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1.
Spreading of partially crystallized oil droplets on an air/water interface   总被引:3,自引:0,他引:3  
The influence of crystalline fat on the amount and rate of oil spreading out of emulsion droplets onto either a clean or a protein-covered air/water interface was measured for β-lactoglobulin stabilized emulsions prepared with either anhydrous milk fat or a blend of hydrogenated palm fat and sunflower oil. At a clean interface, liquid oil present in the emulsion droplets was observed to completely spread out of the droplets unimpeded by the presence of a fat crystal network. Further, the presence of a fat crystal network in the emulsion droplets had no effect on the rate of oil spreading out of the droplets. At a protein-covered interface, the spreading behavior of emulsion droplets containing crystalline fat was evaluated in terms of the value of the surface pressure (ΠAW) at the point of spreading; ΠAW at spreading was unaffected by the presence of crystalline fat. We conclude it is unlikely that the role of crystalline fat in stabilizing aerated emulsions such as whipped cream is to reduce oil spreading at the air/water interface. However, the temperature of the system did have an effect: spontaneous spreading of emulsion droplets at clean air/water interfaces occurred for systems measured at 5 °C, but not for those measured at 22 or 37 °C. Thus, temperature may play a more important role in the whipping process than commonly thought: the entering and spreading of emulsion droplets was favored at lower temperatures because the surface pressure exerted by protein adsorbed at the air/water interface was reduced. This effect may facilitate the whipping process.  相似文献   

2.
Stabilization of emulsions by mixed polyelectrolyte/surfactant systems is a prominent example for the application in modern technologies. The formation of complexes between the polymers and the surfactants depends on the type of surfactant (ionic, non-ionic) and the mixing ratio. The surface activity (hydrophilic–lipophilic balance) of the resulting complexes is an important quantity for its efficiency in stabilizing emulsions. The interfacial adsorption properties observed at liquid/oil interfaces are more or less equivalent to those observed at the aqueous solution/air interface, however, the corresponding interfacial dilational and shear rheology parameters differ quite significantly. The interfacial properties are directly linked to bulk properties, which support the picture for the complex formation of polyelectrolyte/surfactant mixtures, which is the result of electrostatic and hydrophobic interactions. For long alkyl chain surfactants the interfacial behavior is strongly influenced by hydrophobic interactions while the complex formation with short chain surfactants is mainly governed by electrostatic interactions.  相似文献   

3.
By measuring the change in interfacial tension after adding phospholipid vesicles to an aqueous solution of electrolyte, we studied the adsorption behavior of phospholipid vesicles at oil/water interfaces. The effects of concentration of three kinds of electrolyte (NaCl, MgCl2, LaCl3) and of the mixing ratio of two kinds of phospholipids (phosphatidylcholine and phosphatidylserine), on the adsorption behavior at an oil/water interface were examined. The results were interpreted using the DLVO theory.  相似文献   

4.
Over the last decades numerous studies on the interfacial rheological response of protein adsorption layers have been published. The comparison of these studies and the retrieval of a common parameter to compare protein interfacial activity are hampered by the fact that different boundary conditions (e.g. physico-chemical, instrumental, interfacial) were used. In the present work we review previous studies and attempt a unifying approach for the comparison between bulk protein properties and their adsorption films. Among many common food grade proteins we chose bovine serum albumin, β-lactoglobulin and lysozyme for their difference in thermodynamic stability and studied their adsorption at the air/water and limonene/water interface. In order to achieve this we have i) systematically analyzed protein adsorption kinetics in terms of surface pressure rise using a drop profile analysis tensiometer and ii) we addressed the interfacial layer properties under shear stress using an interfacial shear rheometer under the same experimental conditions. We could show that thermodynamically less stable proteins adsorb generally faster and yield films with higher shear rheological properties at air/water interface. The same proteins showed an analog behavior when adsorbing at the limonene/water interface but at slower rates.  相似文献   

5.
Polymer/surfactant interactions at the air/water interface   总被引:1,自引:0,他引:1  
The development of neutron reflectometry has transformed the study and understanding of polymer/surfactant mixtures at the air/water interface. A critical assessment of the results from this technique is made by comparing them with the information available from other techniques used to investigate adsorption at this interface. In the last few years, detailed information about the structure and composition of adsorbed layers has been obtained for a wide range of polymer/surfactant mixtures, including neutral polymers and synthetic and naturally occurring polyelectrolytes, with single surfactants or mixtures of surfactants. The use of neutron reflectometry together with surface tensiometry, has allowed the surface behaviour of these mixtures to be related directly to the bulk phase behaviour. We review the broad range of systems that have been studied, from neutral polymers with ionic surfactants to oppositely charged polyelectrolyte/ionic surfactant mixtures. A particular emphasis is placed upon the rich pattern of adsorption behaviour that is seen in oppositely charged polyelectrolyte/surfactant mixtures, much of which had not been reported previously. The strong surface interactions resulting from the electrostatic attractions in these systems have a very pronounced effect on both the surface tension behaviour and on adsorbed layers consisting of polymer/surfactant complexes, often giving rise to significant surface ordering.  相似文献   

