The lamellar phase in colloidal suspensions of positively charged platelets of layered double hydroxides (LDHs) was studied with synchrotron small angle X-ray scattering and optical observations.

The adsorption isotherm of block copolymer EPE1100 (polyethylene oxide–polypropylene oxide-polyethylene oxide) on the surfaces of Mg-Al LDH particles was determined through a solution depletion method combined with TOC measurement. X-ray diffraction patterns showed that the adsorption of EPE1100 molecules only occurred on the outer surfaces of LDH particles and they did not intercalate into the galleries between the layers. The adsorption of EPE1100 molecules changed the morphology of the particles. The effect of EPE1100 on the colloidal stability of LDH dispersion was investigated from three aspects: after the freezing-melting cycle, after the shearing rotations, and after the addition of electrolyte. The results indicated that the effect of EPE1100 on the colloidal stability of LDH dispersions was strongly related to the state of copolymer adsorption on LDH particle surfaces. It was inferred that the hydrated repulsive force and steric-repulsive force played important roles in determining the stability of the dispersions.

Vesicles can be formed spontaneously in aqueous solution of a single anionic surfactant sodium dodecyl benzenesulfonate (SDBS) just under the inducement of salt, which makes the formation of vesicle much easier and simpler. The existence of vesicles was demonstrated by TEM image using the negative-staining method. The mechanism of the formation may be attributed to the compression of salt on the electric bilayer of the surfactant headgroups, which alters the packing parameter of the surfactant. The addition of the zwitterionic surfactant lauryl sulfonate betaine (LSB) makes the vesicles more stable, expands the range of formation and vesicle size, and reduces the polydispersity of the vesicles. The vesicle region was presented in a pseudoternary diagram of SDBS/LSB/brine. The variations of vesicle size with the salinity and mixing ratios, as well as the surfactant concentration, were determined using the dynamic light scattering method. It is found that the vesicle size is independent of the surfactant concentration but subject to the salinity and the mixing ratio of the two surfactants.

The cloud points (CP) of aqueous solutions of two ethylene oxide–propylene oxide–ethylene oxide tri-block copolymers (EO)10(PO)16(EO)10 and (EO)1(PO)17(EO)1 were measured in the presence of additives, such as salts, alkalis, acids, polymer and ionic surfactant. The results obtained in this study indicated that salts decrease the CP of the two tri-block copolymers in the order of NaCl>CaCl2>MgCl2 and Na3PO4>Na2SO4>NaCl. Alkalis caused a sharp drop of CP of the two tri-block copolymers. Acids increased the CP. Water soluble polymer such as polyvinylpyrrolidone (PVP), hydrolysis polyacrylamide (HPAM) and cation-polyacryamide (cation-PAM) decreased the CP. Ionic surfactants such as sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) increased the CP. The extent of lowering depends on the structure and concentration of additives and the number of ethylene oxide group of tri-block copolymers.

The chemical composition, morphology of the particles of positively charged layered double hydroxides (LDHs) were studied by ICP, Mastersizer, TEM. The preliminary results indicated that with adding LDHs to 1% laponite dispersion the yield stress of laponite/LDHs mixed dispersions increased at first, then decreased dramatically to a minimum, and the yield stress rose again when LDHs increased further.

Liquid-crystalline phases were discovered more than a century ago.1 Up to now, tens of thousands of organic liquid crystals were discovered. In contrast, only a few mineral liquid crystals were characterized. In comparison to organic liquid crystals, inorganic ones may possess enhanced electrical, optical, magnetic properties and thermal stability. 1 The currently known lyotropic mineral liquid crystals, which formed in dispersions of anisometric inorganic particles at some critical concentration, were summarized in two review articles. 2,3 The liquid-crystalline phase of V2O5 suspensions shows an electro-optic effect and is used for measurement of residual dipolar couplings of unlabeled biomolecules. 4,5 Mineral liquid-crystal moieties can differ largely in size from one system to another, but they are in a colloidal range.

The intercalation reaction of polyoxyethylene sulfate (PEGS) withMg-Al-nitrate [Mg-Al-NO3] layered double hydroxide (LDH)wasinvestigated by using X-ray diffraction, infrared spectroscopy, and transmission electron microscopy (TEM). X-ray diffractograms showed that the basal spacing of the [Mg-Al-NO3]LDH with PEGS as the intergallery anion expanded from 0.89 to 2.37nm to form [Mg-Al-(PEGS)], but no expansion of the basal spacing was observed when poly(ethylene glycol) (PEG) reacted with [Mg-Al-NO3]. The characteristic absorption bands of the organic anion in the infrared spectra were obtained after prolonged treatment with deionized water, demonstrating the stability of the intercalation compounds. Furthermore, TEM analysis revealed that [Mg-Al-NO3], which consisted of hexagonal particles approximately 100-120nm in length, changed into monodisperse rigid spheres approximately 200 nm in diameter after the intercalation of PEGS.

The rheological properties of hydrotalcite-like compounds (HTlc)/sodium montmorillonite (MT) suspensions, which have formed gel-like structures, have been investigated. Special emphasis has been placed on the phenomenon of thixotropy. Usually, the structure recovery at rest after steady shear is considered the fundamental thixotropic process. And the recovery process was performed at the amplitude oscillatory shear measurements and the steady shear measurements. The oscillatory experiments were performed in the linear viscoelastic region so as tomakethe recovery process undisturbed. In the oscillatory experiments, η* increases monotonically with the time after the preshear process, and even after 3 h no equilibrium viscosity value of the suspension is reached. A single power law |η*|～tn holds within the time regime from 10 s to 3h, and the exponent n ) 0.158±0.10 is not only independent of the concentration and composition of the clay and the HTlc but also independent of mechanical pretreatment of the suspension. In the oscillatory experiments, two kinds of Na-MT were used, and almost the same value of exponent n was obtained. This type of kinetics has not been reported so far for the thixotropic recovery in the mixed suspension. And the reorganization of the gel structure is interpreted as a cooperative self-delaying process similar to the aging of glassy polymers or precipitation from supersaturated solid solutions. In the steady experiments, the recovery process was monitored at the low shear rate, and è does not always increase with the time. In the recovery process, the formation of the network was disturbed by the shear rate to some extent. When the structure strength (which is indicated by the value of the viscosity) of the system is low, the disturbance of the shear rate on the recovery process is weak, which becomes distinct when the structure strength is high.