Sunflower Proteins at Air-Water and Oil-Water Interfaces

The adsorption of a sunflower protein extract at two air-water and oil-water interfaces is investigated using tensiometry, dilational viscoelasticity, and ellipsometry. For both interfaces, a three step mechanism was evidenced thanks to master curve representations of the data taken at different aging times and protein concentrations. At short times, a diffusion limited adsorption of proteins at interfaces is demonstrated. First, a two-dimensional protein film is formed with a partition of the polypeptide chains in the two phases that depends strongly on the nature of the hydrophobic phase: most of the film is in the aqueous phase at the air-water interface, while it is mostly in the organic phase at the oil-water interface. Then a three-dimensional saturated monolayer of proteins is formed. At short times, adsorption mechanisms are analogous to those found with typical globular proteins, while strong divergences are observed at longer adsorption times. Following the saturation step, a thick layer expands in the aqueous phase and appears associated with the release of large objects in the bulk. The kinetic evolution of this second layer is compatible with a diffusion limited adsorption of the minor population of polymeric complexes with hydrodynamic radius R_H ∼ 80 nm, evidenced in equilibrium with hexameric globulins (R_H ∼ 6 nm) in solution. These complexes could result from the presence of residual polyphenols in the extract and raise the question of the role of these compounds in the interfacial properties of plant protein extracts.

pH-mediated control over the mesostructure of ordered mesoporous materials templated by polyion complex micelles

Ordered mesoporous silica materials were prepared under different pH conditions by using a silicon alkoxide as a silica source and polyion complex (PIC) micelles as the structure-directing agents. PIC micelles were formed by complexation between a weak polyacid-containing double-hydrophilic block copolymer, poly(ethylene oxide)-b-poly(acrylic acid) (PEO-b-PAA), and a weak polybase, oligochitosan-type polyamine. As both the micellization process and the rate of silica condensation are highly dependent on pH, the properties of silica mesostructures can be modulated by changing the pH of the reaction medium. Varying the materials synthesis pH from 4.5 to 7.9 led to 2D-hexagonal, wormlike or lamellar mesostructures, with a varying degree of order. The chemical composition of the as-synthesized hybrid organic/inorganic materials was also found to vary with pH. The structure variations were discussed based on the extent of electrostatic complexing bonds between acrylate and amino functions and on the silica condensation rate as a function of pH.

Complexation of short ds RNA/DNA oligonucleotides with Gemini micelles: a time resolved SAXS and computational study

Gene therapy is based on nucleic acid delivery to pathogenic cells in order to modulate their gene expression. The most used non viral vectors are lipid-based nanoaggregates, which are safer than viral carriers and have been shown to assemble easily with both DNA and RNA. However, the transfection efficiency of non viral carriers still needs to be improved before intensive practise in clinical trials can be implemented. For this purpose, the in depth characterization of the complexes formed by nucleic acids and their transporters is of great relevance. In particular, information on the structure and assembly mechanism can be useful to improve our general knowledge of these artificial transfection agents. In this paper, the complexation mechanism of short interfering RNA and DNA molecules (siRNA and siDNA, respectively) with cationic micelles is investigated by combining small angle X-ray scattering experiments and molecular dynamics simulations. Micelles were obtained by Gemini surfactants with different spacer lengths (12-3-12, 12-6-12). The siRNA and siDNA used were double strand molecules characterized by the same length and homologous sequence, in order to perform a close comparison. We showed that complexes appear in solution immediately after mixing and, therefore, the investigation of complex formation requires fast experimental techniques, such as time resolved synchrotron SAXS (Tr-SAXS). The obtained systems had internal arrangement constituted by layers of squeezed micelles alternating the nucleic acids. Both SAXS and MD analyses allowed us to evaluate the mean size of complexes in the range of a few nanometers, with looser and less ordered stacking for the DNA containing aggregates.

Nano-porous structuresviaself-assembly of amphiphilic triblock copolymers: influence of solvent and molecular weight

Self-assembly of ABA triblock copolymer micelles into porous materials which are subsequently used as filtration membranes.

