Polystyrene in its molecules contains benzene rings. In benzene rings, electrons are delocalized between 6 carbon atoms and move in the benzene ring without resistance. This property increases the electrical conductivity of polystyrene in comparison with polypropylene. For comparison, you can indicate a pair of diamond and graphite. Graphite has a better electrical conductivity than diamond.

Hi Tristan,

Both of these materials are basically zero-conductivity. Hence, I think it is not good idea to discuss about conduction in the molecules. The conduction may be attributed to free electron emmition from the molecules. Even effect of impuritpies maybe the dominant factor for actual measurement.

Polystyrene in its molecules contains benzene rings. In benzene rings, electrons are delocalized between 6 carbon atoms and move in the benzene ring without resistance. This property increases the electrical conductivity of polystyrene in comparison with polypropylene. For comparison, you can indicate a pair of diamond and graphite. Graphite has a better electrical conductivity than diamond.

Agreeing in part with both colleagues I agree that:

- DC conductivity is determined by the charge carrier concentration and mobility

- the charge carriers can be intrinsic (coming from the polymer itself) or extrinsic (from impurities, catalyst residues, additives, antioxidant etc.), or can be injected from the electrodes (so-called ohmic contacts) or generated by external factors, such as irradiation. It is not always obvious to distunguish between these types of charge carriers

- the charge carriers can be electrons, holes or ions

- the charge carriers can be trapped in shallow and deep traps (from shallow traps they can beremoved by thermal activation)

- it is practically impossible to measure the equilibrium conductivity of PS or PP at room temeperture, you will observe a continuously decreasing current, and the final value may depend on the exactness of your zero detection.

Therefore the conductivity of these insulating polymers may depend on several factors:

- purity (additivation level, possible surface oxidation which may generate displacement current which appears together with the ohmic component)

- thermal treatment (recrystallization in PP and possible pyhsical aging in PS)

- quality and material of the electrode, method of electrode aplication

- voltage level (space charge limited currents, Poole-Frenkel effect and so on)

Therefor if you want really to compare these materials you could do the following:

- theoretically you can perform band sructure calculation on linear chains and compare the bandgap etc. perhaps you may imporve your calculations by taing into account local defects (local states in the forbidden gap). These calculations, however, cannot be checked easily experimentally (maybe by photoelctron spectroscopy)

- experimentally you may prepare high purity thin films (e.g. by removing the additives by dissolution and precipitation) of both polymers, sputter gold electode on both sides and (using guard ring!) you may compare the two polymers at identical film thickness at various levels of voltage and at various temperatures or at various levels of extrinsic doping and extrapolate back the behavior to low voltage and room temperature. Then you will have an approximately (!) exact picture of all processes. Then it is meaningful to compare the values.

Thank you for clarifying that it is not that simple to determine the conductivity, mainly due to the fact that it changes with respect to time which i wasn't aware of. Your experimental recommendation using sputtering deposition seems like the most efficient analysis method. I would be very interested in seeing if the two Conductivity vs time graphs converge to a similar value after accounting for extrinsic effects.