Christopher J. Hogan

Christopher J. Hogan
University of Minnesota Twin Cities | UMN · Department of Mechanical Engineering

PhD

About

151
Publications
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4,917
Citations

Publications

Publications (151)
Article
Full-text available
Respiratory particles exhaled when an individual speaks and breathes can facilitate respiratory virus transmission. Portable air purification units can potentially reduce transmission risk by decreasing the overall infectious particle concentration in a room. This is particularly important for rooms with an inability to be ventilated with adequate...
Article
A number of recirculating flow aerosol control technologies have been commercialized to mitigate aerosol-transmitted virus infections. Many of these technologies incorporate filters for particle collection and some may also incorporate technologies for virus inactivation. Given the wide variety of commercially available aerosol control technologies...
Article
Measurement of the gas-phase ion mobility of proteins provides a means to quantitatively assess the relative sizes of charged proteins. However, protein ion mobility measurements are typically singular values. Here, we apply tandem mobility analysis to low charge state protein ions (+1 and +2 ions) introduced into the gas phase by nanodroplet nebul...
Article
Prediction of the charge distribution on particles in an aerosol is critical not only in electrical mobility based characterization methods, but also in understanding the role that charging plays in particle growth in gas phase synthesis reactors. The latter is particularly important in non-thermal plasma synthesis reactors, wherein nanoclusters fo...
Article
Full-text available
In indoor environments with limited ventilation, recirculating portable air filtration (PAF) units may reduce COVID-19 infection risk via not only the direct aerosol route (i.e., inhalation) but also via an indirect aerosol route (i.e., contact with the surface where aerosol particles deposited). We systematically investigated the impact of PAF uni...
Article
Aerosol deposition (AD) is a coating process wherein aerosol particles are impacted on a target substrate. There are fundamental differences between the AD process (cold impact), where particle translational kinetic energy is high and thermal energy is low, and thermal spray deposition (thermal impact), where translational energy is lower but therm...
Article
In an effort to understand the earliest stages of nanocluster growth in gas phase synthesis systems, we apply a flow tube reactor with a differential mobility analyzer-Faraday cage electrometer system to examine nanocluster formation and growth in the sub-3.0 nm mobility diameter range from the decomposition of titanium tetra-isopropoxide (TTIP) in...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-1582.vid Characterization of the aerosol environment in the stratosphere is needed to better understand the role of aerosol particles in high-speed boundary layer transition. This paper presents the development and initial testing of a calibration system for optical particle counters that meas...
Article
This paper describes the extension of the classic Avrami equation to nonisothermal systems with arbitrary temperature time history and arbitrary initial distributions of transformed phase. We start by showing that though examination of phase change in Fourier space, we can decouple nucleation rate, growth rate, and transformed fraction, leading to...
Article
Nanoclusters in the gas phase grow by condensation and coagulation, which heat up nanoclusters, creating thermal non-equilibrium with the surrounding gas. The extent of non-equilibrium for nanoclusters is dependent upon the rate of heating relative to the rate of cooling brought about by nanocluster-gas molecule collisions, hence the latter process...
Article
In chemical mechanical planarization (CMP), a particle slurry is used in polishing semiconductor wafers. Key to its performance is the size distribution of the particles. We evaluate the potential of an aerosol technique, namely differential mobility analysis (in a liquid nanoparticle sizer, LNS, system) to characterize size distributions of CMP sl...
Article
A generalized physics-based expression for the drag coefficient of spherical particles moving in a fluid is developed. The proposed correlation incorporates essential rarefied effects, low-speed hydrodynamics, and shock-wave physics to accurately model the particle-drag force for a wide range of Mach and Knudsen numbers (and therefore Reynolds numb...
Article
Full-text available
When an oil-in-water emulsion is utilized for application in a flat-fan spray, micrometer-sized oil droplets are thought to facilitate hole formation on the spray lamella, leading to an earlier breakup of the spray sheet and an increase in resulting droplet sizes. However, prior work has largely focused on changes to the mean or median droplet size...
Preprint
In indoor environments with limited ventilation, recirculating portable air filtration (PAF) units may reduce COVID-19 infection risk via not only the direct aerosol route ( i.e. , inhalation) but also via an indirect aerosol route ( i.e. , contact with the surface where particles deposited). We systematically investigated the impact of PAF units i...
