1. Selective Staining for Enhanced Spectroscopic
Identification of Domains in Immiscible
Polymer Blends by Micro-Raman Spectroscopy
Nicholas Heller1, Clive Clayton1, Spencer Giles2, James Wynne2, Mark
Walker3, Mark Wytiaz3
November 11, 2014
1: Stony Brook University
2: Naval Research Laboratory
3: The Sherwin-Williams Company

2. Blending of high and low hydroxyl content acrylic polyols leads
to phase separation upon cure
2
Curative No Curative
13.9
0
435 mm 435 mm
• Rendered immiscible due to
vastly different polar and
hydrogen bonding solubility
components from Hansen
Solubility Parameters
• Spectroscopic identification of
phases was problematic due to
relative chemical similarity.
Acrylic Polyurethane Acrylic polyol

3. Green (Top) – Low OH
Red (Middle) – High OH
Blue (Bottom) – 1:1 blend Temperature (˚C)
0 50 100 150 200
Onset x: 95.24˚C
Midpoint: 105.42 ˚C
End x: 115.60˚C
Onset x: 165.46˚C
Midpoint: 177.67˚C
End x: 189.85 ˚C
Onset x: 137.79 ˚C
Midpoint: 137.79 ˚C
End x: 158.14 ˚C
Onset x: 75.87 ˚C
Midpoint: 82.13 ˚C
End x: 75.87 ˚C
HeatFlow(Normalized)(W/g)
DSC results for
films cured with
curative
Increase for
both Tgs from
addition of
extra curative

4. Outline
• Background
• Polyester embedding
• Cross-section micrographs
• Raman Mapping
• Conclusion
4

5. Matte finish paints
• Control of surface topography and chemistry
important for development of exterior coatings
– Durability, chemical resistance, gloss
• Gloss negatively correlated with surface
roughness
• Low gloss induced by high loadings of pigments in
coating binder and film shrinkage upon solvent
evaporation
• How do we achieve the same properties in low
gloss coatings without solvent?

6. Powder Coatings
• Requires no solvents
• Spray ground, electro-statically charged particles of pigment and resin onto
a surface to be coated.
– The charged powder particles adhere to the electrically grounded
surfaces and then are heated and fused into a smooth coating in a curing
oven.
• Low loadings of pigment are necessary for these properties to work,
especially for matte finish
– High loadings compromises film durability and chemical resistance
Work piece
Charged powder particles
Powder feed line
Low Voltage Cable
High Voltage Multiplier

7. Immiscible polymeric domains for lowering gloss
Hare, C. H., Protective Coatings: Fundamentals of Chemistry and
Composition. Technology Publishing Company: 1994.
n2
n2
n2
n2
n2
n2
n2
n2
n1 n2
• The domains compensate for reduced pigment concentration to maintain low gloss via
multiple light scattering
• Tcure = 400 ˚F
• Sprayed on tin panels

8. Gloss has been observed to decrease
as the cure-time increases
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
20
30
40
50
60
70
80
90
100
0 5 10 15
SurfaceRoughnessmicrons
85DegreeGloss
Time (minutes)
• The gloss plateaus at about 4 minutes

9. Cross-section Sample Preparation with Dry
Polishing eliminates contamination
• Coatings peeled off tin substrates
• Samples embedded in polyester resin with peroxide catalyst
• 50% unsaturated polyester, 40% styrene monomer, 10% methyl methacrylate
– Samples cured in Al molds for 72 hours
– Recommended by Metropolitan Museum of Art, NYC
• MOPAS dry hand-polisher (made in Amsterdam, Holland)
– Mass = 400 g  applies uniform downward pressure on sample
– Samples dry polished with 6” square abrasive cloth (micro-mesh) via square-shape
motion
• 0.5–1 hour with successive grits
– Highest grade polish of 1 µm
– No contamination from polishing process
Bottom Embedded layer
sample
Top embedded layer
9

10. Comparison between groups of spectra
Unembedded Samples Polyester Embedded Samples
Epoxy Embedded Sample
Ester
C=O
Aro
AroCurative C=O
Aro
Aro
free
C=O
Ester
C=O
Ester
C=O
Ester
C=O
free
C=O
Ester C=O
C=C Aro
Aro
Curative C=O
free
C=O
Ester
C=O
C=C
Free C=O
Ester C=Ofree
C=O
Low OH
High OH
Blend in Matrix
Domain in Matrix
Free C=O
Low OH
High OH
Blend in Matrix
Domain in Matrix
Ester
C=O
Aro
Aro
C=C
Free C=O
Free C=O
Blend in Matrix
Domain in Matrix
Ester
C=O
Ester
C=O
Aro
Aro
• Curative C=O has
been observed to
decrease WRT to
cure-time
• Free and ester C=O
have vary just
slightly in blend
• Sensitive to
noise and
fluorescence
• Samples are contaminated
by the polyester
embedding resin
• Epoxy does not
contaminate the sample

