Interfacial Dilational Rheology Research Articles

Mechanically Enhanced Liquid Interfaces at Human Body Temperature Using Thermosensitive Methylated Nanocrystalline Cellulose.

The mechanical performance of materials at oil/water interfaces after consumption is a key factor affecting hydrophobic drug release. In this study, we methylated the surface of nanocrystalline cellulose (NCC) by mercerization and dimethyl sulfate exposure to produce thermosensitive biopolymers. These methylated NCC (metNCC) were used to investigate interfacial thermogelation at air/water and medium-chain triglyceride (MCT)/water interfaces at body temperature. In contrast to bulk fluid dynamics, elastic layers were formed at room temperature, and elasticity increased significantly at body temperature, which was measured by interfacial shear and dilatational rheology in situ. This unique phenomenon depends on solvent quality, temperature, and polymer concentration at interfaces. Thus, by adjusting the degree of hydrophobicity of metNCC, the interfacial elasticity and thermogelation of the interfaces could be varied. In general, these new materials (metNCC) formed more brittle interfacial layers compared to commercial methylcellulose (MC A15). Thermogelation of methylcellulose promotes attractive intermolecular forces, which were reflected in a change in self-assembly of metNCC at the interface. As a consequence, layer thickness and density increased as a function of temperature. These effects were measured by atomic force microscopy (AFM) images of the displaced interface and confirmed by neutron reflection. The substantial structural and mechanical change of methylcellulose interfaces at body temperature represents a controllable encapsulation parameter allowing optimization of lipid-based drug formulations.

β-lactoglobulin stabilized nanemulsions—Formulation and process factors affecting droplet size and nanoemulsion stability

To avoid the toxicological concerns associated to synthetic surfactants, proteins might be an alternative for the stabilization of pharmaceutical nanoemulsions. The present study investigates the use of β-lactoglobulin (β-lg) to stabilize oil in water biocompatible nanoemulsions intended for a pharmaceutical use and prepared by high pressure homogenization (HPH). The effects of composition (nature and weight fraction of oil, β-lg concentration) and of process parameters (pressure and number of cycles) on the droplet size and on the stability of nanoemulsions were thoroughly assessed. The nanoemulsions prepared with β-lg at 1wt% and with 5wt% Miglyol 812 (the oil with the lowest viscosity) displayed a relatively small particle size (about 200nm) and a low polydispersity when a homogenization pressure of 100MPa was applied for 4 cycles. These nanoemulsions were the most stable formulations over 30days at least. Emulsification efficiency of β-lg was reduced at higher homogenization pressures (200MPa and 300MPa). The effect of HPH process on the interfacial properties of β-lg was evaluated by drop shape analysis. This treatment had an effect neither on the interfacial tension nor on the interfacial dilatational rheology of β-lg at the Miglyol 812/water interface.

Effect of silica nanoparticles on the interfacial properties of a canonical lipid mixture

The incorporation of silica nanoparticles (NPs) from the subphase into Langmuir lipid monolayers formed by three components, 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) and Cholesterol (Chol), modifies the thermodynamic and rheological behavior, as well as the structure of the pristine lipid film. Thus, the combination of structural characterization techniques, such as Brewster Angle Microscopy (BAM) and Atomic Force Microscopy (AFM), with interfacial thermodynamic and dilational rheology studies has allowed us to deepen on the physico-chemical bases governing the interaction between lipid molecules and NPs. The penetration of NPs driven by the interaction (electrostatic or hydrogen bonds) with the polar groups of the lipid molecules affects the phase behaviour (surface pressure-area, П−A , isotherm) of the monolayer. This can be easily rationalized considering the modification of the packing and cohesion of the molecules at the interface as revealed BAM and AFM images. Furthermore, oscillatory barrier experiments have allowed obtaining information related to the effect of NPs on the monolayer response under dynamic conditions that presents a critical impact on the characterization of biological relevant systems because most of the processes of interest for these systems present a dynamic character.

