There are many determinants of the effect of anion-cation surfactant compounding on surface activity, and there is a synergistic effect in the case of suitable structure of both parties.
In the mixed system of anion-cation surfactants, due to the strong electrostatic attraction of positive/negative ions between molecules, it is easy to form a rod-shaped colloid after compounding with each other, and aggregation occurs after the concentration exceeds the CMC, and turbidity, separation, and so on will occur. Controlling the length of hydrophobic chain, using short-chain surfactants or increasing hydrophilic groups (ethoxylation), it is possible to be in solution without precipitation phenomenon, and make the surface activity than a single component has a substantial increase.
The synergistic effect of anion-cation surfactant compounding is reflected in the following points:
Cationic surfactants can be added in small amounts to anionic surfactant-based detergents as synergists to improve detergency.
In the anion-cation surfactant compound system, with the addition of one surfactant to another surfactant with opposite charge, the polymerization number of the mixed colloid will increase sharply, and the colloid transitions to the rod structure, and the rod colloid has a greater solubilizing capacity for the solubilized material that is solubilized in the core of the colloid.
Electrical attraction exists between anionic and cationic surfactants, and an isometric composition of the adsorbent layer is necessary to maximize the electrical attraction. The charge effect weakens the electrical repulsion between the adsorbent layer and the surface-active ions in the micelles, thus increasing the surface adsorption. The above effects result in a very low surface and interfacial tension of the compounded solution, which inevitably leads to an increase in the foaming force. At the same time, due to the close arrangement of molecules in the adsorption layer and the strong interaction between molecules also makes the surface viscosity increase, the mechanical strength of the surface film increases, so that it is not easy to rupture when subjected to external forces, the loss of liquid in the foam slows down, the gas permeability decreases, prolonging the life of the foam.
As the surface adsorption of anion-cation surfactant compound system is enhanced, the surface tension of the system is lower, so the compound system will have strong wetting ability.
The emulsifying ability of surfactants depends on their hydrophilic and lipophilic balance, the hydrophilic and lipophilic values of the oil phase, and the firmness of the film formed by the surfactant at the oil/water interface. By adding a small amount of cationic surfactant into anionic surfactant or vice versa, the surface activity of the compounded surfactant increases due to the charge effect, and the denseness of the film formed at the oil/water interface increases, so the emulsifying ability is enhanced.
In addition, the compounding system can also have the advantages of two components at the same time. Cationic surface active agent is a better antistatic agent and bactericidal antifungal agent, but the washing effect is not good, and anionic surface active agent can be obtained after compounding of chemical fiber products, excellent detergent, both washing, antistatic, softness, dust and other functions.
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