Davies Rideal method

Table 5.6 Group-contribution values for estimating the HLB according to Davies-Rideal method (Equation 5.5). When hydroxyl or ester groups are parts of a sorbitan molecule, special values are used as indicated.

Example 5.4. Estimation of HLB from the Davies-Rideal method. 

The principle of the drop volume method is of dynamic character and therefore, it can be used for studies of adsorption processes in the time interval of seconds up to some minutes. At small drop times a so-called hydrodynamic effect has to be considered, as discussed in many papers (Davies Rideal 1969, Kloubek 1976, Jho Burke 1983, Van Hunsel et al. 1986, Van Hunsel 1987, Miller et al. 1994a). This hydrodynamic effect appears at small drop times under the condition of constant liquid flow into the drop and gives rise to apparently higher surface tensions. Davies Rideal (1969) discussed two factors influencing the drop formation at and its detachment from the tip of a capillary the so-called "blow up" effect and a "circular current" effect inside the drop. The first effect increases the detaching drop volume and simulates a higher surface tension while the second process leads to an earlier break-off of the drop and results in an opposite effect. A schematic of these two effects on measured drop volumes is shown in Fig. 5.10. 

Reaction at liquid surfaces covers a wide field. However, special experimental methods have been developed mainly for the study of insoluble or partly soluble monolayers at the liquid-air interface. Adsorption and reaction of monolayers at the liquid-air interface and liquid-liquid interfaces can be studied by similar techniques. It is therefore convenient to treat these together. Comprehensive information about liquid interfaces is contained in publications by Adamson, Davies , Alexander , Davies and Rideal and Gaines . ... 

There are a large number of emulsifiers available and making a choice for a new formulation or product is difficult. The use of the hydrophilic-lipophilic balance (HLB) concept originated by Griffin in 1949 can be a useful empirical method of preliminary selection. The HLB number quantifies the balance of hydrophilic-lipophilic characteristics of the surfactant molecule on an arbitrary numerical scale. The least hydrophilic surfactants are assigned the lowest HLB (see Table 14.2). The use of the HLB balance is also well described by Davies and Rideal. ... 

The most weU-known method for estimating the HLB is the group contribution method of Davies and Rideal ... 

The HLB of the two given non-ionic surfactants (poly(ethylene oxide)s) will be estimated with the group contribution method by Davies and Rideal (Table 5.6, Equation 5.5) using the information on the stmcture of the surfactants (see Table 5.1) ... 

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