Characterization of Interfacial Rheology of Protein-Stabilized Air–Liquid Interfaces

In this review, the definition of interfacial dilatational and shear rheology is outlined and the basis of different experimental methods for their characterization is provided. The connection between interfacial rheology and structure of proteins and other macromolecules is highlighted through the application of polymer theories. Key experimental results on interfacial rheology of air–liquid interfaces stabilized by proteins and protein surfactant mixtures are then presented. This is followed by the analysis of the effect of interfacial rheology on stability of air–liquid interface.

Interfacial Properties of Mixed DPPC–Hydrophobic Fumed Silica Nanoparticle Layers

The combination of interfacial thermodynamic, dilational rheology, and Brewster angle microscopy (BAM) has allowed the evaluation of the effect of hydrophobic fumed silica nanoparticles on the interfacial properties of Langmuir monolayers of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC). Fumed silica particles modify the surface pressure–area (Π–A) isotherm of DPPC, modifying both the phase behavior and the collapse conditions. These modifications are strongly dependent on the relative quantity of DPPC and Nanoparticles initially spread at the air–water interface. The incorporation of nanoparticles at the fluid interface alters the balance of interactions within the monolayer, thus leading to the disruption of the interfacial structure and consequently of the lipid packing. Measurements of dilational viscoelastic modulus against the frequency have been carried out by the mean of the oscillatory barrier method at different degrees of compression of the monolayer. The dynamic response is also modified...

A Study of Relationship Between Oil-Water Interfacial Dilational Rheology and Oil Recovery of Alkaline Flooding

AbstractIn order to find out the influence of dilational rheology on chemical flooding systems, the dilational rheology of Zhuangxi crude oil/NaOH solutions interface was investigated by DSA100 interfacial dilatational rheometer (KRÜSS, Germany). The results show that the alkaline system, which can enhance oil recovery, mainly depends on its interfacial dilational rheology, rather than interfacial tension. The greater the interfacial dilational elasticity, the higher the oil recovery is. The greater the interfacial dilational viscosity, the lower the oil recovery is. The conclusion is consistent with the change of displacement pressure in the macro displacement experiment and the change of sweep efficiency in the microscopic displacement experiment.

Comparison of Performances of Different Types of Clarifiers for the Treatment of Oily Wastewater Produced from Polymer Flooding

In this paper, oily wastewater produced from polymer flooding (OWPF) was treated with two different types of clarifiers. One was a cationic polymer (copolymer of acrylamide and acryloyloxyethyl trimethyl ammonium chloride) PAM‐DAC, the other was the non‐ionic polymer (polyoxyalkylated polyethyleneimine) PEI11. The effects of operating conditions on the performances of PAM‐DAC and PEI11 were compared. The performance of PAM‐DAC was not affected by temperature, while temperature had a great influence on that of PEI11. In the same conditions, to obtain the same oil removal performance, PEI11 needed more stirring time, higher dosage, and stronger stirring than PAM‐DAC. The flocs of PAM‐DAC and PEI11 were also different. The PAM‐DAC flocs were viscous and could adhere to the beaker, while the flocs of PEI11 could not. These performance differences were related to their flocculation mechanisms. The results of zeta potential, interfacial tension, and interfacial dilational rheology showed that the flocculation mechanisms of PAM‐DAC were electrostatic charge neutralization and bridging, while the mechanism of PEI11 was demulsification. This comparison is useful for the selection of clarifiers for the treatment of OWPF.

Interfacial dynamic and dilational rheology of polyelectrolyte/surfactant two-component nanoparticle systems at air–water interface

The interfacial characteristics of nanoparticles and consequent inter-particle interactions at the interface are poorly understood. In this work, the interfacial dynamic and corresponding dilational surface rheology of self-assembled polyelectrolyte/surfactant nanoparticles at the air–water interface are characterized. The nanoparticles are prepared from dodecyltrimethylammonium (DTAB) and poly (sodium 4-styrene-sulfonate) (PSS) by mixing them in aqueous solution. The interfacial dynamic characteristics have been carried out by comparing the surface pressure with the dilational rheological response of these nanoparticles at interface. The results indicate that this type of nanoparticles can adsorb at the interface forming a nanoparticle monolayer, which leads to the surface tension decreased markedly. The dependence of surface pressure on time shows the instability and disassembly process of nanoparticles at the interface. On the basis of these observations, it is proposed that the nanoparticles undergo a dynamic process that interface induced nanoparticles disassembly into DTAB/PSS complexes. The presence of PSS in the subphase can promote the process of nanoparticles disassembly. A transition point in dilational elasticity and viscosity response of the nanoparticles versus oscillation frequency further validate the micro dynamic process of nanoparticles and the formation of polyelectrolyte/surfactant complex monolayer at the interface.

