Display omitted
Pendant drop tensiometry offers a simple and elegant solution to determining surface and interfacial tension – a central parameter in many colloidal systems including emulsions, foams ...and wetting phenomena. The technique involves the acquisition of a silhouette of an axisymmetric fluid droplet, and iterative fitting of the Young–Laplace equation that balances gravitational deformation of the drop with the restorative interfacial tension. Since the advent of high-quality digital cameras and desktop computers, this process has been automated with high speed and precision. However, despite its beguiling simplicity, there are complications and limitations that accompany pendant drop tensiometry connected with both Bond number (the balance between interfacial tension and gravitational forces) and drop volume. Here, we discuss the process involved with going from a captured experimental image to a fitted interfacial tension value, highlighting pertinent features and limitations along the way. We introduce a new parameter, the Worthington number, Wo, to characterise the measurement precision. A fully functional, open-source acquisition and fitting software is provided to enable the reader to test and develop the technique further.
Accurately estimating in vivo tendon load non-invasively remains a major challenge in biomechanics, which might be overcome by shear-wave tensiometry. Shear-wave tensiometry measures the speed of ...mechanically induced tendon shear waves by skin-mounted accelerometers. To gauge the feasibility and accuracy of this novel technique, we obtained patellar tendon shear wave speeds via shear-wave tensiometry during sustained or ramp voluntary contractions of the knee extensors in two experiments (n = 8 in both). In experiment one, participants produced a constant knee extension torque of ∼ 50 Nm at five different knee joint angles (i.e. variable tendon load), which resulted in estimated patellar tendon forces between 1005 ± 6N and 1182 ± 16 N. However, wave speed squared did not correlate with estimated tendon force within participants (rrm(31) = -0.19, p = 0.278). In experiment two, averaged correlation coefficients between normalized wave speed squared and torque of maximal and submaximal voluntary contractions across participants ranged between r = 0.43 and r = 0.94, while the time-varying correlation between these normalized signals ranged from r = -0.99 to r = 1.00. Further, the mean absolute errors (MAEs) between normalized wave speed squared and normalized torque across participants ranged between 0.03 and 0.54, which were larger than the MAEs between normalized torque and normalized summed EMG amplitude from the superficial quadriceps muscles (0.03–0.54 versus 0.06–0.26, respectively). In conclusion, there was no simple relation between shear wave speed squared and patellar tendon load, which severely limits the feasibility of shear-wave tensiometry for accurately estimating in vivo tendon load at the knee joint.
Interactions between sodium dodecyl sulfate (SDS) and methylene blue (MB) have been studied in presence of cetylpyridinium chloride (CPC) in aqueous and methanol-water binary solvents via ...conductometric and tensiometric methods. The experiment was conducted to see the possibility of a synergistic effect of the SDS+CPC system and changes in the interactional behavior of SDS with MB in presence of CPC. The value of the molecular interaction parameter for micellization (βM) was found to be negative from the experimental results and the value of |βM| was found to be greater than ln(CMCSDS / CMCCPC), which didn’t describe synergism completely but indicated the strong striking interactions between the oppositely charged surfactants. However, the CMC of the SDS+CPC system was found to be very low as compared to the CMC of SDS alone. This result of CMC based on striking interactions between oppositely charged surfactants was used to calculate various parameters like Gibb’s free energy of micellization (∆Gmo), surface excess(Γmax), minimum surface area (Amin), surface pressure πCMC, standard free energy of adsorption (∆Gadso), pC20, minimum surface free energy (Gmins), packing parameter (P) and association equilibrium constant (K). The addition of methanol as a cosolvent enhances the CMC and α value of the SDS+CPC as well as the SDS+CPC-MB system. Correlation of ∆Gmo with different solvent parameters namely Gordon parameter (G), Reichardt's parameter (ET (30)), viscosity (ηo), and solvophobic parameter (SP) has also been evaluated.
