Dependence of Piezoelectric and Pyroelectric Activities of Aromatic Polyurea Thin Films on Monomer Composition Ratio

Abstract

Thin films of aromatic polyurea were prepared by simultaneous deposition of 4,4'-diamino diphenylmethane (MDA) and 4,4'-diphenylmethane diisocyanate (MDI) on a polyimide film substrate. By changing the evaporation temperature of the monomers, the monomer molar ratio of MDA to MDI of the deposited film was varied to yield MDA-rich, balanced, and MDI-rich films. After poling, the balanced films exhibited the maximum values of pyroelectric and piezoelectric constants, which were stable up to 200°C. Elemental analysis confirmed that oligomers consisting of about five monomers were present in as-deposited films. In the balanced films, an exothermic peak appeared at about 110°C in the first run of DSC measurements and the IR absorption peak due to isocyanate groups disappeared after heat treatment. These results suggest that during the poling process polymerization of oligomers, which forms polar urea bonds, takes place at about 110°C under a high electric field. The large residual polarization thus produced leads to high pyroelectric and piezoelectric activities.

Electric power generation using vibration of a polyurea piezoelectric thin film

“…Unlike a polyvinylidene fluoride (PVDF) film, which requires stretching in a wet process, the polyurea film can be formed using a dry process, and both multi-layered and thin films can be fabricated. The piezoelectric g constant of polyurea is larger than that of PVDF [10][11][12]. In addition, polyurea films can conform to arbitrary configurations, such as curved surfaces, and be embedded in a microelectromechanical system (MEMS).…”

“…Large stress associated with large deformation can be applied to a flexible polyurea film, in contrast to PZT, which has low fracture stress. Although the piezoelectric d constant of polyurea is smaller than that of the PZT ceramics [10][11][12], it can be improved by multi-layering. Investigations of our group have focused on applications of polyurea piezoelectric films, in particular, a multi-focusing thin film transducer [13], a multi-layered transducer [14], an arrayed ultrasonic transducer fabricated by a photolithography process [15] and a 3D acceleration sensor [16].…”

Electric Double Layer Gate Field-Effect Transistors Based on Si

“…Following the previous reports on the codeposited films [12][13][14] , we applied thermal treatment showing the completion of the polymerization reaction 13) . The optical transparency and surface morphology of the film did not change after the thermal treatment.…”

“…They are potentially applicable as key components of flexible memories [2][3][4][5][6] , transducers 7,8) , power sources 9,10) , and printable thermal sensors 11) . Polyurea (PU) has unique characteristics among the piezoelectric polymers because it can be fabricated by vapor deposition polymerization without by-products [12][13][14][15][16] . The high dipole moment (4.9 D) in its unit structure coming from the urea bond is also attractive because the strength of spontaneous polarization strongly depends on the dipole moment.…”

Low-Temperature Polymer Bonding Using Surface Hydrophilic Treatment for Chemical/Bio Microchips

“…In Fig. 8, the as-deposited polyurea film of only about five monomers (n = 5) is formed at room temperature (Wang et al, 1993). Further polymerization takes place (n > 5) when asdeposited films are annealed (without any surface treatment) by consuming the unreacted (Shinohara et al, 2009a) polymer tails to form amid bonds (Takahashi et al, 1991).…”