| 1. |
- Bergström, L, et al.
(författare)
-
Spectroscopic ellipsometry characterisation and estimation of the Hamaker constant of cellulose
- 1999
-
Ingår i: Cellulose. - 0969-0239 .- 1572-882X. ; 6, s. 1-13
-
Tidskriftsartikel (refereegranskat)abstract
- Calculations of Hamaker constants using Lifshitz theory require the availability of accurate dielectric data, especially in the visible-ultraviolet region. We present spectroscopic ellipsometry data on well defined cellulose films of a limited thickness range (100–140 layers) deposited on an oxidised and hydrophobised silicon substrate. The spectral data, representing measurements from a perpendicular orientation to the fibre deposition direction, was used for estimates of the necessary spectral parameters, i.e. the oscillator strengths and characteristic frequencies in the UV-range. Our calculations show that cellulose has a relatively low Hamaker constant in air (58 zJ) and water (8.0 zJ). The implications for the surface energy estimates of cellulose and colloidal interactions between cellulose and various types of fillers and coating colours were discussed.
|
|
| 2. |
- Holmberg, M, et al.
(författare)
-
Surface force studies of Langmuir-Blodgett cellulose films
- 1997
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 186, s. 369-381
-
Tidskriftsartikel (refereegranskat)abstract
- The interactions between cellulose surfaces, between chitosan coated surfaces and between one cellulose surface and one chitosan coated surface have been studied using the interferometric surface forces apparatus (SFA). The cellulose surfaces were prepared by depositing trimethylsilyl cellulose on hydrophobized mica using the Langmuir-Blodgett technique. The surfaces were desilylated in humid HCl atmosphere to obtain regenerated cellulose. ESCA measurements and wetting studies demonstrated that the desilylation process was effective. AFM studies showed the cellulose surfaces to be smooth with a root mean square roughness of 0.16 nm. Surface force and ellipsometry measurements illustrate that the cellulose film swells considerably in humid air and in water, suggesting that it is mostly amorphous. The interaction between two cellulose surfaces is dominated by a steric repulsion caused by a few dangling tails. On separation an attractive force was present both between two cellulose surfaces and between one cellulose surface and one chitosan surface. The long-range interaction between cellulose and chitosan was shown to be attractive.
|
|
| 3. |
- Stemme, S, et al.
(författare)
-
Effect of colloidal silica and electrolyte on the structure of an adsorbed cationic polyelectrolyte layer
- 1999
-
Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 155, s. 145-154
-
Tidskriftsartikel (refereegranskat)abstract
- The interactions between an adsorbed high molecular weight cationic polyacrylamide (C-PAM) and anionic components have been investigated by ellipsometry. The anionic components used were non-aggregated and microaggregated anionic colloidal silica particles (ACS) and an anionic polyacrylamide (A-PAM). The C-PAM was adsorbed to a silica surface and the different anionic components were then added to the system. The effect of adding an electrolyte (NaCl) to some of these systems was also investigated. The thickness of the adsorbed layer, the adsorbed amount and some kinetic aspects of the adsorption and desorption processes were studied. A three-fold expansion was observed for the C-PAM layer when non-aggregated and microaggregated ACS was added. When large amounts of NaCl are added there is a great decrease in layer thickness for a system with non-aggregated ACS. A system with microaggregated ACS particles is less affected by an increase in the electrolyte concentration. More ACS is adsorbed to a C-PAM layer in the presence of NaCl than in its absence. When A-PAM is added to the C-PAM layer, the thickness and adsorbed amount is much less influenced than if ACS is added. A small increase in adsorption and in layer thickness is first observed and then a desorption process starts. Information about the conformation of the adsorbed cationic polyacrylamide has also been obtained. The ellipsometry measurements indicate that the structure of the adsorbed layer changes as the adsorption process proceeds. The polymers adsorbed first to the surface give a more dense layer than the polymers adsorbed last.
|
|
