| 1. |
- Bodvik, Rasmus, et al.
(author)
-
Aggregation of modified celluloses in aqueous solution : transition from methylcellulose to hydroxypropylmethylcellulose solution properties induced by a low molecular weight oxyethylene additive
- 2012
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:38, s. 13562-13569
-
Journal article (peer-reviewed)abstract
- Temperature effects on viscosity and aggregation behaviour of aqueous solutions of three different cellulose ethers: methylcellulose (MC), hydroxypropylmethylcellulose (HPMC) and ethyl(hydroxyethyl)cellulose (EHEC), were investigated using viscosity and dynamic light scattering measurements as well as Cryo-TEM. In all cases increasing temperature reduces the solvent quality of water, which induces aggregation. It was found that the aggregation rate followed the order EHEC > HPMC > MC, suggesting that cellulose ethers containing some bulky and partly hydrophilic substituents assemble into large aggregates more readly than methylcellulose. This finding is discussed in terms of the organization of the structures formed by the different cellulose ethers. The temperature-dependent association behavior of cellulose ethers was also investigated in a novel way by adding diethyleneglycolmonobutylether (BDG) to methylcellulose aqueous solutions. When the concentration of BDG was at and above 5 wt%, methylcellulose adopted HPMC-like solution behaviour. In particular, a transition temperature where the viscosity was decreasing, prior to increasing at higher temperatures, appeared and the aggregation rate increased. This observation is rationalized by the ability of the amphiphilic BDG to accumulate at non-polar interfaces, and thus also to associate with hydrophobic regions of methylcellulose. In effect BDG is suggested to act as a physisorbed hydrophilic and bulky substituent inducing similar constraints on aggregation as the chemically attached hydroxypropyl groups in HPMC and oligo(ethyleneoxide) chains in EHEC.
|
|
| 2. |
- Bodvik, Rasmus, et al.
(author)
-
Aggregation and network formation of aqueous methylcellulose and hydroxypropylmethylcellulose solutions.
- 2010
-
In: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 354:1-3, s. 162-171
-
Journal article (peer-reviewed)abstract
- Solution properties of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) have been investigated as a function of temperature and concentration using a broad range of experimental techniques. Novelties include the extensive comparison between MC and HPMC solutions as well as the combination of techniques, and the use of Cryo transmission electron microscopy (Cryo-TEM). The correlation between rheology and light scattering results clearly demonstrates the relation between viscosity change and aggregation. Cryo-TEM images show the network structures formed. Viscosity measurements show that for both MC and HPMC solutions sudden changes in viscosity occur as the temperature is increased. The onset temperature for these changes depends on polymer concentration and heating rate. For both MC and HPMC solutions the viscosity on cooling is very different compared to on heating, demonstrating the slow equilibration time. The viscosity changes in MC and HPMC solutions are dramatically different; for MC solutions the viscosity increases by several orders of magnitude when a critical temperature is reached, whereas for HPMC solutions the viscosity decreases abruptly at a given temperature, followed by an increase upon further heating. Light and (SAXS) small-angle X-ray scattering shows that the increase in viscosity, for MC as well as for HPMC solutions, is due to extensive aggregation of the polymers. Light scattering also provides information on aggregation kinetics. The SAXS measurements allow us to correlate aggregation hysteresis to the viscosity hysteresis, as well as to extract some structural information. Cryo-TEM images give novel information that a fibrillar network is formed in MC solutions, and the strong viscosity increase occurs when this network spans the whole solution volume. For HPMC solutions the behaviour is more complex. The decrease in viscosity can be related to the formation of compact objects, and the subsequent increase to formation of fibrillar structures, which are more linear and less entangled than for MC.
|
|
| 3. |
- Bodvik, Rasmus, et al.
