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1.
J Phys Chem B ; 2020 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-32569464

RESUMO

The evaporation of liquid solution droplets and solute crystallization can be highly complex and is an important problem, particularly in spray drying where powdered products are produced from sprayed liquid droplets, such as in the food or pharmaceutical industries. In this work, we study the relationship between the evaporation rates of single levitated NaNO3 droplets under varying environmental conditions and the propensity for nucleation of NaNO3 crystals. We use a combination of an electrodynamic balance to study single-droplet evaporation kinetics, SEM imaging of dried particles and modelling of the internal solute distribution inside a drying droplet. We show that the aqueous NaNO3 droplets exhibit broad distributions in the time that crystal nucleation is observed, droplet-to-droplet. The distribution of nucleation time is dependent upon environmental conditions such as the drying temperature, relative humidity (RH) and solute concentration. Even when evaporating in 0 % RH, some droplets do not nucleate crystals in the time taken for all water to evaporate and dry to form an amorphous particle. We believe that this interplay between crystalline or amorphous particle formation is a result of the viscosity of aqueous NaNO3 solutions, which rises by several orders of magnitude as the concentration increases. We show that for droplets with an initial radius of ~ 25 µm the propensity for aqueous NaNO3 droplets to nucleate crystals upon drying increases with a decreasing RH, and increases with an increasing temperature in the range of 278 - 306 K. This work demonstrates the importance of the drying kinetics on the propensity of evaporating droplets to nucleate crystals.

2.
Proc Natl Acad Sci U S A ; 117(15): 8335-8343, 2020 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-32238561

RESUMO

Surface tension influences the fraction of atmospheric particles that become cloud droplets. Although surfactants are an important component of aerosol mass, the surface tension of activating aerosol particles is still unresolved, with most climate models assuming activating particles have a surface tension equal to that of water. By studying picoliter droplet coalescence, we demonstrate that surfactants can significantly reduce the surface tension of finite-sized droplets below the value for water, consistent with recent field measurements. Significantly, this surface tension reduction is droplet size-dependent and does not correspond exactly to the macroscopic solution value. A fully independent monolayer partitioning model confirms the observed finite-size-dependent surface tension arises from the high surface-to-volume ratio in finite-sized droplets and enables predictions of aerosol hygroscopic growth. This model, constrained by the laboratory measurements, is consistent with a reduction in critical supersaturation for activation, potentially substantially increasing cloud droplet number concentration and modifying radiative cooling relative to current estimates assuming a water surface tension. The results highlight the need for improved constraints on the identities, properties, and concentrations of atmospheric aerosol surfactants in multiple environments and are broadly applicable to any discipline where finite volume effects are operative, such as studies of the competition between reaction rates within the bulk and at the surface of confined volumes and explorations of the influence of surfactants on dried particle morphology from spray driers.

3.
Laryngoscope ; 130(4): 880-885, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31145486

RESUMO

OBJECTIVES/HYPOTHESIS: Postoperative uvular necrosis is rare, but can be distressing to the patient when it unexpectedly occurs. Little has been published regarding its predisposing factors and pathophysiology. The purpose of this comprehensive review was to compile cases of postoperative uvular necrosis and identify risk factors and potential causes for this complication. STUDY DESIGN: Retrospective case series. METHODS: The study was performed at an academic tertiary care referral center. Clinical records from four patients treated for postoperative uvular necrosis from 2008 to 2018 were reviewed. A comprehensive literature review was also performed. The MEDLINE, Embase, and Scopus databases were searched, as well as the grey literature. All case reports and literature reviews in the English literature from 1978 to 2018 were systematically identified for review. RESULTS: Four cases of postoperative uvular necrosis diagnosed clinically at our institution were included. The comprehensive literature review identified 26 reports and seven case series, totaling 53 cases of this complication. Use of suction was reported in 19 cases, and six cases reported no use of suction. Ninety-four percent of cases were treated conservatively, whereas 6% underwent excision. Ninety-one percent resolved within 14 days. CONCLUSIONS: Impingement with various devices and vascular trauma from suction each likely play a role in postoperative uvular necrosis. Male oropharyngeal anatomy may be a risk factor, but neither the type of instrumentation nor the type of procedure seem to predict this complication. Proper positioning of the patient and instruments and minimizing suction force help prevent uvular injury. LEVEL OF EVIDENCE: NA Laryngoscope, 130:880-885, 2020.

