Abstract
We develop a new rheology-based method to study the complexation of cyclodextrins with hydrophobes in hydrophobically modified associative polymer solutions. The associative polymers have comb-like structure with hydrophobic groups randomly attached to the polymer backbone. Intermolecular interactions between the hydrophobic groups form a transient network resulting in thickening of the polymer solutions. On addition of cyclodextrins (CD) to the solution, the hydrophobes are encapsulated within the hydrophobic cavity of the cyclodextrins. This reduces viscoelastic properties of the polymer solution by several orders of magnitude. We exploit the existence of a dynamic equilibrium between CD adsorbed to the hydrophobes and free CD in the solution, to develop a rheology-based Langmuir-type adsorption isotherm for estimating the binding constant for molecular complexation. The model is based on the assumption that the amount of CD adsorbed is proportional to the reduction in elastic modulus of the polymer solution due to the encapsulation of the network junctions by CD. The effects of temperature on binding constant are studied to estimate the enthalpy and entropy of complexation. Experiments are conducted with both α-and β-CD at different polymer concentrations and temperatures to estimate the relative strength of binding of the CDs. At a given temperature and a polymer concentration, α-CD has a lower binding constant compared to that of β-CD, indicating higher affinity of α-CD to adsorb onto the hydrophobes. Since α-CDs have a smaller ring size, they can snugly fit to the hydrophobes and the association leads to higher enthalpy and entropy change.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.