RESUMO
The generation and control of heat transport with nanoparticles is an essential objective of thermoplasmonics. Janus nanoparticles consisting of dissimilar materials with contrasting interfacial Kapitza conductance provide a route to control heat transport at the nanoscale. Here we use the recently introduced Atomistic Nodal Approach to map the surface temperature and Kapitza conductance of Janus nanoparticles to individual atoms. We show that the transition in the thermal transport properties between the hydrophobic and hydrophilic interfaces is exceptionally abrupt, occurring over length scales below 1 nm. We demonstrate the generality of this result using coarse-grained and all-atom models of gold nanoparticles. Further, we show how this behaviour provides a route to sustain significant temperature differences, on the order of tens of degrees for µW heat rates, between adjacent molecular layers attached to heated gold nanoparticles. Our work provides fundamental insight into nanoscale heat transport and a principle to design heterogeneous Janus nanoparticles for thermal transport applications.
Assuntos
Nanopartículas Metálicas , Nanopartículas Multifuncionais , Tetranitrato de Pentaeritritol , Ouro , Temperatura AltaRESUMO
Cadmium (Cd) and mercury (Hg) are ubiquitous soil pollutants that promote the accumulation of reactive oxygen species, causing oxidative stress. Tolerance depends on signalling processes that activate different defence barriers, such as accumulation of small heat sock proteins (sHSPs), activation of antioxidant enzymes, and the synthesis of phytochelatins (PCs) from the fundamental antioxidant peptide glutathione (GSH), which is probably modulated by ethylene. We studied the early responses of alfalfa seedlings after short exposure (3, 6, and 24 h) to moderate to severe concentration of Cd and Hg (ranging from 3 to 30 µM), to characterize in detail several oxidative stress parameters and biothiol (i.e., GSH and PCs) accumulation, in combination with the ethylene signalling blocker 1-methylcyclopropene (1-MCP). Most changes occurred in roots of alfalfa, with strong induction of cellular oxidative stress, H2O2 generation, and a quick accumulation of sHSPs 17.6 and 17.7. Mercury caused the specific inhibition of glutathione reductase activity, while both metals led to the accumulation of PCs. These responses were attenuated in seedlings incubated with 1-MCP. Interestingly, 1-MCP also decreased the amount of PCs and homophytochelatins generated under metal stress, implying that the overall early response to metals was controlled at least partially by ethylene.
RESUMO
METHODS: A prospective quasi-experimental study to implement an ASP in a LTCF. Antibiotic prescriptions for suspected infections initiated in any setting for LTCF residents were included. We assessed appropriateness and prospective audits and feedback of each inappropriate antimicrobial prescription were carried out. Associations of variables with appropriate antibiotic prescribing were estimated using logistic regression. RESULTS: A total of 416 antibiotic prescriptions were included. The mean consumption of antibiotics was reduced from 63.2 defined daily doses per 1000 residents days (DRD) in the preintervention period to 22.8 in the intervention period (- 63.8%), with a significant drop in fluoroquinolones (81.4%). Overall, 46.6% of antibiotic prescriptions were judged inappropriate, mainly because of a use not recommended in treatment guidelines (63.2%). Multivariable analysis showed that empirical therapy, some classes of antibiotics (cephalosporins, fluoroquinolones, fosfomycin calcium, macrolides) and prescription initiation in the emergency department were independent predictors of antimicrobial inappropriateness. CONCLUSIONS: Pharmacist-led ASP in a LTCF has being effective in reducing consumption of antibiotics by improving appropriateness of treatment decisions. However, ASP should include interventions in the emergency department because of the high inappropriate use in this setting.