Display omitted
Cocamidopropyl betaine (CAPB) is widely used in personal care and industrial products, due to its mildness, simple synthesis, valuable surface active properties and synergism with other surfactants. ...CAPB is a mixture of amidopropyl betaines of different tail lengths, typically dominated by C12 (lauryl) amidopropyl betaine in commercial formulations. The feedstock used to synthesise this surfactant mixture dictates the specific individual amidopropyl betaine components present, their blend, and ultimately the properties of CAPB. Here, we investigate the surface activity and self-assembly of synthesised pure amidopropyl betaines that are typically found within CAPB. Small-angle neutron scattering, bubble pressure tensiometry, pendant drop tensiometry, foaming studies, and polarising light microscopy are employed to determine each molecule’s behaviour. It is evident that an increase in alkyl tail length controls properties within this class of molecules, leading to greater surface activity and the formation of different micelle geometries in solution, and modulating adsorption dynamics and foaming capabilities. These results indicate potential for optimisation of CAPB feedstocks along with new and facile approaches to tuning the properties of mixed surfactant systems, using carefully selected tailgroup mixtures.
Display omitted
Abstract Recent experimental and theoretical work clarifying the physical chemistry of blood-protein adsorption from aqueous-buffer solution to various kinds of surfaces is reviewed and interpreted ...within the context of biomaterial applications, especially toward development of cardiovascular biomaterials. The importance of this subject in biomaterials surface science is emphasized by reducing the “protein-adsorption problem” to three core questions that require quantitative answer. An overview of the protein-adsorption literature identifies some of the sources of inconsistency among many investigators participating in more than five decades of focused research. A tutorial on the fundamental biophysical chemistry of protein adsorption sets the stage for a detailed discussion of the kinetics and thermodynamics of protein adsorption, including adsorption competition between two proteins for the same adsorbent immersed in a binary-protein mixture. Both kinetics and steady-state adsorption can be rationalized using a single interpretive paradigm asserting that protein molecules partition from solution into a three-dimensional (3D) interphase separating bulk solution from the physical-adsorbent surface. Adsorbed protein collects in one-or-more adsorbed layers, depending on protein size, solution concentration, and adsorbent surface energy (water wettability). The adsorption process begins with the hydration of an adsorbent surface brought into contact with an aqueous-protein solution. Surface hydration reactions instantaneously form a thin, pseudo-2D interface between the adsorbent and protein solution. Protein molecules rapidly diffuse into this newly formed interface, creating a truly 3D interphase that inflates with arriving proteins and fills to capacity within milliseconds at mg/mL bulk-solution concentrations CB . This inflated interphase subsequently undergoes time-dependent (minutes-to-hours) decrease in volume VI by expulsion of either-or-both interphase water and initially adsorbed protein. Interphase protein concentration CI increases as VI decreases, resulting in slow reduction in interfacial energetics. Steady state is governed by a net partition coefficient P = ( C I / C B ) . In the process of occupying space within the interphase, adsorbing protein molecules must displace an equivalent volume of interphase water. Interphase water is itself associated with surface-bound water through a network of transient hydrogen bonds. Displacement of interphase water thus requires an amount of energy that depends on the adsorbent surface chemistry/energy. This “adsorption–dehydration” step is the significant free energy cost of adsorption that controls the maximum amount of protein that can be adsorbed at steady state to a unit adsorbent surface area (the adsorbent capacity). As adsorbent hydrophilicity increases, adsorbent capacity monotonically decreases because the energetic cost of surface dehydration increases, ultimately leading to no protein adsorption near an adsorbent water wettability (surface energy) characterized by a water contact angle → 65 ° . Consequently, protein does not adsorb (accumulate at interphase concentrations greater than bulk solution) to more hydrophilic adsorbents exhibiting < 65 ° . For adsorbents bearing strong Lewis acid/base chemistry such as ion-exchange resins, protein/surface interactions can be highly favorable, causing protein to adsorb in multilayers in a relatively thick interphase. A straightforward, three-component free energy relationship captures salient features of protein adsorption to all surfaces predicting that the overall free energy of protein adsorption Δ G ads o is a relatively small multiple of thermal energy for any surface chemistry (except perhaps for bioengineered surfaces bearing specific ligands for adsorbing protein) because a surface chemistry that interacts chemically with proteins must also interact with water through hydrogen bonding. In this way, water moderates protein adsorption to any surface by competing with adsorbing protein molecules. This Leading Opinion ends by proposing several changes to the protein-adsorption paradigm that might advance answers to the three core questions that frame the “protein-adsorption problem” that is so fundamental to biomaterials surface science.
