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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
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.
19-Jun-07 BIMR workshop on characterization of materials with Electrons, Photons and Neutrons 13
XRD – Powder Diffraction
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 =
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;
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.