Surfactant association structures in the system water,sorbitol, sodium dodecyl sulfate,and hexanol

The phase regions in the system hexanol, sodium dodecyl sulfate, and concentrated aqueous solutions of sorbitol were similar to the corresponding system with glycerol.In addition to the expected phase regions of a water/sugar micellar solution, a lamellar liquid crystalline phase, and the alcohol solution with solubilized sugar and water, a small region was found with an extremely stable emulsion, which could be separated by ultracentrifugation at 108,000 g. This emulsion consisted of micron sized droplets separated by layers of a lamellar liquid crystal.     

The aggregation behavior of poly-(oxyethylene)-poly-(oxypropylene)-poly-(oxyethylene)-block-copolymers in aqueous solution

Aqueous solutions of blockcopolymers, consisting of a polyoxypropyleneblock (POP) with a polyoxyethylene-block (POE) at each side, were studied using surface and interfacial tension measurements, static and dynamic light scattering and smallangle neutron scattering techniques, electric birefringence, rheological and DSC-measurements. The compounds were commercial samples and had an approximate average composition EO₂₀PO₇₀EO₂₀, EO₁₈PO₅₈EO₁₈, and EO₁₀₆PO₆₉EO₁₀₆. All three compounds formed micelles above a critical concentration. The size of the micellar core is determined by the length of the hydrophobic poly-propyleneoxide block. The transfer energy of a propyleneoxide unit from the aqueous to the micellar phase is about 0.3 kT at room temperature and hence a quarter of the corresponding value for a CH₂-group.The aggregation number of the micelles increases strongly with increasing temperature while the hydrodynamic radius remains constant in first approximation. The smallangle neutron scattering (SANS) data show at higher concentrations a strong correlation peak. Both the SANS- and the light-scattering data can be interpreted on the basis of the theory of hard sphere particles.Solutions with a volume fraction beyond about 0.2 gellifie when the temperature is raised above a characteristic value that is at the lowest concentrations slightly above room temperature, shift to lower values with increasing concentrations. Below this gelation temperature DSC-measurements show a phase transition with enthalpies between 40J/g and 80J/g, which is probably due to the dehydration of the PO-groups; this transition can also be observed at low concentrations where no gelation takes place. The position of the correlation peak of the SANS-data is not affected by the gel formation. Some samples, however, show clear evidence of long-range order and seem therefore to consist of cubic liquid crystalline phases. The shear moduli of the gels can qualitatively be understood on the basis of hard sphere models.     

The rheological properties of concentrated cetyltrimethylammonium bromide-salicylic acid solutions in water

Data on the rheological properties of the hexadecyl-trimethylammonium salicylate system (CTAB-SA) in water are reported. Three concentrations were used (0.1, 0.01, and 0.001 M). For the highest concentration, the effect of temperature on the rheology was studied in detail.The rheology of the 0.1 M CTAB-SA solution indicates a very uniform micellar size. By contrast with concentrated polymethyl methycrylate dispersions studied by the author, there was a strong divergence between the viscosity-shear rate and viscosity-frequency data, although the plateau low shear rate and frequency values agreed over a wide range of temperature. This effect could be explained by a shear rate dependent diffusion constant. The large temperature variation of the plateau viscosity and elasticity modulus values could be explained by a combination of micellar number concentration and flexibility changes as the temperature varies.At lower concentrations, the rheological data shows evidence of polydispersity in micellar size. Strong shear thickening and extensional viscosity effects are also evident, probably due to micellar overlap and cluster formation in strong shear fields and the alignment of the very long micelles in elongational flow. The shear thickening effects take some 200 s to relax (0.01 M solution). Recovery of the elasticity after shearing the 0.1 M solution is rapid (a few hundred milliseconds).     

Solvent-induced phase separation in polycarbonate blends PC/TMPC

Compatibility of the polycarbonates of bisphenol A (PC) and tetramethyl bisphenol A (TMPC) was studied in glassy films cast from CH₂Cl₂ at room temperature, and above the glass-transition temperature. Blends with different compositions and of different molecular weights were analyzed by DSC and small-angle neutron scattering (SANS). Solution studies were made with light scattering and microscopy. Some of the blend films were two-phased when cast at room temperature, but all films were one-phased in equilibrium above the glass transition. The SANS data demonstrated that phase separation in the cast films was not caused by inherent incompatibility of PC and TMPC, but was induced by the solvent CH₂Cl₂. The effect is caused by a closed miscibility gap in the ternary solution system PC/TMPC/CH₂Cl₂.     