Assuntos
Anti-Infecciosos , Gestão de Antimicrobianos , Humanos , Farmacêuticos , Assistência de Longa Duração , Antibacterianos/uso terapêutico , Anti-Infecciosos/uso terapêutico , Fluoroquinolonas/uso terapêuticoRESUMO
Phages are viruses that infect bacteria, relying on their genetic machinery to replicate. To survive the constant attack of phages, bacteria have developed diverse defense strategies to act against them. Nevertheless, phages rapidly co-evolve to overcome these barriers, resulting in a constant, and often surprising, molecular arms race. Thus, some phages have evolved protein inhibitors known as anti-CRISPRs (â¼50-150 amino acids), which antagonize the bacterial CRISPR-Cas immune response. To date, around 45 anti-CRISPRs proteins with different mechanisms and structures have been discovered against the CRISPR-Cas type I and type II present in important animal and human pathogens such as Escherichia, Morganella, Klebsiella, Enterococcus, Pseudomonas, Staphylococcus, and Salmonella. Considering the alarming growth of antibiotic resistance, phage therapy, either alone or in combination with antibiotics, appears to be a promising alternative for the treatment of many bacterial infections. In this review, we illustrated the biological and clinical aspects of using phage therapy; furthermore, the CRISPR-Cas mechanism, and the interesting activity of anti-CRISPR proteins as a possible weapon to combat bacteria.
Assuntos
Bacteriófagos , Humanos , Bacteriófagos/genética , Sistemas CRISPR-Cas , Bactérias/genética , Proteínas Virais/genética , Proteínas Virais/metabolismoRESUMO
Thermal fields provide a route to control the motion of nanoparticles and molecules and potentially modify the behaviour of soft matter systems. Janus nanoparticles have emerged as versatile building blocks for the self-assembly of materials with novel properties. Here we investigate using non-equilibrium molecular dynamics simulations the behaviour of coarse-grained models of Janus nanoparticles under thermal fields. We examine the role of the heterogeneous structure of the particle on the Soret coefficient and thermal orientation by studying particles with different internal structures, mass distribution, and particle-solvent interactions. We also examine the thermophoretic response with temperature, targeting liquid and supercritical states and near-critical conditions. We find evidence for a significant enhancement of the Soret coefficient near the critical point, leading to the complete alignment of a Janus particle in the thermal field. This behaviour can be modelled and rationalized using a theory that describes the thermal orientation with the nanoparticle Soret coefficient, the mass and interaction anisotropy of the Janus nanoparticle, and the thermal field's strength. Our simulations show that the mass anisotropy plays a crucial role in driving the thermal orientation of the Janus nanoparticles.
Assuntos
Nanopartículas Multifuncionais , Nanopartículas , Simulação de Dinâmica Molecular , Movimento (Física) , Nanopartículas/química , TemperaturaRESUMO
Interfacial thermal conductance (ITC) quantifies heat transport across material-fluid interfaces. It is a property of crucial importance to study heat transfer processes at both macro- and nanoscales. Therefore, it is essential to accurately model the specific interactions between solids and liquids. Here, we investigate the thermal conductance of gold-water interfaces using polarizable and non-polarizable models. Both models have been fitted to reproduce the interfacial tension of the gold-water interface, but they predict significantly different ITCs. We demonstrate that the treatment of polarization using Drude-like models, widely employed in molecular simulations, leads to a coupling of the solid and liquid vibrational modes that give rise to a significant overestimation of the ITCs. We analyze the dependence of the vibrational coupling with the mass of the Drude particle and propose a solution to the artificial enhancement of the ITC, preserving at the same time the polarization response of the solid. Based on our calculations, we estimate ITCs of 200 MW/(m2 K) for the water-gold interface. This magnitude is comparable to that reported recently for gold-water interfaces [279 ± 16 MW/(m2 K)] using atomic fluctuating charges to account for the polarization contribution.
