Time-dependent Contact Angle Measurements Research Articles

Corrosion of Commercial Mg–Al Alloys: AZ31B, AM60, and AZ91D

Aqueous corrosion, atmospheric corrosion, and ionic liquid dissolution studies were performed on commercial alloys AZ31B, AM60, and AZ91D and compared with previously reported results for single-phase binary Mg–Al alloys containing similar Al concentrations (αMg-2 at% Al, αMg-5 at% Al, and Mg-8 at% Al). Polarization studies in 0.6 M NaCl were used to characterize the aqueous free corrosion behavior during 20-h free immersion. Accelerated corrosion testing was performed using a rotating-disk electrode which revealed the evolution of an Al-rich mud-cracking and platelet morphology. Atmospheric droplet testing showed rapid pH increases that depended on the Al concentration in the alloy. Time-dependent contact angle measurements showed that the degree of droplet wetting increased during free corrosion by ∼50° over 20 h in 0.6 M NaCl. Ionic liquid dissolution studies in 1:2 M choline chloride:urea deep eutectic solvent were performed in order to examine the current-voltage behavior of these alloys in the absence of water and hydrogen reduction. The results of these studies revealed the formation of nanowire corrosion morphologies within a honeycomb lattice structure which we attribute to selective dissolution of Mg via a two-dimensional step-flow process.

Enhanced Supercapacitor Performance By Tuning the Wettability of Vapor Grown Carbon Nanofibers Using Oxygen Plasma Treatment

Carbon based materials have been explored widely for supercapacitor applications in commercial perspective. Despite that their poor performance in terms of volumetric and gravimetric capacitance seems bottleneck in high performance supercapacitor device applications. The major reason for the same is their poor wettability. Generally, carbon based materials are found to be hydrophobic which limits their electrode – electrolyte interfacial interaction and hence, suppresses the charge storage performance. In this work, we report vapor grown carbon nano fibers (CNF) at large scale using chemical vapor deposition adopting simple catalytic approach. CVD grown CNF showed crystalline 1 D morphology confirmed by detailed electron microscopy. As grown CNF shows hydrophobic nature. Supercapacitor measurements revealed 14.6 mF/cm2 aerial capacitance. In order to improve electrode - electrolyte interfacial interaction, the wettability factor has to be improved and hence O2 plasma treatment has been adopted to convert hydrophobic CNF into hydrophilic. Time dependent contact angle measurements revealed the absence of ageing effect due to changes in microstructure after plasma treatment which was confirmed by electron microscopic investigations. Further, comparative electrochemical measurements proved remarkable enhancement in supercapacitor performance of plasma treated CNF in terms of aerial capacitance (162.5 mF/cm2) compared to as grown CNF. The change in wettability led to superior supercapacitor performance along with high Coulombic efficiency. Taking this work to one step further CNF were uniformly encapsulated with MoO3 in 1 D core – shell fashion where CNF acts as core and MoO3 acts as shell in the subsequent CVD process. This approach provides a path in developing low cost - high energy density supercapacitor using simple methods.

Sol-gel synthetic route to improve interaction of polyester/cotton blended fabric with anionic dyes

A different chemical nature of PET/cotton fibers hinders to attain solid shade during the coloration process. To overcome this problem in current the attempt, surface functionalization of PET/cotton fabric by simple and cost effective sol-gel technology was investigated. By this simple coating method, different anchor sites were introduced onto the PET/cotton fabric surface such as amine, epoxy or hydroxyl. Incorporation of such groups was conducted using two different alkoxysilanes, namely 3-Aminopropyltriethoxysilane (APTES) or 3-Glycidyloxypropyltrimethoxysilane (GPTMS) as coupling agents for C.I. reactive blue 5 and C.I. acid blue 80 dyes. The sol-gel synthesis reactions of used alkoxysilanes were preceded under either acidic or basic condition. The chemistry and morphology of APTES and GPTMS modified PET/cotton surface were studied by utilizing some surface sensitive techniques such as streaming potential measurements, ATR-FTIR, X-ray photoelectron spectroscopy (XPS), time-dependent contact angle measurements as well as scanning electron microscopy (SEM). In addition, color strength and fastness tests of the prints were examined to test the effectiveness of the fabric surface modification. It was observed that the isoelectric point value of PET/cotton fabric coated with base-hydrolyzed APTES is shifted toward higher pH value in comparison with PET/cotton fabric coated with base-hydrolyzed GPTMS. Furthermore, the hydrophobicity of sol-gel modified PET/cotton fabric was increased. The results also presented that the PET/cotton blend fabrics after treatment with base-hydrolyzed APTES showed improvement in K/S value and fastness properties.

