| 1. |
- Jansson, Helen, 1964, et al.
(author)
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The Influence of Silica Species Configuration on the Hydration of Alkali-Activated Ground Granulated Blast-Furnace Slag
- 2014
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In: RILEM Proceedings: 2nd International Conference on Advances in Chemically-Activated Materials (CAM-China). - Bagneux : Rilem publications. - 1461-1147. - 9782351581421 ; 92, s. 309-318
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Conference paper (peer-reviewed)abstract
- There are indications on that the initial setting time is dependent on the relative ratio of Na2O to SiO2 when sodium silicate solutions (Na2SiO3) are used for the alkali-activation of ground granulated blast-furnace slag (GGBS). One possible reason for this is that the ratio (called modulus) not only influences the pH but also the viscosity of the solution. The viscosity is, in turn dependent on the structures in the liquid. Therefore, we have investigated the structure of sodium silicate solutions of different moduli by infrared spectroscopy (IR) and silicon nuclear magnetic resonance (Si-29-NMR). The results, which show that the silica configuration is highly dependent on the modulus, will be discussed in relation to the initial setting time of corresponding measurements on GGBS hydration
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| 2. |
- Jansson, Helen, 1964, et al.
(author)
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The Initial Setting Time of Ground Granulated Blastfurnace Slag GGBS and Its Relation to the Modulus of the Alkali-Activating Solution
- 2014
-
In: 2nd International conference on Advances in chemically-activated materials (CAM'2014), RILEM Proceedings. - 1461-1147. - 9782351581421 ; 92, s. 309-318
-
Conference paper (peer-reviewed)abstract
- There are indications on that the initial setting time is dependent on the relative ratio of Na2O to SiO2 when sodium silicate solutions (Na2SiO3) are used for the alkali-activation of ground granulated blast-furnace slag (GGBS). One possible reason for this is that the ratio (called modulus) not only influences the pH but also the viscosity of the solution. The viscosity is, in turn dependent on the structures in the liquid. Therefore, we have investigated the structure of sodium silicate solutions of different moduli by infrared spectroscopy (IR) and silicon nuclear magnetic resonance (Si-29-NMR). The results, which show that the silica configuration is highly dependent on the modulus, will be discussed in relation to the initial setting time of corresponding measurements on GGBS hydration
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| 3. |
- Bergman, Rikard, 1966, et al.
(author)
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Slow Debye-type peak observed in the dielectric response of polyalcohols
- 2010
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In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 132:4
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Journal article (peer-reviewed)abstract
- Dielectric relaxation spectroscopy of glass forming liquids normally exhibits a relaxation scenario that seems to be surprisingly general. However, the relaxation dynamics is more complicated for hydrogen bonded liquids. For instance, the dielectric response of monoalcohols is dominated by a mysterious Debye-like process at lower frequencies than the structural alpha-relaxation that is normally dominating the spectra of glass formers. For polyalcohols this process has been thought to be absent or possibly obscured by a strong contribution from conductivity and polarization effects at low frequencies. We here show that the Debye-like process, although much less prominent, is also present in the response of polyalcohols. It can be observed in the derivative of the real part of the susceptibility or directly in the imaginary part if the conductivity contribution is reduced by covering the upper electrode with a thin Teflon layer. We report on results from broadband dielectric spectroscopy studies of several polyalcohols: glycerol, xylitol, and sorbitol. The findings are discussed in relation to other experimental observations of ultraslow (i.e., slower than the viscosity related alpha-relaxation) dynamics in glass formers.
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| 4. |
- Berntsen, Peter, 1974, et al.
(author)
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Dielectric and calorimetric studies of hydrated purple membrane
- 2005
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In: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 89:5, s. 3111-3128
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Journal article (peer-reviewed)abstract
- Purple membranes (PM) from halobacteria were hydrated to ∼0.4 and ∼0.2 g H 2 O/g of PM and studied by dielectric spectroscopy and differential scanning calorimetry between 120 and 300 K. The dielectric process, attributed to a local (β) relaxation of the confined supercooled water, shows an Arrhenius temperature behavior at low temperatures. In the case of the most hydrated PM a small deviation from the Arrhenius behavior occurs at 190-200 K together with a pronounced endothermic process and an increased activation energy. The observed crossover is accompanied by a reduction of the interlayer spacing due to the partial loss of the intermembrane water. All these effects at ∼200 K are consistent with a scenario where the local relaxation process merges with a nonobservable α-relaxation of the interlayer water, giving rise to a more liquid-like behavior of the interfacial water. For the less hydrated sample the effects are less pronounced and shift to a slightly higher temperature. © 2005 by the Biophysical Society.
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| 5. |
- Bohlin, Karl, 1989, et al.
