REVERSE INSULATOR DIELECTROPHORESIS: UTILIZING DROPLET MICROENVIRONMENTS FOR DISCERNING MOLECULAR EXPRESSIONS ON CELL SURFACES

Lab-on-a-chip (LOC) technologies enable the development of portable analysis devices that use small sample and reagent volumes, allow for multiple unit operations, and couple with detectors to achieve high resolution and sensitivity, while having small footprints, low cost, short analysis times, and portability. Droplet microfluidics is a subset of LOCs with the unique benefit of enabling parallel analysis since each droplet can be utilized as an isolated microenvironment. This work explored adaptation of droplet microfluidics into a unique, previously unexplored application where the water/oil interface was harnessed to bend electric field lines within individual droplets for insulator dielectrophoretic (iDEP) characterizations. iDEP polarizes particles/cells within non-uniform electric fields shaped by insulating geometries. We termed this unique combination of droplet microfluidics and iDEP reverse insulator dielectrophoresis (riDEP). This riDEP approach has the potential to protect cell samples from unwanted sample-electrode interactions and decrease the number of required experiments for dielectrophoretic characterization by ~80% by harnessing the parallelization power of droplet microfluidics. Future research opportunities are discussed that could improve this reduction further to 93%. A microfluidic device was designed where aqueous-in-oil droplets were generated in a microchannel T-junction and packed into a microchamber. Reproducible droplets were achieved at the T-junction and were stable over long time periods in the microchamber using Krytox FSH 157 surfactant in the continuous oil FC-40 phase and isotonic salts and dextrose solutions as the dispersed aqueous phase. Surfactant, salts, and dextrose interact at the droplet interface influencing interfacial tension and droplet stability. Results provide foundational knowledge for engineering stable bio- and electro-compatible droplet microfluidic platforms. Electrodes were added to the microdevice to apply an electric field across the droplet packed chamber and explore riDEP responses. Operating windows for droplet stability were shown to depend on surfactant concentration in the oil phase and aqueous phase conductivity, where different voltage/frequency combinations resulted in either stable droplets or electrocoalescence. Experimental results provided a stability map for strategical applied electric field selection to avoid adverse droplet morphological changes while inducing riDEP. Within the microdevice, both polystyrene beads and red blood cells demonstrated weak dielectrophoretic responses, as evidenced by pearl-chain formation, confirming the preliminary feasibility of riDEP as a potential characterization technique. Two additional side projects included an alternative approach to isolate electrode surface reactions from the cell suspension via a hafnium oxide film over the electrodes. In addition, a commercially prevalent water-based polymer emulsion was found to adequately duplicate microchannel and microchamber features such that it could be used for microdevice replication

Thermodynamics and dynamics of micellization and micelle-solute interactions in block-copolymer and reverse micellar systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1994.Includes bibliographical references.by Paschalis Alexandridis.Ph.D

The effect of surfactants, enzymes and temperature on soils investigated using electrochemical and crystallisation techniques for detergency applications

