Views: 4 Author: Site Editor Publish Time: 2022-05-18 Origin: Site
When cellulose ether HPMC is added into aqueous solution containing salt ions, its dissolution process and mechanism will change correspondingly. Because different salt ions have different roles with water, they may have different effects on the stability or destruction of structures formed between water molecules and solutes. Accordingly, salt ions can be roughly divided into two categories: salt-out effect ions and salt-in effect ions. Studies show that anions have stronger effect than cations, and are the dominant factor in determining the salting out or salt dissolution effect of salts. Hofmeisterll9J sorted some typical anions as follows according to the influence of ions on the hydrophobicity of solutes: S 042->F->Cl->Br->N0-3>CI04 '>1->S CN-. The ions on the left show strong interactions with water molecules, so they have a salting out effect or increase the hydrophobicity of the solute in water. In contrast, the ions on the right have difficulty interacting with water and exhibit a salt-solubility effect, which increases the solubility of nonpolar solutes in water.
Yirong Xu et al. studied the influence of ions on methyl cellulose aqueous solution by selecting chloride ion and iodide ion. In this case, sodium chloride acts as a salt out. Because of chloride ions and water molecules between role than between water molecules and hydrogen bonding between water molecules and cellulose ether molecules, so the chloride ion in the competition with large molecules and water molecules to gain the upper hand, leading to some originally in macromolecular and has been the destruction of the formation of hydrogen bonds between water molecules, And methyl cellulose molecules and water molecules between the formation of the "cage" structure is therefore destroyed, cellulose ether water solubility decreased. At the same temperature, chlorine ion solution than does not contain chlorine ion in the solution more hydrophobic formed by the macromolecular aggregation, there is less "cage" structure needed by heating to damage, therefore, chlorine ion solution will show a lower lower critical solution temperature, join the chloride ion concentration is higher, lower critical solution temperature drop. On the other hand, iodide ion showed the opposite effect with chloride ion, the preparation and properties of hydroxypropyl methyl cellulose hot 'I hydrogel it has very weak effect with water. In methyl cellulose solution, the iodine ion ACTS like hydrophobic particles or another independent besides water solvent, seems to macromolecular is dispersed in the iodine ion of these large hydrophobic, contact each other between macromolecules and combining with the risk is relatively low, and at the same temperature, compared with excluding iodine ion in the solution, the difficulty of the formation of hydrophobic aggregation is greater. Therefore, the solubility of the polymer is improved, and its low critical dissolution temperature is also increased. If the solution contains more than one kind of ion, the influence of these ions on solubility needs to be considered comprehensively.
In addition, adding surfactant can also affect the dissolution of cellulose ether. Qiqiang Wang et al. studied methyl cellulose aqueous solution with sodium dodecyl sulfate (SDS). Using light transmission, thermal analysis, and rheological tests, they found that the effect of sodium dodecyl sulfate on the dissolution of cellulose ether is affected by the Concentration of surfactant, that is, below the Critical Micellization Concentration, it shows salinization. Above the critical micelle concentration, there is a salt solution. When the concentration of sodium dodecyl sulfate added is lower than the critical micelle concentration, it is not enough to form micelles surrounding macromolecules. The molecules exist in the solution in the form of monomer, which can attract water molecules, thus reducing the water molecules that can bind with methyl cellulose molecules, and increasing the hydrophobicity of the polymer. Therefore, the hydrophobic binding effect of methyl cellulose appears at a lower temperature, and its low critical dissolution temperature also decreases. If the surfactant concentration is higher than the critical gel Cambodia concentration, the sodium dodecyl sulfate molecules form micelles that surround the hydrophobic groups in the macromolecular chain. The micellar action here is different from that of surfactant in pure water and is called polymer-induced micellar action. These formed by sodium dodecyl sulfate micellar can and large molecules to form the "cage" structure, than the "cage" structure of water molecules to form a more conducive to the stability of the methyl cellulose molecules in the water and dissolved, and the hydrophobic aggregation of large molecules are more difficult. As a result, the solubility of the polymer increases, so does its low critical solution temperature.