4.
Ann Otol Rhinol Laryngol ; 128(11): 1086-1091, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31291740

RESUMO

BACKGROUND: Spindle cell lipomas (SCLs) are benign tumors that are characteristically present on the upper back and neck, but in rare cases present throughout the respiratory mucosa, causing hoarseness, stridor, dyspnea, and obstruction. OBJECTIVE: To highlight the importance of considering SCL in the diagnosis of benign respiratory tract tumors, a literature review identified all published cases of respiratory tract SCLs, including 2 from our institution: one case in the nasopharynx and 1 in the nasal valve. METHODS: All case reports, series and literature reviews from the English literature from 1975 through March 2018 were systematically identified for review in the MEDLINE, EMBASE, and Scopus databases. Two additional cases from our institution were described. RESULTS: In total, 24 cases of SCL in the respiratory tract were identified for review. Two cases from our institution are described here, bringing the total of reported cases to 26. Extensive analyses of oral cavity SCLs already exist, so we excluded this site from our review and focused on sites where SCLs may present with respiratory symptoms. Excluding the oral cavity and oropharynx, the most common location described is the larynx. All 26 cases were treated with excision. One tumor required a second surgery, but there were no other complications nor recurrences. CONCLUSION: Although rare, SCLs may arise from throughout the respiratory tract and cause dyspnea, hoarseness and stridor. Spindle cell lipoma should be considered in the differential diagnosis of a respiratory tract mass. This diagnosis confers a good prognosis and patients may be reassured that surgery is almost always curative.


Assuntos
Dispneia/diagnóstico , Lipoma/diagnóstico , Neoplasias Bucais/diagnóstico , Idoso , Biópsia , Diagnóstico Diferencial , Dispneia/etiologia , Humanos , Lipoma/complicações , Masculino , Pessoa de Meia-Idade , Neoplasias Bucais/complicações , Tomografia Computadorizada por Raios X
5.
6.
Pharm Res ; 36(7): 100, 2019 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-31089892

RESUMO

PURPOSE: Evaporation and particle formation from multi-solvent microdroplets containing solid excipients pertaining to spray-drying of therapeutic agents intended for lung delivery were studied. Various water and ethanol co-solvent systems containing a variety of actives and excipients (beclomethasone, budesonide, leucine, and trehalose) were considered. METHODS: Numerical methods were used to predict the droplet evaporation rates and internal solute transfers, and their results verified and compared with results from two separate experimental setups. In particular, an electrodynamic balance was used to measure the evaporation rates of multicomponent droplets and a monodisperse droplet chain setup collected dried microparticles for further analytical investigations and ultramicroscopy. RESULTS: The numerical results are used to explain the different particle morphologies dried from solutions at different co-solvent compositions. The obtained numerical data clearly show that the two parameters controlling the general morphology of a dried particle, namely the Péclet number and the degree of saturation, can change with time in a multi-solvent droplet. This fact complicates product development for such systems. However, this additional complexity vanishes at what we define as the iso-compositional point, which occurs when the solvent ratios and other composition-dependent properties of the droplet remain constant during evaporation, similar to the azeotrope of such systems during distillation. CONCLUSIONS: Numerical and experimental analysis of multi-solvent systems indicate that spray-drying near the iso-compositional ratio simplifies the design and process development of such systems.