Article
Full-text available
Background As researchers race to understand the nature of COVID-19 transmission, healthcare institutions must treat COVID-19 patients while also safeguarding the health of staff and other patients. One aspect of this process involves mitigating aerosol transmission of the SARS-CoV2 virus. The U.S. Centers for Disease Control and Prevention (CDC) p...
Article
Objective: To quantify the efficacy of masking and "social distancing" on the transmission of airborne particles from a phantom aerosol source (simulating an infected individual) to a nearby target (simulating a healthy bystander) in a well-controlled setting. Methods: An aerosol was created using monodisperse polystyrene latex beads in place of...
Article
Exhalation of infectious micrometer-sized particles has been strongly implicated in respiratory infection spread. An important fundamental question is then the fate of infectious exhaled particles in indoor spaces, i.e., whether they will remain suspended in an aerosol until ventilation leads to their clearance or whether they will deposit, and if...
Article
Full-text available
Recirculating air purification technologies are employed as potential means of reducing exposure to aerosol particles and airborne viruses. Toward improved testing of recirculating air purification units, we developed and applied a medium-scale single-pass wind tunnel test to examine the size-dependent collection of particles and the collection and...
Article
Aerosol deposition (AD) is a coating technique wherein particles are inertially impacted onto a target substrate at reduced pressures and supersonic particle impact velocities lead to coating consolidation. The limiting step in AD application is often not supersonic deposition system operation, but instead aerosolization of powder particles with th...
Preprint
Full-text available
This study concerns the effects of pressure, spatial location, and application of oil emulsions on the resulting droplet size, eccentricity, as well as velocity distributions, all of which are crucial information in determining the dispersion dynamics of the droplets during the spray applications. Experiments were conducted with the abovementioned...
Article
Full-text available
Laser heating of gold nanospheres (GNS) is increasingly prevalent in biomedical applications due to tunable optical properties that determine heating efficiency. Although many geometric parameters (i.e. size, morphology) can affect optical properties of individual GNS and their heating, no specific studies of how GNS aggregation affects heating hav...
Article
Nonthermal plasma flow tube reactors are industrially scalable systems for the production of nanocrystal (NC) based materials and coatings. One key advantage of nonthermal plasma synthesis is the ability to both synthesize NC and deposit films in a single reactor, as at the reactor outlet, NCs can be inertially deposited onto a target substrate. Th...
Article
Ion attachment and ion drag to dust particles near the edge of a nonthermal plasma sheath are of interest to better understand how particles become trapped in such sheath regions. While electron-particle collisions in plasmas and sheaths can often be described by orbital motion limited theory, quantification of ion transport about dust particles in...
Preprint
Full-text available
A generalized physics-based expression for the drag coefficient of spherical particles moving in a fluid is derived. The proposed correlation incorporates essential rarefied physics, low-speed hydrodynamics, and shock-wave physics to accurately model the particle-drag force for a wide range of Mach and Knudsen numbers (and therefore Reynolds number...
Article
Control technologies to inactivate airborne viruses effectively are needed during the ongoing SARS-CoV-2 pandemic, and to guard against airborne transmitted diseases. We demonstrate that sealed UV−C flow reactors operating with fluences near 253 ± 1 nm of 13.9−49.6 mJ cm −2 efficiently inactivate coronaviruses in an aerosol. For measurements, porci...
Article
The charge reduction of multiply charged macromolecular ions via recombination with small ions in the gas phase is commonly employed to modulate the charge on macromolecules prior to mass spectrometric and mobility analyses. We employ a recently developed continuum-Molecular Dynamics (MD) calculation approach to determine the recombination rate coe...
Article
The structure and resulting physical properties of aerosol deposited particulate films are governed by the size distribution and morphology of the depositing particles as well as the physics governing particle deposition. While particulate film deposition processes are qualitatively understood, the link between particle characteristics and depositi...
Article
Rationale: Aerosol generation with modes of oxygen therapy such as high-flow nasal cannula and noninvasive positive-pressure ventilation is a concern for healthcare workers during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. The amount of aerosol generation from the respiratory tract with these various oxygen modalitie...
