Janet Mary Smith

Gelation of silicone fluids using 1,3:2,4-dibenzylidene sorbitol

A variety of silicone fluids have been found to gel using low concentrations (typically < 4 wt.%) of 1,3:2,4-dibenzylidene sorbitol (DBS). DBS is known to be a chiral gelator for many organic solvents. Gels were formed when small amounts of DBS were introduced into the silicone fluids either by heating to high temperatures or at ambient temperatures with the use of a co-solvent. Optical and electron microscopy of neat silicon–DBS gels (concentration as low as 0.005 wt.%), revealed the formation of two types of fibrous network. One consisted of ribbon-like macrofibres (average width, ca. 2–3 µm) present in the opaque region of the gels and the other consisted of dense intertwined microfibres (average width, ca. 100 nm) present in the clear portion of the gels. The gels prepared in the presence of a co-solvent consisted only of the microfibrous network. N-Methylpyrrolidone was found to be a very effective co-solvent for the phenyl-containing siloxanes producing firm clear gels. Dynamic mechanical measurements indicated that the storage modulus (G′) of these gels increased with increasing DBS content over the range 1–6 wt.% DBS. Comparison with propylene glycol–DBS gels showed the silicone gels to differ in that they comprised mostly an isotropic phase with no detectable crystalline phase present.

Preparation and characterization of encapsulated solid particles, composed of partially hydrolysed aluminium and zirconium oxochlorides

Partially hydrolysed aluminium oxochlorides (ACH) and aluminium–zirconium–glycine oxochlorides (AZG) have been encapsulated using lipophilic carboxylic acids from H2O–silicone solvent systems. The encapsulated materials (E-materials) precipitate out of solution in the form of spherical beads. Their particle size varies with agitation conditions. Distributions from a few tenths to a few hundreds of micrometres are easily produced.ESCA sputtering experiments and elemental analysis indicate that the beads are composed of a water-soluble ACH or AZG inner core that is surrounded by a thin lipophilic shell a few angstroms in thickness. We believe that the encapsulant is held around the core via, hydrogen bonding and coulombic interactions. Atomic absorption spectrometry was used to measure the release rates of ACH and AZG from the E-materials in ethanol–water systems. The release rates are affected by the amount of H2O in the mixed solvents, the type of encapsulant, and the particle size of the beads.