Tuning the Optical and Electrical Properties of Polymer-Based Nanocomposites by Plasmon-Induced Electromagnetic Field

Significance 

The synergistic effect between different construction materials endows composite materials with unique properties. For polymer-based nanocomposites, the arrangement of nanoscale materials within the polymer matrix results in special optical and electrical properties desirable for various applications. Different strategies have been adopted to fabricate polymer-based nanocomposites with controllable and desirable properties. This requires good control of the nanoscale material arrangement within the polymer matrix.

Inorganic nanocrystals in the polymer matrix are commonly used to fabricate large-scale and flexible nanocomposites with excellent electrical conductivity, which strongly depends on the metal nanocrystal arrangement in the matrix. For instance, nanocomposites with well-dispersed metal nanocrystals have higher electrical conductivity than those with agglomerated nanocrystals. Consequently, those fabricated by filling noble metal nanocrystals in polymer matrix exhibit unique electrical properties. Overall, the shape and size of the nanocrystals and their arrangement in the polymer matrix play a fundamental role in manipulating the properties of the resulting nanocomposites. However, the effect of EF around plasmonic nanocrystals on the electrical and optical properties of these nanocomposites under light irradiation is sparsely explored. Particularly, there are no reports on the effects of polymer alignment on the electrical and optical properties of plasmonic metal-polymer nanocomposites.

On this account, Mr. Shih-Lun Peng and Mr. Gang-Yi Chen and led by Professor Su-Wen Hsu from Nation Cheng Kung University systematically studied the effects of plasmon-induced localized EF around nanocrystals on the electrical and optical properties of polymer-based nanocomposites under light irradiation. The nanocomposites were fabricated by dispersing highly anisotropic nanocrystals, specifically silver nanocubes, in a conducting polymer matrix. Additionally, highly conductive polymers poly-p-TPA and PVK and nonconductive polymer polystyrene were used as matrices to investigate the influence of plasmonic-induced EF on the silver nanocrystal environment. The work is now published in the journal, Advanced Materials Interfaces.

The research team showed that the dielectric constant change in the polymer matrix was only present in conducting polymers like poly-p-TPA and not in nonconducting polymers like polystyrene. Under light irradiation, the electrical conductivity of the polymer nanocomposite in the plasmonic mode was higher than its nonconducting counterpart. The optical properties were mainly influenced by the “local” and “overall” dielectric environment of the nanocomposites. The plasmon resonance wavelengths of nanocomposites composed of conducting polymers used as ligands and polymer matrices showed a significant change characterized by blueshift ~ 10 nm under plasmon-induced EF. The changes in the dielectric environment were attributed to the realignment of the polymer chains of the polymer matrix and ligands along with EF around the plasmonic nanocrystals.

The authors’ findings showed that the electrical conductivity of the nanocomposites fabricated in conducting polymer matrix increased by three orders of magnitude under plasmon-induced EF. The polymer matrix and the intrinsic electrical conductivities of the coated ligands played a fundamental role in tunning and controlling the nanocomposite properties under external stimuli. While the electrical properties of the nanocomposites were only affected by the matrix, the plasmonic resonance could be tuned by altering the matrices or the ligands coated on the nanocrystals.

In summary, the new study demonstrated the tunability of the optical and electrical properties of plasmonic nanocrystal–polymer nanocomposites under plasmon-induced EF. The choice of silver nanocrystals as the building block for the nanocomposites was attributed to its outstanding plasmon resonance properties induced by the strong localized EF and plasmonic interaction with light. The electrical and optical properties of the nanocomposite were highly sensitive to the external environment. In a statement to Advances in Engineering, Professor Su-Wen Hsu said the generated plasmonic nanocrystal polymer nanocomposites are potential candidates for application in photonic sensors and electromagnetic fields.

Reference

Peng, S., Chen, G., & Hsu, S. (2022). Tuning the Optical and Electrical Properties of Polymer‐Based Nanocomposites by Plasmon‐Induced Electromagnetic FieldAdvanced Materials Interfaces, 9(15), 2200089.

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