Assuntos
Excipientes/química , Nebulizadores e Vaporizadores , Solventes/química , Administração por Inalação , Beclometasona/química , Budesonida/química , Dessecação , Etanol/química , Cinética , Leucina/química , Pós/química , Teoria Quântica , Trealose/química , Água/química
7.
J R Soc Interface ; 16(150): 20180779, 2019 01 31.
Artigo em Inglês | MEDLINE | ID: mdl-30958165

RESUMO

The airborne transmission of infection relies on the ability of pathogens to survive aerosol transport as they transit between hosts. Understanding the parameters that determine the survival of airborne microorganisms is critical to mitigating the impact of disease outbreaks. Conventional techniques for investigating bioaerosol longevity in vitro have systemic limitations that prevent the accurate representation of conditions that these particles would experience in the natural environment. Here, we report a new approach that enables the robust study of bioaerosol survival as a function of relevant environmental conditions. The methodology uses droplet-on-demand technology for the generation of bioaerosol droplets (1 to greater than 100 per trial) with tailored chemical and biological composition. These arrays of droplets are captured in an electrodynamic trap and levitated within a controlled environmental chamber. Droplets are then deposited on a substrate after a desired levitation period (less than 5 s to greater than 24 h). The response of bacteria to aerosolization can subsequently be determined by counting colony forming units, 24 h after deposition. In a first study, droplets formed from a suspension of Escherichia coli MRE162 cells (108 ml-1) with initial radii of 27.8 ± 0.08 µm were created and levitated for extended periods of time at 30% relative humidity. The time-dependence of the survival rate was measured over a time period extending to 1 h. We demonstrate that this approach can enable direct studies at the interface between aerobiology, atmospheric chemistry and aerosol physics to identify the factors that may affect the survival of airborne pathogens with the aim of developing infection control strategies for public health and biodefence applications.


Assuntos
Escherichia coli/metabolismo , Viabilidade Microbiana , Modelos Biológicos , Aerossóis
8.
Anal Chem ; 91(8): 5074-5082, 2019 04 16.
Artigo em Inglês | MEDLINE | ID: mdl-30921513

RESUMO

Measurements of the water activity-dependent viscosity of aerosol particles from two techniques are compared, specifically from the coalescence of two droplets in holographic optical tweezers (HOT) and poke-and-flow experiments on particles deposited onto a glass substrate. These new data are also compared with the fitting of dimer coagulation, isolation, and coalescence (DCIC) measurements. The aerosol system considered in this work are ternary mixtures of sucrose-citric acid-water and sucrose-NaNO3-water, at varying solute mass ratios. Results from HOT and poke-and-flow are in excellent agreement over their overlapping range of applicability (∼103-107 Pa s); fitted curves from DCIC data show variable agreement with the other two techniques because of the sensitivity of the applied modeling framework to the representation of water content in the particles. Further, two modeling approaches for the predictions of the water activity-dependent viscosity of these ternary systems are evaluated. We show that it is possible to represent their viscosity with relatively simple mixing rules applied to the subcooled viscosity values of each component or to the viscosity of the corresponding binary mixtures.

9.
J Otolaryngol Head Neck Surg ; 48(1): 15, 2019 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-30885260

RESUMO

BACKGROUND: Cocaine has traditionally been the topical decongestant most frequently used for visualization of the surgical field in Endoscopic Sinus Surgery (ESS). Alternatives include xylometazoline, oxymetazoline, and epinephrine. The understanding of the safety profile of each agent is changing, as are the practices of Otolaryngologists-Head & Neck Surgeons. The objective of this study is to determine decongestant use practices in ESS across Canada, which has not previously been studied. METHODS: A cross-sectional survey design using a 24-item electronic questionnaire was distributed to actively practicing members of the Canadian Society of Otolaryngology-Head and Neck Surgery via email. A French translated version of the survey was also available. Questions explored the respondents' demographics and decongestion practices for ESS. RESULTS: Ninety-six surveys from otolaryngologists practicing in Canada were completed (19% response rate). The average time in practice was 16.5 years (range 1-50 years, SD 12.0 years). Twenty-six (27%) of respondents use some form of cocaine solution for topical decongestion in ESS. Over a total of over 1500 combined practice-years, eight respondents (8%) personally experienced an adverse event that could be attributed to cocaine, including two mortalities. One cardiac even was directly attributable to the patients' use of recreational cocaine in the immediate pre-operative period. CONCLUSION: The popularity of cocaine for topical decongestion in ESS in present-day Canada is less than in surveys from other countries. However, there are few reported adverse events with long-term consequences that are attributable to intraoperative cocaine. Considering the beneficial effects of cocaine for visualization and pain control, this change in practice warrants further investigation.


