1. J. Ilavsky#, P. Jemian§, L. Clapp&, R. Schwartz&
IMPLICATIONS OF AGGREGATION AND MASS FRACTAL NATURE OF AGGREGATES ON THE PROPERTIES OF ORGANIC PIGMENTS AND POLYMER COMPOSITES By
N. Agashe*, G. Beaucage*, D. Kohls*, S. Sukumaran*, G. Skillas†, G. Long‡,
J. Ilavsky#, P. Jemian§, L. Clapp&, R. Schwartz&
*Department of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45220, USA
†Inst. f. Verfahrenstechnik, ETH Zentrum ML F24, CH–8092 Zurich, Switzerland.
‡Ceramics Division NIST, Gaithersburg, MD 20899, USA.
#University of Maryland, College Park, MD 20742, USA.
§University of Illinois at Urbana–Champaign, IL , USA.
&Colors Group, Sun Chemical Corp., Cincinnati, OH , USA.

2. What are Pigments ?? Most Common types of Pigments are,
Inorganic Pigments
Organic Pigments
Other types include Metallic and Pearlescent.
The smallest size of an aggregate necessary for scattering is given by Bragg’s Law,
The optimum size of the aggregate can be estimated by integrating the Guinier Law,

3. Why Organic Pigments ?
Most of the research in the pigment industry is concentrated on inorganic pigments like titania.
Until now all work on organic pigments has examined only the surface fractal nature of the organic pigment particles.
We make the first attempt to study the aggregation of organic pigments, the mass fractal nature of these aggregates and their relationship to the optical properties.
The typical size of primary particles of organic pigments is 0.05 to 0.1 mm. The optimal size necessary for good scattering is about 0.5 mm.

4. Fractal Structures – have Fractional Dimension
Surface Fractal Object, (ds)
Irregular Surface
Mass Fractal Object, (df)
Irregular Structure

5. Denotation: C.I. PR 122 (Pigment Red 122)
Common Organic Pigments are,
Azo Pigments: Monoazo (-NH-) or Diazo (-N=N-)
Quinacridones, Naphthol Reds, Diarylides, Rhodamines, and Naphthoic Acid.
Phthalocyanines: (Naphthol) & (-CN)
Metal and Non-metal
Perylenes
Carbazoles
Triphenyl Methane
Anthraquinone and Indigoid Pigments
Denotation: C.I. PR 122 (Pigment Red 122)

6. Regimes of Aggregation
Diffusion Limited Aggregation, df < 2 (df ~ 1.8)
Reaction Limited Aggregation, df > 2 (df ~ 2.5)
Intermediate Regime
Transport
Limited
Reaction

7. Aggregation of Organic Pigments
Forces behind aggregation of organic pigments are weak electrostatic forces like van Der Waal’s forces, static charge, chemical polarity and surface tension.
Processing also dictates the nature of the aggregates.
Color is produced in pigments by scattering.
Any Scattering
Best Scattering
For visible light, l ~ 0.5 mm
The typical particle size for organic pigments is 0.05 to 0.1 mm. Aggregation is necessary for good scattering.

8. Scattering in Organic Pigments
Mie Scattering
Dilute Systems, Large Particles,
Higher Index Difference
Rayleigh Ganz Approximation
All Systems, All Particles Particles,
Lower Index Difference
For X-Rays, the comparable contrast difference is very small between the pigment and the polymer.

9. Small and Ultra Small Angle X-Ray Scattering (SAXS/USAXS)
Range of q for SAXS is 0.01 to 0.1, while USAXS can go down to q value of B3 B2 B1
Log (I)
Log (q) (q in Å-1)
- 4
- df
G2, Rg2
G1, Rg1
df is the mass fractal dimension
For fractal objects,

10. Unified Function for Mass Fractal Model
Unified Function, used to fit the scattering data, is based on six parameters,
Guinier Prefactors: G1 and G2
Radius of Gyration: Rg1 and Rg2
Power law Prefactor: B1
Fractal Dimension: df
The diameter of a sphere having similar Rg as the aggregate can be used to estimate the size of the aggregate.

11. Results
The results are a survey of some of the behavior seen when organic pigments are milled into polymers.
This is the first attempt to characterize the aggregation according to the process by which the aggregates are formed.
The mass fractal behavior of these aggregates is studied.
The primary particle of each organic pigment is examined to see if it is made up of a single crystal or multi crystals.

