Micelle structure in isotropic aqueous colloids of a poly(oxyethylene) amphiphile C12E8

Micelle structure in aqueous colloids in the isotropic liquid phase (L₁) of a nonionic amphipile (n-dodecyl octa(oxyethylene glycol) monoether (C₁₂E₈) has been investigated as a function of concentration and temperature using light scattering (LS), viscometry, NMR, and small-angle X-ray scattering (SAXS).The spherical micelles, having a radius of 28–31 Å, remain in a wide concentration range from very dilute to ca. 42 wt %. The micelle size increases sligthly with increasing temperature in the range of 25–60 °C. In the concentrated colloids, the spherical micelles are likely to be arranged in a certain ordered structure. Even at such a high concentration as 30 wt %, the isotropic colloid shows Newtonian flow. This suggests that interaction between micelles in the ordered structure is very weak and the structure is very fragile. Moreover, coexistence of the isotropic phase and the ordered structure in L₁ phase is discussed.     

Interaction between amphiphiles and water molecules in concentrated bilayer aqueous colloids

Interaction between amphiphiles and water molecules in micelle or bilayer structure has been investigated using aqueous colloids of various amphiphiles through the rheological data and the spin-lattice relaxation timeT ₁ of the proton of water molecule.T ₁ of the water proton has been measured by the inversion recovery method and determined as a single exponential relaxation process.The chemical shift of the water proton is almost independent of the amphiphilic concentration; however, it shifts toward a higher magnetic field with increasing temperature in a way similar to that in pure water and in the amphiphilic aqueous systems. These facts mean that there is no significant difference in the magnetic field environment of the water protons in these systems.The water molecule is not necessarily bound in the fully developed micelle or bilayer (rod-like or lamella) structure which induces the high viscosity or high rigidity of the colloidal system. On the other hand, the water molecule is bound in the micelle colloids of amphoteric amphiphiles or amphiphiles whose molecular assembly creates a relatively strong electrostatic field. The activation entropy of the bound water is negative and this suggests that water molecules assume some ordered structure in the bound state.     

Internal and interfacial structure of small vesicle in aqueous colloid of didodecyldimethylammonium bromide

The vesicle structure and interfacial structure of a two-chain amphiphile didodecyldimethylammonium bromide (DMA) in aqueous colloid have been studied by small-angle x-ray scattering. The radius of the DMA small vesicle is ca. 64 Å, and the thickness of the bilayer, which is the surface layer of the vesicle, is ca. 41 Å. The small vesicle has a core space at the center, whose radius is ca. 23 Å. The specific inner surface of the small vesicle has also been calculated and the surface area of the vesicle has been estimated to be five times larger than that of the smooth sphere.     

A model of flocculation by very-high-molecular-weight polymers

A simple model is proposed to describe flocculation of fine particles by high polymers. The model is based on the assumption that the number of colloid particles attached to a single polymer molecule is a random quantity, and that a minimum number of particles must be attached to a polymer molecule to trigger its removal from the system. The predictions of the model are confronted with experimental data concerning the stability of the system polyacrylamide-sol AgJ.     

Thermotropic rigid chain copolymers I. crystallization kinetics and thermodynamic properties

The kinetics of structure formation and the thermal properties of the ordered phase were analyzed calorimetrically for a rigid polymer, characterized by an irregular chemical structure. The transition from the nematic melt to a partially ordered state was found to involve two different processes, a fast and a slow one. The fast one corresponds apparently to a thermally activated nucleation and growth mechanism, whereas the slow one is strongly self delaying. Its transition rate is only weakly dependent on the temperature. The thermal properties of the ordered phase, resulting from this process, vary strongly with the annealing temperature and annealing time. The enthalpy and entropy of fusion, characteristic for the pure ordered phase, are lower by a factor of about 10 in comparison to the corresponding values of flexible chain molecules.     

