Low Molecular Weight Surfactants Research Articles

Aggregation behavior of amphiphilic random copolymer of 2-(acrylamido)-2-methylpropanesulfonic acid and tris(trimethylsiloxy)silylpropylmethacrylate in aqueous solution

Aggregation behavior including dilute solution property and surface-activity of the amphiphilic random copolymer composed of 2-(acrylamido)-2-methylpropanesulfonic acid and tris(trimethylsiloxy)silylpropylmethacrylate (AMPS/TRIS copolymer) in aqueous solution were studied by static light scattering (SLS), dynamic light scattering (DLS), surface tension measurement, and transmission electron microscopy (TEM). The surface tension measurement made it clear that AMPS/TRIS copolymer exhibited weaker surface-activity than a typical low-molecular weight surfactant sodium dodecyl sulfate in water, that is, there were no plateau of surface tension γ versus concentration and no critical micelle concentration (CMC) in the whole concentration studied. SLS and DLS analyses, and TEM revealed that AMPS/TRIS copolymer self-associated into imperfect core-shell micelles having hydrophobic TRIS core surrounded by hydrophilic AMPS shell in water. AMPS shell was considered as a hard shell due to the stiffness of AMPS chain in water. TRIS chain could not densely aggregate in water due to the large steric hindrance between bulky trimethylsiloxy groups despite its hydrophobic nature, thereby providing TRIS core with less-dense structure. The balance between the spreading force of stiff AMPS chain and the cohesion force of bulky TRIS chain provides the driving force for forming the unique micelle having less-dense TRIS core and hard AMPS shell. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Block copolymers as polymeric stabilizers in non‐aqueous emulsion polymerization

AbstractThis review summarizes the background and recent advances of block copolymer stabilized oil‐in‐oil emulsions. For non‐polymerizable emulsions which have promising application possibilities for biomedical and cosmetic formulations, it is shown that tailor‐made block copolymers are by far the most efficient stabilizers with respect to low molecular weight surfactants. The characteristic features of oil‐in‐oil emulsions comprising one polymerizable phase are described. These types of non‐aqueous emulsions are of interest as nanoreactor systems for the polymerization of moisture‐sensitive monomers or catalysts. Furthermore they are the starting point of novel heterophase polymerization processes for the preparation of sterically stabilized polymer particles, as well as of ‘liquid‐filled polymeric materials’. The concept of oil‐in‐oil emulsions is finally extended to those systems where the two phases are polymerizable by distinct polymerization mechanisms. This approach could offer attractive possibilities for the development of special coatings with neither water nor solvent evaporation in their drying or curing step. Copyright © 2011 Society of Chemical Industry

Comparison of a low molecular weight and a macromolecular surfactant as foaming agents for injectable self setting hydroxyapatite foams: Polysorbate 80 versus gelatine

Hydroxyapatite foams are potential synthetic bone grafting materials or scaffolds for bone tissue engineering. A novel method to obtain injectable hydroxyapatite foams consists in foaming the liquid phase of a calcium phosphate cement. In this process, the cement powder is incorporated into a liquid foam, which acts as a template for macroporosity. After setting, the cement hardens maintaining the macroporous structure of the foam. In this study a low molecular weight surfactant, Polysorbate 80, and a protein, gelatine, were compared as foaming agents of a calcium phosphate cement. The foamability of Polysorbate 80 was greater than that of gelatine, resulting in higher macroporosity in the set hydroxyapatite foam and higher macropore interconnectivity. Gelatine produced less interconnected foams, especially at high concentrations, due to a higher liquid foam stability. However it increased the injectability and cohesion of the foamed paste, and enhanced osteoblastic-like cell adhesion, all of them important properties for bone grafting materials.

Surface protein coverage and its implications on spray-drying of model sugar-rich foods: Solubility, powder production and characterisation

