Crystallinity in Polymers
Crystallinity in Polymers
Crystallinity in Polymers
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<strong>Crystall<strong>in</strong>ity</strong> <strong>in</strong> <strong>Polymers</strong><br />
Brandon Rawl<strong>in</strong>gs<br />
February 12, 2009
Crystall<strong>in</strong>e Structures<br />
S<strong>in</strong>gle Crystals<br />
Polymer Spherulites<br />
Sharmistha Datta & David J. W. Grant, Nature Reviews Drug Discovery 3,<br />
42-57 (January 2004)
Physical State Transitions<br />
Amorphous Polymer<br />
Crystall<strong>in</strong>e Polymer<br />
Increas<strong>in</strong>g Temperature <br />
Liquid<br />
Gum<br />
Rubber<br />
Liquid<br />
Flexible<br />
Thermoplastic<br />
T m<br />
T g<br />
T g<br />
Glass
Crystall<strong>in</strong>e Structures<br />
Spherulite Morphology<br />
Fold<strong>in</strong>g and “Re-entry”“Re<br />
(from Odian)<br />
Youyong Li and William A. Goddard III<br />
Macromolecules 2002 35 (22), 8440-8455
<strong>Crystall<strong>in</strong>ity</strong> by DSC<br />
Experiment Setup
<strong>Crystall<strong>in</strong>ity</strong> by DSC<br />
Example:<br />
<strong>Crystall<strong>in</strong>ity</strong> of<br />
Polyethylene<br />
obs<br />
∆H<br />
f<br />
% <strong>Crystall<strong>in</strong>ity</strong> = ×100%<br />
°<br />
∆H<br />
Table: Heats of fusion of 100%<br />
crystall<strong>in</strong>e polymers<br />
f<br />
Q: “Where is my polymer <strong>in</strong><br />
this table?”
Dilatometry<br />
Dilation or change <strong>in</strong><br />
specific volume<br />
Comput<strong>in</strong>g crystall<strong>in</strong>ity<br />
∆V<br />
Liquid of<br />
known density<br />
and thermal<br />
expansion<br />
coefficient<br />
Polymer<br />
% C<br />
=<br />
v<br />
amorphous<br />
v<br />
amorphous<br />
− v<br />
− v<br />
partially<br />
crystall<strong>in</strong>e<br />
totally crystall<strong>in</strong>e
Dilatometry<br />
Example: Nylon<br />
How would you f<strong>in</strong>d<br />
the density (i.e.<br />
specific volume) of<br />
this crystal given the<br />
size and shape?<br />
% C<br />
=<br />
v<br />
amorphous<br />
v<br />
amorphous<br />
− v<br />
− v<br />
partially<br />
crystall<strong>in</strong>e<br />
totally crystall<strong>in</strong>e<br />
Youyong Li and, William A. Goddard III<br />
Macromolecules 2002 35 (22), 8440-8455
Wide angle x-ray<br />
scatter<strong>in</strong>g/diffraction<br />
X-rays: light with<br />
wavelength ~0.1-<br />
10Å – the same<br />
length scale as<br />
<strong>in</strong>teratomic<br />
distances<br />
Diffraction occurs<br />
only at specific<br />
angles, given by the<br />
Bragg eqn.<br />
n λ = 2d s<strong>in</strong>θ
X-ray Scatter<strong>in</strong>g Crystal Planes<br />
n λ = 2d s<strong>in</strong>θ
Wide angle x-ray<br />
scatter<strong>in</strong>g/diffraction<br />
Why 2θ?
What if it’s not a s<strong>in</strong>gle crystal?<br />
Polycrystall<strong>in</strong>e<br />
samples look<br />
different.<br />
Example: Highly<br />
crystall<strong>in</strong>e polymer<br />
with (mostly)<br />
oriented crystallites.<br />
Diffraction spots are<br />
blurred <strong>in</strong>to l<strong>in</strong>es.
What if it’s not a s<strong>in</strong>gle crystal?<br />
Polycrystall<strong>in</strong>e<br />
samples look<br />
different.<br />
Example: Highly<br />
crystall<strong>in</strong>e polymer<br />
with no orientation<br />
of crystallites.<br />
Diffraction spots are<br />
blurred <strong>in</strong>to full<br />
circles.
What if it’s not crystall<strong>in</strong>e?<br />
Diffraction circles<br />
become much less<br />
def<strong>in</strong>ed and blurred.<br />
Sharpness of circles<br />
gives a clue to<br />
crystall<strong>in</strong>ity.
An estimate of crystall<strong>in</strong>ity<br />
The crystall<strong>in</strong>ity can be<br />
estimated by compar<strong>in</strong>g<br />
the areas of the peaks<br />
due to the amorphous<br />
polymer with those of<br />
the crystall<strong>in</strong>e phase:<br />
%C=A cr / (A cr + A am )<br />
K.A. Moly et al. / European Polymer Journal 41<br />
(2005) 1410–1419;
Example: Stra<strong>in</strong>-<strong>in</strong>duced<br />
Crystallization<br />
S. Toki et al. / Polymer 41 (2000) 5423–<br />
5429
Other methods: IR & NMR<br />
Y<strong>in</strong>g Zheng,, Merl<strong>in</strong> L. Bruen<strong>in</strong>g, and,<br />
Gregory L. Baker<br />
Macromolecules 2007 40 (23), 8212-<br />
8219
Conclusion: A comparison<br />
Method of<br />
Analysis<br />
Differential<br />
Scann<strong>in</strong>g<br />
Calorimetry<br />
Dilatometry<br />
X-ray scatter<strong>in</strong>g<br />
Polarized Optical<br />
Microscopy<br />
Advantages<br />
Fast, easy; You’re probably<br />
go<strong>in</strong>g to use DSC anyway for T g<br />
,<br />
etc.<br />
A simple way to measure<br />
polymer crystall<strong>in</strong>ity based on<br />
changes <strong>in</strong> volume.<br />
Can determ<strong>in</strong>e precise crystal<br />
structure.<br />
A quick way to see if a polymer<br />
is crystall<strong>in</strong>e.<br />
Disadvantages<br />
Need literature values of<br />
heat of fusion for 100%<br />
crystall<strong>in</strong>e polymer for<br />
comparison; thermal<br />
history an issue.<br />
Pure crystall<strong>in</strong>e specific<br />
volume must be known.<br />
Difficult to analyze data,<br />
determ<strong>in</strong>e structure.<br />
Other factors (like stra<strong>in</strong><br />
<strong>in</strong> the polymer) can<br />
cause birefr<strong>in</strong>gence;<br />
difficult to quantify.
Conclusion<br />
Offshoot: A comb<strong>in</strong>ation of methods<br />
may be the best solution (e.g. x-ray x<br />
scatter<strong>in</strong>g, DSC)<br />
Polymer crystall<strong>in</strong>ity contributes to the<br />
strength of many polymeric materials.<br />
Questions?