Pendant Drop Measurements Research Articles

Understanding the Buoy Effect of Surface-Enriched Pt Complexes in Ionic Liquids: A combined ARXPS and Pendant Drop Study.

Recently, we demonstrated that Pt catalyst complexes dissolved in the ionic liquid (IL) [C4C1Im][PF6] can be deliberately enriched at the IL surface by introducing perfluorinated substituents, which act like buoys dragging the metal complex towards the surface. Herein, we extend our angle-resolved X-ray photoelectron spectroscopy (ARXPS) studies at complex concentrations between 30 and 5%mol down to 1%mol and present complementary surface tension pendant drop (PD) measurements under ultra clean vacuum conditions. This combination allows for connec-ting the microscopic information on the IL/gas interface from ARXPS with the macroscopic property surface tension. The surface enrichment of the Pt complexes is found to be most pronounced at 1%mol. It also displays a strong temperature dependence, which was not observed for 5%mol and above, where the surface is already saturated with the complex. The surface enrichment deduced from ARXPS is also reflected by the pronounced decrease in surface tension with increasing concentration of the catalyst. We furthermore observe by ARXPS and PD a much stronger surface affinity of the buoy-complex as compared to the free ligands in solution. Our results are highly interesting for an optimum design of ionic catalyst solutions contact areas with a surrounding reactant/product phase, such as in SILP catalysis.

Surface activity characterization of synthesized polyvinyl alcohol-based nanogel at air-water interface under highly dynamic conditions

The ability to predict the behavior of nanogels at the air-water interface is critical for developing intelligent drug delivery systems. In this investigation, polyvinyl alcohol (PVA)-based nanogels were synthesized via the self-assembly crosslinking method employing fructose. The nanogels were characterized by means of FE-SEM, FTIR, and DLS analyses. The FE-SEM images confirmed the spherical morphology of the nanogels with an average diameter in the range of 18–30 nm. The polydispersity index of the nanogels, as assessed by the DLS test, was approximately 0.4. Subsequently, the impact of pure PVA and its produced nanogels on the hydrodynamics of a single air bubble ascending in aqueous solutions was explored, revealing that the presence of these molecules at the air-water interface results in a decrease in the local velocity profile (LVP) due to their surface activities. Finally, the results of the pendant drop measurements demonstrate that nanogels are more surface active than PVA.

Surface tension and viscosity of binary ionic liquid mixtures from high vacuum up to pressures of 10 MPa

In the present study, we investigated the surface tension and viscosity of binary ionic liquid (IL) mixtures at or close to saturation conditions from high vacuum conditions up to elevated pressures. We studied four different mixtures of 1,3-bis(2-(2-methoxyethoxy)ethyl)imida-zolium iodide ([(mPEG2)2Im]I) and 1-methyl-3-octylimidazolium hexafluorophosphate ([C8C1Im][PF6]) with [C8C1Im][PF6] mole contents between (4.6 and 49.8) mol%. Argon (Ar) gas of relatively low solubility was used to vary the applied pressure between (0.1 and 10) MPa. For temperatures from (303 to 363) K, the surface tension obtained by the pendant-drop (PD) method was used to determine the saturated liquid viscosity from surface light scattering (SLS). These studies are complemented by additional PD measurements under ultraclean high vacuum (HV) conditions in a second setup. At about 0.1 MPa, the surface tension and viscosity of the IL mixtures show negative deviations from a linear mixing rule based on the molar bulk composition, which is more pronounced at lower temperatures. The surface tension values at 0.1 MPa and under HV agree with each other and lie closer to the values of [C8C1Im][PF6] that has a distinctly lower surface tension than [(mPEG2)2Im]I and is surface-active. For the equimolar IL mixture at 303 K, an increase in the pressure up to 10 MPa has a negligible influence on the viscosity, while it causes a distinct reduction in the surface tension compared to the value at 0.1 MPa. The pressure-dependent relative change for the viscosity of the ternary mixtures of the two ILs and Ar corresponds well to the mean values of the positive and negative relative changes observed for the two binary [(mPEG2)2Im]I-Ar and [C8C1Im][PF6]-Ar subsystems, respectively. For the surface tension, the absolute changes at a given pressure are very similar regardless of the IL bulk composition, suggesting a similar weak Ar enrichment at the gas–liquid interface.

