polymers Flashcards by keira Holmes

What is a polymer?

Large molecules linked by monomer units.

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Name three examples of monomer units.

Vinyl chloride
Styrene
Glucose

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What is PVC an abbreviation for?

Polyvinyl chloride.

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List the four main types of polymers.

Natural (Biopolymers)
Semi-Synthetic Polymers
Synthetic Polymers
Co-polymers

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What are natural polymers? Give examples.

Natural Fibres
Proteins
DNA

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Give two examples of semi-synthetic polymers.

Rayon fibres
Cellophane

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Name three synthetic polymers.

PVC
Polystyrene
PTFE

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What are co-polymers?

Polymers made from different linker monomers.

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What is Styrene-butadiene rubber (SBR) used for?

Tyres and rubber articles.

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What is the structure of random co-polymers?

Monomer units are arranged randomly.

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Describe the structure of block co-polymers.

Consists of long sequences of one type of monomer followed by another.

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What are thermoplastics?

Polymers that are hard at room temperature but soften when heated.

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What are thermosetting polymers?

Polymers that become highly cross-linked and solidify upon heating.

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What are elastomers?

Polymers that can stretch and return to their original shape.

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Define fibres.

Thin threads used in various applications.

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Why are fibres important in forensic analysis?

They are the largest category of polymer evidence analyzed in crime investigations.

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List the sources of natural fibres.

Animal source
Plant source
Mineral

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What is a characteristic of kapok fibres?

Smooth, hollow, thin-walled cylinders.

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Describe the structure of hemp fibres.

Colourless, transparent cylinders with surface irregularities.

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What are the two types of bast fibres?

Primary Bast Fibres
Secondary Bast Fibres

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What is rayon made from?

Regenerated cellulose extracted from wood pulp or cotton.

What is unique about nylon as a synthetic fibre?

It is a step-growth polymer.

What is Kevlar known for?

Its high strength and use in bulletproof vests.

What is chain growth polymerization?

A method where monomers are added one at a time to form a polymer.

What initiates cationic polymerization?

An electrophilic initiator attacks a nucleophilic monomer.

What is the result of anionic polymerization?

Formation of a polymer through the reaction of a nucleophilic initiator with an electrophilic group.

What is the characteristic of isotropic substances?

Light travels with the same velocity in all directions.

Define birefringence.

The difference in the refractive indices of two rays in an anisotropic substance.

What is dichroism?

Exhibiting two different colors.

What is pleochroism?

Exhibiting more than two colors.

How is the refractive index of a fibre determined?

By placing a fibre on a glass slide and immersing it in oil of specific RI.

What occurs when light is broken into two polarised rays?

They travel at different velocities due to different refractive indices.

What is the relationship between refractive index and velocity for perpendicular rays?

Higher RI = slower velocity.

What is the relationship between refractive index and velocity for parallel rays?

Lower RI = higher velocity.

What does birefringence indicate?

The absolute difference in the refractive indices of the two rays.

What is the first step in determining the refractive index of a fibre?

A fibre is placed onto a glass slide.

What is done after placing the fibre on a glass slide in refractive index determination?

The fibre is immersed in a drop of oil of specific RI.

What observation indicates that the oil and fibre have the same refractive index?

If no interference pattern is observed.

What should be tested if the oil and fibre have different refractive indices?

A series of oils of known refractive indices.

What is the method to determine the birefringence of a fibre?

Observe RI in two orientations: Parallel RI and Perpendicular RI.

What does the sign of elongation (+) indicate in birefringent fibres?

The fibre is elongated in the direction of the light.

What does the sign of elongation (-) indicate in birefringent fibres?

The fibre is contracted in the direction of the light.

What is the difference between isotropic and anisotropic substances/fibres?

Isotropic substances exhibit uniform properties; anisotropic substances produce interference colours.

What are interference colours produced by?

Double refraction and different degrees of retardation.

At what angle is maximum brightness observed in interference colours?

45° and 135°.

At what angle does extinction occur in interference colours?

90° and 180°.

Name one method used in forensic analysis of fibres.

Raman spectroscopy, FTIR, or visible microspectroscopy.

What is the duPont Fibre Identification Stain No.4 used for?

Identifying different types of fibres.

What is the Herzog Test used for?

Testing vegetable fibres.

What are the twist directions of hydrated and dried Flax and Hemp under the microscope?

Different twist directions: S-Twist and Z-Twist.