Since chitosan protonated in acidic solution (pH under 6), and surface tension depends on solvent concentration (when I change the acetic acid concentration from 10% to 90% it will decrease the surface tension of CS , depends on the amount of protonated Chitosan), if I add small amount of salt, eg NaCl it will dissociate into Na+ and Cl-, and will cover up -NH3- with covalent bond.
Is that true? and will it affect the surface tension and viscosity?, whether these changes can be observed and measured?.
If chitosan has protonated -NH3+ groups, and if it has some surface activity (isn't it quite hydrophilic?), then it will act as a surface active ion and will be sensitive to the counterion. The surface tension will depend on its mean ion activity, equal approximatelly to gamma*[Chitosan(z+)]^1/(z+1) * [Cl(-) + CH3COO(-)]^z/(z+1); gamma is the activity coefficient, z is chitosan's charge number. So if you increase Cl(-), the surface tension decreases as if you add chitosan.
The Cl(-) ion is not forming covalent bond with -NH3(+).
Viscosity will also change, since ionic strength affects strongly the conformation of the polyelectrolyte. In dilute solution the chain will be extended due to the repulsion between -NH3(+). When you add electrolyte, you screen the repulsion, the chain will shrink, the viscosity must decrease (I think).
Small amounts of salt (smaller than the concentration of dissociated acid) will not change a lot. But if you add salt of concentration similar to the acid, you should easily measure both effects.
OK thank you very much Mr. Radomir for your clear explanation . I work with Chitosan:PVA , if I want to gain more decrease in the surface tension and viscosity, i think I should add the salt after chitosan is protonated and blend with PVA.
and this is the following step that i used to dissolved chitosan;PVA solution:
1. PVA dissolved in acetic acid 1%
2. add some chitosan into PVA solution stir until homogenous
3. add x gram of NaCl into chitosan:PVA.
is there any suggestion? Thank You
The addition of electrolytes or counterions always affect the polyelectrolytes solutions. The Manning Two-Phase Model Theory (among others) deals to a great deal with the condensation of the counterions, and predicts to a great extent their influence, since the overall dimensions, the solubility, surfance tension and water structure are all altered.
Acetic acid at natural pH (~3) has dissociation degree of about 1%, but your pH won't be natural after adding the chitosan. At pH 7, acid dissociation is ~99%.
At pH 3, the ionic strength of the acid is 1 mM (I guess you use weight %). You'll see a strong effect if you add more than 1mM NaCl,
At pH 7, the ionic strength of the acid is 150 mM. You'll see an effect if you add more than 150mM NaCl,
Theorists. And why it is simple not to measure a surface tension and viscosity?
Some literature states that surfactants can reduce surface tension, both ionic and non-ionic surfactants. but I found that surfactants such as TWEEN 20, brijj 35, DTAB, and SDS was not significant enough to lower the surface tension (PEO: chitosan in 50% acetic acid). Yet. The most effective is to raise the concentration of acetic acid from 50% to 90%.
Then I tried to mix the salt into the polymer solution: CS. Salt theoretically able to change it, but I need to measure in order to know how big the changes.
But whether these changes can be measured, because i only add a small amount of salt, but maybe I will take Mr Vladomir suggestion as reference.
Уour work from this opera:
http://www.chitin.ru/news.php?id=222
http://www.science-education.ru/pdf/2012/4/314.pdf
http://www.findpatent.ru/patent/248/2487701.html
http://www.chem.msu.su/rus/jvho/2008-1/84.pdf
http://www.google.com/patents/WO2007018452A2?cl=ru
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