Contact Angle Goniometry Research Articles

The effect of wool surface and interior modification on subsequent photostability

AbstractWool surface and interior modification can impart favorable properties, such as felting/shrink resistance, settability, or improved affinity for dyes. However, in principle such modification may have an either beneficial or adverse effect on the subsequent photostability of the modified wool. In this study, a range of representative physical and chemical modification approaches including the use of helium gas plasma, papain, acylation with acid anhydride, and permanganate oxidation were applied to wool fabrics, and the subsequent effects characterized using scanning electron microscopy, FTIR‐ATR, contact angle goniometry, fluorescence spectrophotometry, and tensile strength test. The relative photostability of control and treated wool were evaluated in terms of coloration changes under UVA, UVB, and blue light irradiation. We have shown that the subsequent photostability of modified wool fabrics is highly dependent on the modification type, and this factor should be carefully considered in the design and application of wool treatments. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Immobilization of Heparin on the Surface of Polypropylene Non-Woven Fabric for Improvement of the Hydrophilicity and Blood Compatibility

A polypropylene non-woven fabric (PPNWF) was exposed to oxygen plasma to produce peroxides on its surface. These peroxides were used to initiate graft polymerization of acrylic acid (AA) on the surface of PPNWF. Direct heparinization was accomplished via a reaction between heparin and PP-PAA (AA grafted PPNWF) which was activated by EDC (N-ethyl-N’-[3-(dimethylamino)propyl] carbodiimide). Indirect heparinized PPNWF was prepared by grafting poly(ethylene oxide) (PEO) on a PP-PAA surface to form PP-PAA-PEO, followed by reaction with heparin which was activated by EDC before use. The surface modified PPNWFs were characterized by attenuated total reflection Fourier transform infrared (ATR–FT-IR) spectroscopy, electron spectroscopy for chemical analysis (ESCA) and contact angle goniometry. It was found that hydrophilicity was greatly improved, as indicated by the decrease of the water contact angle from 142 to 33°. In vitro blood compatibility evaluation of modified PPNWFs, including hemolysis rate, platelet adhesion, plasma protein adsorption and activated partial thromboplastin time (APTT) was investigated. The results suggested that both heparinized PPNWFs showed lower hemolysis rates and better platelet anti-adhesion than non-heparinized controls. Furthermore, PPNWF obtained via indirect immobilization of heparin showed better hydrophilicity and blood compatibility than direct heparinization of PPNWF.

Effect of reaction duration in the formation of superhydrophobic polymethylsilsesquioxane nanostructures on cotton fabric

The shape and size of the surface roughness induced by nanostructured materials have a significant effect on the wetting behavior of superhydrophobic surfaces. In this work, the effect of organosilane reaction duration on the formation of polymethylsilsesquioxane (PMSQ) nanostructures on cotton fibers surface has been investigated. The reaction was performed in methyltrichlorosilane (MTCS) solution at different duration time. The surface morphology and surface chemistry were investigated with scanning electron microscopy (SEM), attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and energy dispersive X-ray (EDX) spectroscopy. The wetting properties of fabrics were elucidated by means of contact angle (CA) goniometry and sliding angle (SA) measurements. The results revealed that reaction duration has a significant effect on the morphology of nanostructures and also their covering density, which can influence the hydrophobic state of the surface. For fabrics with fine nanogrooves and low surface coverage, adhesion between droplets and the surface is high so that droplets cannot slide off even when the fabric was turned upside down (‘sticky’ surface) whereas for the fabrics with the high area density of the entangles nanofilaments, adhesion is low and droplets can roll off by tilting the plate (‘slippery’ surface). Mechanical properties of fabrics as well as washing durability were carried out. These findings would be helpful in understanding the role of the surface coverage and morphology of nanostructures on the superhydrophobic behavior of fabrics and guiding the design of perfect artificial superhydrophobic textiles for extended practical application.

