@article{pai_srinivasarao_khan_2002, title={Evolution of microstructure and rheology in mixed polysaccharide systems}, volume={35}, ISSN={["1520-5835"]}, DOI={10.1021/ma0115545}, abstractNote={Synergistic biopolymer blends composed of xanthan and enzymatically modified guar galactomannan are investigated in terms of their time-dependent properties. In particular, a side-chain cleaving enzyme, α-galactosidase, is used to cleave off galactose sugar units from guar to produce modified galactomannans with varying galactose contents of 25.2 and 16.2%. Laser scanning confocal microscopy and dynamic rheology are used to monitor the properties of each of these two modified guar gum in solution as well as in blends with xanthan as they are allowed to age over a period of 3 weeks. Our results indicate that solutions of guar with a higher galactose (25.2%) content undergo no rheological change over the period of observation and show a constant gel elastic modulus (G‘) in blends with xanthan. Confocal images of the solutions and the blends also indicate that the systems are stable over a period of 3 weeks. In contrast, guar gum with a lower galactose content (16.2%) forms interchain associations in solutio...}, number={5}, journal={MACROMOLECULES}, author={Pai, V and Srinivasarao, M and Khan, SA}, year={2002}, month={Feb}, pages={1699–1707} }
 @article{pai_khan_2002, title={Gelation and rheology of xanthan/enzyme-modified guar blends}, volume={49}, ISSN={["0144-8617"]}, DOI={10.1016/S0144-8617(01)00328-9}, abstractNote={The rheological behavior and synergistic character of mixed polysaccharide systems are examined for blends of xanthan with enzymatically-modified guar. In particular, the enzyme α-galactosidase is used to selectively cleave off the galactose side chains of guar in order to obtain galactomannans with tailored molecular architecture: EMG1 with a relatively high galactose content of 33.6% and a mannose (M) to galactose (G) ratio of 1.85, and EMG2 with a lower galactose content (25.2%) and an M/G ratio of 2.86. Blends of xanthan with enzymatically-modified guar gum samples are examined in terms of their dynamic rheological properties and compared to those of xanthan — locust bean gum blends. The extent of synergism, illustrated by the gel elastic modulus G′ and yield stress τc, is found to increase with increasing extent of enzymatic modification. At constant ionic strength, the EMG2 and locust bean blends behave similarly, with increasing extent of synergy as the temperature of mixing is increased. Additionally, at a fixed mixing temperature, the blends made in water have a higher elastic modulus than those made in salt. In contrast, the EMG1 blends are weaker and the dynamic moduli are unaffected by changes in the mixing temperature or ionic strength. These results are consistent with those of other researchers and are directly related to both the level of disorder in the xanthan molecule as well as the galactose content and fine structure of the galactomannan.}, number={2}, journal={CARBOHYDRATE POLYMERS}, author={Pai, VB and Khan, SA}, year={2002}, month={Aug}, pages={207–216} }
 @article{tayal_pai_khan_1999, title={Rheology and microstructural changes during enzymatic degradation of a guar-borax hydrogel}, volume={32}, ISSN={["1520-5835"]}, DOI={10.1021/ma990167g}, abstractNote={Hydrogels composed of borax cross-linked guar galactomannans are enzymatically degraded using endo-β-mannanase, an enzyme which cleaves the polymer chain backbone. Dynamic rheological measurements show the elastic (G‘) and viscous (G‘ ‘) moduli to be sensitive to gel structure and to reduce significantly during the enzymatic hydrolysis process. The reduction in rheological properties shows three distinct regimes:  an initial large decrease, a slower reduction rate at intermediate times, and an accelerated reduction at longer degradation times. In contrast, the polymer chain molecular weight, obtained from gel permeation chromatography, reduces rapidly at short times and at a slower rate subsequently. We therefore find the kinetics of moduli reduction to be dictated by the relationship between gel structure and rheological properties, rather than purely the rates of chain scission. At short times, the large decrease in moduli is analogous to changes in molecular weight and can directly be attributed to cha...}, number={17}, journal={MACROMOLECULES}, author={Tayal, A and Pai, VB and Khan, SA}, year={1999}, month={Aug}, pages={5567–5574} }