Director – Degrees of Order in Liquid Crystals - Revision history

Cmditradmin: /* Order as a function of Temperature */

2010-07-20T16:57:59Z

Order as a function of Temperature

← Older revision		Revision as of 09:57, 20 July 2010
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	Positional order is the degree to which the position of an average molecule or groups of molecules exhibit translational symmetry.		Positional order is the degree to which the position of an average molecule or groups of molecules exhibit translational symmetry.

			[[Image:Lc phasechange.png\|thumb\|300px\|Ordering and temperature ]]
	In liquid crystal there are cohesive forces between the molecules that makes them try to orient in one direction. At the same time the temperature is causing entropy in the system. So the interplay between cohesive forces and thermal entropy that enable liquid crystal states and determine the order parameter with respect to temperature.		In liquid crystal there are cohesive forces between the molecules that makes them try to orient in one direction. At the same time the temperature is causing entropy in the system. So the interplay between cohesive forces and thermal entropy that enable liquid crystal states and determine the order parameter with respect to temperature.
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Cmditradmin: /* Enthalpy of Phase Transitions */

2010-07-07T18:59:49Z

Enthalpy of Phase Transitions

← Older revision		Revision as of 11:59, 7 July 2010
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	[[Image:DSC_marder.png\|thumb\|400px\|A DSC graph shows heat flow during phase changes. A dip indicates an endothermic process such as melting. A flat line indicates a linear heating curve.]]		[[Image:DSC_marder.png\|thumb\|400px\|A DSC graph shows heat flow during phase changes. A dip indicates an endothermic process such as melting. A flat line indicates a linear heating curve.]]

	This liquid crystal was made in the Marder lab. The differential scanning calorimetry (DSC) measures the amount of the amount of energy that must be added to a sample to change the temperature 1 degree. Differential scanning calorimetry can be used to characterize the temperature at which phase transitions occur, as can optical microscopy. If a system has an enthalpy change there can be an absorption of energy without a change in temperature. For example when water goes from ice to liquid state a lot of energy is added without a change in temperature. This is expressed in the DSC in the form of a heat flow without temperature change. If you know the precise amount of material and then ~~calculated~~ the area under the curve you can calculate the heat delivered and therefore the enthalpy of a transition.		This liquid crystal was made in the Marder lab. The differential scanning calorimetry (DSC) measures the amount of the amount of energy that must be added to a sample to change the temperature 1 degree C. Differential scanning calorimetry can be used to characterize the temperature at which phase transitions occur, as can optical microscopy. If a system has an enthalpy change there can be an absorption of energy without a change in temperature. For example when water goes from ice to liquid state a lot of energy is added without a change in temperature. This is expressed in the DSC in the form of a heat flow without temperature change. If you know the precise amount of material and then calculate the area under the curve you can calculate the heat delivered and therefore the enthalpy of a transition.

	The first transition is the crystal to nematic transition (K→N), the second dip is the nematic to isotropic transition (N→I). The enthalpy for the liquid crystal to isotropic transition is substantially lower than the crystalline to nematic transition. If the reverse process is run in the opposite direction the same curve result possibly with some hysteresis (displacement of the lines) if the system is not run sufficiently slowly. If these are true liquid crystals, and there is no decomposition, it should be possible to cycle back and forth between crystalline, liquid crystalline and isotropic states.		The first transition is the crystal to nematic transition (K→N), the second dip is the nematic to isotropic transition (N→I). The enthalpy for the liquid crystal to isotropic transition is substantially lower than the crystalline to nematic transition. If the reverse process is run in the opposite direction the same curve result possibly with some hysteresis (displacement of the lines) if the system is not run sufficiently slowly. If these are true liquid crystals, and there is no decomposition, it should be possible to cycle back and forth between crystalline, liquid crystalline and isotropic states.

