Dear Fatima Ahmad,

swelling is inverselly proportional to the crosslink density. Crystallinity may also be a factor if it is not altered by the solvent and swelling process, sine it is the amorphous phase which is concerned at first. The attached files gives more details. Regards

Dear Fatima,

A1 to Q1 : cellulose can be used to investigate swelling method . You need to add some cross linker, and then you have made hydrogel. You can use MCC, but consider also CMC (carboxymethyl cellulose), HEC (hydroxyethyl cellulose), etc...

A2 to Q2 : water is definitely appropriate medium.

Mr. Abdelkader answered your Q3.

Best regards.

Hi,

Basically swelling can be described as penetration of solvent molecules in between polymeric chains. swelling also depends on various factors such as crystallinity of polymer, molecular weight, polarity of the functional groups in the polymer, solubility parameter, similarity between functional groups of solvent and polymer, temperature etc. This is basic parameters for polymers. So in general a solvent which doesn't dissolve the polymer can swell the polymer to some extent.

In cross-linked polymer chains are attached to each other strongly and structure is more compact thus it me behave differently. In general for swelling studies of cross-link polymer systems more polar solvents such as THF, Chloroform, dicholromethane, NMP.DMF, DMSO and DMAc are preferred. 

Also some polymers are water soluble while some are water insoluble hence it also depends on type of polymer whether it will get swelled or not in water.

The crosslinking denity was determined onthe basis of solvent-swelling measurements using Flory-Rehner equation where v-1/2MC

Hello

In the case of crystallinity versus sorption/swelling, the first answer is correct - increasing the crystallinity will decrease the swelling. For a detailed description of this phenomenon, although for a synthetic polymer (PE), you can check our recent paper (https://www.researchgate.net/publication/271539730_Equilibrium_sorption_of_ethylene_in_polyethylene_Experimental_study_and_PC-SAFT_simulations)

Regarding water, if your polymer swells in water but does not dissolve, then you can surely use it.

And Flory-Rehner theory: yes it works, but you have to be careful with the interpretation to some extent, as the method can have large uncertainties.

Regards, Josef

Article Equilibrium sorption of ethylene in polyethylene: Experiment...

Thank you for all the valuable answers, they were very helpful. I have some follow up questions:

1) As mentioned before my polymer swells in water but does not dissolve so most people answered that since it swells water is ok to use as a solvent. The polymer is soluble in a NaOH/urea solvent system is it ok to do the swelling test using this solvent? or are they some conditions regarding solvents that can be used?

2) I was planning on calculating the swelling percentage the simple way (Final weight-Initial weight / Initial weight *100). I just need to prove if there is any change in the swelling behavior and this seemed like the simplest method to do so, however is this enough? or is it necessary to use the Flory Rehner equation (which i'm afraid seems rather complicated).

I am completely new to this topic and all answers are of great help.

Hello

1) You can not use a solvent, in which the polymer dissolves. You would lose a part of your material and this would render your swelling data incorrect. So the NaOH/urea is not suitable for you.

2) The Flory-Rehner equation enables you to estimate the extent of cross-linking based on the measured swelling behavior and some additional parameters. It is not a way of evaluating the degree of swelling. Weighing the sample is ok, but you have to be careful about the procedure. If the sample will be fragile, you can have problems with manipulation. You must also dry the sample prior to weighing so that you do not measure liquid on the surface. It is therefore highly preferable to have the polymer in a compact form (e.g., film). This method is sometimes used for studying the sorption of liquids in polymer membranes, so you can try to find a paper on this topic as inspiration for your experiment. My former colleagues tested the same method for PE films, but it is sadly not yet published.

Regards, Josef