Janus Colloids Actively Rotating on the Surface of Water

Biological or artificial microswimmers move performing trajectories of different kinds such as rectilinear, circular, or spiral ones. Here, we report on circular trajectories observed for active Janus colloids trapped at the air-water interface. Circular motion is due to asymmetric and nonuniform surface properties of the particles caused by fabrication. Motion persistence is enhanced by the partial wetted state of the Janus particles actively moving in two dimensions at the air-water interface. The slowing down of in-plane and out-of-plane rotational diffusions is described and discussed.

Phase transfer of TiO2 nanoparticles from water to ionic liquid triggered by phosphonic acid grafting

Controlling the interface between TiO₂ nanocrystals and ionic liquids is of high fundamental and applied interest for energy storage and conversion devices. Phase transfer of nanoparticles from a synthesis medium to a processing or an application medium plays a significant role in nanotechnology. Here we demonstrate that surface modification with phosphonic acids bearing cationic end-groups can trigger the phase transfer of TiO₂ nanoparticles from an aqueous sol to a typical water-immiscible ionic liquid, [Emim][NTf₂]. The transfer involves both the grafting of the phosphonic acid moiety and the exchange of the counter ion of the cationic end-group by NTf₂ anions, as demonstrated by solid-state NMR, elemental analysis and independent grafting and ion exchange experiments. Furthermore, the colloidal stability of the TiO₂ sols in [Emim][NTf₂] strongly depends on the hydrophobic character of the cationic end-groups.

Self-assembly of PS-PNaSS-PS triblock copolymers from solution to the solid state

Morphological development of block copolymer assemblies from solution to the solid state is explored to yield nanostructured materials.

MHz Ultrasound Induced Roughness of Fluid Interfaces

The interface between two fluids is never flat at the nanoscale, and this is important for transport across interfaces. In the absence of any external field, the surface roughness is due to thermally excited capillary waves possessing subnanometric amplitudes in the case of simple liquids. Here, we investigate the effect of ultrasound on the surface roughness of liquid-gas and liquid-liquid interfaces. Megahertz (MHz) frequency ultrasound was applied normal to the interface at relatively low ultrasonic pressures (<0.6 MPa), and the amplitudes of surface fluctuations have been measured by light reflectivity and ellipsometry. We found a dramatic enhancement of surface roughness, roughly linear with intensity, with vertical displacements of the interface as high as 50-100 nm. As a consequence, the effective contact area between two fluids can be increased by ultrasound. This result has a clear impact for enhancing interface based processes such as mass or heat transfer.

Translational viscous drags of an ellipsoid straddling an interface between two fluids

We study the dynamics of individual polystyrene ellipsoids of different aspect ratios trapped at the air-water interface. Using particle tracking and in situ vertical scanning interferometry techniques we are able to measure translational drags and the protrusion in air of the ellipsoids. We report that translational drags on the ellipsoid are unexpectedly enhanced: despite the fact that a noticeable part of the ellipsoid is in air, drags are found larger than the bulk one in water.

Multiwalled Carbon Nanotube/Cellulose Composite: From Aqueous Dispersions to Pickering Emulsions

A mild and simple way to prepare stable aqueous colloidal suspensions of composite particles made of a cellulosic material (Sigmacell cellulose) and multiwalled carbon nanotubes (MWCNTs) is reported. These suspensions can be dried and redispersed in water at pH 10.5. Starting with rather crude initial materials, commercial Sigmacell cellulose and MWCNTs, a significant fraction of composite dispersed in water could be obtained. The solid composites and their colloidal suspensions were characterized by electronic microscopy, thermal analyses, FTIR and Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and light scattering. The composite particles consist of tenuous aggregates of CNTs and cellulose, several hundred nanometers large, and are composed of 55 wt % cellulose and 45 wt % CNTs. Such particles were shown to stabilize cyclohexane-in-water emulsions. The adsorption and the elasticity of the layer they form at interface were characterized by the pendant drop method. The stability of the oil-in-water emulsions was attributed to the formation of an elastic network of composite particles at interface. Cyclohexane droplet diameters could be tuned from 20 to 100 μm by adjusting the concentration of composite particles. This behavior was attributed to the limited coalescence phenomenon, just as expected for Pickering emulsions. Interestingly, cyclohexane droplets were stable over time and sustained pH modifications over a wide range, although acidic pH induced accelerated creaming. This study points out the possibility of combining crude cellulose and MWCNTs through a simple process to obtain colloidal systems of interest for the design of functional conductive materials.