RESUMO
High refractive index (HRI) dielectric nanostructures offer a versatile platform to control the light-matter interaction at the nanoscale as they can easily support electric and magnetic modes with low losses. An additional property that makes them extraordinary is that they can support low radiative modes, so-called anapole modes. In this work, we propose a spectrally tunable anapole nanoheater based on the use of a dielectric anapole resonator. We show that a gold ring nanostructure, a priori nonresonant, can be turned into a resonant unit by just filling its hole with an HRI material supporting anapole modes, resulting in a more efficient nanoheater able to amplify the photothermal response of the bare nanoring. As proof of concept, we perform a detailed study of the thermoplasmonic response of a gold nanoring used as heating source and a silicon disk, designed to support anapole modes, located in its center acting as an anapolar resonator. Furthermore, we utilize the anapole excitation to easily shift the thermal response of these structures from the shortwave infrared range to the near-infrared range.
RESUMO
Pharmacists may be tasked to lead antibiotic stewardship programmes (ASP) implementation in small hospitals in absence of infectious diseases (ID) physicians. The objectives are to evaluate the effectiveness of a pharmacist-led ASP in a hospital without ID physician support, with special focus on indicators of the hospital use of antimicrobial agents based on consumption and asess the potential clinical and economic impact of pharmacist interventions (PIs) through the CLEO tool. A prospective quasi-experimental study to implement an ASP in a 194-bed hospital. We evaluated changes in antimicrobial use measured as mean defined daily doses per 1000 patient-days (AUD) for intervention versus preintervention period. A total of 847 antimicrobial PIs were proposed, being 88.3% accepted. Discontinuation due to excessive duration was the most frequently performed PI (23.4%). Most of PIs was classified as major or moderate clinical impact, 41.7% and 37.8% respectively. The global consumption of antimicrobial was reduced from 907.1 to 693.8 AUD, with a signifcant drop in carbapenems and quinolones. Direct expenditure of antibiotics decreased significantly. Pharmacist-led ASP has being effective in reducing consumption of antibiotics. In the absence of ID physician´s support and oversight, pharmacists could lead the improvement of the use of antimicrobials.
Assuntos
Anti-Infecciosos , Gestão de Antimicrobianos , Doenças Transmissíveis , Médicos , Antibacterianos/uso terapêutico , Anti-Infecciosos/uso terapêutico , Doenças Transmissíveis/tratamento farmacológico , Hospitais , Humanos , Farmacêuticos , Estudos ProspectivosRESUMO
The Interfacial Thermal Conductance (ITC) is a fundamental property of materials and has particular relevance at the nanoscale. The ITC quantifies the thermal resistance between materials of different compositions or between fluids in contact with materials. Furthermore, the ITC determines the rate of cooling/heating of the materials and the temperature drop across the interface. Here, we propose a method to compute local ITCs and temperature drops of nanoparticle-fluid interfaces. Our approach resolves the ITC at the atomic level using the atomic coordinates of the nanomaterial as nodes to compute local thermal transport properties. We obtain high-resolution descriptions of the interfacial thermal transport by combining the atomistic nodal approach, computational geometry techniques, and "computational farming" using non-equilibrium molecular dynamics simulations. We use our method to investigate the ITC of nanoparticle-fluid interfaces as a function of the nanoparticle size and geometry, targeting experimentally relevant structures of gold nanoparticles: capped octagonal rods, cuboctahedrons, decahedrons, rhombic dodecahedrons, cubes, icosahedrons, truncated octahedrons, octahedrons, and spheres. We show that the ITC of these very different geometries varies significantly in different regions of the nanoparticle, increasing generally in the order face < edge < vertex. We show that the ITC of these complex geometries can be accurately described in terms of the local coordination number of the atoms in the nanoparticle surface. Nanoparticle geometries with lower surface coordination numbers feature higher ITCs, and the ITC generally increases with the decreasing particle size.