6.
Silver nanoparticles and nanoplates were prepared at the air/AgNO3 aqueous solution interfaces under poly(9-vinylcarbazole) (PVK) monolayers when illuminated by UV-light at room temperature and elevated temperatures, respectively. When the illuminated films at the air/water interfaces were covered by carbon-coated copper grids, nanoplates were formed even at room temperature, and the size of the nanoplates was much larger than those formed at the air/water interface under the same experimental conditions, indicating that copper took part in the formation of Ag nanoplates through the galvanic displacement reaction between Cu and Ag+ ions with the help of carbon layer to conduct electrons. It was found that the basal plane of these nanoplates is the (1 1 1) face of a face-centered cubic (fcc) Ag crystal. Although platelike structure can be formed at the carbon-coated copper grid/AgNO3 aqueous solution interface without PVK film, it shows different features from those with PVK films, indicating that PVK film plays an important role in the formation of regular large nanoplates. Further observations indicate that special restrained microenvironment, adsorption of PVK molecules on a specific crystal face, anisotropic growth and attachment of the nanoparticles are responsible for the formation of the nanoplates.  相似文献   

7.
In the present study, we have performed molecular dynamics simulations to describe the microscopic behaviors of the anionic, nonionic, zwitterion, and gemini surfactants at oil/water interface. The abilities of reducing the interfacial tension and forming the stable interfacial film of the four surfactants have been investigated through evaluating interfacial thickness, interface formation energy and radial distribution function. The results show that the four kinds of surfactants can form in stable oil/water interface of monolayer, and the gemini surfactant can form the more stable monolayer. The results of the above three parameters demonstrate that the gemini surfactant has the best simulation effect in the four surfactants. From the calculated interfacial tension values, the gemini surfactant possess the more powerful ability of reducing the interfacial tension than others, so it is more suitable to be used as the surfactant for flooding. In addition, the effects of different electric field intensities on surfactants were calculated, through the radial distribution function of the hydrophilic group in the surfactant and the oxygen atom in the water. We have found that the adding of the periodic electric field can significantly affect the diffusion behavior of the molecules, and nonionic surfactant has stronger demulsification capability than others.  相似文献   

8.
Lupin seed protein isolates adsorbed at the corn oil–water interface formed, after long ageing times, interfacial films with viscoelastic properties. The viscoelastic parameters of the films, derived by analysis of creep compliance–time curves, were markedly influenced by the aqueous phase protein concentrations, pH, ageing time and isolate preparation methods. Instantaneous elastic modulus, E0(s), showed maxima at a certain concentration which probably corresponded to monolayer saturation coverage and at pH 5.5, i.e. near to its isoelectric point, where the protein molecules are in a more compact form than at other pH values. The full fat lupin seed protein fractions gave the highest viscoelasticity values under all conditions and this in turn have an effect on the corresponding emulsion/foam stability.  相似文献   

9.
This study relates interfacial interactions of bovine serum albumin (BSA) molecules in dilute solutions with its dilatational rheology. Dynamic surface tension and the associated dilational elastic modulus and viscosity for BSA and mixtures of BSA with Hofmeister electrolytes—NaCl, NaClO4, Na2SO4, NaF and Na2HPO4 have been studied using a sinusoidal surface compression and expansion for frequencies ranging from 0.01 to 0.4 Hz. at solution/air interface. In all the BSA + electrolyte systems, both the elastic modulus and viscosity show unusually high values compared with pure BSA or pure electrolytes. In the presence of NaF and Na2SO4 the viscosity of protein increases almost by 50–80-fold and the corresponding elastic modulus also changes by 30–50-fold. Hydrated Hofmeister ions surely influence the measured rheological properties. In addition, the synergistic effect of the hydrated protein and the vicinal hydrated electrolytes possibly contribute to the high viscosity and elasticity due to change in dynamics of these assemblies. Thus the behavior of BSA is effected by salts in different ways, especially due to the dynamics and strength of the water molecules in the assembly.  相似文献   

