Ultra-slow water diffusion in aqueous sucrose glasses

Abstract

We present measurements of water uptake and release by single micrometre-sized aqueous sucrose particles. The experiments were performed in an electrodynamic balance where the particles can be stored contact-free in a temperature and humidity controlled chamber for several days. Aqueous sucrose particles react to a change in ambient humidity by absorbing/desorbing water from the gas phase. This water absorption (desorption) results in an increasing (decreasing) droplet size and a decreasing (increasing) solute concentration. Optical techniques were employed to follow minute changes of the droplet's size, with a sensitivity of 0.2 nm, as a result of changes in temperature or humidity. We exposed several particles either to humidity cycles (between ∼2% and 90%) at 291 K or to constant relative humidity and temperature conditions over long periods of time (up to several days) at temperatures ranging from 203 to 291 K. In doing so, a retarded water uptake and release at low relative humidities and/or low temperatures was observed. Under the conditions studied here, the kinetics of this water absorption/desorption process is controlled entirely by liquid-phase diffusion of water molecules. Hence, it is possible to derive the translational diffusion coefficient of water molecules, D(H(2)O,) from these data by simulating the growth or shrinkage of a particle with a liquid-phase diffusion model. Values for D(H(2)O)-values as low as 10(-24) m(2) s(-1) are determined using data at temperatures down to 203 K deep in the glassy state. From the experiment and modelling we can infer strong concentration gradients within a single particle including a glassy skin in the outer shells of the particle. Such glassy skins practically isolate the liquid core of a particle from the surrounding gas phase, resulting in extremely long equilibration times for such particles, caused by the strongly non-linear relationship between concentration and D(H(2)O). We present a new parameterization of D(H(2)O) that facilitates describing the stability of aqueous food and pharmaceutical formulations in the glassy state, the processing of amorphous aerosol particles in spray-drying technology, and the suppression of heterogeneous chemical reactions in glassy atmospheric aerosol particles.

Gas–particle partitioning of atmospheric aerosols: interplay of physical state, non-ideal mixing and morphology

“…4a) from percolation theory 16 based on the hygroscopic growth data presented in Fig. 2 and D H 2 O in aqueous sucrose glasses 40 which is thought to have similar viscosity as SOA (see Appendix C for additional details). Fig.…”

“…42 D H 2 O is estimated to decrease to values as low as 10 À20 cm 2 s À1 at temperatures characteristic of the middle to upper troposphere, resulting in kinetic limitations of water mass transport with t hg E hours to days. 40,43 As a consequence, glassy organicinorganic aerosol particles (not fully equilibrated with the ambient RH) may act preferentially as heterogeneous ice nuclei, rather than as cloud condensation nuclei forming liquid water droplets. 44,45 …”

“…76 As no direct measurements of D H 2 O,SOA are available, we assume 10 À12 -10 À8 cm 2 s À1 , which is in the range of observed bulk diffusivity of water in aqueous sucrose glasses at room temperature. 40 For uncertainty estimates (green shaded area in Fig. 4a), f was varied from 0.65 to 1 73,75,77 and Z was varied between 8 and 16.…”

Experimental evidence for excess entropy discontinuities in glass-forming solutions

“…The high viscosity of these particles could kinetically limit water uptake and thus inhibit the formation of cirrus clouds. [15][16][17] These limitations in water uptake could also explain the high supersaturations and impeded freezing of liquid droplets found by field studies [18][19][20][21] at these altitudes.…”

A Molecular Rotor that Measures Dynamic Changes of Lipid Bilayer Viscosity Caused by Oxidative Stress

“…In this work, we utilized BODIPY‐C 10 17, 18 (Figure 1), a fluorophore that belongs to a group of dyes termed ‘molecular rotors’ that have viscosity‐dependent fluorescence quantum yields, lifetimes,19, 20 and depolarization 21, 22. When combined with fluorescence lifetime imaging microscopy (FLIM), molecular rotors can be used to obtain spatially resolved viscosity maps of microscopic objects,17, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 as well as to observe dynamic change in viscosity during relevant processes of interest 37, 39, 41, 42. Thus, we aimed to use BODIPY‐C 10 , which is known to completely embed into the fluid‐phase lipid bilayers40 to directly examine how photooxidation during PDT affects viscoelastic properties of model lipid membranes, with spatial‐ and time‐resolution.…”