Coagulation kinetics of amorphous colloidal silica suspensions with and without hydroxypropyl cellulose polymer

The coagulation rate constant of submicron silica has been measured as a function of solution pH, salt concentration and hydroxypropyl cellulose (HPC) polymer concentration. Results show that the colloidal stability of silica is dominated by the cation concentration in the presence of salt in the pH range 3–9.5. The stability increases as cation concentration decreases. At low salt concentration and a minimum colloid stability was found in the intermediate pH range 4–8. These results show that differences in the literature values of the critical coagulation constant by relative light-scattering experiments can be explained by the use of the coagulation rate constant analysis. When HPC polymer was present in the solution, the colloid stability of the silica increased. The adsorption of polymer stabilizes the silica suspensions, both at low pH near the isoelectric point and at high ionic strength where it coagulates without the polymer. A monolayer coverage was necessary to provide steric stabilization. At 10^–3 M KCl a smaller equilibrium concentration of HPC in solution is needed to give monolayer coverage and steric stabilization than at 1 M KCl and pH 4.2.     

Electrically conducting,thermally stable,and mechanically strong CuS-poly(parabanic acid) composite films and their shielding effect of electromagnetic wave

Poly(parabanic acid)-CuS composite film (wt-% of CuS=20–50) prepared by using organosol of CuS (=1500 Å) showed electrical conductivity of 0.1–70 S cm^–1, high thermal stability up to 250°C, high mechanical strength (breaking stress=7.0–12 × 10⁷ Pa), and good shielding effect of electromagnetic wave.     

Refraction effects and structural changes of hard elastic polypropylene (HEPP) during stretching

Small angle X-ray diffraction from hard elastic polypropylene 5M-45B (HEPP) of Celanese shows a sharp long streak along the equator indicating total reflection and refraction effects equivalent to 2000 Å long cylindrical parts within the fibre. The well known amorphous phase therefore does not exist in high modulus fibres similar to 11-times stretched samples of PE with fully extended chains. A new method is described which explains the observed scattering by means of shape functions. One term depends on the lamellae, the other one on the fibrils, whilst the third takes care of the correlations between terms 1 and 2. The latter does not interfere with the calculation because it is simply another well separated component of the equatorial scattering analysis previously described by Guinier. Fibrils exist between the lamellae for extensions greater than= 40%. Below this value the diffuse equator scattering is explained by 100 Å long gaps between the chain molecules; from 5 vol. % packing density at =0 % they increase to about 50 vol. % at=40 %. Here the gaps change their functions to become the surroundings of the fibrils. This thermodynamically-induced metamorphosis explains the metastable nature of the lamellae, the gaps and the fibrils, observed at=40 %. The pseudo-Hook domain disappears gradually during iterated strain-relaxation operations after 100 cycles. The stress-strain curve is similar, then, to that of a sulphur vulcanized natural rubber except that theE-modulus is now 100 times larger. The small angle scattering changes according to these phenomena: The number of lamellae becomes smaller and their mean distance increases to 2000 Å or more along the chain direction.     

The pH dependence of dispersion of TiO2 particles in aqueous surfactant solutions

The pH dependence of dispersion of titanium dioxide (TiO₂) particles has been examined in the presence of surfactant molecules in water. Whereas particles were dispersed in water at acid and alkaline regions rather than at neutral region, the dispersion was enhanced at neutral region in an aqueous sodium dodecyl sulfate (SDS) solution and at acid and alkaline regions in an aqueous dodecyldimethylamine oxide (C₁₂DAO) solution. Considering the pH dependence of zeta potential, the adsorption models of surfactant molecules on a particle were estimated on the basis of the modes of hemimicelle and double-layer compression. While the particles that adsorbed Al³⁺ were remarkably dispersed around pH 6, their dispersion does not largely depend on pH in the addition of SDS, indicating the adsorption of SDS molecules to form double-layer compression in the whole pH region. Dynamic light-scattering measurement and electron microscopic observation suggested that the particles were dispersed in water as small flocs.     

