Name: synthesis and exfoliation of discotic zirconium phosphates to obtain colloidal liquid crystals
Uploaded: 2016-05-25T13:00:00
Description: Watch this Scientific Journal Video about Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals at JoVE.com

This work is partially supported by NSF (DMR-1006870) and NASA (NASA-NNX13AQ60G). X. Z. Wang acknowledges support from the Mary Kay O'Connor Process Safety Center (MKOPSC) at Texas A&amp;M University. We also thank Min Shuai for her guidance.

1. Synthesis of &#945;-ZrP Using Hydrothermal Method
<ol>
	<li>Dissolve 6&#160;g of zirconyl chloride octahydrate (ZrOCl2&#183;8H2O) in 3.75&#160;ml deionized (DI) water in a 150 ml round bottom flask.</li>
	<li>Add 48&#160;ml of 15&#160;M phosphoric acid (H3PO4) dropwise to the ZrOCl2 solution prepared in step 1.1 followed by adding 8.25 ml&#160; deionized (DI) water under vigorous stirring.</li>
	<li>Pour resulting gel-like mixture into Teflon-lined pressure vess...

<ol>
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The reflux method is a good option for making a smaller size of &#945;-ZrP with a uniform diameter and thickness. Similar to the hydrothermal method, the reflux method is limited by the preparation time. In general, it takes longer time for the crystals to grow.
The longer reaction time required for reflux method may result in nanodisks with a larger size. The average size of exfoliated nanodisks is measured by dynamic light scattering (DLS). In this study, the size of exfoliated ZrP nanodisks...

Discotic colloids are naturally abundant in the form of clay, asphaltene, red blood cells, and nacre. A range of applications in many engineered systems, including polymer nanocomposites1, biomimetic materials, functional membranes2, discotic liquid crystal studies3 and Pickering emulsion stabilizers4 are developed based on discotic colloidal nanodisks. Nanodisks with uniformity and low polydispersity is important for studying phases and transformations of liquid crystals. Zirconium phosphate (ZrP) is a synthetic nanodisks with well-ordered layered structure and controllable aspect ratio (thickness over diameter). Therefore, the exploration of different synthesis of ZrP helps to establish fundamental understanding of discotic liquid crystal system.
The structure of ZrP was elucidated by Clearfield and Stynes in 19645. For the synthesis of layered crystals of ZrP, hydrothermal and reflux methods are commonly adopted6,7. Hydrothermal method gives a good control on size ranging from 400 to 1,500 nm and polydispersity within 25%6, while reflux method gives smaller crystals for the same duration time. Microwave heating has been proven to be a promising method for synthesis of nanomaterials8. However, there are no papers describing synthesis of ZrP based on microwave-assisted route. The effective control over size, aspect ratio, and mechanism of the crystal growth by hydrothermal method was systematically studied by our group6.
ZrP can be easily exfoliated into monolayers in aqueous suspensions, and the exfoliated ZrP have been well established as liquid crystal materials in Cheng&#39;s group3,9-13. So far, exfoliated ZrP nanodisks with various diameters, say different aspect ratios, have been studied to conclude that larger ZrP had the I (isotropic)-N (nematic) transition at lower concentration compared to smaller ZrP3. The polydispersity3, salt9 and temperature10,11 effects on the formation of nematic liquid crystal phase have been also considered. Moreover, other phases, such as sematic liquid crystal phase, have been investigated as well13,14.
In this article, we demonstrate experimental realization of such a colloidal ZrP nanodisks suspension. Layered ZrP crystals are synthesized via different methods, and then are exfoliated in aqueous media to obtain monolayer nanodisks. At the end, we show liquid crystal phase transitions exhibited by this system. A notable aspect of these disks is their highly anisotropic nature that the thickness to diameter ratio is in the range of 0.0007 to 0.05 depending on the size of disks3. The highly anisotropic monolayer nanodisks establish a model system to study phase transitions in the suspensions of nanodisks.

