Qhov sib txawv tseem ceeb ntawm nematic smectic thiab cholesteric kua crystals yog lawv cov qauv. Nematic kua muaju tsis muaj cov qauv ntawm cov molecules, thiab smectic kua crystals muaj ib txheej molecular qauv, whereas cholesteric kua crystals muaj cov molecules nyob rau hauv ib tug twisted thiab chiral kev npaj.
Lub sij hawm ua kua siv lead ua tuaj yeem txhais tau tias yog theem ntawm cov teeb meem uas muaj cov khoom nyob nruab nrab ntawm cov khoom ntawm cov kua dej thiab cov khoom siv lead ua. Piv txwv li, cov kua siv lead ua kua tuaj yeem ntws zoo li cov kua, tab sis cov molecules ntawm cov kua siv lead ua kua zoo li yuav tsum tau coj mus rau qhov zoo li siv lead ua. Muaj peb theem loj nyob rau hauv uas cov kua siv lead ua kua yuav tshwm sim: thermotropic kua crystals, lyotropic kua crystals, thiab metallotropic kua crystals. Muaj ntau hom thermotropic kua siv lead ua ib yam. Cov hom no muaj xws li nematic crystals, smectic crystals, chiral theem lossis twisted nematics, discotic theem, thiab conic theem.
Nematic Liquid Crystals yog dab tsi?
Nematic kua muaju yog ib yam ntawm cov kua siv lead ua feem ntau. Lo lus "nematic" los ntawm Greek keeb kwm uas nws muaj lub ntsiab lus "xov". Qhov no yog vim hais tias lo lus no originated los ntawm lub topological tsis xws luag uas tshwm raws li threads. Feem ntau, cov teeb meem saum toj no hauv nematics yog hu ua disclinations. Tsis tas li ntawd, nematics yuav nthuav tawm ib hom kab mob hu ua "hedgehog" topological defects.
Feem ntau, cov theem nematic muaj calamitic lossis pas nrig-zoo li cov organic molecules uas tsis muaj qhov kev txiav txim. Tab sis cov molecules no zoo li nws tus kheej ua kom haum kom muaj qhov ntev-ntev kev coj ua uas muaj cov axes ntev uas sib npaug rau ib leeg. Yog li ntawd, cov molecules nyob rau theem no yog dawb ntws, thiab qhov nruab nrab ntawm qhov loj ntawm cov molecules nyhav randomly faib, zoo ib yam li cov kua. Txawm li cas los xij, cov molecules no zoo li tswj xyuas qhov ntev-ntev kev coj ua zoo ib yam li cov theem khoom.
Feem ntau, cov theem nematic yog uniaxial. Qhov no txhais tau tias cov molecules muaj ib axis (nws yog hu ua "directrix") uas ntev. Qhov no yog qhov nyiam axis, thiab ob lub axes yog sib npaug rau ib leeg, thiab peb tuaj yeem kwv yees lawv li lub tog raj kheej lossis cov pas nrig. Tsis tas li ntawd, muaj peev xwm muaj biaxial nematics tsis yog tsuas yog kev taw qhia zoo ib yam hauv lawv cov axis ntev, tab sis kuj lawv nyiam mus rau kev taw qhia raws tus axis thib ob.
Cov molecules ntawm nematic theem qhia fluidity uas zoo ib yam li cov fluidity hauv cov kua isotropic zoo tib yam. Txawm li cas los xij, peb tuaj yeem yooj yim kho cov molecules nyob rau theem no los ntawm kev siv cov hlau nplaum sab nraud lossis hluav taws xob. Thaum cov molecules tau ua raws li qhov kev txiav txim, theem nematic qhia pom cov khoom siv kho qhov muag ntawm uniaxial muaju, thiab yog li ntawd, cov theem no muaj txiaj ntsig zoo hauv cov kua siv lead ua kua.
Smectic Liquid Crystals yog dab tsi?