RESUMO
Janus nanoparticles (JNPs) feature heterogeneous compositions, bringing opportunities in technological and medical applications. We introduce a theoretical approach based on nonequilibrium molecular dynamics simulations and heat transfer continuum theory to investigate the temperature fields generated around heated spherical JNPs covering a wide range of particle sizes, from a few nm to 100 nm. We assess the performance of these nanoparticles to generate anisotropic heating at the nanoscale. We demonstrate that the contrasting interfacial thermal conductances of the fluid-material interfaces arising from the heterogeneous composition of the JNPs can be exploited to control the thermal fields around the nanoparticle, leading to a temperature difference between both sides of the nanoparticle (temperature contrast) that is significant for particles comprising regions with disparate hydrophilicity. We illustrate this idea using coarse-grained and atomistic models of gold nanoparticles with hydrophobic and hydrophilic coatings, in water. Furthermore, we introduce a continuum model to predict the temperature contrast as a function of the interfacial thermal conductance and nanoparticle size. We further show that, unlike homogeneous nanoparticles, the interfacial fluid temperature depends on the interfacial thermal conductance of Janus nanoparticles.
RESUMO
Antimicrobials are the most frequently prescribed drugs in long-term care facilities (LTCF). Antibiotic stewardship programs (ASP) are coordinated interventions promoting the responsible use of antibiotics to improve patient outcomes and reduce antibiotic resistant bacterias. The objectives are to evaluate the effectiveness of a pharmacist-led ASP in a LTCF, to characterise antibiotic therapy and assess the appropriateness of antibiotic prescriptions. A prospective quasi-experimental study to implement an ASP in a LTCF. Antibiotic prescriptions for suspected infections initiated in any setting for LTCF residents were included. We assessed appropriateness and prospective audits and feedback of each inappropriate antimicrobial prescription were carried out. Associations of variables with appropriate antibiotic prescribing were estimated using logistic regression. A total of 416 antibiotic prescriptions were included. The mean consumption of antibiotics was reduced from 63.2 defined daily doses per 1000 residents-days (DRD) in the preintervention period to 22.8 in the intervention period (- 63.8%), with a signifcant drop in fluoroquinolones (81.4%). Overall, 46.6% of antibiotic prescriptions were judged inappropriate, mainly because of a use not recommended in treatment guidelines (63.2%). Multivariable analysis showed that empirical therapy, some classes of antibiotics (cephalosporins, fluoroquinolones, fosfomycin calcium, macrolides) and prescription initiation in the emergency department were independent predictors of antimicrobial inappropriateness. Pharmacist-led ASP in a LTCF has being effective in reducing consumption of antibiotics by improving appropriateness of treatment decisions. However, ASP should include interventions in the emergency department because of the high inappropriate use in this setting.
RESUMO
Some fungal endophytes of forest trees are recognized as beneficial symbionts against stresses. In previous works, two elm endophytes from the classes Cystobasidiomycetes and Eurotiomycetes promoted host resistance to abiotic stress, and another elm endophyte from Dothideomycetes enhanced host resistance to Dutch elm disease (DED). Here, we hypothesize that the combined effect of these endophytes activate the plant immune and/or antioxidant system, leading to a defense priming and/or increased oxidative protection when exposed to the DED pathogen Ophiostoma novo-ulmi. To test this hypothesis, the short-term defense gene activation and antioxidant response were evaluated in DED-susceptible (MDV1) and DED-resistant (VAD2 and MDV2.3) Ulmus minor genotypes inoculated with O. novo-ulmi, as well as two weeks earlier with a mixture of the above-mentioned endophytes. Endophyte inoculation induced a generalized transient defense activation mediated primarily by salicylic acid (SA). Subsequent pathogen inoculation resulted in a primed defense response of variable intensity among genotypes. Genotypes MDV1 and VAD2 displayed a defense priming driven by SA, jasmonic acid (JA), and ethylene (ET), causing a reduced pathogen spread in MDV1. Meanwhile, the genotype MDV2.3 showed lower defense priming but a stronger and earlier antioxidant response. The defense priming stimulated by elm fungal endophytes broadens our current knowledge of the ecological functions of endophytic fungi in forest trees and opens new prospects for their use in the biocontrol of plant diseases.