(author)
-
Temperature-dependent adsorption of cellulose ethers on silica and hydrophobized silica immersed in aqueous polymer solution
- 2011
-
In: RSC ADVANCES. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 1:2, s. 305-314
-
Journal article (peer-reviewed)abstract
- The influence of temperature on adsorption and the adsorbed layer properties of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) were investigated on silica and hydrophobized silica surfaces immersed in aqueous polymer solution. To achieve a concise understanding a quartz crystal microbalance with dissipation, ellipsometry, and atomic force microscopy imaging were employed. These techniques provide complimentary information on the structure, mass and viscoelastic properties of the polymer layers. Adsorption was first allowed at 25 degrees C. Next, the temperature was increased step-wise up to 50 degrees C and then decreased again. This procedure highlights the temperature dependence of the adsorbed material, as well as the hysteresis in the adsorption due to temperature cycling. A change in temperature not only affects the adsorbed amount, but also the properties of the layer as illustrated by measurements of its water content, thickness and viscoelasticity.
|
|
| 4. |
- Bodvik, Rasmus, et al.
(author)
-
Temperature-Dependent Competition between Adsorption and Aggregation of a Cellulose Ether-Simultaneous Use of Optical and Acoustical Techniques for Investigating Surface Properties
- 2012
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:25, s. 9515-9525
-
Journal article (peer-reviewed)abstract
- Adsorption of the temperature-responsive polymer hydroxypropylmethylcellulose (HPMC) from an aqueous solution onto hydrophobized silica was followed well above the bulk instability temperature (T-2) in temperature cycle experiments. Two complementary techniques, QCM-D and ellipsometry, were utilized simultaneously to probe the same substrate immersed in polymer solution. The interfacial processes were correlated with changes in polymer aggregation and viscosity of polymer solutions, as monitored by light scattering and rheological measurements. The simultaneous use of ellipsometry and QCM-D, and the possibility to follow layer properties up to 80 degrees C, well above the T-2 temperature, are both novel developments. A moderate increase in adsorbed amount with temperature was found below T-2, whereas a significant increase in the adsorbed mass and changes in layer properties were observed around the T-2 temperature where the bulk viscosity increases significantly. Thus, there is a clear correlation between transition temperatures in the adsorbed layer and in bulk solution, and we discuss this in relation to a newly proposed model that considers competition between aggregation and adsorption/deposition. A much larger temperature response above the T-2 temperature was found for adsorbed layers of HPMC than for layers of methyl cellulose. Possible reasons for this are discussed.
|
|
| 5. |
- Bodvik, Rasmus, et al.
(author)
-
Temperature responsive surface layers of modified celluloses
- 2011
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:10, s. 4260-4268
-
Journal article (peer-reviewed)abstract
- The temperature-dependent properties of pre-adsorbed layers of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) were investigated on silica and hydrophobized silica surfaces. Three different techniques, quartz crystal microbalance with dissipation monitoring, ellipsometry, and atomic force microscopy imaging, were used, providing complementary and concise information on the structure, mass and viscoelastic properties of the polymer layer. Adsorption was conducted at 25 degrees C, followed by a rinsing step. The properties of such pre-adsorbed layers were determined as a function of temperature in the range 25 degrees C to 50 degrees C. It was found that the layers became more compact with increasing temperature and that this effect was reversible, when decreasing the temperature. The compaction was more prominent for MC, as shown in the AFM images and in the thickness data derived from the QCM analysis. This is consistent with the fact that the phase transition temperature is lower, in the vicinity of 50 degrees C, for MC than for HPMC. The water content of the adsorbed layers was found to be high, even at the highest temperature, 50 degrees C, explored in this investigation.
|
|
| 6. |
- Eriksson, Leif E. B., et al.
(author)
-
Evaluation of new spaceborne SAR sensors for sea-ice monitoring in the Baltic Sea
- 2010
-
In: Canadian journal of remote sensing. - : CANADIAN AERONAUTICS SPACE INST. - 0703-8992 .- 1712-7971. ; 36, s. S56-S73
-
Journal article (peer-reviewed)abstract
- In this study, synthetic aperture radar (SAR) data from the Advanced Land Observing Satellite (ALOS) and the Envisat, RADARSAT-2, and TerraSAR-X satellites were compared to evaluate their usefulness for sea-ice monitoring in the Baltic Sea. Radar signature characteristics at different frequencies, polarizations, and spatial resolutions are presented for three examples from 2009. C-band like-polarization data, which have been used for operational sea-ice mapping since the early 1990s, serve as a reference. Advantages and disadvantages were identified for the different SAR systems and imaging modes. One conclusion is that cross-polarized data improve the discrimination between sea ice and open water. Another observation is that it is easier to identify ice ridges in L-band data than in images from shorter wavelengths. The information content of X-and C-band images is largely equivalent, whereas L-band data provide complementary information. L-band SAR also seems to be less sensitive to wet snow cover on the ice.
|
|
| 7. |
- Eriksson, Leif, 1970, et al.
