I know the general background of using light scattering for determining e.g. molecular weights. I would appreciate, however, comments on the uses of light scattering on the characterization of polymer networks in dry or in wet/organic solvent swollen state. I am specially interested in assessing crosslink density, mobilty and homogeneity of network formation. I did some preliminary literature search but I am not a specialist in this field, therefore I would welcome comments from colleagues, who have practical experience in this field. If it can be used for network homogeneity assessment, hat is the experimental arranegement? What is the spatial resolution?
I think quantitatively Pdi which is an index of polydispersivity of the particle sizes can be helpful and qualitatively the oscillation in the count rate may also be a representative of the homogeneity of the dispersion. DLS can measure particle sizes from less than 1 nm up to 10000 nm. Although I have not heard about the resolution of DLS, I know that the beam diameter in Malvern Zetasizer ZS is 0.63 mm and the position of the incident beam can be adjusted. To investigate the homogeneity of a dispersion, one way can be that you monitor the molecular weight or size over time and figure out if there is any fluctuation over time, while you have placed the incident beam position near the wall of the cuvette. Moreover, in this way you can understand whether the system is an aggregating one pr not by observing the trend in the data over time.
Overall, to me DLS does not differentiate two spatial points of the sample in order to determine the homogeneity of the sample. But by using different samples from a given dispersion/solute or by monitoring one sample over time, one may gain information about homogeneity.
Thank you for your advice. In this case, however, I do not want to get particle size distribution. Polymer gels in swollen state or in dry state but above the glass transition temperature are more like concentrated poymer solutions, thus separate particles cannot be distinguished. What may vary is the distribution of inter-crosslink molecular wieights, i.e. the crosslink density - and I am interested in determining this factor.
I would be interested if this is indeed possible. Looking at molecular weights between crosslinks usually require either assumptions (e.g. perfect network with no dangling end; combine that assumption with classic rubber elasticity theory), or else special conditions (e.g., in rare cases where the number of crosslinks can actually be counted because the crosslink entity happens to be chemically distinguishable enough to be measured). My short assessment is, I don't think it can be done without some elaborate labelling scheme of your monomers.
Hello, maybe you can find additional references to static light scattering methods to quantifiy crosslinking heterogeneity in our recent review article (DOI: 10.1039/C4PY01677G).
Dear Fany! Wow, this is something I have been looking for. Many thanks. Gyorgy
Hi guys! A stupid question from a theoretician -- are you sure that the METHOD of light scattering can be applied to studies of dense polymer solutions? At university I was taught that UV-vis, CD and light scattering work up to semi-dilute regime of polymer solution, but not for concentrated. Since then the Nature may have changed, but I strongly doubt that ;-)
Mea culpa - I did not understand the question correctly. On the heterogeneity of crosslinks in a polymer network, indeed light scattering can be used. RS Stein's paper in 1969 addresses this (it involves looking at scattered light whose polarization is the same as that of the incident light). Link is attached. The manuscript by Di Lorenzo & Seiffert might address the exact same issue (unfortunately, I do not have subscription to the journal where it was published, so I did some digging elsewhere for the topic-appropriate reference).
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