Evaporation of alcohol droplets on surfaces in moist air.

Droplets of alcohol-based formulations are common in applications from sanitizing sprays to printing inks. However, our understanding of the drying dynamics of these droplets on surfaces and the influence of ambient humidity is still very limited. Here, we report the drying dynamics of picoliter droplets of isopropyl alcohol deposited on a surface under controlled humidity. Condensation of water vapor in the ambient environment onto alcohol droplets leads to unexpectedly complex drying behavior. As relative humidity (RH) increases, we observed a variety of phenomena including enhanced spreading, nonmonotonic changes in the drying time, the formation of pancake-like shapes that suppress the coffee-ring effect, and the formation of water-rich films around an alcohol-rich drop. We developed a lubrication model that accounts for the coupling between the flow field within the drop, the shape of the drop, and the vapor concentration field. The model reproduces many of the experimentally observed morphological and dynamic features, revealing the presence of unusually large spatial compositional gradients within the evaporating droplet and surface-tension-gradient-driven flows arising from water condensation/evaporation at the surface of the droplet. One unexpected feature from the simulation is that water can evaporate and condense concurrently in different parts of the drop, providing fundamental insights that simpler models based on average fluxes lack. We further observed rim instabilities at higher RH that are well-described by a model based on the Rayleigh-Plateau instability. Our findings have implications for the testing and use of alcohol-based disinfectant sprays and printing inks.

In Situ Self-Assembly of Nanoscale Particles into Macroscale Ordered Monolayers with Enhanced Memory Performance.

In situ fabrication of macroscale ordered monolayers of nanoparticles (NPs) on targeted substrates is highly desirable for precision electronic and optical devices, while it remains a great challenge. In this study, a solution is provided to address this challenge by developing a colloidal ink formulation and employing the direct-ink-writing (DIW) technique, where on-demand delivery of ink at a targeted location and directional evaporation with controllable rate are leveraged to precisely guide the deposition of polystyrene-grafted gold NPs (Au@PS NPs) into a macroscale monolayer with an ordered Au NP array embedded in a PS thin film. A 2D steady-state diffusion-controlled evaporation model, which explains the parameter dependence of the experimental results and gives semiquantitative agreement with the experimental evaporation kinetics is proposed. The ordered monolayer is used as both nanocrystal floating gates and the tunneling layer for nonvolatile memory devices. It shows significantly enhanced performance compared with a disordered NP film prepared by spin coating. This approach allows for fine control of NP self-assembly to print macroscaleordered monolayers directly onto substrates, which has great promise for application in broad fields, including microelectronic and photoelectronic devices, sensors, and functional coatings.

Evaporation of Binary-Mixture Liquid Droplets: The Formation of Picoliter Pancakelike Shapes.

Small multicomponent droplets are of increasing importance in a plethora of technological applications ranging from the fabrication of self-assembled hierarchical patterns to the design of autonomous fluidic systems. While often far away from equilibrium, involving complex and even chaotic flow fields, it is commonly assumed that in these systems with small drops surface tension keeps the shapes spherical. Here, studying picoliter volatile binary-mixture droplets of isopropanol and 2-butanol, we show that the dominance of surface tension forces at small scales can play a dual role: Minute variations in surface tension along the interface can create Marangoni flows that are strong enough to significantly deform the drop, forming micron-thick pancakelike shapes that are otherwise typical of large puddles. We identify the conditions under which these flattened shapes form and explain why, universally, they relax back to a spherical-cap shape toward the end of drop lifetime. We further show that the formation of pancakelike droplets suppresses the "coffee-ring" effect and leads to uniform deposition of suspended particles. The quantitative agreement between theory and experiment provides a predictive capability to modulate the shape of tiny droplets with implications in a range of technologies from fabrication of miniature optical lenses to coating, printing, and pattern deposition.

Wetting and Drying of Aqueous Droplets Containing Nonionic Surfactants CnEm.

