristics of Chemically Modified Banana Fibre for Composite Manufacturing

In this work banana fibre was chemically modified using various chemical agents. The surface energy of the fibre is an important parameter and one which governs the interaction of fibre with polymeric matrices. This paper describes the influence of various chemical treatments on the surface energy of the banana fibre investigated by contact angle measurements, spectroscopic analysis and surface morphology studies. The surface energy, work of adhesion, polarity, spreading coefficient, interfacial energy and interaction parameter were determined in the case of raw and chemically modified fibres. Chemical modification has been found to have a profound effect on the surface energy. The polar and dispersive components of the surface energy were also found to be dependent on the chemical treatment involved. The chemical modifications done in this work were: alkali treatment, silanation, benzoylation, formylation, potassium permanganate treatment and acetylation. Of all the modifications, the relative surface energy was found to be a maximum for alkali treated fibre and minimum for silanated fibre. Contact angle measurements were found to be an effective tool in predicting the possible interaction of the fibres with phenol formaldehyde matrix resin. Atomic force microscopy roughness analysis revealed a significant decrease in surface roughness for the chemically modified fibre. An increase both in fibre/matrix adhesion and interfacial shear strength has been observed for all surface modified fibres except for those modified by benzoylation and acetylation.     

Investigation of the surface rearrangement of poly(imide-siloxane) using dynamic contact angle measurements

Dynamic contact angle measurements and X-ray photoelectron spectroscopy (XPS) were used to investigate the surface compositions and surface rearrangement of poly(imide-siloxane) with various molecular weights and contents of amine-terminated poly(dimethyl siloxane) (ATPDMS). Four different water contact angles were measured to study the poly(imide-siloxane) surface: the initial advancing angle, the equilibrium advancing angle, the initial receding angle, and the equilibrium receding angle. Poly(imide-siloxane) with 2350 and 4300 g/mol of ATPDMS showed higher initial and equilibrium advancing contact angles than those of poly(imide-siloxane) with 433 g/mol of ATPDMS. Since the mobility of ATPDMS segments depended on the chain length of ATPDMS, the molecular weight of ATPDMS determined the surface composition of poly(imide-siloxane), the rate of surface rearrangement, and the contact angle hysteresis. Poly(imide-siloxane)s with 2850 and 4300 g/mol of ATPDMS were mostly covered with ATPDMS even if just 1 wt% of ATPDMS was incorporated, while poly(imide-siloxane) with 433 g/mol of ATPDMS was mostly covered with polyimide segments and partially with ATPDMS. The rate of surface rearrangement and the contact angle hysteresis decreased with the increasing molecular weight as well as content of ATPDMS. The actual ATPDMS-enriched layer thickness was also investigated by XPS. The actual thickness of the ATPDMS-enriched layer was about 15 nm for 2850 g/mol and 4300 g/mol of ATPDMS-modified poly(imide-siloxane) and about 7.5 nm for 433 g/mol of ATPDMS-modified poly(imide-siloxane)     

Calendar of events

The influence of the gas type, air or nitrogen, and the treatment time in an RF glow discharge treatment on the shrink resistance properties of knitted wool fabric and wetting properties of keratin fibres were studied. Wetting properties were determined by means of contact angle measurements on single keratin fibres. This method allows measuring accurately the influence of the plasma gas type and treatment time on fibre hydrophilicity, and its modification with the time elapsed after plasma treatment. The modification of the surface properties should be taken into account, especially, when a biopolymer after-treatment is applied to achieve wool shrink resistance. Surface chemical changes were studied by means of XPS. Topographical changes in the wool fibre surface were observed by scanning electron microscopy (SEM) and surface damage was evaluated by means of the Herbig sac formation. Both air and nitrogen plasma treatments impart shrink resistance to wool fabric and hydrophilic properties to the keratin fibres. Even short exposure times are found to be enough to decrease drastically the advancing water contact angle and, therefore, to increase the shrink resistance effect. Slight differences were observed between the air and nitrogen plasma treatments. The time elapsed after the plasma treatment promotes an increase of the advancing contact angle and a decrease of chitosan adsorption. The plasma treatments studied here modify chemically the epicuticle but it is not removed.     