Adsorption of anionic surfactants on positively charged polystyrene particles II

In the case of cationic polystyrene latex, the adsorption of anionic surfactants involves a strong electrostatic interaction between both the particle and the surfactant, which may affect the conformation of the surfactant molecules adsorbed onto the latex-particle surface. The adsorption isotherms showed that adsorption takes place according to two different mechanisms. First, the initial adsorption of the anionic surfactant molecules on cationic polystyrene surface would be due to the attractive electrostatic interaction between both ionic groups, laying the alkyl-chains of surfactant molecules flat on the surface as a consequence of the hydrophobic interaction between these chains and the polystyrene particle surface, which is predominantly hydrophobic. Second, at higher surface coverage the adsorbed surfactant molecules may move into a partly vertical orientation with some head groups facing the solution. According to this second mechanism the hydrophobic interactions of hydrocarbon chains play an important role in the adsorption of surfactant molecules at high surface coverage. This would account for the very high negative mobilities obtained at surfactant concentration higher than 5×10^–7 M. Under high surface-coverage conditions, some electrophoretic mobility measurements were performed at different ionic strength. The appearance of a maximum in the mobility-ionic strength curves seems to depend upon alkyl-chain length. Also the effects of temperature and pH on mobilities of anionic surfactant-cationic latex particles have been studied. The mobility of the particles covered by alkyl-sulphonate surfactants varied with the pH in a similar manner as it does with negatively charged sulphated latex particles, which indicates that the surfactant now controls the surface charge and the hydrophobic-hydrophilic character of the surface.Dedicated to the memory of Dr. Safwan Al-Khouri IbrahimPresented at the Euchem Workshop on Adsorption of Surfactants and Macromolecules from Solution, Åbo (Turku), Finland, June 1989     

The effect of pH on emulsion polymerization of styrene in the presence of an amphoteric emulsifier

An emulsion polymerization of styrene in the presence of an amphoteric emulsifier of the betaine type; N,N-dimethyl-n-laurylbetaine (LNB), has been studied at various pH values. The relationships between the physicochemical properties of LNB aqueous solutions, the emulsion polymerization process and the characteristics of the synthesized latex particles were studied under various pH conditions. The polymerization rate and the particle number concentration decreased with increasing pH of LNB aqueous solution and changed in shape at both ca. pH 4 and pH 8–10. The properties of LNB aqueous solution also changed with the pH and changed in shape at the same pH as that of the emulsion polymerization. These pH values were in good agreement with the pH at which the LNB molecule changed its ionic form. The number of synthesized latex particles was proportional to the number of LNB micelles in the solution, below pH 10. The particle size of the synthesized latex particles and the molecular weight of the latex polymers also changed with the properties of LNB aqueous solutions, accompanying the change of the ionic form of LNB molecules.     

Rigid-rod polymers with flexible side chains

Modeling studies were performed for a rigid-rod polyester with hexadecyloxy side chains (n=16) in order to simulate x-ray scattering curves in the medium angle scattering region (s=4 sin / from 0.2 Å^–1 to 2.2 Å^=t–1). The experimental ones were taken from a material obtained by cooling to room temeperature from the smectic mesophase at 150°C. The wide-angle x-ray diffractograms were calculated for given conformations and molecular arrangements using Debye's equation. The theoretical result thus obtained for a great variety of possible packing models and structures was compared to the experimental result. The size of the effective scattering region is found to be 61×18×52=6×10⁴ ų and consists of approximately five layers, each of which is composed of two rigid rods and 20 side chains. The planes form by the rigid rods, together with the side chains, have a distance of 3.6 Å, the distance between the rods being 26 Å. As the main result, it was found that the side chains form regions with a denser ordering (clustering). The interchain distance for side chains decreases in the regions from 5.3 Å to 4.8 Å.     