This paper presents a systematic study of the wetting and drying of aqueous pico-liter droplets containing nonionic surfactants polyoxyethylene alkyl ethers (CnEm; n = 10, 12, 14, m = 6 or 8) in comparison with the anionic surfactant sodium dodecyl sulfate (SDS). The spreading and drying of droplets on hydrophilic substrates were studied by tracking the three-phase contact line (TCL) and by interferometry. CnEm droplets undergo phase separation during drying: a water-rich droplet retracts and leaves behind a thin film that is postulated to be a surfactant mesophase. This thin film either retracts or breaks up into small droplets on a longer time scale. The receding contact angle of the water-rich droplet on the thin film in the late stage of drying of CnEm droplets is independent of hydrophobicity of substrates, supporting the inference that a mesophase is present on the surface. Both CnEm and SDS solutions inhibit spreading on hydrophilic surfaces, which is attributed to Marangoni contraction as a result of a surface tension gradient across the gas-liquid interface. More pronounced suppression of spreading is observed in the case of CnEm solutions, possibly due to the phase transition of surfactant solution in the vicinity of the initial TCL leading to a viscous phase at the TCL that pins the droplet. Tracer particle measurements reveal that mild Marangoni flows exist for droplets with surfactant concentrations well above the critical micelle concentration (CMC). Origins of the surfactant gradients that result in Marangoni flows are discussed.

Viral etiology and epidemiology of pediatric patients hospitalized for acute respiratory tract infections in Macao: a retrospective study from 2014 to 2017.

BACKGROUND: Acute respiratory infections (ARIs) are among the leading causes of hospitalization in children. Understanding the local dominant viral etiologies is important to inform infection control practices and clinical management. This study aimed to investigate the viral etiology and epidemiology of respiratory infections among pediatric inpatients in Macao. METHODS: A retrospective study using electronic health records between 2014 and 2017 at Kiang Wu Hospital was performed. Nasopharyngeal swab specimens were obtained from hospitalized children aged 13 years or younger with respiratory tract diseases. xMAP multiplex assays were employed to detect respiratory agents including 10 respiratory viruses. Data were analyzed to describe the frequency and seasonality. RESULTS: Of the 4880 children enrolled in the study, 3767 (77.1%) were positive for at least one of the 13 viral pathogens tested, of which 2707 (55.5%) being male and 2635 (70.0%) under 2 years old. Among the positive results, there were 3091 (82.0%) single infections and 676 (18.0%) multiple infections. The predominant viruses included human rhinovirus/enterovirus (HRV/EV 27.4%), adenovirus (ADV, 15.8%), respiratory syncytial virus B (RSVB, 7.8%) and respiratory syncytial virus A (RSVA, 7.8%). The detection of viral infection was the most prevalent in autumn (960/1176, 81.6%), followed by spring (1095/1406, 77.9%), winter (768/992, 77.4%), and summer (944/1306, 72.3%), with HRV/EV and ADV being most commonly detected throughout the 4 years of study period. The detection rate of viral infection was highest among ARI patients presented with croup (123/141, 87.2%), followed by lower respiratory tract infection (1924/2356, 81.7%) and upper respiratory tract infection (1720/2383, 72.2%). FluA, FluB and ADV were positive factors for upper respiratory tract infections. On the other hand, infection with RSVA, RSVB, PIV3, PIV4, HMPV, and EV/RHV were positively associated with lower respiratory tract infections; and PIV1, PIV2, and PIV3 were positively associated with croup. CONCLUSIONS: This is the first study in Macao to determine the viral etiology and epidemiology of pediatric patients hospitalized for ARIs. The study findings can contribute to the awareness of pathogen, appropriate preventative measure, accurate diagnosis, and proper clinical management of respiratory viral infections among children in Macao.

Drug Utilization for Pain Management during Perioperative Period of Total Knee Arthroplasty in China: A Retrospective Research Using Real-World Data.