RESUMO
Abatacept (ABA) is an immunosuppressant indicated for treatment of rheumatoid arthritis (RA). Effectiveness might be influenced by clinical RA variants and single-nucleotide polymorphisms (SNPs) in genes encoding protein FCGR2A (His131Arg) and FCGR3A (Phe158Val) involved in pharmacokinetics of ABA. An observational cohort study was conducted in 120 RA Caucasian patients treated with ABA for 6 and 12 months. Patients with the FCGR2A rs1801274-AA genotype (FCGR2A-p.131His) showed a better EULAR response (OR = 2.43; 95% CI = 1.01-5.92) at 12 months and low disease activity (LDA) at 6 months (OR = 3.16; 95% CI = 1.19-8.66) and 12 months (OR = 6.62; 95% CI = 1.25-46.89) of treatment with ABA. A tendency was observed towards an association between the FCGR3A rs396991-A allele (FCGR3A-p.158Phe) and better therapeutic response to ABA after 12 months of treatment (p = 0.078). Moreover, we found a significant association between the low-affinity FCGR2A/FCGR3A haplotypes variable and LDA after 12 months of ABA treatment (OR = 1.59; 95% CI = 1.01-2.58). The clinical variables associated with better response to ABA were lower age at starting ABA (OR = 1.06; 95% CI = 1.02-1.11) and greater duration of ABA treatment (OR = 1.02; 95% CI = 1.01-1.04), lower duration of previous biological therapies (OR = 0.99; 95% CI = 0.98-0.99), non-administration of concomitant disease-modifying antirheumatic drugs (DMARDs) (OR = 24.53; 95% CI = 3.46-523.80), non-use of concomitant glucocorticoids (OR = 0.12; 95% CI = 0.02-0.47), monotherapy (OR = 19.22; 95% CI = 2.05-343.00), lower initial patient's visual analogue scale (PVAS) value (OR = 0.95; 95% CI = 0.92-0.97), and lower baseline ESR (OR = 0.92; 95% CI = 0.87-0.97). This study showed that high-affinity FCGR2A-p.131His variant, low-affinity FCGR3A-p.158Phe variant, and combined use of FCGR2A/FCGR3A genetic variations could affect ABA effectiveness. Further studies will be required to confirm these results.
RESUMO
Long-lived trees benefit from fungal symbiotic interactions in the adaptation to constantly changing environments. Previous studies revealed a core fungal endobiome in Ulmus minor which has been suggested to play a critical role in plant functioning. Here, we hypothesized that these core endophytes are involved in abiotic stress tolerance. To test this hypothesis, two core endophytes (Cystobasidiales and Chaetothyriales) were inoculated into in vitro U. minor plantlets, which were further subjected to drought. Given that elm genotypes resistant to Dutch elm disease (DED) tend to show higher abiotic stress tolerance than susceptible ones, we tested the endophyte effect on two DED-resistant and two DED-susceptible genotypes. Drought stress was moderate; endophyte presence attenuated stomata closure in response to drought in one genotype but this stress did not affect plant survival. In comparison, long-term in-vitro culture proved stressful to mock-inoculated plants, especially in DED-susceptible genotypes. Interestingly, no endophyte-inoculated plant died during the experiment, as compared to high mortality in mock-inoculated plants. In surviving plants, endophyte presence stimulated root and shoot growth, photosynthetic rates, antioxidant activity and molecular changes involving auxin-signaling. These changes and the observed endophyte stability in elm tissues throughout the experiment suggest endophytes are potential tools to improve survival and stress tolerance of DED-resistant elms in elm restoration programs.