12. Diazo Pigment Red 170 (235-0170) TEM – Dpp = 0.2 mm LS – Dagg = 0.4 mm
Powder – Non Mass Fractal
Dpp = 0.2 mm
20% in PMMA – Mass Fractal, df = 2.5 (RLA)
Dagg = 2.35 mm

13. Diazo Pigment Red 170 (235-1170) Higher Luminosity TEM – Dpp = 0.15 mm
LS – Dagg = 0.35 mm
Powder – Non Mass Fractal
Dpp = mm
20% in PMMA – Mass Fractal, df = 2.67 (RLA)
Dagg = 2.01 mm

14. PMMA, used earlier, is a non-crystalline polymer.
PP is a semi-crystalline polymer. The addition of pigments has an effect on the crystallinity of PP.

15. Monoazo Pigment Red 122 TEM – Dpp = 0.1 mm (length) LS – Dagg = 0.2 mm
C. I. PR 122
Powder – Non Mass Fractal
Dpp = 0.13 mm
1% in PP – Mass Fractal, df = 1.91 (DLA)
5% in PP – Mass Fractal, df = 1.5 (DLA)

16. Monoazo Pigment Violet 19
TEM – Dpp = 0.05 mm
LS – Dagg = 0.4 mm
C. I. PV 19
Powder – Mass Fractal, df = 2.32 (RLA)
Dpp = 0.03 mm, Dagg = 1.2 mm
1% in PP – Mass Fractal, df = 1.55 (DLA)
Dpp = 0.16 mm, Dagg = 1.0 mm
5% in PP – Mass Fractal, df = 1 (DLA)
Dpp = 0.26 mm

17. Disazo Pigment Yellow 13 TEM – Dpp = 0.1 mm LS – Dagg = 0.5 mm
C. I. PY 13
Powder – Mass Fractal, df = 2.34 (RLA)
Dpp = mm, Dagg = 0.32 mm
5% in PP – Mass Fractal, df = 2.7 (RLA)
Dpp = mm, Dagg = 0.49 mm

18. Disazo Pigment Yellow 14 TEM – Dpp = 0.1 mm LS – Dagg = 0.5 mm
C. I. PY 14
Powder – Mass Fractal, df = 2.63 (RLA)
Dpp = mm, Dagg = 0.52 mm
5% in PP – Mass Fractal, df = 2.77 (RLA)
Dpp = 0.08 mm, Dagg = 0.43 mm

19. Pigment Yellow 83 TEM – Dpp = 0.1 mm (length) LS – Dagg = 1.2 mm
C. I. PY 83
Powder – Non Mass Fractal
Dpp = 0.14 mm
1% in PP – Mass Fractal, df = 1.4 (DLA)
Dpp = 0.14 mm, Dagg = 1.1 mm
5% in PP – Mass Fractal, df = 1.62 (DLA)
Dpp = 0.12 mm, Dagg = 4.5 mm

20. Phthalocyanine Pigment Green 7
X=Cl
TEM – Dpp = 0.05 mm
LS – Dagg = 0.1 mm
Powder – Non Mass Fractal
Dpp = mm
50% in PE – Mass Fractal, df = 1.4 (DLA)
Dpp = mm, Dagg = mm

21. Effect of Pigments on the lamellar thickness of PP
The Long Period decreased from 233Å to 131Å on addition of pigments

22. Conclusions
Organic pigments field has ignored the importance of aggregates to optical properties. Mass fractal aggregates were observed for all the pigments when milled into polymers.
The size of a crystal is too small to scatter visible light. Aggregation is critical to have good optical properties, and this issue has been dealt with for the first time.
There is an incredible range of behavior in terms of aggregation, based on the polarity of the compound and the particle size.
Some contradictions in the behavior can be seen.
There is a potential to control and design the aggregate size and structure of organic pigments if we had a bit more understanding.

23. Future Work
Carry out mass fractal analysis using different pigments from different classes and different polymers.
Study of processing effects on the nature of aggregates.
Study of effect of additives on the behavior of aggregates.
Mass fractal analysis of digital electron micrographs of organic pigment powders and polymer samples.
Simulations of the process of formation of aggregates starting from primary particles.
Simulate growth processes for different systems like asymmetric particles, polydispersity and roughness of surfaces.

24. Acknowledgements Dr Gregory Beaucage. Dr George Skillas.
Sun Chemical Corporation.
Advanced Photon Source, ANL.
Research Group and the Department.
My friends and my family.