Plasma-assisted surface modification of polyester fabric for developing halochromic properties

In the field of textiles, introducing pH-sensitive dyes onto fibrous materials is a promising approach for the development of flexible sensor. In this study, poly(ethylene terephthalate) (PET) textile surface with halochromic properties was fabricated by plasma-assisted sol-gel coating, followed by immobilization of two different azo pH-indicator dyes; namely Brilliant yellow and Congo red by conventional printing technique of fabrics. 3-aminopropyltriethoxysilane (APTES) was used as a coupling agent for attaching the pH-sensitive dyes through its terminal amines. The surface immobilization of APTES on PET fabric was conducted by the pad-dry-cure method. Moreover, the influence of oxygen plasma pre-treatment and the method of post-treatment either by oxygen plasma or by thermal treatment on the stability of sol-gel based matrix was investigated. The morphology and chemistry of 3-aminopropyltriethoxysilane coated PET surfaces were examined by using surface sensitive methods including electrokinetic and time-dependent contact angle measurements as well as X-ray photoelectron spectroscopy (XPS). In addition, fastness tests of the printed fabrics and color strength were carried out to assess the effectiveness of the fabric surface modification. Results indicate that sol-gel matrix exhibited a more stability by thermal post-treatment at 150 C for 5 min. Also, the results revealed that the printed fabrics with halochromic properties demonstrated sufficient stability against leaching by washing. The current work opens up a novel opportunity to develop flexible sensors based on fibrous materials, which have the potential to be employed in variable industrial applications.

Different plasma-based strategies to improve the interaction of anionic dyes with polyester fabrics surface

Low-pressure plasma treatments with subsequent immobilization of functional macromolecules from aqueous solution have gained an increasing popularity for its applications in new industrial processes. In this work, two different strategies to endow polyester fabrics (PET) with accessible primary amino groups are compared.(a) NH2 groups were produced directly using low-pressure ammonia plasma. (b) Negatively charged groups were introduced by low-pressure oxygen plasma to hydrophilize the fabric surfaces and used as anchor groups for the immobilization of water-borne polyelectrolyte copolymers poly(vinyl amine-co-vinyl amide) (PVAm).To study the effects of these surface modifications, a combination of various surface-sensitive characterization techniques such as X-ray photoelectron spectroscopy (XPS), streaming potential measurements and time-dependent contact angle measurements were used. Furthermore, the influence of the pre-treatments on the interaction of PET fabrics with water-soluble dyes was evaluated. For that purpose, color strength and fastness tests were carried out to prove the effectiveness of pre-treatments.

Photochemical Microcontact Printing by Thiol−Ene and Thiol−Yne Click Chemistry

This article describes the microstructured immobilization of functional thiols on alkene- and alkyne-terminated self-assembled monolayers on silicon oxide substrates by photochemical microcontact printing. A photochemical thiol-ene or thiol-yne “click” reaction was locally induced in the area of contact between stamp and substrate by irradiation with UV light (365 nm). The immobilization reaction by photochemical microcontact printing was verified by contact angle measurements, X-ray photoelectron spectroscopy, atomic force microscopy, and time-of-flight secondary ion mass spectrometry. The reaction rate of photochemical microcontact printing by thiol-ene chemistry was studied using time dependent contact angle measurements. The selective binding of lectins to galactoside microarrays prepared by photochemical microcontact printing was also demonstrated. It was found that photochemical microcontact printing results in a high surface coverage of functional thiols within 30 s of printing even for dilute (mM) ink solutions.

Modification of Poly(propylene) Membranes for Electrochemical Cells by Low-Temperature Plasma Treatment

Poly(propylene) membranes for battery systems were modified by surface oxidation using radio frequency (RF) and microwave (MW) plasma techniques. The plasmas were generated in two different gases: O2 and CO2. Impedance spectroscopy, time-dependent contact angle measurements and pure water permeability were utilized to characterize the properties of the membranes. It was found that the best improvement in ion conductivity (an increase by four orders of magnitude) was achieved using the O2 MW plasma. Wettability of the membrane surface and the water permeability through the membrane also increase distinctly after such a treatment.

