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