Assuntos
Ascomicetos/fisiologia , Basidiomycota/fisiologia , Endófitos/fisiologia , Fotossíntese , Raízes de Plantas/crescimento & desenvolvimento , Plântula/fisiologia , Ulmus/fisiologia , Secas , Genótipo , Longevidade/fisiologia , Doenças das Plantas/genética , Raízes de Plantas/microbiologia , Ulmus/crescimento & desenvolvimento , Ulmus/microbiologiaRESUMO
Several studies on aeroterrestrial microalgae are unravelling their resistance mechanisms to different abiotic stressors, including hazardous metals, pointing to their future role as bioremediation microorganisms. In the present study, physiological and molecular alterations of four phycobionts of genus Trebouxia (T. TR1 and T. TR9) and Coccomyxa (C. subellipsoidea and C. simplex) exposed to Cd were studied. Cd accumulation and subcellular distribution, cell wall structure, production of biothiols (GSH and phytochelatins), reactive oxygen species (ROS) formation, expression of key antioxidant genes and ROS-related enzymes were evaluated to determine the physiological differences among the four microalgae, with the aim to identify the most suitable microorganism for further biotechnological applications. After 7 days of Cd exposure, Coccomyxa algae showed higher capacity of Cd intake than Trebouxia species, with C. subellipsoidea being the highest Cd accumulator at both intracellular and, especially, cell wall level. Cd induced ROS formation in the four microalgae, but to a greater extent in both Coccomyxa algae. Trebouxia TR9 showed the lowest Cd-dependent oxidative stress probably due to glutathione reductase induction. All microalgae synthetized phytochelatins in response to Cd but in a species-specific and a dose-dependent manner. Results from this study agree with the notion that each microalga has evolved a distinct strategy to detoxify hazardous metals like Cd and to cope with oxidative stress associated with them. Coccomyxa subellipsoidea and Trebouxia TR9 appear as the most interesting candidates for further applications.
Assuntos
Clorófitas , Líquens , Microalgas , Cádmio/toxicidade , Clorófitas/genética , Microalgas/genética , Estresse OxidativoRESUMO
CONTEXT AND OBJECTIVE: Risk-sharing agreements(RSA) allow decision-makers to manage the uncertainty associated with effectiveness and costs of treatments. Our objective was to estimate the economic impact of RSA implementation on treatment of patients diagnosed with rheumatoid arthritis(RA) with certolizumab pegol(CZP) and assess the potential impact of alternative RSA. METHODS: Under original RSA, treatment with CZP was reimbursed when the response was optimal (DAS28 score <3.2) or satisfactory (DAS28 score ≥3.2 and reduction from baseline ≥1.2) at 12 weeks. Alternative RSA would additionally include a 50 % reimbursement for moderate responders(DAS28 score >3.2 and ≤5.1, and reduction from baseline between 0.6 and 1.2). We estimated average savings per patient for hospital's pharmacy service(HPS) at 12 weeks, taking into account the pharmacological cost of CZP. Uncertainty associated with effectiveness of CZP was assessed through 1000 Monte Carlo simulations. RESULTS: After 12 weeks of treatment, 57.8 % (n = 52) and 22.2 %(n = 20) of patients had optimal and satisfactory responses, respectively, and average disease activity improved by 1.77 points. Average savings for HPS amounted to 876.9 and 706.4 per patient under original and alternative RSA, respectively. Savings in simulated cohort reached 846.2 and 681.8 per patient, respectively, leading to estimated net savings for HPS of 846,209 and 681,790, respectively. CONCLUSIONS: RSA implementation on patients with RA treated with CZP has generated savings and improved efficiency within HPS.
