Crystal Design of High Performance Pigments

25 сентября, 2015

Pokraskin

Peter Erk

With few exceptions, pigments exist as crystalline solids, and all of their essential properties depend on structural and morphological features associated with the solid state. For an efficient design of high-performance pigments it is necessary to analyze and to understand the molecular reasons behind those solid properties which give rise to the technical performance of these materials (Table 8.1).

Table 8.1 Microscopic (molecular and crystal) and solid state properties of crystalline materials related to their technical performance.

Molecular	Crystal properties	Solid	Technical performance
		Hardness	Agglomeration/flocculation
	Lattice energy	Refraction	Wetting/dispersibility
Crystal structure	Particle size	Cohesion	Thermal stability
Polarizability	Crystal habit	^-potential	Color/optical properties
Dipole moment	Density	Solubility	Weatherfastness
Conformation	Defects	Absorption	Filtration/caking
Constitution	Surface structure	Conductivity	Dispersion rheology
	Band structure	Magnetism	Compaction properties
		Brittleness	Powder flow/density

Crystal design covers aspects of crystal engineering [1] (designing the bulk structure), morphology control [2] (designing particle size and shape), and interfacial engineering of pigment particles. Computational tools are the backbone of crystal design, and most of them have just become available because of the dramatic increase of computing power over the last decade. With their help, general properties of crystalline solids can be investigated by statistical analysis [3], structural features may quickly be visualized, and computational simulations can help to analyze and to interpret the observed features. Guidance for the design of new pigments may then be drawn by combining these insights with chemical and crystallographic knowledge, experience, and intuition [4].

For conceptual reasons this chapter is restricted to organic pigments. Although there are some fundamental differences between organic and inorganic pigments which originate from different bonding situations in the solids, many of the principles outlined here for organic pigments may be applied to inorganic pigments as well.

8.2