We have investigated the amount of protein required to produce amorphous sugar powders through spray-drying. Pea protein isolate was used as a model plant protein and sodium caseinate was used as a model dairy protein. Powder recovery in a laboratory spray dryer was used as a measure of the ease of spray drying for a given formulation. More than 80% of amorphous sucrose and fructose was produced with the addition of sodium caseinate, while the pea protein isolate was able to produce only recoveries of less than 50% of amorphous sucrose. Sensitivity of low molecular weight surfactants has been demonstrated using both ionic (sodium stearoyl lactylate) and non-ionic (polysorbate-80) surfactants. Spray-dried powders were subjected to physico-chemical characterisation and dissolution experiments. The maximum solubility of all powders was obtained after 5min of dissolution. The solubility of the sodium caseinate increased by 6–7% in the presence of fructose and low molecular weight surfactants. The solubility of the amorphous powders of sucrose–pea protein isolate was found to be lower than amorphous powders of sucrose–sodium caseinate and fructose–sodium caseinate. The addition of sucrose in water increased the solubility of the pea protein isolate from 16.84% to more than 83%. The non-ionic surfactant (Tween-80) has reduced the solubility of sucrose–pea protein isolate–Tween-80 powders significantly (p<0.05) compared to those of sucrose–pea protein isolate–sodium stearoyl lactylate powders. The solubility of sucrose–sodium caseinate powders was comparable to that of pure sodium caseinate, indicating that addition of sucrose into 0.13% sodium caseinate does not have any significant effect on the solubility of this protein at this concentration.

Inhibition of lipase-catalyzed hydrolysis of emulsified triglyceride oils by low-molecular weight surfactants under simulated gastrointestinal conditions

The effect of low-molecular weight surfactants on the digestibility of lipids in protein-stabilized corn oil-in-water emulsions was studied using an in vitro digestion model. The impact of non-ionic (Tween 20, Tween 80, Brij35), anionic (SDS), and cationic (DTAB) surfactants on the rate and extent of lipid digestion was studied. All surfactants were found to inhibit lipid digestion at sufficiently high concentrations, with half-maximal inhibitory concentrations (IC50) of 1.2% for Tween 20, 0.7% for Tween 80, 2.8% for Brij35, 1.1% for SDS, and 1.4% for DTAB. The effectiveness of the surfactants at inhibiting lipid digestion was therefore not strongly correlated to the electrical characteristics of the surfactant head group, since the IC50 increased in the following order: Tween 80 > SDS > Tween 20 > DTAB > Brij35. The ability of these low-molecular weight surfactants to inhibit lipid digestion was attributed to a number of potential mechanisms: (i) prevention of lipase/co-lipase adsorption to the oil–water interface; (ii) formation of interfacial complexes; (iii) direct interaction and inactivation of lipase/co-lipase. Interestingly, DTAB increased the rate and extent of lipid digestion when present at relatively low concentrations. This may have been because this cationic surfactant facilitated the adsorption of lipase to the droplet surfaces through electrostatic attraction, or it bound directly to the lipase molecule thereby changing its structure and activity. A number of the surfactants themselves were found to be susceptible to enzyme digestion by pancreatic enzymes in the absence of lipids: Tween 20, Tween 80, Brij35, and DTAB. This work has important implications for the development of emulsion-based delivery systems for food and pharmaceutical applications.

Preparation and characterizations of a novel deoxycholic acid–O-carboxymethylated chitosan–folic acid conjugates and self-aggregates

O-carboxymethylated chitosan (OCMC) was firstly hydrophobically modified with various deoxycholic acid (DOCA) to obtain a novel kind of amphiphilic polymer, and then covalently bound with folic acid (FA) to develop a new potential cancer-targeted drug delivery system. Structural characterizations of the conjugates were investigated using FTIR, 1H NMR and XRD. The physicochemical properties of self-aggregates in aqueous media were studied by 1H NMR, zetasizer, zeta potential, fluorescence spectroscopy, and transmission electron microscopy (TEM). The mean diameter of self-aggregates in PBS solution (pH 7.4) decreased with the degree of substitution (DS) of DOCA increasing. Zeta potential of self-aggregates exhibited near −20 mV in PBS solution (pH 7.4), indicating these nanoparticles were covered with negatively charged OCMC shells. The critical aggregation concentrations (cac) of the conjugates were dependent on the DS of DOCA and were significantly lower than those of low molecular weight surfactants. TEM images demonstrated that the shape of self-aggregates was spherical.

Rheology of interfaces stabilized by a 2D suspension of anisotropic particles: a classical irreversible thermodynamics theory

Surface rheological properties have a significant impact on the stability of particle-stabilized emulsions and foams. Interfaces stabilized by anisotropic particles display a highly nonlinear surface rheology, even at relatively small deformation rates. The nonlinearity of the response is the result of changes in the microstructure of the interface, induced by the applied deformation. The particles are oriented in the direction of the imposed flow field, and this leads to a decrease in the surface shear viscosity (shear thinning). In this paper we derive nonlinear constitutive equations for the surface stress tensor of an interface stabilized by a mixture of anisotropic particles and low molecular weight surfactants, using the classical irreversible thermodynamics formalism. These equations are valid in the low shear regime, where departures from linear behavior are still small. The effect of the microstructure of the interface on the rheological response is incorporated through the particle orientation tensor Qs. The constitutive equations are able to predict the shear thinning behavior observed experimentally for this type of interface.