Article
Vapor assisted mobility shift measurements were made with atmospheric pressure drift tube ion mobility-mass spectrometry (IM-MS) to determine the thermodynamic properties of weakly bound ion-molecule clusters formed from protonated phenylalanine and neutral vapor molecules with hydroxyl functional groups. Relative binding energies and gas-phase ass...
Article
Si nanocrystals (NCs) are synthesizable in low-pressure plasmas with narrow diameter distributions because of unipolar negative charging in the plasma. However, NCs must pass into a spatial afterglow, where NCs may decharge and aggregate. We use both low-pressure differential mobility analysis and quantitative TEM image analysis to examine Si NCs s...
Article
Full-text available
Background To mitigate potential exposure of healthcare workers (HCWs) to SARS-CoV-2 via aerosol routes, we have developed a portable hood which not only creates a barrier between HCW and patient, but also utilizes negative pressure with filtration of aerosols by a HEPA filter. Material and Methods The hood has iris-port openings for access to the...
Article
Monopolar electrosurgical pencils are used extensively in surgical operations. With such pencils, electric current passes to the tissue, and as such, electrosurgical pencil operation generates a significant amount of thermal energy, which in turn leads to the generation of electrosurgical smoke (ES). The health risks of ES are dependent on the size...
Preprint
Full-text available
The measurements of size distribution of small particles (e.g. dusts, droplets, bubbles, etc.) are critical for a broad range of applications in environmental science, public health, industrial manufacturing, etc. Laser diffraction (LD), a widely used method for such applications depends on model-based inversion with underlying assumptions on parti...
Article
A low cost, easy-to-manufacture particle classification device for coarse mode, supermicrometer particles and droplets remains important for a variety of industries and environmental measurements, including agricultural sprays, pharmaceutical powders, spray drying processes, precipitation, and dust storms. While optical techniques can typically be...
Article
Accurate calculation of the ion–ion recombination rate coefficient has been of long-standing interest as it controls the ion concentration in gas phase systems and in aerosols. We describe the development of a hybrid continuum-molecular dynamics (MD) approach to determine the ion–ion recombination rate coefficient. This approach is based on the lim...
Article
Oxide nanoparticle growth from vapor phase precursors occurs in high temperature aerosol reactors first via the formation of nanoclusters, which are nanometer-scale condensed-phase species composed of 10¹-10² atoms. The binding rate for nanoclusters, defined as the rate at which two nanoclusters collide with and stick to one another, is hence of in...
Preprint
Accurate calculation of the ion-ion recombination rate coefficient has been of long-standing interest, as it controls the ion concentration in gas phase and aerosol systems. We describe the development of a hybrid continuum-molecular dynamics approach to determine the ion-ion recombination rate coefficient. The approach is based on the limiting sph...
Article
Full-text available
Multidimensional techniques that combine fully or partially orthogonal characterization methods in a single setup often provide a more comprehensive description of analytes. When applied to nanoparticles, they have the potential to reveal particle properties not accessible to more conventional 1D techniques. Herein, we apply recently developed 2D c...
Article
Nanoclusters can form and grow by nanocluster-monomer collisions (condensation) and nanocluster-nanocluster collisions (coagulation). During growth, product nanoclusters have elevated thermal energies due to potential and thermal energy exchange following a collision. Even though nanocluster collisional heating may be significant and strongly size...
Article
Aerosol deposition (AD) with gas phase‐synthesized chain‐like nanoaggregates can yield dense coatings from the impaction of particles on a substrate; however, dense coating formation is not well understood. Here, we study coating consolidation at the single nanoaggregate level. Flame spray pyrolysis‐made tin oxide nanoaggregates are mobility (size)...
Article
The discovery of new thermoelectric materials has the potential to benefit from advances in high-throughput methodologies. Traditional synthesis and characterization routes for thermoelectrics are time-consuming serial processes. In contrast, high-throughput materials discovery is commonly done by thin film growth, which may produce microstructures...
Preprint
Nanoclusters can form and grow by nanocluster-monomer (condensation) and nanocluster-nanocluster (coagulation) collisions. During growth, product nanoclusters have elevated thermal energies due to potential and thermal energy exchange following a collision. Even though nanocluster collisional heating may be significant and strongly-size dependent,...
