**8. CO2-philic surfactants for foam**

The leading group of researchers have informed that non-fluorinated, hydrocarbon-based systems can be created in a way that they are CO2-philic in nature. These surfactants resolve the above mentioned foam problems [23–26]. Since CO2 is a weak solvent, the polar and high molecular weight substances are only partially soluble, but CO2 can dissolve in other few volatile and low molecular weight solvents. The carbon dioxide is a Lewis acid because it has an accepting electron nature, in spite of the fact that it has low polarisable properties [27]. The CO2 can take part in Lewis acid–base interactions because of CO2 having an electron accepting property. Many researchers have proved this kind of carbon dioxide bonding with other stuff like polymers and surfactants, etc. Fin and Lei Hong have expressed this kind of collaboration in their phenomena.

Fin also stated in his work that ab initio molecular simulation research have shown that the O2 (ester or ether) in the side chain play an major role in promoting philicity of carbon dioxide because of the carbonyl oxygen. They recognised the three different ways the CO2 linked with a hydrocarbon end of the molecule.

**145**

*CO2-Philic Surfactants Structural Morphology Prerequests for CO2 Philicity for Foam Durability…*

They need the Isopropyl acetate molecule as a sample. In the picture below, the red colour imitate oxygen, black represents carbon and white is used for atoms of

Maximum attraction with the CO2 and minimum intermolecular attractions are the basic requirements involved in designing a CO2-philic molecule. Few of the Carbon dioxide philic appearance are splitting, less molecular weight hydrophobes, tip tail, and presence of groups of carbonyl, methyl, propylene oxide (PO), tertbutyl tip and a minimum number of methylene groups [22, 27, 33, 34]. A detailed discussion of the important factors that favour the carbon dioxide philicity of a

The surfactants branching *is* a key factor for the carbon dioxide philicity of the hydrophobic part. It is because of the effect that when chain length decreases, the CMC (aqueous) increases; while, an increase in branching increases the solubility in CO2. According to Ben Tan branching in the diacid as well as diol moiety has the increasing effect on solubility, and acyl chains branching increases the solubility up

It is observed that in case of CO2-philic compounds the solubility is greatly affected by the tail number. With the increase in the number of tails the dissolved surfactants in the carbon dioxide increases. A huge and emergent part of literature is fixated on the phenomena of interfacial of the carbon dioxide/H2O interface and proposes that there should be more contact with the interface for a double tail surfactant and as a result offers more stability for the micro emulsion. When a third chain is added in the surfactant structure the surfactant's solubility is increased in

In the past the relationship of CO2-philicity with the tail length has been widely studied and the interdependency of CO2-philic properties and surfactant tail structure was observed. At various temperature and pressure values, different double tail fluorinated surfactants have been studied for the phase behaviour [6, 7, 39]. This study leads to specifications for the optimization of tail length which is suitable for the maximum water/carbon dioxide emulsion formation at micro level. The phase behaviour for the oligomers is altered by the end-group modification of the oligomer PVAc-OH. Audrey DuPont examined P and T phase stability, chain structure effect and the aggregation structure. Surfactant free volume and surfactant packing are the parameters to view the effects of the chain lengths. Carbon dioxide solubility in esters is significantly affected by small structural changes in them. Depending upon the number of carbon atoms we can observe even/odd effects on solubility of carbon dioxide. According to observations made by Bray Christopher the acyl chain length is important with the carbon dioxide solubility for the molecule. With the increase in length of the chain by 10 carbon atoms the solubility increases in a systematic way. The influence of minor structural changes to the solubility of CO2

**9. Requirements for CO2-philic surfactants for CO2-philicity**

surfactant will be followed in the next few sections.

*DOI: http://dx.doi.org/10.5772/intechopen.90994*

hydrogen [17, 28–32].

**9.1 Branches**

to 20 times.

**9.2 Number of tails**

carbon dioxide even more [35–38].

**9.3 Tail length and tip**

*CO2-Philic Surfactants Structural Morphology Prerequests for CO2 Philicity for Foam Durability… DOI: http://dx.doi.org/10.5772/intechopen.90994*

They need the Isopropyl acetate molecule as a sample. In the picture below, the red colour imitate oxygen, black represents carbon and white is used for atoms of hydrogen [17, 28–32].
