Recently J. Kim and
The actuation phenomenon of EAPap and its characteristics are illustrated in Figure below. EAPap is made with a cellulose film (cellophane) on which gold electrodes are deposited on both sides. An EAPap actuator was supported vertically in environment chamber
Figure : Concept of electroactive paper actuator (EAPap).
EAPap can be controlled the humidity and temperature. By excitation of voltage application to the actuator a bending deformation is evoked. The tip displacement of the EAPap actuator is dependent on applied electric field, its frequency, EAPap sample thickness and temperature but predominantly on humidity. The humidity affects the displacement, where a high relative humidity leads to a large displacement.
The authors believed that the
actuation is due to a combination of two mechanisms: ion migration and dipolar
orientation. Citied: “The
EAPap material has large regions of disordered cellulose chains, where water
molecules can be found attached to hydroxyl groups (see Figure). During the
Obviously, at first look, their explanation is wrong and irrational. At least a diffusion of sodium ions to cathode (not anode) is very slowly in comparison with practical observation of actuation.
Explanation according to SCHL theory
An orientation of water molecules in immobilised layers around cellulose macromolecules in stratified structure of EAPap actuator is determined by presence of proton donor groups or proton acceptor groups at their surfaces. The overall film structure and its shape are formed among structural cellulosic units due to both the hydrogen-bonding bridging in dry state and the hydration-bonding bridging in wet state. Extent and intensity of this bonding system is determined by size, concentration and distribution of nano-domains either with the attractive or the repulsive force action, i.e. among interacting opposite nano-surfaces with reversal or identical basic orientation of water molecules, respectively. The basic orientation of water molecule is given by presence of surface proton donor groups or proton acceptor groups of cellulose. Whilst hemiacetal and glycosidic oxygen in cellulose is typical proton-acceptor groups the hydroxyl groups can behave as proton-donor and proton-acceptor groups. Nevertheless, one is supposed that mostly behaviour of hydroxyl groups in cellulosic materials has more a proton-donor character.
In consequence of this preposition, the domains of prevailing hydration-bonding bridging are regularly distributed within cellulosic material with flat formation. In any case of disturbing this distribution, the paper strip curling is evoked because the inner tension equilibrium is broken. As schematically presented in Figure, by application of oriented electric field on cellulosic material in wet state the water molecules in bonding nano-domains contained nearest the electrodes are reoriented. However, reorientation at cathode is different of the reorientation at anode – at anode are reoriented only all the water molecules having been oriented to this pole with hydrogen atoms and at cathode only these ones having been oriented to this pole with oxygen atoms at basic origin state. Moreover, the distribution of attractive forces formed around both the A and D and the D and A nano-centres is not the same – it is supposed a prevailing A - D structure orientation in bonding domains. At this situation, an application of dc electric field is evoked a weaker bond system in layers laying near anode and vice-versa a stronger bond system in layers near cathode. Due to this effect the paper strip gets to bend to anode. Logically, the effect is strongly dependent upon relative humidity, the reorientation of water molecules is independent on diffusion process and it is relatively quickly.
Obviously, by similar effect, but in microscale, a muscles movement is possible to explain. The main preposition – the non-symmetrical distribution of attractive forces formed around both the A and D and the D and A nano-centres.
Schematically representation of water molecules reorientation in nano-localities around electrodes of electric input field.
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