The disaccharide trehalose is accumulated by microorganisms, such as yeasts, and multicellular organisms, such as tardigrades, when conditions of extreme drought occur. In this way these organisms can withstand dehydration through the formation of an intracellular carbohydrate glass, which, with its high viscosity and hydrogen-bonding interactions, stabilizes and protects the integrity of complex biological structures and molecules. This property of trehalose can also be harnessed in the stabilization of liposomes, proteins and in the preservation of red blood cells, but the underlying mechanism of bioprotection is not yet fully understood. Here we use positron annihilation lifetime spectroscopy to probe the free volume of trehalose matrices; specifically, we develop a molecular picture of the organization and mobility of water in both amorphous and crystalline states. Whereas in amorphous matrices, water increases the average intermolecular hole size, in the crystalline dihydrate it is organized as a confined one-dimensional fluid in channels of fixed diameter that allow activated diffusion of water in and out of the crystallites. We present direct real-time evidence of water molecules unloading reversibly from these channels, thereby acting as both a sink and a source of water in low-moisture systems. We postulate that this behaviour may provide the overall stability required to keep organisms viable through dehydration conditions.

The molecular packing of amorphous maltodextrin-glycerol matrices is systematically explored by combining positron annihilation lifetime spectroscopy (PALS) with thermodynamic measurements and dilatometry. Maltodextrin-glycerol matrices are equilibrated at a range of water activities between 0 and 0.54 at T = 25 °C to analyze the effect of both water and glycerol on the average molecular hole size and the specific volume of the matrices. In the glassy state, glycerol results in a systematic reduction of the average molecular hole size. In contrast, water interacts with the carbohydrate matrix in a complex way. Thermodynamic clustering theory shows that, at very low water contents the water molecules are well dispersed and are closely associated with the carbohydrate chains. In this regime water acts as an antiplasticizer, whereby it reduces the size of the molecular holes. Conversely, at higher water contents, while still in the glassy state, water acts as a plasticizer by increasing the average hole volume of the carbohydrate matrices. This plasticization-dominated mechanism is likely to be due to the interplay between the ability of water to form hydrogen bonds with the hydroxyl residues on the carbohydrate chains and its mobility, which is significantly decoupled from the bulk mobility of the matrix. Our findings are of key importance for the understanding of the effect of glycerol on the biostabilization performance of these carbohydrate matrices, as it provides a first insight on how molecular packing can relate to the dynamics in such matrices.

The specific volume and the nanostructure of the free volume of amorphous blends of maltose with a narrow molecular weight distribution maltopolymer were systematically studied as a function of temperature, water content, pressure, and blend composition. Correlations between the hole free volume and the specific volume were investigated in the glassy and rubbery phases and in solution using positron annihilation lifetime spectroscopy (PALS) and pressure-volume-temperature (PVT) measurements, with the aim to provide a consolidated mechanistic understanding of the relation between changes in molecular packing and at the molecular level and the behavior of the specific volume at the macrolevel. Both specific volume and hole volume show a linear dependence on the temperature, but with a slope which is higher in the rubbery state than in the glassy state. As a function of temperature, the hole volume and the specific volume are linearly related, with no discontinuity at the glass transition temperature (T(g)). In the glassy state, both the specific volume and the hole volume decrease nonlinearly with the addition of maltose to the maltopolymer matrix, due to a more efficient molecular packing. For variations in carbohydrate composition, a linear dependence between the hole volume and the specific volume was again observed. The role of water was found to be significantly more complex, with increasing water content causing an increase in density in both the glassy and rubbery phases indicating that water exists in a highly dispersed state with a significantly lower specific molar volume than in bulk water. At very low water contents, the hole volume and the specific volume both decrease with increasing water content, which suggests that water acts as both a hole filler and a plasticizer. In the glassy state at slightly higher water contents, the specific volume continues to slowly decrease, but the hole size passes through a minimum before it starts to increase. This gives rise to a negative correlation between the hole volume and the specific volume which has not previously been observed and which can be interpreted in terms of water molecules which are dispersed within the glassy carbohydrate matrix and which thereby influence the hydrogen bonding between the carbohydrate molecules.

The relationship between the structure of the polymer and the charge carrier mobility and the ionic conductivity has been studied for a new class of gel electrolytes on the basis of alternating copolymers. These gel electrolytes were prepared by photopolymerization of maleic anhydride and oligo(ethylene glycol) 4 divinyl ether in the presence of various oligo(ethylene glycol) n dimethyl ethers with molar masses between 134 and 2000 g/mol, and LiCF 3 SO 3 . Thermal properties of the materials were studied by differential scanning calorimetry and dynamic mechanical analysis, which additionally gives structural information. Changes in the free volume as a function of the content of the plasticizer and the salt were studied by positron annihilation lifetime (PAL) spectroscopy. The self-diffusivity of charge carriers and plasticizer in the gel electrolytes was investigated by pulsed field gradient NMR. The ionic conductivity and its pressure dependence were determined by the impedance technique. The gel electrolytes studied are heterogeneous materials composed of a highly crosslinked polymer network (M c ≈ 600 g/mol) with a T g ≈ 100 °C and of a plasticizer-salt solution with a T g ≈ -70 °C. Hence, two hole size distributions were measured by PAL spectroscopy around 0.26 and 0.34 nm related to the network and the liquid phase, respectively. The activation volume V* calculated from the pressure dependence of the ionic conductivity was V* ) 22.7 cm 3 /mol. It is concluded that the charge carrier transport occurs in the liquid phase of the gel electrolytes. However, the network is too dense to provide sufficient distribution and mobility of the plasticizer-salt solution. Self-diffusivity and conductivity of the gel electrolytes studied are not related according to the Nernst-Einstein equation. The ortho-positronium (o-Ps) lifetime τ 3 and its intensity I 3 in the gel were found to be changed if salts were added to the gel. The o-Ps lifetime is discussed in terms of o-Ps bubbles in the plasticizer-salt solution. The o-Ps intensity I 3 , which decreases with the salt concentration, mirrors inhibition reactions of the o-Ps formation attributed to the anions of the salt.