Name: orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets
Uploaded: 2017-05-15T13:00:00.000+00:00
Duration: 6 min 26 s
Description: Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

Questo lavoro è stato supportato da JSPS KAKENHI con il numero 16H06037. Ringraziamo sinceramente il dottor Yuji Sasaki presso l&#39;Università di Hokkaido per l&#39;assistenza tecnica per HR-DSC.

1. Preparazione dello strato di allineamento del cristallo liquido di un perfluoropolimero su substrati di vetro <ol><li> Preparazione della soluzione di perfluoropolimero <ol><li> Preparare 1 mL della soluzione di perfluoropolimero sciogliendo una soluzione di perfluoropolimero (9% in polimero di%) in un solvente commerciale in un rapporto di 1: 2; Questo assicura film uniformi da 0,5 a 1 μm di spessore per essere spin-coated. NOTA: consultare l&#39;elenco dei materiali per la soluzione e il solvente utilizzato. </li></ol></li><li> Rivestimento del perfluoropolimero su substrati di vetro pulito <ol><li> Lavare i supporti di vetro (dimensione tipica: 1 cm x 1 cm) per sonicazione a 38 o 42 kHz in un detergente alcalino. Risciacquare ripetutamente con acqua distillata. In genere, sciacquare più di 10 volte, con 5 minuti di sonicazione ogni volta. </li><li> Sostituire i substrati al detergente UV-O 3 per 10 min. </li><li> Gocciola 20 μL della soluzione del punto 1.1 sul substrato di vetro pulitoTES. Immediatamente spin-cappella la soluzione a 3.500 giri / min e la temperatura ambiente per 70 s. Cuocere la pellicola a 80 ° C per 60 minuti per rimuovere il solvente e a 200 ° C per 60 minuti per la polimerizzazione. </li></ol></li></ol> 2. Preparazione delle cellule LC <ol><li> Incollare due substrati di vetro rivestiti con film insieme utilizzando una resina foto-curabile e una lampada a LED con una lunghezza d&#39;onda di 365 nm (1,1 W / cm 2 ). Regolare lo spessore del divario tra i due substrati entro l&#39;intervallo di 2-100 μm utilizzando particelle di vetro di dimensioni micrometriche o pellicole di polietilene naftalato. </li><li> Introdurre un materiale LC, 4&#39;-butil-4-eptil-bicicloesil-4-carbonitrile (CCN47; 0,2-10 μL) 9 alle cellule LC preparate usando una spatola sotto forza capillare ad una temperatura superiore al liquido isotropico (I) - temperatura di transizione di fase non statica (N). NOTA: CCN47 ha un&#39;anisotropia dielettrica negativa e la sequenza di fase è Cry 298.6 K SmA 301.3 KN 331.3 KI, dove Cry e SmA stanno per fasi cristalline e smectic. Non introdurre CCN47 nella fase N o SmA, poiché l&#39;allineamento indotto dal flusso sarebbe stato promosso. </li></ol> 3. Caratterizzazione del campione <ol><li> Osservazione della struttura mediante polarizzazione della microscopia ottica (POM) 10 <ol><li> Osservare le celle LC sotto POM con lenti obiettivo 4-100X in combinazione con una fase a caldo per controllare la temperatura del campione