Hybrid method involving atmospheric plasma treatment and inkjet deposition for the development of conductive patterns on flexible polymers

In this study, the flexible polymer substrate polyethylene naphthalate (PEN) was modified under two different plasma chemistries, namely helium–oxygen (He–O2) and helium–water vapor (He–H2O) plasmas at atmospheric pressure and room temperature. Surface changes related to wettability, chemical functionalization, surface energy, and morphology after plasma treatment were investigated using water contact angle (WCA) goniometry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Each plasma resulted in a more hydrophilic PEN surface, with WCA decreasing by 68% and 85% for He–O2 and He–H2O plasma treated PEN, respectively, after only 1.0s of exposure. An aging study of plasma treated PEN shows an increase in WCA that is still 30° lower than that of the as-received PEN after 1month. XPS and AFM results show that improved wettability of the plasma modified PEN is due to the oxidation of the surface and not due to the increased surface roughness. To promote a roll-to-roll process of atmospheric plasma treatment and inkjet deposition, printing was performed using the conductive polymer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) on the as-received and plasma treated PEN surfaces where the shape and morphology of the lines were studied. Each plasma treated PEN surface exhibited well-defined, uniform inkjet-printed lines due to the improved wettability and increased surface energy. After scanning electron microscopy (SEM) analysis of the PEDOT:PSS dispersion of a single drop on each substrate, the He–H2O plasma treated surface led to less agglomeration of PEDOT:PSS and a more homogeneous drop deposit.

Characterization of an Ice Adhesion Reduction Coating for the Space Shuttle Liquid Hydrogen and Liquid Oxygen Umbilical Systems

NASA has recently developed an ice adhesion reduction coating given the designation Shuttle Ice Liberation Coating (SILC). SILC provides reduced adhesion of ice to a variety of substrate materials commonly found on the Space Shuttle External Tank (ET) and Orbiter. ET thermal protection system (TPS) material substrates, Stepanfoam BX-265, North Carolina Foam Industries (NCFI) 24-124, and Polymer Development Laboratory (PDL)-1034, were tested in tensile mode to evaluate ice adhesion. Tensile testing of ice grown onto these substrates was conducted at −18°C (0°F) and −7°C (20°F). For all tests the ice adhesion to the sample was reduced by approximately 90% for test samples coated with SILC compared with uncoated test samples. The durability of the SILC material was demonstrated by consistently good performance after multiple test cycles. SILC durability was verified by X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive Spectroscopy (EDS) and contact angle goniometry experiments on pristine, mechanically tested and weathered and aged samples. SILC development, mechanical testing, and testing of flight hardware for ice adhesion on Space Shuttle hardware in relevant atmospheric conditions demonstrated the ability of SILC to reduce and affect the formation of ice and its ability to adhere.

Synthesis, characterization, topographical modification, and surface properties of copoly(imide siloxane)s

Novel copoly(imide siloxane)s were synthesized from commercially available aminopropyl terminated siloxane oligomers, aromatic dianhydrides, and diamines. This synthetic approach produced copolymers with well-defined siloxane blocks linked with imide units in a random fashion. The copoly(amide acid)s were characterized by solution viscosity and subsequently used to cast thin films followed by thermal imidization in an inert atmosphere. Thin films were characterized using contact angle goniometry, attenuated total reflection Fourier transform infrared spectroscopy, confocal and optical microscopy, and tensile testing. Adhesion of micron-sized particles was determined quantitatively using a sonication device. The polydimethylsiloxane moieties lowered the copolymer surface energy due to migration of siloxane moieties to the film’s surface, resulting in a notable reduction in particle adhesion. A further reduction in particle adhesion was achieved by introducing topographical features on a scale of several to tens of microns by a laser ablation technique.

