Micellar parameters of diblock copolymers and their interactions with ionic surfactants |
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Authors: | Noor Rehman Abbas Khan Iram Bibi Mohammad Siddiq |
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Institution: | Noor Rehman(a,b),Abbas Khanc,Iram Bibia and Mohammad Siddiq(a**) a Department of Chemistry,Quaid-I-Azam University,Islamabad 45320,Pakistan b Instituto de Quimica,Universidade Federal do Rio Grande do Sul,UFRGS PO Box 15010,CEP 91501-930,Porto Alegre/RS/Brazil c Department of Chemistry,Abdul Wali Khan University,Mardan K-Pukhtoonkhwa,Pakistan |
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Abstract: | The interactions of non-ionic amphiphilic diblock copolymer poly(oxyethylene/oxybutylene) (E39B18) with anionic surfactant sodium dodecyl sulphate (SDS) and cationic surfactant hexadecyltrimethylammonium bromide (CTAB)
were studied by using various techniques such as surface tension, conductivity, steady-state fluorescence and dynamic light
scattering. Surface tension measurements were used to determine the critical micelle concentration (CMC) and thereby the free
energy of micellization (ΔG
mic), free energy of adsorption (ΔG
ads), surface excess concentration (Γ) and minimum area per molecule (A). Conductivity measurements were used to determine the critical micelle concentration (CMC), critical aggregation concentration
(CAC), polymer saturation point (PSP), degree of ionization (α) and counter ion binding (β). Dynamic light scattering experiments were performed to check the changes in physiochemical properties of the block copolymer
micelles taken place due to the interactions of diblock copolymers with ionic surfactants. The ratio of the first and third
vibronic peaks (I
1/I
3) indicated the polarity of the pyrene micro environment and was used for the detection of micelle as well as polymer-surfactant
interactions. Aggregation number (N), number of binding sites (n) and free energy of binding (ΔG
b) for pure surfactants as well as for polymer-surfactant mixed micellar systems were determined by the fluorescence quenching
method. |
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Keywords: | Surface tension Conductivity Dynamic light scattering steady-state fluorescence Micellization |
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