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Juan Fernandez de la Mora

Juan Fernandez de la Mora
Yale University | YU · Department of Mechanical Engineering and Materials Science

Ph.D.

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203
Publications
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Publications

Publications (203)
Article
Time of flight (TOF) and energy analysis in vacuum are used in series to determine jet velocity U j , diameter d j , electrical potential V j and energy dissipated Δ V at the breakup point of electrified nanojets of the ionic liquid 1-Ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (EMI-FAP) (Ignat'ev et al. , J. Fluorine Chem. ,...
Article
Hypothesis: While the lack of efficient tools yielding controllable uniform saturation ratios (S) has delayed basic experimental heterogeneous nucleation studies, common diffusive condensation particle counters (DCPCs) could fill this gap if their S-variation was minimized by increasing the proportion of sheath gas (σ) surrounding a central core of...
Article
When the particle-to-target radius ratio R and the inverse Peclet number 1/P are small, particle capture by interception and diffusion by cylinders at low Reynolds numbers may be described via Friedlander’s single similarity parameter Π ≡ R·P1/3, in the full range 0 < Π < ∞. Particle inertia may substantially enhance this capture efficiency, even a...
Article
We predict the capture fraction η(Pe, R, Stk, Re) for cylinders at subcritical Stokes numbers Stk < Stk*, at small values of: the Reynolds number (Re), the inverse Peclet number (1/Pe), and the particle/fiber radius ratio (R = ap/af). Inertial effects are described by matching an outer deterministic region with an inner near-wall region. In the fir...
Article
Analysis of large electrosprayed biopolymers by electrical mobility alone is greatly facilitated by reducing their charge to unity. Here we combine within a single chamber a positive aqueous electrospray (ES) producing multiply charged protein cations with a negative methanolic ES yielding small singly charged anions. Both solutions produce very sm...
Poster
Current particle number related vehicle emission legislation is limited down to 23 nm. The rationale behind the 23 nm cut-off size is based on the avoidance of significant uncertainties created during sampling and measuring sub-23 nm solid particles. Difficulties in introducing a robust measurement protocol in this particle size range led regulatio...
Article
Two differential mobility analyzers (DMAs) acting as narrow band mobility filters are coupled in series, with a thermal fragmentation cell placed in between, such that parent ions selected in DMA1 are fragmented in the cell at atmospheric pressure, and their product ions are analyzed on DMA2. Additional mass spectrometer analysis is performed for i...
Article
We explore the effect of an applied homogeneous magnetic field on the electrospraying characteristics of a ferrofluid in the cone-jet mode. A sulfolane-based ferrofluid mixed with the ionic liquid ethyl ammonium nitrate has been synthesized. These mixtures have negligible volatility under ambient conditions and remain stable under a very wide range...
Article
The feasibility of detecting explosives in the atmosphere at concentrations as low as 0.01 ppq hinges on the poorly known question of what interfering species exist at these or higher concentrations. To clarify the issue, hundreds of samples of ambient air, either clean or loaded with explosives (from lightly contaminated environments) have been co...
Conference Paper
The reliable measurement and understanding of particles emitted by road vehicle engines below the currently adopted 23 nm size cut-off is now under intense study in an effort to derive future European legislation on particle emissions, as recommended by the JRC Science and Policy Report (Giechaskiel and Martini, 2014). Here we present the modificat...
Article
High-resolution DMAs requiring hundreds of l/min of sheath gas flow Q to classify 1 nm particles have not been previously examined and optimized under the modest Q values (tens of l/min) needed to classify particles well above 10 nm. Here we study the resolving power R (based on the relative width of the transfer function) of the Halfmini DMA, at s...
Article
The differential mobility analyzer (DMA) is a narrow-band linear ion mobility filter operating at atmospheric pressure. It combines in series with a quadrupole mass spectrometer (Q-MS) for mobility/mass analysis, greatly reducing chemical noise in selected ion monitoring. However, the large flow rate of drift gas (~1000 L/min) required by DMAs comp...
