Volume dependence of thermal conductivity and bulk modulus for poly(propylene glycol)

• 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%.

Ämnesord

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Nyckelord

Thermal conductivity

high pressure

heat capacity

specific heat

bulk modulus

equation of state

poly(propylene glycol)

PPG

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