Combined Surface Light Scattering and Pendant-Drop Experiments for the Determination of Viscosity and Surface Tension of High-Viscosity Fluids Demonstrated for Ionic Liquids

The present study provides a strategy for the determination of the viscosity and surface tension of high-viscosity fluids in the form of ionic liquids (ILs) at equilibrium conditions by combining surface light scattering (SLS) and the pendant-drop (PD) method within one experimental setup. Through the study of the same sample under identical conditions by both methods inside a closed system, the surface tension determined via the PD method can be directly used to evaluate the dynamics of surface fluctuations of ILs with an overdamped behavior probed by SLS for accessing their viscosity. In connection with the SLS experiments, variations in the applied detection geometries in reflection and transmission direction and in the probed wave vectors down to relatively small values were also addressed. The reliability and self-consistency of SLS and the PD method applied within the same sample cell has been proven by investigating the reference fluids tris(2-ethylhexyl) trimellitate (TOTM) and n-dodecane featuring relatively high and low viscosities. For the two studied model ILs of opaque to non-transparent color, i.e., the hydrophobic 1-methyl-3-octylimidazolium hexafluorophosphate ([OMIM][PF6]) and the hydrophilic 1,3-bis(2-(2-methoxyethoxy)ethyl)imidazolium iodide ([(mPEG2)2Im]I), the combination of PD measurements and SLS experiments in reflection direction performed at ambient pressure between (303 and 373) K allowed access to the viscosity and surface tension with typical relative expanded uncertainties of (4 and 2) %. These results agree well with own viscosity data from capillary viscometry and experimental data in the literature, demonstrating the performance of the novel approach for the contactless in-situ measurement of viscosity and surface tension of fluids with relatively high-viscosity such as ILs.

Emulsification Characteristics and Electrolyte-Optimized Demulsification of Produced Liquid from Polymer Flooding on Alaska North Slope

Summary The first-ever polymer flooding pilot test is currently implemented in heavy oil reservoirs on Alaska North Slope (ANS). One of the major concerns of field engineers is the impact of polymer on oil/water separation after polymer breakthrough. This paper aims to predict the influence of polymer on emulsification characteristics of produced liquid and seek a cost-effective method to treat the produced liquid from polymer flooding. In this study, emulsions, at moderate and vigorous shearing conditions, were prepared by mechanically mixing 25 vol% of the ANS heavy oil with 75 vol% of the polymer solution. Bottle test method, microscope, and pendant drop technique were utilized to investigate the effect of polymer on emulsification characteristics in terms of separation behavior, drop size distribution (DSD), and interfacial properties [i.e., interfacial tension (IFT) and interfacial dilational rheology], respectively. As for chemical demulsification, the performance and interfacial behavior of four commercial demulsifiers and an inorganic salt, that is, potassium chloride (KCl), was measured using simulated produced liquid. The bottle test results demonstrated that polymer could enhance the emulsion stability, resulting in a slower separation rate, poorer water quality, and greater thickness of the intermediate layer. The pendant drop measurements showed that the IFT and interfacial dilational rheology were independent of polymer concentration. Thus, the stabilization effect of the polymer was mainly attributed to the increased viscosity of the continuous phase and the decreased drop size of the dispersed oil phase. As for the chemical demulsification tests, compound demulsifier E12 + E18 exhibited the best demulsification performance as well as the lowest IFT and interfacial elastic modulus. Nevertheless, a multifold dosage of E12 + E18 was required to demulsify the emulsion under vigorous mixing, leading to a potential increase in the chemical cost. A less expensive electrolyte, KCl, was able to work synergistically with demulsifier E12 + E18 to promote oil/water separation and reduce the demulsifier usage. In this proposed demulsifier formula, the mechanism for the effectiveness of the commercial demulsifier was its destructive effect on the interfacial film, while the effectiveness of KCl was mainly dependent on its viscosity reduction effect on the continuous phase. This study illustrates the intermediate layer elimination, and the water quality is the major challenge for produced liquid from polymer flooding and provides both practical and theoretical guidance in advance for the corresponding demulsification strategy of the produced liquid from the ongoing first-ever polymer flooding pilot on ANS.