Vesicular structures in mixed block copolymer/surfactant solutions

Vesicular structures composed of different components are attracting significant attention from the soft matter community both in terms of basic understanding of such complex assemblies of amphiphiles and in view of potential nanotechnological applications. In this article current developments in research concerning mixed vesicular structures assembled through interactions between synthetic block copolymers and low molecular weight surfactants are highlighted. Some future directions and perspectives for further advancement in the field are also discussed.

The effects of proteins and low molecular weight surfactants on spray drying of model sugar-rich foods: Powder production and characterisation

The effects of proteins and low molecular weight surfactants (LMS) on spray drying and powder characteristics of model sugar-rich foods have been studied. Fructose and sucrose were selected as model sugar-rich foods and sodium caseinate (NaCas) was selected as a model protein. Sodium stearoyl lactylate (SSL) and Polysorbate 80 (Tween-80) were chosen as model ionic and non-ionic low molecular weight surfactants. The feed solutions for spray drying had 25% solid concentration in all. To achieve identical powder recoveries of the order of 80% much higher NaCas:fructose ratio (30:70) was required compared to NaCas:sucrose ratio (0.5:99.5) which corresponded to 7.89% and 0.13% of sodium caseinate (initial bulk concentration), respectively. There was no change in powder recovery when the SSL concentration was increased from 0.01% to 0.05% in fructose–NaCas–SSL solution and also addition of 0.01% Tween-80 into fructose–NaCas solution did not affect the powder recovery (76.7 ± 2.3%), however, it was slightly affected with the increase of Tween-80 to 0.05% (69.0 ± 1.9%). At NaCas concentration above critical micelle concentration of NaCas (>3% w/w), the presence of up to 0.05% low molecular weight surfactants had either no effect or minimal effect on the surface coverage of the droplets/particles and also on the powder recovery depending on the nature of the low molecular weight surfactants. The surface protein coverage and the recovery of the powder in sucrose–protein systems were very sensitive in the presence of low molecular weight surfactants due to being below the critical micelle concentration of NaCas. SSL displaced 2.0% and 29.3% of proteins from the droplet surface of sucrose–NaCas–SSL, respectively, when its concentration was varied from 0.01% to 0.05% thereby reducing the powder recovery from 75.5% to 30%. The addition of 0.01% Tween-80 in sucrose–NaCas solution resulted in a 48.2 ± 1.5% reduction in powder recovery and at 0.05% concentration, it displaced a substantial amount of NaCas from the droplet surface and no powder was recovered. These phenomena are explained on the basis of surface-glass transition temperature, dynamic surface tension, nature of surfactants and glass transition temperature of sugars used. X-ray diffraction and scanning electron microscopy results showed that the powders of sucrose–NaCas, sucrose–NaCas with 0.01% SSL and all powders of fructose were amorphous.

The rheology of highly concentrated emulsions stabilized with different surfactants

An investigation was performed into the effect of surfactants on the rheology of water-in-oil highly concentrated emulsions (HCE). The surfactants were oligomers of the PIBSA-type with different headgroups and low-molecular-weight sorbitan monooleate (SMO). The rheological properties of HCE are presented by flow curves with clearly expressed yield stress and dynamic modulus which does not depend on frequency but does on the amplitude of deformations. The changes in modulus and the yield stress depend on the nature of the headgroups as well as the addition of low molecular weight surfactant. It was shown that an increase in the surfactant concentration results in the decrease in the rheological parameters. This shows the significance of micellar structure on the rheological behaviour of HCE. The dependencies of elastic modulus as well as the yield stress on droplet size are deviated from scaling by Laplace pressure. This means that some additional arguments to explain the elasticity of “compressed” HCE emulsions should be included for comparison with the classical models based on the conception of increase in the surface area of droplets. Finally, it was found that the scaling of shear modulus with reciprocal squared droplet size fulfil the zero intercept condition for this variation.

