Printing small dots from large drops.

Printing of droplets of pure solvents containing suspended solids typically leads to a ring stain due to convective transport of the particles toward the contact line during evaporation of the solvent. In mixtures of volatile solvents, recirculating cells driven by surface tension gradients are established that lead to migration of colloidal particles toward the center of the droplet. In favorable cases, a dense disk of particles forms with a diameter much smaller than that of the droplet.

Effect of film thickness and particle size on cracking stresses in drying latex films.

The stress at which latex films crack during drying was investigated using beam bending. Two systems were investigated: (i) poly(methyl methacrylate/butyl acrylate) particles cast as thin films to examine the effect of film thickness on cracking film stress and (ii) polystyrene particles dried as drops to investigate the effect of particle size. Results indicated an inverse relationship between film thickness and film stress, whilst film stress was shown to be independent of the original particle size.

Evolving stresses in latex films as a function of temperature.

Latex films were dried on a flexible substrate, and the substrate deflection was monitored over time to give an averaged film stress-evolution profile. Films were dried at various temperatures below and above the minimum film-formation temperature of the latex dispersion. The effect of polymer rheology, which is a temperature-dependent parameter, on film formation, was investigated.

Dye diffusion from microcapsules with different shell thickness into mammalian skin.

Oil-in-water microcapsules with varying shell thicknesses were fabricated via a coacervation technique, whereby evaporation of volatile solvents induced the shell-forming polymer to precipitate, phase separate and migrate to the oil/water interface to form microcapsules. These microcapsules encapsulated a lipophilic dye within their cores and were applied topically onto porcine skin for 6h. Results indicated that the dye preferentially accumulated within the skin furrows and hair follicles, though the dye did not penetrate beyond the stratum corneum.

Release profiles of encapsulated actives from colloidosomes sintered for various durations.

This paper presents the formation of low temperature colloidosomes from colloidal poly(styrene-co-butyl acrylate) particles for both water-in-oil and oil-in-water systems. An investigation into the sintering conditions examines the ultimate shell morphology formed, with longer sintering times and higher sintering temperatures producing less porous microcapsules. This has been verified by the release of an encapsulated dye from the aqueous core microcapsules, in which slower release has been detected for longer sintering times.

Anomalous viscosity jump during the volume phase transition of poly(N-isopropylacrylamide) particles.

Dilute dispersions of cross-linked poly(N-isopropylacrylamide) (PNIPAM) microgels are studied by viscosity at low stress, dynamic light scattering and microelectrophoresis. The rheological measurements at low stress demonstrate that upon heating through the volume phase transition temperature (VPTT) there is a stress-dependent increase in viscosity that passes through a maximum before falling close to the value of water. On cooling only a much smaller viscosity rise is seen in the region of the VPTT.

Formation of liquid core-polymer shell microcapsules.

Polymer shell microcapsules with liquid cores are used in a wide variety of industries, from food and flavour protection to inkless paper. There is a number of production methods, each with different characteristics and this article reviews a number of them. The methods considered are colloidosome formation, polymer precipitation by phase separation, polycondensation interfacial polymerisation, layer-by-layer polyelectrolyte deposition, polymer growth by surface polymerisation and copolymer vesicle formation.