Drop Shape Research Articles

Shape of sessile drops at small contact angles

The shape of a sessile drop on a horizontal substrate depends upon the Bond number $Bo$ and the contact angle $\alpha$ . Inspired by puddle approximations at large $Bo$ (Quéré, Rep. Prog. Phys., vol. 68, 2005, p. 2495), we address here the limit of small contact angles at fixed drop volume and arbitrary $Bo$ . It readily leads to a pancake shape approximation, where the drop height and radius scale as $\alpha$ and $\alpha ^{-1/2}$ , respectively, with capillary forces being appreciable only near the edge. The pancake approximation breaks down for $Bo=\textrm {ord}(\alpha ^{2/3})$ . In that distinguished limit, capillary and gravitational forces are comparable throughout, and the drop height and radius scale as $\alpha ^{2/3}$ and $\alpha ^{-1/3}$ , respectively. For $Bo\ll \alpha ^{2/3}$ these scalings remain, with the drop shape turning into a spherical cap. The asymptotic results are compared with a numerical solution of the exact problem.

Scaling of Anisotropic Wetting Behavior of Water Drop Configuration Arising from Parallel Groove-Textured Stainless Steel Surfaces

Understanding the wetting behavior of stainless steel surfaces can help in resolving many socio-economic challenges faced by modern day engineering developments. In this research paper, investigations have been carried out to understand the role of surface unidirectional microgrooves on the wetting behavior by the water drop liquid using the liquid drop shape configuration, captured in the view direction parallel and orthogonal to surface microgrooves. Because of the variation in wetting characteristics between these two directions, i.e., anisotropic wetting behavior, the liquid drop has attained ellipsoidal shape configuration in the microgroove-textured stainless steel surfaces. Detailed investigation has been carried out in understanding the role of microgroove geometrical sizes, i.e., width and depth and the spacing between the grooves on the wetting behavior in terms of contact diameter (D) and contact angle (θ). Overall, the wetting dynamics has been characterized by looking at the variation of eccentricity (ε, as a ratio between D in the direction parallel to microgroove and the spreading diameter in the direction orthogonal to microgroove) and wetting anisotropy (Δθ, as a difference in θ between the direction orthogonal and parallel to microgroove) with the microgroove depth parameter (ϕ as a ratio between the microgroove depth and width) and the groove spacing parameter (ξ as a ratio of the spacing between the grooves and the groove width). By and large, with increase in surface non-dimensional geometrical parameters, ϕ and ξ, the parameters quantifying eccentricity, ε and Δθ decrease, so the liquid drop shape configuration shifts towards spherical cap from ellipsoidal cap.

Quantifying the spontaneous emulsification of a heavy hydrocarbon with the presence of a strong surfactant

The rate of spontaneous emulsification phenomenon of heavy hydrocarbon in a non-ionic surfactant solution was studied experimentally. The size of a diminishing oil droplet was monitored photographically with the presence of an electrolyte. The obtained data were analysed using Axisymmetric Drop Shape Analysis (ADSA) software to measure the flux of emulsion droplets formed spontaneously. In contrast to all previous reports, a stable layer confined between the oil and aqueous solution was observed with a relatively constant thickness, ∼ 100 µm. The result shows that the rate of emulsification is reduced with the presence of electrolytes and is inversely correlated to its concentration. Considerable variation of the influence of electrolyte type on the kinetic of the spontaneous emulsification process for a given condition has been observed. Consequently, a new diffusion-control mechanism has been proposed, creating an extendable model to describe the process theoretically. The experimental data of emulsifying hexadecane in Triton X-100 micellar solution with the presence of potassium chloride and sodium chloride was well fitted to the proposed model. The results have important implications for surfactant-based cleaning processes.