Interaction of pepsin–[C16mim]Br system: interfacial dilational rheology and conformational studies

The interfacial rheological property is closely related to the stabilities of foams and emulsions, yet there have been limited studies on the interaction between proteins with ionic liquid-type imidazolium surfactants at the decane-water interface as well as in the bulk. Herein, we investigated the interfacial and bulk properties of pepsin (PEP) and an ionic liquid (IL), 1-hexadecyl-3-methylimidazolium bromide, [C(16)mim]Br. The interfacial pressure and dilational rheology studies were performed to describe the formation of [C(16)mim]Br-pepsin complexes. The influence of the oscillating frequency and the bulk concentration of [C(16)mim]Br on the dilational properties were explored. The conformational changes were studied by monitoring the fluorescence and far UV-CD spectra. The results reveal that the globular structure of pepsin is one of the decisive factors controlling the nature of the interfacial film. The monotonous increase in the dilational elastic modulus of pepsin-[C(16)mim]Br solutions with the surface age indicates that no loops and tails had formed. Interestingly, with an increase in the concentration of [C(16)mim]Br, the εd-c curve first passes through a plateau value due to steric hindrance and the electrostatic barrier of already absorbed tenacious pepsin-[C(16)mim]Br complexes. With the further addition of [C(16)mim]Br, the remarkable decrease in dilational elastic modulus indicates that the compact structure is destroyed gradually. The results of the fluorescence spectra and far UV-CD spectra confirm that [C(16)mim]Br did not produce perceptible changes in pepsin at the concentrations studied in the dilational experiment. Possible schematic programs of the pepsin-[C(16)mim]Br interaction model at the interface and in bulk phase are proposed.

Characterisation and use of β-lactoglobulin fibrils for microencapsulation of lipophilic ingredients and oxidative stability thereof

There is a growing interest in using fibrils from food grade protein, e.g. β-lactoglobulin, as functional ingredients. In the present study, the functionality of fibrillar β-lactoglobulin from whey protein isolate (WPI) was compared to native WPI in terms of interfacial dilatational rheology and emulsifying activity at acidic conditions (pH 2.0 and 3.0). We report here for the first time data on microencapsulation of fish oil by spray-drying as well as oxidative stability of the oil in emulsions and microcapsules in dependence of WPI conformation. WPI fibrils exerted a significantly higher elasticity at the oil–water (o/w) interface and a better emulsifying activity at a fixed oil content compared to native WPI. Microencapsulation efficiency was also higher with fibrillar WPI (>95%) compared to native WPI (∼90%) at pH 2.0 and a total oil and protein content of 40% and 2.2%, respectively, in the final powder. The oxidative deterioration was lower in emulsions and microcapsules prepared with fibrillar than with native WPI. This was attributed to improved interfacial barrier properties provided by fibrils and antioxidative effects of coexisting unconverted monomers, particularly hydrophilic peptides.

Synergistic interfacial properties of soy protein–stevioside mixtures: Relationship to emulsion stability