Background and Objective: Total knee arthroplasty (TKA) is one of the most painful procedures and perioperative pain usually requires the use of many analgesics to relieve it. The appropriate use of analgesics to relieve patient pain is an important issue of TKA. To characterize the drug utilization for pain management during perioperative period of TKA in China using real-world data of electronic medical records. Materials and Methods: This research used the data of all inpatients who received TKA at 145 hospitals covered 31 provinces in China from 1 January 2016 to 31 December 2018. The exclusion criteria included pregnancy and cancer diagnosis. In the analysis of drug utilization mode (DUM), medicines were classified into 5 groups: non-steroidal anti-inflammatory drugs (NSAIDs), opioids, non-opioid central analgesics, acetaminophen and others. Results: Among the 2017 patients included in this study, there were 1537 (76.20%) female and 480 (23.80%) male, aged 65.77 ± 7.73 years. Regarding the surgery characteristics, 1658 (82.20%) were unilateral; 1220 (60.49%) was graded Level 4; 1312 (65.05%) used local anesthesia as the main anesthesia method, and 1450 (71.89%) lasted for more than 2 h. The most common DUM was "NSAIDs + opioids" (55.92%), followed by "NSAIDs only" (17.85%), and "NSAIDs + Opioids + Non-opioid central analgesics" (17.15%). The results of the Chi-square test showed that differences in DUM were associated with surgery types, surgery levels, surgery duration, and types of anesthesia used. Up to 81.14% of the total drug expenses for pain management was spent on NSAIDs. Due to the limitation of database, this study could not subdivide operation stages, anesthesia methods, dosage forms of drugs. Conclusion: In China, the use of analgesics in perioperative period of TKA was diversified and influenced by a number of surgery characteristics. The rational use of analgesics should be considered in combination with surgery type, surgery level, surgery duration and anesthesia method.

Rad18 confers hematopoietic progenitor cell DNA damage tolerance independently of the Fanconi Anemia pathway in vivo.

In cultured cancer cells the E3 ubiquitin ligase Rad18 activates Trans-Lesion Synthesis (TLS) and the Fanconi Anemia (FA) pathway. However, physiological roles of Rad18 in DNA damage tolerance and carcinogenesis are unknown and were investigated here. Primary hematopoietic stem and progenitor cells (HSPC) co-expressed RAD18 and FANCD2 proteins, potentially consistent with a role for Rad18 in FA pathway function during hematopoiesis. However, hematopoietic defects typically associated with fanc-deficiency (decreased HSPC numbers, reduced engraftment potential of HSPC, and Mitomycin C (MMC) -sensitive hematopoiesis), were absent in Rad18(-/-) mice. Moreover, primary Rad18(-/-) mouse embryonic fibroblasts (MEF) retained robust Fancd2 mono-ubiquitination following MMC treatment. Therefore, Rad18 is dispensable for FA pathway activation in untransformed cells and the Rad18 and FA pathways are separable in hematopoietic cells. In contrast with responses to crosslinking agents, Rad18(-/-) HSPC were sensitive to in vivo treatment with the myelosuppressive agent 7,12 Dimethylbenz[a]anthracene (DMBA). Rad18-deficient fibroblasts aberrantly accumulated DNA damage markers after DMBA treatment. Moreover, in vivo DMBA treatment led to increased incidence of B cell malignancy in Rad18(-/-) mice. These results identify novel hematopoietic functions for Rad18 and provide the first demonstration that Rad18 confers DNA damage tolerance and tumor-suppression in a physiological setting.

Monocytes from Irf5-/- mice have an intrinsic defect in their response to pristane-induced lupus.