11. Cross-section digital optical micrographs for blend at 1-6 min cure-times
at 400 F show evolution of domain structure
1 min 2.5 min
Bilayer structures in domains
Elongated domains emerge
–> adhered to tin substrate
11
100 µm
100 µm
Large domains are already evident, and
may exist before start of cure
4 min
Domains adhered to substrate are getting longer
Gloss flat lines here, but domains continue to evolve
100 µm 100 µm
6 min
Adhered domains begin to become more common
than globular domains

12. Cross-section of 12 minute cure at optical and
transmission electron microscopies
Top Polyester layer
Large
Domain
• Relatively few large globules remain
• Adhered domains continue lengthening
• Given enough time, all domains may merge into one
layer at the bottom half of the polymer film
1 µm
4 µm
Domains may have
enlarged by the merging
of several smaller domains
100 µm
• TEM section is 80 nm thick
• Reveals several small globules
that were previously unseen in
polished XS
• Still not enough to ID domains

13. low high
C=C /Aromatic peak height ratio
1630 cm-1 peak  alkene
functionality from styrene contaminant
Free C=O
Ester C=O
Ester C=O
Free C=O
Aromatic
First Raman map taken after dry
polishing showed distinct chemistry
within domain of polymer embedded in
polyester
Aromatic
30 µm
Polymer Matrix
Domain
C=C

14. • High and low OH cross-section styrene
staining
– Low OH resin shows infiltration by styrene
similar to blended system polymer matrix
C=C peak height
low high
Domain Identificationusing Micro RamanMapping
polyester embedded high and low OH homopolymers
Hence: Domain = high OH resin
Low OH
C=C/aromatic peak height ratio
30 µm
30 µm
High OH
Free C=O
Ester C=O
AromaticC=C
Free C=O
Ester C=O
Aromatic

15. Mapping with peak height ratios
domain
0–0.2 1.1–1.3
Styrene Peak Height Ratio = hC=C/haryl
matrix
Polyester
Advantages of styrene peak height ratio maps
• Defined as hC=C/haryl
–1630 cm-1/1600 cm-1
• semi-quantitative measure of relative styrene
concentration, especially for within large domains
• Good for distinguishing boundary between
polyurethane and polyester
Aromatic = 1600 cm-1
Conj. alkene = 1630 cm-1
hC=C
Polyester
haro

16. 1760 cm-1 Free C=O peak height
Embedding blend in epoxy does not contaminate specimen and domains
in the cross-section can be revealed by mapping with C=O peaks
• C=O concentration may be different in
domains because of urethane crosslinks
• Less intense 1760 cm-1 C=O observed peak
in domain
• Suggests that C=O can be an additional
moiety for chemical mapping but only for
cross-section
low high
16
50 µm
Free
C=O
aromatic
aromatic
aromatic
Ester
C=O
Free
C=O
Ester
C=O
Epoxy
Matrix
Domain
30 µm

17. C=O peaks are problematical for mapping of cross-sections when
compared to to C=C and aromatic peaks from styrene
C=C/aromatic peak height ratio
polyester
polyester
C=C peak height
Encapsulated matrix
Ester C=O peak height
Free C=O peak height
0.10 1.25
17
Concentration gradient for
styrene infiltration
100 µm
50 µm
Advantages of peak height maps
• Peak height map good for domain resolution
• Raman intensity counts lower in domains
–domain geometry clearer
• For C=C, boundary between polyurethane &
polyester difficult to discern
• C=O maps are often unreliable
50 µm
50 µm
50 µm

18. High OH film
aromatic
C=O
aromatic
C=C
Domain
Matrix
Low OH film
Styrene vapor can selectively stain matrix surfaces of blend and low
OH film
No styrene peaks
72 hours in styrene atmosphere
Similar results for all three samples after 24 hours of
vapor staining

19. C=C/aromatic peak height ratio
• On surface, domain is still
impervious to styrene
infiltration
• Small domains surrounding
the big domain in the center
can be detected
30µm
C=C peak height
19
One hour vapor exposure effective to stain the
matrix on the surface
C=C
C=C
Free
C=O
Free
C=O
Free
C=O
Aromatic
30 µm
Low OH
Matrix
Domain
Ester
C=O
Ester
C=O
Ester
C=O
Aromatic
Aromatic
30 µm

20. Conclusion
• The styrene from the polyester embedding resin saturated the matrix of
the blend and the low OH homopolymer
• The styrene was unable to infiltrate the domains in the blend and the high
OH homopolymer
• This selective infiltration became strong evidence that the domains
originate from the high OH acrylic polyol, and the matrix from the low OH
acrylic polyol
• This selective infiltration became the foundation of a selective staining
protocol with styrene solvent for enhanced Raman mapping of separated
phases in a polymeric film
• Degree of styrene infiltration can be controlled through vapor staining
• Raman mapping with the carbonyl peaks were far less sensitive to domain
morphology
• The most sensitive Raman peak for mapping was found to be the alkene
peak at 1630 cm-1
20

21. Thank you!