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1.
Kardiologiia ; 63(12): 72-76, 2023 Dec 27.
Article in Russian, English | MEDLINE | ID: mdl-38156493

ABSTRACT

Aim    To study the incidence and effect of non-alcoholic fatty liver disease (NAFLD) on clinical outcomes in patients with decompensated chronic heart failure (DCHF).Material and methods    The study included 338 patients with NYHA functional class III-IV DCHF (51.2% men, mean age 72.8±11.7 years), arterial hypertension (AH) in 90%, myocardial infarction in 37%, atrial fibrillation in 64%, chronic kidney disease (CKD) in 42%, type 2 diabetes mellitus (T2DM) in 35%, left ventricular ejection fraction (LVEF) <40% in 27%. NAFLD was diagnosed based on the 2021 Clinical Guidelines of the Russian Scientific Medical Society of Therapists and the Scientific Society of Gastroenterologists of Russia. The stage of liver steatosis was determined using transient elastometry with assessment of the controlled attenuation parameter (CAP) of ultrasound (S, dB/m) using a FibroScan device. Threshold CAP values <294 dB/m corresponded to the degree of steatosis: S0; S1, 295-309 dB/m; S2, 310-330 dB/m; S3, ≥331 dB/m.Results    NAFLD was diagnosed in 28.9% of patients. The patients were divided into two groups: group 1 included patients with CHF and NAFLD (n=98 (28.9%), 50.0% men) and group 2 included patients with CHF without NAFLD (n=240 (71.0 %), 51.6% men). A multivariate regression analysis showed that independent predictors of NAFLD were systolic blood pressure ≥130 mm Hg (odds ratio (OR), 3.700; p <0.001), history of T2DM (OR, 2.807; p <0.005), and waist circumference >111 cm (OR, 2.530; p <0.012). Patients with CAP ≥331 dB/m (S3) had a worse prognosis during the 2-year follow-up for the composite adverse outcome (all-cause mortality + readmission) (Kaplan-Meier curves - Log-Rank p=0.035).Conclusions    NAFLD was detected in almost one-third of patients hospitalized for DCHF. AH, T2DM, and abdominal obesity were associated with a high risk of NAFLD. However, only severe steatosis (S3) was an independent predictor of adverse clinical outcomes during a 2-year period after adjustment for known risk factors.


Subject(s)
Diabetes Mellitus, Type 2 , Heart Failure , Non-alcoholic Fatty Liver Disease , Male , Humans , Middle Aged , Aged , Aged, 80 and over , Female , Non-alcoholic Fatty Liver Disease/complications , Non-alcoholic Fatty Liver Disease/diagnosis , Non-alcoholic Fatty Liver Disease/epidemiology , Diabetes Mellitus, Type 2/complications , Diabetes Mellitus, Type 2/epidemiology , Prognosis , Prevalence , Stroke Volume , Body Mass Index , Ventricular Function, Left , Heart Failure/diagnosis , Heart Failure/epidemiology
2.
Kardiologiia ; 62(11): 3-10, 2022 Nov 30.
Article in Russian, English | MEDLINE | ID: mdl-36521038

