Bernard P. Binks (Hull)
The scientific achievements of Bernard P. Binks are out-
standing; he is one of the best-known members of the Colloid
and Interface Science community. His first work with micro- emulsions revealed his research style: to address complex prob- lems and find remarkably clear solutions, paving the way for future work. He is successful in areas, where many others spent years of investigations in vain. His fundamental research soon attracted industrial interest, prompting him to patent several discoveries, which subsequently led to efficient industrial processes.
Binks is best known for his Pickering (particle-stabilized) emulsion work, that he start- ed at the end of the 90’s. At that time, the field, despite being old, was rather unex- plored. He decided to commence systematic studies on well-defined systems in order to establish the basic rules governing the replacement of surfactants (then currently used to stabilize emulsions) by particles. He completely renewed the field, using his deep knowledge on surfactants and a wise choice of stabilizing particles. His early work es- tablished the conditions necessary to stabilize oil+water emulsions with particles alone. He showed the importance of particle wettability on both emulsion type and stability, and suggested the link with the energy of detachment of a single particle from the in- terface. He put forward the two main and accepted mechanisms of emulsion stabiliza- tion by particles: bilayer formation or bridging monolayer formation, dependent on par- ticle wettability.
Binks demonstrated how emulsion inversion could be achieved by simple variation of the oil/water ratio, which is impossible using surfactants. He developed a theory for the contact angle of a particle at an interface, that he applied in studies on emulsions of perfume oils and water; this has been extensively used since in predicting emulsion type. He also clarified the phenomenon of limited coalescence in Pickering emulsions. Other notable work included an interferometric method for determining the particle contact angle directly and studies on clay, microgel, starch and natural spore particles, stimuli- responsive particles, stable multiple emulsions, bicontinuous jammed emulsion gels. Re- cently, he has established the conditions necessary to stabilize emulsions of immiscible oils and has begun work on water/water emulsions.
Binks extended his emulsion work to particle-stabilized foams, rapidly attracting inter- est by researchers involved with minerals flotation. These foams also act as precursors of porous solid foams, of current interest in car industry as shock absorbers/bumpers. He set forth conditions where particles halt both disproportionation and coalescence insta- bilities, which prevail with surfactant foams. He showed for the first time the phase in- version of an air-in-water foam to a water-in-air powder, something not achievable with surfactants. Dry water has great interest for food and cosmetics companies, as water can be delivered on demand by gentle shearing. Combining Pickering emulsions with dry wa- ter technology enabled Binks to produce stable powdered emulsions, in which oil (water) drops are dispersed in water (oil) themselves dispersed in air. Dry water was commercial- ized in 2009 by Shiseido as a cosmetic (Benefiance Luminizing Powder-C Essence). Since his pioneering studies, interest has grown enormously and a number of companies are now exploiting the technology.
Binks extended his work to functionalizing particles in situ by addition of suitable sur- factants; such systems are now included in many commercial formulations. Recently, he used a novel surfactant whose behavior can be switched between being surface-active or surface-inactive using CO2 or N2 gas. Such switching can be transferred to silica particles stabilizing emulsions. He thereby prepares unique switchable emulsions, that are readily stabilized or destabilized by the use of a simple trigger. This idea has also been extended to switchable foams with success.