Associations in Mixtures of Hydrophobically Modified Polymer and Surfactant in Dilute and Semidilute Aqueous Solutions. A Rheology and PFG NMR Self-Diffusion Investigation

• Published in: Macromolecules Vol. 33; no. 26; pp. 9641 - 9649
• Main Authors: Nilsson, Susanne, Thuresson, Krister, Lindman, Björn, Nyström, Bo
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 26-12-2000
• Subjects: Applied sciences; Cellulose and derivatives; Exact sciences and technology; Natural polymers; Physicochemistry of polymers; Cellulose(ethyl hydroxyethyl); Semidilute solution; Experimental study; Lateral group; Lauryl sulfate; Intermolecular interaction; Anionic surfactant; Self diffusion; Concentration effect; Dilute solution; Hydrophobic group; Aqueous solution; Cellulose ether
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma001203a

Viscosity (dilute regime) and surfactant and polymer NMR self-diffusion (dilute and semidilute regime) measurements were carried out on aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) and of a hydrophobically modified analogue, with (HM4-EHEC) and without (HM0-EHEC) a spacer, in the presence of various amounts of sodium dodecyl sulfate (SDS). Strong polymer−surfactant interactions were revealed. From the binding isotherm the critical aggregation concentration (cac ≈ 3 mm) was obtained for the EHEC/SDS system. By comparing the results from the binding isotherms with those from the rheological measurements, molecular interactions could be correlated to macroscopic properties. The polymer self-diffusion results suggest that the spin-echo attenuation can be described by a log-normal distribution (distribution of self-diffusion coefficients), giving a median polymer self-diffusion coefficient D ME. There is no difference in the trend of D ME between EHEC and the hydrophobically modified analogues at various SDS concentrations. The NMR signal decays of highly viscous samples of the modified analogues are initially described by a distribution mode followed by a single exponential (slow component). The effect of hydrophobic modification is seen in the existence of a slowly diffusing component (D net ≈ 10-14 m2 s-1) (not observed for the unmodified analogue) that is related to a strong and long-lived network, at least of the order of the NMR time scale (ca. 0.5 s).