10.
The adsorption of bovine serum albumin (BSA) at the air/water interface and its effect on the transport of dipalmitoylphosphatidylcholine (DPPC) to form a surface film were studied with tensiometry, infrared reflection absorption spectroscopy (IRRAS), and ellipsometry. For 1, 10, 100, and 1000 ppm BSA solutions, the steady-state tension ranges from 55 to 50 mN m−1. At pulsating area (at 20 cycles min−1), both the minimum and maximum tensions decrease with increasing bulk concentration. Even though the steady-state tension is similar for 100 and 1000 ppm BSA, IRRAS and ellipsometry results indicate that the adsorbed density is higher for 1000 ppm BSA. For 1000 ppm/1000 ppm BSA/DPPC mixture, the tension behavior was found to be similar to that of 1000 ppm BSA when alone. Results from IRRAS and ellipsometry also demonstrate that BSA is the dominant adsorbed component at the air/water interface. Thus, at 1000 ppm, by adsorbing fast and possibly irreversibly, BSA interferes with the transport and adsorption of DPPC and inhibits its ability to lower the surface tension. However, when DPPC is introduced via a spread monolayer mechanism, DPPC expels partly or completely the adsorbed BSA monolayer and then controls the tension behavior with little or no inhibition by BSA. Thus, the competitive adsorption of DPPC and BSA depends strongly on the path or mechanism of introducing DPPC to the surface and involves path-dependent nonequilibrium adsorption phenomena.  相似文献   

11.
DNA–didodecyldimethylammonium (DNA–DDDA) electrostatic complex was prepared and characterized through Fourier transformation infrared (FT-IR), 1H NMR and circular dichroism (CD) spectroscopy. When the dye molecule aqueous solutions were used as the subphase, the interaction between three dye molecules, acridine orange (AO), ethidium bromide (EB) and 5,10,15,20-tetrakis(4-N-methylpyridyl)porphine tetra(p-toluenesulfonate) (TMPyP) and the complex at air/solution interface were investigated through the surface pressure–area (πA) isotherms, Brewster angle microscopy and UV-Vis spectroscopy, respectively. Our investigation indicates that the interaction capabilities of the three dyes to DNA–DDDA complex are different and present an order of TMPyP>AO>EB. For the interaction forms, we believe that TMPyP intercalates into the double helix of DNA, and AO adsorbs onto the surface of the DNA. As for EB, the measured signal is too weak to give a definite interaction form in the present experiment.  相似文献   

12.
The thermodynamic equations for examining aggregate formation in an oil phase and adsorption at the oil/water interface of a nonionic solute were derived. The total differentials of chemical potentials of species and the oil/water interfacial tension were expressed as functions of temperature, pressure, and the total concentration of solute in the oil phase after explicit consideration of aggregate formation. The partial derivatives of the chemical potentials and the interfacial tension with respect to the independent variables were found to provide the thermodynamic quantities of aggregate formation and adsorption from oil phase to the interface by introducing the concept of an ideally dilute associated solution. These equations were applied to the cyclohexane solution of oleyl alcohol/water system, and the adsorption and aggregate formation was examined.  相似文献   

13.
14.
The composition and properties of the adsorption films of dodecylammonium chloride/sodium dodecyl sulfate at the air/water interface depend on interactions between the film molecules and equilibria in the bulk phase (monomer-micelle and/or monomerprecipitate equilibria).The negative value of surface molecular interaction parameter mon calculated using the regular solution theory indicates strong attractive interactions between adsorbed molecules. Electrostatic interactions between oppositely charged ionic head groups enhance the adsorption of surfactants and decrease the minimum molar area of surfactant molecules at the air/water interface. The addition of an oppositely charged surfactant enhances packing at the air/water interface and transition from a liquid expanded to a liquid condensed state. Surface potential measurements reveal positive values for the mixtures investigated, implying the cationic surfactant ions are closer to the surface than the anionic ones.  相似文献   

15.
The block polyethers with various branch structure, such as TEPA[(PO)36(EO)100]7, TEPA[(PO)36(EO)100(PO)36]7, and TEPA[(PO)36(EO)100(PO)56]7 were synthesized. Moreover, the aggregation behavior was investigated via the measurements of equilibrium surface tension, dynamic surface tension, and surface dilational viscoelasticity, in order to probe the effect of the block structure on the property of the branched block polyethers. The surface tension results show that the efficiency and effectiveness of the block polyethers to lower surface tension increase with the increase of the PO group numbers. The maximum surface excess concentration (Γmax) values and the minimum occupied area per molecule at the air/water interface (Amin) values of the branched block polyethers obtained from Gibbs adsorption equations increase and decrease with the increases of the PO group numbers, respectively. The dynamic parameters n and t* representing the diffusion speed of the polyether molecules from bulky solution to the subsurface and from the subsurface to the air/water surface are obtained according to the equation proposed by Rosen. The results show that the n values firstly increase and then decrease and t* values decrease with the increase of the polyether concentrations. The results of surface dilational viscoelasticity show that the dilational modulus of TEPA[(PO)36(EO)100(PO)56]7 is the largest among the three block copolymers at the low concentration (<1 mg L−1) but that of TEPA[(PO)36(EO)100]7 is the largest at the high concentration (>1 mg L−1).  相似文献   