Article
The transfer function of TSI's widely used 3071 Differential Mobility Analyzer (DMA) widens drastically when the flow rate Q of sheath gas exceeds 30–40 lit/min, limiting its ability to resolve very small particles. This flow instability is unexpected at the prevailing relatively small Reynolds number (Re < 400). Here, we note that the rings holdin...
Article
The few clusters [B⁻nA⁺n+1]⁺ (n = 0,1) with resolvable mobilities formed in electrosprays of large salts have been used for nanoparticle instrument testing and calibration at sizes smaller than 2 nm. Extensions of this modest size range by charge reduction with uncontrolled gas phase ions has resulted in impure singly charged clusters. Here, we com...
Article
Full-text available
Two fast electrometer circuits (10¹¹ and 10¹² V/A) are installed in a Faraday cage having a relatively small residence time. Removing readily distinguishable occasional spikes, the root mean square (r.m.s.) noise level at 10¹² V/A is 0.11 fA when acquiring data at 1 Hz. This value is close to the expected thermal resistor noise at room temperature...
Article
The development of efficient blowers for battery-operated vacuum cleaners is exploited to increase the portability of high resolution DMAs. A Halfmini DMA run by the blower of the irobot Roomba 500 powered by a variable DC voltage is tested with electrosprayed molecular ions and the serum albumin protein. Sheath gas flow rates Q from 13 Lit/min up...
Article
Electrophoretic losses at the outlet of Differential Mobility Analyzers result from the need to transport the aerosol from the high voltage _V__Bias_ typically applied to the inner electrode, to the ground potential at which a particle detector is usually connected. Here we examine the sample transmission efficiency η for mobility-selected ions bro...
Article
Many mobility studies (IMS) of electrospray ions with charge states z reduced to unity have shown a singular ability to analyze large protein complexes and viruses, though with wide mobility peaks (fwhm ∼ 20%). Here we confirm that this limitation arises primarily when early charge reduction precedes drop evaporation (suppressing secondary atomizat...
Article
A procedure is described to electrospray the relatively large ions tetrahexadecylammonium (C16H33)4N⁺ and tetraoctadecylammonium (C18H37)4N⁺ from their commercially available bromide salts. Their low solubility and the corresponding low conductivity of their alcohol solutions complicates their electrospraying by the convenient method of applying th...
Article
Prior work with electrosprays in vacuum of mixtures of ionic liquids (ILs) and the moderately high boiling point (Tb) solvents formamide (FM) and propylene carbonate (PC) (Tb of 210 and 241 °C) has shown that the charged drops produced have reasonably narrow charge/mass distributions, controllable over a wide mass/charge range. This enables their u...
Article
The electrical mobilities of hundreds of mass-selected, multiply charged nanodrops (2-6 nm in diameter) of the ionic liquid EMI-BF4 have been measured in air and CO2 at temperatures, T, ranging from 20 to 100 °C, extending previous studies, based on EMI-N(CN)2 nanodrops in air at 20 °C, to other temperatures and drift gases. The known compressibili...
Article
Ion mobility mass spectrometry (IMS-MS) is used to investigate the abundance pattern, n z (m) of Poly-(ethyleneglycol) (PEG) electrosprayed from water/methanol as a function of mass and charge state. We examine n z (m) patterns from a diversity of solution cations, primarily dimethylammonium and triethylammonium. The ability of PEG chains to initia...
Article
Full-text available
We report on the development of an electrospray (ES) microthruster that, by emitting fast nanodroplets, covers a wide range of specific impulse and thrust at high (>50%) propulsion efficiency. To achieve a useful thrust, many ES microthrusters must operate in parallel (multiplexing). The multiplexed electrospray microthruster (MES) is packaged in a...
Article
The electrical mobilities of multiply-charged nanodrops of the ionic liquid 1-ethyl, 3-methylimidazolium dicyanamide (EMI-N[CN]2) were accurately measured in air at 20 °C for mass-selected clusters of composition [EMI-N[CN]2] n [EMI(+)] z , with 2 ≤ n ≤ 369 and 1 ≤ z ≤ 10. We confirm prior reports that the mobility Z of a globular ion of mass m is...