The combined effect of roughness and heterogeneity on contact angles: the case of polymer coating for stone protection

The individual effects of heterogeneity and roughness on contact angles have been repeatedly analysed in the literature, but the application of the accepted models to practical situations is often not correctly performed. In the present paper the combined effects of roughness and heterogeneity on the contact angles of water on stone surfaces protected by a hydrophobic polymer coating are considered. Two different kinds of calcareous stone with different surface roughnesses and porosities were protected against the effect of water absorption by two different polymer coatings. The contact angles of water on the protected stone surfaces were measured by the Wilhelmy and the sessile drop techniques. A comparison of the results obtained shows not only the limits of the static sessile drop technique, but also the combined effect of roughness and heterogeneity. Some considerations are developed on the application of commonly accepted models to surfaces with a combination of roughness and heterogeneity. Some other results obtained with techniques such as roughness measurements, mercury porosimetry, energy dispersive X-ray spectroscopy (EDXS), thermogravimetric analysis (TGA), water absorption by capillarity experiments (WAC), all able to show the structure and properties of the obtained films, are also compared with those obtained from contact angle measurements. It is concluded that the static contact angle is not well correlated with the degree of protection; on the contrary, the receding contact angles are well correlated with the degree of protection actually obtained. An ideal protecting agent should have a receding contact angle greater than 90°.     

On the determination of the surface energetics of porous polymer materials

The solid surface tension γsv of hydrophobic polymer powders has been determined using the capillary penetration technique. By plotting Kγlv cos ζ, where K is a geometric factor, versus the liquid surface tension γlv, the following values of γsv were directly derived from the curves: poly(tetrafluoroethylene) γsv = 20.4 mJ/m², polypropylene γsv = 30.2 mJ/m², polyethylene γsv = 34.4 mJ/m², and polystyrene γsv = 27.5 mJ/m². These values are in good agreement with the γsv values obtained from contact angle measurements on flat and smooth solid surfaces of the same materials. If the contact angles were first calculated from the capillary penetration experiments, which is the usual procedure applied in the literature, distinctly higher contact angles were obtained. Obviously these angles are affected by the powder morphology and are therefore meaningless contact angles in terms of a surface energetic interpretation.     

Stress analysis and strength evaluation of bonded shrink fitted joints subjected to torsional loads

This paper deals with the stress analysis and strength evaluation of bonded shrink fitted joints subjected to torsion. The stress distributions in the adhesive layer of bonded shrink fitted joints are analyzed by the axisymmetric theory of elasticity when an external torsion is applied to the upper end of the shaft. The effects of the outer diameter and the stiffness of rings on the interface stress distributions are clarified by numerical calculations. Using the interface stress distributions, the joint strength is predicted. In addition, the joint strength was measured experimentally. It is seen that rupture of the adhesive layer is initiated from the upper edge of the interface when torsion is applied to the upper end of the shaft. The numerical results are in fairly good agreement with the experimental results. It was found that the joint strength of bonded shrink fitted joints is greater than that of shrink fitted joints.     

Surface modifications of EVA copolymers induced by low pressure RF plasmas from different gases and their relation to adhesion properties

Two ethylene vinyl acetate (EVA) copolymers (12 and 20 wt% of vinyl acetate,VA, content) have been treated with low pressure RF plasmas from non-oxidizing gases (Ar, N₂) and oxidizing gases (air, a mixture of 4N₂: 6O₂ (v/v), O₂ and CO₂). The formation of polar moieties on both EVAs was more noticeable by treatment with plasmas from non-oxidizing gases than from oxidizing ones (the higher the reactivity, the lower the difference with respect to untreated EVA surfaces). The surface etching with the non-oxidizing plasmas, giving rise to a high roughness, depends on the wt% of VA in the composition of the copolymer because of the different resistances of VA (low) and PE (high) to the non-oxidizing plasma particles bombardment. The adhesion properties obtained using a polyurethane adhesive (PU) showed high T-peel strength values and adhesion failure in EVAs treated with plasmas from oxidizing gases, due to roughness produced causing mechanical interlocking of the adhesive. Lower T-peel strength values were obtained with non-oxidizing plasmas: the values for EVA12 being, in general, lower than those obtained for EVA20. The durability of the treated EVAs/PU adhesive joints after ageing in humidity and temperature was quite good.     

The effects of nanostructure and composition on the hydrophobic properties of solid surfaces

The effects of nanoroughness and chemical composition on the contact and sliding angles on hydrophobic surfaces were studied theoretically and experimentally. A theoretical model based on forces developed at the contact area between a liquid drop and hydrophobic smooth or nanoroughened surface was developed and compared with the existing models, which are based on forces developed at the periphery between the drop and the solid surface. The contact area based model gives rise to an interfacial adhesion strength parameter that better describes the drop-sliding phenomenon. Consequently, relationships were derived describing the dependence between the interfacial adhesion strength of the liquid drop to the surface of a given composition, the mass of the drop, the measured contact angles and the sliding angle. For a given surface chemistry, the sliding angle on a nanometric roughened surface can be predicted based on measurements of contact angles and the sliding angle on the respective smooth surface. Various hydrophobic coatings having different surface nanoroughnesses were prepared and, subsequently, contact angles and sliding angles on them as a function of drop volume were measured. The validity of the proposed model was investigated and compared with the existing models and the proposed model demonstrated good agreement with experimental results.