(author)
-
Evaluation of multi-polarization SAR data at L-, C- and X-band for sea-ice monitoring in the Baltic Sea
- 2010
-
In: Proceedings of the ESA Living Planet Symposium 2010, 28 June - 2 July 2010, Bergen, Norway. ; ESA SP-686
-
Conference paper (other academic/artistic)abstract
- SAR data from the satellites ALOS, Envisat, Radarsat-2 and TerraSAR-X were compared in order to evaluate their usefulness for sea ice monitoring in the Baltic Sea. Different advantages and disadvantages were identified for the SAR systems and imaging modes. It has been shown that cross-polarized data improve the discrimination between sea-ice and open water. Another observation is that it is easier to identify ice ridges in L-band data than in images from shorter wavelengths. The information content of X- and C-band images is largely equivalent, whereas L-band data provide complementary information. L-band SAR also seems tobe less sensitive to wet snow cover on the ice.
|
|
| 8. |
- Eriksson, Leif, 1970, et al.
(author)
-
Evaluation of new spaceborne SAR sensors for sea-ice monitoring in the Baltic Sea
- 2010
-
In: Canadian journal of remote sensing. - : Informa UK Limited. - 0703-8992 .- 1712-7971. ; 36:1, s. S56-S73
-
Journal article (peer-reviewed)abstract
- In this study, synthetic aperture radar (SAR) data from the Advanced Land Observing Satellite (ALOS) and the Envisat, RADARSAT-2, and TerraSAR-X satellites were compared to evaluate their usefulness for sea-ice monitoring in the Baltic Sea. Radar signature characteristics at different frequencies, polarizations, and spatial resolutions are presented for three examples from 2009. C-band like-polarization data, which have been used for operational sea-ice mapping since the early 1990s, serve as a reference. Advantages and disadvantages were identified for the different SAR systems and imaging modes. One conclusion is that cross-polarized data improve the discrimination between sea ice and open water. Another observation is that it is easier to identify ice ridges in L-band data than in images from shorter wavelengths. The information content of X- and C-band images is largely equivalent, whereas L-band data provide complementary information. L-band SAR also seems to be less sensitive to wet snow cover on the ice.
|
|
| 9. |
|
|
| 10. |
- Hakonen, Aron, 1970, et al.
(author)
-
A potential tool for high-resolution monitoring of ocean acidification.
- 2013
-
In: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670 .- 1873-4324. ; 786, s. 1-7
-
Journal article (peer-reviewed)abstract
- Current anthropogenic carbon dioxide emissions generate besides global warming unprecedented acid-ification rates of the oceans. Recent evidence indicates the possibility that ocean acidification and lowoceanic pH may be a major reason for several mass extinctions in the past. However, a major bottleneck forresearch on ocean acidification is long-term monitoring and the collection of consistent high-resolutionpH measurements. This study presents a low-power (<1 W) small sample volume (25l) semiconductor based fluorescence method for real-time ship-board pH measurements at high temporal and spatialresolution (approximately 15 s and 100 m between samples). A 405 nm light emitting diode and the blueand green channels from a digital camera was used for swift detection of fluorescence from the pH sen-sitive dye 6,8-Dihydroxypyrene-1,3-disulfonic acid in real-time. Main principles were demonstrated byautomated continuous measurements of pH in the surface water across the Baltic Sea and the Kattegatregion with a large range in salinity (∼3–30) and temperature (∼0–25◦C). Ship-board precision of salinityand temperature adjusted pH measurements were estimated as low as 0.0001 pH units.
|
|
