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R Miller - One of the best experts on this subject based on the ideXlab platform.

  • foaming properties and the dynamics of adsorption and Surface Rheology of silk fibroin at the air water interface
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2020
    Co-Authors: Xiuying Qiao, R Miller, Emanuel Schneck, Kang Sun
    Abstract:

    Abstract In this study, the Surface adsorption, Surface viscoelasticity and foamability of silk fibroin (SF) at the air/water interface are investigated and the relationship between the Surface Rheology and foaming properties is discussed. The SF molecules adsorb at the air/water interface and form viscoelastic Surface films with high Surface viscoelasticity modulus. Increasing concentrations of SF leads to thicker adsorbed layers and enhances the Surface mechanical strength and foam stability. However, after the SF concentration exceeds a critical value, the Surface dilatational modulus starts to decrease due to the imperfect arrangements of SF molecules at jamming state, and the Surface tension and Surface shear modulus do not show any significant changes at saturated adsorption.

  • β lactoglobulin adsorption layers at the water air Surface 2 dilational Rheology effect of ph and ionic strength
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2017
    Co-Authors: V Ulaganathan, B A Noskov, I Retzlaff, J Y Won, G Gochev, Deniz Z Gunes, Cecile Gehindelval, Martin E Leser, R Miller
    Abstract:

    Abstract The dynamic Surface pressure Π and the two components E’ (real part) and E” (imaginary part) of the dynamic Surface dilational modulus of adsorbed β-lactoglobulin (BLG) layers at the water/air interface were measured by oscillating drop/bubble profile analysis tensiometry with the aim to enlarge information on the Surface Rheology of solutions of this practically important protein. The effects of the solution pH and ionic strength (represented by the buffer concentration C buff ) on the kinetic dependences of Π, E’ and E” were monitored for various protein concentrations in the range 5×10 −9 –2×10 −4  M. Combining the E’(t) and E”(t) data with the Π(t) data allowed for obtaining the dependences E’(Π) and E”(Π). The real part E’ was found to increase monotonically with increasing Π, while the E”(Π) data exhibit a maximum in the Surface pressure range 14–18 mN/m. The height of the maximum in the E”(Π) dependence was found to increase with increasing protein concentration. Apparently, in these interfacial layers, relaxation processes take place and their relaxation strengths depend on the history of the layer formation, i.e. the rate of adsorption. After the maximum in the E”(Π) dependence the E”-values progressively diminish, which can be assumed to occur due to solidification of the protein gel-like network accompanied by less energy dissipation and high elasticity of the interfacial layer. BLG layers at pH 5 (close to the isoelectric point pI ≈ 5.1) exhibit the highest E’-values and the lowest E”-values measured in this study, which suggest the formation of a strong protein network at these (isoelectric) conditions. Variations of the buffer concentration strongly influence the kinetic dependences of E’ and E” for BLG layers at pH ≠ pI, while at pH → pI no effect was detected. The viscoelastic characteristics of BLG layers adsorbed from buffer-free solutions containing NaCl or CaCl 2 were also studied. For the first time, hysteresis in the frequency dependence of the Surface dilational modulus of protein layers measured during repeating cycles of oscillations is reported. Such hysteresis is typical for BLG layers adsorbed at any solution conditions used in this study.

  • adsorption of proteins at the solution air interface influenced by added nonionic surfactants at very low concentrations for both components 3 dilational Surface Rheology
    Journal of Physical Chemistry B, 2015
    Co-Authors: V B Fainerman, E V Aksenenko, S V Lylyk, Marzieh Lotfi, R Miller
    Abstract:

    The influence of the addition of the nonionic surfactants C12DMPO, C14DMPO, C10OH, and C10EO5 at concentrations between 10–5 and 10–1 mmol/L to solutions of β-casein (BCS) and β-lactoglobulin (BLG) at a fixed concentration of 10–5 mmol/L on the dilational Surface Rheology is studied. A maximum in the viscoelasticity modulus |E| occurs at very low surfactant concentrations (10–4 to 10–3 mmol/L) for mixtures of BCS with C12DMPO and C14DMPO and for mixtures of BLG with C10EO5, while for mixture of BCS with C10EO5 the value of |E| only slightly increased. The |E| values calculated with a recently developed model, which assumes changes in the interfacial molar area of the protein molecules due to the interaction with the surfactants, are in satisfactory agreement with experimental data. A linear dependence exists between the ratio of the maximum modulus for the mixture to the modulus of the single protein solution and the coefficient reflecting the influence of the surfactants on the adsorption activity of the...

