Combined Rheological Methods: From Rheo-Optics to Magneto-Rheology and Beyond

Nowadays a wide variety of different accessories used in combination with rotational rheomters are available. Such techniques range from rheo-optical methods to applying external pressures and electrical or magnetical fields. In addition systems transforming the rotational movement of the rheometer allow investigations on extensional rheology or tribology with a rheometer. INTRODUCTION Rheological measurements reveal information on macroscopic material properties as a function of temperatures. The combination of additional techniques with rheological measurements became more popular in recent years. We classify all methods into three main categories. The first contains all techniques providing additional structural information. Since the mechanical material properties are strongly dependent on the microstructure, information on the microstructure is often valuable for a better understanding of the rheological behavior. The second category includes all systems in which the rheological behavior as a function of an additional parameter is studied. The third category contains techniques transforming the rotational or the axial movements of the rheometer into different types of flow conditions. The geometries or accessories used impose mechanical loads in different geometrical forms onto various types of samples. The aim of the paper is to give an overview over such widely used combined rheological techniques and to discuss their respective advantages and limitations. However, here we limit ourselves to techniques which can be mounted optionally as special accessories into the MCR rheometer from Anton Paar. METHODS GIVING ADDITIONAL STRUCTURAL INFORMATION Establishing a connection between the changes of the microstructure of a fluid in a flow field and their consequences on its macroscopic properties leads to a better understanding of the behavior of complex fluids and allows an optimization of their parameters. The decision on which technique to choose is based on the size and type of the structure as well as on the general sample properties to be investigated. The proper method for investigating a certain sample depends on the length scale but also on the special requirements needed for the experiment. For the characterization of materials in the mesoscopic scale, i.e. in the range from one to several hundred nm, techniques like Small Angle X-ray Scattering (SAXS) or Small Angle Neutron Scattering (SANS) Combined Rheological Methods: From Rheo-Optics to Magneto-Rheology and Beyond