Aspects of Coatings on Buckypaper as a Study into the Expected Effects of Coatings on Carbon Nanotube Wires

Buckypaper (BP) was used as an accumulation of nanotubes to simulate as carbon nanotube (CNT) wires to study the interaction between four different insulating coating materials and CNTs. The wettability and electrical conductivity performance of each CNT/coating pair was assessed. The BP was prepared by filtering a sonicated solution of single-walled carbon nanotubes and N,N-Dimethylformamide, through a polytetrafluoroethylene (PTFE) membrane of 0.45 µm pore size. It was observed with Scanning Electron Microscopy, its chemical composition determined by X-ray Photoelectron Spectroscopy, its imperfections and purity measured by Raman Spectroscopy and the porosity (%) and pore distribution obtained by Nitrogen Physisorption. The results showed similar porosity and surface structure to that of reported CNT wires. The surface free energy of the BP was obtained through the Owens-Wendt method, and surface tension of the coatings was calculated with pendant drop measurements to find the adhesion and wettability parameters. Epoxy resin showed the highest wettability and adhesion, which resulted in infiltration into the BP that decreased electrical conductivity by 65%. In contrast, the insulating varnish showed much lower level of wettability and adhesion which resulted in the lowest decrease in conductivity (9.3%).

Molecular Transport across Oil-Brine Interfaces Impacts Interfacial Tension: Time-Effects in Buoyant and Pendant Drop Measurements.

The buoyant drop method is a ubiquitous tool for addressing phenomena at the liquid-liquid interface via the determination of the interfacial tension (IFT) between two immiscible phases. Here, the focus is on how electrolytes (in an aqueous phase) and carboxylic acids (in a decane phase) impact the interfacial layer between the two phases. The IFT measurement provides a single number, which is not fulfilling when it comes to deducing information about a complex multiparameter system. Furthermore, the temporal evolution of IFT does not always reach a steady-state value on a time scale, which is realistic to use for comparative studies. We have investigated the temporal evolution of IFT in a series of experiments with varying compositions of the decane-carboxylic acid phase and the brine phase. The results show that there are at least two opposing effects in play. For water-soluble acids, the IFT initially increases with time until a turnover point is reached from where there is a gradual decay. The IFT at the turnover point is close to that of the pure water-decane system. For a poorly water-soluble acid, the IFT shows a much smaller increase and the turnover happens much faster. For a water-soluble acid, there is a high degree of sensitivity toward the electrolyte; it determines the position (in time) of the IFT peak and the steepness of the subsequent decay. Now, if the phases are reversed, that is, by placing a drop of brine in the decane-surfactant phase, the IFT decreases with time regardless of the acid and with little impact of the electrolyte and its concentration in the brine. We propose an explanation for the observed behavior (supported by COSMO-RS calculations), which is based on diffusion in and out of the two phases, solubility, and interfacial reactivity (i.e., aggregation between electrolytes and carboxylic acids).

A Way of Measuring the Surface Tension of a Suspension of Bentonites

Results are presented from pendant and sessile drop measurements of the dependence of surface tension σ of aqueous suspensions of bentonites on the period of surface formation. It is established that the sedimentation of particles is the most important factor affecting the accuracy and reproducibility of measurements of σ in suspensions of bentonites. A procedure is proposed that neutralizes the effect this factor has on the value of σ. Ways of measuring σ in which sedimentation is directed differently relative to the surface are used. Sedimentation is thus directed to the surface in the pendant drop approach, and away from the surface in the sessile drop technique. Measuring σ in these ways and averaging the results considerably reduces the error caused by sedimentation. Analysis of the concentration dependence of σ on the suspensions of bentonite shows that the sedimentation factor is almost completely eliminated when using this procedure.