  • dynamic properties of mixed nanoparticle surfactant adsorption layers
    Soft Matter, 2013
    Co-Authors: P A Yazhgur, Giuseppe Loglio, Libero Liggieri, R Miller, B A Noskov, Shiyow Lin, Francesca Ravera
    Abstract:

    The adsorption films of silica nanoparticles modified by a cationic surfactant (cetyltrimethylammonium bromide, CTAB) at the air–water interface were investigated by the dilational Surface Rheology and optical methods. Special attention was paid to the slow changes of Surface properties with the Surface age. The Surface tension and dynamic dilational Surface elasticity were measured as a function of CTAB concentration. The whole surfactant concentration range can be divided into four regions characterized by different Surface rheological behavior. Depending on the CTAB concentration, the Surface elasticity close to the equilibrium may reach extremely high values (∼1000 mN m−1) and strongly depends on the applied Surface strain. This occurs at surfactant concentrations below the region where the dispersion becomes turbid, indicating particle aggregation in the bulk. The Brewster angle microscopy and ellipsometry show that the adsorption layer becomes fragile and inhomogeneous in this region.

  • adsorption layer properties and foam film drainage of aqueous solutions of tetraethyleneglycol monododecyl ether
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011
    Co-Authors: D Arabadzhieva, Francesca Ravera, R Miller, Elena Mileva, Plamen Tchoukov, Libero Liggieri
    Abstract:

    Abstract The aim of the present study is to clarify how the surfactant adsorption layer properties are related to the course of the drainage parameters of microscopic foam films in the special case of aqueous solutions of the non-ionic amphiphile tetraethyleneglycol monododecyl ether (C 12 E 4 ), containing premicellar nanostructures. The scope of the research covers adsorption dynamics, construction of equilibrium adsorption isotherms, studies on Surface Rheology of the interfacial layers and microscopic foam film drainage kinetics. It is established that in the premicellar concentration domain considerable irregularities of the adsorption layer properties are observed: two plateau regions are registered in the experimental Surface tension isotherm along with unusual changes of the Surface rheological characteristics. The systematic investigation of the drainage of microscopic foam films obtained from these solutions show that the dependencies of basic kinetic parameters of the films on the amphiphile concentration run in synchrony with the changes in the adsorption layer properties. This fact is related to the presence of smaller surfactant aggregates (premicelles). They are presumed to be organized as Platonic bodies. The premicelles play also a significant role in the kinetic stability of the films. The importance of this research is in providing better insight into the initial stages of self-assembling phenomena and into the factors determining the adsorption layer properties and the drainage behaviour of thin liquid films.

Leonard M C Sagis - One of the best experts on this subject based on the ideXlab platform.

  • effect of cmc degree of substitution and gliadin cmc ratio on Surface Rheology and foaming behavior of gliadin cmc nanoparticles
    Food Hydrocolloids, 2020
    Co-Authors: Weiping Jin, Dengfeng Peng, Miriam Arts, Jack Yang, Leonard M C Sagis
    Abstract:

    Abstract To understand the influence of the degree of substitution (DS) of sodium carboxymethyl cellulose (CMC) and gliadin:CMC ratio on the Surface and foaming behaviors of gliadin-CMC nanoparticles (G-CMC NPs) at pH 3, three DS (0.7–1.2) and four ratios (G:CMC~1:0.5–1:2) were investigated. Gliadin NPs with a pH of 3 were utilized as a control. Results showed that G-CMC NPs at all investigated DS and ratios possessed higher foamability and foam stability when compared to the control. This indicated that adding CMC to gliadin NP suspensions could greatly improve their foaming properties. G-CMC NPs with a DS of 0.7 and 0.9, had lower Surface charge than G-CMC1.2 NPs, resulting in a weaker electrostatic repulsion, thus leading to faster adsorption kinetics and higher foamability. By increasing the G:CMC ratio from 1:0.5 to 1:2, the particle size gradually rose, and the zeta potential remained unchanged. At a ratio of 1:2, the highest foam stability was observed. This might be ascribed to the high continuous phase viscosity at this ratio, which could slow down the drainage rate and protect the bubbles against coalescence and disproportionation. It was worth mentioning that G-CMC NPs at all ratios exhibited impressive foamability (~220%) even at a very low concentration of G-CMC NPs (gliadin was fixed at 1 mg/mL). This implies that G-CMC NPs could act as a new efficient foaming agent, and based on its simple preparation, have the potential to be widely applied in foamed food.

