Physical methods are used to characterize pigments, surfactants, emulsions and dispersions. Particle size and shape, flow properties, surface tension, thermal properties, and fading under sunlight are topics of the analyses.
- Particle Size
- particle diameter > 1µm
- particle diameter < 1µm
- Surface Activity
- Thermal Methods
- Light and Weather Fastness
- Further Tests
Microscope techniques are used to study the size and shape of particles. Furthermore, object surfaces, powder morphology, emulsion structures and liquid crystal phases of surfactants can be studied.
- Transmission Electron Microscope
- Primary particle size of pigments via image analysis
- Scanning Electron Microscope
- Light Optical Microscope
- Particle size distribution via automatic image analysis
Laser diffraction is the method of choice for the 1 - 1000 µm region. Powders, granulates, emulsions und dispersions can be measured. Samples may be dispersed in water or solvent. Powders can be measured dry using compressed air.
- Laser diffraction
- Optical microscopy + image analysis (for special cases)
- dry powder dispersion
For some types of sample laser diffraction can also be used in the submicron region.
Only few selected techniques are able to yield reliable results for the primary particle size of pigments, which is always in the submicron size range. Fine emulsions and polymer dispersions are analyzed via dynamic light scattering.
- TEM and image analysis
Primary particle size of pigments
- Disc centrifuge
Pigment dispersions, solvent borne or water born
- Dynamic light scattering
Fine emulsions and polymer dispersions
- TEM and image analysis
In many cases, rheological properties are important application technical parameters. Modern rotational viscometers equipped with plate cone or cylinder geometry are used for the studies.
- Flow curve
- Yield point
- Viscoelastic properties
- Pigments media, e.g., printing inks, paints and pigment preparations
- Polymer gels, emulsions, concentrated surfactants solutions, shampoos
Surface activity is the chief characteristic of surfactants. It is mainly studied by observing the reduction in surface tension. Various experimental techniques are available for this. Dynamic surface tension is important for applications where the adsorption equilibrium is not reached. Interfacial tension measurements are relevant for liquid-liquid systems. The contact angle gives information on the wetting of solid surfaces.Application areas:
- Fast coating processes
- Spraying (esp. crop protection)
- Surfactant characterisation
Flash point is one of the most widely used criteria for estimating the hazards associated with flammable liquids.
Differential Scanning Calorimetry (DSC) and TGA (thermogravimetry) are the most common methods for studying a variety of endothermic and exothermic processes. It is often used as a screening test to judge the danger of an exothermic decomposition.Areas of application:
- Glass transitions (polymers)
- Paraffin crystallization (Diesel)
- Specific heat
In many cases, pigments have to maintain stable colors under the impact of sunlight and weather for many years. The weathering machines used by CC Analytical Services allow reproducible tests in compliance with international standards (e.g., ISO 11341, 4892).
- Filtered Xenon arc radiation
- Light/weather exposure under standardized conditions
- Visual judgement (vs. blue wool scale) or color metrics
- Outdoor exposure near Frankfurt, Germany
Basic physical properties of emulsions, dispersions and powders are determined as “physical parameters”. This includes a number of special tests for pigments.
- Density of liquids
- Refractive Index
- Electrical conductivity
- Calculated parameters
Specific tests for pigments
- Physical parameters
- Fastness to solvents
- pH and conductivity
- Volatile components
- Sieve residue
- Specific surface area
- Bulk density of powders