Light-induced deformation of side-chain azo-polymer: Insights from atomistic modeling

Abstract

In this study, we apply, for the first time, the fully atomistic force field approach to modeling light-induced deformations of azo-polymers, thereby establishing a relationship between macroscopic parameters and the microscopic molecular architecture of the used azo-polymers. We apply an orientation potential to mimic the illumination of the sample, in which the action of light is represented through controlled redistribution of azo-chromophores relative to the polarization direction. This strategy allows us to capture both the microscopic details of chromophore behaviour and the collective, anisotropic response of the polymer matrix. By combining these complementary perspectives, the simulations not only resolve the local mechanism of light-induced motion but also provide a pathway to bridge molecular-scale dynamics with mesoscopic deformation phenomena in azo-polymer films.

Figures (11)

• Figure 1: (a) The monomeric unit of azo-polyester with a stiff backbone and oxymethyl group as a spacer to azobenzene. (b) The monomeric unit of azo-polyacrylate with a flexible backbone and longer spacer to azobenzene consisting of ester- and ethyloxy group.
• Figure 2: Determination of T$_g$$\approx$ 450 K for two simulated chain lengths $N_{mol}=10$ (blue squares) and $20$ (red crosses).
• Figure 3: (a) Orientational order parameter $S_{azo}$ for $N_{mol}=20$ at $T=550$ K and different light-induced torques $V_0$. (b) The double-logarithmic plot shows that time evolution of the order parameter magnitude $|S_{azo}|$ exhibits three regimes : 1) initial delay in reorientation, 2) exponential growth, 3) slow approach to the steady state.
• Figure 4: (a) Orientational order parameter $S_{azo}$ for $N_{mol}=20$ at $T=400$ and different light-induced torques $V_0$. (b) The double-logarithmic plot shows that time evolution of the order parameter magnitude $|S_{azo}|$ exhibits three regimes: 1) slow exponential growth, 2) fast exponential growth, 3) slow approach to the steady state.
• Figure 5: (a) Orientational order parameter $S_{azo}$ for $N_{mol}=20$ at $V_0=10$ kcal/mol and different temperatures $T$. (b) The logarithmic plot shows the magnitude of order parameter $\ln|S_{azo}|$.