Dynamic Wetting Measurements Research Articles

An Eco-Friendly Surface Modification Method of Para-Aramid by Supercritical CO<sub>2</sub>

The structures and properties of para-aramid yarn were investigated under different treatment temperatures from 80 °C to 200 °C with supercritical CO2 and air, respectively, which were observed by Scanning electron microscopy (SEM), Dynamic wetting measurements, Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), and Thermogravimetric instrument (TG). It is confirmed that the surface morphology of para-aramid yarn was changed remarkably with the supercritical CO2 treatment temperature increasing compared to untreated yarn and treated with air, and the oligomers and disaggregates of yarn were migrated to the yarn surface. Furthermore, the water contact angle of para-aramid was reduced significantly from 136.22° to 91.37° with supercritical CO2 treatment at 200 °C, and the wettability was improved. Overall, supercritical CO2 modification for para-aramid has been proved to be feasible.

An investigation for the performance of meta-aramid fiber blends treated in supercritical carbon dioxide fluid

The physicochemical performance of meta-aramid fiber blends treated in supercritical carbon dioxide fluid was studied at different temperatures. The effects of treatment temperatures on the surface morphology, wettability, chemical and crystal structures, thermal and antistatic properties were investigated by employing Scanning electron microscopy, Dynamic wetting measurements, Fourier transform infrared spectrometry, X-ray diffraction, Thermal analysis and Static half period method, respectively. The result showed that the surface of the treated meta-aramid fiber blends was changed with the treatment temperature increasing and more mild grooves and stripes appeared. The dynamic wetting measurements showed that the water contact angles and absorption time for treated fibers were decreased with temperature increasing. The slight shifts of the characteristic bands of the treated meta-aramid fiber blends were observed in FT-IR spectra with the system temperature increasing. Meanwhile, XRD analysis showed that the diffraction intensities of treated samples were improved in the supercritical carbon dioxide fluid because some re-arrangements and re-crystallizations of the molecule chains generated. TG-DTG analysis indicated that the thermal property of meta-aramid fiber blends could be improved at various temperatures. In addition, supercritical carbon dioxide fluid had little negative influence on the physical and antistatic properties of the meta-aramid fiber blends.

Effect of treatment pressure on structures and properties of PMIA fiber in supercritical carbon dioxide fluid

ABSTRACTThe effects of treatment pressure on the structures and properties of PMIA fiber were investigated by Scanning electron microscopy, Dynamic wetting measurements, Fourier transform infrared spectrometry, X‐ray diffraction, thermogravimetric analysis, and mechanical properties test technology in supercritical carbon dioxide. The results indicated that the surface morphology, the water contact angle, the interaction of macromolecules, the crystal structure, the thermal property, and tensile strength of PMIA fibers were changed during supercritical carbon dioxide treatment, particularly the surface morphology and the wettability of fiber changed the most obviously with the increase of treatment pressure. Furthermore, the thermal property and tensile strength of treated PMIA fiber sample were improved in comparison with those of untreated sample. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41756.

Surface roughness and wettability of wool fabrics loaded with silver nanoparticles: Influence of synthesis and application methods

Hydrophilization of wool fabrics was performed by silver nanoparticles with different surface charge using three different methods: exhausting, pad–dry–cure and in situ synthesis. Dynamic wetting measurements and surface topography analysis were used to evaluate surface changes on wool fabrics. The wool samples in situ loaded revealed the highest fabric roughness and porosity, while the use of the pad–dry–cure method leads to the lowest fabric porosity, and its roughness values approximately were the same as those for samples loaded with the exhaustion method. The results revealed that loading silver nanoparticles with high surface charges onto wool fabrics via the exhaustion method can significantly improve the hydrophilicity of wool fibre surface. The possible reasons for this improvement are discussed.

Dependence of Wetting Behavior on the Thickness of Highly Viscoelastic Films

Both static and dynamic contact angle measurements were used to examine the impact of thickness on the wetting of highly viscoelastic films. The films are composed of a thermally stripped, solvent-borne acrylic polymer. Results show that wetting behavior is strongly influenced for polymer coatings < 10 μm thick and plateaus above this. This dependency is attributed to the extent to which surface tension forces can induce deformation. For thinner coatings, surface deformation is limited, which allows propagation of the three-phase line, resulting in low contact angles for sessile drop measurements and little or no discernible pinning in dynamic wetting measurements. With increasing film thickness, residual deformations due to the pinning of the wetting line start to appear and become quite distinct at thicknesses corresponding to the plateau wetting behavior. The onset of pinning is accompanied by nonwetting contact angles for sessile drops and stick-and-break propagations in dynamic measurements. The observed relationship between wetting behavior and decreased coating weight is similar to that reported previously between (static and dynamic) contact angle and increased wetting rate. It appears both relationships result from an increase in the elastic response of the film. The findings reviewed demonstrate that both film thickness and wetting rate can be used to control drop movement on viscoelastic surfaces.