Micellization Behavior of Long-Chain Substituted Alkylguanidinium Surfactants

Surface activity and micelle formation of alkylguanidinium chlorides containing 10, 12, 14 and 16 carbon atoms in the hydrophobic tail were studied by combining conductivity and surface tension measurements with isothermal titration calorimetry. The purity of the resulting surfactants, their temperatures of Cr→LC and LC→I transitions, as well as their propensity of forming birefringent phases, were assessed based on the results of ¹H and (13)C NMR, differential scanning calorimetry (DSC), and polarizing microscopy studies. Whenever possible, the resulting values of Krafft temperature (TK), critical micelle concentration (CMC), minimum surface tension above the CMC, chloride counter-ion binding to the micelle, and the standard enthalpy of micelle formation per mole of surfactant (ΔmicH°) were compared to those characterizing alkyltrimethylammonium chlorides or bromides with the same tail lengths. The value of TK ranged between 292 and 314 K and increased strongly with the increase in the chain length of the hydrophobic tail. Micellization was described as both entropy and enthalpy-driven. Based on the direct calorimetry measurements, the general trends in the CMC with the temperature, hydrophobic tail length, and NaCl addition were found to be similar to those of other types of cationic surfactants. The particularly exothermic character of micellization was ascribed to the hydrogen-binding capacity of the guanidinium head-group.

Wetting and orientation of catalytic Janus colloids at the surface of water

Janus colloidal particles show remarkable properties in terms of surface activity, self-assembly and wetting. Moreover they can perform autonomous motion if they can chemically react with the liquid in which they are immersed. In order to understand the self-propelled motion of catalytic Janus colloids at the air–water interface, wetting and the orientation of the catalytic surface are important properties to be investigated. Wetting plays a central role in active motion since it determines the contact between the fuel and the catalytic surface as well as the efficiency of the transduction of the chemical reaction into motion. Active motion is not expected to occur either when the catalytic face is completely out of the aqueous phase or when the Janus boundaries are parallel to the interfacial plane. The design of a Janus colloid possessing two hydrophilic faces is required to allow the catalytic face to react with the fuel (e.g. H₂O₂ for platinum) in water and to permit some rotational freedom of the Janus colloid in order to generate propulsion parallel to the interfacial plane. Here, we discuss some theoretical aspects that should be accounted for when studying Janus colloids at the surface of water. The free energy of ideal Janus colloidal particles at the interface is modeled as a function of the immersion depth and the particle orientation. Analytical expressions of the energy profiles are established. Energetic aspects are then discussed in relation to the particle’s ability to rotate at the interface. By introducing contact angle hysteresis we describe how the effects of contact line pinning modifies the scenario described in the ideal case. Experimental observations of the contact angle hysteresis of Janus colloids at the interface reveal the effect of pinning; and orientations of silica particles half covered with a platinum layer at the interface do not comply with the ideal scenarios. Experimental observations suggest that Janus colloids at the fluid interface behave as a kinetically driven system, where the contact line motion over the defects decorating the Janus faces rules the orientation and rotational diffusion of the particle.

Nanocomposites with both structural and porous hierarchy synthesized from Pickering emulsions

Templating polycondensation of furfural and phloroglucinol by O/W emulsions stabilized by CNT-carboxymethylcellulose composite particles allowed preparing conductive and magnetic microcapsules.