The effects of bulk protein concentration, Cp, (0.01, 0.1, 1 wt%), pH (3, 4.7 and 7) and heat treatment (unheated or 95 °C for 30 min) on whey protein isolate (WPI) stabilized interfaces were ...examined. The interfacial pressure and shear rheology of WPI-stabilized sunflower oil-water (o/w) interfaces were characterized using a pendant drop tensiometer and a rheometer equipped with a Du Nöuy ring. The rate of WPI adsorption was faster at higer Cp and pH 3. Heat-enhanced surface activity was more pronounced at pH 7 compared to pH 3 as a result of greater heat stability of WPI at acidic pH. The elastic modulus of WPI stabilized interfaces increased with Cp (≤0.1 wt%). A further increase in Cp (to 1 wt%) resulted in monolayer collapse and weaker films. Non-heated (NHT) WPI formed less elastic interfacial films at pH 3 than at pH7. Heat treatment enhanced the elastic behavior of interfacial films with longer relaxation times. This may be associated with the formation of intermolecular β-sheets. The knowledge gained on the nature of WPI-stabilized interfaces can be used to better understand the stability of dairy emulsions during subsequent processing, digestion or storage.
Display omitted
•Conformational state of individual whey protein species at acidic pH facilitated faster adsorption.•Greater heat stability of whey proteins at low pH resulted in less enhanced interfacial activity by heat treatment.•At protein concentration above that required to form a condensed monolayer led to weaker interfacial films.•pH induced preferential adsorption and protein surface charge had significant impacts on the strength of interfacial films.•The enhancement of intermolecular interactions following heat treatment led to more solid-like interfacial structure.
This review focuses on the current understanding regarding lipid crystallisation at oil-water interfaces. The main aspects of crystallisation in bulk lipids will be introduced, allowing for a more ...comprehensive overview of the crystallisation processes within emulsions. Additionally, the properties of an emulsion and the impact of lipid crystallisation on emulsion stability will be discussed. The effect of different emulsifiers on lipid crystallisation at oil-water interfaces will also be reviewed, however, this will be limited to their impact on the interfacial crystallisation of monoglycerides and diglycerides. The final part of the review highlights the recent methodologies used to study crystallisation at oil-water interfaces.
Display omitted
•Association/interfacial/thermodynamic properties of drug and benzethonium chloride mixture.•The cmc value was obtained lower than cmcid due to interaction between components.•Excess free energy ...showed the higher stability of mixed system than pure system.•FT-IR showed shift in frequency signify the interaction amid ingredients.•Existing results revealed that surfactant as an efficient drug delivery vehicle.