The behaviour of surfactant at an oil-water interface is of fundamental importance across a range of application, one of which is detergency. For the characterisation of various anionic and non-ionic surfactants, which make up commercial detergent solution, at the aqueous-organic interface, electrochemical methods combined with conductivity, electrocapillary curves and optical microscopy were employed. The findings have revealed that the adsorption and partitioning of the anionic surface active ions at the interface between two immiscible electrolyte solutions can cause reproducible chaotic effects at the region of transfer potentials of the surfactant ions. Factors such as the Marangoni effect and spontaneous emulsification at the phase boundary, as well as the presence of micelles, micellar emulsification and transfer of emulsion droplets across the interface have been found to contribute to these chaotic currents at the organic-water interface. By applying cyclic voltammetry and chronoamperometry techniques, it was established that the irregular oscillations became more pronounced as the concentration of sodium dodecylbenzene sulphonate (SDBS) was increased from 1.5 mM -13.4 mM and the current spikes dissipated as the concentration of triton- x- 114 was increased from 8.6 mM - 114 mM in the aqueous phase consisting of 13.4 mM of SDBS. Similar results were obtained using P&G’s Y and N surfactants. The rise in current instability due to enhanced concentration of the SDBS, which was used as the standard surfactant, was confirmed using chronoamperometry, conductivity measurements and electrocapillary curves. The interfacial instability was prominent in the presence of electrolytes at the aqueous-1,2-DCE/oil phase boundaries which was visually evident in the optical microscopic images obtained. Furthermore, needle-like crystals were identified at the aqueous-1,2-DCE interface with electrolytes, with and without the addition of anionic/non-ionic surfactants. This suggests that a crystallisation process was initiated by the presence of dehydrated salt ions at the phase boundary, which is likely to be promoted by the surfactant ions. Lard has been used as the fat ‘model’ for washing experiments since it is composed of more problematic high melting point components compared to other sources of fat. Lard was deposited onto fabrics and left to age over a period of 4 hours at 20 oC and also, at the temperatures of -10 oC, 10 oC, 20 oC and 30 oC for 5 days. These samples, when analysed using the small angle X-ray scattering (SAXS) technique, revealed peaks at

Towards In situ extraction of fine chemicals and biorenewable fuels from fermentation broths using Ionic liquids and the Intensification of contacting by the application of Electric Fields

Cost-effective synthesis of fine chemicals/biorenewable fuels via fermentation invariably hinges upon efficient separations from the dilute broth. Biphasic/in situ extraction can positively impact both upstream fermentation and the downstream product separations. For developing environmentally sustainable processes, ionic liquids are touted as greener alternative to organic solvents not only because of their relatively low volatility but also due to the ability to tune their properties and design new ionic liquids for task specific needs. Solvent selection for in situ fermentation is depended on high solute partitioning and their biocompatibility with the microorganisms. Such information for these new set of solvents, ionic liquids that comprise of ions is very limited compared to organic solvents. Here, a new methodology to enable successful use of ionic liquids in in situ extraction is developed by focusing on two model systems: 1. Fine chemical - (1R,2S)-1,2-napthalene dihydrodiol (NDHD), produced from the biotransformation of naphthalene by Escherichia coli strain JM109(DE3) pDTG141 and 2. Biorenewable fuel - Biobutanol (along with Acetone and Ethanol), produced from the Fermentation of sugars by Clostridia. The partitioning of each of the solutes, NDHD, Acetone, 1-butanol and ethanol between water and ionic liquid has been measured in the range of concentrations typical of actual fermentations. Different cationic classes of ionic liquids including 1-alkyl-3-methylimidazolium ([RMIm]), trialkylmethylammonium ([TRMAm]) and trihexyltetradecylphosphonium ([P6,6,6,14]) were investigated along with anions such as halides and hydrophobic bis(trifluoromethylsulfonyl)imide [Tf2N] and (trifluorotris(perfluoroethyl)phospate [FAP]. The model ionic liquid, [HMIm][Tf2N] (an IUPAC/IACT standard), demonstrated the highest affinity for NDHD (KC = 2.8) while phosphonium and ammonium ionic liquids with bulkier alkyl side chains had the lowest extractability (KC 2) illustrating the role of molecular design for improvement. Ternary diagrams for the extraction of ABE solutes from water using model ionic liquid, [HMIm][Tf2N] were developed. Acetone and 1-butanol solutes were favorably extracted from water with high selectivities while its affinity for ethanol was low. NRTL activity coefficient model was used to model the ternary data and a regression program was written to obtain the binary interaction parameters for the ternary system. Simulation of 1-butanol extraction using [HMIm][Tf2N] was conducted using process simulator, Aspen Plus. Energy analysis was performed on an optimized flowsheet and these results along with equipment costs were compared with traditional organic solvent extraction and distillation. The toxicity of twenty different ionic liquids to the mutant strain of E. coli was tested with results varying from biocompatible to antimicrobial evidenced from EC50 values of growth rates. Here, the molecular toxicity was measured and EC50 refers to concentration of the ionic liquid that reduces cell growth rate by 50% at molecular level; the EC50 was compared with water solubilities, to determine if the ionic liquid was toxic at molecular level. As widely known, the increase of alkyl-chain length increased the toxicity. However, even highly alkylated cations may become biocompatible by the choice of anion, for e,g, trioctylmethylammonium bromide was antimicrobial while with [Tf2N] anion, it was biocompatible. The mechanism of growth inhibition in presence of ionic liquids was studied through imaging and initial explanations of possible inhibition mechanisms includes the effect of dissociation of these ionic liquids on how the cations/anions interact with the cell membrane. Fermentation broths can be viscous and exhibit non-Newtonian behavior and efficient liquid-liquid contacting is required for higher mass transfer rates and hence faster extractions. Intensification of contacting of non-Newtonian rheology fluids was studied by the application of electric fields. Continuous phase was Mineral oil containing a rheological modifier while aqueous carboxymethylcellulose (CMC) solutions were used as dispersed phase with the apparent viscosities varying between 1 cP to 1000 cP. Significant reduction in drop size was observed when the applied voltages were varied between 0 to 15 kV; viscosity of the continuous phase resulted in lower terminal velocities while dispersed phase viscosity affected the droplet formation times. Empirical correlations for droplet diameter as a function of physical properties, nozzle dimensions and electric field strength were developed and discussed here

