Statistical Theory of Surface Tension and Molecular Orientations at the Free Surface in Nematic Liquid Crystals

Kimura, Hiroyuki; Nakano, Huzio

doi:10.1143/jpsj.54.1730

Cited by 59 publications

(49 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3g. These results agree with the general understanding that rod-like mesogenic groups tend to be anchored vertically at the free surface17181920.…”

Section: Resultssupporting

confidence: 91%

“…Although the importance of the free surface (air-contacting surface) in the anchoring of mesogen orientations has long been recognized theoretically1718 and experimentally1920, no attempt had been made to utilize the free surface to exert active orientation control over the LC. In this communication, we report the first examples of polymer LC systems commanded by a skin layer at the free surface (Fig.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Free-surface molecular command systems for photoalignment of liquid crystalline materials

et al. 2014

View full text Add to dashboard Cite

The orientation of liquid crystal molecules is very sensitive towards contacting surfaces, and this phenomenon is critical during the fabrication of liquid crystal display panels, as well as optical and memory devices. To date, research has focused on designing and modifying solid surfaces. Here we report an approach to control the orientation of liquid crystals from the free (air) surface side: a skin layer at the free surface was prepared using a non-photoresponsive liquid crystalline polymer film by surface segregation or inkjet printing an azobenzene-containing liquid crystalline block copolymer. Both planar-planar and homoeotropic-planar mode patterns were readily generated. This strategy is applicable to various substrate systems, including inorganic substrates and flexible polymer films. These versatile processes require no modification of the substrate surface and are therefore expected to provide new opportunities for the fabrication of optical and mechanical devices based on liquid crystal alignment.

show abstract

“…3g. These results agree with the general understanding that rod-like mesogenic groups tend to be anchored vertically at the free surface17181920.…”

Section: Resultssupporting

confidence: 91%

mentioning

confidence: 99%

Free-surface molecular command systems for photoalignment of liquid crystalline materials

et al. 2014

View full text Add to dashboard Cite

show abstract

“…Owing to the preformed parallel orientation, LPL irradiation efficiently leads to homogeneous in-plane alignment orthogonal to the electric field of the LPL (top right schemes for both processes). The homeotropic anchoring of rodlike LC molecules at the free surface has been predicted by theoretical considerations, [10,20] and experimental observations of side-chain LC polymer thin films are in agreement with this. [21] When the free surface is covered with a segregated layer, the excluded volume effect from the plane solid substrate should dominate.…”

supporting

confidence: 69%

Liquid‐Crystalline Polymer and Block Copolymer Domain Alignment Controlled by Free‐Surface Segregation

et al. 2013

View full text Add to dashboard Cite

The surface effects and anchoring of liquid crystals (LCs) have long been significant concerns for material chemists and physicists.[1] The surface alignment of LCs by mechanical rubbing [2] is a widely recognized phenomenon and of particular significance in technological applications for display device fabrication.[3] Surface molecular orientations [4] and topographical grooves and undulations [5] of the substrate provide LC alignment effects. Furthermore, in the past two decades, the photoalignment of LCs on photoreactive polymer film surfaces by anisotropic irradiation [6] has become a significant method and an alternative to mechanical rubbing processes. The aligning substrates are not limited to polymer surfaces; various types of surfaces, such as hard inorganic materials [7] and soft bio-related interfaces, [8] can be used for the alignment induction. In addition to low-molecular-mass LCs, polymer LC materials are also aligned by the surface effect.[9] Despite the tremendous amount of accumulated knowledge and the number of potential applications, the surface alignment processes developed to date mostly involve manipulations on the surfaces of solid or condensed phases.Herein, we report on LC alignment alternation, which is attained by a modification of the free surface (air-film interface). The homeotropic surface anchoring effect and layer structuring at the free surface of calamitic LC molecules have been shown experimentally [10] and have been further verified by theoretical simulations.[11] To modify the free surface, the present approach adopts the surface segregation [12,13] of a small amount of a free-surface-active polymer. We demonstrate here that the coverage of the surface with the free-surface-active polymer leads to a homeotropic-to-parallel orientation change of LC mesogens, which further leads to an efficient in-plane photoalignment of microphase separation (MPS) domains of a relevant LC block copolymer by linearly polarized light (LPL).[14] With regard to the MPS alignment control, the important role of a top coat layer has recently been demonstrated by Bates et al. [15] In this case, a polar-to-nonpolar chemical conversion of the top layer is achieved to fulfill the requirement of spin-casting from an aqueous solvent and to provide a neutral (non-preferential) layer for the hydrophobic block copolymer during the annealing. In the present approach, in contrast, no additional coating procedure is required, providing a simple, versatile method for the desired alignment control of MPS domains.First, the alignment behavior of an LC azobenzene (Az) homopolymer (PAz in Figure 1 a; M n = 8.0 10 4 , M w /M n = 1.13, and g-43 8C-SmC-100 8C-SmA-120 8C-iso) was examined. A spincast film of PAz was prepared (thickness: 100-200 nm) from a chloroform solution. After annealing at 130 8C (above the isotropization temperature) for 10 min followed by gradual cooling via a smectic LC phase to room temperature, this film spontaneously formed the out-of-plane (perpendicular) orientation of Az side mesogens, a...

show abstract

“…The polyacrylate backbone is flexible; therefore, the mesogens adopt a vertical orientation at the free surface as theoretically expected. 12 In contrast, the rigid polymethacrylate backbone may disturb such an expected orientation. We have so far obtained information only on the mesogen orientation.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Alternation of Side-Chain Mesogen Orientation Caused by the Backbone Structure in Liquid-Crystalline Polymer Thin Films

et al. 2015

View full text Add to dashboard Cite

In side-chain-type liquid-crystalline (LC) polymers, the main chain rigidity significantly affects the LC structure and properties. We show herein a relevant new effect regarding the orientation of side-chain mesogenic groups of LC polymers in a thin-film state. A subtle change in the main chain structure, i.e., polyacrylate and polymethacrylate, leads to a clear alternation of mesogens in the homeotropic and planar modes, respectively. This orientational discrimination is triggered from the free surface region (film-air interface) as revealed by surface micropatterning via inkjet printing.

show abstract

Statistical Theory of Surface Tension and Molecular Orientations at the Free Surface in Nematic Liquid Crystals

Cited by 59 publications

References 11 publications

Free-surface molecular command systems for photoalignment of liquid crystalline materials

Free-surface molecular command systems for photoalignment of liquid crystalline materials

Liquid‐Crystalline Polymer and Block Copolymer Domain Alignment Controlled by Free‐Surface Segregation

Alternation of Side-Chain Mesogen Orientation Caused by the Backbone Structure in Liquid-Crystalline Polymer Thin Films

Contact Info

Product

Resources

About