<table border="0" cellpadding="0" cellspacing="0" height="202" width="928">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:209px;">Material</td>
			<td style="width:208px;"></td>
			<td style="width:164px;"></td>
			<td style="width:352px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Zirconyl Chloride Octahydrate</td>
			<td>Fischer Scientific (Acros Organics)</td>
			<td>AC20837-5000</td>
			<td>98% +&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">o-Phosphoric Acid</td>
			<td>Fischer Scientific</td>
			<td>A242-1</td>
			<td>&#62;= 85 %</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tetra Butyl Ammonium Hydroxide</td>
			<td>Acros Organics (Acros Organics)</td>
			<td>AC176610025</td>
			<td>40% wt. (1.5M)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Reaction Oven</td>
			<td>Fischer Scientific</td>
			<td>CL2 centrifuge</td>
			<td>Isotemperature Oven (Temperature Upto 350&#160;C)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Centrifuge&#160;</td>
			<td>Thermo Scientific</td>
			<td>Not Available&#160;</td>
			<td>Rotation Speed : 100 - 4000 rpm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microwave Reactor</td>
			<td>CEM Corporation</td>
			<td>Discover and Explorer SP</td>
			<td>Temp. Upto 300oC, Power upto 300W, Pressure upto 30bar</td>
		</tr>
	</tbody>
</table>

synthesis and exfoliation of discotic zirconium phosphates to obtain colloidal liquid crystals

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and engineers. Growth of such anisotropic nanocrystals through a simple chemical method is a challenging task. In this study, we fabricate discotic nanodisks of zirconium phosphate [Zr(HPO4)2&#183;H2O] as a model material using hydrothermal, reflux and microwave-assisted methods. Growth of crystals is controlled by duration time, temperature, and concentration of reacting species. The novelty of the adopted methods is that discotic crystals of size ranging from hundred nanometers to few micrometers can be obtained while keeping the polydispersity well within control. The layered discotic crystals are converted to monolayers by exfoliation with tetra-(n)-butyl ammonium hydroxide [(C4H9)4NOH, TBAOH]. Exfoliated disks show isotropic and nematic liquid crystal phases. Size and polydispersity of disk suspensions is highly important in deciding their phase behavior.

Figure 1a-c show SEM images of &#945;-ZrP nanodisks obtained from hydrothermal, reflux, and microwave-assisted methods, respectively. It was observed that &#945;-ZrP nanodisks show hexagonal in shape and different thickness depending on synthesis conditions and prepared methods. A previously reported study from our group6 suggests that for the crystal growth time 48 hours or above, the edge of the disks become sharper. Usually, the reflux method yields nanodisk...

Watch this Scientific Journal Video about Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals at JoVE.com

Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals

A two dimensional model material of discotic zirconium phosphate was developed. The inorganic crystal with lamellar structure was synthesized by hydrothermal, reflux, and microwave-assisted methods. On exfoliation with organic molecules, layered crystals can be converted to monolayers, and nematic liquid crystal phase was formed at sufficient concentration of monolayers.

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and ...