Functional finishing of aminated polyester using biopolymer‐based polyelectrolyte microgels

This study focuses on a microgel-based functionalization method applicable to polyester textiles for improving their hydrophilicity and/or moisture-management properties, eventually enhancing wear comfort. The method proposed aims at achieving pH-/temperature-controlled wettability of polyester within a physiological pH/temperature range. First, primary amine groups are created on polyester surfaces using ethylenediamine; second, biopolymer-based polyelectrolyte microgels are incorporated using the natural cross-linker genipin. The microgels consist of the pH-responsive natural polysaccharide chitosan and pH/thermoresponsive poly(N-isopropylacrylamide-co-acrylic acid) microparticles. Scanning electron microscopy confirmed the microgel presence on polyester surfaces. X-ray photoelectron spectroscopy revealed nitrogen concentration, supporting increased microscopy results. Electrokinetic analysis showed that functionalized polyester surfaces have a zero-charge point at pH 6.5, close to the microgel isoelectric point. Dynamic wetting measurements revealed that functionalized polyester has shorter total water absorption time than the reference. This absorption time is also pH dependent, based on dynamic contact angle and micro-roughness measurements, which indicated microgel swelling at different pH values. Furthermore, at 40 °C functionalized polyester has higher vapor transmission rates than the reference, even at high relative humidity. This was attributed to the microgel thermoresponsiveness, which was confirmed through the almost 50% decrease in microparticle size between 20 and 40 °C, as determined by dynamic light scattering measurements.

Moisture absorption capacity of polyamide 6,6 fabrics surface functionalised by chitosan-based hydrogel finishes

The present study aims at investigating the moisture absorption capacity of polyamide 6,6 fabrics when their surface is functionalised by chitosan-based hydrogels. For the finishing procedure, bulk hydrogels of chitosan (CS) with different contents of embedded thermosensitive microparticles of poly( N-isopropylacrylamide- co-acrylic acid) (PNIAA) were used. In practice, hydrogel incorporation into the fabric surface layer was achieved by crosslinking primary amine groups of chitosan with the end amine groups of polyamide, using the natural crosslinker genipin. Among other analytical techniques, Scanning Electron Microscopy (SEM) was used to characterize the surface morphology of both hydrogel and fabric samples, Differential Scanning Calorimetry (DSC) to determine the Lower Critical Solution Temperature (LCST) of PNIAA, and X-ray Photoelectron Spectroscopy (XPS) to analyse the fabric surface chemical composition. The fabric moisture contents were determined by weight measurements at different temperatures and relative humidity values (RH). Liquid porosimetry, water vapour transmission (WVT) and dynamic wetting measurements were also performed to assess the fabric pore volume distribution, permeability and wetting times, respectively. It was found that the moisture absorbed by the functionalised polyamide fabrics can be regulated at different conditions of temperature and relative humidity according to the PNIAA/CS ratio in the hydrogel. For example, at 40 °C (i.e. above the PNIAA LCST) and even at high RH (85%), the higher the PNIAA/CS ratio was in the incorporated hydrogel, the lower were the moisture contents of the functionalised fabrics, compared to the reference. In all cases, the presence of CS increased significantly the polyamide fabric wetting times.

Modification of plasma pre-treated PET fabrics with poly-DADMAC and its surface activity towards acid dyes

In the recent years, there has been a growing interest in the substrate-independent coloration for the textile materials industries. This concern may be achieved by so-called tailored surfaces to be enriched by a certain kind of functional groups in order to increase substantivity of chemically diverse substrates toward a single class of dyes or develop of a single class of dyes that can be applied to all substrates. The approach introduced in this work comprises the formation of negatively charged groups on poly (ethylene terephthalate) fabrics, PET, surfaces by using low-temperature oxygen plasma. Subsequently, the positively charged polyelectrolyte poly(diallyldimethylammonium chloride), poly-DADMAC, was applied. This leads to stable surface modification with accessible quaternary ammonium groups that provide a high substantivity to acid dyes via complementary electrostatic attractions. Surface-sensitive characterization techniques such as X-ray photoelectron spectroscopy (XPS), streaming potential measurements, and dynamic wetting measurements were used to characterize the treated fabrics. Finally, color strength and fastness tests of printed fabrics were carried out to evaluate the effectiveness of surface modification.

