The behavior of monolayers of monodisperse prolate ellipsoidal latex particles with the same surface chemistry but varying aspect ratio has been studied experimentally. Particle monolayers at an air-water interface were subjected to compression in a Langmuir trough. When surface pressure measurements and microscopy observations were combined, possible structural transitions were evaluated. Ellipsoids of a sufficiently large aspect ratio display a less abrupt increase in the compression isotherms than spherical particles. Microscopic observations reveal that a sequence of transitions is responsible for this more gradual increase of the surface pressure. When a percolating aggregate network is used as the starting point, locally ordered regions appear progressively. When it reaches a certain surface pressure, the system "jams", and in-plane rearrangements are no longer possible at this point. A highly localized yielding of the particle network is observed. The compressional stress is relieved by flipping the ellipsoids into an upright position and by expelling particles from the monolayer. The latter does not occur for spherical particles with similar dimensions and surface chemistry. In the final stage of compression, buckling of the monolayer as a whole was observed. The effect of aspect ratio on the pressure area isotherms and on the obtained percolation and packing thresholds was quantified.

A control over the nature of deposit pattern obtained after the evaporation of solvent from a sessile drop containing dispersed materials has been demonstrated to have applications in materials engineering, separation technology, printing technology, manufacture of printed circuit boards, biology, and agriculture. In this article, we report an experimental investigation of the effect of particle shape and DLVO (Derjaguin-Landau-Verwey-Overbeek) interactions on evaporation-driven pattern formation in sessile drops. The use of a model system containing monodisperse particles where particle aspect ratio and surface charge can be adjusted reveals that a control over the nature of deposit pattern can be achieved by tuning the particle-particle and particle-substrate interactions. A clear coffee-ring formation is observed when the strength of particle-particle repulsion is higher than the particle-substrate attraction. However, complete suppression of ringlike deposits leading to a uniform film is achieved when particle-substrate and particle-particle interactions are attractive. Results illustrate that for the system of submicron ellipsoids that are hydrophilic, the nature of deposit patterns obtained after evaporation depends on the nature of interactions and not on particle shape.

The recent surge to explore and exploit the effect of particle shape has led to several interesting and unique observations in various diverse fields, ranging from biology to material science. To this end, the development of novel synthesis methods has contributed immensely, and has directed this exciting research on the role of particle shape in colloidal systems and other diverse fields. Furthermore, such investigations have resulted in the development of advanced materials, which are novel and multifunctional. In this article, we review recent advances in the study of suspensions containing shape anisotropic particles. In particular, we investigate those pertaining to rod-like or ellipsoidal particles and highlight recent results in three areasevaporation driven assembly, packing, interfacial behavior and the use of these particles in emulsion stabilization.

In this study we explore the fundamental aspects of Pickering emulsions stabilized by oppositely charged particles. Using oppositely charged latex particles as a model system, Pickering emulsions with good long-term stability can be obtained without the need for any electrolyte. The effects of parameters like oil to water ratio, mixed particle composition, and pH on emulsion type and stability are explored and linked to the behavior of the aqueous particle dispersion prior to emulsification. The particle composition is found to affect the formation of emulsions, viz., stable emulsions were obtained close to a particle number ratio of 1:1, and no emulsion was formed with either positively or negatively charged particles alone. The emulsions in particle mixtures exhibited phase inversion from oil-in-water to water-in-oil beyond an oil volume fraction of 0.8. Morphological features of emulsion droplets in terms of particle arrangement on the droplets are discussed.