Crystallinity in Polymers

Crystalline Structures

Single CrystalsSingle Crystals Polymer SpherulitesPolymer Spherulites

Sharmistha Datta & David J. W. Grant, Sharmistha Datta & David J. W. Grant, Nature Reviews Drug DiscoveryNature Reviews Drug Discovery 3, 3, 42-57 (January 2004)42-57 (January 2004)

Physical State Transitions

Glass

Incr

eas

ing

Te

mpe

ratu

re Liquid

Flexible Thermoplastic

Gum

Rubber

Amorphous PolymerAmorphous Polymer Crystalline PolymerCrystalline Polymer

Tg

Tg

LiquidTm

Crystalline Structures

Spherulite MorphologySpherulite Morphology Folding and “Re-entry”Folding and “Re-entry”

Youyong Li and William A. Goddard IIIMacromolecules 2002 35 (22), 8440-8455

(from Odian)

19-Jun-07 BIMR workshop on characterization of materials with Electrons, Photons and Neutrons 5

XRD2 – 2D Powder Diffraction

Fiber axis∥[001]

Polyethylene(PE)

Hamburan oleh kristal

Sebuah kristal dapat menghamburkan sinar-x ke arah tertentu dan saling

menguatkan.

TEORI DASAR DIFRAKSI KRISTALTEORI DASAR DIFRAKSI KRISTALHukum Bragg Hukum Bragg

KristalKristal

2 sinhkl hkld θ λ=

Deteksi Radiasi

Difraksi

Difraksi

sinhkl hkld nθ λ=

Susunan Kristal dalam BahanBidang (110)Bidang (100) Bidang (210)

Kristal tunggal

2θ

Pada 20.6 °2θ, Hk Bragg terpenuhi pada bidang (100) & menghasilkan sebuah puncak difraksi.

Bidang (110) seharusnya menghasilkan difraksi pada 29.3 °2θ; tetapi tidak ‘properly aligned’. Hanya acah latar yang terlihat.

Bidang (200) paralel dengan bidang (100), sehingga menghasilkan difraksi.

Polikristal

2θ 2θ 2θ

19-Jun-07 BIMR workshop on characterization of materials with Electrons, Photons and Neutrons 13

XRD – Powder Diffraction

Crystallinity by DSCExperiment SetupExperiment Setup

TabDSC and DTA

Tg & Tm

Differential thermal analyzer Differential thermal analyzer (DMA)(DMA) Ref. such as AluminaRef. such as Alumina At const. rate of T increaseAt const. rate of T increase Endotherm: TmEndotherm: Tm Small amount of sample, fast Small amount of sample, fast

data and accuracydata and accuracy Disadv: weak signal for Disadv: weak signal for

crystallinecrystalline

Heat change – Differential Heat change – Differential scanning calorimetry (DSC)scanning calorimetry (DSC) Keep temperature of sample Keep temperature of sample

the same as that of Referencethe same as that of Reference Monitor the current flowMonitor the current flow

Crystallinity by DSCExample: Example:

Crystallinity of Crystallinity of PolyethylenePolyethylene

%100% ×∆∆

= °f

obsf

H

HityCrystallin

Q: “Where is my polymer in this table?”

Table: Heats of fusion of 100% crystalline polymers

DilatometryDilation Dilation or change in or change in specific volumespecific volume Computing crystallinityComputing crystallinity

Liquid of known density and thermal expansion coefficient

Polymer

∆V

ecrystallintotallyamorphous

ecrystallinpartiallyamorphous

vv

vvC

−−

=%

Dilatometry

Example: NylonExample: Nylon How would you find How would you find

the density (i.e. the density (i.e. specific volume) of specific volume) of this crystal given the this crystal given the size and shape?size and shape?

ecrystallintotallyamorphous

ecrystallinpartiallyamorphous

vv

vvC

−−

=%

Youyong Li and, William A. Goddard IIIMacromolecules 2002 35 (22), 8440-8455

Wide angle x-ray scattering/diffraction X-rays: light with X-rays: light with

wavelength ~0.1-wavelength ~0.1-10Å – the same 10Å – the same length scale as length scale as interatomic interatomic distancesdistances

Diffraction occurs Diffraction occurs only at specific only at specific angles, given by the angles, given by the Bragg eqn.Bragg eqn.

