The transport kinetics and equilibrium concentrations of n‐pentane at high penetrant activities in cast, annealed polystyrene were determined and compared with similar measurements in biaxially‐oriented polystyrene. The rate of Case II (relaxation‐controlled) sorption in biaxially‐oriented polystyrene is three to four times faster than the sorption rate in cast, annealed polystyrene. The Case II sorption process in biaxially‐oriented polystyrene is more highly temperature dependent than in cast, annealed film. The higher activation energies coupled with the larger relaxation‐controlled sorption rates in biaxially‐oriented polystyrene imply the involvement of larger polymer segments in the rate controlling polymer relaxations. The sorption in cast, annealed polystyrene was a position‐dependent relaxation controlled transport process; in contrast the sorption in biaxially oriented polystyrene, albeit relaxation‐controlled, was not position dependent. The position dependence of the Case II sorption appears to be a consequence of the presence of residual benzene in the film which accelerates the rate‐determining relaxations. Desorption measurements at very low penetrant activities were quite similar for both biaxially oriented and cast, annealed polystyrene. The desorption kinetics were Fickian and were only a weak function of polymer orientation at these low activities.

The effects of temperature and penetrant activity on the sorption kinetics and equilibria of a series of alkanes in glassy, biaxially oriented polystyrene were studied. Normal isomers of pentane, hexane, and heptane cause crazing of polystyrene film samples at high penetrant activities (> 0.85). Crazing kinetics are identical to the kinetics of Case II transport. Transport of these normal hydrocarbons in glassy polystyrene in the temperature range 25 to 50°C is markedly non‐Fickian; limiting Case II transport is observed at activities in exces of 0.6. Sorption appears to be controlled by highly activated relaxation processes including primary bond breakage at these high penetrant activities. Fickian diffusion behavior is approached, however, as penetrant activity is reduced. Sorption of the branched isomers of these compounds does not result in polymer microfailure. The sorption kinetics of the branched isomers, although time dependent, appear to be controlled primarily by thermally activated diffusion rather than large scale polymer relaxations which control Case II transport.

A cost-effective and sustainable approach was used to enhance the thermoelectric performance of printable thermoelectric composite films. Using this approach, we are trying to get rid of the highly energy-intensive (high temperature and long duration) and time-consuming process of manufacturing thermoelectric generators. This study presents a unique approach of using an environmental-friendly and naturally occurring binder, a heterogeneous particle size distribution and applied mechanical pressure to fabricate n-type thermoelectric composite films. Recently spotlighted biomaterial, chitosan, was employed as a binder and it provided enough binding strength to the composite thermoelectric films. Bi 2 Te 2.7 Se 0.3 is an attractive n-type thermoelectric material because of its high thermoelectric performance. In this work, we are using two different (100-mesh and 325-mesh) n-type Bi 2 Te 2.7 Se 0.3 thermoelectric conductive particles for thermoelectric composite films to understand the role of wide-range particle distribution on thermoelectric composite films. In addition, two different weight ratios (1:2000 and 1:5000) of binders to Bi 2 Te 2.7 Se 0.3 particle and two different applied pressures (150 MPa and 200 MPa) were used for this study. The application of pressure and the use of a heterogenous particle distribution improves the packing density which leads to well-aggregated and coalesced polycrystal bulk-like structure in chitosan 100-mesh (heterogeneous particle distribution) Bi 2 Te 2.7 Se 0.3 thermoelectric composite films and hence improves the overall electrical conductivity and power factor. The best performing composite film was made with an ink of a 1:2000 weight ratio of binder to100-mesh Bi 2 Te 2.7 Se 0.3 and the applied pressure was 200 MPa. The electrical conductivity was 200 ± 7 S cm À1 , the Seebeck coefficient was À201 ± 6 lV K À1 , the power factor was 808 ± 69.7 lW m À1 K À2 , the thermal conductivity was 0.6 W m À1 K À1 , and the figure of merit was 0.4 at room temperature. Using energy efficient, sustainable, and cost effective method we achieved ZT of 0.40 for n-type thermoelectric composite films which is comparable to other printed n-type TE composite films. A 2-leg n-type Bi 2 Te 2.7 Se 0.3 device was fabricated with a power output of 0.48 lW at a closed circuit voltage of 2.1 mV and DT of 12 K.

This work presents an energy efficient technique for fabricating flexible thermoelectric generators while using printable ink. We have fabricated thermoelectric composite thick films using two different mesh sizes of n-type bismuth particles, various binder to thermoelectric material weight ratios, and two different pressures, 200 MPa and 300 MPa, in order to optimize the thermoelectric properties of the composite films. The use of chitosan dissolved in dimethylsulfoxide with less than 0.2 wt. % of chitosan, the first time chitosan has been used in this process, was sufficient for fabricating TE inks and composite films. Low temperature curing processes, along with uniaxial pressure, were used to evaporate the solvent from the drop-casted inks. This combination reduced the temperature needed compared to traditional curing processes while simultaneously increasing the packing density of the film by removing the pores and voids in the chitosan-bismuth composite film. Microstructural analysis of the composite films reveals low amounts of voids and pores when pressed at sufficiently high pressures. The highest performing composite film was obtained with the weight ratio of 1:2000 binder to bismuth, 100-mesh particle size, and 300 MPa of pressure. The best performing bismuth chitosan composite film that was pressed at 300 MPa had a power factor of 4009 ± 391 μW/m K2 with high electrical conductivity of 7337 ± 522 S/cm. The measured thermal conductivity of this same sample was 4.4 ± 0.8 W/m K and the corresponding figure of merit was 0.27 at room temperature.