Carbon Nanotube Based Polymeric Composites—A Review

Since they have the ability to act as both a sensor and an actuator, piezoelectric materials have been described as a ‘natural’ smart material. With the development of piezoceramic fibers and fabrics, functional composites consisting of these fibers within a polymeric matrix will allow designers to construct electromechanical devices having unique or superior characteristics. An essential need of these designers is the ability to predict the piezoelastic response of such composites. Recently, an analytical model has been developed to predict the effective piezoelastic properties of woven, braided and unidirectional piezoceramic fiber/polymer matrix composites. Piezoceramic fiber composites offer the possibility of achieving property gradients within an electromechanical device by varying the volume fraction of fibers throughout the matrix. This may prove helpful in solving some problems seen in the development of very large displacement actuators. Existing designs utilize the longitudinal strain of a piezoelectric element by coupling it to an inactive layer (unimorph) or a piezoelectric layer straining in the opposite direction (bimorph), which results in bending. While typical bender actuators utilize piezoelectric elements having a basic structural shape, such as disk, rod or plate, advances in ceramics processing techniques, such as the Fused Deposition of Ceramics (FDC) have allowed the production of piezoceramic elements of novel geometries. Current research has focused on utilizing these novel geometries to maximize actuator displacement and results show very large displacements are possible when using spiral shaped actuators. Additional studies indicate that spiral actuators using a bimorph configuration have tremendous potential. The performance of these layered or laminated actuators is dependent on the adhesive bond between the layers. Deterioration of the bond results in a rapid decrease in the actuator properties. It is thought that the ability to process property gradients within a device, deleterious stress concentrations between layers can be minimized.