PolymersRET LESSON

MR. Groff Marlington High School

What is a polymer?

Lets see if you know! What is a polymer?

Do you use any in every day life?

What are they made of?

LARGE MOLECULES

POLYMER:

A Large Molecule made up of many repeating subunits!!!

http://www.youtube.com/watch?v=8b_3T7Ss4_M

What are the repeating subunits called?

What every day item can we compare these large molecules to?

Common Polymer Types

Plastics!

Rubber!

Glass !

http://en.wikipedia.org/wiki/Polyethylene_terephthalate#mediaviewer/File:Plastic_bottle.jpg

http://commons.wikimedia.org/wiki/File:Reading-Glasses.jpg

PDMS ---polymer“Polydimethylsilo

xane”

Picture from ref. 2.

How we will make it

Silicone Base + Curing Agent (cross linker)+ Heating (crosslinking catalyst)

Then we have cross-linked material!

Now, if we want a certain thickness, and we are going to make it in glass petri dishes…how will we know how much to use……???

DENSITY=Mass/Volume

D PDMS= 965.00 kg/m³

What variables from the Density Formula do we need…?Lets break them down

1. Volume First---Thickness

2. Mass 2nd for CRL Ratio

Entropy and Potential Energy.

What causes certain materials to return after being stretched? Why do rubber bands “go back”?

These questions can be answered through a simple understanding of ENTROPY.

ENTROPY: a measure of molecular disorder. Through altering a material, by cross-linking it for example, one can give order to the disorder. This can cause properties such as elasticity.

By stretching an elastic polymer you can cause the entropic spring result and amounts to saying: upon stretching a polymer chain you are doing work on the system, thereby increasing its potential energy due to dragging it away from its (preferred) equilibrium state. An example of this is a common elastic band, composed of long chain (rubber) polymers

Visual-crosslinking

(A) is an unstressed polymer; (B) is the same polymer under stress. When the stress is removed, it will return to the A configuration. (The dots represent cross-links)

Force Applied

Entropic Spring Result (restoring force)

Picture from ref. 3

Young’s ModulusSTRESS vs. STRAIN

Stress—The Internal Force per unit area associated with a strain.

Strain–- The Relative change in shape or size of an object due to externally applied forces.

Stress/Strain=Young’s Modulus.

VisualArea= (x)(z)

xz L L

ΔL

Force Applied

Entropic Spring Result (restoring force)

Young’s Cont.Stress = (Force/Cross sectional area)

Strain= (Change in Length/ Initial Length)

E= Young’s Modulus

Equation from ref. 4.

Stress Strain and Hooke’s Law

Picture from ref 6.Picture from ref 5.

CHOOSE!!!!Young’s Modulus due to CRL Ratio

20:1 or 10:1 or 8:1

Young’s Modulus due to Thickness of Sample

1mm 2mm 4mm

Bibliography1. Polymer physics. (2014, July 7). In Wikipedia, The Free Encyclopedia. Retrieved 14:21, July 14, 2014, from http://en.wikipedia.org/w/index.php?title=Polymer_physics&oldid=615926552

2. Polydimethylsiloxane. (2014, June 27). In Wikipedia, The Free Encyclopedia. Retrieved 14:22, July 14, 2014, from http://en.wikipedia.org/w/index.php?title=Polydimethylsiloxane&oldid=614644275

3. Elastomer. (2014, May 13). In Wikipedia, The Free Encyclopedia. Retrieved 14:30, July 14, 2014, from http://en.wikipedia.org/w/index.php?title=Elastomer&oldid=608353943

4. Young's modulus. (2014, June 26). In Wikipedia, The Free Encyclopedia. Retrieved 14:46, July 14, 2014, from http://en.wikipedia.org/w/index.php?title=Young%27s_modulus&oldid=614521775

5. Stress–strain curve. (2014, July 5). In Wikipedia, The Free Encyclopedia. Retrieved 14:49, July 14, 2014, from http://en.wikipedia.org/w/index.php?title=Stress%E2%80%93strain_curve&oldid=615693329

6. Hooke's law. (2014, July 9). In Wikipedia, The Free Encyclopedia. Retrieved 15:00, July 14, 2014, from http://en.wikipedia.org/w/index.php?title=Hooke%27s_law&oldid=616204891