Characteristics and durability of fluoropolymer thin films

The use of plasma-polymerised fluoropolymer (CFxOy) thin films in the manufacture of microelectromechanical systems (MEMS) devices is well-established, being employed in the passivation step of the deep reactive ion etching (DRIE) process, for example. This paper presents an investigation of the effect of exposure to organic and aqueous liquid media on plasma-polymerised CFxOy thin films. Atomic force microscopy (AFM), scanning electron microscopy (SEM), ellipsometry, X-ray photoelectron spectroscopy (XPS) and dynamic wetting measurements were all employed as characterisation techniques. Highly basic aqueous solutions, including known silicon etchants, were found to cause delamination via degradation of the countersurface below the CFxOy thin film. Films were found to be stable in organic solvents, acidic aqueous solutions and slightly basic aqueous solutions.

Short time wetting dynamics on soft surfaces

The wetting of solid surfaces by fluids has been studied for more than two centuries. However, it was only in recent years that investigations of the first milliseconds of spontaneous drop spreading on solid surfaces started. For non-deformable surfaces, this fast dynamic wetting process is known to be dominated by inertia and controlled by surface wettability. In this work we studied spontaneous spreading of liquids on soft, viscoelastic rubber films with shear moduli |G| between 0.2 and 510 kPa and thickness d between 30 and 160 μm. We found that the early stage of fast wetting of soft surfaces is also dominated by inertia and that the wetting dynamics follows a power law which mainly depends on wettability, but not on softness. This finding allows us to apply fast dynamic wetting measurements for inferring the equilibrium contact angle θeq on soft surfaces. On such surfaces static contact angle measurements with sessile drops would not yield univocal results and Young's equation is not directly applicable. On the other hand, the duration of the fast inertial wetting is controlled by surface softness. This is an indication of a viscoelastic dissipation process occurring during wetting that starts after some characteristic time dependent on the surface tension of the liquid, on the viscosity of the surface, and on the speed of wetting.

Effects of Topographic Structure on Wettability of Differently Woven Fabrics

Optical analysis of roughness operating on the principle of chromatic aberration and dynamic wetting measurements have been used to investigate the surface properties of polyester fabrics with different woven structures. The results revealed differences in the two basic types of weave — plain and twill — with respect to the penetration behavior of water. Additionally, plain weave fabrics were manufactured using differently profiled fibers — round and cruciform. It was established that fabrics composed of fibers having a cruciform cross section are more hydrophobic than those that are round. It was shown that topographical characteristics of the fabrics strongly depend on their construction parameters such as the type and fineness of filaments, yarn fineness, yarn density, and, consequently, the type of weave. The results provide further insight into the relationship between construction parameters of fabrics of the same chemical nature and their topographic and wetting properties.

Surface morphology and wetting properties of surfaces coated with an amphiphilic diblock copolymer

X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and dynamic wetting measurements with the Wilhelmy plate method were used to characterize layers of three polystyrene- b-poly(acrylic acid) (PS-PAA) diblock copolymers (differing by their block lengths) created by dip coating or spin coating on glass and gold substrata. The copolymer layers were thick and continuous, whatever the substratum, with a preferred exposure of PS chains at the extreme surface for the copolymers with a small PS block. The surface roughness decreased as the PAA/PS block length ratio increased and was larger for dip-coated than for spin-coated layers. The dip-coated layers obtained with the copolymer with the large PAA block presented self-assembled nanostructures of worm-like type. Dynamic wetting measurements showed that the coated layers were able to reorganize, upon immersion–emersion in solution at different pH, due to the deprotonation and swelling of the PAA chains. This phenomenon was dependent on the block length and on the pH. A water contact angle typical of pure PS was obtained with the large PS block. A hydrophilic surface was obtained for the large PAA block after immersion at pH 11. In intermediate situations (large PAA block in water, large PS block at pH 11), the advancing contact angle was dependent on the time of contact with air subsequent to the preceding immersion. This demonstrates the possibility to modulate hydrophobicity-hydrophilicity switching and pH sensitivity of the coatings by the copolymer composition.