Smectic kua crystals yog ib hom kua siv lead ua uas muaj cov txheej txheem zoo ntawm cov molecules uas muaj peev xwm swb dua ib leeg. Tus cwj pwm no zoo ib yam li cov zawv zawg cuam tshuam los ntawm xab npum. Ntxiv mus, smectic kua muaju tshwm sim ntawm qhov kub thiab txias qis dua li ntawm cov kua nematic. Lo lus smectic originates los ntawm Latin lo lus "smectius" uas txhais tau tias "tu"; hauv lwm lo lus, nws txhais tau hais tias muaj cov khoom zoo li xab npum. Yog li ntawd, theem smectic yog positioned nyob rau hauv kev txiav txim raws ib qho kev taw qhia.
Daim duab 01: Smectic A theem nyob rau sab laug thiab smectic C theem nyob rau sab xis
Peb tuaj yeem soj ntsuam ob theem sib txawv xws li smectic A theem thiab smectic C theem. Lub smectic A theem muaj cov molecules oriented nrog rau cov txheej txheem ib txwm, whereas smectic C muaj nws cov molecules tilted deb ntawm nws. Ntxiv mus, hom theem no tshwm sim raws li cov kua hauv cov khaubncaws sab nraud povtseg. Txawm li cas los xij, tuaj yeem muaj ntau hom smectic theem sib txawv ntawm ib leeg raws li hom thiab qib ntawm txoj haujlwm thiab kev taw qhia.
Cov kua roj (cholesterol) yog dab tsi?
Cholesteric kua siv lead ua yog ib hom kua siv lead ua kua ua los ntawm chiral molecules xwb. Hom theem no qhia tau hais tias chirality. Feem ntau, peb hu rau theem no yog chiral theem lossis ib theem twisted nematic vim nws chirality. Lo lus cholesteric los ntawm nws thawj qhov kev soj ntsuam qhov twg theem ntawm cov teeb meem no tau tshwm sim thawj zaug hauv cov roj cholesterol derivatives. Peb tuaj yeem soj ntsuam cov theem no uas nthuav tawm qhov sib tw ntawm cov molecules, uas yog nyob rau ntawm tus thawj coj qhov twg cov axis molecular yog sib npaug rau tus thawj coj.
Daim duab 02: Cholesteric Phase
Muaj lub kaum sab xis kawg ntawm cov molecules uas nyob ib sab nyob rau theem no vim yog cov asymmetric packing ntawm cov molecules. Hom kev ntim khoom no ua rau lub sijhawm ntev chiral xaj. Feem ntau, peb txhais chiral pitch los yog "p" hais txog cov khoom ntawm cholesteric kua crystals qhov twg nws hais txog qhov kev ncua deb ntawm cov kua siv lead ua kua molecules undergo ib tug tag nrho-lub voj voog twist (360-degree twist).
Qhov txawv ntawm Nematic Smectic thiab Cholesteric Liquid Crystals yog dab tsi?
Nematic, smectic, thiab cholesteric theem yog peb theem sib txawv ntawm cov teeb meem uas tuaj nyob rau hauv cov kua dej thermotropic. Qhov sib txawv tseem ceeb ntawm nematic smectic thiab cholesteric kua crystals yog cov kua siv lead ua kua nematic tsis muaj cov qauv ntawm cov molecules, thiab smectic kua crystals muaj cov txheej txheem molecular, whereas cholesteric kua crystals muaj molecules nyob rau hauv ib tug twisted thiab chiral kev npaj.
Hauv qab no yog cov ntsiab lus ntawm qhov sib txawv ntawm nematic smectic thiab cholesteric kua crystals hauv daim ntawv.
Summary – Nematic Smectic vs Cholesteric Liquid Crystals
Nematic, smectic, thiab cholesteric theem yog peb theem sib txawv ntawm cov teeb meem uas tuaj nyob rau hauv cov kua dej thermotropic. Qhov sib txawv tseem ceeb ntawm nematic, smectic, thiab cholesteric kua crystals yog cov kua siv lead ua kua nematic tsis muaj cov qauv ntawm cov molecules, thiab smectic kua crystals muaj cov txheej txheem molecular, whereas cholesteric kua crystals muaj cov molecules nyob rau hauv ib tug twisted thiab chiral kev npaj.