con una precisione di ± 0,1 K. Registrare le texture in più di 5 fotogrammi, a intervalli regolari per Kelvin. Utilizzare una fotocamera digitale a colori in sequenza, sia al raffreddamento che al riscaldamento nell&#39;intervallo 291-343 K. </li></ol></li><li> Spettroscopia dielettrica (DS) 11 <ol><li> Preparare le celle LC, con elettrodi ITO - che possono avere una forma quadrata o circolare e possono essere acquistati in commercio - su entrambi i substrati. Saldare un filo di piombo ad ogni substrato. NOTA: Consultare l&#39;elenco dei materiali per i substrati utilizzati. </li><li> Misurare la capacità o la costante dielettrica delle celle LC, esattamente come utilizzata per POM, utilizzando un analizzatore di impedenza commerciale / fase di guadagno. Assicurarsi che lo stato dei campioni sia equilibrato prima di ogni misurazione. Misurare la dipendenza temporale della capacità o della costante dielettrica delle cellule LC misurando manualmente la capacità delle cellule LC ogni 5 min. </li><li> Avviare la misura DS solo se la costante o la costante dielettrica delle cellule LC diviene non dipendente dal tempo. </li></ol></li><li> Calorimetria di scansione differenziale ad alta risoluzione (HR-DSC) 12 <ol><li> Mettere le celle LC in un HR-DSC fatto in casa da esaminare, esattamente come in POM ( non utilizzare mai le teglie DSC). Fare riferimento al Reference 12 per progettare e costruire un HR-DSC e per imparare ad usarlo. Eseguire le misurazioni con le velocità di scansione di 0,05-0,10 K / min per migliorare il pow di risoluzione della temperatura minimaER. </li></ol></li><li> Diffrazione a raggi X incidenti di pascolo (GI-XRD) 13 <ol><li> Posizionare la cella LC (utilizzata per POM o DSC) o un campione con una goccia di CCN47 da 2 a 5 μl su un substrato rivestito sullo stadio di campione GI-XRD, che dovrebbe essere dotato di un regolatore di temperatura. </li><li> Equilibrare il campione per più di 10 minuti alle temperature desiderate nell&#39;intervallo 291-343 K, sia a raffreddamento che a riscaldamento. </li><li> Usare un fascio a raggi X incidente sul campione, con un angolo di incidente minuto attorno allo 0,05-0,10 °, per estrarre informazioni sulla superficie sull&#39;orientamento molecolare e le ordinazioni / strutture. Swing l&#39;angolo incidente del raggio a raggi X per trovare l&#39;angolo di incidente ottimale in cui la forza della diffrazione è la più forte. Prendere le misure all&#39;angolo ottimale dell&#39;incidente. NOTA: Tenete presente che GI-XRD consente di sondare le peculiarità interfacciali sulla scala nanometrica, massimizzando così il segnale da sottileAyers riducendo al minimo il segnale dalla massa. Si noti che le geometrie normali di XRD, diverse da GI-XRD, non sono metodi sensibili alla superficie, poiché il raggio di raggi X ha una grande profondità di penetrazione nei materiali. </li></ol></li></ol>