Influence of nanoparticle addition on the properties of wormlike micellar solutions

The addition of positively charged, 30 nm diameter silica nanoparticles to cationic wormlike micellar solutions of cetyltrimethylammonium bromide and sodium nitrate is studied using a combination of rheology, small angle neutron scattering, dynamic light scattering, and cryo-transmission electron microscopy. The mixtures are single phase up to particle volume fractions of 1%. The addition of like-charged particles significantly increases the wormlike micelle (WLM) solution's zero shear rate viscosity, longest relaxation time, and storage modulus. The changes are hypothesized to originate from a close association of the particles with the micellar mesh. Small angle neutron scattering measurements with contrast matching demonstrate associations between particles mitigated by the WLMs. The effective interparticle interactions measured by SANS can explain the observed phase behavior. Dynamic light scattering measurements confirm the dynamic coupling of the particles to the micellar mesh.     

Small angle neutron scattering studies on micellar systems part 1. Ammonium octanoate,ammonium decanoate and ammonium perfluoroocatanoate

Small angle neutron scattering has been used to examine the size and shape of micelles of ammonium octanoate, ammonium decanoate and ammonium perfluoro-octanoate. Ammonium octanoate was found to form micelles with a micellar weight of 1640 and ammonium decanoate with a micellar weight of 12,576; both materials appeared to form spherical micelles. Ammonium perfluoro-octanoate formed micelles with a micellar weight of 17,610. Evidence from the scattering experiments suggested that the micelles were cylindrical and a model for the micelle is proposed.     

Small-angle neutron scattering on shear-induced micellar structures

Small-angle neutron scattering (SANS) experiments on sheared aqueous surfactant solutions of tetradecyltrimethylammoniumsalicylate (TTMA-Sal) are reported. A5-mM-solution without shear shows a weak correlation peak at a momentum transfer of 0.09 nm^–1 which has its origin in the micellar interaction. For shear rates above a threshold value of =40 s^–1 the scattering pattern shows an irregular increase in anisotropy. The analysis of the anisotropic pattern reveals the existence of two types of micelles: Small rodlike micelles which are weakly aligned and very large rodlike aggregates which are strongly aligned and which are present above the threshold value of. The two micelles are in equilibrium with each other and the equilibrium shifts with increasing shear rate to the side of the large oriented micelles.     

Temperature dependent phase behavior of PNIPAM microgels in mixed water/methanol solvents

Temperature dependent phase behavior of poly(N-isopropylacylamide) (PNIPAM) microgels in water/methanol mixtures of different composition was studied with dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Using DLS, it is possible to measure the diffusion coefficient, and thus the size of particles exactly and directly; the variation of the phase transition temperature in the different solvents is also easy to detect by this method. With SANS measurements in D₂O/MeOD mixtures, some of the DLS results were confirmed. Moreover, SANS measurements give valuable information on the particle structure in different solvents. The experiments were compared with the theory of competitive hydration introduced by Tanaka et al. We found a good agreement of theory and experiment, and obtained the theoretical predictions: around the transition temperature, the composition of the bound methanol along the chains is higher than that of the outer solution, while the whole methanol composition inside the gel is lower. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013, 51, 1100–1111     

Aggregation phenomena in the suspension polymerization of VCM

In the suspension polymerization of VCM, insoluble polymer particles are formed inside the monomer droplets. The growth and aggregation of these particles are responsible for important polymer properties, such as porosity. It is well established that the most characteristic polymer particles, the primary particles, are of a narrow distribution with a size (diameter) ranging from 0.10–0.20 m. This work studied the formation of primary particles based on the aggregation phenomena that take place inside a monomer droplet. This was done by formulating a population balance equation, which was based on the following considerations: a) polymerization occurs in both the monomer and the polymer phases; b) there is continuous formation of the basic particles in the monomer phase; c) the growth of the polymer particles occurs as a result of both polymerization in the polymer phase and aggregation of the particles; d) the colloidal properties of the particles that are responsible for the aggregation phenomena were considered to be the net result of attraction and repulsion energies.It was shown that for particles carrying a constant charge it was not possible to predict the formation of primary particles of size 0.10–0.20 m. The particle size distribution had a mode diameter equal to the diameter of the basic particles. Consequently, the particle charge was allowed to vary in a way proportional to the particle radius raised to a power coefficient. For values of the coefficient greater than zero, i. e., when the particle charge increased during polymerization, the aggregation of the basic particles was efficient enough to result in the formation of large primary particles.     