Thermotropic gelation of ovalbumin 1. Viscoelastic properties of gels as a function of heating conditions and protein concentration at various pH values

A study has been undertaken of stress relaxation in ovalbumin thermotropic gels with a concentration of 8–20%, depending on time and temperature of heating (respectively, 20–60 min, 70°–110°C), at pH 2.5–10.0. In all instances, the dependence of the initial gel elasticity modulus on heating has a single maximum. Gelation conditions corresponding to this maximum are considered optimal. Optimal gelation time is 30 min, regardless of pH. On the other hand, the optimal heating temperature depends on pH. To the right and left of the isoelectric point of protein (2.5pH<4.0 and 5.5G) of gels on heating conditions, pH and protein concentration (X ₁,X ₂,X ₃,X ₄), as well as on time of relaxation (t) may be generally described asG(X ₁,X ₁,X ₁,X ₁,t)=G _e(X ₁,X ₂,X ₃,X ₄)f(t), whereG _e is the equilibrium value of the elasticity modulus, and f(t) the relaxation function. Thus, a change in the parameters only affects the value of the equilibrium elasticity modulus, and exerts no effect on the relaxation time spectrum. For this reason, all the relaxation curves obtained may be transformed into two normalized relaxation functions:f(t)=f(t)/f(1)=G(X ₁,X ₂,X ₃,X ₄,t)/G(X ₁,X ₂,X ₃,X ₄, 1)Each of these normalized functions corresponds to one of the homologous groups. Rheological similarity of gels in each homologous group evidently points to their structural similarity. Invariance of the gel relaxationproperties with regard to protein concentration, leads to a concentration dependence of the equilibrium modulus at various pH values. These dependences are curvilinear on a double logarithmic scale. The slope of the curve exceeds 2 in the entire concentration interval studied. In other words, the dependences obtained cannot be described by the usual law of squares. On the other hand, they adequately match Hermans theoretical relation for a network formed by random association of identical polyfunctional particles without cyclization. This simple model evidently gives a true picture of the major regularities of thermotropic gelation for ovalbumin. An agreement between this theory and experiment was achieved for a protein concentration ofC ^*=6.0±1.0% at the gel point regardless of pH. Invariance of gelpoint position with regards to pH demands further confirmation.List of symbols T _h,t _h heating temperature and time - T _h ^* ,t _h ^* optimal heating temperature and time - C protein concentration - C ^* protein concentration in gel-point - G relaxation modulus - G _e equilibrium modulus - f(t) relaxation function - t time of relaxation - f(t) normalized relaxation function - fT _A (t), f _B (t) normalized relaxation functions of groups A and B - G ₁ T _h,t _h-reduced modulus - G ₂ T _h,t _h, pH-reduced modulus - G ₃ C-reduced modulus - b ₁ T _h, t_h reduction parameter of modulus - b ₂ pH reduction parameter of modulus - b ₃ C reduction parameter of modulus - W_g gel-fraction     

Influence of the exchangeable cations on stability and rheological properties of montmorillonite suspensions

The effects of NaCl and CaCl₂ on the colloid stability and rheological properties of Na- and Ca-montmorillonite dispersions were studied. The distribution of cations between the surface and the bulk phase was determined. For both of monocationic montmorillonite, the critical coagulation concentration were 250 mmol NaCl/dm³ and 2 mmol CaCl₂/dm³. The changes in the Bingham yield stresses of Na- and Ca-montmorillonite dispersions as functions of the NaCl and CaCl₂ concentration could be explained in terms of the surface excess amount and equilibrium concentration of the cations, the second electroviscous effect and the formation of a gel structure.     

Complex associations between membrane proteins analyzed by analytical ultracentrifugation: Studies on the erythrocyte membrane proteins band 3 and ankyrin

Associations between different water-soluble proteins can be studied by sedimentation equilibrium experiments in the analytical ultracentrifuge and subsequent mathematical analysis of thec(r)-distributions obtained. The analysis can be simplified by labelling one of the proteins with a dye absorbing at wavelengths >300 nm. The method can also be applied to intrinsic membrane proteins in solutions of a nonionic detergent. The present paper both reviews the method and reports application to the associations between two proteins of the human erythrocyte membrane: 1) band 3, the membrane's main intrinsic protein which, in detergent solutions and presumably also in the erythrocyte membrane, is in a monomer/dimer/tetramer association equilibrium, and 2) the cytoskeletal protein ankyrin which links the membrane skeleton to the lipid bilayer by binding to band 3. Ankyrin was labelled with fluorescein isothiocyanate and the detergent used was C₁₂E₉. It was found that the only aggregate of ankyrin and band 3 occurring in significant amounts was a complex of one ankyrin molecule and four band 3 molecules. This strongly suggests that, in the erythrocyte membrane, the band 3 tetramer represents the high affinity ankyrin binding site.This paper was presented at the VI. Symposium on Analytical Ultracentrifugation, Marburg, F.R.G., February 16–17, 1989.     