Isolating the interface of an emulsion using X-ray scattering and tensiometry to understand protein-modulated alkylglyceride crystallisation

HypothesisDairy proteins and mono- and diglycerides (MDG) are often used in unison to tailor the properties of dairy-based emulsions. However, there are significant gaps in our understanding of how proteins affect lipid crystallisation at the oil–water interface. We have used a unique combination of interfacially-sensitive techniques to elucidate the impact of dairy proteins on interfacial MDG crystal formation. ExperimentsThe formation temperature of interfacial MDG crystals was assessed through interfacial tension studies via drop shape analysis. Small and Wide-Angle X-ray Scattering measurements were performed on isolated oil–water interfaces, allowing for in-situ interrogation of MDG crystal structure and concentration at and near the interface. FindingsDairy proteins are seen to reduce the temperature at which MDG crystals form at the oil–water interface. The displacement of proteins upon interfacial crystal formation was also clearly observed in interfacial tension measurements. For the first time, lipid crystals formed at the oil–water interface have been characterised using X-ray scattering. All scattering studies showed no change to the MDG crystal structures at the oil–water interface in the presence of adsorbed proteins. The results demonstrate that informed selection of emulsifier components is critical to controlling interfacial crystallisation with concomitant impact on emulsion stability.

Surface Characterization as a Tool for Identifying the Factors Affecting the Dissolution Rate of Amorphous Solid Dispersion Tablets.

An amorphous solid dispersion (ASD) is a commonly used approach to enhancing the dissolution of poorly aqueous soluble drugs. Selecting the desired polymer and drug loading can be time-consuming. Surface properties, such as surface composition and wetting behavior, are essential factors controlling the dissolution of ASD tablets. Thus, our study aims to use surface characterization to understand the factors that affect the dissolution rate of ASD tablets. In this work, we prepared ASDs with itraconazole and hypromellose acetate succinate (HPMCAS) using spray drying. ASDs were prepared using three grades of HPMCAS and different drug loading levels (10%, 30%, and 50%). We prepared ASD tablets with two porosities. For each tablet, contact angles were measured using the Drop Shape Analyzer; surface free energies, disperse, and polar fractions were calculated based on the contact angles. We conducted near-infrared (NIR) and dissolution measurements of ASD tablets. Principal component analysis (PCA) was carried out to investigate the NIR spectra further. The relative PCA scores were reported with other sample properties. A partial least square (PLS) model using NIR scores, tablets' wetting properties, and dissolution rates revealed that water and buffer contact angles, surface free energy, and polar fraction are the most significant factors attributing to the dissolution rate of ASD tablets. This work understood the interplay between the surface properties and the dissolution rate of ASD tablets. Moreover, surface characterization can be the tool to screen the formulation and compaction process of ASD tablets in early development.

Drop shape stability vs shape shifting: Role of surfactant adsorption layer

Emulsion droplets, composed of long linear molecules (e.g. n-alkanes) and stabilized by long chain surfactants, can spontaneously change their shape upon cooling and morph from spheres into regular polyhedra, polygonal platelets, rods and thin fibers. Until now, these dynamic shape changes have been studied upon continuous temperature decrease. Therefore, it had remained unclear whether the observed shapes were stable or they appeared as intermediate states during the transformation of the initial sphere into some final shape(s). In the current study, we performed dedicated experiments at fixed temperature to distinguish between the stable, metastable and unstable shapes and to define the factors which affect the kinetics of the observed transitions. The results showed that the stable shapes are equilateral triangular platelets (in all surfactant solutions) and the rod-like particles, when stabilized by surfactants with narrow compositional variations. The distorted octahedrons (seen as hexagonal platelets in transmitted light) were metastable and preserved their shape for many minutes. The other shapes, e.g. the flat hexagonal and tetragonal platelets, were unstable and continued to transform until they reached one of the stable states or alternatively – until they formed spheroidal droplets extruding thin fibers from their bodies. These experimental results are in general agreement with the theoretical model developed by Haas et al. (Phys. Rev. Lett. 2017, Phys. Rev. Res. 2019). The rate of shape transformations increased with the level of subcooling and/or with the decrease of drop size.

Brushed creation of liquid marbles

A method where particulates are transferred via a cosmetic brush onto liquid drops created on a highly non-wetting substrate with a hole to generate talc and graphite liquid marbles (LMs) and talc-graphite Janus liquid marbles is described. van der Waals forces facilitated the attachment of particulates to the dry brush bristles. Subsequently, the surface tension forces that developed from particle interaction with water (which were O(102) higher than the van der Waals forces) could then engender transfer of the particulates to the liquid-gas interface of the drop. Forces below 1 mN applied by a dangling foil on the LM ensured preservation of the drop shape when the force was removed. During the application of this force, the contact angles at the contact lines behaved differently from sessile drops that are inclined on surfaces. This preparation method portends the ability to automate the creation of LMs and Janus LMs for various applications.