<ol>
	<li>Woltman, S. J., Jay, G. D., Crawford, G. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liquid-Crystal+Materials+Find+a+New+Order+in+Biomedical+Applications.">Liquid-Crystal Materials Find a New Order in Biomedical Applications.</a> Nat. Mater. 6 (12), 929-938 (2007).</li><li>Carlton, R. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+and+Biological+Sensing+Using+Liquid+Crystals.">Chemical and Biological Sensing Using Liquid Crystals.</a> Liq. Cryst.Rev. 1 (1), 29-51 (2013).</li><li>Patel, J. S., Yokoyama, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+Anchoring+Transition+in+Liquid+Crystals.">Continuous Anchoring Transition in Liquid Crystals.</a> Nature. 362, 525-527 (1993).</li><li>Senyuk, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+alignment,+anchoring+transitions,+optical+properties,+and+topological+defects+in+the+nematic+phase+of+thermotropic+bent-core+liquid+crystal+A131.">Surface alignment, anchoring transitions, optical properties, and topological defects in the nematic phase of thermotropic bent-core liquid crystal A131.</a> Phys Rev E. 82 (4 Pt 1), 041711 (2010).</li><li>Bechhoefer, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Critical+Behavior+in+Anchoring+Transitions+of+Nematic+Liquid+Crystals.">Critical Behavior in Anchoring Transitions of Nematic Liquid Crystals.</a> Phys. Rev. Lett. 64 (16), 1911-1914 (1990).</li><li>Dhara, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anchoring+Transitions+of+Transversely+Polar+Liquid-Crystal+Molecules+on+Perfluoropolymer+Surfaces.">Anchoring Transitions of Transversely Polar Liquid-Crystal Molecules on Perfluoropolymer Surfaces.</a> Phys. Rev. E. 79 (6 Pt 1), 60701 (2009).</li><li>Aya, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stepwise+heat-capacity+change+at+an+orientation+transition+in+liquid+crystals.">Stepwise heat-capacity change at an orientation transition in liquid crystals.</a> Phys. Rev. E. 86 (2), 022512 (2014).</li><li>Aya, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermodynamically+Anchoring-Frustrated+Surface+to+Trigger+Bulk+Discontinuous+Orientational+Transition.">Thermodynamically Anchoring-Frustrated Surface to Trigger Bulk Discontinuous Orientational Transition.</a> Langmuir. 32 (41), 10545-10550 (2016).</li><li>Dhara, S., Madhusudana, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physical+characterisation+of+4'-butyl-4-heptyl-bicyclohexyl-4-carbonitrile.">Physical characterisation of 4'-butyl-4-heptyl-bicyclohexyl-4-carbonitrile.</a> Phase Trans. 81 (6), 561-569 (2008).</li><li>Dierking, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Textures of Liquid Crystals. , (2003).</li><li>Perkowski, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Technical+aspects+of+dielectric+spectroscopy+measurements+of+liquid+crystals.">Technical aspects of dielectric spectroscopy measurements of liquid crystals.</a> Opto-Electronics Review. 16 (3), 271-276 (2008).</li><li>Inaba, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nano-watt+stabilized+DSC+and+ITS+applications.">Nano-watt stabilized DSC and ITS applications.</a> J Therm Anal Calorim. 79 (3), 605-613 (2005).</li><li>Leveiller, F., Boehm, C., Jacquemain, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-dimensional+crystal+structure+of+cadmium+arachidate+studied+by+synchrotron+X-ray+diffraction+and+reflectivity.">Two-dimensional crystal structure of cadmium arachidate studied by synchrotron X-ray diffraction and reflectivity.</a> Langmuir. 10 (3), 819-829 (1994).</li><li>de Gennes, P. G., Prost, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Physics of Liquid Crystals (Second Edition). , (1993).</li><li>Aya, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Critical+Behavior+in+an+Electric-Field-Induced+Anchoring+Transition+in+a+Liquid+Crystal.">Critical Behavior in an Electric-Field-Induced Anchoring Transition in a Liquid Crystal.</a> Phys. Rev. E. 86 (1 Pt 1), 10701 (2012).</li><li>Avrami, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetics+of+Phase+Change.+I+General+Theory.">Kinetics of Phase Change. I General Theory.</a> J. Chem. Phys. 7, 1103-1112 (1939).</li><li>Avrami, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetics+of+Phase+Change.+II+Transformation-Time+Relations+for+Random+Distribution+of+Nuclei.">Kinetics of Phase Change. II Transformation-Time Relations for Random Distribution of Nuclei.</a> J. Chem. Phys. 8 (2), 212-224 (1939).</li><li>Avrami, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Granulation+Phase+Change,+and+Microstructure+Kinetics+of+Phase+Change.+III.">Granulation Phase Change, and Microstructure Kinetics of Phase Change. III.</a> J. Chem. Phys. 9, 177-184 (1941).</li><li>Sasaki, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distinctive+Thermal+Behavior+and+Nanoscale+Phase+Separation+in+the+Heterogeneous+Liquid-+Crystal+B4+Matrix+of+Bent-Core+Molecules.">Distinctive Thermal Behavior and Nanoscale Phase Separation in the Heterogeneous Liquid- Crystal B4 Matrix of Bent-Core Molecules.</a> Phys. Rev. Lett. 107 (23), 237802 (2011).</li></ol>