  • Surface Rheology and structure of model triblock copolymers at a liquid vapor interface a molecular dynamics study
    Macromolecules, 2020
    Co-Authors: Ahmad Moghimikheirabadi, Leonard M C Sagis, Patrick Ilg, Martin Kroger
    Abstract:

    The structure and Surface Rheology of two model symmetric triblock copolymers with different degrees of hydrophobicity but identical polymerization degree, spread at an explicit liquid/vapor interf...

  • the influence of protein phospholipid ratio on the physicochemical and interfacial properties of biomimetic milk fat globules
    Food Hydrocolloids, 2019
    Co-Authors: Min Chen, Leonard M C Sagis
    Abstract:

    Abstract The effect of protein/phospholipid ratio on the physicochemical and interfacial properties of biomimetic milk fat globules (BMFGs) was investigated. Butter milk phospholipid (BMP) vesicles prepared with ultrasonication were mixed with whey protein isolate (WPI) at different protein/phospholipid ratios (w/w). After emulsification, the Turbiscan stability index (TSI) was used to quantify the initial stability of BMFGs. At different pH values, visual observation and CLSM were performed to obtain the macro stability and microstructure of BMFGs. In addition, large amplitude oscillatory Surface Rheology was applied and analysed with Lissajous curves, to explore the oil/water interfacial properties of BMFGs in the nonlinear viscoelastic regime. The TSI indicated a faster creaming rate of BMP stabilized droplets compared to those stabilized by WPI. The macro stability of WPI/BMP co-stabilized BMFGs at different pH was dominated by WPI and BMFGs prepared at the WPI/BMP ratio of 20:80 phase separated from pH 3.0 to 5.0. At acidic pH, the WPI/BMP ratios strongly affected the coalescence and flocculation of BMFGs at the micro level. The Surface elasticity indicated that WPI dominated the rheological properties of WPI/BMP co-stabilized oil/water interfaces. Besides, the significant dependence of Surface elasticity on deformation amplitudes within the nonlinear regime of WPI stabilized oil/water interfaces indicated a clearly different structure from BMP stabilized interfaces. Conclusively, results of this study showed that the physicochemical and interfacial properties of BMFGs were significantly influenced by the protein/phospholipid ratio in the bulk, which needs to be considered in the design and application of biomimetic milk fat globules.

  • relaxation behavior and nonlinear Surface Rheology of peo ppo peo triblock copolymers at the air water interface
    Langmuir, 2019
    Co-Authors: Ahmad Moghimikheirabadi, Martin Kroger, Peter Fischer, Leonard M C Sagis
    Abstract:

    Surface dilatational viscoelasticity of adsorbed layers of pluronics triblock copolymers at the air–water interface was measured using the oscillating barrier technique. The effect of molecular arc...

  • non linear Surface dilatational Rheology as a tool for understanding microstructures of air water interfaces stabilized by oligofructose fatty acid esters
    Soft Matter, 2013
    Co-Authors: Silvia E H J Van Kempen, Henk A Schols, Erik Van Der Linden, Leonard M C Sagis
    Abstract:

    In this paper, the rheological response of air/water interfaces, stabilized by various oligofructose fatty acid esters, to oscillatory dilatational deformations was studied and compared to the response of interfaces stabilized by sucrose esters. We have followed a traditional approach to Surface Rheology, where the development of the modulus as a function of time is studied as well as the frequency dependence of the modulus. We also adopted a different approach where we investigate in detail the amplitude dependence of the modulus. Finally, we studied the temperature dependence. We show that for an accurate characterization of the dilatational Rheology of fluid–fluid interfaces with a complex microstructure, a protocol should be used that not only involves variations of Surface pressure, frequency, and temperature, but also establishes amplitude dependence. We show that Lissajous plots of Surface pressure versus deformation can be useful tools to help interpret Surface dilatational behavior in terms of interfacial microstructure. The rheological response of interfaces stabilized by oligofructose esters differed significantly from the response of those stabilized by sucrose esters. Sucrose esters behaved like typical low molecular weight surfactants, and gave interfaces with relatively low moduli, a frequency scaling of the dilatational modulus with an exponent close to 0.5, and displayed no asymmetries in Lissajous plots. In contrast, the oligofructose esters gave, depending on the fatty acid tail, relatively high moduli, almost independent of frequency. Significant asymmetries were observed in the Lissajous plots, with strain hardening during compression and strain softening during extension. Our results suggest that the unusual rheological properties of interfaces stabilized by oligofructose esters may be the result of the formation of a two-dimensional soft glass phase by the oligofructose part of the ester.

B A Noskov - One of the best experts on this subject based on the ideXlab platform.

  • formation of protein surfactant adsorption layer as studied by dilational Surface Rheology
    Advances in Colloid and Interface Science, 2017
    Co-Authors: B A Noskov, Michael M Krycki
    Abstract:

    Abstract The review discusses the mechanism of formation of protein/surfactant adsorption layers at the liquid – gas interface. The complexes of globular proteins usually preserve their compact structure a low surfactant concentrations. Therefore a simple kinetic model of the adsorption of charged compact nanoparticles is discussed first and compared with experimental data. The increase of surfactant concentrations results in various conformational transitions in the Surface layer. One can obtain information on the changes of the adsorption layer structure using the dilational Surface Rheology. The kinetic dependencies of the dynamic Surface elasticity are strongly different for the adsorption of unfolded macromolecules and compact globules, and have local maxima in the former case corresponding to different steps of the adsorption. These distinctions allow tracing the changes of the tertiary structure of protein/surfactant complexes in the Surface layer. The adsorption from mixed solutions of ionic surfactants with β-casein, β-lactoglobulin, bovine serum albumin and myoglobin is discussed with some details.

  • β lactoglobulin adsorption layers at the water air Surface 2 dilational Rheology effect of ph and ionic strength
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2017
    Co-Authors: V Ulaganathan, B A Noskov, I Retzlaff, J Y Won, G Gochev, Deniz Z Gunes, Cecile Gehindelval, Martin E Leser, R Miller
    Abstract:

    Abstract The dynamic Surface pressure Π and the two components E’ (real part) and E” (imaginary part) of the dynamic Surface dilational modulus of adsorbed β-lactoglobulin (BLG) layers at the water/air interface were measured by oscillating drop/bubble profile analysis tensiometry with the aim to enlarge information on the Surface Rheology of solutions of this practically important protein. The effects of the solution pH and ionic strength (represented by the buffer concentration C buff ) on the kinetic dependences of Π, E’ and E” were monitored for various protein concentrations in the range 5×10 −9 –2×10 −4  M. Combining the E’(t) and E”(t) data with the Π(t) data allowed for obtaining the dependences E’(Π) and E”(Π). The real part E’ was found to increase monotonically with increasing Π, while the E”(Π) data exhibit a maximum in the Surface pressure range 14–18 mN/m. The height of the maximum in the E”(Π) dependence was found to increase with increasing protein concentration. Apparently, in these interfacial layers, relaxation processes take place and their relaxation strengths depend on the history of the layer formation, i.e. the rate of adsorption. After the maximum in the E”(Π) dependence the E”-values progressively diminish, which can be assumed to occur due to solidification of the protein gel-like network accompanied by less energy dissipation and high elasticity of the interfacial layer. BLG layers at pH 5 (close to the isoelectric point pI ≈ 5.1) exhibit the highest E’-values and the lowest E”-values measured in this study, which suggest the formation of a strong protein network at these (isoelectric) conditions. Variations of the buffer concentration strongly influence the kinetic dependences of E’ and E” for BLG layers at pH ≠ pI, while at pH → pI no effect was detected. The viscoelastic characteristics of BLG layers adsorbed from buffer-free solutions containing NaCl or CaCl 2 were also studied. For the first time, hysteresis in the frequency dependence of the Surface dilational modulus of protein layers measured during repeating cycles of oscillations is reported. Such hysteresis is typical for BLG layers adsorbed at any solution conditions used in this study.

