Rheometer biconical

FIGURE 9 Effect of pressure level on torque in biconical rheometer. 

The concepts of the cone-plate and biconical rheometers developed in the 1940s (Fig. 13). The cone-plate instrument is due to Freeman and Weissenherg [FIO] and intended for modest-viscosity fluids. It has the basis of his rheogo-niometer which also measured normal stresses. The biconical rheometer was developed in the same period by Piper and Scott [P12] of the BRMRA and was from the beginning intended for rubber. Similar instruments are discussed by Turner and Moore [T12] and Montes et al. [M37, M38]. In the latter instruments, the pressure is controlled by charging the rubber into the rheometer by an attached pressure-driven device. 

A particular type of rheometer developed by Monsanto, now known as Alpha Technologies. The mechanical portion of the rheometer consists of a biconical disc embedded in an elastomeric specimen contained in a specially designed... 

Rheometrv. The following rheometers were used in this study An Instron capillary rheometer, a Rheometries mechanical spectrometer, used in both cone and plate mode as well as in the biconical mode, and a Brabender Plastograph (4). 

FIG. 4.22 Schematic of biconical tool for surface rheology measurements using the Paar Physica interfacial rheometer. (Courtesy of American Institute of Physics.)... 

A biconical disk interfacial rheometer is available from Anton Paar, known as the Physica Interfacial Rheology System (IRS). A schematic of the rheometer tool is shown in Figure 4.22. Current specifications of the instrument include a torque range of 0.02 xNm to 150 mNm with temperature control from 5 to 70°C. All rheological test modes are available for the interfacial rheometer including oscillatory testing [59],... 

Wasan and his research group focused on the field of interfacial rheology during the past three decades [15]. They developed novel instruments, such as oscillatory deep-channel interfacial viscometer [20,21,28] and biconical bob oscillatory interfacial rheometer [29] for interfacial shear measurement and the maximum bubble-pressure method [15,29,30] and the controlled drop tensiometer [1,31] for interfacial dilatational measurement, to resolve complex interfacial flow behavior in dynamic stress conditions [1,15,27,32-35]. Their research has clearly demonstrated the importance of interfacial rheology in the coalescence process of emulsions and foams. In connection with the maximum bubble-pressure method, it has been used in the BLM system to access the properties of lipid bilayers formed from a variety of surfactants [17,28,36]. 

Laboratory measur ent of curing characteristics have been somewhat revolutionized by the introduction of the cure meters. There were two types of cure meter the reciprocating paddle type as in the Wallace-Shawbury curometer, and the oscillating disc type such as the Monsanto rheometer. In the oscillating disc type (ODR) a biconical disc is embedded in the rubber in a closed cavity. The disc is oscillating through constant angular displacement, and the torque required monitored. 

In 1983, Steinbom and Flock studied the rheology of crude oils and water-in-oil emulsions (58). Emulsions with high proportions of water exhibited pseudoplastic behavior and were only slightly time dependent at higher shear rates. Omar et al. also measured the rheological characteristics of Saudi crude oil emulsions (59). NonNewtonian emulsions exhibit pseudoplastic behavior and followed a power-law model. Mohammed et al. studied crude oil emulsions using a biconical bob rheometer suspended at the interface (60). More stable emulsions displayed viscoelastic behavior and a solid-like interface. Demulsifiers changed the solid-like interface into a liquid one. 

In our laboratory, we have applied biconical bob rheom-etry to highly elastic films formed at asphal-tene-containing, model oil-water interfaces (80). Instead of using a torsion wire, however, we have utilized a commercially available, highly sensitive dynamic stress rheometer in conjunction with a serrated edge stainless steel bob. As we will show, the results of the rheometry method compare well with measures of emulsion stability under comparable conditions. Thus, this method provides useful insights into the... 

The TMS rheometer has been used to study mould release in rubbers. It contains a biconical rotor (representing the mould surface). The polymer is placed in the transfer chamber, injected around the rotor and cures in situ. Fig. 1. The shear stress required to free the rotor is taken as the mould-sticking index . The rheometer has the advantage that small experimental mixes of rubber can be evaluated. Further, the rotors are easily changed, so as to evaluate changes in mould surface, and the parted surfaces are amenable to examination by XPS and other methods of surface analysis. The obvious disadvantage is that access to special equipment (the TMS rheometer) is required. The same basic concept could be adapted for the study of mould adhesion of non-elastomeric polymers. 

A torsion pendulum device was developed by the scientists at the Department of Colloid Chemistry of Moscow State University, that is, by Izmaylova et al. [35-37]. This device, shown schematically in Figure 4.11, allows one to evaluate the mechanical characteristic of thin-film behavior at both the liquid-air interface and the liquid-liquid interfaces. Nowadays, similar studies can be conducted with commercial high-sensitivity shear rheometers using a special bicone tool. 

For interfacial shear rheology measurements, an interfacial shear rheometer (MCR301, Anton Paar, Ostfildem, Germany) was used equipped with a biconical disc geometry as described in Riihs et al. [60]. For all interfacial experiments, MCT oil was used as the oil phase. Surface-active constituents were removed from the oil through adsorption onto solid particles. The absence was confirmed through measurement of the interfacial tension. 

Capillary rheometers are the most widely used rheological instruments for polymer melts. They are, however, generally limited to rather high shear rates. Rotational rheometers can provide data at lower shear rates. Cone-plate and parallel disc instruments have been popular with thermoplastic melts. Pressurized instruments, such as biconical or Mooney shearing disc instruments, are used with elastomers to prevent slippage [39]. Sandwich rheometers are used at the lowest shear rates and shear stresses. 

Some time ago another characterisation method was developed utilising a transient shear measurement at a very low deformation rate [22]. In the present study this method is used to discriminate between the samples. Figure 12.16 shows torque-time curves, which were obtained with a rotational rheometer with a biconical rotor [23] at a rotational speed of 0.045 rpm. 

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