Herein, the impact of numerous media of fixed concentration (H2O, NaCl (50 mmol·kg−1), urea (U, 300 mmol·kg−1) and thiourea (TU, 300 mmol·kg−1)) on the association, interfacial, and thermodynamic properties of promethazine hydrochloride (PMT) and benzethonium chloride (BTC, cationic antimicrobial surfactant)) mixture in several compositions were examined via tensiometry method at room temperature (298.15 K). Along with tensiometry, the interaction between PMT and BTC was also assessed by applying the UV–visible as well as FTIR spectroscopy in an aqueous solution. PMT is used for the symptomatic relief of various allergic conditions. The employed systems critical micelle concentrations (cmc) value was acquired much lower than their calculated corresponding ideal cmc value (cmcid) owing to the interaction between components (PMT and BTC) and the interaction amongst PMT and BTC further increases through increase in mole fraction (α1) of first component (BTC). Diverse solution and surface parameters, thermodynamic parameters, etc. have been processed by use of several purported theoretical models. In NaCl media, the cmc value of singular along with mixed species (PMT + BTC) of each composition were found fewer in magnitude than aqueous media while magnitude increased in U/TU media and TU is more valuable in boosting the cmc than U. Activity coefficient value in each case was continuously found below one due to attractive interaction amongst PMT and BTC. The attained Γmax and Amin value of PMT + BTC implies that the formed mixed interface is the closer packing of PMT and BTC. Excess free energy (ΔGex) was attained negative, exhibiting that the mixed micellar/mixed monolayer stability was higher with the singular component’s micelles/monolayer. The shift in frequency of pure component were attained by FT-IR study by addition of other component that also signifies the straightforward interaction among ingredients. Existing research outcomes revealed a straightforward methodology to design the employed surfactant as an efficient ingredient as a drug delivery vehicle for phenothiazine drug.
Surfactants are employed in microfluidic systems not just for drop stabilisation, but also to study local phenomena in industrial processes. On the scale of a single drop, these include foaming, ...emulsification and stability of foams and emulsions using statistically significant ensembles of bubbles or drops respectively. In addition, surfactants are often a part of a formulation in microfluidic drop reactors. In all these applications, surfactant dynamics play a crucial role and need to be accounted for. In this review, the effect of surfactant dynamics is considered on the level of standard microfluidic operations: drop formation, movement in channels and coalescence, but also on a more general level, considering the mechanisms controlling surfactant adsorption on time- and length-scales characteristic of microfluidics. Some examples of relevant calculations are provided. The advantages and challenges of the use of microfluidics to measure dynamic interfacial tension at short time-scales are discussed.
Display omitted
•Microfluidic time scales are comparable with characteristic adsorption time.•Dynamic interfacial tension is relevant for microfluidic drop formation.•Surfactant dynamics affect flow patterns inside microfluidic drops.•Surfactant dynamics affect microfluidic drop coalescence and subsequent mixing.•Microfluidics enable measurement of dynamic interfacial tension on millisecond scale.
Proteins and their mixtures with surfactants are widely used in many applications. The knowledge of their solution bulk behavior and its impact on the properties of interfacial layers made great ...progress in the recent years. Different mechanisms apply to the formation process of protein/surfactant complexes for ionic and non-ionic surfactants, which are governed mainly by electrostatic and hydrophobic interactions. The surface activity of these complexes is often remarkably different from that of the individual protein and has to be considered in respective theoretical models. At very low protein concentration, small amounts of added surfactants can change the surface activity of proteins remarkably, even though no strongly interfacial active complexes are observed. Also small added amounts of non-ionic surfactants change the surface activity of proteins in the range of small bulk concentrations or surface coverages. The modeling of the equilibrium adsorption behavior of proteins and their mixtures with surfactants has reached a rather high level. These models are suitable also to describe the high frequency limits of the dilational viscoelasticity of the interfacial layers. Depending on the nature of the protein/surfactant interactions and the changes in the interfacial layer composition rather complex dilational viscoelasticities can be observed and described by the available models. The differences in the interfacial behavior, often observed in literature for studies using different experimental methods, are at least partially explained by a depletion of proteins, surfactants and their complexes in the range of low concentrations. A correction of these depletion effects typically provides good agreement between the data obtained with different methods, such as drop and bubble profile tensiometry.
Display omitted
•The adsorption of proteins and their mixtures with surfactants is described.•The understanding of the mixed layers is supported by thermodynamic theories.•The models for the adsorption isotherms allow us to describe also the dilational viscoelasticity.•Due to the interaction with surfactants the interfacial activity of proteins is changed.•Even small amounts of added surfactants can increase the protein's activity.
PDF