Method to disperse lipids as aggregates in oil for bilayers production

Several techniques to assemble artificial lipid bilayers involve the zipping of monolayers. Their efficiency is determined by the renewal of the saturated monolayers to be zipped and this proceeds by adsorption of lipids dispersed in oil as aggregates. The size of these lipids aggregates is a key parameter to ensure both the stability of the suspension and a fast release of lipids at the interface. We propose a new method inspired from the solvent-shifting nucleation process allowing to control and tune the lipid aggregates size and that improves the production of artificial membranes. It is simpler and faster than current methods starting from a dry lipid film, which are highly sensitive to environmental conditions. This method opens the route to bilayer production processes with new potentialities in membrane composition.

Drug-Polymer Electrostatic Complexes as New Structuring Agents for the Formation of Drug-Loaded Ordered Mesoporous Silica

Using aminoglycoside antibiotics as drug models, it was shown that electrostatic complexes between hydrophilic drugs and oppositely charged double-hydrophilic block copolymers can form ordered mesophases. This phase behavior was evidenced by using poly(acrylic acid)-block-poly(ethylene oxide) block copolymers in the presence of silica precursors, and this allowed preparing drug-loaded mesoporous silica directly from the drug-polymer complexes. The novel synthetic strategy of the hybrid materials is highly efficient, avoiding waste and multistep processes; it also ensures optimal drug loading and provides pH-dependence of the drug release from the materials.

Enhanced active motion of Janus colloids at the water surface

We have investigated the active motion of self-propelled colloids confined at the air-water interface and explored the possibility of enhancing the directional motion of self-propelled Janus colloids by slowing down their rotational diffusion. The two dimensional motion of micron-sized silica-platinum Janus colloids has been experimentally measured by particle tracking video-microscopy at increasing concentrations of the catalytic fuel, i.e. H2O2. Compared to the motion in the bulk, a dramatic enhancement of both the persistence length of trajectories and the speed has been observed. The interplay of colloid self-propulsion, due to an asymmetric catalytic reaction occurring on the colloid, surface properties and interfacial frictions controls the enhancement of the directional movement. The slowing down of the rotational diffusion at the interface, also measured experimentally, plays a pivotal role in the control and enhancement of active motion.

Brownian diffusion of a partially wetted colloid

The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories suggests that such dynamics is governed by a viscous force lower than that observed in the more viscous fluid. Here, we show experimentally that a particle straddling an air/water interface feels a large viscous drag that is unexpectedly larger than that measured in the bulk. We suggest that such a result arises from thermally activated fluctuations of the interface at the solid/air/liquid triple line and their coupling to the particle drag through the fluctuation-dissipation theorem. Our findings should inform approaches for improved control of the kinetically driven assembly of anisotropic particles with a large triple-line-length/particle-size ratio, and help to understand the formation and structure of such arrested materials.

Electrostatic interaction between nonuniformly charged colloids: experimental and numerical study

The influence of the surface charge distribution on the interaction between nanosized particles in water is reported. The distribution of charges at the surface of initially neutral microemulsion droplets has been modulated by additions of various oligomeric cationic surfactants. The osmotic compressibility of the doped microemulsions was measured by light and small-angle neutrons scattering and reveals that the overall effective interaction induced by the ionic groups is repulsive. However, particular charge distributions decrease the osmotic compressibility much less than others. Independent measurements of the activity of the bromide counterions with specific electrodes evidence a significant decrease in the effective charge, which, however, cannot account for the osmotic compressibility in the framework of the primitive model. The q dependence of the structure factor reveals an attractive contribution over a short distance. Numerical studies assign this attractive contribution to the overlap of hydration shells that are extended as a result of the charge localization.

In situ assessment of the contact angles of nanoparticles adsorbed at fluid interfaces by multiple angle of incidence ellipsometry

Here multiple angle of incidence ellipsometry was successfully applied to in situ assess the contact angle and surface coverage of gold nanoparticles as small as 18 nm, coated with stimuli-responsive polymers, at water-oil and water-air interfaces in the presence of NaCl and NaOH, respectively. The interfacial adsorption of the nanoparticles was found to be very slow and took days to reach a fairly low surface coverage. For water-oil interfaces, in situ nanoparticle contact angles agree with the macroscopic equilibrium contact angles of planar gold surfaces with the same polymer coatings, whilst for water-air interfaces, significant differences have been observed.