Organogels from water-in-oil microemulsions

A new family of organogels is described. They originate from water-in-oil microemulsions, from which the name microemulsion gels or microemulsion-based gels is derived. Two different types of such gels are presented here, referred to asgelatine gels andlecithin gels, respectively. In the case of gelatine gels, the initial ternary system typically consists of isooctane, AOT (bis 2-ethylhexyl sodiumsuccinate) and water; gelation is induced by solubilization of gelatine in the water microphase above a critical concentration. In the case of lecithin gels no polymeric material is needed. Starting from a reverse micellar solution of lecithin (50–200 mM) in an organic solvent, gelation is induced by the addition of a small amount of water. The molar ratio of water to lecithin typically varies between 1 and 12 for the 50 different solvents investigated to date. These gels are isotropic, thermoreversible and optically transparent.For both microemulsion gels the influence of the concentration of the components on gelation is presented in the form of preliminary phase diagrams.The physico-chemical properties of these organogels were characterized using a variety of techniques such as NMR, DSC, dynamic shear viscosity measurements, and light scattering. Based on these measurements, preliminary models for the structure of these novel systems were developed.It is possible to co-solubilize a variety of reactive molecules in these gels. Therefore, it may be possible to use these organogels for a number of chemical, pharmaceutical, and cosmetic applications.Paper presented at the Workshop on Ringing Gels and Cubic Phases, Bayreuth, October 25–26, 1988.     

On Tanaka-Fillmore's kinetics swelling of gels

Tanaka and Fillmore treated the swelling of a gel as a process where a crosslinked polymer network having been initially under uniform stress is expanded by osmotic pressure, sucking up the surrounding fluid medium. We point out that their physical reasoning is unnatural and leads to an unacceptable conclusion; we propose a more sound approach to the same problem. Our treatment assumes that the gel network is extended not by the osmotic pressure of the gel, but rather by the swelling pressure which is generated by the excess fluid penetrating in against the real nature of a polymer network that tends to shrink. The diffusion equation of the fluid, hence, plays a dominant role and gives the distribution of fluid concentration in contrast to Tanaka-Fillmore's scheme. The expression for the distribution of local strain in a spherical gel is deduced from the relation of mechanical balance between two forces, the one is due to the elasticity of the network and the other due to the gradient in the chemical potential of the fluid. The results obtained have forms analytically similar to Tanaka-Fillmore's, but are differ in the physical meanings.     

Effect of coexistent hydrocarbon phase on the volume behavior of adsorbed film and micelle of dodecyltrimethylammonium chloride

Interfacial tension () between aqueous dodecyltrimethylammonium chloride (DTAC) solution and benzene was measured as a function of pressure (p) and concentration. The/p was observed to change discontinuously at the critical micelle concentration; this indicates that the micelle formation of DTAC in the aqueous solution coexisting with benzene can be treated like the appearance of a macroscopic phase. It was shown by drawing the vs.A curves that hydrocarbon, such as benzene, cyclohexane, and hexane, make the adsorbed film of DTAC expand. The volume behavior of the micelle with benzene molecules solubilized was found to bear a strong resemblance to that of the adsorbed film at the water/benzene interface. The difference in the molar volume value of adsorbed DTAC among the coexistent hydrocarbon phases was attributed to the difference in the contribution of the hydrocarbon molecules to the interfacial excess volume; the number of the solubilized hydrocarbon molecules was evaluated to be one or two a micelle.     

Photochemically induced phase transitions in the system cetyltrimethyl-ammonium bromide-water containing N-methyl-N,N-diphenylamine

Phase transition temperatures from lyotropic liquid crystals to the isotropic micellar solution of the system cetyltrimethylammonium bromide-water (CTAB-H₂O) were measured in the presence of 0.1-0.9 weight % of N-methyl-N,N-diphenylamine (MPA). They were determined by optical and viscometric methods and were found to increase as a function of MPA concentration in solutions containing 21 and 23 weight % of CTAB. This effect was reversed when MPA was in situ photochemically converted to N-methylcarbazole, allowing photochemically induced phase transitions.     

Enthalpy of solution of phenoxyalcohols solubilized in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solutions

The enthalpy of solution of phenoxy 2-ethanol, 1 phenoxy,-3 propanol and benzylalcohol was determined at 25 °C in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solution, up to 0.2 mol/kg surfactant concentration. Using the pseudo-phase model, the standard enthalpy of transfer and the partition coefficient of the alcohols between micelle and water are calculated. The latter quantity is found to be systematically larger when derived from enthalpy than from free energy measurements. Using the so-called compensation plot, the solution thermodynamics of aromatic and aliphatic alcohols in aqueous sodium dodecylsulfate and in the octane+water systems are compared. Aromatic alcohols display an anomalous behavior in the octane+ water system but not in the micellar one.The standard enthalpy of solution of various alcohols presents, when plotted against hexadecyltrimethylammonium bromide concentration, a shoulder in the region around 0.05 mol/kg; a discussion is presented on the evidence for alleged micellar structural changes in aqueous micellar systems.     