Cmditradmin: /* The Director */

2009-09-02T21:49:50Z

The Director

← Older revision		Revision as of 14:49, 2 September 2009
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	Thus, when θ is 0° for all the molecules, the orientation parameter is one, which is the case for a crystal in the space group P1 for example. When θ is 57° the orientational order is by this definition 0.		Thus, when θ is 0° for all the molecules, the orientation parameter is one, which is the case for a crystal in the space group P1 for example. When θ is 57° the orientational order is by this definition 0.
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	=== Order as a function of Temperature ===		=== Order as a function of Temperature ===

Cmditradmin: /* The Director */

2009-09-02T21:49:33Z

The Director

← Older revision		Revision as of 14:49, 2 September 2009
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	=== The Director ===		=== The Director ===
			[[Image:Director_lc.png\|thumb\|100px\|The director is average direction of the long molecular axes of all molecules in the liquid crystal. Individual molecules may be more or less aligned with this vector.]]

	Rod like liquid crystals are generally oriented with their moments of inertia roughly aligned along an axis that is called the '''director'''.		Rod like liquid crystals are generally oriented with their moments of inertia roughly aligned along an axis that is called the '''director'''.

Cmditradmin: /* Degrees of Order in Liquid Crystals */

2009-09-02T21:49:24Z

Degrees of Order in Liquid Crystals

← Older revision		Revision as of 14:49, 2 September 2009
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	The optical properties of a molecule only are useful when they translate into optical properties of a bulk material. The order of liquid crystals in material is critical to their functionality.		The optical properties of a molecule only are useful when they translate into optical properties of a bulk material. The order of liquid crystals in material is critical to their functionality.
	=== Degrees of Order in Liquid Crystals ===		=== Degrees of Order in Liquid Crystals ===

	[[Image:Director_lc.png\|thumb\|100px\|The director is average direction of the long molecular axes of all molecules in the liquid crystal. Individual molecules may be more or less aligned with this vector.]]
	There of typically three types of order that characterize liquid crystals: I) orientational order, ii) positional order and iii) bond orientational order		There of typically three types of order that characterize liquid crystals: I) orientational order, ii) positional order and iii) bond orientational order
	The degree of orientation and positional order in LC phases can vary and depending upon this degree the material may be more liquid-like or more crystal-like. It takes more or less energy to change the orientation of various liquid crystals.		The degree of orientation and positional order in LC phases can vary and depending upon this degree the material may be more liquid-like or more crystal-like. It takes more or less energy to change the orientation of various liquid crystals.
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	As a function of temperature, it is therefore possible to see several transitions with increasing temperature upon a transition the newly created phase has increased disorder.		As a function of temperature, it is therefore possible to see several transitions with increasing temperature upon a transition the newly created phase has increased disorder.


	=== The Director ===		=== The Director ===

Cmditradmin at 21:48, 2 September 2009

2009-09-02T21:48:52Z

← Older revision		Revision as of 14:48, 2 September 2009
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	</table>		</table>

			The optical properties of a molecule only are useful when they translate into optical properties of a bulk material. The order of liquid crystals in material is critical to their functionality.
	=== Degrees of Order in Liquid Crystals ===		=== Degrees of Order in Liquid Crystals ===

Cmditradmin: /* Degrees of Order in Liquid Crystals */

2009-09-02T21:44:56Z

Degrees of Order in Liquid Crystals

← Older revision		Revision as of 14:44, 2 September 2009
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	As a function of temperature, it is therefore possible to see several transitions with increasing temperature upon a transition the newly created phase has increased disorder.		As a function of temperature, it is therefore possible to see several transitions with increasing temperature upon a transition the newly created phase has increased disorder.

	Rod like liquid crystals are generally oriented with their moments of inertia roughly aligned along an axis that is called the director.
			=== The Director ===

			Rod like liquid crystals are generally oriented with their moments of inertia roughly aligned along an axis that is called the '''director'''.

	The smaller the average angle of displacement of the moment of inertia from the director, the more ordered the liquid crystal is. The order parameter is given by		The smaller the average angle of displacement of the moment of inertia from the director, the more ordered the liquid crystal is. The order parameter is given by

