The Build-Up of Polyelectrolyte Multilayers of Microfibrillated Cellulose and Cationic Polyelectrolytes
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- 作者：Lars Wå ; gberg ; Gero Decher ; Magnus Norgren ; Tom Lindströ ; m ; Mikael Ankerfors ; Karl Axnä ; s
- 刊名：Langmuir
- 出版年：2008
- 出版时间：February 5, 2008
- 年：2008
- 卷：24
- 期：3
- 页码：784 - 795
- 全文大小：468K
- 年卷期：v.24,no.3(February 5, 2008)
- ISSN：1520-5827
文摘
A new type of nanocellulosic material has been prepared by high-pressure homogenization of carboxymethylatedcellulose fibers followed by ultrasonication and centrifugation. This material had a cylindrical cross-section as shownby transmission electron microscopy with a diameter of 5-15 nm and a length of up to 1 
m. Calculations, usingthe Poisson-Boltzmann equation, showed that the surface potential was between 200 and 250 mV, depending on thepH, the salt concentration, and the size of the fibrils. They also showed that the carboxyl groups on the surface ofthe nanofibrils are not fully dissociated until the pH has reached pH = ~10 in deionized water. Calculations of theinteraction between the fibrils using the Derjaguin-Landau-Verwey-Overbeek theory and assuming a cylindricalgeometry indicated that there is a large electrostatic repulsion between these fibrils, provided the carboxyl groups aredissociated. If the pH is too low and/or the salt concentration is too high, there will be a large attraction between thefibrils, leading to a rapid aggregation of the fibrils. It is also possible to form polyelectrolyte multilayers (PEMs) bycombining different types of polyelectrolytes and microfibrillated cellulose (MFC). In this study, silicon oxide surfaceswere first treated with cationic polyelectrolytes before the surfaces were exposed to MFC. The build-up of the layerswas monitored with ellipsometry, and they show that it is possible to form very well-defined layers by combinationsof MFC and different types of polyelectrolytes and different ionic strengths of the solutions during the adsorptionof the polyelectrolyte. A polyelectrolyte with a three-dimensional structure leads to the build-up of thick layers ofMFC, whereas the use of a highly charged linear polyelectrolyte leads to the formation of thinner layers of MFC.An increase in the salt concentration during the adsorption of the polyelectrolyte results in the formation of thickerlayers of MFC, indicating that the structure of the adsorbed polyelectrolyte has a large influence on the formationof the MFC layer. The films of polyelectrolytes and MFC were so smooth and well-defined that they showed clearlydifferent interference colors, depending on the film thickness. A comparison between the thickness of the films, asmeasured with ellipsometry, and the thickness estimated from their colors showed good agreement, assuming thatthe films consisted mainly of solid cellulose with a refractive index of 1.53. Carboxymethylated MFC is thus a newtype of nanomaterial that can be combined with oppositely charged polyelectrolytes to form well-defined layers thatmay be used to form, for example, new types of sensor materials.
m. Calculations, usingthe Poisson-Boltzmann equation, showed that the surface potential was between 200 and 250 mV, depending on thepH, the salt concentration, and the size of the fibrils. They also showed that the carboxyl groups on the surface ofthe nanofibrils are not fully dissociated until the pH has reached pH = ~10 in deionized water. Calculations of theinteraction between the fibrils using the Derjaguin-Landau-Verwey-Overbeek theory and assuming a cylindricalgeometry indicated that there is a large electrostatic repulsion between these fibrils, provided the carboxyl groups aredissociated. If the pH is too low and/or the salt concentration is too high, there will be a large attraction between thefibrils, leading to a rapid aggregation of the fibrils. It is also possible to form polyelectrolyte multilayers (PEMs) bycombining different types of polyelectrolytes and microfibrillated cellulose (MFC). In this study, silicon oxide surfaceswere first treated with cationic polyelectrolytes before the surfaces were exposed to MFC. The build-up of the layerswas monitored with ellipsometry, and they show that it is possible to form very well-defined layers by combinationsof MFC and different types of polyelectrolytes and different ionic strengths of the solutions during the adsorptionof the polyelectrolyte. A polyelectrolyte with a three-dimensional structure leads to the build-up of thick layers ofMFC, whereas the use of a highly charged linear polyelectrolyte leads to the formation of thinner layers of MFC.An increase in the salt concentration during the adsorption of the polyelectrolyte results in the formation of thickerlayers of MFC, indicating that the structure of the adsorbed polyelectrolyte has a large influence on the formationof the MFC layer. The films of polyelectrolytes and MFC were so smooth and well-defined that they showed clearlydifferent interference colors, depending on the film thickness. A comparison between the thickness of the films, asmeasured with ellipsometry, and the thickness estimated from their colors showed good agreement, assuming thatthe films consisted mainly of solid cellulose with a refractive index of 1.53. Carboxymethylated MFC is thus a newtype of nanomaterial that can be combined with oppositely charged polyelectrolytes to form well-defined layers thatmay be used to form, for example, new types of sensor materials.