Search

The effects of liquid properties, such as pH and conductivity, on the thermal stability of electrostatically interacting colloidal silica crystals generated from heterogeneous nuclei were investigated mainly by measuring relative reflection spectra. The melting behavior of the colloidal crystals was also investigated. The melting points of both negatively and positively charged 3-aminopropyltriethoxysilane (APS)-treated substrates with different surface charges increased or decreased with increasing or decreasing pH. For both substrates, pH 5.5 was the modulation point of the crystal melting, and the melting point increased with increasing pH. For the negatively charged substrate, the melting point increased slowly as the pH decreased from pH 5.5. Meanwhile, the melting point of the APS-treated substrate increased more with decreasing pH from 5.5 than that of the negatively charged substrate. The cationisation of the substrate increased with decreasing pH, resulting in stronger electrostatic interactions with the negatively charged colloidal crystals and enhanced thermal stability. Next, we investigated the size of colloidal crystal grains in sample bottles for different liquid properties, and the results show that at the higher pH, the smaller crystal grains, indicating that pH affects both the substrates and crystals. Moreover, the binding effect of the APS-treated substrate on the crystals became stronger at lower pH, thereby enhancing the thermal stability of the crystals. [ABSTRACT FROM AUTHOR]

The effect of the substrate surface groups on the thermal stability of colloidal crystals formed via heterogeneous nucleation was investigated by observing the melting behavior of the colloidal crystals on three types of substrate: one charged negatively by silanol groups, one with introduced amino groups, and one with introduced quaternary ammonium groups. The degree of particle binding by the substrate in the colloidal dispersion was evaluated in terms of the particle arrangement formed through a dry deposition process that involved drying the dispersion on each substrate. The particle mobility on the substrates was higher in the order of the negatively charged substrate, the substrate with introduced amino groups, and the substrate with introduced quaternary ammonium groups. The melting temperature was measured in terms of the colloidal crystals formed on each substrate and was found to be 40.5 °C on the negatively charged substrate, 46.0 °C on the substrate with introduced amino groups, and 52.4 °C on the substrate with introduced quaternary ammonium groups. The increase in melting temperature was derived from the decrease in the particle mobility on the substrates with introduced positively charging groups, which resulted in an increase in the thermal stability of the colloidal crystalline lattice in relation to the Brownian motion due to the reduction in the particle mobility through the interaction between the negatively charged particles and the substrates. [ABSTRACT FROM AUTHOR]

We studied the influence of the surface charge of the substrate on the heat stability of electrostatic interactional colloidal silica crystals grown through heterogeneous nucleation from the substrate by relative reflection spectroscopy and optical microscopy. During the crystal growth stage on a negatively charged substrate, a large blue shift of the reflection peak was observed in the reflection spectrum. On the other hand, during crystallisation on a positively charged substrate, the blue shift occurring on the negatively charged substrate was completely suppressed. This blue shift indicates a reduction in the lattice spacing when the crystals push each other during crystal growth. The melting behaviour of the crystal was also investigated in the case of heating from the substrate side. The melting point of the crystal on the positively charged surface was higher than that on the negatively charged surface. The blue shift in the spectrum of the crystals on the positively charged substrate was suppressed in the stage before melting; however, the blue shift increased when the crystal started to melt from the substrate surface. Colloidal crystals formed from heterogeneous nuclei on a positively charged substrate were stabilised by the interaction between the negatively charged colloidal particles in the substrate's vicinity and the positively charged substrate surface. [ABSTRACT FROM AUTHOR]

Polyethylene glycol (PEG)-modified amino acid surfactant-based vesicles were prepared to improve the stability and cellular delivery of drugs. The vesicles comprised PEG-2000, sodium N-lauroylsarcosinate hydrate (SNLS), 1-decanol, and deionized water. The complex showed vesicular structures that were almost the same as the original vesicles, and their size distribution was (100-150 nm). Transmission electron microscopy (TEM) results revealed that no fusion occurred at 1.25 wt.% PEG concentration. The steric hindrance present among the vesicles prevented aggregation of the particles. No visual phase separation was observed for 6 months at room temperature 28 ºC. At higher molar concentration of PEG, fusion and wrinkling occurred owing to the association of PEG chains. The decreasing bending curvature led to the formation of fused vesicles with multilayer structure, as revealed by TEM and differential scanning calorimetry (DSC). [ABSTRACT FROM AUTHOR]

Melting temperature ( T) of colloidal crystals of monodispersed polystyrene and silica spheres has been measured for the completely deionized suspensions as a function of sphere concentration. More than 3 weeks are needed before achievement of the completely deionized state. Tincreases substantially as the deionization process of the suspension proceeds. The most reliable values of Tobserved for the completely deionized suspensions are successfully analyzed again with the theory of Williams et al. The new Tvalues are compared also with the theory of Robbins et al., which treats the repulsive Yukawa potential between colloidal spheres. [ABSTRACT FROM AUTHOR]

The melting temperature ( T) of colloidal crystals of monodisperse silica spheres in ethanol-water and ethylene glycol-water suspensions has been measured by reflection spectroscopy. A sphere of 110 nm in diameter and 0.041 in monodispersity index is used after purification and deionization processes. Transformation from the body-centered cubic lattice to the face-centered cubic lattice subphases is observed as the suspension temperature rises, which is similar to the purely aqueous suspension of the same sphere. A phase diagram including liquid-like and crystal-like structures is obtained in the presence of ion-exchange resins coexisted. The data of T are analyzed successfully with the theory of Williams, Crandall, and Wojtowicz. The heat of melting decreases by the addition of ethanol or ethylene glycol in the mixtures. [ABSTRACT FROM AUTHOR]