Time resolved SAXS to study the complexation of siRNA with cationic micelles of divalent surfactants

The complexation of siRNA (small interfering RNA) with cationic micelles was studied using time dependent synchrotron SAXS. Micelles were formed by two types of divalent cationic surfactants, i.e. Gemini bis(quaternary ammonium) bromide with variable spacer length (12-3-12, 12-6-12, 12-12-12) and a weak electrolyte surfactant (SH14) with triazine head. Immediately after mixing (t < 50 ms), new large aggregates appeared in solution and the scattering intensity at low q increased. Concomitantly, the presence of a quasi-Bragg peak at q ∼ 1.5 nm(-1) indicated core structuring within the complexes. We hypothesize that siRNA and micelles are alternately arranged into "sandwiches", forming domains with internal structural coherence. The process of complex reorganization followed a first-order kinetics and was completed in less than about 5 minutes, after which a steady state was reached. Aggregates containing Geminis were compact globular structures whose gyration radii Rg depended on the spacer length and were in the order of 7-27 nm. Complexes containing SH14 (Rg = 14-16 nm) were less ordered and possessed a looser internal arrangement. The obtained data, joint with previous structural investigation using Dynamic Light Scattering, Zeta Potential and Small Angle Neutron Scattering, are encouraging evidence for using these systems in biological trials. In fact we showed that transfection agents can be obtained by simply mixing a micelle solution of the cationic surfactant and a siRNA solution, both of which are easily prepared and stable.

Surfactant behavior of ionic liquids involving a drug: from molecular interactions to self-assembly

Aggregates formed in an aqueous medium by three ionic liquids CnMImIbu made up of 1-alkyl-3-methyl-imidazolium cation (n = 4, 6, 8) and ibuprofenate anion are investigated. Dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), (1)H nuclear magnetic resonance measurements, and atom-scale molecular dynamics simulations are used to shed light on the main interactions governing the formation of the aggregates and their composition. At high concentration, mixed micelles are formed with a composition that depends on the imidazolium alkyl chain length. For the shortest alkyl chain, micelles are mainly composed of ibuprofenate anions with some imidazolium cations intercalated between the anions. Upon increasing the alkyl chain length, the composition of the aggregates gets enriched in imidazolium cations and aggregates of stoichiometric composition are obtained. Attractive interactions between these aggregates led to the formation of larger aggregates. As suggested by molecular simulations, these larger aggregates might constitute the early stage of phase separation. Transitions from micelles to vesicles or ribbons are observed due to dilution effects and changes in the chemical composition of the aggregates. We also show that aggregation can be probed using simple microscopic quantities such as radial distribution functions and average solvation numbers.

Capillary force on a micrometric sphere trapped at a fluid interface exhibiting arbitrary curvature gradients

We report theoretical predictions and measurements of the capillary force acting on a spherical colloid smaller than the capillary length that is placed on a curved fluid interface of arbitrary shape. By coupling direct imaging and interferometry, we are able to measure the in situ colloid contact angle and to correlate its position with respect to the interface curvature. Extremely tiny capillary forces down to femtonewtons can be measured with this method. Measurements agree well with a theory relating the capillary force to the gradient of Gaussian curvature and to the mean curvature of the interface prior to colloidal deposition. Numerical calculations corroborate these results.

Effect of charge inhomogeneity and mobility on colloid aggregation

The aggregation of inhomogeneously charged colloids with the same average charge is analyzed using Monte Carlo simulations. We find aggregation of colloids for sizes in the range 10-200 nm, which is similar to the range in which aggregation is observed in several experiments. The attraction arises from the strongly correlated electrostatic interactions associated with the increase in the counterion density in the region between the particles; this effect is enhanced by the discreteness and mobility of the surface charges. Larger colloids attract more strongly when their surface charges are discrete. We study the aggregation as functions of the surface charge density, counterion valence, and volume fraction.

