ABSTRACT
Stearic acid and triethanolamine (TEA) in a molar ratio of 2:1 were mixed in aqueous solution at 80 degrees C and subsequently cooled to ambient temperature. The structural evolution of the resultant sample during storage was characterized by using light microscopy, Cryo-SEM, differential scanning calorimetery, pH, infrared spectroscopy, elemental analysis, and simultaneous small and wide-angle X-ray diffraction. It was found that a lamellar liquid crystalline phase was formed when stearic acid and TEA solution were mixed at 80 degrees C and multilamellar spheres of a few microns diameter were formed initially after cooling. A hydrolysis reaction (i.e., the reverse reaction of neutralization between stearic acid and TEA) occurred thereafter that caused the breakdown of the lamellar gel phase and the formation of platelet stearic acid crystals. Three polymorphs of stearic acid (defined following previous work as the A, C, and E forms) were formed as the result of hydrolysis reaction, which gave rise to a strong optically pearlescent appearance.
Subject(s)
Ethanolamines/chemistry , Stearic Acids/chemistry , Particle Size , Soaps/chemistry , Temperature , Water/chemistryABSTRACT
We study the spontaneous size selection in lyotropic cholesteric (W/O) and thermotropic nematic (O/W) liquid crystal emulsions. The droplet sizes have been characterized by dynamic light scattering, which indicates a narrow monomodal distribution of droplets achieved spontaneously even without emulsion filtration. Anchoring of the director, provided by the chosen surfactant on the interface, may generate a topological defect inside the droplet. Below the critical radius R = K/W, determined by the ratio of Frank elastic and the surface anchoring constants, the effective anchoring strength is weak and droplets are not topologically charged; this allows them to coalesce freely, depleting the size distribution in this range. Large droplets possess a topological charge of +1 and present a high elastic energy barrier for pair coalescence; the resulting size distribution is skewed, with R > R, and effectively frozen.
ABSTRACT
We studied a new kind of W/O emulsions based on a lyotropic liquid crystal as the aqueous droplet phase. The cholesteric phase, a solution hydroxypropyl cellulose in water was dispersed in the continuous oil matrix, paraffin oil or heptane. We made a specific choice of surfactant in order to impose director anchoring conditions at the oil-water interface and orient the liquid crystal inside the droplet. The strong anchoring conditions resulted in a topological defect inside the droplets of size above the critical value R(*). The defect elastic energy creates a barrier against droplet coalescence, the effect of topological size selection. We have studied the orientation of the director inside the droplets and their size distribution.
Subject(s)
Cellulose/chemistry , Emulsions/chemistry , Polymers/chemistry , Water/chemistry , Biophysical Phenomena , Biophysics , Cellulose/analogs & derivatives , Cholesterol/chemistry , Heptanes/chemistry , Paraffin/chemistry , Particle Size , Surface Properties , Surface-Active Agents/chemistry , ThermodynamicsABSTRACT
Crystals of partially neutralized stearic acid with triethanolamine (TEA) were prepared by mixing these two materials above 80 degrees C and then cooling. The crystalline composition and the structure and melting behavior of the resultant products were characterized with small-angle and wide-angle X-ray diffraction, thermal analysis, microscopy, and infrared spectroscopy. It was discovered that an acid-soap complex of 2:1 fixed stoichiometric ratio exists between stearic acid and TEA stearate. A binary phase diagram of stearic acid and TEA soap is built based on the experimental results; this is the first published record of a binary phase diagram for amine-based soap. Its behavior is significantly different from that of binary systems of fatty acid and alkali soap.
Subject(s)
Ethanolamines/chemistry , Soaps/chemistry , Stearic Acids/chemistry , Acids/chemistry , Crystallization , Crystallography, X-Ray , Hot Temperature , Infrared Rays , Spectroscopy, Fourier Transform Infrared , Temperature , X-Ray DiffractionABSTRACT
The kinetics of phase separation were observed in the gelatin/maltodextrin and gelatin/maltodextrin/gum arabic systems, where gum arabic was added as a minority component, using small-angle light scattering, turbidity measurement, and confocal scanning laser microscopy. Phase separation occurred by spinodal decomposition for quenches both above and below the temperature at which gelatin gelled. Coarsening of the phase-separated microstructure was hindered by gelation, and a hydrodynamic mechanism, observed when the gelatin remained in the liquid state, was suppressed. Gum arabic, containing both polysaccharide and polypeptide components, was hypothesized to be potentially interfacially active in the gelatin/maltodextrin system, in analogy with synthetic block copolymer compatibilizers in demixed synthetic polymer systems. The hypothesis was experimentally refuted under the chosen experimental conditions, as no evidence was found to suggest that it altered the phase separation behavior.