Design and Optimization of Polyphosphazene Functionalized Fiber Matrices for Soft Tissue Regeneration

Electrospun polycaprolactone nanofiber matrices surface functionalized with poly[(ethyl alanato), (p-methyl phenoxy),] phosphazene were fabricated for the purpose of soft skeletal tissue regeneration. This preliminary study reports the effect of fiber diameter and polyphosphazene surface functionalization on significant scaffold properties such as morphology, surface hydrophilicity, porosity, tensile properties, human mesenchymal stem cell adhesion and proliferation. Six fiber matrices comprised of average fiber diameters in the range of 400-500, 900-1000, 1400-1500, 1900-2000, 2900-3000 and 3900-4000 nm were considered for primary evaluation. After achieving the greatest proliferation while maintaining moderate tensile modulus, matrices in the diameter range of 2900-3000 nm were selected to examine the effect of coating with 1%, 2% and 3% (weight/volume) polyphosphazene solutions. Polyphosphazene functionalization resulted in rougher surfaces that correlated with coating solution concentration. Analytical techniques such as energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, elemental analysis, differential scanning calorimetry, water contact angle goniometry and confocal microscopy confirmed the presence of polyphosphazene and its distribution on the functionalized fiber matrices. Functionalization achieved through 2% polymer solutions did not affect average pore diameter, tensile modulus, suture retention strength or cell proliferation compared to PCL controls. Surface polyphosphazene functionalization significantly improved the matrix hydrophilicity evidenced through decreased water contact angle of PCL matrices from 130 degrees to 97 degrees. Further, enhanced total protein synthesis by cells during in vitro culture was seen on 2% PPHOS functionalized matrices over controls. Improving PCL matrix hydrophilicity via proposed surface functionalization may be an efficient method to improve cell-PCL matrix interactions.

Facing 2012, the Ninth Year of Challenges for PPP

Facing 2012, the Ninth Year of Challenges for PPP

Phenylboronic Ester- and Phenylboronic Acid-Terminated Alkanethiols on Gold Surfaces

In this work, it is shown that a well-organized monolayer of phenylboronic ester-terminated thiol (BOR-capped) on gold surfaces can be prepared. Our results also show that the BOR-capped molecular system can be cleaved directly on the surface, resulting in an unprotected BOR-uncapped monolayer with the boronic acid functional groups available for coordination to diol molecules in the ambient media. The monolayers of BOR-capped and BOR-uncapped were characterized using infrared spectroscopy, near edge X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and contact angle goniometry. The X-ray photoelectron spectroscopy results showed that both BOR-capped and BOR-uncapped are chemically linked to the gold substrate. According to the infrared spectroscopy results, the main component of the C═O vibrational mode present in the amide moiety is perpendicular oriented relative to the gold surface normal for the BOR-capped molecular system. The near edge X-ray absorption fi...

Cellular and transcriptomic analysis of human mesenchymal stem cell response to plasma-activated hydroxyapatite coating

Atmospheric pressure plasma has recently emerged as a technique with a promising future in the medical field. In this work we used the technique as a post-deposition modification process as a means to activate hydroxyapatite (HA) coatings. Contact angle goniometry, optical profilometry, scanning electron microscopy morphology imaging and X-ray photoelectron spectroscopy analysis demonstrate that surface wettability is improved after treatment, without inducing any concomitant damage to the coating. The protein adsorption pattern has been found to be preferable for MSC, and this may result in greater cell attachment and adhesion to plasma-activated HA than to untreated samples. Cell cycle distribution analysis using flow cytometry reveals a faster transition from G1 to S phase, thus leading to a faster cell proliferation rate on plasma-activated HA. This indicates that the improvement in surface wettability independently enhances cell attachment and cell proliferation, which is possibly mediated by FAK phosphorylation. Pathway-specific polymerase chain reaction arrays revealed that wettability has a substantial influence on gene expression during osteogenic differentiation of human MSC. Plasma-activated HA tends to enhance this process by systemically deregulating multiple genes. In addition, the majority of these deregulated genes had been appropriately translated, as confirmed by ELISA protein quantification. Lastly, alizarin red staining showed that plasma-activated HA is capable of improving mineralization for up to 3weeks of in vitro culture. It was concluded from this study that atmospheric pressure plasma is a potent tool for modifying the biological function of a material without causing thermal damage, such that adhesion molecules and drugs might be deposited on the original coating to improve performance.