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Le immagini POM 10x usate utilizzando una cella LC da 5 μm ( Figura 1a e b ) mostrano chiaramente che lo stato di orientamento delle molecole di massa LC trascorre tra gli orientamenti V e V sulla variazione di temperatura in modo di primo ordine. Questo è caratterizzato da processi di nucleazione e di crescita del dominio, con un nuovo orientamento diverso dall&#39;orientamento iniziale di 90 °. Le temperature di transizione dopo raffreddamento e riscaldamento sono rispettivamente 3...

Negli ultimi anni, è cresciuto interesse ad apprendere come le caratteristiche molecolari dinamiche e le strutture delle molecole superficiali in risposta a stimoli esterni potrebbero influenzare l&#39;orientamento di massa dei materiali negli stati LC. Un esempio è quello di utilizzare biosensori LC come una nuova applicazione di LC 1 , 2 . Per quantificare quante specie bio-target vengono rilevate, è importante sapere come i LC interfacciali che contattano le molecole target aderenti cambiano e si evolvono, pur rilevando e come trasferiscono / traducono le proprie proprietà in massa. Utilizzando modelli per perseguire queste risposte, abbiamo cominciato con sistemi che hanno il loro orientamento molecolare di superficie e ordinazioni a corto raggio che variano termodinamicamente. Questi sistemi ci permettono di correlare in modo sistematico i cambiamenti dell&#39;orientamento e delle ordinazioni di superficie con l&#39;orientamento bulk risultante. Recentemente, abbiamo trovato diversi sistemi LC che mostrano oTransizioni rientazionali, dove un orientamento molecolare spontaneo di massa cambia con la temperatura. In linea di principio, le transizioni orientazionali possono essere classificate in transizioni di 5 , 6 , 7 e 8 quasi secondi di 3 , 4 o quasi-ordine. Il primo è accompagnato da una reorientazione molecolare continua continua sui cambiamenti della temperatura, mentre quest&#39;ultima dimostra una discontinuità. In questo articolo descriviamo una transizione orientazionale nel modo quasi ordinario tra gli stati P e gli orientamenti V. Si procede nella singola fase nematica (N) cambiando la temperatura. I dettagli saranno forniti nei risultati rappresentativi e nella discussione. Poiché la modifica orientazionale della massa deve essere governata da una modifica dell&#39;orientamento molecolare della superficie e breve- ordini di ordinamento, è evidente che questo sistema può potenzialmente offrire approfondimenti su come la variazione termodinamica dell&#39;orientamento molecolare di superficie e delle ordinazioni a corto raggio influenzino l&#39;orientamento di massa. In questo articolo, con l&#39;obiettivo di comprendere i problemi sopra citati, abbiamo affrontato tre problemi utilizzando quattro metodi complementari ( cioè POM, DS, HR-DSC e GI-XRD): (1) Cosa sembra la transizione orientazionale? (2) La transizione orientazionale è riscontrabile termicamente? (3) Perché e come avviene la transizione orientazionale?

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orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets

Nella chimica fisica a cristalli liquidi (LC), le molecole vicine alla superficie svolgono un grande ruolo nel controllo dell&#39;orientamento di massa. Finora, principalmente per ottenere gli stati di orientamento molecolare desiderati nelle esposizioni LC, è stata studiata intensamente la proprietà superficiale &quot;statica&quot; di LC, cosiddetta anchoring a superficie. Come regola generale, una volta che l&#39;orientamento iniziale di LCs viene &quot;bloccato&quot; da trattamenti superficiali specifici, come ad esempio lo sfregamento o il trattamento con uno specifico livello di allineamento, difficilmente cambia con la temperatura. Qui presentiamo un sistema che mostra una transizione orientazionale sulla variazione di temperatura, che è in conflitto con il consenso. Proprio al momento della transizione, le molecole di massa LC sperimentano la rotazione orientazionale, con 90 ° tra l&#39;orientamento planare (P) alle alte temperature e l&#39;orientamento verticale (V) a basse temperature nel modo transitorio del primo ordine. Abbiamo monitorato il comportamento di ancoraggio termodinamico mediante la polarizzazione della microscopia ottica (pOM), la spettroscopia dielettrica (DS), la calorimetria di scansione differenziale ad alta risoluzione (HR-DSC) e la diffrazione a raggi X di incidenza di pascolo (GI-XRD) e raggiunto una spiegazione fisica plausibile: che la transizione è innescata da una crescita della superficie Fogli di bagnatura, che impongono l&#39;orientamento V localmente contro l&#39;orientamento P nella massa. Questo paesaggio fornirà un collegamento generale che spiega come l&#39;orientamento bulk dell&#39;equilibrio sia influenzato dall&#39;orientamento localizzato localizzato in molti sistemi LC. Nella nostra caratterizzazione, POM e DS sono vantaggiose offrendo informazioni sulla distribuzione spaziale dell&#39;orientamento delle molecole LC. HR-DSC fornisce informazioni sulle informazioni termodinamiche precise sulle transizioni, che non possono essere affrontate con strumenti convenzionali DSC a causa della risoluzione limitata. GI-XRD fornisce informazioni sull&#39;orientamento molecolare specifico della superficie e sulle ordinazioni a corto raggio. L&#39;obiettivo di questo documento è quello di presentare un protocollo per la preparazione di un campione che mostra i transiE dimostrare come la variazione strutturale termodinamica, sia in massa sia su superfici, possa essere analizzata attraverso i suddetti metodi.