The dynamic interfacial tension and dilatational rheology of soy protein isolate (SPI) and stevioside (STE) mixtures at the oil–water interface were investigated to study the underlying stabilization mechanism for emulsions. The physical properties and long-term stability of emulsions prepared by SPI–STE mixtures were also evaluated. With bulk concentration of SPI fixed at 0.5%, the interfacial dilational properties and emulsion characteristics were markedly affected by the presence of low STE concentration (0.1%), although the interface was still dominated by SPI. With increasing STE concentrations to intermediate level (0.25–1%), synergistic effects in interfacial tension decays and a plateau in the elasticity for mixed SPI–STE interfaces were clearly observed. The effects should be mainly attributed to the formation of SPI–STE complex, enhancing interfacial protein–protein and protein–STE interactions, thus resulting in the presence of a plateau in the elastic behavior. These interfacial properties were positively reflected in the emulsions prepared by SPI–STE mixtures. The emulsions exhibited a fine formation ability and long-term stability after 120 days, which was believed to be due to their better response to external deformations. At high STE content (2%), STE dominated the formation of interface mainly by the preferential adsorption of STE molecules, as evidenced by the results of interfacial properties and surface protein load of emulsions. These findings would provide a potential strategy for designing emulsified foods with long-term stability.

Effect of the Surfactant C<sub>12</sub>mimBr on the Aggregation Behavior of Gemini12-2-12 at an Air/Water Interface, Investigated Using an Interfacial Dilational Rheology Method

采用界面扩张流变技术研究了季铵盐偶联表面活性剂C12-（CH2）2-C12？2Br （Gemini12-2-12）及其与离子液体表面活性剂溴化1-十二烷基-3-甲基咪唑（C12mimBr）复配体系的动态界面张力、扩张流变性质和界面弛豫过程等，探讨了C12mimBr对C12mimBr/Gemini12-2-12混合体系界面性质的影响及C12mimBr对Gemini12-2-12界面聚集行为影响的机制。结果表明，随着离子液体表面活性剂的不断引入，体系界面吸附达到平衡所需的时间逐渐缩短，扩张模量和相角明显降低，界面吸附膜由粘弹性膜转变为近似纯弹性膜；同时，界面及其附近的弛豫过程也发生显著变化，慢弛豫过程消失，快弛豫过程占主导地位，且离子液体浓度越高，快弛豫的贡献越大。这些界面性质的变化主要归因于离子液体表面活性剂C12mimBr参与界面形成及两表面活性剂在界面竞争吸附的结果。少量离子液体表面活性剂C12mimBr的加入可以填补疏松的Gemini12-2-12界面上的空位，形成混合界面吸附膜。随着C12mimBr含量的增加，嵌入界面的C12mimBr分子数不断增多，导致界面上相互缠绕的Gemini12-2-12烷基链“解缠”，在体相和界面分子扩散交换的过程中“解缠”的Gemini12-2-12分子从界面上解吸回到体相，与此同时， C12mimBr分子相对较小的空间位阻及较强的疏水作用促使其优先扩散至界面进而取代Gemini12-2-12分子，最终界面几乎完全被C12mimBr分子所占据。

PH Effects on the Molecular Structure of β-Lactoglobulin Modified Air–Water Interfaces and Its Impact on Foam Rheology

Macroscopic properties of aqueous β-lactoglobulin (BLG) foams and the molecular properties of BLG modified air-water interfaces as their major structural element were investigated with a unique combination of foam rheology measurements and interfacial sensitive methods such as sum-frequency generation and interfacial dilatational rheology. The molecular structure and protein-protein interactions at the air-water interface can be changed substantially with the solution pH and result in major changes in interfacial dilational and foam rheology. At a pH near the interfacial isoelectric point BLG molecules carry zero net charge and disordered multilayers with the highest interfacial dilatational elasticity are formed at the air-water interface. Increasing or decreasing the pH with respect to the isoelectric point leads to the formation of a BLG monolayer with repulsive electrostatic interactions among the adsorbed molecules which decrease the interfacial dilational elasticity. The latter molecular information does explain the behavior of BLG foams in our rheological studies, where in fact the highest apparent yield stresses and storage moduli are established with foams from electrolyte solutions with a pH close to the isoelectric point of BLG. At this pH the gas bubbles of the foam are stabilized by BLG multilayers with attractive intermolecular interactions at the ubiquitous air-water interfaces, while BLG layers with repulsive interactions decrease the apparent yield stress and storage moduli as stabilization of gas bubbles with a monolayer of BLG is less effective.

