Tuning Surface Plasmon Band Shift Of Gold Nanopatricle Film By Phase Change Of Liquid Crystals

As incident photon frequency is resonant with the collective oscillation of theconduction electrons for noble metal nanoparticles on the surface of metalnanostructures or other nanostructures, an obvious surface plasmon absorption bandknown as localized surface plasmon resonance (LSPR) is produced. It has been appliedon the chemical sensing, environmental monitoring, biomedical imaging and polymersurface analysis. Coupling the metal nanostructures which can produce LSPR withstimulus-responsive materials can also be used to prepare stimulus-responsive opticalcell.Among a large quantity of commonly used stimulus-responsive materials, Liquidcrystals (LCs) attract much attention for its electro-optic and thermal-optic effect,together with the phase transition. As an outstanding medium example of anelectro-optically active dielectric medium, it has major applications in displays, opticalperiodical structures and color tunable polymer gratings. When immersed in liquidcrystals, the LSPR of the metal nanostructures can be regulated through the control ofthe optical properties of liquid crystal, achieving the applications of this coupled metallicnanostructures-LC optical devices in the display areas and controllable electro-opticaldevice.In this paper, we first prepare gold nanoparticles by liquid phase synthesis, and thegold nanoparticle film is prepared by horizontal lifting of gold nanoparticles to the SiO2substrate. By adjusting the annealing temperature, the gold nanoparticles couple with eachother and dewet, and the wavelength and the intensity of the LSPR can be controlled. Thenthe LCs is covered to the surface, by changing the LCs molecurlar arrangement, therefractive index can be changed so the LSPR shift. Coupling metal nanoparticles with LCswe can prepare optical cell, which also possess surface plasmon resonance. By changing thestimuli to the Liquid crystal, such as the electric field intensity, angular of the light incidence and temperature, we can achieve the tuning LSPR of the gold nanoparticles. Bychanging the input voltage, the liquid crystal molecules rearrange, the refractive indexaround the gold nanoparticle changes, and LSPR shifts. This tuning behavior is achievedwhen the electric field intensity is very low, thus it provides an effective and economic wayto research on liquid crystals. Using birefringence of liquid crystal, and by changing theangle of the incidence, we find that after the introduction of liquid crystal, the sensitivity ofLSPR detection is amplified. This may provide a new method for the research on the tinyand indistinct change of the gold nanoparticles’ LSPR, and it also provides a new approachfor the future to achieve lower detection limit of the LSPR. For the thermal response ofliquid crystals, we find an intuitionistic way to sense the LCs’ temperature dependence bythe LSPR shift, and also the clear point of an unknown LC or the mixture can be intuitivelypredicted by the LSPR peak. It also should be mentioned that under the condition of theexternal electric field or temperature, the phase change of liquid crystal occurs, resulting therefractive index change on the metal surface, thereby enabling the position and intensity ofLSPR surface changes. This stimulus-response of the optical properties change possessesgood reversibility, and the optical cell possesses good repeatability. Coupled with simplepreparation and easy-obtained reactants, it has potential applications in areas such assensing and displays.