  • protein conformational transitions at the liquid gas interface as studied by dilational Surface Rheology
    Advances in Colloid and Interface Science, 2014
    Co-Authors: B A Noskov
    Abstract:

    Abstract Experimental results on the dynamic dilational Surface elasticity of protein solutions are analyzed and compared. Short reviews of the protein behavior at the liquid–gas interface and the dilational Surface Rheology precede the main sections of this work. The kinetic dependencies of the Surface elasticity differ strongly for the solutions of globular and non-globular proteins. In the latter case these dependencies are similar to those for solutions of non-ionic amphiphilic polymers and have local maxima corresponding to the formation of the distal region of the Surface layer (type I). In the former case the dynamic Surface elasticity is much higher (> 60 mN/m) and the kinetic dependencies are monotonical and similar to the data for aqueous dispersions of solid nanoparticles (type II). The addition of strong denaturants to solutions of bovine serum albumin and β-lactoglobulin results in an abrupt transition from the type II to type I dependencies if the denaturant concentration exceeds a certain critical value. These results give a strong argument in favor of the preservation of the protein globular structure in the course of adsorption without any denaturants. The addition of cationic surfactants also can lead to the non-monotonical kinetic dependencies of the dynamic Surface elasticity indicating destruction of the protein tertiary and secondary structures. The addition of anionic surfactants gives similar results only for the protein solutions of high ionic strength. The influence of cationic surfactants on the local maxima of the kinetic dependencies of the dynamic Surface elasticity for solutions of a non-globular protein (β-casein) differs from the influence of anionic surfactants due to the heterogeneity of the charge distribution along the protein chain. In this case one can use small admixtures of ionic surfactants as probes of the adsorption mechanism. The effect of polyelectrolytes on the kinetic dependencies of the dynamic Surface elasticity of protein solutions is weaker than the effect of conventional surfactants but exceeds the error limits.

  • dynamic properties of mixed nanoparticle surfactant adsorption layers
    Soft Matter, 2013
    Co-Authors: P A Yazhgur, Giuseppe Loglio, Libero Liggieri, R Miller, B A Noskov, Shiyow Lin, Francesca Ravera
    Abstract:

    The adsorption films of silica nanoparticles modified by a cationic surfactant (cetyltrimethylammonium bromide, CTAB) at the air–water interface were investigated by the dilational Surface Rheology and optical methods. Special attention was paid to the slow changes of Surface properties with the Surface age. The Surface tension and dynamic dilational Surface elasticity were measured as a function of CTAB concentration. The whole surfactant concentration range can be divided into four regions characterized by different Surface rheological behavior. Depending on the CTAB concentration, the Surface elasticity close to the equilibrium may reach extremely high values (∼1000 mN m−1) and strongly depends on the applied Surface strain. This occurs at surfactant concentrations below the region where the dispersion becomes turbid, indicating particle aggregation in the bulk. The Brewster angle microscopy and ellipsometry show that the adsorption layer becomes fragile and inhomogeneous in this region.

  • formation of protein surfactant adsorption layer at the air water interface as studied by dilational Surface Rheology
    Journal of Physical Chemistry B, 2011
    Co-Authors: A A Mikhailovskaya, Giuseppe Loglio, B A Noskov, Shiyow Lin, R Miller
    Abstract:

    The dynamic dilatational Surface elasticity of mixed solutions of globular proteins (β-lactoglobulin (BLG) and bovine serum albumin (BSA)) with cationic (dodecyltrimethylammonium bromide (DTAB)) and anionic (sodium dodecyl sulfate (SDS)) surfactants was measured as a function of the surfactant concentration and Surface age. If the cationic surfactant concentration exceeds a certain critical value, the kinetic dependencies of the dynamic Surface elasticity of BLG/DTAB and BSA/DTAB solutions become nonmonotonous and resemble those of mixed solutions of proteins with guanidine hydrochloride. This result indicates not only the destruction of the protein tertiary structure in the Surface layer of mixed solution but also a strong perturbation of the secondary structure. The corresponding kinetic dependencies for protein solutions with added anionic surfactants are always monotonous, thereby revealing a different mechanism of the adsorption layer formation. One can assume that the secondary structure is destroye...