Le immagini POM, i dati DS, i dati HR-DSC e gli schemi GI-XRD sono stati raccolti durante la variazione di temperatura, in particolare nelle vicinanze della transizione orientazionale sia sul raffreddamento che sul riscaldamento. La figura 1 rappresenta l&#39;evoluzione della struttura eseguita con le misurazioni POM e DS durante l&#39;osservazione POM della transizione orientazionale dal P orient...

Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Qui presentiamo un protocollo per attivare una transizione orientazionale di un cristallo liquido in risposta alla temperatura. Sono descritte metodologie per la preparazione di un campione per osservare la transizione e l&#39;evoluzione transizionale dettagliata.

Transizione orientativa in un cristallo liquido innescata dalla crescita termodinamica delle lastre di interfaccia

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

orientational-transition-liquid-crystal-triggered-thermodynamic

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7.1K Views.  RIKEN Center for Emergent Matter Science (CEMS).  Qui presentiamo un protocollo per attivare una transizione orientazionale di un cristallo liquido in risposta alla temperatura. Sono descritte metodologie per la preparazione di un campione per osservare la transizione e l'evoluzione transizionale dettagliata. 

Video: Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Dry Oxidation and Vacuum Annealing Treatments for Tuning the Wetting Properties of Carbon Nanotube Arrays

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.1,2 These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.2 Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.3-5
The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

This article describes a simple method to fabricate vertically aligned carbon nanotube arrays by CVD and to subsequently tune their wetting properties by exposing them to vacuum annealing or dry oxidation treatment.

Ossidazione a secco e vuoto ricottura Trattamenti per accordare le proprietà di bagnabilità di matrici di nanotubi di carbonio

In this article, we describe a simple method to reversibly  tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays.  Here, CNT ...

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Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via stereotactic radiotherapy where positioning accuracy allows delivering very high doses per fraction in a small volume of the patient. Dosimetric measurements on medical accelerators are conventionally realized using air-filled ionization chambers. However, in small beams these are subject to nonnegligible perturbation effects. This study focuses on liquid ionization chambers, which offer advantages in terms of spatial resolution and low fluence perturbation. Ion recombination effects are investigated for the microLion detector (PTW) used with the Cyberknife system (Accuray). The method consists of performing a series of water tank measurements at different source-surface distances, and applying corrections to the liquid detector readings based on simultaneous gaseous detector measurements. This approach facilitates isolating the recombination effects arising from the high density of the liquid sensitive medium and obtaining correction factors to apply to the detector readings. The main difficulty resides in achieving a sufficient level of accuracy in the setup to be able to detect small changes in the chamber response.

A growing number of radiation therapy devices offer the advantage of delivering the dose through very small beams to the tumor, allowing for increased conformity and higher doses per fraction. Many different detectors can be used for the dosimetry of these small fields. In the present study, the effect of ion recombination is investigated for a liquid ionization chamber using a stereotactic radiation therapy system.

Caratterizzazione degli effetti di ricombinazione in una ionizzazione Camera liquido utilizzato per la dosimetria di un Acceleratore radiochirurgico

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via ...

Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for the purpose of investigating phase change of those liquid segments. The magnetic beads were externally controlled using a magnet, allowing for the beads to bridge the air valve between the adjacent liquid segments. A hydrophobic coating was applied to the inner surface of the tube to enhance the separation between two liquid segments. The applied magnetic field formed an aggregate cluster of magnetic beads, capturing a certain liquid amount within the cluster that is referred to as carry-over volume. A fluorescent dye was added to one liquid segment, followed by a series of liquid transfers, which then changed the fluorescence intensity in the neighboring liquid segment. Based on the numerical analysis of the measured fluorescence intensity change, the carry-over volume per mass of magnetic beads has been found to be ~2 to 3 &#181;l/mg. This small amount of liquid allowed for the use of comparatively small liquid segments of a couple hundred microliters, enhancing the feasibility of the device for a lab-in-tube approach. This technique of applying small compositional variation in a liquid volume was applied to analyzing the binary phase diagram between water and the surfactant C12E5 (pentaethylene glycol monododecyl ether), leading to quicker analysis with smaller sample volumes than conventional methods.