Dynamic characteristics of ellipsoidal Janus drop impact on a solid surface

Impinging Janus drops can be stably produced by adding a high-viscosity drop to a low-viscosity drop. Here, we investigate the dynamic features of bouncing Janus drops on a solid substrate for an exploration of the effects of the viscosity ratio, initial drop shape, and impact velocity on altering the hydrodynamics. Numerical results show that the low-viscosity component evolves into liquid alignment along the principal direction with the help of a preferential flow, thereby resulting in the partial detachment from the mother Janus drops. We establish a regime map of the separation ratio of the drop and discuss how the parameters affect the asymmetry in the bounce and separation behavior. The low-viscosity components can be more likely to be detached from Janus drops as the viscosity ratio, drop's ellipticity, and/or impact velocity increase. This phenomenon is explained by the residence time and breakup of symmetry in the horizontal momentum between the low- and high-viscosity components. The peculiar dynamic characteristics of the Janus drop can provide potential for various applications, such as liquid purification and separation.

Drop deformation during diffusiophoresis

Diffusiophoresis refers to the motion of a colloidal particle in a solute concentration gradient, animated by particle–solute interactions. We present a theoretical analysis of the diffusiophoretic motion of a viscous drop in a gradient of neutral solute at zero Reynolds number. In a spatially uniform gradient, the translational velocity of a spherical drop was found by Anderson et al. (J. Fluid Mech., vol. 117, 1982, pp. 107–121). Here, we show additionally that the drop experiences no tendency to deform, regardless of the magnitude of the interfacial tension at the interface of the drop and suspending fluid. Next, we consider a non-uniform gradient, where the ambient solute concentration takes the form of a quadrupole around the drop centroid. This gradient does not induce drop translation, due to symmetry, but does induce a deformation in the drop shape, which is spheroidal to first order in the capillary number $Ca=\beta k_B T R^2 K/\gamma$ , where $\beta$ is the magnitude of the quadrupolar variation in solute concentration, $k_B T$ is the thermal energy, $R$ is the drop radius, $K$ is the Gibbs adsorption length, and $\gamma$ is the interfacial tension. Whether the drop becomes prolate or oblate depends on whether the solute–drop interaction is attractive or repulsive. Therefore, our work shows that in principle, a drop could undergo deformation during diffusiophoresis in a non-uniform solute gradient.

Foaming and sensory properties of bovine milk protein isolate and its associated enzymatic hydrolysates

The surface tension, foaming, bitterness and colour properties of bovine milk protein isolate (MPI) and MPI hydrolysates generated with Flavourzyme™, Neutrase™ and Protamex™ were evaluated. The surface tension of the hydrolysate samples (46.6–48.3 mN m−1), measured using pendant drop shape analysis, was reduced compared with the intact protein samples (49.1–49.6 mN m−1). The foam half-life of the hydrolysates (58.1–214 s) at 25 °C was significantly reduced compared with the intact protein (783–850 s). The L∗ value of the hydrolysates (69.9–77.4) was significantly lower than the intact protein (84.3–86.0). The Flavourzyme™ hydrolysate (60 min incubation) demonstrated a mean bitterness score (2.14) comparable with the intact protein (1.52–1.57). All other hydrolysates displayed increased bitterness; Neutrase™ and Protamex™ hydrolysates had the highest mean bitterness scores (8.80–9.39). The hydrolysate foaming and sensory properties were enzyme and DH dependent; bitterness development may be minimised by using Flavourzyme™ as the hydrolytic enzyme due to the presence of exopeptidase activities.

Interfacial Dilational Rheology of Molecular Films in DC Electric Fields.

We present a novel technique to measure the interfacial dilational rheology of a molecular film adsorbed at a water-oil interface in a direct-current (dc) electric field. A film of a highly polar subfraction of asphaltenes was allowed to adsorb at a water drop interface, surrounded by an organic phase and subjected to a dc electric field. The measurements involved calculations of the dynamic interfacial tension (IFT), while the drop was sinusoidally oscillated, using our in-house axisymmetric drop shape analysis (ADSA) algorithm adapted for electric fields. The amplitude of the IFT waveform over equilibrium IFT and the phase difference from the applied area oscillations were used in the estimation of surface moduli. The asphaltene films were found to become more elastic on increasing bulk concentrations and electric field strengths. However, the effect was not monotonous and observed to be governed by combinations of these parameters. The Lucassen-van den Tempel (LVDT) model was used to further elucidate the experimentally obtained interfacial dilational moduli.