Hybrid polyion complex micelles formed from double hydrophilic block copolymers and multivalent metal ions: size control and nanostructure

Hybrid polyion complex (HPIC) micelles are nanoaggregates obtained by complexation of multivalent metal ions by double hydrophilic block copolymers (DHBC). Solutions of DHBC such as the poly(acrylic acid)-block-poly(acrylamide) (PAA-b-PAM) or poly(acrylic acid)-block-poly(2-hydroxyethylacrylate) (PAA-b-PHEA), constituted of an ionizable complexing block and a neutral stabilizing block, were mixed with solutions of metal ions, which are either monoatomic ions or metal polycations, such as Al(3+), La(3+), or Al(13)(7+). The physicochemical properties of the HPIC micelles were investigated by small angle neutron scattering (SANS) and dynamic light scattering (DLS) as a function of the polymer block lengths and the nature of the cation. Mixtures of metal cations and asymmetric block copolymers with a complexing block smaller than the stabilizing block lead to the formation of stable colloidal HPIC micelles. The hydrodynamic radius of the HPIC micelles varies with the polymer molecular weight as M(0.6). In addition, the variation of R(h) of the HPIC micelle is stronger when the complexing block length is increased than when the neutral block length is increased. R(h) is highly sensitive to the polymer asymmetry degree (block weight ratio), and this is even more true when the polymer asymmetry degree goes down to values close to 3. SANS experiments reveal that HPIC micelles exhibit a well-defined core-corona nanostructure; the core is formed by the insoluble dense poly(acrylate)/metal cation complex, and the diffuse corona is constituted of swollen neutral polymer chains. The scattering curves were modeled by an analytical function of the form factor; the fitting parameters of the Pedersen's model provide information on the core size, the corona thickness, and the aggregation number of the micelles. For a given metal ion, the micelle core radius increases as the PAA block length. The radius of gyration of the micelle is very close to the value of the core radius, while it varies very weakly with the neutral block length. Nevertheless, the radius of gyration of the micelle is highly dependent on the asymmetry degree of the polymer: if the neutral block length increases in a large extent, the micelle radius of gyration decreases due to a decrease of the micelle aggregation number. The variation of the R(g)/R(h) ratio as a function of the polymer block lengths confirms the nanostructure associating a dense spherical core and a diffuse corona. Finally, the high stability of HPIC micelles with increasing concentration is the result of the nature of the coordination complex bonds in the micelle core.

Tailoring of Transition Metal Alkoxides Via complexation For The Synthesis of Hybrid Organic-Inorganic Sols and Gels

The chemical control of hydrolysis-condensation reactions of transition metal alkoxides can be performed through the modification of the transition metal coordination sphere by using strong complexing ligands (SCL). Complexing organic groups can be bonded to the transition metal oxide network in two different ways, as network modifiers or network formers. Different illustrations of the role of complexing ligands on Ti(IV) and Zr(IV) alkoxides are presented. As a network modifier, SCL act as termination agents for condensation reactions allowing a control of particle growth. The complexing ligands being located at the periphery of the oxo core open many opportunities for colloid surface protection. SCL carrying organofunctional groups which exhibit non linear optical (NLO) properties have also been used as probes to study sol-gel transformations. SCL functionalized with organic polymerizable functions act as network formers. Hybrid organic-inorganic copolymers intimately interpenetrated on a nanometer size scale were synthesized from zirconium oxo polymers chemically bonded to polymeric methacrylate chains via a complexing function.

Growth and branching of charged wormlike micelles as revealed by dilution laws

The successive transitions of morphology in aqueous solutions of interacting micelles are directly evidenced by the position q* of the correlation peak of the small angle neutron scattering profiles. As the volume fraction Phi increases, q* successively fits to the dilution laws expected for spheres and cylinders, and eventually gets close to the one expected for sheets when the micelles get branched. Data in between the swelling laws are quantitatively analyzed in terms of aggregation number and junction density. Varying the temperature in the dilute regime yields the end-cap energy which varies with molecular structure and scales as Phi(-1/2). In the semidilute regime, the junction density scales as nu(j) approximately Phi(1.8), close but slightly faster than theoretically expected. The boosting effect of intermicellar repulsion on growth and branching is pointed out by the present results which directly show that both condensation processes keep the micelles further apart.