Assuntos
Anestésicos Locais/uso terapêutico , Cocaína/uso terapêutico , Endoscopia , Otolaringologia , Seios Paranasais/cirurgia , Padrões de Prática Médica , Administração Tópica , Canadá , Estudos Transversais , Humanos , Descongestionantes Nasais/uso terapêutico , Inquéritos e Questionários
10.
J Phys Chem A ; 123(8): 1648-1660, 2019 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-30707027

RESUMO

The validation of approaches to predict the hygroscopicity of complex mixtures of organic components in aerosol is important for understanding the hygroscopic response of organic aerosol in the atmosphere. We report new measurements of the hygroscopicity of mixtures of dicarboxylic acids and amino acids using a comparative kinetic electrodynamic balance (CK-EDB) approach, inferring the equilibrium water content of the aerosol from close to a saturation relative humidity (100%) down to 80%. We show that the solution densities and refractive indices of the mixtures can be estimated with an accuracy of better than ±2% using the molar refractive index mixing rule and densities and refractive indices for the individual binary organic-aqueous solutions. Further, we show that the often-used mass-, volume-, and mole-weighted mixing rules to estimate the hygroscopicity parameter κ can overestimate the hygroscopic parameter by a factor of as much as 3, highlighting the need to understand the specific nonideal interactions that may arise synergistically in mixtures and cannot be represented by simple models. Indeed, in some extreme cases the hygroscopicity of a multicomponent mixture can be very close to that for the least hygroscopic component. For mixtures of similar components for which no additional synergistic interactions need be considered, the hygroscopicity of the mixed component aerosol can be estimated with high accuracy from the hygroscopic response of the binary aqueous-organic aerosol. In conclusion, we suggest that the hygroscopicity of multicomponent organic aerosol can be highly nonadditive and that simple correlations of hygroscopicity with composition may often misrepresent the level of complexity essential to interpreting aerosol hygroscopicity.

11.
J Strength Cond Res ; 33(6): 1512-1523, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29189581

RESUMO

Hodgson, DD, Quigley, PJ, Whitten, JHD, Reid, JC, and Behm, DG. Impact of 10-minute interval roller massage on performance and active range of motion. J Strength Cond Res 33(6): 1512-1523, 2019-Roller massage (RM) has been shown to increase range of motion (ROM) without subsequent performance deficits. However, prolonged static stretching (SS) can induce performance impairments. The objective of this study was to examine the effects of combining SS and RM with and without subsequent RM on ROM and neuromuscular performance. Subjects (n = 12) participated in 5 sessions: (a) SS only (SS_rest), (b) SS + RM (SS + RM_rest), (c) SS with RM at 10 and 20 minutes after stretch (SS_RM), (d) SS + RM with RM at 10 and 20 minutes after stretch (SS + RM_RM), and (e) control. For the SS conditions, the quadriceps and hamstrings received passive SS for 2 × 30 seconds each. For the SS + RM conditions, SS was applied to the quadriceps and hamstrings for 30 seconds each, and RM was performed for 30 seconds per muscle. SS_RM and SS + RM_RM conditions received an additional 30-second RM at 10 and 20 minutes after warm-up, whereas sessions without additional RM rested for the same duration. Testing measures included hip flexion (HF) and knee flexion (KF) active and passive ROM, hurdle jump height and contact time, countermovement jump height, and maximal voluntary isometric contraction force. Initial KF and HF ROM improvements provided by SS_RM and SS + RM_RM were sustained up to 30 minutes after intervention. Furthermore, SS_RM exhibited greater ROM compared with sessions lacking additional RM in active and passive HF as well as active and passive KF. Similarly, SS + RM_RM elicited greater KF and HF ROM improvements than SS_rest. In conclusion, active KF and HF ROM improvements were prolonged by additional RM, whereas neuromuscular performance remained relatively unaffected.


