Squeezing a drop of nematic liquid crystal with strong elasticity effects

Abstract

The One Drop Filling (ODF) method is widely used for the industrial manufacture of liquid crystal devices. Motivated by the need for a better fundamental understanding of the reorientation of the molecules due to the flow of the liquid crystal during this manufacturing method, we formulate and analyse a squeeze-film model for the ODF method. Specifically, we consider a nematic squeeze film in the asymptotic regime in which the drop is thin, inertial effects are weak, and elasticity effects are strong for four specific anchoring cases at the top plate and the substrate (namely, planar, homeotropic, hybrid aligned nematic (HAN), and π-cell infinite anchoring conditions) and for two different scenarios for the motion of the top plate (namely, prescribed speed and prescribed force). Analytical expressions for the leading-and first-order director angles, radial velocity, vertical velocity, and pressure are obtained. Shear and couple stresses at the top plate and the substrate are calculated and are interpreted in terms of the effect that flow may have on the alignment of the molecules at the plates, potentially leading to the formation of spurious optical defects ("mura").

Young and Young–Laplace equations for a static ridge of nematic liquid crystal, and transitions between equilibrium states

“…The range of anisotropic wetting and dewetting phenomena occurring in this nematic system may also be useful from a technological perspective; for instance, for tailored dewetting of liquid films, as discussed in §1 [2,6,19,44,45]. The variety of possible transitions between two-dimensional equilibrium states will have similar forms in three dimensions, which may be relevant to applications such as the one-drop-filling method of LCD manufacturing [66–68] and adaptive-lens technologies [4,5]. In order to explore such applications, further theoretical and experimental investigations, particularly into the dynamics of transitions, would be needed.…”

Young and Young--Laplace equations for a static ridge of nematic liquid crystal, and transitions between equilibrium states

“…The range of anisotropic wetting and dewetting phenomena occurring in this nematic system may also be useful from a technological perspective, for instance, for tailored dewetting of liquid films, as discussed in Section 1 [2,6,18,41,42]. The variety of possible transitions between two-dimensional equilibrium states will have similar forms in three dimensions, which may be relevant to applications such as the One Drop Filling method of LCD manufacturing [64][65][66] and adaptive-lens technologies [4,5]. In order to explore such applications, further theoretical investigations, particularly into the dynamics of transitions, and experimental investigations would be needed.…”

Transient flow-driven distortion of a nematic liquid crystal in channel flow with dissipative weak planar anchoring

“…In particular, flow-driven misalignment of the orientation of the molecules in the alignment layers may be the cause of spurious optical effects known as "ODF mura" [5][6][7]. We have previously proposed a simple model for the formation of ODF mura due to coalescing droplets of a nematic [7] and have investigated how they might arise in the context of squeeze-film flow of a nematic [8]. In the present work we investigate a rather different fundamental aspect of the ODF method that may bring new insight into the formation of ODF mura, namely the possibility that significant transient flow-driven distortion of the nematic molecules at the substrates from their required orientation may occur during this method.…”

“…The timescale of the ODF method, denoted by τ ODF , is the timescale over which the substrates are squeezed together. We take the horizontal length scale to be the typical diameter of a nematic droplet used in the ODF method, namely L = 10 −2 m [7,8], the typical ODF timescale τ ODF = 10 −1 s [7], and the speed at which the substrates are squeezed together to be w p = 10 −3 m s −1 [7,8], which yields an estimate of the pressure gradient in the ODF method of G = 10 12 Pa m −1 . Table I shows order-of-magnitude estimates of the timescales τ 1 , τ 2 , τ 3 and τ 4 in the ODF method using the estimated parameter values given above.…”