The physicochemical properties and contact angle of sodium dodecyl sulfate in water–acetone with and without sodium nitrate (NaNO3)

Conductivity measurements at room temperature were performed to study the physicochemical behavior of anionic surfactant SDS in water and acetone–water mixture in the presence and absence of NaNO3.The concentration of SDS was 0.05 M and the concentration of NaNO3 was 0.01 M and 0.05 M. We calculated the degree of dissociation (α) and critical micelle concentration (CMC) from the pre-micellar (S1) and post-micellar slopes (S2). When acetone is added to SDS, CMC and α increase, but decreased with an increase in NaNO3.The standard free energy of micellization (ΔGm°) was evaluated using CMC and α. Micellization becomes less likely when the acetone content is higher as the negative values of ΔGm° decrease, indicating less spontaneous micellization. Due to the electrostatic repulsion of the head groups, adding salt NaNO3 decreases the CMC of SDS. A drop shape analyzer (DSA-25E) was used to measure the contact angles (CAs). For SDS, acetone and NaNO3 molecules mixed at varying concentrations, simulations were conducted.

Field Application and Experimental Investigation of Interfacial Characteristics of Surfactant and CO2 Alternative Injection.

CO2 injection and water alternating gas (WAG) injection are crucial to improve the oil recovery method and have optimized development in numerous oil fields. Many issues, such as gas channeling, water clogging, and a shortage of gas injection capacity, are addressed in the studies. Considering these conflicts, we suggest in this work a unique method of surfactant alternating gas (SAG) injection. Additionally, axisymmetric drop shape analysis and other approaches are utilized to explore the interface properties of a variety of systems, including CO2/carbonated water/water/surfactant/oil systems. SAG injection combines the advantages of surfactant and WAG injection. Although CO2 molecules have an effect on surfactant aggregation at the oil–water interface in the SAG system, carbonated water has little effect on surfactant performance in lowering oil–water interface tension. Pilot studies reveal that a SAG ratio of 3:2 at 74 °C and 0.5 wt% concentration significantly improves oil recovery.

Substrate-independent fabrication of superhydrophilic membrane based on dopamine methacrylamide and zwitterionic substance for effective oil-in-water emulsion separation

BackgroundThe fouling caused by oils and other contaminants is the critical obstacle for the membrane application in oil-in-water emulsion separation. MethodTo increase the hydrophilicity of the membrane, a substrate-independent approach was developed, in which the catechol derivative dopamine methacrylamide (DMA) was deposited on the membrane followed by UV copolymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC). Both hydrophobic membrane, poly(vinylidene fluoride), and hydrophilic membrane, polyethersulfone, became superhydrophilic after modification. The obtained membranes were characterized by Fourier-transform infrared spectroscopy (FTIR), Drop shape analyzer (DSA), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and membrane pore-size analyzer. Additionally, pure water flux and oil-in-water emulsion separation performance were evaluated for the selected samples. Significant findingsThe pure water flux of the modified membrane was increased from 490 L/m2 h and 612 L/m2 h to 1564 L/m2 h and 2219 L/m2 h under the optimal concentration of MPC for PVDF and PES membranes, respectively, which is more than three times that of the pristine membrane. Furthermore, the obtained membrane demonstrated enhanced oil-in-water emulsion separation efficiency as well as superior antifouling capabilities. The developed strategy is not restricted by the membrane materials, and might provide a new strategy for membrane surface modification aimed at oil-in-water emulsion separation.