Doctor of Philosophy

dissertationThis work studied the relationship between surfactant, oil, and water, by building ternary phase diagrams, the goal of which was to identify the oil-in-water phase composition. The resulting nano-sized emulsion was coated with dicalcium phosphate by utilizing the ionic affinity between calcium ions and the emulsion surface. Since the desired function of the particle is as an oxygen carrier, the particle stability, oxygen capacity, and oxygen release rate were investigated. The first step in the process was to construct ternary phase diagrams with 1,2-dioleoyl-sn-glycero-3-phosphate (DOPA) and soy derived lecithin. The results showed that the lecithin surfactant formed an oil-in-water phase region that was 36 times greater than that of DOPA. With the desired phase composition set, the lecithin emulsion was extruded, resulting in a well-dispersed nanosized particle. A pH titration study of the emulsion found an optimized calcium phosphate coating condition at pH 8.8, at which, the calcium ion had a greater affinity for the emulsion surface than phosphate. A Hill plot was used to show calcium cooperativeness on the emulsion surface which suggested one calcium ion binds to one lecithin molecule. The lecithin emulsion particles were then coated with calcium phosphate using a layering technique that allowed for careful control of the coating thickness. The overall particle hydrodynamic radius was consistent with the growth of the calcium phosphate coating, from 8 nm to 28 nm. This observation was further supported with cryo-TEM measurements. The stability of the coated emulsion was tested in conditions that simulate practical thermal, physical, and time-dependent conditions. Throughout the tests, the coated emulsion exhibited a constant mono-dispersed particle size, while the uncoated emulsion size fluctuated greatly and exhibited increased polydispersion. The fast mixing method with the stopped-flow apparatus was employed to test the product as an oxygen carrier, and it was shown that particles with thicker calcium phosphate coatings released smaller amounts of oxygen in a given timeframe. This study proved the hypothesis by showing a fundamental understanding of emulsion science, coating the flexible emulsion surface with a biocompatible material, and a strong particle performance with regard to stability and as an oxygen carrier

Conference Proceedings: 1st International Conference on Nanofluids (ICNf2019), 2nd European Symposium on Nanofluids (ESNf2019)

Conference proceedings of the 1st International Conference on Nanofluids (ICNf2019) and 2nd European Symposium on Nanofluids (ESNf2019), 26-28 June 2019 in Castelló (Spain), organized by Nanouptake Action (CA15119) and Universitat Jaume

Integrated Chemical Processes in Liquid Multiphase Systems

The essential principles of green chemistry are the use of renewable raw materials, highly efficient catalysts and green solvents linked with energy efficiency and process optimization in real-time. Experts from different fields show, how to examine all levels from the molecular elementary steps up to the design and operation of an entire plant for developing novel and efficient production processes