Assuntos
Músculos Isquiossurais/fisiologia , Massagem/métodos , Exercícios de Alongamento Muscular , Músculo Quadríceps/fisiologia , Amplitude de Movimento Articular , Adolescente , Adulto , Teste de Esforço , Feminino , Articulação do Quadril/fisiologia , Humanos , Contração Isométrica , Articulação do Joelho/fisiologia , Masculino , Movimento , Distribuição Aleatória , Exercício de Aquecimento , Adulto Jovem
12.
Phys Chem Chem Phys ; 20(36): 23453-23466, 2018 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-30182100

RESUMO

Numerous analytical models have been applied to describe the evaporation/condensation kinetics of volatile components from aerosol particles for use in many applications. However, the applicability of these models for treating cases that lead to substantial and rapid changes in particle temperature due to, for example, evaporative cooling remain to be compared with measurements. We consider three typical treatments, comparing predictions of the evaporation rates of pure water droplets over a wide range in gas phase relative humidity (RH) and exploring the sensitivity of the predictions to uncertainties in the thermophysical gas and condensed-phase parameters. We also compare predictions from the three treatments to measurements of the evaporation rates of pure water droplets with varying RH using an electrodynamic balance (EDB), concluding that only two of the model treatments are sufficiently able to account for the level of evaporative cooling (typically as high as 12 K). Finally, we show that the RH can be inferred accurately from the evaporation rate of pure water droplets over the full range in accessible RH and comparison with the model predictions (within absolute uncertainties of 2.5% RH over the range 20% to 95% RH), considering the level of agreement with independent measurements made through determining the equilibrated size of aqueous sodium chloride and sodium nitrate droplets.

13.
J Phys Chem Lett ; 9(13): 3708-3713, 2018 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-29924626

RESUMO

Responding to changes in the surrounding environment, aerosol particles can grow by water condensation changing rapidly in composition and changing dramatically in viscosity. The timescale for growth is important to establish for particles undergoing hydration processes in the atmosphere or during inhalation. Using an electrodynamic balance, we report direct measurements at -7.5, 0, and 20 °C of timescales for hygroscopic condensational growth on a range of model hygroscopic aerosol systems. These extend from viscous aerosol particles containing a single saccharide solute (sucrose, glucose, raffinose, or trehalose) and a starting viscosity equivalent to a glass of ∼1012 Pa·s, to nonviscous (∼10-2 Pa·s) tetraethylene glycol particles. The condensation timescales observed in this work indicate that water condensation occurs rapidly at all temperatures examined (<10 s) and for particles of all initial viscosities spanning 10-2 to 1012 Pa·s. Only a marginal delay (<1 order of magnitude) is observed for particles starting as a glass.

14.
Eur J Appl Physiol ; 118(7): 1427-1445, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29721606

RESUMO

Evidence for performance decrements following prolonged static stretching (SS) has led to a paradigm shift in stretching routines within a warm-up. Rather than SS, dynamic stretching (DS) and dynamic activity (DA) have replaced SS within warm-up routines. The objective of the present study was to compare the effect of differing lower limb SS durations (30 [SS30s], 60 [SS60s] or 120 s [SS120s] of SS per muscle group or no-stretch control) within a comprehensive warm-up protocol consisting of aerobic activity, DS and DA. Sixteen male participants completed the four stretching conditions in a randomized order, after a 5-min low-intensity (cycle) warm-up and before a DS/DA component on separate days. Tests included passive hip and knee ranges of motion (ROM), maximum voluntary knee extensor/flexor force, force produced at 100 ms (F100), vertical jump height and evoked knee extensor contractile properties. For hip flexion (hamstrings) ROM, SS120s provided the largest increase (5.6-11.7%) followed by SS60s (4.3-11.4%), control (4.4-10.6%) and SS30s (3.6-11.1%). For knee flexion (quadriceps) ROM, SS30s provided the largest increase (9.3-18.2%) followed by SS120s (6.5-16.3%), SS60s (7.2-15.2%) and control (6.3-15.2%). There were decreases in quadriceps F100 following SS in SS120s (29.6%) only. There were increases in vertical jump performance in the control (6.2%), SS60s (4.6%) and SS30s (3.3%). While 120 s SS per muscle increased ROM, even within a comprehensive warm-up routine, it also elicited notable performance decrements. However, moderate durations of SS were observed to improve ROM whilst either having negligible or beneficial (but not detrimental) effects on specific aspects of athletic performance.


