Characteristic properties of ionic Gemini surfactants
(1) Easier to adsorb on gas/liquid surfaces, thus reducing the surface tension of aqueous solutions more effectively.
(2) It is easier to aggregate to form gels.
(3) The tendency of Gemini to reduce the surface tension of aqueous solution is much larger than the tendency of aggregation to generate clusters, and the efficiency of reducing the surface tension of aqueous solution is quite outstanding.
(4) It has a very low Krafft phase transfer point.
(5) In terms of the ability to reduce the surface tension of aqueous solution and the efficiency of reduction, Gemini and ordinary surfactants, especially the compounding with nonionic surfactants can produce a greater synergistic effect.
(6) It has good calcium soap dispersion properties.
(7) On many occasions, it is an excellent wetting agent.
Gemini surfactants are becoming the research direction of the main groups in the field of colloid and interface science in the world.
3.AB-type block polymer surfactants
The dispersion of pigment fillers in coatings has successively used inorganic dispersants such as polyphosphates, silicates, carbonates, traditional small molecule surfactants and polymer compounds such as polycarboxylates and polypropionates. Polymer compounds mainly use spatial site resistance to stabilize the filler particles, which is better than the electrostatic repulsion of small molecule surfactants. Studies have shown that among the many types of polymer dispersants, the most effective and efficient is the AB-type block polymer surfactant. From the molecular structure, AB type block macromolecule is oversized surfactant, A block and B block are similar to the hydrophilic head group and hydrophobic tail chain of surfactant respectively.AB block
macromolecule surfactant adopts the tail-type adsorption morphology on the surface of pigment and filler, A block is the anchoring group of pro-pigment, and B block is the solvent solvation tail chain of pro-solvent.A block can be the functional group of acid, amine, alcohol, phenol and so on, and it can be adsorbed by ionic bonding, covalent bonding, covalent bonding and covalent bonding. A block can be acid, amine, alcohol, phenol and other functional groups, which are adsorbed on the surface of particles through the interaction of ionic bonding, covalent bonding, ligand bonding, hydrogen bonding and van der Waals force, etc. Due to the multiple adsorption points, it can effectively prevent the dispersant from molecules from desorbing, so that the adsorption is close and long-lasting.B block can be a group of polyether, polyester, polyolefin, polyacrylate, etc., which is respectively applicable to polar and nonpolar solvents. The structure of a typical AB block type polymer surfactant is shown in the figure. The stabilizing particles mainly rely on the spatial site resistance generated by the adsorption layer formed by B block, so the length and homogeneity of B block as the solventized tail chain have very high requirements, and it is hoped that a moderate thickness and homogeneous adsorption layer can be formed, and if the B block is too long, it may act as a bridging effect, causing an increase in the viscosity of dispersed system, or even flocculation and precipitation. It is usually believed that the best stabilization effect can be achieved when the thickness of the site resistance layer is 20nm.
AB block type polymer surfactants
The synthesis of AB block polymer surfactants with clear molecular structure and controllable relative molecular mass is the development direction of coating dispersing additives, which requires the use of controlled polymerization technology. However, only a few companies such as BYK, Ciba, Rhodia, etc. have controlled polymerization technology. Shenzhen Oceanpower company is developing a new dispersant is also AB-type block polymer surfactants.
4.Bola-type surfactants
Bola-type surfactants are compounds bonded by two polar head groups connected by one or more hydrophobic chains, which are named because they resemble a weapon of the South American natives, the Bola (a rope with a ball attached to each end), and the structure of the simplest Bola-type surfactants is shown in Figure 3. Typical associative thickeners are shown in Figure 4.
Bola-type macromolecular surfactants
The hydrophobic groups at both ends of the molecule play a role in binding, which is equivalent to the 2 terminal groups of Bola-type surfactants, and is the determining factor for thickening, usually oleyl, octadecyl, dodecylphenyl, nonylphenol, etc. The hydrophilic chain is equivalent to the 2 terminal groups of Bola-type surfactants, which is the determining factor for thickening. Hydrophilic chain is equivalent to the connecting chain of Bola-type surfactants, which can provide chemical stability and viscosity stability, commonly used is polyether, such as polyoxyethylene and its derivatives. The molecular chain of an associative thickener is extended by polyurethane groups, and the polyurethanes used are IPDI, TDI and HMDI. Such molecular structure makes the molecules of the associative thickener can form micelles like macromolecule surfactant, the hydrophilic end and water molecules with hydrogen bonding, and the hydrophobic end and emulsion particles, surfactants and other hydrophobic structures adsorption and bonding together, forming a three-dimensional mesh structure in the water to achieve the effect of thickening.
5.Dendrimer type surfactant
Dendrimer is a dendritic macromolecule, which is a central nucleus molecule from the branching monomer level by level by diffusion to stretch out the structure, or by the center of the nucleus, several layers of branched units and peripheral groups connected by chemical bonds. There have been types such as polyethers, polyesters, polyamides, polyaromatics, and polyorganosilicones. Dendritic macromolecules are characterized by their regular molecular structure, and the molecular volume, shape, and terminal functional groups can be designed and controlled at the molecular level, making them a popular subject in the polymer discipline. By modifying the end groups according to the needs, the corresponding dendrimer surfactants are obtained. Dendritic macromolecules have also attracted the attention of the coatings industry, which has developed this type of dispersant, cross-linking agents and special resins. The use of dendritic surfactants as coating dispersants has two advantages. Firstly, by modifying their end groups, multiple pigment affinity groups can be generated to enhance the interaction with pigments. Secondly, due to the consistent molecular structure and approximate ellipsoidal shape, it is easier to obtain lower viscosity in the dispersed system. Hyperbranched polyurethanes modified with polyethylene glycol or propylene oxide copolymers are a new type of pigment dispersant for high-solids, solvent-borne or water-borne coatings. With commercial hyperbranched polyester, polyester-amide, polyethyleneimine as the skeleton, and modified to develop a core-shell type pigment anchoring mechanism of the dispersant, the advantage is that the pigment dispersion stability at low viscosity.
6. Low-foaming or non-foaming surfactant
Low-foaming or non-foaming surfactants are modified on the basis of the original surfactant, so that its original foaming groups to lose or reduce the foaming properties, but also with isomeric alcohols plus EO and PO to adjust the foam size of the production made. The market has low-foaming surfactant LT-601, non-foaming surfactant 8550, 8551.