θλ sin2dn =

X-ray Scattering Crystal Planes

θλ sin2dn =

Wide angle x-ray scattering/diffraction

Why 2θ?

What if it’s not a single crystal?

Polycrystalline Polycrystalline samples look samples look different.different.

Example: Highly Example: Highly crystalline polymer crystalline polymer with (mostly) with (mostly) oriented crystallites.oriented crystallites.

Diffraction spots are Diffraction spots are blurred into lines.blurred into lines.

What if it’s not a single crystal?

Polycrystalline Polycrystalline samples look samples look different.different.

Example: Highly Example: Highly crystalline polymer crystalline polymer with no orientation with no orientation of crystallites.of crystallites.

Diffraction spots are Diffraction spots are blurred into full blurred into full circles.circles.

What if it’s not crystalline?

Diffraction circles Diffraction circles become much less become much less defined and blurred.defined and blurred.

Sharpness of circles Sharpness of circles gives a clue to gives a clue to crystallinity.crystallinity.

Polymers (see Roe: Methods of X-ray and Neutron Scattering in Polymer Science (2000))

semicrystalline poly(3-hydroxybuyrate)

Polymers (see Roe: Methods of X-ray and Neutron Scattering in Polymer Science (2000))

semicrystalline poly(3-hydroxybuyrate)

note amorphous scattering region

Polymers (see Roe: Methods of X-ray and Neutron Scattering in Polymer Science (2000))

Degree of crystallinity

Pattern consists of relatively sharp crystalline peaks +amorphous scattering

Comparing intensities of the two ––> % crystallinity

Polymers (see Roe: Methods of X-ray and Neutron Scattering in Polymer Science (2000))

Degree of crystallinity

Pattern consists of relatively sharp crystalline peaks +amorphous scattering

Comparing intensities of the two ––> % crystallinity

Problems:

small crystallite size broadens peaksextensive amounts of crystal imperfectionsthermal motion

Polymers (see Roe: Methods of X-ray and Neutron Scattering in Polymer Science (2000))

Degree of crystallinity

Pattern consists of relatively sharp crystalline peaks +amorphous scattering

Comparing intensities of the two ––> % crystallinity

Methods for separation:

guessmeasure 100% amorphous specimen

Polymers (see Roe: Methods of X-ray and Neutron Scattering in Polymer Science (2000))

semicrystalline polydimethylpropiolactone

How was this photo taken?

Why does it look like this?

An estimate of crystallinity

The crystallinity can be The crystallinity can be estimated by comparing estimated by comparing the areas of the peaks the areas of the peaks due to the amorphous due to the amorphous polymer with those of polymer with those of the crystalline phase:the crystalline phase:

%C=A%C=Acrcr / (A / (Acrcr + A + Aamam))

K.A. Moly et al. / European Polymer Journal 41 (2005) 1410–1419;

Example: Strain-induced Crystallization

S. Toki et al. / Polymer 41 (2000) 5423–5429

Other methods: IR & NMR

Ying Zheng,, Merlin L. Bruening, and, Gregory L. BakerMacromolecules 2007 40 (23), 8212-8219

Conclusion: A comparisonMethod of Analysis

Advantages Disadvantages

Differential Scanning Calorimetry

Fast, easy; You’re probably going to use DSC anyway for Tg, etc.

Need literature values of heat of fusion for 100% crystalline polymer for comparison; thermal history an issue.

Dilatometry A simple way to measure polymer crystallinity based on changes in volume.

Pure crystalline specific volume must be known.

X-ray scattering Can determine precise crystal structure.

Difficult to analyze data, determine structure.

Polarized Optical Microscopy

A quick way to see if a polymer is crystalline.

Other factors (like strain in the polymer) can cause birefringence; difficult to quantify.