Glue with an On and Off switch

Researchers at the University of Sheffield, in the UK, have made an adhesive that can be turned on and off with an external switch. The switch is the acidity of the solution surrounding the glue: two different kinds of polymers in the glue attract each other based on the solution's acidity. By repeatedly making the solution less or more acidic, Mark Geoghegan and his colleagues can switch the adhesive's stickiness, making two surfaces bond together and then come apart up to five times

http://www.technologyreview.com/Nanotech/19120/