Effect of interfacial dilational rheology on the breakage of dispersed droplets in a dilute oil–water emulsion

Surfactants reduce the interfacial tension of oil–water and hence favor emulsification; however, attention has rarely been focused on the effect of interfacial dilational rheology on drop breakage. The aim of this work is to rheologically characterize the interfacial properties of oil–water droplets and the effect on drop breakage during emulsification. The dispersed holdups are fixed in dilute dispersion where breakage dominates during mixing. The total number of droplets, the square weighted (sqr-wt) mean diameter and the chord length distribution (CLD) are measured online using the focus beam reflectance method (FBRM). Variations in the dispersed droplets are further analyzed with the interfacial dilational modulus. For emulsions with surfactant concentrations below the critical micelle concentration (CMC), the interfacial tension decreases as the surfactant concentration increases, whereas the mean drop diameter initially shows an increasing trend and then decreases. However, for concentrations above the CMC, the interfacial tension rarely decreases, whereas the mean diameter of the dispersed phase continues to decrease, and the total number of droplets increases as the concentration of Span 80 continues to increase. This indicates that the interfacial dilational elasticity is a key factor that influences the pure breakage emulsification process and the related dispersed modality.

Impact of ionic liquid-type imidazolium surfactant additions on dynamic properties of β-casein adsorption layer

In this article, by means of interfacial dilational rheology and interfacial pressure methods, we have investigated the interfacial properties of adsorbed films at water/decane interface, formed by β-casein and a series of ionic liquid-type imidazolium surfactant [Cnmim]Br (n = 12, 14, 16). The results obtained demonstrate that the addition of ionic liquid-type imidazolium surfactant [Cnmim]Br strongly influenced the dynamic interfacial properties of β-casein solutions due to the β-casein/[Cnmim]Br complex formation. The β-casein/[Cnmim]Br complex has been formed by different charged ions of protein and surfactant, so there is competitive adsorption between the complex and surfactant. In the beginning, the surfactant molecules can adsorb to the interfacial freely according to their higher diffusion coefficient, and the β-casein/[Cnmim]Br complex was not influenced as well. As the interfacial pressure increasing, the interfacial concentration of the complex increases gradually and interactively. At higher surfactant concentrations, the complexes were formed owing to the hydrophobic interactions between the component and the complexes structure have changed. Consequently, the adsorption layer structure and the dynamic elasticity properties also changed. Because of the hydrophobic interactions, the complex became relatively hydrophilic and unstable, the ratio of the free surfactant molecules to the complexes also increased. Moreover, due to the stronger attraction with aromatic rings through π–π interaction resulting from the existence of imidazolium head group, the elasticity of β-casein/[Cnmim]Br system are much higher than that of the traditional surfactant, indicating that the adsorption layer formed by β-casein/[Cnmim]Br are much stronger.

Tailings Pond Surfactant Analogues: Effects on Toluene-Diluted Bitumen Drops in NaHCO3/K2CO3 Solution. Part 2: Dilational Interfacial Viscoelasticity

In this two-part work, we used dilational interfacial rheometry to study the interfaces associated with diluted bitumen in simulated pond water as a function of pH, for three different surfactants: two simple carboxylic acids, one with a straight chain and one having a ring in the tail, and the more complex sodium naphthenates. In part 1 (10.1021/ef400376v), dynamic interfacial tension as a function of time was used to measure adsorption. In part 2, described in the present paper, interfacial dilational rheology was studied as a function of oscillation frequency for three different concentrations of the three surfactants adsorbed at the interface between buffer and toluene-diluted bitumen. The concentrations used were selected on the basis of results from part 1 (10.1021/ef400376v). Our results show that interfacial viscoelasticity depends upon not only the tail complexity in the surfactants but also the surfactant concentration and buffer pH. The adsorbed naphthenates were synergistic with interfacially ...

