| 1. |
- Burrows, Hugh D., et al.
(författare)
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Solubilization of poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} in Water by Non-Ionic Amphiphiles
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:10, s. 5545-5556
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Tidskriftsartikel (refereegranskat)abstract
- In the presence of the nonionic alkyloxyethylene surfactant n-dodecylpentaoxyethylene glycol ether (C12E5), the anionic conjugated polyelectrolyte (CPE) poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) dissolves in water, leading to a blue shift in fluorescence and dramatic increases in fluorescence quantum yields above the surfactant critical micelle concentration (cmc). No significant changes were seen with a poly(ethylene oxide) of similar size to the surfactant headgroup, confirming that specific surfactant-polyelectrolyte interactions are important. From UV-visible and fluorescence spectroscopy, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), and electrical conductivity, together with our published NMR and small-angle neutron scattering (SANS) results, we provide a coherent model for this behavior in terms of breakup of PBS-PFP clusters through polymer-surfactant association leading to cylindrical aggregates containing isolated polymer chains. This is supported by molecular dynamics simulations, which indicate stable polymer-surfactant structures and also provide indications of the tendency of C12E5 to break up polymer clusters to form these mixed polymer-surfactant aggregates. Radial electron density profiles of the cylindrical cross section obtained from SAXS results reveal the internal structure of such inhomogeneous species. DLS and cryo-TEM results show that at higher surfactant concentrations the micelles start to grow, possibly partially due to formation of long, threadlike species. Other alkyloxyethylene surfactants, together with poly(propylene glycol) and hydrophobically modified poly(ethylene glycol), also solubilize this polymer in water, and it is suggested that this results from a balance between electrostatic (or ion-dipole), hydrophilic, and hydrophobic interactions. There is a small, but significant, dependence of the emission maximum on the local environment.
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| 2. |
- Löf, David, et al.
(författare)
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Structural Characterization of Nonionic Mixed Micelles Formed by C(12)EO(6) Surfactant and P123 Triblock Copolymer.
- 2009
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 113:16, s. 5478-5486
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Tidskriftsartikel (refereegranskat)abstract
- A structural characterization of mixed micelles formed in aqueous solution by the PEO-PPO-PEO triblock copolymer P123 and the nonionic surfactant C(12)EO(6) was carried out using various techniques, including ultralow shear viscosimetry, depolarized dynamic light scattering (VH-DLS), depolarized static light scattering (VH-SLS), and small-angle X-ray scattering (SAXS). The sphere-to-rod transition of the mixed micelles was studied in a diluted regime (P123 concentrations ranging from 0.5 to 10 wt %) at C(12)EO(6)/P123 molar ratios of 2.2, 3.2, 6.0, and 11 as well as for the pure C(12)EO(6). The data from VH-SLS and viscosimetry displayed a sharp increase in the intensity and viscosity, respectively, at the sphere-to-rod transition, and the results from the two methods were in accordance. In both techniques, an increased transition temperature with increasing content of C(12)EO(6) (in the molar ratio regime from 2.2 to 11) was observed. SAXS was used as the main technique, and a thorough structural characterization was performed, where indirect Fourier transformation (IFT) and generalized indirect Fourier transformation (GIFT) were employed in the analysis procedure of the SAXS data. The p(r) functions obtained from the IFT (employed at low P123 concentrations, i.e., 1.0 and 2.0 wt %) and GIFT (employed above 2.0 wt %) analyses revealed increased inhomogeneities in the mixed micelles when the molar ratio was increased. This suggested that the C(12)EO(6) organized themselves at the interface between the PPO core and the PEO corona of the P123 micelles, with the C(12) alkyl chain stretching into the hydrophobic core and the EO(6) part residing in the hydrophilic corona. The structure factor parameters obtained with GIFT for a molar ratio of 2.2 at a P123 concentration of 5.0 wt % showed radius values smaller than what was estimated from the p(r) functions. This was explained by an interpenetration of the PEO chains from one mixed micelle into a neighboring one. VH-DLS was performed on the mixed micelles at a temperature 3 degrees C above the transition temperature and at a molar ratio of 2.2. From the analyzed data, the average length L of the rods was estimated to be 102 nm.
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