Shear-Induced Instabilities in Oil-in-Water Emulsions Comprising Partially Crystallized Droplets

We produced triglyceride-in-water emulsions comprising semicrystallized droplets, stabilized by a mixture of protein and low molecular weight surfactant. In these systems, partial (unrelaxed) coalescence could be produced by a thermal treatment referred to as tempering or by the application of a shear. Both primary emulsions and thermally induced gels were submitted to shear strains of variable amplitude, and the resulting transitions were identified. Partial or total destruction of the materials took place and was revealed by the formation of macroscopic clumps. We examined the impact of the initial average droplet size and of the interface composition (controlled by the bulk surfactant-to-protein molar ratio) on the sensitivity to partial coalescence. The evolution under shear occurred via two limiting mechanisms, depending on the susceptibility to partial coalescence. Materials that exhibited fast partial coalescence underwent gelling followed by phase inversion and partial expulsion of the aqueous phase. Alternatively, when the rate of partial coalescence was quite low, large clumps were randomly distributed over the volume and coexisted with a fluid emulsion. The same phenomenology was observed under both oscillatory and steady shear conditions. Interestingly, in oscillatory conditions, clumping was observed above a very well-defined and reproducible value of the strain amplitude independent of the initial state of the system (emulsion or gel).

O/W emulsions stabilised by both low molecular weight surfactants and colloidal particles: The effect of surfactant type and concentration

The stability against coalescence of O/W emulsions in the presence of both surfactants and colloidal particles was investigated. In particular the effect of the surfactant type and concentration in these emulsifier mixtures on the O/W emulsions' stability was studied. Two types of surfactants were selected; those that have the ability to stabilise O/W emulsions on their own (O/W surfactants) and those that cannot (W/O surfactants). Tween 60 and Sodium Caseinate were selected as the O/W surfactants and lecithin as the W/O surfactant. Oil-in-water emulsions prepared with both particles and any of the three surfactants were stable against coalescence but, depending on the type of surfactant, the behaviour of the systems was found to depend on surfactant concentration. The droplet sizes of emulsions stabilised by mixed emulsifier systems containing low concentrations of O/W surfactants (Tween 60 or Sodium Caseinate) were smaller than those solely stabilised by either the surfactant or particles alone. At intermediate O/W surfactants concentrations, the droplet sizes of the emulsions increased. Further increases in the O/W surfactants' concentration, resulted in the complete removal of particles from the interface with the system now behaving as a surfactant-only stabilised emulsion. The behaviour of emulsions stabilised by emulsifier mixtures containing W/O surfactants was not dependent on the concentration of surfactant: no removal of particles was observed.

The effect of protein types and low molecular weight surfactants on spray drying of sugar-rich foods

The effect of protein types and low molecular weight surfactants (LMS) on spray drying of sugar-rich foods has been studied using sucrose as a model sugar and sodium caseinate (NaCas) and pea protein isolate (PPI) as model proteins. Sodium stearoyl lactylate (SSL) and Polysorbate 80 (Tween-80) were chosen as model ionic and non-ionic LMS. The sucrose:NaCas and sucrose:PPI solid ratios were maintained at (99.5:0.5) and (99:1), respectively and spray-dried maintaining 25% solids in feed solutions. It was found that the proteins preferentially migrated to the air–water interface reasonably swiftly and the addition of LMS resulted into partial or complete displacement of the proteins from the air–water interface. More than 80% of amorphous sucrose powder was produced with the addition of 0.13% (w/w) of NaCas in feed solution. PPI was not as effective and produced less than 50% recovery even at 0.26% (w/w) in feed. Addition of 0.01–0.05% SSL displaced 2.0% and 29.3% of proteins from the surface of sucrose–NaCas–SSL droplet, respectively, resulting in a 6.5 ± 1.2% to 51.9 ± 1.9% reduction in powder recovery. The extent of protein displacement was higher when SSL was added into sucrose–PPI solution; however, the powder recovery was not much affected. The addition of 0.01% Tween-80 in sucrose–NaCas solution resulted in a 48.2 ± 1.5% reduction in powder recovery and at 0.05% concentration, it displaced a substantial amount or all the NaCas from the droplet surface and no powder was recovered. The addition of 0.01% and 0.05% Tween-80 into sucrose–PPI solution resulted into very low powder recoveries (24.9 ± 0.4% and 29.5 ± 1.8%, respectively). The glass transition temperature (T g) results revealed that the amount of protein required for successful spray drying of sucrose–protein solutions depends on the amount of proteins present on the droplet surface but not on the bulk concentration. X-ray diffraction and scanning electron microscopy results showed that the powders of sucrose–NaCas/PPI and sucrose–NaCas/PPI with 0.01% SSL were mostly amorphous while those with sucrose–NaCas/PPI–Tween-80 (0.01%), sucrose–PPI–Tween-80 (0.05%) and sucrose–NaCas/PPI–SSL (0.05%) were crystalline.