Interfacial tension in water/n-decane/naphthenic acid systems predicted by a combined COSMO-RS theory and pendant drop experimental study

The interfacial tension of systems containing water, n-decane, and model naphthenic acids were investigated using a predictive model based on COSMO-RS theory and experimental pendant drop measurements. Five naphthenic acid homologues that are considered to be representative of surfactants inherent to crude oil were dissolved in n-decane at equal concentrations. The interfacial tensions of the five systems at an acid concentration of 1.66 mol% relative to n-decane were experimentally determined to be 27–30 mN/m. The interfacial tensions of the five different acid-decane phases against water were also predicted using density functional theory (DFT) calculations and COSMO-RS theory. The accuracy of the predictions was very good as confirmed through pendant drop measurements of the interfacial tension. The mean-absolute-deviation between experimental and predicted values was 2.6 mN/m thus demonstrating the high predictive power of COSMO-RS theory for calculating the interfacial tension at oil–water interfaces in the presence of surface-active compounds.

Impact of mineralogy and wettability on pore-scale displacement of NAPLs in heterogeneous porous media

Subsurface formations often contain multiple minerals with different wettability characteristics upon contact with nonaqueous-phase liquids (NAPLs). Constitutive relationships between microstructure heterogeneity and NAPL fate and transport in these formations are difficult to predict. Several studies have used pore-scale network models with faithful representations of rock pore space topology to predict macroscopic descriptors of two-phase flow, however wettability is usually considered as a spatially random variable. This study attempts to overcome this limitation by considering more realistic representations of rock mineralogy and wettability in these models. This is especially important for heterogeneous rocks where properties vary at the pore-scale. The work was carried out in two phases. First, pore-fluid occupancy maps during waterflooding were obtained by X-ray microtomography to elucidate the impact of pore wall mineralogy and wettability on water preferential flow paths and NAPL trapping within a heterogeneous aquifer sandstone (Arkose). Then, microtomography images of the rock were used to generate a hybrid pore network model (PNM) that incorporated both pore space topology and pore wall mineralogy. In-situ contact angles (CA) measured on the surface of different minerals were assigned to the network on a pore-by-pore basis to describe the exact wettability distribution of the rock (Pore-by-pore model). The equivalent network was used as input in a quasi-static flow model to simulate waterflooding, and the predictions of residual NAPL saturation and relative permeabilities were compared against their experimental counterparts. To examine the sensitivity of the model to the underlying fluid-solid interactions, we also used traditional methods of wettability characterization in the input data and assigned them randomly to the PNM. Wettability in this case was assessed from macroscale CA distribution of oil droplets on the surface of unpolished Arkose substrates released by spontaneous imbibition of water (Arkose model) and from pendant drop measurements on polished quartz (Quartz model). Our results revealed that the Pore-by-pore model predicted waterflooding with the highest accuracy among all three cases. The Arkose model slightly overestimated NAPL removal whereas the Quartz model failed to predict the experiments. More in-depth analysis of the Pore-by-pore and Arkose models showed that macroscopic transport quantities are less dependent to microstructure heterogeneity if minerals are distributed uniformly across the rock. The predictions herein indicate the importance of incorporating mineralogy and wettability maps to improve the prediction capabilities of PNMs especially in systems with high mineral heterogeneity, where minerals are nonuniformly distributed, or selective fluid-mineral interactions are targeted.

