EAPap actuation principle

To successfully transit cellulose EAPap actuators into these applications, it is crucial to ascertain the actuation principle responsible for the performance parameters. Based on the cellulose structure and our processing of the cellulose-based EAPap, we believe that the actuation is due to a combination of two mechanisms ion migration and piezoelectric effect associated with dipolar orientation. In the remainder of this report, we present experimental evidence of both. 

Cellulose EAPap material is composed of molecular chains with a dipolar nature. In particular, the crystal structure of cellulose II is monoclinic, which is noncentro-symmetric and exhibits piezoelectric and pyroelectric properties. To investigate the dipole effects in EAPap, thermally stimulated current (TSC) measurement was conducted (Hongo et al. 1996). The classical procedure in TSC includes (1) heating the sample to a given temperature (200°C) (2) applying 

Further investigation of the actuation behavior of EAPap material, x-ray diffraction (XRD) was tested on the cellophane EAPap sample before and after the electrical actuation. The cellophane EAPap actuator was activated for several hours, then it was removed from the power source and XRD was performed on the surface of the EAPap sample. XRD was measured with an x-ray diffractometer (D/MAX-2500, Rigaku). XRD patterns using Cu-Ka radiation at 40 kV and 30 mA were recorded using 20 = 5-80°. Eigure 18-7 shows the XRD results. Table 18-2 summarizes the XRD peaks before and after the actuation. After actuation, the (110) peak at 12.26° decreased to 12.08° while the (200) peak at 21.64° increased slightly to 22.02°. It is clear that the (110) peak sharpened after the actuation while the (200) peak was changed to blunt. This confirms that the first peak increased and the second peak decreased. 

Notice that the small peak at 16.78° started to appear after the electrical activation. This means that some structural change took place during the electrical actuation, which might be associated with the crystallization of disordered region. In other words, recrystallization of disordered cellulose of EAPap sample could be accelerated by molecular rearrangement during the electrical 

Peaks Before actuation After actuation Cellulose I Cellulose II 

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In the presence of an electric field, the sodium ions surrounded with free water molecules can move to the cathode. Selective ionic and water transport across the polymer under an electric field results in volumetric changes, which in turn lead to bending. When a DC electric field was applied, the cellulose EAPap actuator was bent to the positive electrode, which confirmed the above explanation. The ambient humidity effect on the EAPap actuator performance is further evidence, where ion transport is facilitated when humidity intake is higher. Thus, the actuation principle of cellulose EAPap might be a combination of piezoelectric and ionic migration effects associated with the dipole moment of cellulose material. 

The actuation principle of EAPap actuators was investigated in terms of ion migration and piezoelectric effects. To physically investigate the actuation mechanism, several tests were performed. TSC measurement showed a linear relationship of depolarized current with the applied electric field, indicating dipolar orientation. By comparing XRD spectra before and after electrical activation, the possibility of recrystallization in the cellulose material was observed. Dielectric property measurement indicated a dependence of the dielectric constant on fiber direction. Thus, we conclude that the combination of piezoelectric effect and ionic migration effect might be the actuation principle. 

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