Article
Full-text available
Droplet generation through spray breakup is an unsteady and non-linear process which produces a relatively dense, highly polydisperse aerosol containing non-spherical droplets with sizes spanning several orders of magnitude. Such variability in size and shape can lead to significant sources of error for conventional measurements based on laser scat...
Preprint
Full-text available
Droplet generation through spray breakup is an unsteady and non-linear process which produces a relatively dense, highly polydisperse aerosol containing non-spherical droplets with sizes spanning several orders of magnitude. Such variability in size and shape can lead to significant sources of error for conventional measurements based on laser scat...
Article
Improved methods to probe the reactivity of nano-ions, such as C60⁻, would find utility in nanochemistry, combustion chemistry, and in generally understanding the behavior of matter at the nanometer scale. We demonstrate that ion mobility-mass spectrometry (IM-MS) can be used to probe nano-ion reaction kinetics and apply IM-MS specifically to exami...
Article
Full-text available
Here we present a guide to ion mobility mass spectrometry experiments, which covers both linear and nonlinear methods: what is measured, how the measurements are done, and how to report the results, including the uncertainties of mobility and collision cross section values. The guide aims to clarify some possibly confusing concepts, and the reporti...
Article
Nanometer scale clusters form from vapor phase precursors and can subsequently grow into nanoparticles during atmospheric nucleation events. A particularly interesting set of clusters relevant to nucleation is hybrid iodine pentoxide-iodic acid clusters of the form (I2O5)x(HIO3)y, as these clusters have been observed in coastal region nucleation ev...
Article
Through vapor modification of the counter-current drift gas in an atmospheric pressure drift tube ion mobility spectrometer (IMS), we demonstrate measurement of gas-phase association enthalpies and entropies for select proton bound heterodimers formed from a phosphonic acid with 2-propanol. Previous efforts to determine gas-phase association thermo...
Article
Low pressure (<20 Torr) non-thermal plasma flow tube reactors are commonly used for the synthesis of high purity nanoparticles (NPs) via nucleation and subsequent growth from vapor phase precursors. In spite of their utility, process monitoring (i.e. output NP size characterization) in such reactors is difficult, as there is a dearth of techniques...
Article
Laminar flow condensation particle counters (CPCs) are uniquely sensitive detectors for aerosol particles in the nanometer size range (i.e. below 10 nm in size they can have single particle sensitivity). Their operation hinges upon the creation of supersaturation of a working fluid; particles exposed to supersaturated vapor grow by condensation to...
Article
Full-text available
In this study the process of heterogeneous nucleation was investigated experimentally by coupling a high resolution DMA to an expansion type condensation particle counter, the size‐analyzing nuclei counter SANC. More specifically, we measured the activation probabilities of monoatomic ions of both polarities by using n‐Butanol as condensing liquid....
Preprint
Full-text available
Here we present a guide on ion mobility mass spectrometry experiments, which covers both linear and nonlinear methods: what is measured, how the measurements are done, and how to report the results, including the uncertainties on mobility and collision cross section values. The guide aims to clarify some possibly confusing concepts, and the reporti...
Article
In the fibrous filtration of particles in gas and liquid flows, loading is the act of particles depositing onto fibers. Loaded particles alter the filter microstructure and can have a profound influence on the pressure drop across a filter medium. Of interest is therefore a simple approach to predict the pressure drop across a loaded filter, accoun...
Article
Non-equilibrium plasmas offer a unique environment for nanoparticle synthesis. Particles are homogeneously nucleated and grow at near room temperature as a result of non-thermal decomposition of vapor precursors by electrons and other plasma-excited species. Despite their widespread use, several features regarding particle growth in these systems r...
Article
In gas phase synthesis systems, clusters form and grow via condensation, in which a monomer binds to an existing cluster. While a hard-sphere equation is frequently used to predict the condensation rate coefficient, this equation neglects the influences of potential interactions and cluster internal energy on the condensation process. Here, we pres...
Article
Combining experimental data with computational modeling, we illustrate the capacity of selective gas-phase interactions using neutral gas vapors to yield an additional dimension of gas-phase ion mobility separation. Not only are the mobility shifts as a function of neutral gas vapor concentration reproducible, but also the selective alteration of m...
