Phase transition dynamics of single optically trapped aqueous potassium carbonate particles

Abstract

Fast dynamics (down to 10 ms) during exposure to changing relative humidity of single optically trapped K2CO3 particles were observed in the submicron to micron size range with time-resolved broadband light scattering and Raman spectroscopy. The study shows that complex multiple processes accompany efflorescence and deliquescence of unsupported aerosol particles. Efflorescence can occur in a single process in less than 10 ms (prompt) or proceed via multiple successive processes (multistep) that can last up to more than 10 seconds. The efflorescence relative humidity lies in the range of 9 to 25%. Raman spectra of the effloresced particles reveal that the final state of the particle is independent of the pathway. Deliquescence cycles start with an initial uptake of water followed by multiple complex processes which end at the deliquescence relative humidity (44-50%). The study reveals that complex multiple processes during phase transitions are not limited to deposited particles where heterogeneous processes may occur or large particles in the upper micrometer size range as previously observed.

Morphology and motion of single optically trapped aerosol particles from digital holography

“…The experimental setup sketched in Figure 1 combines a digital in-line holographic microscope with a counter-propagating optical tweezer (CPT) 43,[45][46][47] to isolate a single aerosol particle or multiple aerosol particles in air. The CPT allows trapping of submicron-sized and nonspherical particles 25,48 over extended periods of time (up to several days). The continuous laser of the CPT (Laser Quantum, OPUS 3 532 nm, typical power: 500 mW) is first expanded by a factor of four by using a two lense telescope.…”

“…(a) Time evolution of the peanut-shaped particle position Z measured experimentally and (b) simulated optical force acting on the particle along the Z-axis (F z ). In the simulations, the particle is considered closer to one beam during the first part of the measurement (t ϵ [0, 48] ms) and then closer to the second beam during the second part of the data (t ϵ [48,77] ms), as suggested by the experiment and the previous simulation. Figure 7 and 8 present the rotation of the particle.…”

Characterization and control of droplets optically trapped in air

“…However the importance of aerosol particles remains difficult to evaluate precisely because of their complexity. They show numerous physicochemical properties (size, shape, phase, chemical composition, viscosity, refractive index, pH, mass accommodation coefficient) and they are involved in complex processes, such as evaporation and condensation of gaseous species [5][6][7] , light scattering and absorption 8,9 , photochemistry 6,[10][11][12] , phase transitions [13][14][15] and phase separation 16,17 . Better understanding these processes is interesting for both applied and fundamental research.…”

“…Single particle studies have proven useful to better understand such processes by avoiding ensemble averaging. Identifying stochastic or intermittent processes, such as phase transitions 15 or certain fluorescence processes 19 , would not be possible for a large ensemble of particles. A thorough characterization of particle properties is necessary to better understand the processes in which they are involved.…”

“…In addition, these experiment can be coupled to obtain a more thorough characterization of single particles. The BLS 15,23 , Raman scattering 15 , photoacoustics 7,20,24 and digital holography 25,26 experiments have already been discussed in details elsewhere and will not be discussed further here. This paper explains the feedback control mechanism and the polarizationresolved TAOS measurements.…”