Introduction
Photomobile polymers composed of azobenzene molecules (PMP-Azo) possess specific properties for photomechanical conversion. The mechanical deformation of these devices is based on the photoisomerization principle:
- Under U.V. light exposition the azobenzene molecules switch to “cis” form and the sample curves,
- Exposed to a wavelength above 405 nm the molecules revert back to their initial “trans” form.
This phenomenon is coupled with thermomechanical deformation. Indeed, the PMP-Azo sample is heated because of the light absorbance properties of the material.
Tests description
The samples are alternatively illuminated with UV (385 nm) and visible light (470 nm). The frequency of excitation is monitored by an acquisition board and the displacement of the samples is measured at its tip by a vibrometer laser featuring nanometric resolution.
Figure 1 (c) shows the displacement measurements versus time for several frequencies of excitation from 1 Hz to 25 Hz. It is noticeable that the stroke of the device is reduced with the time of illumination which suggests that it is possible to control the position of the device by adjusting the exposition time.
The thermomechanical effect is also observed. The main consequence is the superposition of a logarithmic curve on the stroke value. This is likely to hinder the control of the device but it could be compensated to some extent (an idea would be to heat the device prior to its usage to set up the initial position).
Figure 1 – PMP-Azo sample tip displacement measurements under UV light (a) and blue light (b) exposure alternance
Applications
These preliminary tests confirms the possibility of the PMP-Azo to be integrated in an optical micro-switch application. The sample is indeed covered with copper which gives it interesting electrical properties that must be further investigated.
