| 1. |
- Evenäs, L., et al.
(author)
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Adsorption Isotherm and Aggregate Properties of Fluorosurfactants on Alumina Measured by 19F NMR
- 2002
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:21, s. 8096-8101
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Journal article (peer-reviewed)abstract
- The adsorption and self-assembly of ammonium perfluorooctanoate (APFO) at surfaces of porous alumina immersed in solution at pH similar to 4 have been studied using F-19 NMR. From the intensity of the APFO NMR signals, the amount of adsorbed surfactant, and thereby the adsorption isotherm, was determined. The adsorption isotherm indicates that APFO forms bilayers on alumina. This result is supported by finding the CF3 signal of adsorbed APFO shifted upfield compared to the signal in aqueous solution with an amount that corresponds to a change from aqueous to fluorocarbon environment. Additionally, faster transverse relaxation of the fluorine nuclei adjacent to the head group compared to that of the CF3 group adds a further argument for the formation of a bilayer. The exchange pattern of surfactants between the adsorbed layer and the aqueous bulk was studied through the CF3 group F-19 signals and their time-averaged behavior. Inside the pores of the alumina particles, the exchange time was found to be fast (much less than1 ms) between adsorbed and dissolved APFO. The presented NMR method to determine the adsorption isotherm could be a powerful new tool when studying systems of mixed surfactants, since the adsorbed amount of chemically different surfactants and their formation in aggregates would become separately quantifiable. The method is readily applicable to any NMR nuclei and thereby to many adsorption problems.
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| 2. |
- Gane, P. A. C., et al.
(author)
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Comparison of NMR cryoporometry, mercury intrusion porosimetry, and DSC thermoporosimetry in characterizing pore size distributions of compressed finely ground calcium carbonate structures
- 2004
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 43:24, s. 7920-7927
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Journal article (peer-reviewed)abstract
- This work investigates for the first time how mercury intrusion porosimetry (MIP), NMR-based cryoporometry, and DSC-based thermoporosimetry compare in revealing the porous characteristics of ground calcium carbonate structures compacted over a range of pressures. The comparison is made using the same source samples throughout. MIP, a much-used method in the characterization of porous structures, has the drawback that the high pressure needed to intrude the mercury may either distort the skeletal porous structure of the sample, especially when compressible materials such as cellulose or binders/latex are present, or lead to a reduction in the measured number of large pores due to the shielding by smaller pores. These effects have previously been addressed using bulk modulus corrections and by modeling the structure permeability to account for the potential shielding. Cryoporometry gives detailed information about the pore size distribution of an imbibition saturated structure. Thermoporosimetry is a relatively new candidate in this field, and it yields both pore size distribution and pore volume. Currently it is somewhat limited in the pore size range detectable, but it is relevant to pigmented coatings. Its potential is identified for capturing the pores involved in the progress of imbibition before saturation is reached.
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| 3. |
- Valiullin, Rustem, et al.
(author)
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Liquid-liquid phase separation in micropores
- 2004
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In: Current applied physics. - : Elsevier BV. - 1567-1739 .- 1878-1675. ; 4:2-4, s. 370-372
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Journal article (peer-reviewed)abstract
- Phase separation of binary liquids with an upper critical temperature in porous materials is studied by H-1 NMR cryoporometry and cross-relaxation spectroscopy and by N-15 NMR spectroscopy. The first method provides domain size distributions of the separating minority component while the other ones verify the segregation of the two liquids on molecular level. We find that metastable structures are formed manifested by bimodal domain size distributions. The kinetic arrest of domain growth may be imposed upon by bottlenecks in the porous structure that block diffusion of entire droplets. Practical applications, if one of the liquid components is polymerized, include mobile polymer particles trapped in porous matrix that can serve, e.g., as filters with microscopically amphiphilic pathways.
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