Micro-CT and Wettability Analysis of Oil Recovery from Sand Packs and the Effect of Waterflood Salinity and Kaolinite

An image-based approach was developed by combining microtomography with electron microscopy and contact angle goniometry to determine the pore-scale distribution of crude oil in plugs after waterflooding and shed light on the molecular-scale mechanisms responsible. The approach was applied to a model rock comprising a pack of quartz sand grains without or with a preapplied lining of kaolinite, imaged prior to and after capillary-driven oil recovery by flooding with a model brine of high or low salinity. The presence of kaolinite increased residual oil and reversed its brine dependence, with high-salinity flooding giving greatest recovery from the clean sand and least recovery from kaolinite-coated sand. These two extremes tended to exhibit the most connected residual oil clusters, while low salinity gave smaller blobs, to the detriment or advantage of oil recovery. Low-salinity flooding in secondary or tertiary recovery mode resulted in comparable oil residuals in kaolinite-coated sand. Surface analysis o...

Thiol–Ene–Thiol Photofunctionalization of Thiolated Monolayers with Polybutadiene and Functional Thiols, Including Thiolated DNA

Self-assembly of organic thiols is the most common way to introduce functional groups onto gold surfaces. Although the gold–sulfur (Au–S) bond is moderately strong (∼45 kcal/mol), it is also prone to oxidation, which substantially weakens the Au–S interaction. In this work, we describe the creation of more robust molecular assemblies on gold. As a first step, a thiolated monolayer is prepared on gold with an α,ω-dithiol. Experiments are also reported for a mercaptosilane monolayer on silicon dioxide. An oligomer of polybutadiene (PBd) was then tethered to these surfaces using thiol–ene chemistry. Residual groups on the PBd are then reacted with thiols, including octadecanethiol (ODT), 1H,1H,2H,2H-perfluoroalkanethiol, and a thiol-terminated 25-mer of DNA. Little nonspecific adsorption of a non-thiolated DNA oligomer was observed. Surface characterization was performed with X-ray photoelectron spectroscopy (XPS), contact angle goniometry, time-of-flight secondary ion mass spectrometry (ToF-SIMS), and spectroscopic ellipsometry. A thiol–gold monolayer and an analogous assembly of the same thiol tethered to gold through PBd on a dithiol monolayer were both exposed to air and light for 2 weeks and then rinsed with water. The monolayer on gold was removed in this process, while the thiol in the assembly appeared unaffected.

Phosphonate-Anchored Monolayers for Antibody Binding to Magnetic Nanoparticles

Targeted delivery of magnetic iron oxide nanoparticles (IONPs) to a specific tissue can be achieved by conjugation with particular biological ligands on an appropriately functionalized IONP surface. To take best advantage of the unique magnetic properties of IONPs and to maximize their blood half-life, thin, strongly bonded, functionalized coatings are required. The work reported herein demonstrates the successful application of phosphonate-anchored self-assembled monolayers (SAMs) as ultrathin coatings for such particles. It also describes a new chemical approach to the anchoring of antibodies on the surface of SAM-coated IONPs (using nucleophilic aromatic substitution). This anchoring strategy results in stable, nonhydrolyzable, covalent attachment and allows the reactivity of the particles toward antibody binding to be activated in situ, such that prior to the activation the modified surface is stable for long-term storage. While the SAMs do not have the well-packed crystallinity of other such monolayers, their structure was studied using smooth model substrates based on an iron oxide layer on a double-side polished silicon wafer. In this way, atomic force microscopy, ellipsometry, and contact angle goniometry (tools that could not be applied to the nanoparticles' surfaces) could contribute to the determination of their monomolecular thickness and uniformity. Finally, the successful conjugation of IgG antibodies to the SAM-coated IONPs such that the antibodies retain their biological activity is verified by their complexation to a secondary fluorescent antibody.

