6533b7d9fe1ef96bd126cbc6

RESEARCH PRODUCT

Binding of Short Alkyl Chain Surfactants to the (Ethylene oxide)13−(Propylene oxide)30−(Ethylene oxide)13and (Ethylene oxide)75−(Propylene oxide)30−(Ethylene oxide)75Copolymers Studied by Microcalorimetry

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The enthalpy of transfer (ΔHt) of neutral copolymers, at a fixed and low concentration ca. 10-3 mol kg-1, from water to the aqueous surfactant solutions as a function of the surfactant concentration (fSmS) was determined at 25 °C. The surfactants studied are sodium octanoate, sodium decanoate, N-octylpyridinium chloride (OPC), and N,N-dimethyloctylamine-N-oxide (ODAO). The copolymers are (ethylene oxide)13−(propylene oxide)30−(ethylene oxide)13 (L64) and (ethylene oxide)75−(propylene oxide)30−(ethylene oxide)75 (F68). The two copolymers show different hydrophilic−hydrophobic ratios, the larger being for F68. As a general feature, the shape of the ΔHt vs fSmS curve depends on the nature of the surfactant whereas the magnitude of the enthalpy depends essentially on the nature of both the surfactant and the copolymer. A quantitative analysis of the experimental data of the systems investigated was done. L64 and F68 in ODAO solutions behave like classical hydrophobic nonionic additives. OPC does not exhibit s...