Binding of benzopurpurin 4B to poly(N-vinyl-2-pyrrolidone): A spectral study on the mechanism of dye binding

The binding mechanism of benzopurpurin 4B to poly(N-vinyl-2-pyrrolidone) was studied by a spectrophotometric absorbance change method at pH 7.1 in 0.05 mol dm^–3 phosphate buffer. The results were analyzed by Scatchard, Hill, and Schwarz methods. The different shapes of the Scatchard plots indicated the varying degrees of cooperativity which depended on the percent saturation of binding sites. The Hill method elucidated the pairwise binding of the dye to polymer at the intermediate saturation and multimolecular binding both at the low and high saturations. The Schwarz method confirmed the interaction between bound dye molecules which led to cooperativity. The difference spectra of the polymer-dye complex evidenced the elucidated binding mechanism.     

Cubic phases as structures of disclinations

We look for possible ordered geometrical configurations with bicontinuous or cellular topologies, optimizing the frustration of a periodic system of frustrated fluid films. The solutions found have the same symmetries as those observed for cubic phases of amphiphilic molecules. This agreement leads to consider cubic structures as structures of defects of rotation, or disclinations.This paper was presented at the workshop Ringing gels and Cubic phases, University of Bayreuth, October 25–26th, 1988.     

Compression studies on aqueous polystyrene latices

An apparatus, that allows simultaneous measurements to be made of excess osmotic pressure and optical diffraction of polymer colloid dispersions, has been constructed. Results are reported for monodisperse polystyrene latices at several salt concentrations. An interesting feature of the results is a clear indication of a co-existence region occurring with particles of 182 nm diameter in sodium chloride concentrations of 10^–4 mol dm^–3     

Relation between syneresis and rheological properties of particle gels

The relation between the tendency to exhibit syneresis of rennet (pH 6.65) and acid (pH 4.6) skim-milk gels and the rheological properties of these gels is discussed. Based on the syneresis model for milk gels of Van Dijk and Walstra [1, 4, 14, 19] it is reasoned that the average lifetime of the protein-protein bonds in the casein strands forming the gel network, the fracture force of these strands, and their flexibility are the main mechanical properties of importance. It is argued that the ratio of the loss modulus to the storage modulus (tan δ) as a function of the time scale of the measurement in dynamic experiments is a good measure of the first property. Results are given for rennet skim-milk gels at 25, 30, and 40°C and for an acid skim-milk gel at 30°C. Moreover, the stress strain relation and fracture behavior of both gels were assessed in creep measurements as a function of the duration of the applied stress. Rennet skim-milk gels have a lower fracture stress σ _f and therefore probably a lower fracture force per strand and a higher tan δ over long time periods than acid gels, while tan δ increases with temperature. As predicted, low fracture stresses and high tan δ correlated with an increased tendency to exhibit syneresis.     

Thermodynamic consideration on the interface formation of water and ethylene glycol isobutyl ether mixture

The interfacial tension of the binary two-phase mixture of water and ethylene glycol isobutyl ether (EIB) was measured as a function of temperature in the vicinity of the lower critical solution temperatureT _c under atmospheric pressure. The interfacial tension decreased with decreasing temperature and approached zero atT _c . The thermodynamic quantities of interface formation were evaluated by applying equations developed previously to the interfacial tension vs temperature curves. The results were compared with those of the water and diethylene glycol diethyl ether system examined previously, and the effect of the molecular structure of the ether molecule on its interfacial behavior was discussed. It was suggested that the hydration of the ethylene oxide groups of ether molecules was an important factor in the interface formation as well as in the mixing of component molecules of the systems investigated here.