Article
Full-text available
Generation of monomobile molecular standards by electrospray (ES) followed by classification in a differential mobility analyzer (DMA) fails at diameters above ∼2 nm because many clusters in different charge states z crowd in a narrow mobility range. Use of a second DMA (DMA2) in series (tandem) with DMA1 is very helpful because, unexpectedly, many...
Conference Paper
We report on the development of a single-propellant ElectroSpray (ES) microthruster able to: (a) cover a wide range of specific impulse (Isp) and thrust at high propulsion efficiency, and (b) provide macroscopic thrust via micro-fabricated emitter arrays. The electrospray is a mature technology for the emission of fast nanodroplets at a propulsive...
Article
Little has been published on the details of design and fabrication of differential mobility analyzers (DMAs) classifying 1 nm particles with resolving powers of 30 or more. These DMAs must operate at Reynolds numbers Reb2000 (supercritical), requiring laminarizers and diffusers that have tended to make them large and heavy. Here we discuss design a...
Article
The charge/mass distribution f(q/m) of nanodrops and ions electrosprayed in vacuum from mixtures of formamide (FM) and methylammonium formate (MAF) is studied by time of flight mass spectrometry at MAF/FM volumetric concentrations of 5%, 10%, 25%, and 50%. Positive and negative polarities yield comparable f(q/m) curves, though the negative mode yie...
Article
The charge distribution of polystyrene nanoparticles electrosprayed from l-methyl-2-pyrrolidone (NMP) dimethylammonium formate (10/1 vol.) is studied by a continuous tandem differential mobility analyzer (TDMA) technique. Two DMAs operated in series as narrow band mobility filters are scanned in a quasi-continuous fashion providing highly informati...
Article
The mass spectrometric (MS) complexity associated with the quasi-continuous distribution of mass and charge (m, z) of electrosprayed industrial polymers may be moderated by use of ion mobility spectrometry (IMS) and MS in series. However, when the high charge levels typical of polar polymers stretch the gas phase ions into linear configurations, th...
Article
The chargedistributionofpolystyrenenanoparticleselectrosprayedfroml-methyl-2- pyrrolidone(NMP)dimethylammoniumformate(10/1vol)isstudiedbya continuous tandem differentialmobilityanalyzer(CTDMA)technique.TwoDMAsoperatedinseries as narrowbandmobilityfiltersarescannedinaquasi-continuousfashionproviding highlyinformativetwo-dimensional(2D)spectra.Thefir...
Article
Full-text available
The reasons for the existence of two gas phase conformers for electrosprayed ions of the large tetradecameric protein complex GroEL are considered. Key features are that: (1) both conformers extrapolate to very similar cross sections in the limit of zero charge; (2) both conformers supercharge above the maximum value permitted by the Rayleigh crite...
Article
Ion mobility spectrometry (IMS) coupled to mass spectrometry (MS) is used to study the gas phase collision cross section Ω(z, n) in CO(2) of multimers C(n) (n = 1-4, 6) of concanavalin A, whose tetramer C(4) has a crystal structure resembling four tetrahedrically arranged globules. C(n)(+z) ions electrosprayed from aqueous solutions of triethylammo...
Article
Full-text available
All known multi-stage aerodynamic lenses able to focus sharply a wide range of particle sizes include decelerating regions where the flow becomes turbulent at Reynolds numbers Re typically of 100 or less. Here, we propose a design for a focusing concentrator operating laminarly at Re of many thousands. The particles are accelerated by the gas throu...
Article
Prior ion-mobility mass-spectrometry (IMS-MS) studies of polyethylene glycol (PEG) ions have identified only two out of many sharply different observed structures: Linear shapes with several individually solvated singly charged cations at high charge states z (beads on a string), and single multiply charged globules at low z. The present study is d...
Article
When ions or electrons are injected into an insulating liquid, they migrate towards its free surface, destabilize it, and form a charged jet. The jet then breaks into uniform drops charged at an approximately constant fraction of the Rayleigh limit, which relates the drop diameter DD to the flow rate of dielectric liquid QD and the injected current...
Conference Paper
Our research focuses on the development of a single-propellant electrospray (ES) microthruster able to cover a wide range of specific impulses Isp and thrust T, at high propulsion efficiency. To facilitate system optimization and debugging, we focus on a 7-nozzle Multiplexed Electrospray Sytem (MES) with each nozzle packed with micrometer-size bead...