Electropolishing of medical-grade stainless steel in preparation for surface nano-texturing

The purpose of this work is to investigate the electropolishing of medical-grade 316 L stainless steel to obtain a clean, smooth, and defect-free surface in preparation for surface nano-texturing. Electropolishing of steel was conducted under stationary conditions in four electrolyte mixtures: (A) 4.5 M H2SO4 + 11 M H3PO4, (B) 7.2 M H2SO4 + 6.5 M H3PO4, (C) 6.4 M glycerol + 6.1 M H3PO4, and (D) 6.1 M H3PO4. The influence of electrolyte composition and concentration, temperature, and electropolishing time, in conjunction with linear sweep voltammetry and chronoamperometry, on the stainless steel surface was studied. The resulting surfaces of unpolished and optimally polished stainless steel were characterized in terms of contamination, defects, topography, roughness, hydrophilicity, and chemical composition by optical and atomic force microscopies, contact angle goniometry, and X-ray photoelectron spectroscopy. It was found that the optimally polished surfaces were obtained with the following parameters: electrolyte mixture A at 2.1 V of applied potential at 80 °C for 10 min. This corresponded to the diffusion-limited dissolution of the surface. The root mean square surface roughness of the electropolished surface achieved was 0.4 nm over 2 × 2 μm2. Surface analysis showed that electropolishing led to ultraclean surfaces with reduced roughness and contamination thickness and with Cr, P, S, Mo, Ni, and O enrichment compared to untreated surfaces.

A general method to determine ionization constants of responsive polymer thin films

A general method has been developed to determine the ionization constants of polymer thin films based on the stimuli-responsiveness of the polymer. Robust polymer films were fabricated on silicon wafers and gold slides using perfluorophenyl azide (PFPA) as the coupling agent. The ionization constants were measured by a number of techniques including ellipsometry, dynamic contact angle goniometry, and surface plasmon resonance imaging (SPRi). Using poly(4-vinylpyridine) (P4VP) as the model system, P4VP thin films were fabricated and the ionization constants of the films were measured taking advantage of the pH responsive property of the polymer. The p K a determined by ellipsometry, ∼4.0, reflects the swelling of the polymer film in response to pH. The p K a value calculated from the dynamic contact angle measurements, ∼5.0, relies on the change in hydrophilicity/hydrophobicity of the films as the polymer undergoes protonation/deprotonation. The p K a value measured by SPRi, ∼4.9, monitors in situ the change of refractive index of the polymer thin film as it swells upon protonation. This was the first example where SPRi was used to measure the ionization constants of polymers.

Laser surface preparation for bonding of aerospace composites

Adhesive bonds are critical to the integrity of built-up structures. Disbonds can often be detected but the strength of adhesion between surfaces in contact cannot be determined without destructive testing. Typically the major problem in a bonded structure is surface contamination, and by extension, surface preparation. Standard surface preparation techniques, including grit blasting, manual abrasion, and peel ply, are not ideal because of variations in their application. Etching of carbon-fibre-reinforced plastic (CFRP) panels using a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser appears to be a highly precise, controlled, and reliable way to both clean a composite surface prior to bonding and provide a bond-promoting patterned surface akin to peel ply without the inherent drawbacks from the same (i.e. debris and curvature). CFRP surfaces prepared using laser patterns conducive to adhesive bonding were compared with typical pre-bonding surface treatments through optical microscopy, contact angle goniometry and post-bonding mechanical testing. This paper is the work of the US Government and is not subject to copyright protection in the USA.

Bottom-Up Assembly of Multicomponent Coordination-Based Oligomers

Transition metal complexes allow a high degree of molecular design flexibility through symmetry considerations and ligand architecture, which can be explored for the fabrication of ordered multilayer assemblies through bottom-up approach. Here we describe the preparation of such assemblies, viz. multicomponent coordination-based oligomer films on siloxane-based templates by wet-chemical layer-by-layer deposition process. In these films we combined optically rich iron and ruthenium polypyridyl complexes having pendant pyridine groups (so-called metallo-ligands) and a coinage metal (copper or silver) that acted as a linker between the polypyridyl complex moieties. The properties and structural parameters of the primary template and the oligomer films were studied by X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, UV–vis spectroscopy, spectroscopic ellipsometry, atomic force microscopy, and contact angle goniometry. A linear increase in the film thickness upon addition of every next layer suggests that the long-range order of the system is determined by the octahedral structure of the metallo-ligand and square-pyramidal/tetrahedral geometry of the coinage metal linker. Spectroscopic data indicate the existence of electronic communication throughout the individual metallo-organic chains.

