Smart materials are defined as materials with properties engineered to change in a controlled manner under the influence of external stimuli. These external influences can include temperature, force, moisture, electric charge, magnetic fields and pH. Nanotechnology is rapidly entering the world of smart materials and taking them to the next level. Perhaps future nanotechnology enabled smart materials may be able to change and recombine much like the shape shifting cyborg in the movie Terminator 2.
Current Smart Materials
Existing smart materials are already an intrinsic part of modern society. These materials include:
• Piezoelectric Materials
• Thermoresponsive Materials
• Shape Memory Alloys
• Polychromic, Chromogenic or Halochromic Materials
Piezoelectric materials either produce a voltage when stressed or alter shape under the influence of an electric charge.
Thermoresponsive materials are sometimes also known as shape memory alloys or shape memory polymers. These materials alter their shape under the influence of the ambient temperature.
Magnetic Shape Memory Alloys
Like thermoresponsive materials that alter their shape under the influence of the ambient temperature, magnetic shape memory alloys change shape due to changes in magnetic fields.
Polychromic, Chromogenic or Halochromic Materials
Polychromic, chromogenic and halochromic materials all change colour due to external influences. These external influences can be alterations in pH, temperature, light or electricity. Materials that change colour due to temperature are normally known as thermochromic materials and those that alter due to light are photochromic materials.
Applications of Smart Nanomaterials
Smart nanomaterials are expected to make their presence strongly felt in areas like:
• Healthcare, with smart materials that respond to injuries by delivering drugs and antibiotics or by hardening to produce a cast on a broken limb.
• Implants and prostheses made from materials that modify surfaces and biofunctionality to increase biocompatibility
• Energy generation and conservation with highly efficient batteries and energy generating materials.
• Security and Terrorism Defence with smart materials that can detect toxins and either render them neutral, warn people nearby or protect them from it.
• Smart textiles that can change colour, such as camouflage materials that change colour and pattern depending upon the appearance of the surrounding environment. These materials may even project an image of what is behind the person in order to render them invisible.
• Surveillance using “Smartdust” and “Smartdust Motes” that are nanosized machines housing a range of sensors and wireless communication devices. Individually they can float undetected in a room with other dust particles. By combining the information gathered from hundreds, thousands or millions of these tiny specs can give a full report on what is occurring with the area including sound and images.
Nanotechnology Enabled Smart Materials
Initial nanotechnology influenced improvements to smart materials will be relatively simple changes to existing technologies. The future however holds possibilities for extremely complex solutions for producing not only smart materials but ones that are highly intelligent.
These new materials may incorporate nanosensors, nanocomputers and nanomachines into their structure. This will enable them to respond directly to their environment rather than make simple changes caused by the environment. As an example materials may be able to shape shift – comfortable, flexible clothing for motorcyclists could go rock hard if it detects an impact, or similar material worn by a police office could detect an approaching projectile and turn itself bullet proof. The current emerging technology of surface treatments for a wall that allows it to change colour might be impressive now, but what if the wall material could change itself to produce a window where and when required.