| 1. |
- Andersson, S. Peter, et al.
(författare)
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Relaxation Studies of Poly(propylene glycol) under High Pressure
- 1998
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 31:9, s. 2999-3006
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Tidskriftsartikel (refereegranskat)abstract
- The effect of pressure on the relaxation processes in poly(propylene glycol) of number-average molecular weights 400 and 4000 g mol-1 (PPG-400 and PPG-4000) has been investigated using dielectric spectroscopy as well as thermal conductivity and heat capacity measurements. The relaxations associated with segmental motions within the polymer chain (α relaxation) and whole chain motions (α' relaxation) have been studied in the temperature range 200-400 K for pressures up to 2 GPa. The two processes display slightly different sensitivities to pressure, and as a consequence, are better separated at high pressures. As a result, high-pressure data exhibit the α' relaxation also in PPG-400, whereas previous investigations at atmospheric pressure have detected it only in PPG of molecular weights above about 1000 g mol-1. At atmospheric pressure, the values for (∂T/∂p)τ=1s of the alpha relaxation are, respectively, 140 and 192 K GPa-1 for PPG-400 and PPG-4000, where τ is the relaxation time. Because of the difference in (∂T/∂p)τ, the relaxation of the α motions and therefore the glass-transition temperature exhibits a more significant dependence on molecular weight at high pressures. At 295 K and 0.3 GPa, the activation volumes for the α and α' processes of PPG-4000 are about the same (approximate to 45 cm3 mol-1). At the same conditions, the activation volume for the α process of PPG-400 is about half of that for PPG-4000. An analysis of the α relaxation in terms of the strong-fragility classification shows that the degree of fragility of both PPG-400 and PPG-4000 increases slightly with increasing pressure.
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| 2. |
- Andersson, S. Peter, et al.
(författare)
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Thermal conductivity, heat capacity, and compressibility of atactic poly(propylene) under high pressure
- 1997
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Ingår i: International journal of thermophysics. - : Springer Science and Business Media LLC. - 0195-928X .- 1572-9567. ; 18:3, s. 845-864
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity λ and the heat capacity per unit volume of atactic poly(propylene) have been measured in the temperature range 90–420 K at pressures up to 1.5 GPa using the transient hot-wire method. The bulk modulus has been measured in the range 200–295 K and up to 0.7 GPa. These data were used to calculate the volume dependence of λ, g=−[∂λ/λ)/(∂V/V)]T, which yielded the following values for the glassy state (T<256 K at atmospheric pressure): 3.80±0.19 at 200 K, 3.74±0.19 at 225 K, 3.90±0.20 at 250 K, 3.77±0.19 at 271 K, and 3.73±0.19 at 297 K. The resultant value for g of the liquid state was 3.61±0.15 at 297 K. Values for g which are calculated at 295 K, using theoretical models of λ(T), agree to within 12% with the experimental value for the glassy state.
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| 3. |
- Andersson, S. Peter, et al.
(författare)
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Thermal conductivity of amorphous Teflon (AF 1600) at high pressure
- 1997
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Ingår i: International journal of thermophysics. - : Springer Nature. - 0195-928X .- 1572-9567. ; 18:1, s. 209-219
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity, λ, of amorphous Teflon AF 1600 [poly(1,3-dioxole-4,5-difluoro-2,2-bis(trifluoromethyl)-co-tetrafluoroethylene)] has been measured at pressures up to 2 GPa in the temperature range 93–392 K. At 295 K and atmospheric pressure, we obtained λ=0.116 W·m−1·K−1. The bulk modulus was measured up to 1.0 GPa in the temperature range 150–296 K and the combined data yielded the following values of g=(∂ln λ/∂ln V)T :2.8±0.2 at 296 K, 3.0±0.2 at 258 K, 3.0±0.2 at 236 K, 3.4±0.2 at 200 K, and 3.4±0.2 at 150 K.
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| 4. |
- Andersson, S. Peter, et al.