Here, we present a protocol to investigate multi-component phase diagrams using externally controlled magnetic beads as liquid carriers in a lab-in-tube approach. This approach can aid in applications that seek to gather further information on phase change in complex liquid systems.

Fase Diagramma Caratterizzazione utilizzando biglie magnetiche come vettori liquidi

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for ...

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.

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.

Sintesi ed esfoliazione della discotici zirconio Fosfati di ottenere cristalli liquidi colloidale

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

Chimica

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

Preparazione delle reti di cristalli liquidi per moto oscillatorio macroscopica indotta da luce

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

Nuove tecniche per l'osservazione dinamica strutturale dei cristalli liquidi fotoresponsivi

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

Preparazione di microfluidica di liquido cristallino elastomero attuatori

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

Misurare la polarizzazione ferroelettrica magneticamente-sintonizzati in cristalli liquidi

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and as soft robots. Here, we demonstrate the preparation of shape-responsive liquid crystal elastomers (LCEs) and LCE nanocomposites along with characterization of their shape-responsiveness, mechanical properties, and microstructure. Two types of LCEs &#8212; polysiloxane-based and epoxy-based &#8212; are synthesized, aligned, and characterized. Polysiloxane-based LCEs are prepared through two crosslinking steps, the second under an applied load, resulting in monodomain LCEs. Polysiloxane LCE nanocomposites are prepared through the addition of conductive carbon black nanoparticles, both throughout the bulk of the LCE and to the LCE surface. Epoxy-based LCEs are prepared through a reversible esterification reaction. Epoxy-based LCEs are aligned through the application of a uniaxial load at elevated (160 &#176;C) temperatures. Aligned LCEs and LCE nanocomposites are characterized with respect to reversible strain, mechanical stiffness, and liquid crystal ordering using a combination of imaging, two-dimensional X-ray diffraction measurements, differential scanning calorimetry, and dynamic mechanical analysis. LCEs and LCE nanocomposites can be stimulated with heat and/or electrical potential to controllably generate strains in cell culture media, and we demonstrate the application of LCEs as shape-responsive substrates for cell culture using a custom-made apparatus.

We demonstrate the preparation of siloxane-based and epoxy-based liquid crystal elastomers (LCEs) and LCE nanocomposites. The LCEs are characterized with respect to reversible strain, liquid crystal ordering, and stiffness. As a potential application, we demonstrate their use as shape-responsive substrates in a custom device for active cell culture.

Preparazione di Monodomain Liquid Crystal Elastomeri e cristallo elastomero Nanocompositi Liquid

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and ...

Bioingegneria

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such as on-demand switchable adhesion technologies, actuators, molecular clutches, and nano-/microscopic mass transporters. Recently it was found that through a special solid-liquid transition, rheological properties can exhibit significant changes, thus providing suitable smart viscoelastic materials. However, designing materials with such a property is complex, and forward and backward switching times are usually long. Therefore, it is important to explore new working mechanisms to realize solid-liquid transitions, shorten the switching time, and enhance the contrast of rheological properties during switching. Here, a light-induced crystal-liquid phase transition is observed, which is characterized by means of polarizing light microscopy (POM), photorheometry, photo-differential scanning calorimetry (photo-DSC), and X-ray diffraction (XRD). The light-induced crystal-liquid phase transition presents key features such as (1) fast switching of crystal-liquid phases for both forward and backward reactions and (2) a high contrast ratio of viscoelasticity. In the characterization, POM is advantageous in offering information on the spatial distribution of LC molecule orientations, determining the type of liquid crystalline phases appearing in the material, and studying the orientation of LCs. Photorheometry allows measurement of a material&#8217;s rheological properties under light stimuli and can reveal the photorheological switching properties of materials. Photo-DSC is a technique to investigate thermodynamic information of materials in darkness and under light irradiation. Lastly, XRD allows studying of microscopic structures of materials. The goal of this article is to clearly present how to prepare and measure the discussed properties of a photorheological material.

This protocol demonstrates the preparation of a photorheological material that exhibits a solid phase, various liquid crystalline phases, and an isotropic liquid phase by increasing temperature. Presented here are methods for measuring the structure-viscoelasticity relationship of the material.

Commutazione fotorheologica ad alto contrasto e veloce di un cristallo liquido nematico Twist-Bend

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such ...