The ability to induce localized heating with desired location and intensity in a complex solid is of great interest to pyrotechnics, explosive handling and material fabrication in general. However, it is so far a rarely achieved feat as typical energy sources, such as laser, electric current and shockwaves, are either non-selectively destructive or limited to specific material compositions. On the other hand, ultrasonic wave is a relatively weak energy but may induce dramatic thermo-mechanical effect if localized in a small region. Such effect has been utilized in ultrasonic welding, and in the clinical removal of tumors by a focused ultrasonic beam. However, how ultrasound could induce localized heating at the interior of a bulk material remains barely explored. In this work, we managed to generate well-controlled hot spots in polymeric composites using ultrasound and study their dynamics with a thermal imaging microscope. It was revealed that ultrasonic energy spontaneously and exclusively concentrates on delaminating polymer-particle interfaces, with local heating up to 30,000 K/s in sub-mm scale, while the rest of the material remains cool and undisturbed. Hot spot locations could hence be precisely controlled by manipulations on interfacial adhesion, and hot spot intensity could be controlled by ultrasonic energy input. Insights this work provides open up possibilities for a new degree of control on the thermal events as well as chemical reactions inside confined polymeric composite structures.

Ultrasonic hot spots in polymeric composites

248th National Meeting (2014)

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