(författare)
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Volume dependence of thermal conductivity and bulk modulus for poly(propylene glycol)
- 1998
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Ingår i: Journal of Polymer Science Part B. - : John Wiley & Sons. - 0887-6266 .- 1099-0488. ; 36:2, s. 345-355
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity λ and heat capacity per unit volume of poly(propylene glycol) PPG (0.4 and 4.0 kg.mol-1 in number-average molecular weight) have been measured in the temperature range 150-295 K at pressures up to 2 GPa using the transient hot-wire method. At 295 K and atmospheric pressure, λ = 0.147 W m-1K-1 for PPG (0.4 kg.mol-1) and λ = 0.151 W m-1K-1 for PPG (4.0 kg.mol-1). The temperature dependence of λ is less than 4 x 10-4 W m-1K-2 for both molecular weights. The bulk modulus has been measured in the temperature range 215-295 K up to 1.1 GPa. At atmospheric pressure, the room temperature bulk moduli are 1.97 GPa for PPG(0.4 kg.mol-1) and 1.75 GPa for PPG (4.0 kg.mol-1). These data were used to calculate the volume dependence of λ, g = -((∂λ/λ)/(∂V/V))T. At room temperature and atmospheric pressure (liquid phase) we find g = 2.79 for PPG (0.4 kg.mol-1) and g = 2.15 for PPG (4.0 kg.mol-1). The volume dependence of g, (∂g /∂ log V)T varies between -19 to -10 for both molecular weights. Under isochoric conditions, g is nearly independent of temperature. The difference in g between the glassy state and liquid phase is small and just outside the inaccuracy of g of about 8%. The theoretical model for λ by Horrocks and McLaughlin yields an overestimate of g by up to 120%.
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| 5. |
- Andersson, S. Peter, et al.
(författare)
-
Volume dependence of thermal conductivity and isothermal bulk modulus up to 1 GPa for poly(vinyl acetate)
- 1998
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Ingår i: Journal of Polymer Science Part B. - : John Wiley & Sons. - 0887-6266 .- 1099-0488. ; 36:9, s. 1451-1463
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity λ and heat capacity per unit volume of poly(vinyl acetate) (260 kg mol-1 in weight average molecular weight) have been measured in the temperature range 150-450 K at pressures up to 1 GPa using the transient hot-wire method, which yielded λ = 0.19 W m-1 K-1 at atmospheric pressure and room temperature. The bulk modulus K has been measured in the temperature range 150-353 K up to 1 GPa. At atmospheric pressure and room temperature, K = 4.0 GPa and (∂K/∂p)T = 8.3. The volume data were used to calculate the volume dependence of λ,g = -((∂λ/λ)/(∂V/V))T.The values for g of the liquid and glassy states were 3.0 and 2.7, respectively, and g of the latter was almost independent of volume and temperature. Theoretical models can predict the value for g of the glassy state to within 25%.
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| 6. |
- Andersson, Ove, et al.
(författare)
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Reorientational relaxation in C60 following a pressure induced change in the pentagon/hexagon equilibrium ratio
- 1995
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Ingår i: Physics Letters A. - : Elsevier Science B.V.. - 0375-9601 .- 1873-2429. ; 206:3-4, s. 260-264
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Tidskriftsartikel (refereegranskat)abstract
- The orientational structure of C60 depends on pressure and temperature. Pressurization below the glass transition temperature Tg can freeze in non-equilibrium orientational structures. The relaxation of such structures on heating through Tg has been studied through thermal conductivity measurements and the effects observed are explained in a simple model.
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| 7. |
- Andersson, Ove
(författare)
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Simulation of a glass transition in a hot-wire experiment using time-dependent heat capacity
- 1997
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Ingår i: International journal of thermophysics. - : Plenum Publishing. - 0195-928X .- 1572-9567. ; 18:1, s. 195-208
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Tidskriftsartikel (refereegranskat)abstract
- The transient hot-wire method is used for simultaneous measurements of the thermal conductivity λ and the heat capacity per unit volume ρcp and yields a peak in λ and a dip in ρcp near a glass transition. Through simulations, it is shown that these anomalous results arise due to a time dependence in cp, which is described by a fractional exponential function: cp(t) = cp(liquid) + [cp(glass) - cp(liquid)] e(-(t/τ)β), where τ is the heat capacity relaxation time and β is a sample dependent parameter (0 < β ≤ 1). By a comparison with experimental data for cyclohexanol and glycerol, it is demonstrated that this model can be used to reproduce the peak and the dip as well as the temperature at which these occur. In addition, it is shown that the maximum in λ occurs at τ = 0.3 s, whereas τ of the minimum in ρcp is dependent on β and moves from 0.4 to 1 s for a change in β from 1 to 0.5. The difference in τ between the peak and the dip is in agreement with the experimental results. It is concluded that the anomalies reveal glass forming characteristics such as a rough classification in terms of strong and fragile glass formers.