Cmditradmin: /* Enthalpy of Phase Transitions */

2009-09-02T21:44:03Z

Enthalpy of Phase Transitions

← Older revision		Revision as of 14:44, 2 September 2009
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	The first transition is the crystal to nematic transition (K→N), the second dip is the nematic to isotropic transition (N→I). The enthalpy for the liquid crystal to isotropic transition is substantially lower than the crystalline to nematic transition. If the reverse process is run in the opposite direction the same curve result possibly with some hysteresis (displacement of the lines) if the system is not run sufficiently slowly. If these are true liquid crystals, and there is no decomposition, it should be possible to cycle back and forth between crystalline, liquid crystalline and isotropic states.		The first transition is the crystal to nematic transition (K→N), the second dip is the nematic to isotropic transition (N→I). The enthalpy for the liquid crystal to isotropic transition is substantially lower than the crystalline to nematic transition. If the reverse process is run in the opposite direction the same curve result possibly with some hysteresis (displacement of the lines) if the system is not run sufficiently slowly. If these are true liquid crystals, and there is no decomposition, it should be possible to cycle back and forth between crystalline, liquid crystalline and isotropic states.

	See Wikipedia on ~~DSC~~ [http://en.wikipedia.org/wiki/Differential_scanning_calorimetry]]		See Wikipedia on [http://en.wikipedia.org/wiki/Differential_scanning_calorimetry Differential scanning calorimetry]

	[[category:liquid crystals]]		[[category:liquid crystals]]

Cmditradmin at 21:29, 2 September 2009

2009-09-02T21:29:18Z

← Older revision		Revision as of 14:29, 2 September 2009
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	<table id="toc" style="width: 100%">		<table id="toc" style="width: 100%">
	<tr>		<tr>
	<td style="text-align: left; width: 33%">[[~~History of Liquid Crystals~~ \|Previous Topic]]</td>		<td style="text-align: left; width: 33%">[[Double Refraction and Birefringence\|Previous Topic]]</td>
	<td style="text-align: center; width: 33%">[[Main_Page#Liquid Crystals and Displays\|Return to Liquid Crystal Menu]]</td>		<td style="text-align: center; width: 33%">[[Main_Page#Liquid Crystals and Displays\|Return to Liquid Crystal Menu]]</td>
	<td style="text-align: right; width: 33%">[[Classification and Examples of Liquid Crystals\|Next Topic]]</td>		<td style="text-align: right; width: 33%">[[Classification and Examples of Liquid Crystals\|Next Topic]]</td>
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	<table id="toc" style="width: 100%">		<table id="toc" style="width: 100%">
	<tr>		<tr>
	<td style="text-align: left; width: 33%">[[~~History of Liquid Crystals~~ \|Previous Topic]]</td>		<td style="text-align: left; width: 33%">[[Double Refraction and Birefringence\|Previous Topic]]</td>
	<td style="text-align: center; width: 33%">[[Main_Page#Liquid Crystals and Displays\|Return to Liquid Crystal Menu]]</td>		<td style="text-align: center; width: 33%">[[Main_Page#Liquid Crystals and Displays\|Return to Liquid Crystal Menu]]</td>
	<td style="text-align: right; width: 33%">[[Classification and Examples of Liquid Crystals\|Next Topic]]</td>		<td style="text-align: right; width: 33%">[[Classification and Examples of Liquid Crystals\|Next Topic]]</td>
	</tr>		</tr>
	</table>		</table>

Cmditradmin: /* Degrees of Order in Liquid Crystals */

2009-06-25T16:35:24Z

Degrees of Order in Liquid Crystals

← Older revision		Revision as of 09:35, 25 June 2009
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	=== Degrees of Order in Liquid Crystals ===		=== Degrees of Order in Liquid Crystals ===

	[[Image:Director_lc.png\|thumb\|100px\|]]		[[Image:Director_lc.png\|thumb\|100px\|The director is average direction of the long molecular axes of all molecules in the liquid crystal. Individual molecules may be more or less aligned with this vector.]]
	There of typically three types of order that characterize liquid crystals: I) orientational order, ii) positional order and iii) bond orientational order		There of typically three types of order that characterize liquid crystals: I) orientational order, ii) positional order and iii) bond orientational order
	The degree of orientation and positional order in LC phases can vary and depending upon this degree the material may be more liquid-like or more crystal-like. It takes more or less energy to change the orientation of various liquid crystals.		The degree of orientation and positional order in LC phases can vary and depending upon this degree the material may be more liquid-like or more crystal-like. It takes more or less energy to change the orientation of various liquid crystals.