The transcription factor IFN regulatory factor (IRF)5 has been identified as a human systemic lupus erythematosus (SLE) susceptibility gene by numerous joint linkage and genome-wide association studies. Although IRF5 expression is significantly elevated in primary blood cells of SLE patients, it is not yet known how IRF5 contributes to SLE pathogenesis. Recent data from mouse models of lupus indicate a critical role for IRF5 in the production of pathogenic autoantibodies and the expression of Th2 cytokines and type I IFN. In the present study, we examined the mechanisms by which loss of Irf5 protects mice from pristane-induced lupus at early time points of disease development. We demonstrate that Irf5 is required for Ly6C(hi) monocyte trafficking to the peritoneal cavity, which is thought to be one of the initial key events leading to lupus pathogenesis in this model. Chemotaxis assays using peritoneal lavage from pristane-injected Irf5(+/+) and Irf5(-/-) littermates support an intrinsic defect in Irf5(-/-) monocytes. We found the expression of chemokine receptors CXCR4 and CCR2 to be dysregulated on Irf5(-/-) monocytes and less responsive to their respective ligands, CXCL12 and CCL2. Bone marrow reconstitution experiments further supported an intrinsic defect in Irf5(-/-) monocytes because Irf5(+/+) monocytes were preferentially recruited to the peritoneal cavity in response to pristane. Taken together, these findings demonstrate an intrinsic role for IRF5 in the response of monocytes to pristane and their recruitment to the primary site of inflammation that is thought to trigger lupus onset in this experimental model of SLE.

Orthogonal printing of uniform nanocomposite monolayer and oriented organic semiconductor crystals for high-performance nano-crystal floating gate memory.

Inkjet printing is of great interest in the preparation of optoelectronic and microelectronic devices due to its low cost, low process temperature, versatile material compatibility, and ability to precisely manufacture multi-layer devices on demand. However, interlayer solvent erosion is a typical problem that limits the printing of organic semiconductor devices with multi-layer structures. In this study, we proposed a solution to address this erosion problem by designing polystyrene-block-poly(4-vinyl pyridine)-grafted Au nanoparticles (Au@PS-b-P4VP NPs). With a colloidal ink containing the Au@PS-b-P4VP NPs, we obtained a uniform monolayer of Au nano-crystal floating gates (NCFGs) embedded in the PS-b-P4VP tunneling dielectric (TD) layer using direct-ink-writing (DIW). Significantly, PS-b-P4VP has high erosion resistance against the semiconductor ink solvent, which enables multi-layer printing. An active layer of semiconductor crystals with high crystallinity and well-orientation was obtained by DIW. Moreover, we developed a strategy to improve the quality of the TD/semiconductor interface by introducing a polystyrene intermediate layer. We show that the NCFG memory devices exhibit a low threshold voltage (<3 V), large memory window (66 V), stable endurance (>100 cycles), and long-term retention (>10 years). This study provides universal guidance for printing functional coatings and multi-layer devices.

Irf5-deficient mice are protected from pristane-induced lupus via increased Th2 cytokines and altered IgG class switching.

Polymorphisms in the transcription factor interferon (IFN) regulatory factor 5 (IRF5) have been identified that show a strong association with an increased risk of developing the autoimmune disease systemic lupus erythematosus (SLE). A potential pathological role for IRF5 in SLE development is supported by the fact that increased IRF5 mRNA and protein are observed in primary blood cells of SLE patients and this correlates with an increased risk of developing the disease. Here, we demonstrate that IRF5 is required for pristane-induced SLE via its ability to control multiple facets of autoimmunity. We show that IRF5 is required for pathological hypergammaglobulinemia and, in the absence of IRF5, IgG class switching is reduced. Examination of in vivo cytokine expression (and autoantibody production) identified an increase in Irf5(-/-) mice of Th2 cytokines. In addition, we provide clear evidence that loss of Irf5 significantly weakens the in vivo type I IFN signature critical for disease pathogenesis in this model of murine lupus. Together, these findings demonstrate the importance of IRF5 for autoimmunity and provide a significant new insight into how overexpression of IRF5 in blood cells of SLE patients may contribute to disease pathogenesis.

Interferon regulatory factor 5 activation in monocytes of systemic lupus erythematosus patients is triggered by circulating autoantigens independent of type I interferons.

