As we, in the northern hemisphere, find ourselves in the endlessly hot days of summer, relaxation and romance saturate the streetscape. Couples, hand in hand sharing ice creams, whispering sweet nothings, wander through the cities, meander along beaches. Tokens pass from one hand to another, flowers, chocolate, cards, symbols drenched in history… and cliché. For the romantic seeking a new way to express her love, a paper in Advanced Functional Materials might be worth a look.
A group from China have developed a new surface which enables the transport of drops of water using only light. They demonstrate the utility of this technique by tracing a love heart with a droplet of water (see left).
The surface is made from a complex array of materials, including a lubricant to aid droplet flow, and also iron oxide nanoparticles. The nanoparticles heat up by around 60 degrees Celsius when hit with a beam of near infra-red light. This generates a localized temperature gradient that impacts nearby liquid droplets in a number of important ways.
The heating of only one side of a droplet gives it a different surface tension from that of its other side. At the same time an internal ‘Marangoni’ flow is created within the droplet. Along with various other driving forces, these combine to push the droplet away from the heat source.
The authors demonstrate that a droplet of water can be pushed over their specialized surface to pick up 8 other droplets arranged in the shape of a love heart. They also show that liquids can be made to collect small bead of solid silica from one position and transport it to another (see below), opening the door to possible industrial applications.
Outside of offering a novel way to tell that special someone how you feel, the authors hope that this technology could find use in various fields, from microengines, to mass transport and the ‘laboratory on a chip’.