Bulk nanobubbles from acoustically cavitated aqueous organic solvent mixtures

We investigate the existence and stability of bulk nanobubbles in various aqueous organic solvent mixtures. Bulk nanobubble suspensions generated via acoustic cavitation are characterized in terms of their bubble size distribution, bubble number density, and zeta potential. We show that bulk nanobubbles exist in pure water but do not exist in pure organic solvents, and they disappear at some organic solvent–water ratio. We monitor the nanobubble suspensions over a period of a few months and propose interpretations for the differences behind their long-term stability in pure water versus their long-term stability in aqueous organic solvent solutions. Bulk nanobubbles in pure water are stabilized by their substantial surface charge arising from the adsorption of hydroxyl ions produced by self-ionization of water. Pure organic solvents do not autoionize, and therefore, nanobubbles cannot exist in concentrated aqueous organic solvent solutions. Because of preferential adsorption of organic solvent molecules at the nanobubble interfaces, the surface charge of the nanobubbles decreases with the solvent content, but the strong hydrogen bonding near their interfaces ensures their stability. The mean bubble size increases monotonically with the solvent content, whereas the surface tension of the mixture is sharply reduced. This is in agreement with literature results on macro- and microbubbles in aqueous organic solutions, but it stands in stark contrast to the behavior of macro- and microbubbles in aqueous surfactant solutions

Nanokompozyty elektrodowe Li-ion z samoorganizującymi się przewodzącymi warstwami węglowym

Basing on the developed and patented technology the nanocomposite cathodes were successfully prepared in a simple and inexpensive process of wet impregnation of polymer carbon precursor followed by controlled pyrolysis. Conductive carbon layers (CCLs) derived from hydrophilic polymers in solvent-free water mediated process, significantly enhances electrical conductivity of the material and improves its thermal properties, moreover the unique pore structure of CCLs assures easy lithium ions diffusion. Proposed solution allows to explore the potential of active material and improves overall performance of Li-ion batteries.Na podstawie opracowanej i opatentowanej technologii otrzymano nanokompozyty elektrodowe Li-ion. Nieskomplikowany i niedrogi proces wytwarzania przewodzących warstw węglowych (CCL) polegał na depozycji w środowisku wodnym prekursora węglowego na powierzchni ziaren materiału aktywnego, a następnie na kontrolowanej jego pirolizie. Otrzymane powłoki węglowe z hydrofilowych polimerów w istotnym stopniu polepszają właściwości elektryczne i termiczne kompozytów elektrodowych, a jednocześnie zapewniają kanały transportu (dyfuzji) jonów litu przez powłokę węglową. Zaproponowane rozwiązanie umożliwia pełne wykorzystanie korzystnych właściwości materiału aktywnego i poprawia ogólne parametry pracy ogniw litowo-jonowych

On the existence and stability of bulk nanobubbles

Bulk nanobubbles are a novel type of nanoscale bubble system. Because of their extraordinary behavior, however, their existence is not widely accepted. In this paper, we shed light on the hypothesis that bulk nanobubbles do exist, they are filled with gas, and they survive for long periods of time, challenging present theories. An acoustic cavitation technique has been used to produce bulk nanobubbles in pure water in relatively large numbers approaching 10⁹ bubble·mL^–1 with a typical diameter of 100–120 nm. We provide multiple evidence that the nanoentities observed in suspension are nanobubbles given that they disappear after freezing and thawing of the suspensions, their nucleation rate depends strongly on the amount of air dissolved in water, and they gradually disappear over time. The bulk nanobubble suspensions were stable over periods of many months during which time the mean diameter remained unchanged, suggesting the absence of significant bubble coalescence, bubble breakage, or Ostwald ripening effects. Measurements suggest that these nanobubbles are negatively charged and their zeta potential does not vary over time. The presence of such a constant charge on the nanobubble surfaces is probably responsible for their stability. The effects of pH, salt, and surfactant addition on their colloidal stability are similar to those reported in the literature for solid nanoparticle suspensions, that is, nanobubbles are more stable in an alkaline medium than in an acidic one; the addition of salt to a nanobubble suspension drives the negative zeta potential toward zero, thus reducing the repulsive electrostatic forces between nanobubbles; and the addition of an anionic surfactant increases the magnitude of the negative zeta potential, thus improving nanobubble electrostatic stabilization

Thermal integration of SOFC and plate heat exchanger desorber

A Plate Heat Exchanger (PHE) desorber is thermally integrated with an SOFC stack via a specially designed tube in tube heat exchanger with internal fins in which thermal oil is heated to the required desorber temperature and then serves as the coupling fluid in the PHE desorber. A modelling approach has been adopted where the PHE desorber is solved for heat and mass transfer using MATLAB &amp; EES and the tube in tube heat exchanger with internal fins has been modelled and optimized using COMSOL multiphysics. The results show that the PHE desorber is able to produce the required quantity of refrigerant needed for a 1 kW cooling load. The use of PHEs as desorbers not only gives a high heat transfer surface area but also leads to considerable reduction in desorber volume when compared to conventional falling film desorbers.</jats:p

