Name: orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets
Uploaded: 2017-05-15T13:00:00
Description: Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

This work was supported by JSPS KAKENHI grant Number 16H06037. We sincerely thank Dr. Yuji Sasaki in Hokkaido University for technical assistance for HR-DSC.

1. Preparation of the Liquid Crystal Alignment Layer of a Perfluoropolymer onto Glass Substrates
<ol>
	<li>Preparation of the perfluoropolymer solution
	<ol>
		<li>Prepare 1 mL of the perfluoropolymer solution by dissolving a perfluoropolymer solution (9 wt% polymer) in a commercial solvent at a ratio of 1:2; this ensures uniform films 0.5-1 &#181;m thick to be spin-coated. 
		NOTE: Please see the Materials List for the solution and solvent used.</li>
	</ol>
	</li>
	<li>Coating of the perf...

<ol>
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The 10x POM images taken using a 5-&#181;m LC cell (Figures 1a and b) clearly show that the orientational state of the bulk LC molecules transits between the P and the V orientations upon temperature variation in a first-order manner. This is marked by the domain nucleation and growth processes, with a new orientation differing from the initial orientation by 90&#176;. The transition temperatures upon cooling and heating are 321.5 K and 325.3 K, respectively. Since CCN47 has a birefringe...

In recent years, there has been growing interest in learning how dynamic molecular features and structures of surface molecules in response to external stimuli might affect the bulk orientation of materials in LC states. One example is to use LC biosensors as a new application of LCs1,2. To quantify how many target bio-species are detected, it is important to know how the interfacial LCs that contact adhering target molecules change and evolve, while also detecting and how they transfer/translate their properties into the bulk.
Using models to pursue these answers, we started with systems that have their surface molecular orientation and short-range orderings varying thermodynamically. These systems allow us to correlate the changes in surface orientation and orderings with the resulting bulk orientation in a systematic way. Recently, we found several LC systems that exhibit orientational transitions, where a spontaneous bulk molecular orientation changes with temperature. In principle, orientational transitions can be categorized into either quasi-second-order3,4 or quasi-first-order transition5,6,7,8. The former is accompanied by a continuous bulk molecular reorientation upon changes in temperature, whereas the latter demonstrates a discontinuous one. In this article, we describe an orientational transition in the quasi-first-order manner between the P and the V orientational states. It proceeds in the single nematic (N) phase by changing the temperature. Details will be provided in the Representative Results and the Discussion.
Since orientational change in the bulk should be governed by a change in the surface molecular orientation and short-range orderings, it is apparent that this system can potentially offer insights into how the thermodynamic variation in surface molecular orientation and short-range orderings affects the bulk orientation. In this article, with the goal of understanding the abovementioned issues, we tackled three problems using four complementary methods (i.e., POM, DS, HR-DSC, and GI-XRD): (1) What does the orientational transition look like? (2) Is the orientational transition thermally detectable? (3) Why and how does the orientational transition occur?

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			<td>Solvent for CYTOP</td>
			<td>Asahi Glass Co. Ltd.</td>
			<td>CT-180 Sol.</td>
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			<td>Alkaline detergent</td>
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			<td>Nematel GmbH &#38; Co. KG</td>
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orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90&#176; between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

POM images, DS data, HR-DSC data, and GI-XRD patterns were collected during temperature variation, especially in the vicinity of the orientational transition upon both cooling and heating.
Figure 1 represents the evolution of the texture made by POM and DS measurements during the POM observation of the orientational transition from the P (V) to the V (P) orientational state during cooling (heating)....

Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

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