Anton Paar Offers Solutions for Material Characterization

Rheological Solutions

Rheology is the branch of science that describes the behavior of materials under flow and deformation. Yield point, pseudoplasticity, thixotropy, or viscoelastic behavior are well-known terms for polymers, building chemicals, and paints and coatings industries. From the past to the present, numerous test methods such as flow cups, glass capillary viscometers, and rotational viscometers have been used to explain the flow and deformation behavior of materials. Some of these methods are still in use today. In order to determine the rheological behavior of all materials from solids to liquids, rheometers have begun to replace viscometers due to many advantages such as wider measurement ranges and the ability to measure different types of samples. Rheometers are used in quality control measurements as well as in research and development work. The Modular Compact Rheometer (MCR) Series presented by Anton Paar enables rotational and oscillatory tests, which are rheological test methods. The choice of which test type to use depends on the properties of the material to be examined and the behavior of the sample. Materials are examined in three basic groups in terms of mechanical properties: ideal viscous, viscoelastic, and ideal elastic. Water and mineral oils are examples of ideal viscous materials; steel springs are examples of ideal elastic materials. Viscoelastic materials have both viscous and elastic characteristics together. When the viscous character is dominant, it is called a viscoelastic liquid; when the elastic character is dominant, it is called a viscoelastic solid or gel. Shampoo and toothpaste are examples of viscoelastic materials. When rotational tests are discussed, the first thing that comes to mind is dynamic viscosity (η) measurements. Rotational tests help us analyze the viscous character of a material. To clarify the behavior of viscoelastic materials with more complex behavior, oscillatory tests are required. The "Loss Modulus" (G'', which defines viscous character), the "Storage Modulus" (G', which defines elastic character), and the loss factor (tan δ = G''/G', damping factor), which expresses the ratio of these two characters to each other, are the main numerical values obtained from oscillatory tests. Oscillatory tests can ideally be used to characterize the rheological properties of all sample types. In routine rheological analysis, the change in the rheological outputs mentioned above is examined and evaluated by varying parameters such as frequency, deformation, shear rate, and shear stress. With Anton Paar rheometers, in addition to routine rheological measurements, the modular design allows the use of special accessories to examine the effects of different parameters. Some of these parameters and related accessories are listed below: • Powder Cell • UV Curing Unit • Dynamic Mechanical Thermal Analysis • Building Material Cell • Humidity Option, etc.

Nano and Micro Particle Characterization

The size and properties of nano and micro particles affect their rheological properties, process behavior, and storage. Anton Paar offers different solutions for a wide range of particle sizes from nano scale to micro scale.

Litesizer™ Series

The Litesizer™ Series operates with light scattering technology. Particles dispersed in a liquid move randomly, and their size affects the speed of this movement. Smaller particles move faster, while as size increases, their speed decreases. In dynamic light scattering technique, light passes through the sample and the scattered light is detected and recorded at a specific angle. The change in scattered light intensity over time shows how fast the particle is moving. From this data, the average particle size and particle size distribution are obtained. The choice of angle is important because the intensity of light scattered backward or sideways may change depending on whether the material is opaque or transparent. In the Litesizer™ 500, the transmittance value is determined during measurement and the appropriate angle is automatically selected. Additionally, transmittance measurements can be performed in both the Litesizer™ 100 and Litesizer™ 500 series. Measurements in the Litesizer™ series can be performed in the particle size range of 0.3 nm to 10 μm. The determination of zeta potential is as important as determining particle size in terms of particle characterization. Especially in suspensions, it is necessary to know the zeta potential in terms of stability. For this purpose, electrophoretic light scattering technique is used. In this technique, the velocities of particles under an applied electric field are examined. An increase in particle velocity indicates a higher zeta potential magnitude. A higher zeta potential (which can be negative or positive) results in a stronger repulsive force between particles, and therefore enables obtaining a more stable suspension. With the patented cmPALS technique, the Litesizer™ 500 enables zeta potential measurements at low electric fields and in very short times, while homogeneous electric fields are provided through specially designed omega cuvettes to increase measurement accuracy. As zeta potential values change with pH, the device can be equipped with an automatic titration unit. In both dynamic light scattering and electrophoretic light scattering techniques, the refractive index value of the solvent, which is required as prior knowledge and parameter, can be measured in the Litesizer™ 500 and does not require an additional separate device for this purpose. Another important information that can be obtained from light scattering technique is molecular weight, and this information can also be obtained with the Litesizer™ 500. For this purpose, measurements of the material at different concentrations are performed and a "Debye plot" is drawn to determine the molecular weight.

Particle Size Measurement by Laser Diffraction Method

Another technique for particle size measurement is the laser diffraction method. In this technique, a laser beam is directed at dispersed particles and the beam is diffracted by the particles. The diffraction pattern is detected and analyzed. Particle size distribution can be obtained according to Fraunhofer and Mie theories. The "Particle Size Analyzer (PSA)" series devices, with more than 50 years of experience, can perform measurements both in dry (powder) form and in suspensions. Particles can be examined in a particle size range of 0.04 μm to 2500 μm. In PSA systems, only one of the dry and suspension measurement options can be provided, or both options can be provided simultaneously in a single device. With both options present in the device, it is possible to switch from one option to the other only with software; no accessory changes are required. This saves time and prevents possible user errors. PSA systems are ideal devices for obtaining information about particle size in cement and building chemicals, food, pharmaceutical and cosmetic, chemical and petrochemical industries. Gizem Akay / Application Engineer / Anton Paar Ölçüm Aletleri Ticaret Ltd. Şti.