(author)
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Karbonatisering av slagg- och flygaskebetong - och dess inverkan på transportegenskaper
- 2016
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In: Bygg och teknik. ; :7, s. 48-52
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Journal article (other academic/artistic)abstract
- Betong som innehåller alternativa bindemedel har en rad önskvärda och positiva egenskaper, vilka bland andra är mindre koldioxidutsläpp, lägre värmeutveckling och högre motståndskraft mot syra-, sulfat- och kloridattack. Dock kan alternativa bindemedel också påverka andra egenskaper, t.ex. ökad karbonatiseringshastighet eller reducerad hållfasthet. För att analysera dessa egenskaper har en studie där inverkan av karbonatisering hos betong med slagg och flygaska genomförts. Hur karbonatiseringen i sin tur påverkar transportegenskaper hos betongen har också undersökts. Syftet var att genomföra en förstudie med accelererade karbonatiseringstester för att ge en större förståelse om effekterna av mineraliska tillsatsmaterial.
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| 6. |
- Chen, Guo, 1969, et al.
(author)
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Formation and distribution of ice upon freezing of different formulations of wheat bread
- 2012
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In: Journal of Cereal Science. - : Elsevier BV. - 1095-9963 .- 0733-5210. ; 55:3, s. 279-284
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Journal article (peer-reviewed)abstract
- The formation and distribution of ice upon the freezing of fresh breadcrumb were investigated using differential scanning calorimetry. Three types of wheat bread containing different amounts of sugar and dietary fiber were measured. Various frozen states were produced through freezing with different cooling rates (0.5, 1, 2, 5, 10, 20 and 30 degrees C/min) to -30 degrees C; they were then analyzed and compared by thawing with the same heating rate (10 degrees C/min) to 20 degrees C. All DSC heating traces exhibited dual endotherms in the temperature range for the melting of ice: The major transition was attributed to the ice formed in the large crumb pores (gas cells) and the minor event, which preceded the major endotherm, was assigned primarily to the ice formed in the nanometer-sized pores within the gluten-starch matrix. The size of ice crystals in the two classes of pores was estimated using the modified Gibbs-Thompson relation. The distributions of ice in these pores depended on the bread compositions. It is concluded that the complex crumb porosity plays an essential role in shaping the activities of water and ice in the breadcrumb.
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| 7. |
- Elamin, Khalid, 1977, et al.
(author)
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Calorimetric and relaxation properties of xylitol-water mixtures
- 2012
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In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 136:10
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Journal article (peer-reviewed)abstract
- We present the first broadband dielectric spectroscopy (BDS) and differential scanning calorimetry study of supercooled xylitol-water mixtures in the whole concentration range and in wide frequency (10(-2)-10(6) Hz) and temperature (120-365 K) ranges. The calorimetric glass transition, T-g, decreases from 247 K for pure xylitol to about 181 K at a water concentration of approximately 37 wt. %. At water concentrations in the range 29-35 wt. % a plentiful calorimetric behaviour is observed. In addition to the glass transition, almost simultaneous crystallization and melting events occurring around 230-240 K. At higher water concentrations ice is formed during cooling and the glass transition temperature increases to a steady value of about 200 K for all higher water concentrations. This Tg corresponds to an unfrozen xylitol-water solution containing 20 wt. % water. In addition to the true glass transition we also observed a glass transition-like feature at 220 K for all the ice containing samples. However, this feature ismore likely due to ice dissolution [A. Inaba and O. Andersson, Thermochim. Acta, 461, 44 (2007)]. In the case of the BDS measurements the presence of water clearly has an effect on both the cooperative a-relaxation and the secondary beta-relaxation. The a-relaxation shows a non-Arrhenius temperature dependence and becomes faster with increasing concentration of water. The fragility of the solutions, determined by the temperature dependence of the a-relaxation close to the dynamic glass transition, decreases with increasing water content up to about 26 wt. % water, where ice starts to form. This decrease in fragility with increasing water content is most likely caused by the increasing density of hydrogen bonds, forming a network-like structure in the deeply supercooled regime. The intensity of the secondary beta-relaxation of xylitol decreases noticeably already at a water content of 2 wt. %, and at a water content above 5 wt. % it has been replaced by a considerably stronger water (w) relaxation at about the same frequency. However, the similarities in time scale and activation energy between the w-relaxation and the beta-relaxation of xylitol at water contents below 13 wt. % suggest that the w-relaxation is governed, in some way, by the beta-relaxation of xylitol, since clusters of water molecules are rare at these water concentrations. At higher water concentrations the intensity and relaxation rate of the w-relaxation increase rapidly with increasing water content (up to the concentration where ice starts to form), most likely due to a rapid increase of small water clusters where an increasing number of water molecules interacting with other water molecules.
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| 8. |
- Elamin, Khalid, 1977, et al.
