There are many determinants of the effect of negative-cationic surfactants on surface activity, and there is a synergistic effect when the structure of both sides is suitable. In the mixed system of negative-cationic surfactants, rod-like micelles are easily formed after mixing with each other due to the strong electrostatic attraction between the positive and negative ions. When the concentration exceeds CMC, it will aggregate, resulting in turbidity and equal division.
Controlling the length of the hydrophobic chain, using a short-chain surfactant or adding a hydrophilic group (ethoxylation), it is possible to avoid precipitation in the solution, and the surface activity is greatly improved than that of a single component.
The synergistic effect of the combination of negative-cationic surfactants is reflected in the following points:
1. Decontamination performance: cationic surfactants can be added to a small amount of anionic surfactant-based detergents as synergists to improve decontamination capacity.
2. Solubilization performance: In the negative-cationic surfactant complex system, with the addition of one surfactant to another surfactant with opposite charge, the polymerization number of the mixed micelles will increase sharply, and the micelles transition to a rod-like structure, which has a greater solubilization ability for the solubilized matter soluble in the micelle core.
3. Foam properties: there is an electrical attraction between the negative and cationic surfactants,
and the proportional composition of the adsorption layer is necessary to achieve the maximum
electrical attraction. The electrical repulsion between the adsorbed layer and the surface active ions
in the micelle is weakened by the charge effect, thus increasing the surface adsorption. The above action
makes the composite solution have a very low surface and interfacial tension, which will inevitably lead to an increase in foaming force. At the same time, due to the close arrangement of molecules in the adsorption
layer and the strong interaction between molecules, the surface viscosity increases, the mechanical strength
of the surface film increases, so that it is not easy to break under external force, the liquid loss rate in the foam
is slow, the gas permeability is reduced, and the life of the foam is extended.
4. Wettability: Due to the enhanced surface adsorption of the negative-cationic surfactant complex system,
the surface tension of the system is low, so the complex system will have a strong wetting ability.
5. Emulsification performance: The emulsification ability of surfactants depends on its hydrophilic and lipophilic balance, the hydrophilic and lipophilic value of the oil phase, and the firmness of the film formed by the surfactant
at the oil and water interface. When a small amount of cationic surfactant is added to the anionic surfactant,
or vice versa, due to the effect of electric charge, the surface activity of the combined surfactant increases, and the film density formed at the oil/water interface increases, so the emulsification ability is enhanced.
In addition, the compound system can also have the advantage of two components at the same time. Cationic surfactant is a good antistatic agent and a bactericidal and mildewproof agent. It can be used as an excellent detergent for chemical fiber products by combining with anionic surfactant. It has the functions of washing, antistatic, soft and dust-proof.