Investigation of spontaneous imbibition induced by wettability alteration as a recovery mechanism in microbial enhanced oil recovery

This paper explores the potential of spontaneous imbibition (SI) induced by wettability alteration to improve incremental oil recovery during microbial enhanced oil recovery (MEOR). A laboratory work is presented that consists of SI and contact angle (CA) tests on reservoir and outcrop sandstone cores. The SI and CA measurements were conducted with aqueous phases with/without MEOR to assess the incremental recovery mechanism triggered by the wettability alteration during MEOR. It was observed that the oil recovery in the SI experiments with the MEOR nutrient solution reached a plateau at 0.62 ± 0.05% of original oil in place (OOIP) while it was 0.32 ± 0.02% of OOIP with the non-MEOR reference SI experiment conducted in outcrop sandstone cores. The CA of the oil droplet measured on polished reservoir rock sample decreased from 120° to 60° when exposed to the MEOR nutrient solutions. The observed changes occurred in parallel to the growth process of the bacteria in both SI and CA tests.The experimental data shows that the wettability alteration needs cell growth because SI experiments performed only with metabolites and without microbial cells exhibited negligible incremental recovery. Numerical models calibrated with SI experiments demonstrated the wettability alteration as one of the potential MEOR mechanisms. The bacterial network that forms a biofilm at the oil-water interface, and hence, creates a viscoelastic layer is thought to be the main cause of wettability alteration, which is supported by the oscillating pendant drop measurements.

Comparison of Nanoparticle and Surfactant Oil/Water-Emulsion Separation Kinetics

Summary Experimental observations, during oil–production operations, regarding the formation of oil/water emulsions stabilized by nanoparticles and surfactants, are presented. Similarities and differences between the two types of emulsions are discussed on the basis of acquired separation profiles, as well as respective fluid interfacial properties. A state–of–the–art portable dispersion–characterization rig (PDCR) was used to run the experiments, and a surveillance camera was deployed to monitor the emulsion separation kinetics. Commercial–grade mineral oil and distilled water were used as the test fluids. Silica nanoparticles of different wettabilities, as well as surfactants with different hydrophilic-lipophilic balance (HLB) values, were deployed to investigate commonalities/differences between the surfactant– and nanoparticle–stabilized emulsions under ambient–temperature and –pressure conditions. Separation profiles were analyzed, and similar behaviors between the corresponding surfactant and nanoparticle emulsions were observed for the 25%–water–cut case. For higher water cuts, however, the surfactant–stabilized emulsions were tighter than their nanoparticle counterparts, displaying much lower separation rates. In the most severe cases, the surfactants totally inhibited the oil–creaming process and oil remained trapped in the emulsion for several hours. Multiple emulsions (O/W/O) were observed in certain cases [for hydrophilic nanoparticles and lipophilic surfactants (Span® 80)]. On the basis of the aforementioned experimental observations, the presence of surfactants caused more–severe problems for the oil/water–separation process than did the presence of an equal concentration of nanoparticles. Pendant–drop measurements indicated that the surfactants significantly lowered the interfacial tension (IFT) between the oil and water, whereas the nanoparticles did not. Finally, a literature model was used to predict separation profiles for the oil/water dispersions and evaluated by comparing the predictions with the acquired experimental data. Current research sets the benchmark for more–thorough investigations aimed at providing guidelines for a more efficient operation of separators that handle surfactant– or nanoparticle–stabilized emulsions and a better understanding of the related phenomena.

Effective surface tension of liquid marbles using controllable nanoparticle monolayers

The effective surface tension (γeff) of liquid marbles is a frequently used, but perplexing concept and clarifying this tension has been challenging, mainly due to difficulties in controlling affecting factors from marble surface particles, including particle agglomeration and areal particle density. In this study, we addressed this issue using water marbles covered by nanoparticle monolayers, which produced a simple physical model with controlled particle coverage. The results from sessile and pendant drop measurements reveal that under high particle density, γeff depends on very specific conditions including the measurement method and all liquid marble parameters such as the shape, smoothness, and coverage ratio. The contradictory deviation of γeff from water surface tension with the two methods implies that γeff can reflect only the macroscopic properties of the marbles rather than interparticle forces as was previously assumed. The surface solidity produced by local or overall particle jamming, which is a common, underappreciated phenomenon, is believed to account for this limitation. The concept of equivalence quality is proposed herein, which describes the degree of shape similarity between a liquid marble and a naked droplet, and is thought to be important when addressing the γeff of liquid marbles.

