Effect of β-Cyclodextrin Upon the Sol-gel Transition of Methylcellulose Solutions in the Presence of Sodium Dodecyl Sulfate

The sol-gel transition temperature of methylcellulose (MC) solution in the presence of sodium dodecyl sulfate (SDS) as well as the mixtures of SDS and beta-cyclodextrin (beta-CD) was measured, and the effect of the two competing interactions, the hydrophobic interaction between SDS and MC and the inclusion interaction between SDS and beta-CD, upon the sol-gel transition of MC solution was studied. It has been found that the inclusion interaction between SDS and beta-CD is much greater than the hydrophobic interaction between SDS and MC. As a result, in the coexistence of SDS and beta-CD, the sol-gel transition temperature of MC solution keeps the same value, independent of the concentration of SDS in solution on condition that the concentration of SDS is less than beta-CD. Our experimental results not only Suggest that the effect of SDS upon the sot-gel transition of MC solution can be screened by beta-CD completely but also indicate the inclusion ratio of SDS to beta-CD can be determined quantitatively by using rheological measurement. The inclusion ratio of SDS to beta-CD is 1:1, which is in good agreement with the inclusion ratio of SDS to beta-CD in the presence of poly(vincyl pyrrolidone) determined by the viscosity measurement but is critically different from the inclusion ratio of SDS to beta-CD in the presence of the oppositely charged polyelectrolyte by using the rheological measurement, mainly due to the reason that the mechanism of the interaction between SDS and MC is critically different from the mechanism of the interaction between SDS and the oppositely charged polyelectrolyte.