Small-angle neutron-scattering study on a structure of microemulsion mixed with polymer networks

The structure of a microemulsion mixed with polymer networks was investigated by means of small-angle neutron scattering (SANS). The system consists of nonionic surfactant, polymer network, oil, and water. The microemulsion and the polymer network employed in this work are known to undergo temperature-induced structural transition and volume phase transition, respectively. Polymer solutions and gels were made by polymerizing monomer solutions in the presence of microemulsion droplets. In the case of a mixture of an N-isopropylacrylamide (NIPA) monomer solution and a microemulsion, the NIPA monomer was found to behave as a cosurfactant. However, polymerization resulted in a phase separation to polymer-rich and -poor phases. Interestingly, SANS results indicated that a well-developed ordered structure of oil domains was formed in polymer network and the structure was very different from its parent systems. Furthermore, the system underwent two different types of structural transitions with respect to temperature. One was originated from the structural transition of microemulsion due to the change of the spontaneous curvature and the other from the volume phase transition of the NIPA gel.     

Solution behavior of two liquid crystalline polymers of different architectures

Solutions of two different liquid crystalline polymers of high molecular weight are investigated by static and dynamic light scattering (LS), membrane osmometry and size-exclusion chromatography (SEC). Measurements in dilute solution in different solvents showed no specific behavior as formation of aggregates or chain stiffening. Large discrepancies between the LS results and the results from osmometry and SEC show that the latter methods are in the present cases not suitable for molecular weight determination. In semi-dilute solution the osmotic modulus and the time correlation function were studied. Behavior of flexible chains was observed. In one system a slight aggregation of small molecules onto longer chains was found causing less interpenetration of the chains in that solvent. At moderately high concentrations cluster formation was observed from i) a small angle excess scattering, ii) a downturn of the osmotic modulus, and iii) the appearance of a slow motion in the time-correlation function.     

Viscoelastic properties of polyacrylonitrile particles stabilised by a poly-2-vinylpyridine/polytert butylstyrene block copolymer

The viscoelastic properties of a dispersion of polyacrylonitrile particles stabilised by a block copolymer poly-2-vinylpyridine/polytert butylstyrene dispersed in solvesso have been measured as a function of particle concentration and frequency at ambient temperatures. At low volume fraction of particles it was found that the loss modulus of the dispersions was larger than the storage modulus, whilst at volume fractions > 0.40 the storage modulus dominates the rheology. This is attributable to there being a steric repulsion between the particles as a result of an increasing concentration of particles and the resultant reduction in interparticle separation in the dispersion. In addition the observed exponential increase of the storage modulus with increasing particle volume fraction mirrors the exponential increase in force with decreasing surface separation of the same type of polymers adsorbed to mica.     

Investigations of the influence on the phase morphology of PP-EPDM-blends on their mechanical properties

This work covers the dependence of the mechanical properties of polymer blends on their composition and their phase morphology. Blends of EPDM-elastomers and polypropylene were prepared covering the whole concentration range. The phase morphology was varied strongly by employing different mixing techniques and its morphology was characterized by means of electron microscopy and light microscopy, as well as by x-ray scattering and calorimetry.Mechanical properties such as the complex shear modulus, the tensile modulus as well as the stress strain behavior were investigated as a function of the composition of the blends and their phase morphology. The experimental finding is that the complex modulus, the tensile modulus, the yield stress, and the ultimate stress are rather insensitive with respect to the phase morphology and vary continuosly with the composition. The elongation at break, on the other hand, as well as the impact strength were found to depend on the phase morphology and to vary discontinously with the composition. One conclusion to be drawn is that one is not always forced to control the phase morphology tightly during processing in order to obtain materials with sufficiently good mechanical properties. Rather, simple theoretical approaches, neglecting details of the phase morphology are frequently able to satisfactorily predict mechanical properties of multiphase blends.     

Small-angle neutron scattering of colloidal silica dispersions in a non-polar solvent

Small-angle neutron scattering studies were performed on dilute dispersions of colloidal silica spheres in mixtures of h₁₂- and d₁₂-cyclohexane. The particles consisted of a SiO₂-core and a layer of stearyl alcohol molecules terminally attached with a chemical bond (Si-O) to the particle surface. The contrast variation method was applied to reveal the internal structure of the particles. The matchpoints determined with this method were in accordance with those calculated from the mass density of the particles and the atomic composition, as determined with elemental analysis.For a detailed interpretation of the scattering curves, we assumed that the particles were spherosymmetrical and consisted of two concentric layers. With the relation we derived between the radius of gyration and the reciprocal contrast for such a model, it was possible to determine all the parameters characterizing the particle in terms of this model. The model calculations performed using these parameters fitted very well to the experimental intensities for high contrasts. For lower contrasts, the fit was somewhat less good. This is probably due to random fluctuations in the scattering length density within the particle core.The different radii as found by neutron scattering, agreed very well with those determined using other techniques, such as light scattering (static and dynamic) and electron microscopy.