Mechanistic Understanding of the Effect of Temperature and Salinity on the Water/Toluene Interfacial Tension

In this work, a series of pendant drop measurements and molecular dynamics (MD) simulations were performed to investigate the effects of temperature and salinity on the interfacial tension (IFT) of water/toluene binary systems. Both experimental measurements and theoretical simulations demonstrated that elevating temperature decreased the IFT, while adding salts resulted in an increment of IFT. Furthermore, it was found that the presence of model asphaltene compound could alleviate the effects of temperature and salinity on the IFTs. That is, in the presence of the model asphaltene compound, the decrement effect of elevating temperature as well as the increment effect of adding salts was reduced. Through detailed analysis of the simulated systems, the underlying mechanisms for the effects of temperature and salinity on the IFTs were clarified for cases with and without the presence of the model asphaltene. The results reported here can help to modulate the IFT values of oil/water interfaces in petroleum p...

Adsorption and rheological behavior of an amphiphilic protein at oil/water interfaces

Hydrophobins are highly surface active proteins which self-assemble at hydrophilic-hydrophobic interfaces into amphipathic membranes. We investigate hydrophobin self-assembly at oil/water interfaces to deepen the understanding of protein behavior in order to improve our biomimetic synthesis. Therefore, we carried out pendant drop measurements of hydrophobin stabilized oil/water systems determining the time-dependent IFT and the dilatational rheology with additional adaptation to the Serrien protein model. We show that the class I hydrophobin H∗Protein B adsorbs at an oil/water interface where it forms a densely-packed interfacial protein layer, which dissipates energy during droplet oscillation. Furthermore, the interfacial protein layer exhibits shear thinning behavior.

A Laboratory Investigation of the Effects of Saturated Steam Properties on the Interfacial Tension of Heavy-Oil/Steam System Using Pendant Drop Method

For about a century, steam injection has been widely used as the most popular thermal recovery method for heavy-oil in sandstone reservoirs. In order to achieve higher recovery efficiency, which corresponds to the lowest possible value of residual oil saturation and economic success of steam injection projects, an accurate laboratory measurement of the interfacial tension between steam and heavy-oil is essential. However, laboratory investigation and visualization of the effects of steam injection on the interfacial tension between heavy-oil and steam as a function of saturation temperature and pressure is not well documented in the literature. The objective of this study is to investigate the influences of the two main factors which affect the interfacial tension of heavy-oil and steam namely saturation pressure and temperature. An optical cell, which was fitted with a goniometer system and a procedure to generate steam for the measurement of interfacial tension have been used. The difference between the density of heavy-oil and steam, which was used for pendant drop measurements, was calculated at specific temperature and pressure conditions using Katz’s method. Meanwhile, the density of steam was obtained from an international steam table. The interfacial tension of heavy-oil/steam was measured in small intervals, ranging from 115 to 181 Celsius and 25 to 150 pounds per square inch. The results show that the interfacial tension decreases when the saturation temperature and pressure increases. This finding might be useful as an important reference for understanding and visualization the mechanism of interfacial tension during steam injection.

Synthesis and Surface‐Active Behavior of New Fluorinated Hyperbranched Polymer

AbstractIn this article, a series of novel hyperbranched fluorinated polymer with polyglycerol (PG) as the hydrophilic core and poly(2,2,2‐trifluoroethyl methacrylate) (PTFEMA) as solvophobic arms were synthesized. When the atom transfer radical polymerization was carried out using N,N‐dimethylformamide (DMF) as the solvent, [M]/[I] ratio of 200, and [CuBr]/[NBr] ratio of 0.1 at 30 °C, controlled polymerization was achieved. The surface active properties of the polymer at the dimethyl sulfoxide (DMSO)/air and chloroform/water interface were studied by pendant drop measurements. The results showed that the copolymers could reduce surface tension (interfacial tension) in a manner analogous to the conventional surfactant in aqueous solutions. Thermodynamic analysis suggested that the solvophobic PTFEMA chains play an important role in determining the driving force of the aggregate formation in DMSO.

