Liquid Crystal Thermometers - Drexel...
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Liquid Crystal Thermometers Anna Fox Electrical and Computer Engineering Drexel University Liquid crystals by Karen Neill: The use of polarized light shows the orientaEon of molecules within a liquid crystal. Regions with the same color have the same orientaEon of their consEtuent molecules. hHp://www.telegraph.co.uk/scienceandtechnology/scienceandtechnologypicturegall/3343156/In‐pictures‐Visions‐of‐Science‐ Awards.html?image=10
Transcript of Liquid Crystal Thermometers - Drexel...
LiquidCrystalThermometers
AnnaFoxElectricalandComputerEngineering
DrexelUniversity
LiquidcrystalsbyKarenNeill:TheuseofpolarizedlightshowstheorientaEonofmoleculeswithinaliquidcrystal.RegionswiththesamecolorhavethesameorientaEonoftheirconsEtuentmolecules.
hHp://www.telegraph.co.uk/scienceandtechnology/scienceandtechnologypicturegall/3343156/In‐pictures‐Visions‐of‐Science‐Awards.html?image=10
SomeHistory
• Discoveredin1888byF.Reinitzer• WhiletryingtomeasurethephysicalproperEesofacholesterol
• Whathefoundwasthissubstancehas2melEngpoints!
hHp://invenEon.smithsonian.org/centerpieces/quartz/inventors/liquid.html
FriedrichReinitzer
WhatareLiquidCrystals?
• Rod‐shapedmolecules• Orientedbetweentheliquidandcrystallinephase
DifferentPhases• Crystallinephase– Highestmolecularorder– Analogoustoice
• Isotropicphase– Lowestmolecularorder– Analogoustowater
• LiquidCrystalPhase– Inbetween‐– astateinwhichtheliquidflows,butsEllhasmolecularorder
ImagecreatedtohHp://sites.google.com/site/prasanthpj/
AcEvity
Materials:PopsicleSEcks
Task1:ArrangethepopsiclesEcksonyourdeskintoanarrayrepresenEngasolid.
Task2:ModifyyourarraytorepresentaliquidCrystal.
Task2:NowarrangethepopsiclesEckstorepresentaliquid?
UsingthepopsiclesEcksandyournewvocabularyexplainthedifferencebetweenaliquidandaliquidcrystal.
ApplicaEonsofLiquidCrystals• LCDdisplays• LiquidCrystalThermometers
• Somethingsfrommyresearch– Liquidcrystalpolymermixtures
– PDLC‐commerciallyfoundinprivacywindow
– H‐PDLC‐researchbasedrightnow
LiquidCrystal(LC)Thermometer
• LCthermometerusescholestericLC’s• AcholestericLChasmolecularorderthatformsahelix
• Analogoustoaspiralstaircase
AcEvity:Whatispitch?Howisitmeasured?Materials:Pipecleaner,pencil,andaruler
Task1.Wrapthepipecleaneraroundthepencil4Emes.Slidethepencilout.Placethecoiledpipecleanernexttotheruler.Howmanyloopsareinoneinch?
Task2:Pulltheendsofthepipecleanerapartslowly,becarefulnottopullitstraight.Nowmeasurethenumberofloopsperinch.
Thepitchisthenumberofturnsperinch,whichexamplehasthehigherpitch?
SoHowDoesItWork?
• CholestericLC“spiralstaircase”structurehasapitchontheorderofthewavelengthoflight
• WhenthepitchdistanceequalshalfofthewavelengthofaparEcularcolor,itwillreflectit
WhyDoesitChangeColor?
• WhenyouwarmupacholestericLC,thehelicalstructureslightlychanges
• Thiscausesadifferentcolortobereflected
AcEvity:MakeanLCThermometer
• Thereare5differentcholestericLCmixturesoutontables
• EachmixtureissensiEvetoadifferenttemperaturerangethatisnearroomtemperature
AcEvity:MakeanLCThermometer
• UseasErtoplaceaverysmalldropofeachmixtureonyourtransparency
• Makesurenottousetoomuch…
• LaminateunderthelaminaEonstrip– Trytosqueezeoutairbubbles
• Nowheatupthedifferentareaswithyourfinger,andwatchthemchangecolor!
• Havefun!
TemperatureRanges
• 20‐25C‐#1• 26.5‐30.5C‐#2• 30‐33C‐#3• 33‐36C‐#4• 37‐40C‐#5
ToconvertCelsiustoFahrenheitusetheformula:
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TF = (9 /5)∗TC + 32