Growth versus Cyclization in the Early Stages of the Polycondensation of Metal Alkoxides

The early steps of the polycondensation of transition metal alkoxide have been studied from the chemical and structural points of view. Polyoxoalkoxides are described like macromolecules by the composition of the repeating unit, the degree of polymerization (N), and the radius of gyration (R). The fraction p of binding sites of the coordination sphere of the metal centers occupied by terminal ligands determines N as follows: N proportional, variant pdf (dA-df), where df is the fractal dimension and dA is defined by Np proportional, variant RdA. This approach addresses difficulties raised by both coordinative unsaturation and cyclization in the modelization of the polycondensation of metal alkoxides. The coordinative unsaturation is accounted for by a particularly small value of dA= 1 in the very early steps, while the cyclization frequency is measured by the difference dA-df. This difference is not constant along the polycondensation process, and its dependence on the extent of reaction provides clues for understanding the high apparent kinetics order of gelation often reported in the literature.

Behavior of adhesive boundary lubricated surfaces under shear: effect of grafted diblock copolymers

The shear behavior and the normal interaction between mica surfaces covered by surfactant or surfactant-polymer mixtures were studied with a Surface Forces Apparatus (SFA) nanotribometer. If the surfaces are compressed while fully immersed in an aqueous surfactant solution that adsorbs in the form of flat bilayers, hemifusion can be induced. When the hemifused surfaces are subject to shear, at least five different dynamic regimes can be recognized. The general behavior may be described by a model based on the kinetics of formation and rupture of adhesive bonds between the shearing surfaces, with an additional viscous term. Once the adsorbed surfactant layer is decorated with physigrafted copolymers, the number of sliding regimes may be reduced to only one, in which the shear stress increases sublinearly with the driving velocity. The adhesion energy and the resistance to hemifusion of the adsorbed surfactant-polymer layers are also strongly modified as the grafting density increases.

Improved immobilization yields by addition of protecting agents in glutaraldehyde-induced immobilization of protease

The effects of peptides and polyethylene glycol (PEG) on the immobilization of protease using glutaraldehyde-activated Lewatit R258-K resin were investigated. When soy peptide was added at 0.1 g/l, the activity recovery and effectiveness factor increased by 20% and 38%, respectively. When PEG4000 (0.5 g/l) was used as a protecting agent, the activity recovery and effectiveness factor were improved by 35% and 60%, respectively, leading to an increased specific activity of the immobilized enzyme. The addition of PEG4000 is suggested to improve the cost-effectiveness for the production of immobilized enzymes.

Optimizing albunex in the left ventricle: an analysis of the technical parameters of four ultrasound systems in canines and humans

Albunex, an intravascular ultrasound contrast agent, has been used clinically to enhance echocardiographic images. The purpose of this study if (1) to determine whether varying the settings on commercially available ultrasound machines has an effect on left ventricular opacification after intravenously administered Albunex and if there is an effect on left ventricular opacification and (2) to determine the ideal settings for each ultrasound scanner. Six canine hearts were imaged with 1 ml injections of intravenously administered Albunex while varying the transducer frequency, preprocessing curves, postprocessing curves, and dynamic range on a variety of ultrasound units. Subsequently 50 human subjects underwent imaging with the various machines while the dynamic range and transducer frequencies were altered. All subjects received two or three intravenous injections of 10 ml Albunex. The opacification of the left ventricular cavitary images in both parts of the study were interpreted visually on a scale of 0 to 4 (0 = none, 1 = trace, 2 = moderate, 3 = dense, and 4 = ideal) by four observers. The maximum compression and transducer frequency of 3.5 MHz showed significant improvement of left ventricular opacification in both canines and humans. These studies have shown that (1) varying the ultrasound unit's parameters affects the quality of left ventricular imaging when Albunex is used to enhance the image, and (2) higher compression and a transducer frequency of 3.5 MHz tend to enhance Albunex images of canine and human hearts.