OBJECTIVE: Genetic variants of interferon regulatory factor 5 (IRF-5) are associated with susceptibility to systemic lupus erythematosus (SLE). IRF-5 regulates the expression of proinflammatory cytokines and type I interferons (IFNs) believed to be involved in the pathogenesis of SLE. The aim of this study was to determine the activation status of IRF-5 by assessing its nuclear localization in the immune cells of SLE patients and healthy donors, and to identify SLE-associated triggers of IRF-5 activation. METHODS: IRF-5 nuclear localization in subpopulations of peripheral blood mononuclear cells from 14 genotyped SLE patients and 11 healthy controls was assessed using imaging flow cytometry. The activation and function of IRF-5 were examined after ex vivo stimulation of healthy donor monocytes with SLE serum or components of SLE serum. Cellular localization was determined by ImageStream flow cytometry, and cytokine expression was analyzed by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. RESULTS: IRF-5 was activated in a cell type-specific manner; monocytes from SLE patients had constitutively elevated levels of nuclear IRF-5, as compared to natural killer cells and T cells. SLE serum was identified as a trigger for IRF-5 nuclear accumulation; however, neither IFNα nor SLE immune complexes could induce nuclear localization. Instead, autoantigens composed of apoptotic/necrotic material triggered IRF-5 nuclear accumulation in monocytes. Production of the cytokines IFNα, tumor necrosis factor α, and interleukin-6 in monocytes stimulated with SLE serum or autoantigens was distinct, yet showed a correlation with the kinetics of IRF-5 nuclear localization. CONCLUSION: This study provides the first formal proof that IRF-5 activation is altered in the monocytes of SLE patients, which can be attributed, in part, to the SLE blood environment.

Entinostat, a class I selective histone deacetylase inhibitor, plus exemestane for Chinese patients with hormone receptor-positive advanced breast cancer: A multicenter, randomized, double-blind, placebo-controlled, phase 3 trial.

Entinostat plus exemestane in hormone receptor-positive (HR+) advanced breast cancer (ABC) previously showed encouraging outcomes. This multicenter phase 3 trial evaluated the efficacy and safety of entinostat plus exemestane in Chinese patients with HR + ABC that relapsed/progressed after ≥1 endocrine therapy. Patients were randomized (2:1) to oral exemestane 25 mg/day plus entinostat (n = 235) or placebo (n = 119) 5 mg/week in 28-day cycles. The primary endpoint was the independent radiographic committee (IRC)-assessed progression-free survival (PFS). The median age was 52 (range, 28-75) years and 222 (62.7%) patients were postmenopausal. CDK4/6 inhibitors and fulvestrant were previously used in 23 (6.5%) and 92 (26.0%) patients, respectively. The baseline characteristics were comparable between the entinostat and placebo groups. The median PFS was 6.32 (95% CI, 5.30-9.11) and 3.72 (95% CI, 1.91-5.49) months in the entinostat and placebo groups (HR, 0.76; 95% CI, 0.58-0.98; P = 0.046), respectively. Grade ≥3 adverse events (AEs) occurred in 154 (65.5%) patients in the entinostat group versus 23 (19.3%) in the placebo group, and the most common grade ≥3 treatment-related AEs were neutropenia [103 (43.8%)], thrombocytopenia [20 (8.5%)], and leucopenia [15 (6.4%)]. Entinostat plus exemestane significantly improved PFS compared with exemestane, with generally manageable toxicities in HR + ABC (ClinicalTrials.gov #NCT03538171).

The cost-effectiveness of once-weekly semaglutide compared with other GLP-1 receptor agonists in type 2 Diabetes: a systematic literature review.

Introduction: As a novel glucagon-like peptide-1receptor agonist (GLP-1 RA) for type 2 diabetes (T2D) treatment, the economic value of once-weekly semaglutide had been assessed in several country settings. The authors' objective was to systematically review the existing pharmacoeconomic literature evaluating the cost-effectiveness associated with once-weekly semaglutide compared with other GLP-1 RAs and provide implications for further researches.Areas covered: We conducted a systematic literature review of cost-effectiveness analysis (CEA) published up to 25 July 2020 in PubMed, web of science, and the ISPOR presentation database, compared once-weekly semaglutide with other GLP-1 RAs in T2D. Nineteen studies were identified, including 8 short-term and 11 long-term studies. General characteristics and main results of the included studies were summarized.Expert opinion: This review provided references for other countries to overview the value of once-weekly semaglutide compared with other GLP-1 RAs in T2D in the healthcare decision-making process and to conduct their CEA studies associated with once-weekly semaglutide. The authors found that the cardiovascular (CV) benefit of once-weekly semaglutide was under-estimated in current studies and suggested that the methods of economic evaluations for novel anti-diabetic drugs with CV benefit should be improved in future researches.

