The size of free-volume holes in neat poly[(ethylene glycol)23dimethacrylate] [poly((EG)23DMA)] and in the same polymer doped with 0.6 mol/kg LiCF3SO3 have been studied as a function of temperature in the range between 100 and 370 K using positron annihilation lifetime spectroscopy. The results are compared with differential scanning calorimetry and ionic conductivity measurements. In both systems, the hole volume νh shows a typical glass-transition behavior, i.e., a small linear increase with temperature below the glass transition temperature Tg and a steeper increase above Tg. From these measurements Tg was estimated to be 233 K (neat polymer) and 240 K (polymer with salt) and the coefficients of the thermal expansion of the hole volume were determined. The fractional free volume (f=0.080) and the number density of holes (Nh=0.6 nm−3) were also estimated. Below Tg the average hole volume of the polymer electrolyte is larger than in the neat polymer. This is consistent with the bulky character of the CF3SO3− anion. Above Tg the salt-doped system shows the lower hole volume of the two systems, probably caused by a reduced segmental mobility as a consequence of the interactions of the Li+ ions with the ethylene oxide units of the polymer. Based on the free-volume theory of Cohen–Turnbull the ionic conductivity σ is correlated with the mean hole volume νh. A linear relation between log(σT 0.5) and 1/νh was observed to be valid for variations of the conductivity over several orders of magnitudes. From these plots critical hole sizes of γν*=0.65 nm3 (neat polymer) and 0.87 nm3 (polymer-salt system) were estimated. The parameters B and T0 of the Vogel–Tamman–Fulcher equation were also determined, as well as the apparent activation volume ΔVapp by pressure-dependent conductivity measurements. The cationic transference number in the polymer-salt system was determined by pulsed field gradient-nuclear magnetic resonance to be t+≈0.3.

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Ethylene oxide based polymer electrolytes which exhibit single-ion (cation Li+ or anion ClO4−) and mixed ion (from the dissociation of LiClO4 salt) conduction were studied by employing positron lifetime annihilation spectroscopy (PALS) and conductivity (σ) measurements in the temperature range between 170 and 370 K. We present experimental evidence for the validity of (i) the linear expansion of local free volume from PALS, (ii) the Vogel–Tammann–Fulcher (VTF) law for σ, and (iii) the Cohen–Turnbull equation that relates σ to the local free volume. These were found to be valid in the temperature range above the end (or freezing) temperature of the glass transition, Tge≈1.06TgPALS≈1.18TgDSC [TgPALS and TgDSC are the Tg’s from PALS and differential scanning calorimetry (DSC), respectively]. From VTF fits to σ we obtained a Vogel temperature of T0≈TgDSC and pseudoactivations energies of B=3.7–5.7 kJ/mol. These parameters disagree with many data published in the literature but are in perfect agreement with the free volume experiments. Moreover, we found T0=TgPALS−(20–28) K and TgDSC=TgPALS−(25–27) K. Indications for the existence of two relaxation processes near Tg were observed in the free volume expansion curves, which were attributed to the motion of free polymer segments and those interacting with ions. The discrepancy between TgDSC and TgPALS can be attributed to the two-phase microseparation of the polymer electrolytes; DSC responds mainly to the polymer segments in the ion-depleted regions while PALS responds to the polymer segments in the ion-rich regions. From the Cohen–Turnbull plots the critical hole volume required for an elementary jump of an ion was estimated to be γν*≈1 nm3 and was found to be independent of the type of ion. This shows that each type of ionic conductivity is associated with the same segmental mobility. Below TgePALS the conductivity is larger than expected from the (extrapolated) VTF law, but smaller than displayed in the frozen-in free volume.

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The lateral spreading of topically applied substances is a competitive process to the penetration into the stratum corneum (SC). The penetration of topically applied UV filter substances into the human SC and the lateral spreading were investigated in vivo. Tape stripping in combination with spectroscopic measurements was used to study both processes of two UV filter substances. The concentration of both UV filters was determined inside and outside the application area by varying the application and tape stripping protocol. A spreading of the topically applied substances from the treated to the untreated areas was observed, which caused a concentration gradient. This lateral spreading depends on the time between application and tape stripping and the size of the treated skin area. Significant amounts of topically applied substances were found adjoining the application area, due to the lateral spreading which takes place on the skin surface. In general, the lateral spreading must be considered to be a competitive process when studying penetration processes of topically applied substances. It has to be considered during drug treatment of small limited skin areas and for the interpretation of recovery rates obtained in penetration studies.

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