Dilational rheological properties of 2, 5-dialkyl benzene sulfonates at air-water and decane-water interfaces

The dilational properties of two anionic surfactants 5–6–4 and 5–6-t4 (2, 5-dialkyl benzene sulfonates) at the air-water and decane-water interfaces were investigated using the drop shape analysis method. The effects of aging time, oscillating frequency, bulk concentration, and surface/interfacial pressure on the dilational elasticity and dilational viscosity were explored. The results show that the slow process and diffusion exchange process control the nature of surface/interfacial films at low and high concentrations, respectively. At low concentrations, the strong interaction between the branched long alkyl chains dominates at the surface. At high concentrations, the surface elasticity of 5–6–4 is higher because of the slower diffusion-exchange process. The insertion of oil molecules disrupts the interactions between branched long alkyl chains and simultaneously enhances the diffusion-exchange process, resulting in lower maximum interfacial dilational elasticity and viscosity for both 5–6–4 and 5–6-t4 molecules. The rigid isobutyl group endows the 5–6-t4 molecule with higher dilational elasticity and viscosity at the interface.

Use of a Geometric Parameter for Characterizing Rigid Films at Oil-Water Interfaces.

Interfacial tension and dilatational rheology are often used to characterize the mechanical response of a liquid interface using axisymmetric drop shape analysis (ADSA). It is important to note that for systems dominated by adsorption/desorption of surfactants, the contributions of extra mechanical stresses are negligible; thus, the Young-Laplace equation remains valid. However, for interfaces dominated by extra stresses, as in the case of particle monolayers or asphaltenes that clearly exhibit a skin (a rigid film), the nature of the elastic response is fundamentally different and the validity of the equation is questionable. Calculation of the interfacial tension and dilatational elasticity using drop shape analysis depends critically on the drop shape following the Young-Laplace equation. If the interface becomes more like a solid, the drop shape will deviate from being purely Laplacian. Indeed, the drop will exhibit a wrinkled surface as collapse continues. The geometric parameter RV/A, defined as the ratio (dV/V)/(dA/A) with V is the volume of the drop and A is the area of the interface), allows one to measure the deviation of the drop shape from purely Laplacian. For a simple interface (pure liquids or surfactant solutions), RV/A is quite close to the theoretical value of 1.5 of a perfect sphere. Nevertheless, if the molecules adsorbed at the interface begin to interact strongly, the ratio can vary. In the limit of long-time-scale experiments, RV/A of some drops approaches 2. We studied the evolution of the parameter RV/A for different systems, from simple to complex, as a function of oscillation frequencies and amplitudes of drop volume. The results obtained were compared to the values of the interfacial moduli and drop shape behavior to better characterize the regime change.

Dynamic interfacial activity and dilational viscoelasticity of polyether demulsifiers at the oil/water interface

A series of polyether demulsifiers with different PO/EO mass ratios and initiators were synthesized. The dynamic interfacial tension curves and dilational interfacial viscoelasticity of these polyethers at different oil/water interfaces were examined using the drop shape analysis method. Dynamic interfacial tension curves indicate weak adsorption of polyether demulsifiers at the diesel/water interface and strong adsorption at the xylene/water interface. Meanwhile, BPF9915 possesses the maximal interfacial activity among these three polyethers at the xylene/water interface, which differs from the diesel/water interface. Therefore, the dynamic interfacial activity of polyethers is related to the oil phase component.The order of dilational modulus of BPF polyethers at the diesel/water interface is BPF9935 > BPF9925 > BPF9915, which is similar to the order of dynamic interfacial activity. However, because of the weak adsorption of BPF polyethers, the values of dilational elasticity of BPF polyethers are small. Although these polyethers reduce the interfacial tension of the xylene/water interface sharply, the values of dilation elasticity of these polyethers at the xylene/water interface are close to those at the diesel/water interface. Therefore, these adsorptive branchedpolyethers exhibit weak intermolecular interaction.At the crude oil/water interface, the addition of polyethers causes the decrease of dilational interfacial elasticity, indicating the destruction of the dense interfacial adsorption layer by the BPF polyether. In addition, a hydrophobic polyether has a better dynamic interfacial activity in the crude oil, thus replacing the interfacial activity materials more effectively from the crude oil/water interface. Furthermore, the essential influencing factor of dynamic interfacial activity is PO/EO mass ratios rather than initiators. The PO/EO mass ratios will change the hydrophile and lipophilic balance, which is very important for the interfacial adsorption of polyether demulsifiers.