16.
A low-resolution 1H NMR relaxometry study on the dynamics of an n-decane/water emulsion stabilized by β-casein is presented. Spin–spin (transverse) relaxation time constants (T2) were used to assess relative mobilities of emulsion components, by a selective deuteration procedure. Data analysis allowed the emulsion investigated to be described by a heterogeneous collection of dynamically distinct populations. A major population of n-decane molecules presented an average mobility that very nearly approached that of pure solvent, which is compatible with its occurrence in the emulsion continuous microphase. β-Casein molecules displayed a prevalent population with significantly decreased mobility as compared to the free protein in solution, which is in accordance with the protein location at the oil/water interface. Also, a major H2O population with significantly lower average T2 as compared to the pure liquid was detected and has been assigned to interfacial water.  相似文献   

17.
Spreading behaviour of the dimeric surfactant polyethylene-glycoldistearate (PEGDS) monolayer at air/water interface has been studied using surface pressure-area (π-A) isotherms as a function of temperature. The isotherms show a plateau suggesting a transition between a liquid expanded (LE) and a condensed state. The condensed state possibly arises due to nucleation and growth of multilayers from the monolayer. Isobaric measurements of bothA-T and π-T at constant area show transitions atT = 295 K. These plots suggest a melting followed by formation of condensed microcrystallites. Structure optimization carried out using various angles of orientation of the alkyl tails with respect to the backbone in PEGDS reveals tilt transitions of the tails in different states which can be related to the packing behaviour seen in the isotherms. Optical microscopy has been used to confirm the structures in these states.  相似文献   

18.
The structure and potential distribution of electric double layers (EDLs) are of close relevance to the performance of electrode materials. In the past years, despite tremendous efforts devoted to this topic, an atomistic picture of the EDL is still lacking, let alone understanding on how the EDL structure is related to the dielectric property of interface water. In this article, we briefly review the recent progress in modeling electrified metal/water interfaces using ab initio molecular dynamics (AIMD). The ab initio methods for EDL modeling is firstly summarized, and then we discuss the structures of interface water on metal electrodes at different potential conditions. Moreover, we illustrate the potential-dependent behavior of chemisorbed water on Pt(111) surface and its relationship with the peak of the differential Helmholtz capacitance observed by experiment. At last, we give some perspective for future development in ab initio modeling of electrochemical interfaces.  相似文献   

19.
The dynamic adsorption and penetration of human serum albumin (HSA) into the monolayers of five biologically important surfactants—DSPC, DPPC, DMPC, DMPE and DMPA—were systematically studied using Brewster angle microscopy, film balance and pendent drop techniques. Isotherms after different adsorption times show that the presence of HSA changed the monolayer phase behavior (e.g. the shifts of the LE→LC phase transition in the mixed phospholipid/HSA monolayers). Apparent inhomogeneous phases—‘honey-comb’ (J. Mol. Liq., 2001, 90, 149), ‘block’ or ‘stripe’ shape phases are formed due to the adsorption and penetration of HSA into these phospholipid monolayers at the air/water interface. Both the phase behavior changes and the morphological changes were confirmed by our recent structure studies in DPPA/HSA and DPPS/HSA monolayers using X-ray diffraction at grazing incidence, which directly shows that HSA penetration can change the tilt angle of phospholipids. It was found that the adsorption and penetration of HSA strongly depends on the phospholipid head-group structure and the physical state of the phospholipid films. The latter played a dominant role by providing enough space for the penetration of HSA and affecting the hydrophobic interactions of HSA with the aliphatic chains of phospholipids in monolayers at the air/water interface. In general, HSA penetrates more efficiently and quickly into monolayers of phospholipids in liquid state (e.g. DMPC compared to DSPC) and with unprotected charges (e.g. PA compared to PE and PC).  相似文献   

20.
Experiments are reported with foam films from aqueous solutions with increasing concentration of a cationic surfactant. A correlation is established between the foam film thickness and the possible variation of diffuse electric layer potential at the air/water interface from a negative value in absence of surfactant to positive values at higher surfactant concentrations. It is concluded that a charge reversal at the air/water interface is expected to occur under increasing concentration of cationic surfactants in aqueous solutions.  相似文献   

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