Segmental Mobility –

Region of Viscoelasticity

Related LOs: > Prior Viewing – Single Chain Conformation-Ideal Chain

> Future Viewing – Unit cells in polymer crystal, Chain Folding-Lamella, Superposition Principle

Course Name: Polymeric Materials Level: UG Author : R.Piramuthu Raja Ashok, PhD Scholar, IIT Madras Mentor: Dr.Susy Varughese

*The contents in this ppt are licensed under Creative Commons Attribution-NonCommercial-ShareAlike 2.5 India license

Segmental Mobility  refers to the transitions occuring in a polymer chain while subjected to

an increase in temperature.

Learning objectives

After interacting with this Learning Object, the learner will be able to: Analyse the different thermal transitions in

polymers.

Differentiate the regimes of viscoelasticity.

Predict the thermal response of a polymer due to segmental mobility.

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Master Layout (Part 1)

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1Part 1: Segmental Mobility-Free Volume

Free Volume

Glassy

Glass- Transition

Rubbery

Viscous Flow

Definitions and Keywords Segmental Mobility1. Free Volume: The space a polymer molecule has for internal

movements/motions.

2. Backbone: simplest representation of the polymer (C-C) chain

where pendant groups are attached.

3. Gamma Transitions: Free volume increase due to localised

bond movements and side chain movements.

4. Beta Transitions: After gamma transitions, the free volume continue to increase; the whole side chains and localized groups of four to eight backbone atoms begin to have enough space to move.

5. Alpha Transitions:

1. In amorphous polymer, the alpha transition is the glass transition temperature, where the polymer transits from a glassy state to a rubbery state.

2. In crystalline polymer, large scale chain slippage occurs resulting in material to flow and the temperature is called melting temperature. 5

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Part 1,Step 1: Free Volume Concepts

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T

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Tg

Occupied Volume

Free Volume

Polymer Sample

Part 1,Step 1:

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Action Description of the action Audio Narration

As shown in animation

1. The animation should start after the audio naration point 1.

2. The sequence is given as an animation in the powerpoint. Kindly follow the same direction.

3. The temperature bar can be altered if u have a sample bar with changing colors.. Or PLEASE use the same as in animation.

1. Segmental Mobility can be best understood from the free volume concepts.

2. Consider a polymer sample inside a heating chamber. When the temperature increases, the free volume of the sample increases. At a particular temperature, there is a change in the rate of increase of free volume. This transition is called glass transition temperature.

3. The occupied volume of the polymer increases linearly with the temperature. Now let us see what happens to the polymer chains when subjected to heating.

Part 1,Step 2:

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T < Tα Increased Free Volume

Temperature

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TγTβ

Tα1

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Molecule as collection of mobile segments

Stretching

BendingRotation

Part 1,Step 1:

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Action Description of the action Audio Narration

As shown in animation

1. The sequence should be as in animation.

2. After the animation is completed, the fig 2 should appear without the arrows and the numbers against them. That callout and the arrow numbers are for animators communication.. Do remove it in original.

3. The arrow number 1 should stretch in both the arrow head direction., i.e, the black line corresponding to arrow 1(polymer chain) should also stretch; same way arrow 2- bending ;arrow 3- rotating. This movements should go alongside the curve.

1. In a polymer chain, when the temperature is increased, the chains vibrate and starting to slip past each other. This stage is where the gamma transitions are prominent. The bond stretching and bending occurs as the chain experiences more and more temperature.

2. As the temperature and the free volume continue to increase, the whole side chains and localized groups of four to eight backbone atoms begin to have enough space to move and the material starts to develop some toughness.This transition, called the beta transition Tβ.

3. At a particular temperature, the glassy state polymer transists into a rubbery state, this transtion is called glass to rubber transtion.

Animation area

Instructions/ Working area

Credits

Name of the section/stage

Interactivityarea

Transtions Modulus- temperature

Button 01

Button 02

Button 03

Free Volume

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Slide 18

Questionnaire:1. In amorphous polymer, the alpha transition is called

a) Metling temperture

b) Glass-rubber transition

c) Beta transition

2. Melting temperature is a ___________ order transition.

a) First

b) Second

c) Zero

d) Third

3. Glass transition is a _______ order transition.

a) First

b) Second

c) Zero

d) Third

4. Free volume is the space occupied by neighbouring polymer chains. Yes/No?

APPENDIX 1

Links for further reading

Reference websites:

http://pslc.ws.htm

http://plc.cwru.edu/tutorial/enhanced/main.htm

Books:

Introduction to Polymer Viscoelasticity, 3rd Edition, Montgomery T.

Shaw, William J. MacKnight, Wiley Publications, 2005.

Polymer Science & Technology, 2nd Edition, Joel.R.Fried, Prentice-

Hall India, 2003.

Polymer Physics, U.W.Gedde, Chapman & Hall, London, 1995.

APPENDIX 2

Summary

APPENDIX 3

Temperature response of polymers and different transitions were studied.

The glass transition temperature using free volume concept.