(author)
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Different behavior of water in confined solutions of high and low solute concentrations
- 2013
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:42, s. 18437-18444
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Journal article (peer-reviewed)abstract
- Water-glycerol solutions confined in 21 angstrom pores of the silica matrix MCM-41 C10 have been studied using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The results suggest a micro-phase separation caused by the confinement. Likely the water molecules coordinate to the hydroxyl surface groups of the pores, leaving most of the glycerol molecules in the centre of the pores. This makes the dynamics of glycerol almost concentration independent up to water concentrations of about 85 wt%. However, at higher water concentrations no substantial clustering of glycerol molecules should occur and the glass transition related dynamics exhibit an anomalous behaviour. Instead of a common plasticization effect of water, as for the corresponding bulk solutions (when no ice is formed), it is evident that water acts as an anti-plasticizer in the confinement at high water concentrations. We propose that the increased water concentration slows down the glass transition related dynamics in the deeply supercooled regime due to that a rigid hydrogen bonded network structure of water molecules is formed at low temperatures and low glycerol concentrations. This is in contrast to the situation in a homogenously mixed bulk solution of a high solute concentration where the water molecules will be less hydrogen bonded, and therefore are typically more mobile than the surrounding solute molecules. An almost complete hydrogen bonded network of water molecules may, even in confinements, be sufficiently rigid to slow down the relaxation of embedded solute molecules. It can also be expressed the other way around, i.e. small amounts of glycerol act as a plasticizer for water, due to its breaking up of the nearly tetrahedral network structure. From the here observed concentration dependent behaviour of the deeply supercooled bulk and confined solutions it seems, furthermore, evident that the T-g value of bulk water cannot be estimated from extrapolations of aqueous solutions.
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| 9. |
- Elamin, Khalid, 1977, et al.
(author)
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Dynamics of aqueous binary glass-formers confined in MCM-41
- 2015
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 17:19, s. 12978-12987
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Journal article (peer-reviewed)abstract
- Dielectric permittivity measurements were performed on water solutions of propylene glycol (PG) and propylene glycol monomethyl ether (PGME) confined in 21 angstrom pores of the silica matrix MCM-41 C10 in wide frequency (10(-2)-10(6) Hz) and temperature (130-250 K) ranges. The aim was to elucidate how the formation of large hydrogen bonded structural entities, found in bulk solutions of PGME, was affected by the confined geometry, and to make comparisons with the dynamic behavior of the PG-water system. For all solutions the measurements revealed four almost concentration independent relaxation processes. The intensity of the fastest process is low compared to the other relaxation processes and might be caused by both hydroxyl groups of the pore surfaces and by local motions of water and solute molecules. The second fastest process contains contributions from both the main water relaxation as well as the intrinsic beta-relaxation of the solute molecules. The third fastest process is the viscosity related alpha-relaxation. Its concentration independency is very different compared to the findings for the corresponding bulk systems, particularly for the PGME-water system. The experimental data suggests that the surface interactions induce a micro-phase separation of the two liquids, resulting in a full molecular layer of water molecules coordinating to the hydrophilic hydroxyl groups on the surfaces of the silica pores. This, in turn, increases the geometrical confinement effect for the remaining solution even more and prevents the building up of the same type of larger structural entities in the PGME-water system as in the corresponding bulk solutions. The slowest process is mainly hidden in the high conductivity contribution at low frequencies, but its temperature dependence can be extracted for the PGME-water system. However, its origin is not fully clear, as will be discussed.
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| 10. |
- Frauenfelder, H., et al.
(author)
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A unified model of protein dynamics
- 2009
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 106:13, s. 5129-5134
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Journal article (peer-reviewed)abstract
- Protein functions require conformational motions. We show here that the dominant conformational motions are slaved by the hydration shell and the bulk solvent. The protein contributes the structure necessary for function. We formulate a model that is based on experiments, insights from the physics of glass-forming liquids, and the concepts of a hierarchically organized energy landscape. To explore the effect of external fluctuations on protein dynamics, we measure the fluctuations in the bulk solvent and the hydration shell with broadband dielectric spectroscopy and compare them with internal fluctuations measured with the Mossbauer effect and neutron scattering. The result is clear. Large-scale protein motions are slaved to the fluctuations in the bulk solvent. They are controlled by the solvent viscosity, and are absent in a solid environment. Internal protein motions are slaved to the beta fluctuations of the hydration shell, are controlled by hydration, and are absent in a dehydrated protein. The model quantitatively predicts the rapid increase of the mean-square displacement above approximate to 200 K, shows that the external beta fluctuations determine the temperature- and time-dependence of the passage of carbon monoxide through myoglobin, and explains the nonexponential time dependence of the protein relaxation after photodissociation.
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