Francesca Ravera - One of the best experts on this subject based on the ideXlab platform.

  • dynamic properties of mixed nanoparticle surfactant adsorption layers
    Soft Matter, 2013
    Co-Authors: P A Yazhgur, Giuseppe Loglio, Libero Liggieri, R Miller, B A Noskov, Shiyow Lin, Francesca Ravera
    Abstract:

    The adsorption films of silica nanoparticles modified by a cationic surfactant (cetyltrimethylammonium bromide, CTAB) at the air–water interface were investigated by the dilational Surface Rheology and optical methods. Special attention was paid to the slow changes of Surface properties with the Surface age. The Surface tension and dynamic dilational Surface elasticity were measured as a function of CTAB concentration. The whole surfactant concentration range can be divided into four regions characterized by different Surface rheological behavior. Depending on the CTAB concentration, the Surface elasticity close to the equilibrium may reach extremely high values (∼1000 mN m−1) and strongly depends on the applied Surface strain. This occurs at surfactant concentrations below the region where the dispersion becomes turbid, indicating particle aggregation in the bulk. The Brewster angle microscopy and ellipsometry show that the adsorption layer becomes fragile and inhomogeneous in this region.

  • dppc dopc langmuir monolayers modified by hydrophilic silica nanoparticles phase behaviour structure and Rheology
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2012
    Co-Authors: Eduardo Guzman, Eva Santini, Michele Ferrari, Libero Liggieri, Francesca Ravera
    Abstract:

    Abstract Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and mixtures of DOPC with 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), at a ratio of 37:63 in weight, spread on pure water and on silica nanoparticle dispersions, have been investigated using a combination of thermodynamic, Surface Rheology, BAM and AFM diagnostics. The compression Surface pressure isotherms were determined in a Langmuir trough as well as the Surface pressure response to harmonic area variation of the monolayer. Composite layers were obtained at selected thermodynamic states by transfer from the fluid interface to solid substrates and then analysed by AFM diagnostics. Aim of this study was to evaluate the effect of the incorporation of silica nanoparticles on the phase behaviour and structural properties of these monolayers. In fact, as shown in previous works on similar lipid systems, the hydrophilic silica nanoparticles dispersed in the sub-phase are transferred into the monolayer due to the interaction with lipid molecules which makes them partially hydrophobic. The results here obtained indicate that the appreciable influence of silica nanoparticles, previously observed for DPPC alone, is also important for DOPC and DOPC–DPPC mixture. Moreover, as confirmed by the AFM results on the deposited layers, these effects are mainly due to the disruption of the molecular packing and to the modification of the miscibility between the two lipid components.

  • adsorption layer properties and foam film drainage of aqueous solutions of tetraethyleneglycol monododecyl ether
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011
    Co-Authors: D Arabadzhieva, Francesca Ravera, R Miller, Elena Mileva, Plamen Tchoukov, Libero Liggieri
    Abstract:

    Abstract The aim of the present study is to clarify how the surfactant adsorption layer properties are related to the course of the drainage parameters of microscopic foam films in the special case of aqueous solutions of the non-ionic amphiphile tetraethyleneglycol monododecyl ether (C 12 E 4 ), containing premicellar nanostructures. The scope of the research covers adsorption dynamics, construction of equilibrium adsorption isotherms, studies on Surface Rheology of the interfacial layers and microscopic foam film drainage kinetics. It is established that in the premicellar concentration domain considerable irregularities of the adsorption layer properties are observed: two plateau regions are registered in the experimental Surface tension isotherm along with unusual changes of the Surface rheological characteristics. The systematic investigation of the drainage of microscopic foam films obtained from these solutions show that the dependencies of basic kinetic parameters of the films on the amphiphile concentration run in synchrony with the changes in the adsorption layer properties. This fact is related to the presence of smaller surfactant aggregates (premicelles). They are presumed to be organized as Platonic bodies. The premicelles play also a significant role in the kinetic stability of the films. The importance of this research is in providing better insight into the initial stages of self-assembling phenomena and into the factors determining the adsorption layer properties and the drainage behaviour of thin liquid films.