Plasma-Oxidized Polystyrene: Wetting Properties and Surface Reconstruction

The surface of oxygen-plasma-treated polystyrene (PSox) was investigated using X-ray photoelectron spectroscopy (XPS), streaming potential measurements and a dynamic study of the wetting properties at different pH (Wilhelmy plate method). The PSox surface is functionalized with various oxygen-containing groups, including carboxyl functions, and must be viewed as covered by a poly-electrolyte which swells depending on pH. The wetting hysteresis, its evolution upon repeated cycles and the influence of pH are controlled by the dissolution of functionalized fragments and the retention of water upon emersion; the retained water may evaporate progressively and allow macromolecule compaction and/or reorientation. Modification of the PSox surface upon aging in dry atmosphere, humid atmosphere, and water was studied using XPS and dynamic wetting measurements. Aging in water provoked the dissolution of PSox macromolecular chains, as indicated by adsorption of released fragments on a check PS sample placed nearby. However, the concentration of functionalized molecules at the surface of water-aged PSox was still sufficient to allow swelling at pH 5.6 and 11.0. Hydrophobicity recovery was faster in humid air (R. H. 95%) compared to dry air (R. H. 5%), due to the plasticizing effect of water. Hydrophobicity recovery upon aging in air was reversed quickly by immersion at pH 5.6 or 11.0, due to deprotonation and swelling.

Surface characterization of polypropylene/(ethylene-propylene) copolymer blends (PP/EP): application to injection-moulded systems

Polypropylene/ethylene–propylene copolymer blends (PP/EP) were characterized by time-of-flight (ToF). SIMS, by dynamic wetting and by atomic force microscopy and force modulation spectroscopy (AFM–FMM). In a first step, model systems of compression-moulded PP/EP physical blends were prepared. With these materials, ToF-SIMS provides linear relationships between the selected peak and the EP content in the material. This indicates that both phases are present at the surface in the same concentrations as in the bulk. However, the EP signal is weak. In dynamic wetting measurements with water, for each tested blend composition the advancing contact angle corresponds to that of PP and the receding contact angle corresponds to that of EP. This method is thus suitable for detecting the presence of the two phases at the surface even for low concentrations of one consituent. The force modulation image gives elastic contrasts between EP and PP and is thus able to reveal the surface morphology. In a second step, these methods were used to characterize injection-moulded PP/EP reactor blends. Both AFM–FMM and ToF-SIMS suggest that a PP skin covers EP nodules at the surface. This is confirmed by electron microscopy examinations of cross-sections. This surface phase segregation leads to the presence of PP in the first 100 nm of the surface and could be explained by preferential wetting of the mould by the phase with the lower viscosity, PP in this case. However, dynamic wetting reveals that the PP skin is not complete. Thus, a low EP concentration may be found at the surface, in the form either of EP nodules or of EP molecules having migrated through the PP skin. Copyright © 1999 John Wiley & Sons, Ltd.

Study of fibre surface treatments for control of interphase properties in composites

Dynamic wetting measurements and micromechanical and macromechanical testing have been used to characterize the fibre/matrix interaction. Unsized glass fibres, glass fibres sized with γ-APS, poly(vinyl alcohol), γ-APS/polyurethane or γ-APS/epoxy, and untreated/unsized or treated/sized carbon fibres have been tested in combination with DGEBA-based epoxy resins of both amine and anhydride curing type. The experimental results of dynamic wetting show that the shape of the tensiogram depends on both fibre surface and resin chemistry. The slope of the force versus stage position plots represents the fibre/matrix interaction as swelling or acid-base interaction and depends on stage speed and fibre roughness. Wilhelmy wetting tests can be used to study the fibre/matrix interaction but conclusions about the resulting interphase can be drawn only in conjunction with micromechanical and macromechanical testing. Interfacial shear strength and transverse tensile strength show evidence of the same ranking and reflect the expected interphase behaviour.

Dynamic wetting in the low capillary number regime

An understanding of dynamic wetting is necessary when considering processes in which one fluid is forced to displace another fluid from a solid substrate. This work examines the forced wetting behavior exhibited by a series of solid-liquid systems in the low capillary number regime. In particular, the effects of specific chemical (i.e. acid-base) interactions between the liquid and the solid and of solid surface roughness on dynamic wetting are investigated. Measurement of the dynamic contact angle as a function of the interline velocity is performed using the technique of microtensiometry. The data are compared with empirical correlations in order to test the hypothesis that a universal correlation may be used to describe wetting behavior. The results suggest that two correlation having the same functional form but different constants are necessary to adequately describe wetting behavior above and below a capillary number of the order of 10 −3. No significant differences are observed between the wetting behavior of systems with only dispersive interactions between the liquid and solid and systems with acid-base interactions, implying that the static contact angle adequately accounts for the effect of acid-base interactions. Surface roughness produces noticeable stick-slip effects in the low capillary number regime when the static contact angle is larger than approximately 15°. While these effects produce a large degree of scatter in the dynamic wetting measurements, they do not alter the constants from those found in the case of smooth interline motion.