Use of ethylcellulose polymers as stabilizer in fat-based food suspensions examined on the example of model reduced-fat chocolate

Surfactants are an important ingredient in the manufacture of chocolate. Their role is to coat the surfaces of the sugar and cocoa particles dispersed in fat, generally cocoa butter, to maintain or enhance the flowability of molten chocolate. Coating the surfaces of the dispersed particles with a surfactant reduces inter-particle interactions responsible for particle aggregation which leads to viscosity reduction of the mixture. Controlled flow behavior of molten chocolate is a requirement for successful processing and for optimal mouthfeel. This becomes in particular crucial in the formulation of fat-reduced chocolate. In fat-reduced chocolate, low molecular weight surfactants such as lecithin and polyglycerol polyricinoleate (PGPR) need to be applied at unacceptably high concentrations to maintain flowability of a chocolate with increased dispersed phase volume. This paper reports on an alternative approach, the use of the polymeric surfactant ethylcellulose. Shear viscosity measurements on model chocolates demonstrated a viscosity reducing effect. The effect of ethylcellulose polymer adsorbed at an oil/water interface was visualized in volume change experiments on macroscopic pendant drops revealing a difference in the nature of the interface compared to an interface covered with a low molecular weight surfactant.

The Effect of Food-Grade Low-Molecular-Weight Surfactants and Sodium Caseinate on Spray Drying of Sugar-Rich Foods

The effect of low-molecular-weight surfactants (LMS) and sodium caseinate (NaCas) on spray drying of sugar-rich foods has been studied. Sucrose and NaCas were selected as a model sugar-rich food and protein, respectively. Sodium stearoyl lactylate (SSL) and Polysorbate 80 (Tween 80) were chosen as model ionic and nonionic LMS. Sucrose–NaCas solutions with the solids ratio of 99.5:0.5 in the absence and presence (0.01% and 0.05%) of SSL and Tween 80 were prepared. The feed solutions had 25% solid concentration in all cases. The dynamic surface tension (DST) values of the solutions were measured for 100 s and the solutions were subsequently spray dried at inlet and outlet temperatures of 165 and 65 °C, respectively. The glass–rubber temperature (T g-r), the surface elemental composition and amorphous–crystalline nature of the powders were also determined. At these concentrations and experimental time frame, it was found that the proteins preferentially migrated to the air–water interface reasonably swiftly. The addition of LMS resulted in partial or complete displacement of the proteins from the air–water interface. For spray-drying trials with the yield of 82.0%, it was found that 52.0% of the powder particle surface was covered with proteins. The powder recovery was greatly reduced by the LMS concentration and type. At 0.05% on dry solid basis, in the case of nonionic surfactant (Tween 80), the displacement of protein from the surface was such that no powder was recovered. The ionic surfactant (SSL) displaced 2.0% and 29.3% proteins from the droplet surface at concentrations of 0.01% and 0.05%, respectively, resulting in 75.5 ± 1.8% and 30.1 ± 1.4% powder yield. The T g-r results revealed that the amount of protein required for successful spray drying of the sucrose–protein solution depends on the amount of proteins present in the droplet surface but not in the bulk. X-ray diffraction and scanning electron microscopy results confirmed that the powders of both sucrose–NaCas and sucrose–NaCas with 0.01% SSL were mostly amorphous, while those with sucrose–NaCas–Tween 80 (0.01%) and sucrose–NaCas–SSL (0.05%) were crystalline.

Encapsulation of submicron-sized silica particles by stimuli-responsive copolymer shell layer

This study examined the encapsulation of submicron-sized silica particles by stimuli-responsive copolymer shell layer. Silica/poly(2-dimethylaminoethyl methacrylate-N-isopropylacrylamide-ethyleneglycol dimethacrylate), abbreviated as silica/P(DM-NIPAM-EGDM) core-shell composite polymer particles, were prepared by the seeded copolymerization of DM, NIPAM and EGDM in the presence of silica particles. The morphology and size distribution were analyzed by scanning electron microscopy. The surface composition showed silica particles covered with a copolymer shell layer consisting of P(DM-NIPAM-EGDM). The temperature and pH dependent adsorption behavior of the low molecular weight surfactants and biomolecules on the silica/P(DM-NIPAM-EGDM) composite polymer particles indicated a stimuli-responsive phase transition. The activity of the adsorbed trypsin (TR) on the composite particles remained high compared to the free TR and adsorbed TR on silica particles.

