Broadband dielectric spectroscopy and positron annihilation lifetime spectroscopy are employed to study the molecular dynamics and effective free volume of 2-ethyl-1-hexanol (2E1H) in the bulk state and when confined in unidirectional nanopores with average diameters of 4, 6, and 8 nm. Enhanced α-relaxations with decreasing pore diameters closer to the calorimetric glass-transition temperature (T(g)) correlate with the increase in the effective free volume. This indicates that the glassy dynamics of 2D constrained 2E1H is mainly controlled by density variation.

Broadband dielectric spectroscopy (BDS) and orthopositronium annihilation lifetime spectroscopy (PALS) are combined to study the molecular dynamics and the free volume of poly­(propylene glycol) terminated with amino end groups (PPG-NH2) in the bulk state and when confined in native and silanized unidirectional silica nanopores with average diameters of 4, 6, and 8 nm. In the bulk state, three dielectric relaxation processes are observed: (i) the fast β-relaxation assigned to the librational fluctuations of the −O–NH2 moiety, (ii) the α-process corresponding to the dynamic glass transition, and (iii) the (slower) chain dynamics or normal mode (NM) relaxation. Under confinement in native nanopores, the β-process becomes slower, while the α and the normal mode relaxation processes become faster and broader and demonstrate a lower dielectric strength with decreasing pore diameter. In silanized nanopores the normal and β-processes are nearly bulklike, but the α-process still remains faster than bulk closer to the T g. All these findings can be comprehended as controlled by the counterbalance between surface and confinement effects. The former are caused by attractive interactions with the solid walls of the nanopores (resulting in an additional slower process which is removed after silanization), and the latter are caused by an increase of the free volume of the polymer segments due to a less efficient packing as proven by orthopositronium annihilation lifetime spectroscopy. These results conform to the cooperative free volume model (CFV).

Glassy dynamics of polymethylphenylsiloxane (PMPS) is studied by broadband dielectric spectroscopy in one-dimensional (1D) and two-dimensional (2D) nanometric confinement; the former is realized in thin polymer layers having thicknesses down to 5 nm, and the latter in unidirectional (thickness 50 μm) nanopores with diameters varying between 4 and 8 nm. Based on the dielectric measurements carried out in a broad spectral range at widely varying temperatures, glassy dynamics is analyzed in detail in 1D and in 2D confinements with the following results: (i) the segmental dynamics (dynamic glass transition) of PMPS in 1D confinement down to thicknesses of 5 nm is identical to the bulk in the mean relaxation rate and the width of the relaxation time distribution function; (ii) additionally a well separated surface induced relaxation is observed, being assigned to adsorption and desorption processes of polymer segments with the solid interface; (iii) in 2D confinement with native inner pore walls, the segmental dynamics shows a confinement effect, i.e., the smaller the pores are, the faster the segmental dynamics; on silanization, this dependence on the pore diameter vanishes, but the mean relaxation rate is still faster than in 1D confinement; (iv) in a 2D confinement, a pronounced surface induced relaxation process is found, the strength of which increases with the decreasing pore diameter; it can be fully removed by silanization of the inner pore walls; (v) the surface induced relaxation depends on its spectral position only negligibly on the pore diameter; (vi) comparing 1D and 2D confinements, the segmental dynamics in the latter is by about two orders of magnitude faster. All these findings can be comprehended by considering the density of the polymer; in 1D it is assumed to be the same as in the bulk, hence the dynamic glass transition is not altered; in 2D it is reduced due to a frustration of packaging resulting in a higher free volume, as proven by ortho-positronium annihilation lifetime spectroscopy.

Understanding the nature and behavior of vacancy-like defects in epitaxial germanium-tin (GeSn) metastable alloys is crucial to elucidate the structural and optoelectronic properties of these emerging semiconductors. The formation of vacancies and their complexes is expected to be promoted by the relatively low substrate temperature required for the epitaxial growth of GeSn layers with Sn contents significantly above the equilibrium solubility of 1 at.%. These defects can impact both the microstructure and charge carrier lifetime. Herein, to identify the vacancy-related complexes and probe their evolution as a function of Sn content, depth-profiled pulsed low-energy positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy were combined to investigate GeSn epitaxial layers with Sn content in the 6.5-13.0 at.% range. The investigated samples were grown by chemical vapor deposition method at temperatures between 300 and 330 °C. Regardless of the Sn content, all GeSn samples showed the same depth-dependent increase in the positron annihilation line broadening parameters, relative to that of epitaxial Ge reference layers. These observations confirmed the presence of open volume defects in as-grown layers. The measured average positron lifetimes were found to be the highest (380-395 ps) in the region near the surface and monotonically decrease across the analyzed thickness, but remain above 350 ps.All GeSn layers exhibit lifetimes that are 85 to 110 ps higher than those recorded for Ge reference layers. Surprisingly, these lifetimes were found to decrease as Sn content increases in GeSn layers.

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of biobased diols with phosgene derivatives [2,4] and the catalytic copolymerization of sustainable epoxides and CO 2 . [5,6] The copolymerization of biobased epoxides and CO 2 is of particular interest as it combines the use of biobased raw materials and the reduction of CO 2 . The anthropogenic emission of CO 2 accumulates to 32 Gt each year, which is caused mainly by the incineration of carbon matter. CO 2 is a greenhouse gas that contributes significantly to the warming of the earth's atmosphere. [7] Global warming increases chances of catastrophic weather phenomena and a rising sea level and, thus, impacts on our everyday life dramatically. Measures have been taken to reduce the emission and to contain the rise of CO 2 levels in the atmosphere in the last few decades. Part of these measures can be described by the concepts of carbon capture and storage/utilization (CCS/CCU). [8][9][10] The CCU deals with the separation and transformation of CO 2 from process gases (e.g., combustion gases in power plants and natural gas) to prevent emission of the greenhouse gas into the atmosphere. The separation step is achieved by the use of either chemical/physical absorbents or organic/inorganic membrane materials. [9,11] The class of absorbents is dominated nowadays by alkanol amine solutions, for example, monoethanolamine and diethanolamine, which require high temperatures for regeneration of the solvent. [12,13] Hence, these "wet-scrubbing" processes are connected to a considerable energy penalty that adds to the total emission of CO 2 . [14] The more energy-efficient-though less developed-technology relies on the use of membrane materials that separate CO 2 from other process gases by size exclusion (mostly hybrid metal-organic frameworks) [15,16] or solubility/diffusivity mechanisms (polymeric membranes), respectively. [17,18] The latter comprise a group of polymeric materials that exhibit permeabilities P (rate of transport through the matrix) and selectivities α (preference of one gas over the other; in this article the "ideal selectivity" is calculated as the ratio of two permeabilities) extending over several orders of magnitude. [19] However, those materials suffer frequently from low long-term stability, known as aging, which has prevented industrial application so far. [20] The large volumes of CO 2 captured in the industrial processes are either stored in gas-tight (often natural) basins (CCS) [10] or transformed into high-value chemicals via various chemical routes (CCU). Some of those routes are The biobased poly(limonene carbonate) (PLimC) synthesized by catalytic copolymerization of trans-limonene oxide and CO 2 unifies sustainability, carbon capture and utilization of CO 2 in one material. Films of PLimC show surprisingly high gas permeation and good selectivity. Additionally, it is not only very permeable to gases, but also to light, while simultaneously being a good heat insulator and mechanically strong, representing a novel type of material that is defined here as "breathing glass." Hence, this stud...

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