A fixture for interfacial dilatational rheometry using a rotational rheometer

In characterizing complex fluid-fluid interfaces, interfacial rheometry has become an important tool to indirectly probe the interfacial microstructure and molecular interactions. It can also be useful to obtain the constitutive properties of an interface for calculating the interfacial flows of complex fluid-fluid interfaces. A number of devices for measuring interfacial shear rheology have been designed and have been thoroughly validated. However, although a range of devices for measuring interfacial dilatational rheology exist, they do not always allow for a proper separation of the effects of dynamic surface tension, curvature elasticity, Marangoni stresses, bulk flow effects and the desired dilatational rheological material functions. In the present work it is investigated if a fixture for a standard rotational rheometer can be designed which probes the dilatational viscoelastic properties of a planar complex fluid-fluid interface. A modification of the double wall ring geometry for shear rheometry is proposed, which creates a mixed but analyzable flow field. The use of a mixed flow field inherently limits the sensitivity for the dilatational properties, but some advantages over existing techniques are presented, in particular for insoluble monolayers. More importantly, the analysis illustrate some generic aspects on the use of mixed interfacial flow fields for measuring the surface rheological properties.

Effect of tea polyphenols on the dilational rheology of human whole saliva (HWS): Part 2, polyphenols–HWS interaction

In the second part of this communication we screen a few tea polyphenols for their ability to interact with pre-adsorbed salivary proteins at the air–liquid interface. Using interfacial dilational rheology characterisation, we measure the variation in surface elasticity of a pre-adsorbed salivary film after exposure to tea polyphenols solutions in order to probe the degree of mutual interaction. We observe that this interaction with salivary proteins varies according to the chemical structure and degree of polyphenols complexity (number of phenols rings). The evolution of the salivary film after exposure to polyphenol solutions is characterised through surface dilational response to appropriate frequency modulation and the results are analysed using a general mixed kinetic model, which reproduces correctly the experimental data except for the galloylated theaflavins.

Ostwald ripening of nanoemulsions stopped by combined interfacial adsorptions of molecular and macromolecular nonionic stabilizers

Aliphatic hydrocarbon oil-in-water nanoemulsions were prepared using mixtures of an amphiphilic nonionic polysaccharide (dextran modified by covalent attachment of hydrocarbon tails) and tetraethylene glycol dodecylether as stabilizers. Nanoemulsions stabilized by amphiphilic polysaccharide alone underwent Ostwald ripening. On the contrary, nanoemulsions prepared with certain mixtures of hydrophobically modified dextran and tetraethylene glycol dodecylether exhibited no significant variation of their average droplet diameter over a period of time that depended strongly on the nature of the dispersed oil. When changing from n-hexane to n-octane and n-dodecane, the period of complete inhibition of Ostwald ripening varied from 3h to several months. Polymer–surfactant interactions and co-adsorption at oil/water interface were demonstrated by dynamic interfacial tension measurements and dilational surface rheology.

Surface activity of saponin from Quillaja bark at the air/water and oil/water interfaces

Surface activity of Sigma's Quillaja bark saponin (QBS) was studied by means of dynamic interfacial tension and surface dilational rheology at three fluid/fluid interfaces with the polarity of the non-aqueous phase increasing in the order: air/water, tetradecane/water and olive oil/water. The equilibrium interfacial tension isotherms were fitted to the generalized Frumkin model with surface compressibility for the air/water and tetradecane/water interfaces, whereas the isotherm for the third interface displays a more complex shape. Upon fast compression of a drop of concentrated “Sigma” QBS solution immersed in olive oil, a clearly visible and durable skin was formed. On the other hand, no skin formation was noticed at the air/water interface, and only a little at the tetradecane/water interface. Addition of a fatty acid, however, improved slightly the skin-formation ability of the QBS at the latter interface. The surface behavior of the QBS from Sigma was compared with that from Desert King, Int. (“Supersap”), employed in a recent study by Stanimirova et al. [22]. The two products exhibit different areas per molecule in the saturated adsorbed layer (0.37nm2 vs. 1.19nm2 for “Sigma” and “Supersap”, respectively). Also their surface rheology is different: although both QBSs form predominantly elastic layers, for “Sigma” the surface storage modulus, εr=103mNm−1, while for “Supersap” εr=73mNm−1 at 10−3moll−1 (i.e., around their cmc). The two saponin products exhibit also different ionic character, as proven by the acid-base titration of their aqueous solutions: QBS from Sigma is an ionic surfactant, while the “Supersap” from Desert King is a non-ionic one.