Preparation and characterization of amphiphilic poly-N-vinylpyrrolidone nanoparticles containing indomethacin

Amphiphilic poly-N-vinylpyrrolidone derivatives (Amph-PVP) with different molecular weight of hydrophilic PVP fragment and one terminal hydrophobic n-alkyl fragment of different length were synthesized for preparation of nano-scaled particles in aqueous media. To estimate novel polymer efficiency and perspective as basis for drug delivery systems, the polymeric micelle-like particles were prepared by dialysis and solvent evaporation methods. Indomethacin was incorporated into hydrophobic inner core of these nanoparticles as a typical model drug. From the dynamic light-scattering measurements, the size of particles formed was less than 200 nm with narrow monodisperse size distribution and nanoparticles size slightly increased with the amount of indomethacin encapsulated into inner core of Amph-PVP particles. The critical aggregation concentration values for prepared polymer samples determined by fluorescence spectroscopy were in micromole range which is lower than it is for common low molecular weight surfactants. As the hydrophobic fragment of amphiphilic polymer increased, the critical aggregation concentration values decreased. An increase of polymer hydrophilic fragment molecular weight produced larger nanoaggregates. In vitro release experiments using indomethacin-loaded Amph-PVP nanoparticles exhibited the sustained release behavior without any burst effect for most polymer samples.

Preparation of Hairy Particles and Antifouling Films Using Brush-Type Amphiphilic Block Copolymer Surfactants in Emulsion Polymerization

Two series of well-defined brush-type amphiphilic block copolymers of polystyrene-b-poly[poly(ethylene glycol) methyl ether methacrylate] (PS-b-P(PEGMA300) and PS-b-P(PEGMA1100)) were synthesized via atom transfer radical polymerization (ATRP) and used as surfactants in emulsion polymerization. The self-assembly behavior of these block copolymers in aqueous solution was studied by dynamic light scattering and cryogenic transmission electron microscopy. The critical micelle concentration of the synthesized polymers was found to depend on the length of the PEG side chains, but neither on the molar mass of the P(PEGMA) blocks nor the temperature. All of the block copolymers form micelles in the nanometer range. Emulsion polymerizations of styrene were carried out using the obtained brush-type amphiphilic block copolymers, and the influence of the block copolymer structure, surfactant concentration, and temperature was studied. The PS-b-P(PEGMA1100) copolymers seem to be the most efficient surfactants at low polymerization temperature, providing good colloidal stability. Monodisperse hairy particles with core−shell structures (observed by cryo-TEM) were obtained using the block copolymers with the long PEG side chain and the highest molar mass. Polystyrene films prepared from the latexes, containing the brush-type copolymers, display a lower contact angle than that obtained in films with conventional low molecular weight surfactants. In addition, the incorporation of PEGMA brushes on the polystyrene particles, and hence on the films, decreases the adsorption of proteins and, in this particular case, of bovine serum albumin.

Non-equilibrium dynamics of block copolymer micelles in solution: recent insights and open questions

The increasing variety and complexity of block copolymers leads to a large morphological diversity of self-assembled structures. This, in turn, opens the way for numerous new applications in fields spanning from drug delivery and templated synthesis of nanoporous materials to oil extraction. However, unlike low-molecular weight surfactants, the dynamics of block copolymer systems can be very slow, which has important consequences for carrying out reliable experiments and for their use in practical applications. This paper highlights the mechanism of non-equilibrium block copolymer dynamics, and discusses micellization and transition kinetics between spherical and rod-like micelles by examining the present knowledge and posing some open questions.

Modelling surface rheology of complex interfaces with extended irreversible thermodynamics

The rheological properties of the interfaces in complex multiphase systems often play a crucial role in the dynamic behavior of these systems. For example, these properties affect the dynamics of emulsions, of dispersions of vesicles, of biological fluids, or of free surface flows. In the past three to four decades a vast amount of literature has been produced dealing with the rheological properties of interfaces stabilized by low molecular weight surfactants, proteins, (bio)polymers, lipids, colloidal particles, and various mixtures of these surface active components. The data of these surface rheological experiments are often analyzed with ad hoc generalizations of rheological models used for the analysis of rheological properties of bulk phases. The validity of these generalizations is in general not discussed. Here we show how the extended irreversible thermodynamics (EIT) formalism can be used to generate a wide range of thermodynamically admissible constitutive models for the surface stress tensor, which not only encompass currently used constitutive models, but also suggest several new ones, particularly useful for modelling the nonlinear response of interfaces.