Quantitative photochemical immobilization of biomolecules on planar and corrugated substrates: a versatile strategy for creating functional biointerfaces.

Methods for the generation of substratespresenting biomolecules in a spatially controlled manner are enabling tools for applications in biosensor systems, microarray technologies, fundamental biological studies and biointerface science. We have implemented a method to create biomolecular patterns by using light to control the direct covalent immobilization of biomolecules onto benzophenone-modified glass substrates. We have generated substrates presenting up to three different biomolecules patterned in sequence, and demonstrate biomolecular photopatterning on corrugated substrates. The chemistry of the underlying monolayer was optimized to incorporate poly(ethylene glycol) to enable adhesive cell adhesion onto patterned extracellular matrix proteins. Substrates were characterized with contact angle goniometry, AFM, and immunofluorescence microscopy. Importantly, radioimmunoassays were performed to quantify the site density of immobilized biomolecules on photopatterned substrates. Retained function of photopatterned proteins was demonstrated both by native ligand recognition and cell adhesion to photopatterned substrates, revealing that substrates generated with this method are suitable for probing specific cell receptor-ligand interactions. This molecularly general photochemical patterning method is an enabling tool for the creation of substrates presenting both biochemical and topographical variation, which is an important feature of many native biointerfaces.

Characterization and application of a surface modification designed for QCM-D studies of biotinylated biomolecules

The rapid development of surface sensitive biosensor technologies, especially towards nanoscale devices, requires increasing control of surface chemistry to provide reliable and reproducible results, but also to take full advantage of the sensing opportunities. Here, we present a surface modification strategy to allow biotinylated biomolecules to be immobilized to gold coated sensor crystals for quartz crystal microbalance with dissipation monitoring (QCM-D) sensing. The unique feature of QCM-D is its sensitivity to nanomechanical (viscoelastic) properties at the sensing interface. The surface modification was based on mixed monolayers of oligo(ethylene glycol) (OEG) disulfides, with terminal –OH or biotin groups, on gold. Mixtures containing 1% of the biotin disulfide were concluded to be the most appropriate based on the performance when streptavidin was immobilized to biotinylated sensors and the subsequent biotinylated bovine serum albumin (BSA) interaction was studied. The OEG background kept the unspecific protein binding to a minimum, even when subjected to serum solutions with a high protein concentration. Based on characterization by contact angle goniometry, ellipsometry, and infrared spectroscopy, the monolayers were shown to be well-ordered, with the OEG chains predominantly adopting a helical conformation but also partly an amorphous structure. Storage stability was concluded to depend mainly on light exposure while almost all streptavidin binding activity was retained when storing the sensors cold and dark for 8 weeks. The surface modification was also tested for repeated antibody–antigen interactions between BSA and anti-BSA (immobilized to biotinylated protein A) in QCM-D measurements lasting for >10h with intermediate basic regeneration. This proved an excellent stability of the coating and good reproducibility was obtained for 5 interaction cycles. With this kind of generic surface modification QCM-D can be used in a variety of biosensing applications to provide not only mass but also relevant information of the structural properties of adlayers.

Boron Nitride Nanosheet Coatings with Controllable Water Repellency

The growth, structure, and properties of two-dimensional boron nitride (BN) nanostructures synthesized by a thermal chemical vapor deposition method have been systematically investigated. Most of the BN nanosheets (BNNSs) were less than 5 nm in thickness, and their purity was confirmed by X-ray energy dispersive spectroscopy, X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and Raman spectroscopy. The effects of the process variables on the morphology and roughness of the coatings were studied using atomic force microscopy and scanning electron microscopy. A smooth BN coating was obtained at 900 °C, while compact BNNS coatings composed of partially vertically aligned nanosheets could be achieved at 1000 °C and higher temperatures. These nanosheets were mostly separated and exhibited high surface area especially at higher synthesis temperatures. The nonwetting properties of the BNNS coatings were independent of the water pH and were examined by contact angle goniometry. The present results enable a convenient growth of pure BNNS coatings with controllable levels of water repellency, ranging from partial hydrophilicity to superhydrophobicity with contact angles exceeding 150°.