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| 8. |
- Andersson, Ove, et al.
(författare)
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Thermal conductivity of C60 at pressures up to 1 GPa and temperatures in the range 50-300 K
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:5, s. 3093-3100
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity λ of C60 shows anomalies near 260 K and 90 K which are associated with the well-established phase transition and glass transition, respectively. Both transition temperatures increase with pressure, at the rates 120 K GPa-1 and 62 K GPa-1, respectively. With increasing temperature, λ of the simple cubic (sc) phase increased below 170 K (glasslike behavior) but decreased above. The glasslike behavior of λ is probably due to a substantial amount of lattice defects. Possible reasons for the change of sign of dλ/dT near 170 K are discussed. In the face centered cubic (fcc) phase (T≳260 K at atmospheric pressure) λ was almost independent of temperature, a behavior which is far from that of an ordered crystal (λ∝T-1 for T≳Debye temperature). This result can be attributed to the molecular orientational disorder of the fcc phase. The relaxation behavior associated with the glassy state and its unusually strong dependence on thermal history are discussed briefly, and data which support a previously reported relaxation model are presented. At room temperature, the density dependencies of λ, (∂ lnλ/∂ lnρ)T, were 5.5 and 9.5 for the fcc and sc phases, which are values typical for an orientationally disordered phase and a normal crystal phase, respectively.
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| 9. |
- Andersson, Ove, et al.
(författare)
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Thermal conductivity of C60 under high pressure
- 1995
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Ingår i: Science and Technology of Fullerene Materials. - Pittsburgh, PA : Materials Research Society. - 155899260X ; , s. 549-554
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Konferensbidrag (refereegranskat)abstract
- We have measured the thermal conductivity lambda of highly pure polycrystalline C60 in the range 50 to 300 K under pressures up to 1 GPa. The results are discussed in terms of the lattice structure and dynamics. In particular, we discuss the phase diagram as delineated by anomalies observed in lambda and cp at the f.c.c.-to-s.c. transition at 260 K and the glass transition at Tg = 90 K, and also the effect on lambda of the orientational motion in the s.c. phase. The results are found to be compatible with a p/T phase diagram recently suggested by us.
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| 10. |
- Andersson, Ove, et al.
(författare)
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Thermal conductivity of normal and deuterated tetrahydrofuran clathrate hydrates
- 1996
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Ingår i: Journal of Physics and Chemistry of Solids. - : Elsevier. - 0022-3697 .- 1879-2553. ; 57:1, s. 125-132
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity λ of normal and deuterated tetrahydrofuran (THF) clathrate hydrates has been measured at temperatures in the range 55-250 K and at pressures up to 0.16 GPa. The normal and deuterated samples exhibited the same values of λ to within 5%. At isobaric heating, the transition from the proton ordered low temperature (LT) phase to the proton disordered high temperature (HT) phase was detected as a discontinuous decrease of λ by about 15% for both the normal and the deuterated samples. The magnitude is nearly the same as that found previously for the related transition phase XI → phase Ih of ice and might be due to a change in the lattice anharmonicity. The thermal conductivity of the LT and HT phases increased slightly with increasing temperature and, hence, these crystalline phases exhibited both a glass-like λ(T). These results can be described using the resonance scattering model in which the phonons are scattered against THF vibrations. The LT phase of both samples exhibited a slight increase of λ with increasing pressure whereas that of the HT phases was roughly independent of pressure, showing that λ does not depend on density.
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