Surfactants property control measures

Monomer conversion can be adjusted by manipulating the feed rate of initiator or catalyst. If on-line M WD is available, initiator flow rate or reactor temperature can be used to adjust MW [38]. In emulsion polymerization, initiator feed rate can be used to control monomer conversion, while bypassing part of the water and monomer around the first reactor in a train can be used to control PSD [39,40]. Direct control of surfactant feed rate, based on surface tension measurements also can be used. Polymer quality and end-use property control are hampered, as in batch polymerization, by infrequent, off-line measurements. In addition, on-line measurements may be severely delayed due to the constraints of the process flowsheet. For example, even if on-line viscometry (via melt index) is available every 1 to 5 minutes, the viscometer may be situated at the outlet of an extruder downstream of the polymerization reactor. The transportation delay between the reactor where the MW develops, and the viscometer where the MW is measured (or inferred) may be several hours. Thus, even with frequent sampling, the data is old. There are two approaches possible in this case. One is to do open-loop, steady-state control. In this approach, the measurement is compared to the desired output when the system is believed to be at steady state. A manual correction to the process is then made, based on the error. The corrected inputs are maintained until the process reaches a new steady state, at which time the process is repeated. This approach is especially valid if the dominant dynamics of the process are substantially faster than the sampling interval. Another approach is to connect the output to the appropriate process input(s) in a closed-loop scheme. In this case, the loop must be substantially detuned to compensate for the large measurement delay. The addition of a dead time compensator can... 

Although the proposed theory has been used effectively in several practical applications, no experimental proof has been given that the oil solubilization rate is a function of surfactant aggregate size. In view of the importance of solubilization and the existence of practical methods of measuring and controlling surfactant aggregate size, we decided to correlate the solubilization rate with micellar properties for some anionic and nonionic surfactants. 

An important case is the application of enzymes in laundry detergents. Market trends in the United States show that consumers prefer liquids to powder detergents by a ratio of 2 to 1. These products are stored with no temperature control on shelves in the presence of harsh surfactants, such as linear alkylbenzyl sulfonate (LAS) and require extraordinary measures for stabilization. LAS, by its nature as an effective cleaning agent, causes surfactant-induced unfolding in proteins. There are countless examples of the development of stabilization systems in the intellectual property space. A common theme is to reduce the water activity and to use borate/glycol stabilizers that bind to the active site of proteases. 

As mentioned above, an important factor that controls the performance and especially the electrical properties of CNTs-reinforced composites is the state of dispersion of CNTs. Ultrasonication has been shown to be more effective in dispersing the nanotubes without the need for surfactants or other chemical treatments. Figure 12.5b presents electrical results of samples prepared by using a different composite processing. MWNTS were dispersed in this case in cyclohexane by ultrasonication and the MWNTs suspension was then mixed into a cyclohexane solution of SBR. Mixing was achieved by a further sonication for 30 minutes. Cyclohexane has been chosen in this case on account of the solubility of the rubbers in this solvent. As revealed in Figure 12.5b, the percolation threshold is shifted to a lower nanotube content and from this point of view, measurements of electrical resistivity appears as an indirect tool to evaluate the state of dispersion. 

The development of improved methods of surfactant design required progress in several other areas (1) understanding the mechanisms of dispersion flow in porous media, to determine which physical properties should be measured, and how their values would affect sweep control (2) measurements of these properties that are valid at the conditions under which the surfactants will be used and (3) understanding of how the values of these parameters depend on phase behavior, molecular structure, and other thermodynamic variables. 

The adsorbed surfactant film is assumed to control the mechanical-dynamical properties of the surface layers by virtue of its surface viscosity and elasticity. This concept may be true for thick films (>100 run) whereby intermolecular forces are less dominant (i.e., foam stability under dynamic conditions). Surface viscosity reflects the speed of the relaxation process which restores the equilibrium in the system after imposing a stress on it. Surface elasticity is a measure of the energy stored in the surface layer as a result of an external stress. 

The motion of bubbles in a surfactant solution depends on the bubble size and the properties of the solution/bubble interface (Malysa 1992). Adsorbed surfactants control the bubble motion in a way not fully understood. With increasing surfactant concentration the floating speed increases, passes a maximum and then decreases again (Loglio et al. 1989). The maximum of the speed of floating is passed at very low surfactant concentration so that the phenomenon can even be used as a measure for the contamination of water by surface active compounds. 

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]. 

Tables 1.8 and 1.9 illustrate the physical properties for selected formulations at TPR times of 130 and 150 seconds. Control physical properties were not evaluated at these extended TPR times since the control formulations I and V had visual surface distortions and severe scalloping. The data in Tables 1.8 and 1.9 demonstrate that the TPR window can be extended by using these newly developed additives without negative impact to the physical properties. In fact, the data indicates that several of the physical properties for the experimental formulations exceed the control formulation properties at the 90 second TPR time. For example, airflow measurements are improved when utilising the extended TPR times. Improvements are greater than 10% with the Dabco BL-53 catalyst and experimental silicone surfactant combinations. Additional improvements are also observed with wet set and 50% humid aged compression set values.

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