Assuntos
Contração Muscular , Exercícios de Alongamento Muscular/métodos , Músculo Esquelético/fisiologia , Exercício de Aquecimento , Adulto , Quadril/fisiologia , Humanos , Joelho/fisiologia , Masculino , Distribuição Aleatória , Amplitude de Movimento Articular
15.
Phys Chem Chem Phys ; 20(22): 15086-15097, 2018 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-29796502

RESUMO

A Dimer Coagulation, Isolation and Coalescence (DCIC) technique is used to probe the phase behaviour and glass transition temperatures of ternary aerosol mixtures. The DCIC technique is used to perform temperature and relative humidity dependent viscosity measurements at viscosities near 5 × 106 Pa s. Measurements include organic-organic and organic-inorganic mixtures composed of sucrose-citric acid and sucrose-sodium nitrate. The data reported here add additional insight into the wide discrepancies in glass transition temperatures reported for pure sodium nitrate. The phase diagram model used in the work of Rothfuss and Petters (Phys. Chem. Chem. Phys., 2017, 19, 6532-6545) is expanded to include multiple solute components. Data and model predictions of the mixtures are in good agreement with the modified model. These measurements are compared with values from Holographic Optical Tweezer (HOT) measurements taken at room temperature. Overall, the viscosities determined from the DCIC and HOT techniques are in good agreement.

16.
Phys Chem Chem Phys ; 20(22): 15560-15573, 2018 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-29808874

RESUMO

Mass transfer between the gas and condensed phases in aerosols can be limited by slow bulk diffusion within viscous particles. During the heterogeneous and multiphase reactions of viscous organic aerosol particles, it is necessary to consider the interplay of numerous mass transfer processes and how they are impacted by viscosity, including the partitioning kinetics of semi-volatile organic reactants, water and oxidants. To constrain kinetic models of the heterogeneous chemistry, measurements must provide information on as many observables as possible. Here, the ozonolysis of maleic acid (MA) in ternary aerosol particles containing water and sucrose is used as a model system. By varying the mass ratio of sucrose to MA and by performing reactions over a wide range of relative humidity, direct measurements show that the viscosity of the particle can be varied over 7 orders of magnitude. Measurements of the volatilisation kinetics of MA show that this range in viscosity leads to a suppression in the effective vapour pressure of MA of 3-4 orders of magnitude. The inferred values of the diffusion coefficient of MA in the particle phase closely mirror the expected change in diffusion coefficient from the Stokes-Einstein equation and the change in viscosity. The kinetics of ozonolysis show a similar dependence on particle viscosity that can be further investigated using the kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB). Two scenarios, one constraining the diffusion coefficients for MA to those expected based on the Stokes-Einstein equation and the other including the diffusion coefficients as a fit parameter, yield similarly adequate representations of the ozonolysis kinetics, as inferred from the experimental decay in the signature of the vinylic C-H stretching vibration of MA. However, these two scenarios provide very different parameterisations of the compositional dependence of the diffusion coefficients of ozone within the condensed phase, yielding qualitatively different time-dependent internal concentration profiles. We suggest that this highlights the importance of providing additional experimental observables (e.g. particle size, heterogeneity in composition) if measurements and models are to be universally reconciled.