Clinical and Economic Evaluation of Salvianolate Injection for Coronary Heart Disease: A Retrospective Study Based on National Health Insurance Data in China.

OBJECTIVE: The study aimed to conduct clinical and economic evaluation of salvianolate injection for patients with coronary heart disease (CHD) in comparison to Danhong injection and alprostadil injection. METHOD: This was a retrospective study using National Health Insurance Data about inpatients diagnosed with CHD in China in 2015 who met the inclusion criteria. The recruited patients were divided into two samples: surgery and non-surgery. The exposed group received salvianolate injection, while the control group received either alprostadil injection or Danhong injection. The medical cost per hospitalization, hospitalization duration, and the rehospitalization rates were used as outcome indicators. Heterogeneity was processed according to disease stratification. Propensity score matching and multivariate analysis were used for statistical analysis to control potential confounding factors. RESULTS: The hospitalization duration of salvianolate injection group was significantly (P < 0.05) shorter than that of Danhong injection group in the non-surgery sample. The hospitalization duration of salvianolate injection group was significantly (P < 0.05) shorter than those of alprostadil injection group in both surgery and non-surgery samples. In the non-surgery sample, the medical cost per hospitalization of salvianolate injection group was significantly (P < 0.05) lower than that of alprostadil injection group. However, there were no statistical differences of rehospitalization rates in salvianolate injection group versus alprostadil injection group or salvianolate injection group versus Danhong injection group in both surgery and non-surgery samples. CONCLUSION: Salvianolate injection showed advantages in reducing hospitalization duration for inpatients with CHD when comparing with alprostadil injection and Danhong injection. The results of this real-world study can help to inform clinical practice for CHD patients.

A general ink formulation of 2D crystals for wafer-scale inkjet printing.

Recent advances in inkjet printing of two-dimensional (2D) crystals show great promise for next-generation printed electronics development. Printing nonuniformity, however, results in poor reproducibility in device performance and remains a major impediment to their large-scale manufacturing. At the heart of this challenge lies the coffee-ring effect (CRE), ring-shaped nonuniform deposits formed during postdeposition drying. We present an experimental study of the drying mechanism of a binary solvent ink formulation. We show that Marangoni-enhanced spreading in this formulation inhibits contact line pinning and deforms the droplet shape to naturally suppress the capillary flows that give rise to the CRE. This general formulation supports uniform deposition of 2D crystals and their derivatives, enabling scalable and even wafer-scale device fabrication, moving them closer to industrial-level additive manufacturing.

Drying of Ethanol/Water Droplets Containing Silica Nanoparticles.

The evaporation of colloidal drop on a substrate with a pinned contact line usually results in a ring stain (the so-called coffee-ring effect). In this paper, we present an investigation of the evaporation of sessile picoliter droplets of binary solvent mixtures containing fumed silica nanoparticles (NPs). The internal flows in ethanol/water droplets are suppressed, and a uniform deposit morphology is achieved with a low loading (0.2-0.5 vol %) of hydrophobic fumed silica NPs. The effective control of the particle deposit morphology is based on a rapid sol-gel transition assisted by preferential evaporation of ethanol. For droplets of dilute suspensions, the fumed silica NPs tend to agglomerate and form an elastic network quickly, starting from the region close to the three-phase contact line and below the gas-liquid interface and growing toward the interior of the droplet as the solvents evaporate and the surface descends. Higher silica particle concentrations, lower ethanol concentrations, and weaker Marangoni flows all contribute to the sol-gel transition and hence to the suppression of the coffee-ring effect.