Assuntos
Antirreumáticos , Artrite Reumatoide , Antirreumáticos/uso terapêutico , Artrite Reumatoide/tratamento farmacológico , Certolizumab Pegol/uso terapêutico , Quimioterapia Combinada , Humanos , Espanha , Resultado do TratamentoRESUMO
Abatacept (ABA) is used as a first-line treatment in patients diagnosed with moderate and severe rheumatoid arthritis (RA). The interindividual response to ABA therapy is very variable in these patients. The objective of our study was therefore to investigate the role of polymorphisms of the CTLA-4, CD80 and CD86 genes, as well as that of clinical factors of the disease, in the response to ABA in patients with RA. A retrospective cohort study was carried out in 109 patients receiving treatment with ABA and diagnosed with RA. The genetic variables were analyzed using real-time PCR with TaqMan® probes. The patients were classified according to the European League Against Rheumatism (EULAR) criteria at 6 and 12 months from start of treatment. The independent variables associated with higher EULAR response were lower duration of previous biologic disease-modifying anti-rheumatic drugs and lower baseline values of the disease activity score 28 after 6 months of ABA treatment; and lower baseline patient's visual analogue scale (PVAS) after 12 months. In addition, a significant association was found between duration of ABA treatment, non-administration of concomitant glucocorticoids and lower baseline values of the number of inflamed joints and erythrocyte sedimentation rate clinical variables, with remission of the disease after 6 months' treatment with ABA. Finally, remission of the disease after 12 months' treatment with ABA was associated with earlier age at start of ABA therapy and lower number of previous biologic therapies (BTs). The CTLA-4rs5742909-T allele and the CTLA-4rs231775-G allele were found to be associated with satisfactory EULAR response and low disease activity (LDA) after 12 months' treatment with ABA (CTLA-4rs5742909 T vs. CC; OR = 5.88; CI95% = 1.48-23.29 and OR = 4.75; CI95% = 1.35-17.94, respectively, and CTLA-4rs231775 G vs. AA, OR = 3.48; CI95% = 1.20-10.09 and OR = 4.68; CI95% = 1.49-17.94, respectively). In conclusion, patients with RA treated with ABA showed better EULAR response and LDA rate when they had the CTLA-4 rs5742909-T or CTLA-4 rs231775-G polymorphisms; furthermore, this remission rate increased in patients that began ABA treatment earlier, those with a lower number of previous BTs and those with a lower PVAS value.
RESUMO
Janus particles (JPs) are a special kind of colloids that incorporate two hemispheres with distinct physical properties. These particles feature a complex phase behavior, and they can be propelled with light by heating them anisotropically when one of the hemispheres is metallic. It has been shown that JPs can be oriented by a homogeneous thermal field. We show using multiscale simulations and theory that the internal mass gradient of the JPs can enhance and even reverse the relative orientation of the particle with the thermal field. This effect is due to a coupling of the internal anisotropy of the particle with the heat flux. Our results help rationalize previous experimental observations and open a route to control the behavior of JPs by exploiting the synergy of particle-fluid interactions and particle internal mass composition.
RESUMO
We investigate the impact of nanoparticle roughness on the phase behaviour of suspensions in models of calcium carbonate nanoparticles. We use a Derjaguin approach that incorporates roughness effects and interactions between the nanoparticles modelled with a combination of DLVO forces and hydration forces, derived using experimental data and atomistic molecular dynamics simulations, respectively. Roughness effects, such as atomic steps or terraces appearing in mineral surfaces result in very different effective inter-nanoparticle potentials. Using stochastic Langevin Dynamics computer simulations and the effective interparticle interactions we demonstrate that relatively small changes in the roughness of the particles modify significantly the stability of the suspensions. We propose that the sensitivity of the phase behavior to the roughness is connected to the short length scale of the adhesive attraction arising from the ordering of water layers confined between calcite surfaces. Particles with smooth surfaces feature strong adhesive forces, and form gel fractal structures, while small surface roughness, of the order of atomic steps in mineral faces, stabilize the suspension. We believe that our work helps to rationalize the contrasting experimental results that have been obtained recently using nanoparticles or extended surfaces, which provide support for the existence of adhesive or repulsive interactions, respectively. We further use our model to analyze the synergistic effects of roughness, pH and ion concentration on the phase behavior of suspensions, connecting with recent experiments using calcium carbonate nanoparticles.