Chapter
Introduction Size Standards Nano-DMAs Nano Condensation Nucleus Counters (CNCs) Summary and Conclusions Acknowledgment List of Abbreviations and Symbols References
Article
Analytical expressions are provided for charged and uncharged particles in the perfect-wetting limit of Fletcher's classical heterogeneous nucleation theory with finite activation energy G*. A dimensionless logarithm of the critical supersaturation can be represented as a single universal curve versus a dimensionless nucleus radius for neutral part...
Article
Full-text available
The validity of the Stokes-Millikan equation is examined in light of mass and mobility measurements of clusters of the ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate (EMI-BF4) in ambient air. The mobility diameter dZ based on the measured mobility and the Stokes-Millikan law is compared with the volume diameter dv, which generalizes th...
Article
We first summarize the early work by Fenn and colleagues on vapor ionization by an electrospray cloud (subsequently dubbed secondary electrospray ionization, or SESI), followed by analysis via an atmospheric pressure ionization mass spectrometer (API-MS). It was in part reported in Ph.D. theses and presented to ASMS conferences, but remains largely...
Article
A parallel-plate differential mobility analyzer and a time-of-flight mass spectrometer (DMA-MS) are used in series to measure true mobility in dry atmospheric pressure air for mass-resolved electrosprayed GroEL tetradecamers (14-mers; ~800 kDa). Narrow mobility peaks are found (2.6-2.9% fwhm); hence, precise mobilities can be obtained for these ion...
Article
Full-text available
The mobilities of electrosprayed proteins and protein multimers with molecular weights ranging from 12.4 kDa (cytochrome C monomers) to 154 kDa (nonspecific concanavalin A hexamers) were measured in dry air by a planar differential mobility analyzer (DMA) coupled to a time-of-flight mass spectrometer (TOF-MS). The DMA determines true mobility at at...
Article
Recent progress in adding a mobility dimension to preexisting API–MS systems without modifying the MS itself is discussed, based on inserting a differential mobility analyzer (DMA) as part of the MS's atmospheric pressure ion source. Design criteria leading to high DMA resolving power R and transmission efficiency η are discussed. Various DMA proto...
Patent
Full-text available
Vapors of relatively heavy species having molecular weights in excess of 290 amu have not been previously detected in the gas phase at ambient temperature. A method to detect them is taught here based on the use of a mass spectrometer with an atmospheric pressure source. Ions produced in detectable quantities from such heavy vapors are claimed as a...
Article
Full-text available
We investigate whether "supercharging" reagents able to shift the charge state distributions (CSDs) of electrosprayed protein ions upward also influence gas-phase protein structure. A differential mobility analyzer and a mass spectrometer are combined in series (DMA-MS) to measure the mass and mobility of monomer and multimeric phosphorylase B ions...
Article
Full-text available
Charge is injected into the bulk of an insulating liquid in the form of nanodrops produced by an immersed Taylor cone of an ionic liquid. The charge then drifts onto the insulator surface, destabilizing it and leading to the formation of an electrified jet that atomizes into approximately monodisperse micron size insulator drops. The approach is si...
Article
A differential mobility analyzer (DMA) is used in atmospheric pressure N(2) to select a narrow range of electrical mobilities from a complex mix of cluster ions of composition (CA)(n)(C(+))(z). The clusters are introduced into the N(2) gas by electrospraying concentrated (approximately 20 mM) acetonitrile solutions of ionic liquids (molten salts) o...
Article
Full-text available
Ion evaporation is an essential step in the formation of charged ions from electrosprays, yet many aspects of the process are poorly understood. The ion evaporation kinetics of the 1-ethyl-3-methyl-imidazolium+ (EMI+) based ionic liquids (ILs) EMI-BF4, EMI-bis(perfluoroethylsulfonyl)imide, EMI-bis(trifluoromethylsulfonyl)imide and EMI-tris(trifluor...