In Situ Fabrication of Polymeric Microcapsules by Ink-Jet Printing of Emulsions.

Phase separation driven by solvent evaporation of emulsions can be used to create polymeric microcapsules. The combination of emulsion solvent evaporation with ink-jet printing allows the rapid fabrication of polymeric microcapsules at a target location on a surface. The ink is an oil-in-water emulsion containing in the dispersed phase a shell-forming polymer, a core-forming fluid that is a poor solvent for the polymer, and a low-boiling good solvent. After the emulsion is printed onto the substrate, the good solvent evaporates by diffusion through the aqueous phase, and the polymer and the poor solvent phase separate to form microcapsules. The continuous aqueous phase contains polyvinyl alcohol that serves as an emulsifier and a binder of the capsules to the substrate. This method is demonstrated for microcapsules with various shell-forming polymers (polystyrene, poly(methylmethacrylate) and poly(l-lactide)) and core-forming poor solvents (hexadecane and a 4-heptanone/sunflower oil mixture). Cargoes such as fluorescent dyes (Nile Red and tetracyanoquinodimethane) or active ingredients (e.g., the fungicide tebuconazole) can be encapsulated. Uniform microcapsules are obtained by printing emulsions containing monodisperse oil droplets produced in a microfluidic device. We discuss the physical parameters that need to be controlled for the successful fabrication of microcapsules in inkjet printing. The method for rapid, in situ encapsulation could be useful for controlled-release applications such as in agrochemical sprays, fragrances, functional coatings, and topical medicines.

Fabrication of monolayers of uniform polymeric particles by inkjet printing of monodisperse emulsions produced by microfluidics.

Emulsion solvent evaporation is a well-established method for generating microparticles from solutions of polymers in volatile organic solvents dispersed in an aqueous medium. Previous work has shown that this approach can also be used to deposit particles by inkjet printing where the particles are formed during the drying of a liquid ink on a substrate. The particle size distribution, however, was very broad. Here we demonstrate that inkjet printing of oil-in-water emulsions produced by microfluidics can generate micron-sized particles with a narrow size distribution (coefficient of variation <6%) and that these particles can self-assemble into ordered arrays with hexagonal packing. The conditions under which drops can be printed with a minimum of break up and coalescence of the oil droplets in the emulsion are explored. Factors affecting the size of the particles and the morphology of the deposit are described. This study uses polystyrene in dichloromethane as a model system, but the approach can be generalized to the production of structured and functional particles.

Combining Inkjet Printing with Emulsion Solvent Evaporation to Pattern Polymeric Particles.

We demonstrate a concept to produce deposits of polymer in the form of particles by inkjet printing an emulsion in which the discrete phase evaporates preferentially. An oil/water emulsion with polymer contained inside the oil phase is used as ink for printing. Circular deposits of spherical polymer particles with uniform thickness are obtained. The effects of the hydrophobicity of substrates and the physical properties of the oil on the morphology of the deposits are explored. The deposit of aggregated polymeric particles can be transformed into a uniform film by annealing if required. This strategy for the patterning of polymer materials in the form of either particles or a film works for mixtures of polymers and functional cargoes.

Printing small dots from large drops.

Printing of droplets of pure solvents containing suspended solids typically leads to a ring stain due to convective transport of the particles toward the contact line during evaporation of the solvent. In mixtures of volatile solvents, recirculating cells driven by surface tension gradients are established that lead to migration of colloidal particles toward the center of the droplet. In favorable cases, a dense disk of particles forms with a diameter much smaller than that of the droplet. In the latter stages of drying, convective transport of the particles radially toward the contact line still occurs. Two strategies are described to fix the distribution of particles in a compact disk much smaller than the initial diameter of the drying droplet. First, a nanoparticulate clay is added to induce an evaporation-driven sol-gel transition that inhibits convective flow during the latter stages of drying. Second, a nonadsorbing polymer is added to induce depletion flocculation that restricts particle motion after the particles have been concentrated near the center of the droplet. The area of the resulting deposit can be as little as 10% of the footprint of the printed droplet.