Lattice-patterned LC-polymer composites containing various nanoparticles as additives

Abstract

In this study, we show the effect of various nanoparticle additives on phase separation behavior of a lattice-patterned liquid crystal [LC]-polymer composite system and on interfacial properties between the LC and polymer. Lattice-patterned LC-polymer composites were fabricated by exposing to UV light a mixture of a prepolymer, an LC, and SiO2 nanoparticles positioned under a patterned photomask. This resulted in the formation of an LC and prepolymer region through phase separation. We found that the incorporation of SiO2 nanoparticles significantly affected the electro-optical properties of the lattice-patterned LC-polymer composites. This effect is a fundamental characteristic of flexible displays. The electro-optical properties depend on the size and surface functional groups of the SiO2 nanoparticles. Compared with untreated pristine SiO2 nanoparticles, which adversely affect the performance of LC molecules surrounded by polymer walls, SiO2 nanoparticles with surface functional groups were found to improve the electro-optical properties of the lattice-patterned LC-polymer composites by increasing the quantity of SiO2 nanoparticles. The surface functional groups of the SiO2 nanoparticles were closely related to the distribution of SiO2 nanoparticles in the LC-polymer composites, and they influenced the electro-optical properties of the LC molecules. It is clear from our work that the introduction of nanoparticles into a lattice-patterned LC-polymer composite provides a method for controlling and improving the composite's electro-optical properties. This technique can be used to produce flexible substrates for various flexible electronic devices.

Figure 1

Chemical structures of the components for prepolymers. (a) EHA, PEGDA, and Darocur 4265 used for the preparation of prepolymers and (b) functionalized SiO₂ nanoparticles with BTMA and MPS.

Figure 2

Polarized optical microscope images of lattice-patterned LC-polymer composites containing non-functionalized SiO₂ nanoparticles as additives.

Figure 3

Polarized optical microscope images of lattice-patterned LC-polymer composites containing functionalized SiO₂ nanoparticles as additives.

Figure 4

The polymer wall thickness of lattice-patterned LC-polymer composites containing non-functionalized and functionalized SiO₂ nanoparticles.

Figure 5

Electro-optical properties of lattice-patterned LC-polymer composites containing non-functionalized SiO₂ nanoparticles as additives. The contrast ratio for a driving voltage of 12.5 V and the driving voltage corresponding to a contrast ratio of 30 in the case of lattice-patterned LC-polymer composites containing non-functionalized SiO₂ nanoparticles as additives.

Figure 6

Electro-optical properties of lattice-patterned LC-polymer composites containing functionalized SiO₂ nanoparticles as additives. The contrast ratio for a driving voltage of 12.5 V and the driving voltage corresponding to a contrast ratio of 30 in the case of lattice-patterned LC-polymer composites containing functionalized SiO₂ nanoparticles as additives.

Figure 7

Schematic diagram of the distribution of SiO₂ nanoparticles in lattice-patterned LC-polymer composites. (a) The mixture of an LC, a prepolymer, and SiO₂ nanoparticles, (b) the distribution of non-functionalized SiO₂ nanoparticles, and (c) the distribution of functionalized SiO₂ nanoparticles after photoinduced phase separation.