Polycarbonate thermal diffusivity

Recall from the beginning of the chapter that a related quantity to the thermal conductivity is the thermal diffusivity, a, which is defined as k/pCp, where k is the thermal conductivity, p is the density and Cp is the heat capacity at constant pressure per unit mass, or specific heat. Below are these thermal properties for polycarbonate. 

Person 1 Determine the density and thermal diffusivity for polycarbonate at 350°C from the plots. 

Combine your information to calculate the thermal diffusivity at 350°C. How does this compare to the value obtained from the plot Can you estimate the melting point of this polycarbonate from these plots ... 

Th-FFF can be applied to almost all kinds of synthetic polymers, like polystyrene, polyolefins, polybutadiene, poly(methyl methacrylate), polyisoprene, polysulfone, polycarbonate, nitrocelluloses and even block copolymers [114,194,220]. For some polymers like polyolefins, with a small thermal diffusion coefficient, high temperature Th-FFF has to be applied [221]. Similarly, hydrophilic polymers in water are rarely characterized by Th-FFF, due to the lack of a significant thermal diffusion (exceptions so far poly(ethylene oxide), poly(vi-nyl pyrrolidone) and poly(styrene sulfonate)) [222]. Thus Th-FFF has evolved as a technique for separating synthetic polymers in organic solvents [194]. More recently, both aqueous and non-aqueous particle suspensions, along with mixtures of polymers and particles, have been shown to be separable [215]. 

Variation of thermal diffusivity with temperature, for amorphous polycarbonate and semi-crystalline polyethylene. 

The temperature difference between the two faces, T(front face) - Tlback face), is measured, from which the experimental decay time constant and the thermal diffusivity can be deduced. Although experimental setup and measurement are relatively simple and straightforward, the theory and mathematical treatment are not and require several assumptions and experimental corrections. This method is reported to give rapid, precise, and fairly accurate results when applied to polymers such as polycarbonate and poly(ethylene terephthalate). 

FIGURE 5.6 Coefficient of thermal conductivity, heat capacity, thermal diffusivity, and density for polycarbonate, a glassy polymer. (Reprinted with permission of the publisher from Tadmor and Gogos, 1979, p. 132.)... 

The subsequent thermal processes201 give rise to diffusion of the polycarbonate substrate into the dye layer, decomposition of the dye, and mechanical deformation of the film due to thermal contraction. Each of these processes can contribute to a reduction in the optical path length of the low-intensity readout beam. The optics within the detector are designed such that phase differences due to the optical path length differences cause the light intensity falling on the detector to be reduced when the beam passes over a recorded mark .196... 

Choudhary, V.R. Akolekar, D.B.. and Singh. A.P.. Single- and multicomponent sorption/diffusion of hydrocarbons from their iso-oclane solution in H-ZMS-5 zeolite. Chem. Eng. Sci.. 44(5). 1047-1060 (1989). Davini, P., Adsorption of sulphur dioxide on thermally treated active carbon. Fuel. 68(2), 145-148 (1989). Frimpong, S. Plank, C.A., and Laukhuf, W.L.S.. Evaluation of sorption and transport of sulfur dioxide in polycarbonate, Chem. Eng. J.. 42( I). 25-36 (1989)... 

When photochromic reactions of spirobenzopyran, azobenzene, and fulgide in polymer films are compared, it is found that the critical free volume n ded fw a reaction is relatively large for spirobenzopyran, but very small for azobenzene and fulgide. The thermal decoloration reaction of spirobenzopyran in a solid film below was much slower than in solutions and was considered diffusion-controlled. Thermal cis to trans isomerization of azobenzene in polycarbonate at room temperature proceeded at a rate comparable to the rate in solutions, except for an anomaly at the initial stage tjjg most part of this reaction can be considered chemically-... 

The diffusion coefficient required to account for penetration of about 500 A is of the order of 10 cm /sec. (for a 200 s. bake). For small molecules (such as the monomeric resist components) this is a quite reasonable number, either above or below 7 (cf. measurements on camphorquinone in polycarbonate 18), which are in the range of 10 — 10 above Tg and 10 — 10 below). Tg of PVA is 85C (29). The situation is less clear with polymer diffusion. PPSQ apparently does not have a distinct Tg (20), but remains assy up to its thermal decomposition temperature (this report is for high material). Wang, et al., ( ) obtained diffusion coefficients of 10 cmVsec for high Af poly(but methacrylate) in latex particles, at temperatures well above Tg. It is possible that the low Af, siloxanes used here diffuse at substantially higher rates. Thus the postulated diffusion is plausible albeit not assured. 

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