Cohesive energy ratio

The first of these to be discussed will be the Cohesive Energy Ratio, R concept (20), Using the concept of cohesive energy between molecules, Winsor recognized four structures. 

Other LAS homolog structural effects on wettability and soil removal were found when the data were analyzed using the cohesive energy ratio, R, the regular solution theories of the... 

Correlation Plot of Cohesive Energy Ratio for LAS Homolog Detergency of Mineral and the Experimental Soil Removal. 

The property of interest to characterize a surfactant or a mixture of surfactants is its hydrophilic-lipophilic tendency, which has been expressed in many different ways through a variety of concepts such as the hydrophiUc-lipophilic balance (HLB), the phase inversion temperature (PIT), the cohesive energy ratio (CER), the surfactant affinity difference (SAD) or the hydrophilic-lipophilic deviation (HLD) [1], which were found to be more or less satisfactory depending on the case. In the next section, the quantification of the effects of the different compounds involved in the formulation of surfactant-oil-water systems will be discussed in details to extract the concept of characteristic parameter of the surfactant, as a way to quantify its hydrophilic-lipophilic property independently of the nature of the physicochemical environment. 

In this expression, he divides the number of calories generated on the lipophile side of the surfactant by the number of calories generated by the hydrophile side of the surfactant. The amount of calories reflects or implies a proportional amount of swelling of the hydrophile and the lipophile, i.e., the greater number of calories on the lipophile side, the more tendency there is to form an oil in water type of emulsion. This definition of the C.E.R. (or Cohesive Energy Ratio) parameter leads to a direct expression which ties HLB to the Cohesive Energy Density parameter directly. The expression is ... 

A more detailed description o the relationship between HLB and Cohesive Energy Ratio is given in one o Beerbower s (10) papers. Also, this allows or a quanti ication o the type o emulsion per the value o the C.E.R. parameter. Thus, the quanti ied C.E.R. values or the three types o emulsions are given below ... 

As shown by the results ound in this table, there is a reeison-able correlation between the Cohesive Energy Ratio and the resultant HLBs using the relationship involving the Cohesive Energy Ratio and HLB values. Beerbower (11) extended this relationship to de ine the interaction between sur actants and oil/aqueous phases. 

For nonionic surfactants, an optimization of the process was achieved by using a similar approach to the so-called Cohesive Energy Ratio (CER) concept developed by Beerbower and Hill for the stability of classical emulsions (H). Its basic assumption is that the partial solubility parameters of oil and emulsifier lipophilic tail and of water and hydrophilic head are perfectly matched. Thus, the Vinsor cohesive energy ratio Ro, which determines the nature and the stability of an emulsion, is directly related to the emulsifier HliB (hydrophile-lipophile balance) by... 

The main features of inverse microemulsion polymerization process have been reviewed with emphasis given to a search for an optimal formulation of the systems prior to polymerization. By using cohesive energy ratio and HLB concepts, simples rules of selection for a good chemical match between oils and surfactants have been established this allows one to predict the factors which control the stability of the resultant latices. The method leads to stable uniform inverse microlatices of water-soluble polymers with high molecular weights. These materials can be useful in many applications. 

Four different emulsifier selection methods can be applied to the formulation of microemulsions (i) the hydrophilic-lipophilic-balance (HLB) system (ii) the phase-inversion temperature (PIT) method (iii) the cohesive energy ratio (CER) concept and (iv) partitioning of the cosurfactant between the oil and water phases. The first three methods are essentially the same as those used for the selection of emulsifiers for macroemulsions. However, with microemulsions attempts should be made to match the chemical type of the emulsifier with that of the oil. A summary of these various methods is given below. 

The cohesive energy ratio was originally defined by Winsor (see Eq. (15.28). 

Combining Equations (15.31) and (15.33), the following general expression for the cohesive energy ratio is obtained,... 

It was a century ago that researchers started to study the factors affecting the behaviour of water-oil-surfactant systems but it is only with the introduction of Winsor s R theory (1954) that the formulation effects could be interpreted. Winsor s R theory was the first qualitative description of the formulation, paving the way to an understanding of how intermolecular interactions among the different chemical species present in a system are related to its behaviour. Throughout the following decades, several empirical experimental correlations such as the phase inversion temperature (PIT), semiempirical ones such as the cohesive energy ratio (CER), and models based on thermodynamics such as the surfactant affinity difference (SAD) or the hydrophilic-lipophilic deviation (HLD) [15, 143, 144] led... 

The choice of emulsifier is critical since it controls the stability of the emulsions prior to and after polymerization. Moreover, polymerization conditions typically represent destabilizing factors vigorous stirring, temperature rise and evolution of acrylamide content in the aqueous phase. In the case of inverse emulsions, the HLB values mostly used by the formulators range between 4 and 6. Some attempts were made to predict quantitatively the optimal HLB value corresponding to the most stable dispersions [18,19]. The treatment was based on the so-called cohesive energy ratio (CER) concept devekq)ed by Beer-bower and Hill for conventional emulsions [20]. Tins approach is based on a perfect chemical match between the partial solubility parameters of oil (ig)... 

I summarize briefly below the basic concepts of this approach, which is derived from that developed by Beerbower and Hill [31] for the stability of classical nonionic emulsions, which is referred to as the cohesive energy ratio (CER) concept. The treatment lies in a perfect chemical match between the partial solubility parameters of oil ( ) and surfactant lipophilic tail 6]) and of water and hydrophilic head. Under these conditions, one obtains for the optimum HLB (hydrophile-lipophile balance) of the surfactant the relation... 

In a tentative approach to attain a formulation concept with both the theoretical content of Winsor s R and the down-the-bench numerical data feature of the Hl-B. Beerbower and collaborators introduced the cohesive energy ratio (CER) approach in 1971 (53.. i4). From the conceptual point of view it was very similar to Winsor interaction energies ratio, but this time it was the ratio between the adhesion energy of the surfactant "layer" with the oil phase and the adhesion energy of the surfactant "layer" with the water phase, It must be recalled that the cohesion energy between molecules of a pure component system is calculated as ... 

Research into optimal formulations is based on the idea of cohesive energy ratio (CER). This was originally developed to stabilise classic non-ionic surfactant emulsions [6.13]. Despite its limitations, the CER concept unifies the ideas of solubility parameters and HUB. Recall that the HLB is a measure of the emulsifying power of surfactants and is based on their hydrophile-lipophile balance [6.3]. It can be calculated from a simple formula involving only relative weights of sequences HLB = 20 x Mh/Mt, where Mh is the molecular weight... 

Due to these drawbacks. Che final numerical value of the cohesive energy ratio was as inaccurate as the HLB number and even worse in some cases, and it had to be dropped. 

Cohesive Energy Ratio (CER) Concept for Emulsifier Selection... 

The selection of different surfactants in the preparation of EWs emulsion is still made on an empirical basis. This is discussed in detail in Chapter 6, and only a summary is given here. One of the earliest semi-empirical scales for selecting an appropriate surfactant or blend of surfactants was proposed by Griffin [49, 50] and is usually referred to as the hydrophilic-lipophilic balance or HLB number. Another closely related concept, introduced by Shinoda and co-workers [51-53, 58], is the phase inversion temperature (PIT) volume. Both the HLB and PIT concepts are fairly empirical and one should be careful in applying them in emulsifier selection. A more quantitative index that has received little attention is that of the cohesive energy ratio (CER) concept introduced by Beerbower and Hill [54] (see Chapter 6). The HLB system that is commonly used in selecting surfactants in agrochemical emulsions is described briefly below. 

---