Sensitivity-Enhancing Modified Holographic Photopolymer of PQ/PMMA

Abstract

Phenanthrenequinone-doped poly(methyl methacrylate) (PQ/PMMA) photopolymers are potential holographic storage media owing to their high-density storage capacities, low costs, high stability, and negligible shrinkage in volume holographic permanent memory. However, because of the limitations of the substrate, conventional Plexiglas materials do not exhibit a good performance in terms of photosensitivity and molding. In this study, the crosslinked structure of PMMA was modified by introducing a dendrimer monomer, pentaerythritol tetraacrylate (PETA), which increases the photosensitivity of the material 2 times (from ~0.58 cm/J to ~1.18 cm/J), and the diffraction efficiency is increased 1.6 times (from ~50% to ~80%). In addition, the modified material has a superior ability to mold compared to conventional materials. Moreover, the holographic performance enhancement was evaluated in conjunction with a quantum chemical analysis. The doping of PETA resulted in an overall decrease in the energy required for the reaction system of the material, and the activation energy decreased by ~0.5 KJ/mol in the photoreaction stage.

Keywords: dendritic crosslinker; high photosensitivity; holographic storage; photopolymer; quantum chemical analysis.

Figure 1

(a) Methyl methacrylate space structure (red: O atom; cyan: C atom; gray: H atom). (b) 2,2-azobis(2-methylpropionitrile) space structure (purple: N atom; cyan: C atom; gray: H atom). (c) Pentaerythritol tetraacrylate space structure (red: O atom; cyan: C atom; gray: H atom). (d) Phenanthraquinone space structure (red: O atom; cyan: C atom; gray: H atom).

Figure 2

(a) PQ/PETA-PMMA molding case (2 h baking). (b) PQ/PMMA molding case (20 h baking).

Figure 3

(a) Comparison between the diffraction efficiencies of PQ/PETA-PMMA and conventional PQ/PMMA. (b) Comparison of the optimal diffraction efficiency and photosensitivity of PQ/PETA-PMMA with those of conventional PQ/PMMA.

Figure 4

(a) Comparison between the diffraction efficiency of the modified and conventional materials with different baking times. (b) Comparison between the diffraction efficiency of the modified and conventional materials using different mass percentages of the crosslinking agent.

Figure 5

(a) FTIR spectra of the modified materials with different baking times. (b) FTIR spectra of the crosslinkers using different mass percentages of modified materials. (c) DSC curves of the modified materials with different curing times.

Figure 6

(a) FTIR spectra of double-bond changes during the PETA and PQ photoreactions. (b) Infrared spectra showing the functional group changes in PETA and PQ during the photoreaction of PETA with PQ. (c) Raman spectra of PETA and PQ indicating the formation of new bonds.

Figure 7

(a) Molecular surface electrostatic potential and extreme points of MMA. (b) Molecular surface electrostatic potential and extreme points of PETA. (c) Molecular surface electrostatic potential and extreme points of PQ. (d) Number of each atom in the PQ molecule. (e) PQ electron jump density (S₀ to S₁, isovalue: 0.01 a.u.). (f) PQ TDM (S₀ to S₁). (g) Energy of the PQ reaction with MMA. (h) Energy of the PQ reaction with PETA.

Figure 7

(a) Molecular surface electrostatic potential and extreme points of MMA. (b) Molecular surface electrostatic potential and extreme points of PETA. (c) Molecular surface electrostatic potential and extreme points of PQ. (d) Number of each atom in the PQ molecule. (e) PQ electron jump density (S₀ to S₁, isovalue: 0.01 a.u.). (f) PQ TDM (S₀ to S₁). (g) Energy of the PQ reaction with MMA. (h) Energy of the PQ reaction with PETA.

Figure 8

(a) Absorption of sheet-modified materials versus those of conventional materials. (b) UV–Vis absorption spectrum of PQ. (c) PQ electron excitation model. (d) Comparison of light reaction rates in the experiments.