High-precision drop shape analysis on inclining flat surfaces: Introduction and comparison of this special method with commercial contact angle analysis

Drop shape analysis is one of the most important and frequently used methods to characterise surfaces in the scientific and industrial communities. An especially large number of studies, which use contact angle measurements to analyse surfaces, are characterised by incorrect or misdirected conclusions such as the determination of surface energies from poorly performed contact angle determinations. In particular, the characterisation of surfaces, which leads to correlations between the contact angle and other effects, must be critically validated for some publications. A large number of works exist concerning the theoretical and thermodynamic aspects of two- and tri-phase boundaries. The linkage between theory and experiment is generally performed by an axisymmetric drop shape analysis, that is, simulations of the theoretical drop profiles by numerical integration onto a number of points of the drop meniscus (approximately 20). These methods work very well for axisymmetric profiles such as those obtained by pendant drop measurements, but in the case of a sessile drop onto real surfaces, additional unknown and misunderstood effects on the dependence of the surface must be considered. We present a special experimental and practical investigation as another way to transition from experiment to theory. This procedure was developed to be especially sensitive to small variations in the dependence of the dynamic contact angle on the surface; as a result, this procedure will allow the properties of the surface to be monitored with a higher precession and sensitivity. In this context, water drops onto a 111 silicon wafer are dynamically measured by video recording and by inclining the surface, which results in a sequence of non-axisymmetric drops. The drop profiles are analysed by commercial software and by the developed and presented high-precision drop shape analysis. In addition to the enhanced sensitivity for contact angle determination, this analysis technique, in combination with innovative fit algorithms and data presentations, can result in enhanced reproducibility and comparability of the contact angle measurements in terms of the material characterisation in a comprehensible way.

Interaction Forces between Bubbles in the Presence of Novel Responsive Peptide Surfactants

Reversibly switchable surfactants are increasingly important for controlling foam stability in many industrial applications because they can be recycled as foaming and antifoaming agents. Novel stimuli responsive peptide surfactants have been previously studied to classify the molecular conformation at the air-water interface before and after switching. In this study, Atomic Force Microscopy (AFM) was used to correlate the peptide conformation to directly measured changes in colloidal interaction forces between immobilized air bubbles before and after switching. The surface tension values extracted from the AFM force measurements were compared to macroscopic pendant drop measurements to help elucidate the importance of desorption in the switching mechanisms for some of the peptides. Results were compared to previous studies of macroscopic foam-column stability using these peptides. Differences in foam stability and the AFM force measurements were apparent, highlighting variations in directly measured equilibrium colloidal interactions to macroscopic bulk behavior. These results help elucidate the connection between the switching mechanism of novel stimuli responsive peptide surfactants and their effect on colloidal scale interactions between bubbles.

Evaluation of the compatibility between low pressure melamine (LPM) film printing substrates and inkjet inks

Surface coated wood-based panels play a major role in the forest products industry as materials for construction and furniture elements in numerous interior and exterior applications. Their most important feature besides appropriate mechanical performance and chemical durability is an appealing visual appearance. In this contribution, recent research on the compatibility between two UV-curable inks and different melamine formaldehyde based surface films is presented. The surface texture properties of the printing substrates were investigated by roughness measurements. Substrate surface free energy was measured by contact angle measurements using three different testing liquids covering a wide range of polarities (glycerol, ethylene glycol and diiodomethane). The physical shape of the inkjet ink drops which were placed on the LPM printing substrates was monitored and recorded over time and used as an indicator for the wetting behavior of the tested inks and hence the printability. By combining contact angle and pendant drop measurements the surface tension of the inks was determined. The theoretical findings were confirmed by technological printing tests. To this end, as a hands-on method to establish ink-substrate wetting and compatibility flow coating tests were run and the most suitable ink was selected for printing. The printing results were closely related to the surface properties of the printing substrates.