Interactions between the Non-ionic Surfactant C12E5 and Poly(ethylene oxide) Studied Using Dynamic Light Scattering and Fluorescence Quenching

• Published in: Macromolecules Vol. 29; no. 6; pp. 2169 - 2178
• Main Authors: Feitosa, Eloi, Brown, Wyn, Hansson, Per
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11.03.1996
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties; Ethylene oxide polymer; Hydrodynamic radius; Phase diagram; Non ionic surfactant; Concentration effect; Dilute solution; Temperature effect; Aqueous solution; Experimental study; Complexes; Conformation
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma950516g

Dynamic light scattering measurements have been made to elucidate changes in the coil conformation of a high molecular weight poly(ethylene oxide) (PEO) fraction when the non-ionic surfactant C12E5 is present in dilute solutions. The measurements were made at 20 °C as functions of (a) the C12E5 concentration at constant PEO concentration, (b) the PEO concentration at constant C12E5 concentration, and (c) the C12E5/PEO concentration ratio. The influence of temperature on the interactions in terms of the relaxation time distributions was also examined up to the cloud point. It was found that when the C12E5/PEO weight ratio was >2 and when the temperature was >14 °C, the correlation functions became bimodal with well-separated components. The fast mode derives from individual surfactant micelles which are present in the solution at high number density. The appearance of the slow mode, which dominates the scattering, is interpreted as resulting from the formation of micellar clusters due to an excluded-volume effect when the high molar mass (M = 6 × 105) PEO is added to the surfactant solution. It is shown that the micellar clusters form within the PEO coils and lead to a progressive swelling of the latter for steric reasons. The dimensions of the PEO/C12E5 complex increase with increasing surfactant concentration to a value of R H ≈ 94 nm (R g ≈ 208 nm) at C C 12 E 5 = 3.5%. Fluorescence quenching measurements show that the average aggregation number of C12E5 increases significantly on addition of the high molar mass PEO. With increasing temperature toward the cloud point the clusters increase in number density and/or become larger. The cloud point is substantially lower than that for C12E5 in water solution and is strongly dependent on the PEO concentration.