Spontaneous Formation of Fractal Structures on Triglyceride Surfaces with Reference to Their Super Water-Repellent Properties

Alkylketene dimer (AKD), a kind of wax, has been known to form fractal surfaces spontaneously and show super water-repellency. Such formation of water-repellent and fractal surfaces was also found in this work for triglycerides. Since the crystal phase transitions of these waxes were well studied, we studied the formation of their fractal surfaces through contact angle measurements, differential scanning calorimetry (DSC), and X-ray diffraction (XRD). From time-dependent contact angle measurements, it was found that the formation of super water-repellent surfaces with fractal structures occurred spontaneously also on the triglyceride surfaces at different temperatures. The freshly solidified triglyceride surfaces were almost transparent, and their initial contact angles of water were close to 110 degrees. The surfaces then became rough and clouded after being incubated for a certain time at a specified temperature. The super water-repellent surfaces were quite rough and showed fractal structures with the dimension of ca. 2.2 calculated from the scanning electron microscopic (SEM) images by the box-counting method. The phase transformation from a metastable state to a stable cystalline one after the solidification from the melt of triglycerides was clearly observed by DSC and XRD measurements. The fractal crystalline structures and the super water-repellency resulted from this phase transformation and the crystal growth. Ensuring the initial sample solidified into the metastable state and curing the surface at an appropriate temperature are key factors for the successful preparation of fractal triglyceride surfaces by the solidification method.

Hydrophilicity and hydrophobicity study of catalyst layers in proton exchange membrane fuel cells

The catalyst layer is one of the key components of PEMFCs. As the electrochemical reaction occurs at the three-phase interface of the catalyst layer, it is necessary to investigate the hydrophobicity and/or hydrophilicity properties of catalyst layers, which have a large impact on the water transport and even on the performance of the PEMFC. In this paper, time dependent contact angle measurements and porosity analyses have been performed to characterize the catalyst-coated membranes. For the first time, environmental scanning electron microscopy (ESEM) has been used to measure the hydrophilicity and hydrophobicity in the catalyst layer microstructure. The micro-contact angle distribution is given based on the microstructure. It shows a micro-scale hydrophobicity and hydrophilicity study, especially for an inhomogenous material. By means of conventional time-dependent contact angle measurements, porosity measurements and micro-contact angle measurements by ESEM, the hydrophobicity and hydrophilicity of catalyst-coated membranes have been investigated. Useful information has been gained to assist the understanding of catalyst layers from catalyst-coated membranes.

Growth kinetics and thermodynamic stability of octadecyltrichlorosilane self-assembled monolayer on Si (100) substrate

We have studied the growth kinetics and thermodynamic stability of octadecyltrichlorosilane (OTS) self-assembled monolayers on Si (100) substrate in order to understand its role in controlling the adhesion and surface hydrophobicity. Time-dependent contact angle measurements, using water as a function of OTS concentration, show rapid monolayer formation in the initial stage followed by a slow attainment of full coverage and the overall kinetics approximately follows the Langmuir adsorption isotherm. The adsorption rate constant (ka=150 M−1 s−1) is found to be significantly greater than the desorption rate constant (kd=0.156 s−1) while the Gibbs free energy (ΔGads) change amounts to −4.2 kcal/mol suggesting thermodynamic stability of OTS monolayer on a silicon surface. Partial monolayer formation by a ‘uniform’ growth mechanism, even at low coverage, is revealed by atomic force microscopy (AFM) in conjunction with grazing angle FTIR spectroscopy. Analysis of the interfacial adhesion properties using Zisman plot suggests a critical surface tension (γc) of 20.7 dyn/cm for OTS monolayer on Si (100) surface.

Interaction of water with different cellulose ethers: a Raman spectroscopy and environmental scanning electron microscopy study

Different non-ionic cellulose ethers like methyl cellulose (MC), hydroxypropyl cellulose (HPC) and hydroxypropylmethyl cellulose (HPMC) were investigated. The characterization of the cellulose ethers was carried out by thermogravimetry and sorption/desorption isotherms. Differences in the properties of the cellulose ether films were described by time-dependent contact angle measurements. Changes in molecular structure of the raw materials, gels and films caused by water contact were studied using Raman spectroscopy. Differences between the substitution types and changes due to the gel or film formation were observed. An environmental scanning electron microscopy (ESEM) technique was used to distinguish the morphological behaviour of the cellulose ether films in contact with water. Based on in-situ ESEM experiments, the swelling and drying behaviour of the various stages of cellulose ether films (film-hydrated film-dried film) were quantified by using image analysis.

Surface restructuring of polymers

Time-dependent contact angle measurements are employed to follow the dynamics of surface modifications of various polymeric surfaces of different hydrophilicities. The equilibration of a hydrophilic polymer in a strong polar environment (such as water) induces an increase in the polarity of the surface; the subsequent exposure of the restructured solid to a nonpolar environment decreases the polarity of the surface. The dynamics of these processes depends on the history of the specimen. Various phenomena, such as surface restructuring by the reorientation of the buried polar or nonpolar moieties, water penetration into the polymer, and the reorganization of water in the neighborhood of the surface, are suggested to be responsible for the time evolution of the dynamic contact angles.