confinement of 5cb between lyotropic...

Cory Dolbashian

Dr. Rizwan Mahmood

Physics Dept.

Slippery Rock University

Confinement of 5CB Between Lyotropic Bilayers

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We have attempted to confine a hydrophobic liquid crystal (5CB) within bilayers of lipid-resembling liquid crystal (DDAB).

After creating this system, we wish to gather optical data for this mixture.

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Bilayers in the body.

Drug delivery and Transport.

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Rod-like

Disc-Shaped

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Isotropic

Temperature

Nematic Smectic A

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5CB - (4cyano- 4’-pentylbiphenyl) ◦ Thermotropic liquid crystal. -Phase change f ( T, P)

DDAB - Dimethyldioctadecylammonium bromide

◦ Lyotropic liquid crystal. -Phase change f (T, Concentration)

Liquid Crystals Used

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+ + Surfactant = Microemulsion

+ + = Microemulsion

5CB DDAB

OIL H20

H20

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Micelle of Oil in Water

• Hydrophilic heads face

outward.

• Hydrophobic tails face

inward.

• Oil (5CB) is trapped

inside.

Reverse Micelle of Water in Oil

• Hydrophobic tails face

outward

• Hydrophilic heads face

inward.

• Water is trapped inside.

Hydrophobic tails

Hydrophilic Head

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Change concentration (Φ =% {75% DDAB and 25% H20}) of Microemulsion. o Φ=0% to 90%.

Observe how Orientational Ordering changes as a function of T and Concentration.

Map a phase diagram for our system.

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Refraction of light waves.

Propagation of light changed by medium.

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Birefringence as f (T, Φ). ◦ Vary Φ from 0 to 90%

Use Birefringence data to understand orientational ordering.

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-4.16E-16

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0.11

0.12

0.13

0.14

0.15

26 27 28 29 30 31 32 33 34 35 36

Bir

efr

ing

en

ce

Temperature

Birefringence vs. Temperature (100% 5CB)

Birefringence

Birefringence Vs. Temperature (oC )

oC

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In liquid crystal systems, alignment is very important. ◦ Polarization

Without surface treatment. ◦ Homeotropic.

◦ Isotropic.

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In Liquid crystal systems, alignment is very important. ◦ Polarization

With Surface Treatment ◦ Parallel alignment.

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100µm______

Originally, sample cells were prepared using a mixture of 1% Polyvinyl Alcohol (PVA), and 99% Distilled Water, as a surface treatment.

◦ PVA in our system suspected to result in a homeotropic alignment

◦ Surface anchoring energies were not strong enough for parallel alignment.

MEOH solution (N-OctadecylDimethyl[3-(Trimethoxysilyl) Propyl) surface treatment produces the desired Parallel Alignment. ◦ Treatment is 95% {95% ethyl alcohol and 5% distilled water} and 5% MEOH

Solution

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Seemingly Isotropic at all T for samples when Φ < 0.6 . ◦ Observed Transparent Nematic Phase (TN)

◦ Thin samples succumb to homeotropic anchoring.

Unable to detect Nematic phase under cross polarization (Yamamoto & Tanaka 2001)

Appearance of “Maltese Cross” structure ◦ Reversible phase separation

◦ Phase separations occur with low anchoring energies within the Nematic phase (Matsuyama 2012)

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100µm______

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100µm______

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100µm______

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100µm______

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100µm______

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50µm______

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100µm______

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Thick Sample (~1mm)

Pinpoint Φ for the onset of Lamellar phase. ◦ Between Φ =0.65 and 0.75.

Complete phase diagram.

Birefringence Measurements.

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We would like to thank the Dean’s office for providing funding and support for the project.

Professor Noel A. Clark of University of Boulder, CO, has drawn our attention to this problem.

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35

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10% 5CB 88.4C

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15% 5CB 51.7C

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10% 5CB 79.1C

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