Hello,
in the following article, it was found that increasing concentrations of PEG dissolved in water droplets decrease the evaporation rate of the water.
Article Evaporation from Water−Ethylene Glycol Liquid Mixture
However, I wonder what the exact mechanism of this is?
Among others, two papers cite the above. In one paper, it was found that "there is no difference in the water evaporation rate and its activation energy between a solution of soluble surfactant and purified water, being contrary to the case of insoluble monolayer in which the water evaporation is retarded due to the presence of monolayer just at the air/solution interface.”
Article Surface adsorption and vesicle formation of dilauroylphospha...
So the amphile reduces the evaporation rate of water simply due its physical presence after partitioning to the interface?
However, this papers states that "the strong hydrogen bonds formed between EG molecules and water molecules prevented the evaporation of water molecules."
Article Conductive MXene Nanocomposite Organohydrogel for Flexible, ...
In my system, I use "dots" of PEG (5 kDa), covalently attached to a silicon dioxide surface and condense water on them.
Would you expect to see the same retardation of evaporation rate here? In contrast to the first paper, the PEG molecules cannot diffuse freely and are not expected partition to the liquid/air interface.
Kind regards
Philipp
1) If it forms a solution, it will lower evaporation rates. If the solution is ideal (solvent and solut with similar intermolecular interactions), it will follow Raoult's law (and as you said, just the physical presence of the solute is enough for reducing the rate, as it lowers the gibbs energy of the system by increasing the entropy). If the solution is an ideal diluted it will follow Henry's law. In more complexes cases, the activity coeficient of solute will influence a lot, and you have to determine first the activity of the solute.
2) In your case, not ideal as the intensity of interaction between solvent-solute is quite different from solvent-solvent and solvent-solute, and probably not diluted as well, those intermolecular interactions like hydrogen bonding will reduce a lot more the gibbs energy of your system by the favourable enthalpy of mixture.
3) I wouldn't expect the same rate, as the molecules are not the same, but I would expect a reduction rate based on 1 and 2.
1) If it forms a solution, it will lower evaporation rates. If the solution is ideal (solvent and solut with similar intermolecular interactions), it will follow Raoult's law (and as you said, just the physical presence of the solute is enough for reducing the rate, as it lowers the gibbs energy of the system by increasing the entropy). If the solution is an ideal diluted it will follow Henry's law. In more complexes cases, the activity coeficient of solute will influence a lot, and you have to determine first the activity of the solute.
2) In your case, not ideal as the intensity of interaction between solvent-solute is quite different from solvent-solvent and solvent-solute, and probably not diluted as well, those intermolecular interactions like hydrogen bonding will reduce a lot more the gibbs energy of your system by the favourable enthalpy of mixture.
3) I wouldn't expect the same rate, as the molecules are not the same, but I would expect a reduction rate based on 1 and 2.
Philipp Selenschik
If you have dissolved any non-electrolyte (PEG), then, according to Raoult's law, the vapor pressure above the solution will be less than above pure water.
Monolayers of surfactants (cetyl alcohol) upset the equilibrium in the liquid-vapor process. They seem to close the liquid in the container with a lid.
Silicon dioxide itself is used to dry the air. If there is PEG on the surface, the air drying may be greater. There is a decrease in the relative humidity of the atmospheric air due to the adsorption of water on your modified silicon. Condensation is a phase transition. Adsorption is the concentration of water on the surface, accompanied by a decrease in the Gibbs energy of the vapor-modified silicon dioxide system.
Yuri Mirgorod Thanks for your reply!
I wasn't sure whether polymers obey Raoult's law?
Luiz Fernando de Sousa Lima
thanks for reply to my question! I have a follow-up on this one: What do you mean by "not ideal as the intensity of interaction between solvent-solute is quite different from solvent-solvent and solvent-solute."?The interactions between PEG and H2O are hydrogen-bonds, just like in the solvent (H2O). However, I am pretty sure the solution is non-ideal and does not obey Raoults law? I think it has a negative Flory Huggings coefficient (the mixing is exothermic). Will the interaction between solvent and solute then still reduce the vapor pressure of the solvent?
Kind regards Philipp :)
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