Wettability of shale–brine–H2 system and H2-brine interfacial tension for assessment of the sealing capacities of shale formations during underground hydrogen storage

Replacement of fossil fuels with clean hydrogen has been recognized as the most feasible approach of implementing CO2-free hydrogen economy globally. However, large-scale storage of hydrogen is a critical component of hydrogen economy value chain because hydrogen is the lightest molecule and has moderately low volumetric energy content. To achieve successful storage of buoyant hydrogen at the subsurface and convenient withdrawal during the period of critical energy demand, the integrity of the underground storage rock and overlying seal (caprock) must be assured. Presently, there is paucity of information on hydrogen wettability of shale and the interfacial properties of H2/brine system. In this research, contact angles of shale/H2/brine system and hydrogen/brine interfacial tension (IFT) were measured using Krüss drop shape analyzer (DSA 100) at 50 °C and varying pressure (14.7–1000 psi). A modified form of sessile drop approach was used for the contact angles measurement, whereas the H2-brine IFT was measured through the pendant drop method. H2-brine IFT values decreased slightly with increasing pressure, ranging between 63.68° at 14.7 psia and 51.29° at 1000 psia. The Eagle-ford shale with moderate total organic carbon (TOC) of 3.83% attained fully hydrogen-wet (contact angle of 99.9°) and intermediate-wet condition (contact angle of 89.7°) at 14.7 psi and 200 psi respectively. Likewise, the Wolf-camp shale with low TOC (0.30%) attained weakly water-wet conditions, with contact angles of 58.8° and 62.9°, at 14.7 psi and 200 psi respectively. The maximum height of hydrogen that can be securely trapped by the Wolf-camp shale was approximately 325 meters whereas the value was merely 100 meters for the Eagle-ford shale. Results of this study will aid in assessment of hydrogen storage capacity of organic-rich shale (adsorption trapping), as well as evaluation of the sealing potentials of low TOC shale (caprock) during underground hydrogen storage.

Evaporation progress of macroscopic-scale droplets on heated substrates

Evaporation progress of a macroscopic-scale sessile droplet with the pinned triple line on heated isothermal substrates has been experimentally investigated in the terrestrial gravity, in order to study the interface effect, heat and mass transfer behaviours during the phase change process. The experiments were carried out in a closed chamber in which the environment temperature and pressure were regulated. The contact radius, liquid volume and contact angle during evaporating were observed to study the influence of the gravity effect on the drop shape. The instant evaporation rate was calculated and compared with the theoretical prediction to analyse the coupling influence of diffusion and thermal convection. The effect of substrate temperature on the heat flux were also focused on. It was found that the evolution of heat flux density could be separated into four stages, began with the rapid increase and warm up, then switched to the long-time stable stage and ended up with the final rapid decrease stage.

Exploration of spray pyrolysis technique in preparation of absorber material CFATS: Unprecedented hydrophilic surface and antibacterial properties

In this study, we achieve the production of nontoxic Cu2Fe1-xAlxSnS4 films (x = 0, 0.25, 0.50, 0.75 and 1) by substituting Fe with Al atoms. Physical properties of the investigated films were studied using: Energy dispersive X-ray spectrometry (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, spectrophotometer and drop shape analysis system (DSA). The formation of new quaternary Cu3Al0.6Sn1S6 (CATS) chalcogenide for x = 1 was proven from EDX study. Notably, the major diffraction peaks were located at 2θ = 28.34°, 47.43° and 55.93° which are respectively tagged as (1 1 2), (2 0 4), and (3 1 2) plans, confirming the stannite crystal structure of Cu3Al0.6Sn1S6 film. The morphological states show a nanofiber structure accompanied with voids and cavities for CATS films. Tauc-relation plot reveals direct energy bandgap, close to 1.52 eV, which proves the absorber film type of Cu3Al0.6Sn1S6. The effluent toxicity of the obtained thin films has been assessed using the inhibition of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and indicated good antibacterial activity of the CATS/SnO2:F heterojunction. The viability rates against S. aureus achieved 40 %, 31 % and 15% for SnO2:F, Cu3Al0.6Sn1S6 films and CATS/SnO2:F heterojunction. These results highlight the great antibacterial activity of coupled CATS/SnO2:F. Therefore this research underscores the effectiveness of CATS/SnO2:F surface which demonstrates self-disinfecting and self-cleaning with hydrophilicity and high antibacterial activity.