Overall efficiency gains
Compared with the single surfactant, the surface activity of the hybrid system is greatly improved. On the one hand, it improves the efficiency of reducing surface tension, and the surface tension of the mixed system can be as low as 25mN/m or even lower, and on the other hand, it greatly improves the efficiency of reducing surface tension, and the cmc of the mixed system is smaller than that of the cmo of each pure component surfactant, and even shows a reduction of several orders of magnitude. Thus, it shows a comprehensive synergistic effect.
The synergistic effect of the mixed system is also manifested in the reduction of oil-water interfacial tension.
The interfacial tension at the interface of n-heptane-water solution can be as low as 0.2 mN/m in the molar compound system of cationic surfactant C8H17N(CH3)Br (hereinafter denoted as C8N) and anionic surfactant C8H17SO4Na (hereinafter denoted as C8S), while the corresponding interfacial tensions of the two pure surfactant solutions are much higher (14 mN/m and 11 mN/m, respectively). mN/m respectively). Therefore, by compounding, it is possible to make some “marginal” surfactants with poor surface activity also have high surface activity.
Although the positive and negative ionic surfactant complex system has a strong synergistic effect, and its surface activity is higher than that of a single component. However, one of the main drawbacks of the mixed system of positive and negative ionic surfactants is that due to the strong electrical interaction, it is easy to form precipitation or flocculent suspension, and therefore the aqueous solution of the mixed system is not very stable. Once the concentration exceeds cmc, the solution is prone to stratification and precipitation or coalescence, or even precipitation (especially in equimolar mixed systems), which produces a negative effect and even causes the surfactant to lose its surface activity, thus adversely affecting the practical application. After years of research and practical application, the following methods can be used.
Non-equimolar compounding
Positive and negative ionic surfactants used in conjunction, to make it not precipitation or floc suspension, to achieve the maximum synergistic effect, the two ratios are very important. Unequal ratios (one of them only accounts for a small portion of the total) will still produce high surface activity and synergistic effect. A surfactant component in excess of a lot of compounds than equal moles of the compound solubility is much larger, the solution is therefore less likely to appear turbid, so you can use the lower price of the anionic surfactant-based, with a small amount of cationic surfactant to get a very high surface activity of the composite surfactant.
Reduction of hydrophobic chain length symmetry
When the total length of hydrophobic chain (total number of carbon atoms) is certain, the more asymmetric the length of two hydrophobic chains, the better the solubility of the mixed system.
Increase the volume of polar groups
The reason why the mixed system of positive and negative ionic surfactants is easy to form precipitation can be attributed to the strong electrostatic attraction between the heteroelectric ionic head groups, which leads to partial or total neutralization of the electrical properties (of course, this is precisely the reason why it has high surface activity), so it is possible to increase the volume of the polar group, increase the spatial resistance between the ionic head groups in order to reduce the strong electrostatic attraction between the ionic head groups. For example: the common alkyltrimethylammonium replaced with alkyltriethylammonium (i.e., alkyltrimethylammonium ion head of the three methyl for three ethyl), the solubility of the mixed system is greatly improved, such as octyltriethylammonium bromide and different chain lengths of alkylsulfate sodium equimolar mixture of solutions can be formed in a homogeneous solution, and its Krafft point is very low, can be used at low temperatures.