Expansion of human mesenchymal stem/stromal cells on temporary liquid microcarriers

BACKGROUND: Traditional large-scale culture systems for human mesenchymal stem/stromal cells (hMSCs) use solid microcarriers as attachment substrates. Although the use of such substrates is advantageous because of the high surface-to-volume ratio, cell harvest from the same substrates is a challenge as it requires enzymatic treatment, often combined with agitation. Here, we investigated a two-phase system for expansion and non-enzymatic recovery of hMSCs. Perfluorocarbon droplets were dispersed in a protein-rich growth medium and were used as temporary liquid microcarriers for hMSC culture. RESULTS: hMSCs successfully attached to these liquid microcarriers, exhibiting similar morphologies to those cultured on solid ones. Fold increases of 3.03 ± 0.98 (hMSC1) and 3.81 ± 0.29 (hMSC2) were achieved on day 9. However, the maximum expansion folds were recorded on day 4 (4.79 ± 0.47 (hMSC1) and 4.856 ± 0.7 (hMSC2)). This decrease was caused by cell aggregation upon reaching confluency due to the contraction of the interface between the two phases. Cell quality, as assessed by differentiation, cell surface marker expression and clonogenic ability, was retained post expansion on the liquid microcarriers. Cell harvesting was achieved non-enzymatically in two steps: first by inducing droplet coalescence and then aspirating the interface. Quality characteristics of hMSCs continued to be retained even after inducing droplet coalescence. CONCLUSION: The prospect of a temporary microcarrier that can be used to expand cells and then ‘disappear’ for cell release without using proteolytic enzymes is a very exciting one. Here, we have demonstrated that hMSCs can attach and proliferate on these perfluorocarbon liquid microcarriers while, very importantly, retaining their quality

Process parameters for the high-scale production of alginate-encapsulated stem cells for storage and distribution throughout the cell therapy supply chain

AbstractWith the ever-increasing clinical application of cell-based therapies, it is considered critical to develop systems that facilitate the storage and distribution of cell therapy products (CTPs) between sites of manufacture and the clinic. For such systems to be realized, it is essential that downstream bioprocessing strategies be established that are scalable, reproducible and do not influence the viability or function of the living biologic. To this end, we examined alginate-encapsulation as a method to heighten the preservation of human adipose-derived stem cells (hASCs) during hypothermic storage, and establish a scalable process for high-volume production. A drop-wise method for scalable alginate bead generation, using calcium as the cross-linker, was modified to enable the yield of up to 3500 gelled beads per minute. The effect of alginate concentration on the viscosity of non-gelled sodium alginate and the mechanical properties and internal structure of calcium-crosslinked alginate in response to different alginate and calcium concentrations were investigated. Mechanical strength was chiefly dependent on alginate concentration and 1.2% alginate cross-linked with 100mM calcium chloride could withstand stress in the order of 35kPa. Upon selection of appropriate parameters, we demonstrated the suitability of using this method for immobilizing human stem cells. Encapsulated hASCs demonstrated no loss in cell viability, and had a uniform distribution after high-volume production. Following storage, released cells were able to attach and recover a normal morphology upon return to culture conditions. Thus we present a scalable method for stem cell encapsulation and storage for application within the cell therapy supply chain

The effect of scale and interfacial tension on liquid–liquid dispersion in in-line Silverson rotor–stator mixers

AbstractThe effect of scale, processing conditions, interfacial tension and viscosity of the dispersed phase on power draw and drop size distributions in three in-line Silverson rotor–stator mixers was investigated with the aim to determine the most appropriate scaling up parameter. The largest mixer was a factory scale device, whilst the smallest was a laboratory scale mixer. All the mixers were geometrically similar and were fitted with double rotors and standard double emulsor stators. 1wt.% silicone oils with viscosities of 9.4mPas and 339mPas in aqueous solutions of surfactant or ethanol were emulsified in single and multiple pass modes. The effect of rotor speed, flow rate, dispersed phase viscosity, interfacial tension and scale on drop size distributions was investigated.It was found that for all three scales, power draw is the sum of the rotor and flow contributions, with proportionality constants, PoZ and k1, that are practically scale independent. Sauter mean drop size appeared to correlate better with tip speed than energy dissipation rate. For ethanol/water solutions, mean drop size correlated well with Weber number based on interfacial tension, but for surfactant solutions effective interfacial tension gave better correlations with Weber number