Figure 3.

Schematic illustrations describing the temperature-responsive shape changing properties of hydrogels, liquid crystal networks, shape memory polymers, and the working principle of a light responsive molecular switch. (A) An example of an insoluble polymer network which below the LCST retains significant amounts of water. In transitioning through this LCST the network becomes hydrophobic as the intermolecular bonds are disrupted and the network shrinks considerably. (B) A uniaxially aligned liquid crystal network manifests anisotropic thermal expansion by axial contraction and transverse expansion at elevated temperature. (C) A shape memory polymer can be deformed manually into a “programmed” shape. The polymer chains are then immobilized through cooling, and the deformed shape is “memorized” after unloading and can be recovered by heating the polymer. (D) The light-sensitive azobenzene absorbed electromagnetic radiation to isomerize from the extended trans isomer to the unstable cis isomer. The length of the anisotropically shaped molecules is significantly reduced in this isomerization. The reverse isomerization occurs when exposed to a different (longer) wavelength of light or by heating.