17.
Nat Commun ; 9(1): 956, 2018 03 06.
Artigo em Inglês | MEDLINE | ID: mdl-29511168

RESUMO

The importance of organic aerosol particles in the environment has been long established, influencing cloud formation and lifetime, absorbing and scattering sunlight, affecting atmospheric composition and impacting on human health. Conventionally, ambient organic particles were considered to exist as liquids. Recent observations in field measurements and studies in the laboratory suggest that they may instead exist as highly viscous semi-solids or amorphous glassy solids under certain conditions, with important implications for atmospheric chemistry, climate and air quality. This review explores our understanding of aerosol particle phase, particularly as identified by measurements of the viscosity of organic particles, and the atmospheric implications of phase state.

18.
J Chem Phys ; 147(22): 220901, 2017 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-29246075

RESUMO

Aerosols are found in a wide diversity of contexts and applications, including the atmosphere, pharmaceutics, and industry. Aerosols are dispersions of particles in a gas, and the coupling of the two phases results in highly dynamic systems where chemical and physical properties like size, composition, phase, and refractive index change rapidly in response to environmental perturbations. Aerosol particles span a wide range of sizes from 1 nm to tens of micrometres or from small molecular clusters that may more closely resemble gas phase molecules to large particles that can have similar qualities to bulk materials. However, even large particles with finite volumes exhibit distinct properties from the bulk condensed phase, due in part to their higher surface-to-volume ratio and their ability to easily access supersaturated solute states inaccessible in the bulk. Aerosols represent a major challenge for study because of the facile coupling between the particle and gas, the small amounts of sample available for analysis, and the sheer breadth of operative processes. Time scales of aerosol processes can be as short as nanoseconds or as long as years. Despite their very different impacts and applications, fundamental chemical physics processes serve as a common theme that underpins our understanding of aerosols. This perspective article discusses challenges in the study of aerosols and highlights recent chemical physics advancements that have enabled improved understanding of these complex systems.

19.
Phys Chem Chem Phys ; 19(47): 31634-31646, 2017 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-29164191

RESUMO

The physicochemical changes experienced by organic aerosol particles undergoing dehydration into the surrounding gas phase can be drastic, forcing rapid vitrification of the particle and suppressing internal diffusion. Until recently, experimental studies have concentrated on quantifying diffusional mixing of either water or non-volatile components, while relatively little attention has been paid to the role of semivolatile organic component (SVOC) diffusion and volatilisation in maintaining the equilibrium between the gas and particle phases. Here we present methods to simultaneously investigate diffusivities and volatilities in studies of evolving single ternary aerosol particle size and composition. Analysing particles of ternary composition must account for the multiple chemical species that volatilise in response to a step change in gas phase water activity. In addition, treatments of diffusion in multicomponent mixtures are necessary to represent evolving heterogeneities in particle composition. We find that the contributions to observed size behaviour from volatilisation of water and a SVOC can be decoupled and treated separately. Employing Fickian diffusion modelling, we extract the compositional dependence of the diffusion constant of water and compare the results to recently published parametrisations in binary aerosol particles. The treatment of ideality and activity in each case is discussed, with reference to use in multicomponent core shell models. Meanwhile, the evaporation of an SVOC into an unsaturated gas flow may be treated by Maxwell's equation, with slow diffusional transport manifesting as a suppression in the extracted vapour pressure.

20.
Ther Deliv ; 8(12): 1051-1061, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-29125064

RESUMO

Aerosols are dynamic systems, responding to variations in the surrounding environmental conditions by changing in size, composition and phase. Although, widely used in inhalation therapies, details of the processes occurring on aerosol generation and during inhalation have received little attention. Instead, research has focused on improvements to the formulation of the drug prior to aerosolization and the resulting clinical efficacy of the treatment. Here, we highlight the processes that occur during aerosol generation and inhalation, affecting aerosol disposition when deposited and, potentially, impacting total and regional doses. In particular, we examine the response of aerosol particles to the humid environment of the respiratory tract, considering both the capacity of particles to grow by absorbing moisture and the timescale for condensation to occur. [Formula: see text].


Assuntos
Aerossóis/química , Administração por Inalação , Portadores de Fármacos/química , Humanos , Umidade , Cinética , Pneumopatias/tratamento farmacológico , Tamanho da Partícula , Preparações Farmacêuticas/administração & dosagem , Preparações Farmacêuticas/química
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