Atomic force microscopy investigation of smart superabsorbent hydrogels based on carboxymethyl guar gum: Surface topography and swelling properties

Atomic force Microscopy (AFM) is commonly used to study various mechanical, functional, and electrical properties of materials at the nanoscale, as well as for characterizing the topography and surface properties. Up to our knowledge, this is the first investigation to study the surface properties of some carboxymethyl guar gum-based smart superabsorbent hydrogels before and after swelling. In this regard, three sets of modified carboxymethyl guar gum (CMGG) hydrogels were prepared via reaction with different weight ratios of acrylate monomers. The chemical composition of these hydrogels was assured via the IR spectroscopy and the morphology of the dry and swelled gels was studied via the ESEM. The swelling data were correlated with the chemical composition of the prepared hydrogels together with a detailed AFM study of their maps. The chemical modifications were also confirmed by a recent model of AFM. The data reveal that the highest swelling was achieved by C2 in which the weight ratio of acrylate monomers is twice that of guar gum (Qmax = 676 g g after 150 min) It was also found that the swelling capacity of all the prepared hydrogels decreases slightly from the first to the third swelling cycle. For instance, the swelling performance for C2 is as following: 767, 750 and 734 g g for the first, second and third cycles respectively. The data extracted from the AFM showed that surface roughness increases from 15.62 nm to 22.47 and the height rises from 11.2 nm to 43.9 nm as a result of chemical modification for guar gum into carboxymethyl guar gum.