Wired‐up bacteria: Confocal Raman microscopy in combination with 3D structural analysis is used in the measurement of redox gradients in electricity‐producing biofilms in vivo. The approach provides new relevant information for the understanding of electron conduction mechanisms in these systems.

A remarkable morphology transition occurs with a change in temperature for a diblock copolymer [poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS40-b-PDMS480, PDI = 1.01)] in n-decane solution. This polymer, which forms nanotubes at 25 degrees C, rearranges to form short dense rods when the solution is heated to 50 degrees C. When the solution is cooled to 25 degrees C, the system evolves back to nanotubes. These experiments demonstrate that both structures are dynamic and represent equilibrium states of the material. Contrast matching static light-scattering measurements on the short dense rods show that the insoluble PFS core is rigid and has a length distribution similar to that seen in electron microscopy images.

It has been well documented that the use of dry optics in depth profiling by confocal Raman microspectroscopy significantly distorts the laser focal volume, thus negatively affecting the spatial resolution of the measurements. In that case, the resulting in-depth confocal profile is an outcome of several contributions: the broadening of the laser spot due to instrumental factors and diffraction, the spreading of the illuminated region due to refraction of the laser beam at the sample surface, and the influence of the confocal aperture in the collection path of the laser beam. Everall and Batchelder et al. developed simple models that describe the effect of the last two factors, i.e., laser refraction and the diameter of the pinhole aperture, on the confocal profile. In this work, we compare these theoretical predictions with experimental data obtained on a series of well-defined planar interfaces, generated by contact between thin polyethylene (PE) films (35, 53, 75, and 105 microm thickness) and a much thicker poly(methyl methacrylate) (PMMA) piece. We included two refinements in the above-mentioned models: the broadening of the laser spot due to instrumental factors and diffraction and a correction for the overestimation in the decay rate of collection efficiency predicted by Batchelder et al. These refinements were included through a semiempirical approach, consisting of independently measuring the Raman step-response in the absence of refraction by using a silicon wafer and the actual intensity decay of a thick and transparent polymer film. With these improvements, the model reliably reproduces fine features of the confocal profiles for both PE films and PMMA substrates. The results of this work show that these simple models can not only be used to assist data interpretation, but can also be used to quantitatively predict in-depth confocal profiles in experiments carried out with dry optics.

The diffusion of a liquid polymer into a glassy polymer matrix has been studied in a range of temperatures below the glassy matrix glass transition temperature (T g) and for different diffusion times. The liquid polymer used is low-molecular-weight polystyrene (PS) with a narrow molecular weight distribution, and the glassy matrix is poly(phenylene oxide); the two are miscible at any concentration. A simple physical diffusion model is proposed to correlate and predict diffusion rates, assuming a relatively rapid dissolution of the high-Tg polymer at the liquid-solid interface and a relatively slow diffusion process that produces a thick interphase. The local chemical compositions, local glass transition temperatures, and local PS monomeric friction coefficients change markedly along the diffusion path across the interphase; these changes are well predicted by the diffusion model and have also been experimentally verified. The large changes in local T g values cause huge changes in the PS monomeric friction factor across the interphase, and this fact explains the asymmetrical local chemical composition profiles experimentally measured for the PS-rich interphase. The results obtained by other authors for the diffusion of liquid polymers and bulky plasticizers into glassy matrixes are analyzed and discussed on the basis of the diffusion model predictions, and it is found that all of them behave following the same pattern as was observed in our experiments. It is concluded that the Case II diffusion mechanism must not be expected for the diffusion of liquid polymers into glassy matrixes, because of the negligible osmotic pressure. Furthermore, all of the analyzed data for diffusion of liquid polymers and bulky plasticizers into glassy matrixes show evidence for relatively rapid dissolution of the glassy matrix at the interface, together with a relatively slow diffusion process across the interphase.

We describe polymer diffusion and its temperature dependence in poly(vinyl acetate-co-dibutyl maleate) [P(VAc−DBM)] latex films prepared from 4:1 w/w ratio of VAc:DBM. Two sets of polymers were investigated:  one set containing 50% gel (high-M); the other set, with M w ≈ 250 000 (M 250K), free of a measurable gel content. Despite their similar chemical compositions, as determined by 1H NMR, these two sets of samples exhibited different glass transition temperatures (T g). Latex particles were labeled with 9-methacryloxymethylphenanthrene as the donor dye and 2‘-acryloxy-4‘-methyl-4-(N,N-dimethylamino)benzophenone as the acceptor. Polymer diffusion was monitored by nonradiative energy transfer (ET), and apparent diffusion coefficients (D app) were calculated from the ET data using a simple diffusion model. These values increased with temperature and were characterized by an apparent activation energy (E a) of 37 ± 2 kcal/mol for the high-M polymer and 45 ± 2 kcal/mol for the M 250K sample. Rheology measurements at different fixed temperatures were carried out to follow the response of the dynamic moduli (G ‘, G ‘ ‘) with respect to frequency (ω). A master curve based on the Williams−Landel−Ferry (WLF) equation could be constructed as a plot of shift factors vs 1/T, and shift factors for D app for both sets of polymers as well as for the G ‘, G ‘ ‘ values fell on the same curve. Thus, the difference in E a values for the polymer diffusion can be ascribed to changes in the microscopic friction coefficient and the differences in T g of the two sets of samples.

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Liquid−liquid diffusion at the interphase between poly(vinyl−methyl ether) (PVME) and polystyrene (PS) was experimentally studied using confocal Raman microspectroscopy. A combination of a specially designed experimental setup and a direct and precise quantification for the corrections to be applied to the Raman measurements allowed us to measure directly the PVME concentration along the diffusion path for a wide range of diffusion times. An already proposed and tested liquid−liquid diffusion model (based on liquid dynamics controlled by monomeric friction coefficients) was used to correlate and predict the detailed shape of the PVME concentration profiles and the diffusion rates as functions of diffusion time and temperature. The results obtained allowed us to discern among several approaches previously proposed in the literature to calculate monomeric friction coefficients in this system. Only the approach that considers independent monomeric friction coefficient values for PS and PVME (obtained from tracer diffusion measurements) gave good agreement between experimental results and model calculations. Calculations performed using literature data for a common monomeric friction coefficient for both PS and PVME (obtained from estimated blend viscosity data) do not agree with experimental measurements. The success of the model used for this work clearly ruled out the need for combinations of Fickean and Case II models used previously to describe PS−PVME polymer diffusion.

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