  • Surface Rheology as a tool for the investigation of processes internal to surfactant adsorption layers
    Faraday Discussions, 2005
    Co-Authors: Libero Liggieri, Michele Ferrari, Daniela Mondelli, Francesca Ravera
    Abstract:

    The description of adsorption at liquid interfaces has been largely improved after incorporation into models of dynamic processes internal to the adsorption layers, such as surfactant re-orientation, aggregation and chemical reactions. Evidence for most of these processes has been given by qualitative studies utilising direct imaging techniques or by tensiometric investigations. These processes strongly influence the dilational rheological features of the adsorption layer, i.e. the response of interfacial tension to perturbations of the interfacial area. The investigation of the dilational Rheology is then very effective to assess the existence of these processes and to characterise their kinetic parameters and equilibrium properties. To this aim specific models and experimental techniques have been recently developed. Here the Surface visco-elasticity of adsorbed surfactant layers, e, at liquid–air and liquid–liquid interfaces is measured by means of different oscillating drop/bubble methods, which are based on the interfacial tension response to harmonic perturbations of the interfacial area and have been implemented in capillary pressure and in drop shape tensiometers. The comparison of this data with theoretical predictions allows at the same time the validation of the models and the quantification of the kinetic features of the internal processes.

  • adsorption and Surface Rheology of n dodecanol at the water air interface
    Journal of Colloid and Interface Science, 2004
    Co-Authors: Michele Ferrari, Francesca Ravera, Libero Liggieri, Hubert Motschmann, J Kragel, R Miller
    Abstract:

    Adsorption layers of n-dodecanol at the water/air interface show phase transitions at low temperatures [Vollhardt, Fainerman, Emrich, J. Phys. Chem. B 104 (2000) 8536]. Using a drop shape technique it is shown that the dilational elasticity disappears in the coexistence region of the adsorption layer. The relaxation time between the condensed and liquid-like Surface states is in the sub-second time range.

Libero Liggieri - One of the best experts on this subject based on the ideXlab platform.

  • dynamic properties of mixed nanoparticle surfactant adsorption layers
    Soft Matter, 2013
    Co-Authors: P A Yazhgur, Giuseppe Loglio, Libero Liggieri, R Miller, B A Noskov, Shiyow Lin, Francesca Ravera
    Abstract:

    The adsorption films of silica nanoparticles modified by a cationic surfactant (cetyltrimethylammonium bromide, CTAB) at the air–water interface were investigated by the dilational Surface Rheology and optical methods. Special attention was paid to the slow changes of Surface properties with the Surface age. The Surface tension and dynamic dilational Surface elasticity were measured as a function of CTAB concentration. The whole surfactant concentration range can be divided into four regions characterized by different Surface rheological behavior. Depending on the CTAB concentration, the Surface elasticity close to the equilibrium may reach extremely high values (∼1000 mN m−1) and strongly depends on the applied Surface strain. This occurs at surfactant concentrations below the region where the dispersion becomes turbid, indicating particle aggregation in the bulk. The Brewster angle microscopy and ellipsometry show that the adsorption layer becomes fragile and inhomogeneous in this region.

  • dppc dopc langmuir monolayers modified by hydrophilic silica nanoparticles phase behaviour structure and Rheology
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2012
    Co-Authors: Eduardo Guzman, Eva Santini, Michele Ferrari, Libero Liggieri, Francesca Ravera
    Abstract:

