Effect of surface condition on liquid crystal photoalignment by light-induced azo dye adsorption phenomena

Abstract

The effect of surface condition on the photoalignment of light-induced methyl red (MR) adsorption phenomena on various substrates based on azo dye-doped liquid crystals is investigated. The results show that the polar surface energy determines the initiation of MR adsorption phenomena. The surface polarity energy of different substrates, which are modulated by oxygen plasma treatment (OPT), is further examined using the sessile drop method. The results also indicate that the uniformity and efficiency of MR adsorption can be enhanced by OPT. Light intensity influences the MR adsorption rate. The uniformity of MR adsorption onto various substrates is analysed via polarised optical microscopy. ARTICLE HISTORY

Understanding of Face-On Crystallites Transitioning to Edge-On Crystallites in Thiophene-Based Conjugated Polymers

“…Another factor that is believed to affect molecular packing and orientation is the polymer/substrate interface . To investigate the possible impact of such an interface on the re-orientation observed in the case of RP-3T, we further applied GIWAXS to characterize RP-3T films coated on two additional substrates, bare glass (surface energy of bare glass: 63.9 mJ/m 2 ) and PEDOT:PSS-coated glass (surface energy of PEDOT:PSS: 71.65–73.43 mJ/m 2 ); all such films were annealed under the same condition used to prepare otherwise identical films on Si wafers (surface energy of Si wafer: 54.1 mJ/m 2 ) . GIWAXS patterns of these films show a very similar tendency (i.e., face-on crystallites start to disappear at 170 °C, inducing the re-orientation of crystallites from face-on orientation to edge-on orientation) as we observed for RP-3T films on Si wafer (Figure S8).…”

Dyes as guests in ordered systems: current understanding and future directions

“…[8] The incorporation of dyes that undergo photochemical isomerisation into guest-host systems gives scope for their use in optical storage devices, [9] as well as their use in optically controlled diffraction gratings that exhibit high efficiency and rapid response times, [10] and use as active components for the photoalignment of liquid crystals. [11][12][13] The use of multiple cells with a variety of surface alignment orientations containing guest-host mixtures can yield devices with complex polarised absorption properties, and such systems have been proposed for use in security devices. [14] Electrically switched guest-host devices have also been suggested for use within applications outside of displays, such as in smart windows using polymerdispersed liquid crystal hosts that enable the transmittance of the windows to be electrically controlled.…”

pH Tunable Thin Film Gradients of Magnetic Polymer Colloids for MRI Diagnostics

“…The values of contact angle and their corresponding surface energies are given in Table 3 . As can be seen clearly that as the contact angle decreases with the increase of the number of bilayers in all samples due to an increase in surface roughness and their corresponding surface energy increases [ 49 ]. The surface energy is an important parameter that will determine not only the change in hydrophilic properties of films but also other properties like adhesion of water molecules to the surface and frictional forces at the interface [ 50 ].…”