Hi there. I've been having a puzzle explaining the experimental results with the citrate anions and PEG modified polyacrylamide:
According to the experimental data there is a hydrogel swelling whenever citrate is added to a 10mM PBS solution. However, according to the Hofmeister series, citrate is a well known salting-out agent, which would absorb water, thus make the hydrogel contract. In addition that, the swelling is diminished when the concentration of salts (ionic strength) is increased in a bulk solution. Any ideas?
Zygimantas Gricius
In your system, citrate works as a cross-linking agent. Nitrogen amide acts as the base polyacrylamide block for acid citrate. Its ionic strength decreases. Check the IR band shift response of the mixture versus polyacrylamide.
Dear all, swellability also decreases with increasing crosslink density. What are the other conditions mainly temperature? Polyacrylamides and PEG both are less sensitive to salts or hardness if they are really neutral, however polyacrylamide is prone to hydrolysis for the whole spectrum of pH (amide group is converted to carboxylic acid or carboxylate groups). My Regards
One more thing to mention - polyacrylamide alone does not change its dimensions when exposed to citrate.
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