Article
Like and oppositely charged particles or dust grains in linear shear flows are often driven to collide with one another by fluid and/or electrostatic forces, which can strongly influence particle-size distribution evolution. In gaseous media, collisions in shear are further complicated because particle inertia can influence differential motion. Exp...
Article
Tandem mobility and mass measurements of aerosol particles, performed with a differential mobility analyzer-aerosol particle mass analyzer-condensation particle counter (DMA-APM-CPC) or DMA-centrifugal particle mass analyzer-CPC, find increasing application in the analysis of combustion derived aerosols and complex aerosol mixtures. In addition to...
Article
Full-text available
We utilize ion mobility-mass spectrometry with an atmospheric pressure differential mobility analyzer coupled to a time-of-flight mass spectrometer (DMA-MS) to examine the formation of ion-vapor molecule complexes with seed ions of K+, Rb+, Cs+, Br-, and I- exposed to n-butanol and n-nonane vapor under subsaturated conditions. Ion-vapor molecule co...
Article
A benchmark comparison between two ion mobility and collision cross-section (CCS) calculators, MOBCAL and IMoS, is presented here as a standard to test the efficiency and performance of both programs. Utilizing 47 organic ions, results are in excellent agreement between IMoS and MOBCAL in He and N2, when both programs use identical input parameters...
Article
Drift tube-ion mobility spectrometers (DT-IMSs) are used to separate and characterize the structures of gas phase ions. Recent work in coupling an atmospheric pressure DT-IMS to a condensation particle counter (CPC) has extended the application of drift tube ion mobility spectrometry to nanoparticle analysis, with measurements possible for singly c...
Article
Full-text available
The uptake of vapor molecules by nanometer scale aerosol particles (clusters) is of fundamental importance in aerosol science; uptake is the first step of condensational growth in both the ambient as well as in condensation based particle detectors. However, uptake is not well understood at the nanometer scale. We examined the uptake of organic vap...
Article
Native mass spectrometry is widely used to determine the stoichiometries and binding constants of noncovalent interactions in solution. One challenge is that multiple analytes in a single electrospray droplet can aggregate during solvent evaporation, which will bias the distribution of oligomeric states observed during gas-phase measurements. Here,...
Article
Protein binding and protein-induced nanoparticle aggregation are known to occur for a variety of nanomaterials, with the extent of binding and of aggregation highly dependent on nanoparticle surface properties. However, often lacking are techniques that enable quantification of the extent of protein binding and aggregation, particularly for nanopar...
Article
A promising route to cancer treatment is hyperthermia, facilitated by superparamagnetic iron oxide nanoparticles (SPIONs). After exposure to an alternating external magnetic field, SPIONs generate heat, quantified by their specific absorption rate (SAR, in W g(-1) Fe). However, without surface functionalization, commercially available, high SAR SPI...
Article
We applied an atmospheric pressure differential mobility analyzer (DMA) coupled to a time-of-flight mass spectrometer to examine the stability, mass-mobility relationship, and extent of hydration of dimethylamine-sulfuric acid cluster ions, which are of relevance to nucleation in ambient air. Cluster ions were generated by electrospray ionization a...
Article
Despite the importance of examining the formation of nanoparticle-protein conjugates, there is a dearth of routine techniques for nanoparticle-protein conjugate characterization. The most prominent change to a nanoparticle population upon conjugate formation is a shift in the nanoparticle size distribution function. However, commonly employed dynam...
Article
Optical metafluids that consist of colloidal solutions of plasmonic and/or excitonic nanomaterials may play important roles as functional working fluids or as means for producing solid metamaterial coatings. We demonstrate water-based metafluids that act as broadband electromagnetic absorbers in a spectral range of 200 nm-3,300 nm and feature a nar...
Article
Full-text available
We apply liquid nebulization (LN) in series with ion mobility spectrometry (IMS, using a differential mobility analyzer coupled to a condensation particle counter) to measure the size distribution functions (the number concentration per unit log diameter) of gold nanospheres in the 5-30 nm range, 70 nm × 11.7 nm gold nanorods, and albumin proteins...