Analyses of the Diffraction Efficiencies, Birefringence, and Surface Relief Gratings on Azobenzene-Containing Polymer Films

Abstract

Dynamical experimental studies on the diffraction efficiencies and the formation of birefringence grating and surface relief grating on doped and/or covalently bonded azobenzene derivatives containing polymer films were carried out using laser beams with different polarizations. From polarization analyses of the first-order ((1) diffracted beams, the contributions to the diffraction efficiency are separated into an anisotropic (or birefringence) part and a surface relief part. During the growth of the gratings the dynamical responses of both contributions appear to be quite distinct, and estimates of the time variations of the anisotropic phase shift, ∆ , due to the induced birefringence and of the surface relief height, 2∆d, due to the polymer mass transport are obtained. Calculations and simulations of the theoretical expressions allow us to confirm the experimental findings and to reproduce all the observed polarized first-order diffraction curves with good agreement, even when the surface relief is important in the covalently bonded azobenzene polymer films. In these functionalized systems we thus conclude that very efficient permanent surface relief gratings are formed using right-circular and left-circular interfering laser beams.

Rigid and flexible azopolymers modified with donor/acceptor groups. Synthesis and photochromic behavior

“…The precise identification of the parameters influencing the surface structure is not an easy task and will need further experiments involving azo-polymers with different donor/acceptor groups and substitution degrees, in order to selectively modify each feature of the materials. Additionally, the investigation of the relative contributions of the birefringence grating, resulting from the photoinduced azobenzene molecules angular redistribution, and the surface grating can be an efficient tool in understanding the influence of the material chemical structure on the nano-structuration mechanisms [33][34][35]. Preliminary tests to determine the ability of the azopolysiloxanic films to support cell growth were also performed using the HepG2 and HeLa cell lines, of human hepatic and epithelial origin.…”

Light-Triggered Formation of Surface Topographies in Azo Polymers

“…Furthermore, most SRGs do not show erasure during a second illumination below the glass transition. Utilizing azo dye-doped polymers [33,34], the gratings are not formed by migration of the polymer chain, but rather by the movement of the azobenzenes themselves, and the resulting structures are very weak. The first reported gratings [35,36] formed by azobenzene-containing polymers were side-chain azo polymers.…”

“…This light-initiated erasure of the gratings is more appealing than thermal erasure due to its capability of generating "on" and "off" states that can be controlled remotely, affect the film locally, and on-demand. Numerous efforts have been made to remove gratings remotely by light, but generally have resulted in no or only partial erasure [34,65,[87][88][89]. As described by Priimagi and co-workers, the ability to affect light-induced erasure seems to depend highly on the material's properties (including glass transition temperature, molecular weight, and so on) [90].…”

“…Generally, the erasure process, or the ability to erase a SRG from a polymer coating, is expected to be related to the chemical structure, molecular weight, photo-orientation and photoinduced mechanical changes in the materials [90]. generally have resulted in no or only partial erasure [34,65,[87][88][89]. As described by Priimagi and coworkers, the ability to affect light-induced erasure seems to depend highly on the material's properties (including glass transition temperature, molecular weight, and so on) [90].…”

“…Solid, light induced surface structures can be made in both linear and cross-linked polymer network materials containing azobenzene molecules without the need of a solvent (Figure 1b). Azo-containing polymers can range from azo dye doped [33,34], to azo side-chain [35][36][37], to azo main-chain amorphous polymers, and even azo functionalized LC polymers. The interaction of the chromophore and the polymer skeletal structure determines the efficiency of the topography formation.…”