Article
Several ionic liquids (ILs) of relatively high electrical conductivity (K) and surface tension (γ) are electrosprayed under vacuum from electrochemically sharpened and roughened tungsten wires with tip radii R varying from 2 to 80 μ m . All our tips exhibit a purely ionic emission, confirming the versatility of these ionic liquid ion sources (ILIS)...
Article
Full-text available
A large number of data on mobility and mass have been newly obtained or reanalyzed for clusters of a diversity of materials, with the aim of determining the relation between electrical mobility (Z) and mass diameter d m = (6m/ π ρ ) 1/3 (m is the particle mass and ρ the bulk density of the material forming the cluster) for nanoparticles with d m ra...
Article
Vapors released by the skin in the hand of one human subject are detected in real time by sampling them directly from the ambient gas surrounding the hand, ionizing them by secondary electrospray ionization (SESI, via contact with the charged cloud from an electrospray source), and analyzing them in a mass spectrometer with an atmospheric pressure...
Article
We determine the sensitivity of several commercial atmospheric pressure ionization mass spectrometers towards ambient vapors, ionized by contact with an electrospray of acidified or ammoniated solvent, a technique often referred to as secondary electrospray ionization (SESI). Although a record limit of detection of 0.2 x 10(-12) atmospheres (0.2 pp...
Article
Real time analysis of human breath is achieved in an atmospheric pressure ionization mass spectrometer (API-MS) by negatively charging exhaled vapors via contact with an electrospray cloud. The spectrum observed is dominated by a wide range of deprotonated fatty acids, including saturated chains up to C14. Above C14, the background from cutaneous s...
Article
An effort to systematize published and new data on the surface tension gamma of ionic liquids (ILs) is based on the hypothesis that the dimensionless surface tension parameter gamma V v (2/3)/ kT is a function of the void fraction x v = V v/ V m. The void volume V v is defined as the difference between the liquid volume V m occupied by an ion pair...
Article
Dibutyl phthalate vapor nucleation induced by positive polyethylene glycol (PEG) ions with controlled sizes and charges was experimentally studied. The ions were produced by electrospray ionization, classified in a high-resolution differential mobility analyzer, and studied in a nano condensation nucleus counter of the mixing type. Ionic radii of P...
Article
The formation of cone-jets in charged liquids with electrical conductivities larger than 10−4 S/m is reviewed for steady supported menisci and transient Coulomb fissions in charged drops. Taylor's hydrostatic model does not apply strictly, but it forms the basis for subsequent developments. The jet structure is critically dependent on the model use...
Article
Ionic liquid ion sources (ILISs) are externally wetted and electrochemically etched and sharpened tungsten tips used as electrospraying sources for ionic liquids in a vacuum. They have recently shown an ability to operate as emitters of pure ion beams (no drops), even with ionic liquids of moderate surface tension (γ<40 dyn/cm) and electrical condu...
Article
A combined experimental and numerical approach is used to extract information on the kinetics of ion evaporation from the region of high electric field around the tip of a Taylor cone of the neutral solvent propylene carbonate (PC) mixed with two ionic liquids. On the numerical side, the electric field on the surface of the liquid is computed in th...
Article
Full-text available
The emissions of Taylor cones from a wide range of ionic liquids (ILs) have been tested in vacuo in an attempt to identify what physical properties favor the purely ionic regime (PIR). This regime is well known in the case of Taylor cones of liquid metals. For nonmetallic liquids, it has been previously observed in conventional (capillary tube) ele...
Chapter
A purely ionic regime (PIR) of charge emission from Taylor cones of ionic liquids (ILs) held in a vacuum exists, giving ion beams of high quality. This regime is favored by ionic liquids of high electrical conductivity K and high surface tension γ. The present search for such ILs relies on an improved form of the capillary rise method using sample...
Article
Recent work by Zenobi and colleagues [H. Chen, A. Wortmann, W. Zhang, R. Zenobi, Angew. Chem. Int. Ed. 46 (2007) 580] reports that human breath charged by contact with an electrospray (ES) cloud yields many mass peaks of species such as urea, glucose, and other ions, some with molecular weights above 1000Da. All these species are presumed to be inv...