    Abstract Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and mixtures of DOPC with 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), at a ratio of 37:63 in weight, spread on pure water and on silica nanoparticle dispersions, have been investigated using a combination of thermodynamic, Surface Rheology, BAM and AFM diagnostics. The compression Surface pressure isotherms were determined in a Langmuir trough as well as the Surface pressure response to harmonic area variation of the monolayer. Composite layers were obtained at selected thermodynamic states by transfer from the fluid interface to solid substrates and then analysed by AFM diagnostics. Aim of this study was to evaluate the effect of the incorporation of silica nanoparticles on the phase behaviour and structural properties of these monolayers. In fact, as shown in previous works on similar lipid systems, the hydrophilic silica nanoparticles dispersed in the sub-phase are transferred into the monolayer due to the interaction with lipid molecules which makes them partially hydrophobic. The results here obtained indicate that the appreciable influence of silica nanoparticles, previously observed for DPPC alone, is also important for DOPC and DOPC–DPPC mixture. Moreover, as confirmed by the AFM results on the deposited layers, these effects are mainly due to the disruption of the molecular packing and to the modification of the miscibility between the two lipid components.

  • adsorption layer properties and foam film drainage of aqueous solutions of tetraethyleneglycol monododecyl ether
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011
    Co-Authors: D Arabadzhieva, Francesca Ravera, R Miller, Elena Mileva, Plamen Tchoukov, Libero Liggieri
    Abstract:

    Abstract The aim of the present study is to clarify how the surfactant adsorption layer properties are related to the course of the drainage parameters of microscopic foam films in the special case of aqueous solutions of the non-ionic amphiphile tetraethyleneglycol monododecyl ether (C 12 E 4 ), containing premicellar nanostructures. The scope of the research covers adsorption dynamics, construction of equilibrium adsorption isotherms, studies on Surface Rheology of the interfacial layers and microscopic foam film drainage kinetics. It is established that in the premicellar concentration domain considerable irregularities of the adsorption layer properties are observed: two plateau regions are registered in the experimental Surface tension isotherm along with unusual changes of the Surface rheological characteristics. The systematic investigation of the drainage of microscopic foam films obtained from these solutions show that the dependencies of basic kinetic parameters of the films on the amphiphile concentration run in synchrony with the changes in the adsorption layer properties. This fact is related to the presence of smaller surfactant aggregates (premicelles). They are presumed to be organized as Platonic bodies. The premicelles play also a significant role in the kinetic stability of the films. The importance of this research is in providing better insight into the initial stages of self-assembling phenomena and into the factors determining the adsorption layer properties and the drainage behaviour of thin liquid films.

  • Surface Rheology as a tool for the investigation of processes internal to surfactant adsorption layers
    Faraday Discussions, 2005
    Co-Authors: Libero Liggieri, Michele Ferrari, Daniela Mondelli, Francesca Ravera
    Abstract:

    The description of adsorption at liquid interfaces has been largely improved after incorporation into models of dynamic processes internal to the adsorption layers, such as surfactant re-orientation, aggregation and chemical reactions. Evidence for most of these processes has been given by qualitative studies utilising direct imaging techniques or by tensiometric investigations. These processes strongly influence the dilational rheological features of the adsorption layer, i.e. the response of interfacial tension to perturbations of the interfacial area. The investigation of the dilational Rheology is then very effective to assess the existence of these processes and to characterise their kinetic parameters and equilibrium properties. To this aim specific models and experimental techniques have been recently developed. Here the Surface visco-elasticity of adsorbed surfactant layers, e, at liquid–air and liquid–liquid interfaces is measured by means of different oscillating drop/bubble methods, which are based on the interfacial tension response to harmonic perturbations of the interfacial area and have been implemented in capillary pressure and in drop shape tensiometers. The comparison of this data with theoretical predictions allows at the same time the validation of the models and the quantification of the kinetic features of the internal processes.

  • adsorption and Surface Rheology of n dodecanol at the water air interface
    Journal of Colloid and Interface Science, 2004
    Co-Authors: Michele Ferrari, Francesca Ravera, Libero Liggieri, Hubert Motschmann, J Kragel, R Miller
    Abstract:

    Adsorption layers of n-dodecanol at the water/air interface show phase transitions at low temperatures [Vollhardt, Fainerman, Emrich, J. Phys. Chem. B 104 (2000) 8536]. Using a drop shape technique it is shown that the dilational elasticity disappears in the coexistence region of the adsorption layer. The relaxation time between the condensed and liquid-like Surface states is in the sub-second time range.