liquid crystals (copy) 5

what is the fourth state of matter

liquid and crystal

liquid properties (4)

• isotropic

• optically transparent

• 1 refractive index

• flow

crystal properties (4)

• anisotropic

• direction dependent

• 3 refractive indicies

• doesnt flow

when something is mesogenic what is it

a liquid crystal

what is a mesophase

a liqud crystal phase

what is isotrophy

uniformity in all directions

what is isotropic in?

liquid phase

what is anisotropy?

directionally dependent

when something is thermotropic what is it

behaviour as a function of temperature

what is lyotropic

solutions of compounds that have liquid crystal behaviour

where are lyotropic crystals formed?

In surfactant solutions

what is birefringence, and what does this mean

the ability to rotate plane polarised light

types of thermotropic liquid crystal (3)

• nematic

• smectic

• cholesteric

organic thermotropic liquid crystal properties (4)

• organic

• elongated

• flat

• rigid

• easily polarisable

• contain dipoles

• nematic

what functional groups do organic thermotropic liquid crystals have

• esters

• anils

• azo compounds

• azoxy compounds

how do liquid crystal displays come about (LCD)

weak electrical signals emit an optical response

What doesn’t LCD emit?

Light

How do LCDs modify light?(2)

Scattering

Change in optical density or colour

What do LCDs use?

Low voltages

What is low in LCDs?

Power consumption

Heat produced

What LCDs give?

Good contrast in strong light

Why can’t molecules be parallel?

Due to chiral interaction there is a slight angle between them

Where are cholesteric LC’s used? (4)

Sensors

Thermometers

Fabrics

Display devices

When do cholesterics refract light?

With a wavelength equal to the pitch

What does the cholesteric pitch depend on? (3)

Temp

Press

Electric & Magnetic fields

How are tumours different to surrounding tissues?

Temperature

What are the essential structural features of Lyotropic Liquid Crystals (LLC)

–Amphiphiic

•Polar – head group

•Non-polar – alkyl chain

What is the structure of a potassium stearate surfactant molecule?

non-polar tail

Polar head

Amphiphilic

What happens to the soluble part of potassium stearate(polar head)?

ut’s attracted to the water and is solvated

What happens to the non-soluble part of potassium stearate(non-polar tail)?

hates water and is shielded from the solvent(water)

What happens you add a potassium stearate with a solvent?

Spontaneous formation of aggregates

what is formed in an aqueous solvent?

micelle

what is formed in a non-polar solvent?

inverse micelle

What happens when we have a very low surfactant concentration?

a monomeric solution is formed

What happens at the Critical micelle concentration (CMC)?

where we have enough micelles added they start to form spheric aggregates(micelles)

What do you get once you keep increasing surfactant concentration

micellar solution

What does a micellar solution do? (3)

Increase number of micelles

Increase size of micelles

Change shape of micelles- rods or discs

What does the hexagonal phase consist of?

close packed rod-like micelles separated by continuous water region.

Describe cell membranes? (2)

Amphiphilic molecules- Phospholipids

Regularly stacked layers

How does matter leave and enter cells?

Lipid bilayer

Proteins

What is the role of lipid bilayers

Fluid and let water in n out

What is the role of proteins?

Act as gates and switches in membranes

What materials can behave as liquid crystals(5)?

Cells

Lipids

Protein n polypeptide solution

DNA n RNA

Polysaccharides