Article
The ionic liquid ion sources (ILISs) recently introduced by Lozano and Martinez Sanchez [J. Colloid Interface Sci. 282, 415 (2005)] , based on electrochemically etched tungsten tips as emitters for Taylor cones of ionic liquids (ILs), have been tested with ionic liquids [A+B−] of increasing molecular weight and viscosity. These ILs have electrical...
Article
A novel isopotential differential mobility analyzer (DMA) concept described by Labowsky and Fernández de la Mora [(2006). Novel ion mobility analyzers and filters. Journal of Aerosol Science, 37, 340–362.] is tested experimentally. Its aerosol inlet and outlet lines are grounded, while the electric field is created with a metallic grid electrode th...
Article
Full-text available
The original project goal was to develop sources of heavy ions for space propulsion based on Taylor cones of heated ionic liquids(ILs). Many commercially available heated ILs have been discovered that reach the purely ionic regime (PIR) of emissions (no drops), offering a new high-efficiency ion source for electrical propulsion. A few commercial IL...
Article
As previously demonstrated by the technique of gas-phase electrophoretic mobility molecular analyzer (GEMMA) introduced by Kaufman and colleagues, differential mobility analysis (DMA) of charge-reduced electrospray ions in the gas phase is a useful complement to MS for studying large proteins and their weakly bound complexes. Several limitations of...
Article
The differential mobility analyzer (DMA) commercialized by RAMEM under the nickname Río Arriba has been evaluated with an emphasis on its transonic operation. The DMA is designed to have a very low pressure drop, with (i) an inner electrode supported upstream in a region of wide cross section, and (ii) a fully axisymmetric exhaust system including...
Article
The capillary rise method is used to measure the room temperature surface tension of several ionic liquids, selected mainly for their high electrical conductivity. They include salts based on the cations 1-ethyl-3-methylimidazolium (EMI+), 1-butyl-3-methylimidazolium (BMI+), and 1,3-dimethylimidazolium (DMI+), paired with anions such as GaCl4−, FeC...
Article
Aerodynamic focusing of particles in spatially periodic flows is investigated numerically in model potential two-dimensional flows with axial harmonic modulations of the stream function. A distinction is made between cases where the two walls oscillate approximately in phase (antisymmetric) or with a phase difference of 180∘ (symmetric). The latter...
Article
Various novel mobility analyzer (MA) designs useful for the separation of gas phase ions and charged particles according to their electrical mobilities are discussed. Traditional differential mobility analyzer (DMA) designs have mostly been restricted to two-elements (electrodes) of either parallel or coaxial cylindrical geometries, with the inlet...
Article
A technique for generating charged aerosols of polystyrene (pSty) with narrow size distributions has been developed. It is based on electrospraying commercial narrow mass standards of pSty dissolved in l-methyl-2-pyrrolidone (NMP) seeded with the newly synthesized salt dimethyl ammonium formate. This salt imparts a much larger electrical conductivi...
Article
Full-text available
A variant of the Vienna DMA (Winklmayr et al. 199127. Winklmayr , W. , Reischl , G. P. , Lindner , A. O. and Berner , A. 1991. A New Electromobility Spectrometer for the Measurement of Aerosol Size Distributions in the Size Range From 1 to 1000 nm. J. Aerosol Sci., 22: 289–296. [CROSSREF][CSA] [CrossRef], [Web of Science ®], [CSA]View all refer...
Article
The mobility distributions of electrosprays from solutions of relatively large tetraalkyl ammonium halide salts A+B- produce a series of sharp peaks associated to clusters of the form (A+)z(AB)n, dominated by the bare cation A+. In order to facilitate their use as standards of mass and mobility (in air), these properties are characterized via tande...
Article
Full-text available
Acoustic waves produced by pressure fluctuations in the turbulent exhaust region of differential mobility analyzers (DMAs) are radiated upstream, making the flow in the working region slightly unsteady and reducing DMA resolution. This claim is demonstrated in a variety of settings. First, a resonance has been observed in several DMAs where the res...
Article
The rate of ion evaporation from the surface of electrically charged liquid drops may be inferred from observations of the minimum drop charge q present on drops of a given radius R. This critical relation q(R) is measured here from the fossil solid residues left by the drops after complete solvent evaporation. We obtain mobility distributions of s...