The overall goal of this zirconium phosphate synthesis by three methods and its exfoliation is to obtain various aspect ratio nano platelets which can serve as a model discotic liquid crystal system. This method can help answer key questions in the synthesis of different sizes of zirconium phosphate in the exfoliation techniques field. Such is how to control the aspect ratio of the zirconium phosphate by various synthesis methods, and importantly how to obtain nearly mono dispersed zirconium phosphate nano platelets.The minute one day of the technique that we demonstrated is that where they will obtain zirconium phosphate nano plates off sizes ranging from 200 nanometers to 2, 000 nanometers with good control and for proper disposary. This method provide insight into liquid crystal model materials it can also be applied for other systems such as pickling emulsifiers. To synthesize alpha zirconium phosphate using the hydrothermal method dissolve six grams of zirconochloride octahydrate in 3.75 mL of deionized water in a beaker.Add 48 mL of 15 molar phosphoric acid into a teflon lined pressure vessel followed by 8.25 mL of water. Then add the zirconochloride solution drop wise to the phosphoric acid solution under vigorous stirring. Place the vessel into a hydrothermal autoclave composed of a stainless steel shell, pressure plate, and lid and then tighten it well.Place the hydrothermal autoclave into a convection oven at 200 degrees Celsius for 24 hours. After the reaction, allow the hydrothermal autoclave to cool down eight hours to room temperature under ambient cooling. Transfer the supernatant liquid portion in the reactor to a waste disposal container since it contains unreacted phosphoric acid which is corrosive.Collect alpha zirconium phosphate nano platelets in two centrifuge tubes. Add 40 mL of water to each centrifuge tube and vortex for one minute. After centrifuging the tubes at 2, 500 x g for five minutes, remove the top liquid in the tubes.Repeat this step three times to ensure that all of the acid is washed away. Dry the zirconium phosphate water sticky mixture in an oven at 65 degrees Celsius for eight hours and then grind it using a mortar and pestle. To synthesize alpha zirconium phosphate using the reflux method, mix six grams of zirconochloride octahydrate with 60 mL of 12 molar phosphoric acid in a 150 mL round bottom flask.Reflux the prepared mixture in an oil bath at 94 degrees Celsius for 24 hours. Wash the product with deionized water three times as done for hydrothermal synthesis and then dry the zirconium phosphate water sticky mixture in the oven at 65 degrees Celsius for eight hours. Grind the dried bulky sample into powder using a mortar and pestle and stock for later use.To synthesize alpha zirconium phosphate using the microwave assisted method add one gram of zirconochloride octahydrate into 10 mL of 12 molar phosphoric acid solution and stir the resulting mixture well in a 20 mL scintillation vial. Pour 5 mL of the resulting mixture into a 10 mL glass vessel specified for a microwave reactor. Set the reaction temperature to 150 degrees Celsius, set the pressure limit to 300 psi and allow the reaction to happen for one hour.After the reaction, let the glass vessel cool down for about 15 minutes and then follow the same procedure as before for acid washing and drying of alpha zirconium phosphate crystals. Disperse one gram of alpha zirconium phosphate into 7.8 mL of deionized water in a 45 mL centrifuge tube. Add 2.2 mL of TBAOH then vortex for at least 40 seconds.Notice that the molar ratio of zirconium to TBAOH is kept at 1:1. Sonicate the resulting concentrated suspension for one to two hours. Leave the sonicated suspension for two to three days to allow full intercalation of tetrabutyl ammonium cations and complete exfoliation of crystals.Optionally, concentrated suspension can be diluted with water to obtain better exfoliation. In this case, add 20 mL of water to 10 mL of exfoliated suspension. Centrifuge the exfoliated samples at high rotation speed for half an hour to remove the bottom sediment and the top liquid.Collect the middle part in another container. Add another five mL of water and centrifuge again for half an hour. After letting the suspension settle over night remove the top liquid and stock the remaining suspension for liquid crystal study.The suspension can be diluted at different ratios to see isotropic, nomadic and other possible phases. Scanning electron microscopy, or SCM, images of pristine alpha zirconium phosphate prepared via the hydrothermal method, the reflux method, and the microwave assisted method are shown. Shown here are transmission electron microscopy images of the microwave assisted growth of zirconium phosphate crystals at 150 degrees Celsius.The phosphate nano platelet is shown at 10 minutes and at 60 minutes. In this image the left bottle contains unexfoliated zirconium phosphate suspended in water and the right bottle has exfloliated zirconium phosphate nano platelets. Different dilutions of stock suspension are shown to exhibit liquid crystal and isotropic nomadic co-existent phase except for the last two vials which are fully nomadic.The image is a snapshot of the suspensions placed between crossed polarizers. Once mastered this technique can be done in one hour to synthesize layered zirconium phoshate nano platelets in the four days to obtain liquid crystals if it is performed properly. While working out this procedure, one should make sure that the precursors are mixed well.Following this procedure other studies like nano plates stabilize pickling motion can be also performed in other through answer additional questions such as two dimensional materials in pickling emulsifications. After its development this technique for the researchers in the field of software and condense matter to explore liquid crystals of inorganic and aquatic systems. After watching this video you should have the understanding how to synthesize nearly mono dispersed zirconium phosphate nano platelets.And then use them for different applications in the fundamental studies on liquid crystals. Don't forget working with phosphoric acid can be extremely hydrous so when you are doing experiments don't forget the personal protective equipment and also you need to deal with the wasted acid properly.

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