ABSTRACT

Aim      To determine the clinical and prognostic significance of subclinical pulmonary congestion, as evaluated by stress ultrasound (stress-US) examination of the lungs, in the development of heart failure (HF) during the postinfarction period after acute myocardial infarction (AMI) and percutaneous coronary intervention (PCI).Material and methods  This prospective observational study included 103 patients with no history of HF and with the first AMI and successful PCI. Standard laboratory tests, including the measurement of NT-proBNP, echocardiography, stress-US of the lungs with a 6-min walk test (6MWT), were performed for all patients. Pulmonary congestion was diagnosed with the total number of B lines ≥2 during stress: mild (2-4 B lines), moderate (5-9 B lines), and severe (≥10 В lines). Subclinical pulmonary congestion implied the absence of clinical signs of congestion in the presence of ultrasonic signs of pulmonary congestion (>2 В lines) during stress. The phenomenon of "wet" lung was identified when the total number of B lines was <2 at rest ("dry" lung) and ≥2 after stress. When the total number of B lines was >2 at rest ("wet" lung at rest) and ≥2 after stress, the phenotype was identified as "very wet" lung. The endpoint was hospitalization for HF during 1.5 years.Results The study showed a high incidence of subclinical pulmonary congestion as determined by the results of stress-US test of the lungs, mild (18.4 %), moderate (37.9 %) and severe (42.7 %), and of "wet" and "very wet" lung phenotypes (65 %). The "wet/very wet" lung phenotypes correlated with the body weight index (R=0.236; p=0.016), troponin concentration upon admission and at 6-12 h (R=0.231; p=0019 and R=0.212; p=0.033, respectively), NT-proBNP concentration (R=0.276; p=0.035), Е peak (R=0.241; p=0.019), global longitudinal strain (GLS) (R=-0.208; p=0.034), and left ventricular end-diastolic dimension (R=0.351; p=0.0004). The higher probability of hospitalization for HF during 1.5 years after the discharge from the hospital correlated with a LV EF ≤48 % (OR, 4.04; 95 % CI: 1.49-10.9; р=0.006), a post-stress total number of B lines ≥10 (OR, 3.10; 95 % CI: 1.06-9.52; р=0.038), a pulmonary artery systolic pressure >27 mm Hg (OR, 3.7; 95 % CI: 1.42-9.61; р=0.007).Conclusion      Stress-US of the lungs with evaluation of the total number of B lines should be performed for patients after the first AMI and PCI and with no clinical signs of congestion, for stratification of the risk for HF in the postinfarction period.


Subject(s)
Heart Failure , Myocardial Infarction , Percutaneous Coronary Intervention , Pulmonary Edema , Humans , Prognosis , Percutaneous Coronary Intervention/adverse effects , Pulmonary Edema/diagnosis , Pulmonary Edema/etiology , Heart Failure/diagnosis , Heart Failure/etiology , Heart Failure/epidemiology , Lung/diagnostic imaging , Myocardial Infarction/complications , Myocardial Infarction/diagnosis
3.
Sci Rep ; 12(1): 18328, 2022 10 31.
Article in English | MEDLINE | ID: mdl-36316348

ABSTRACT

In mountain areas, the phenology and productivity of grassland are closely related to snow dynamics. However, the influence that snow melt timing has on grassland growing still needs further attention for a full understanding, particularly at high spatial resolution. Aiming to reduce this knowledge gap, this work exploits 1 m resolution snow depth and Normalized Difference Vegetation Index observations acquired with an Unmanned Aerial Vehicle at a sub-alpine site in the Pyrenees. During two snow seasons (2019-2020 and 2020-2021), 14 NDVI and 17 snow depth distributions were acquired over 48 ha. Despite the snow dynamics being different in the two seasons, the response of grasslands greening to snow melt-out exhibited a very similar pattern in both. The NDVI temporal evolution in areas with distinct melt-out dates reveals that sectors where the melt-out date occurs in late April or early May (optimum melt-out) reach the maximum vegetation productivity. Zones with an earlier or a later melt-out rarely reach peak NDVI values. The results obtained in this study area, suggest that knowledge about snow depth distribution is not needed to understand NDVI grassland dynamics. The analysis did not reveal a clear link between the spatial variability in snow duration and the diversity and richness of grassland communities within the study area.


Subject(s)
Grassland , Snow , Seasons , Temperature
4.
J Colloid Interface Sci ; 608(Pt 1): 792-799, 2022 Feb 15.
Article in English | MEDLINE | ID: mdl-34689111

ABSTRACT

HYPOTHESIS: Ice adhesion to rigid materials is reduced with low energy surfaces of high receding contact angles. However, their adhesion strength values are above the threshold value to be considered as icephobic materials. Surface deformability is a promising route to further reduce ice adhesion. EXPERIMENTS: In this work, we prepared elastomer surfaces with a wide range of elastic moduli and hydrophobicity degree and we measured their ice adhesion strength. Moreover, we also explored the deicing performance of oil-infused elastomeric surfaces. The ice adhesion was characterized by two detachment modes: tensile and shear. FINDINGS: The variety of elastomeric surfaces allowed us to simultaneously analyze the ice adhesion dependence with deformability and contact angle hysteresis. We found that the impact of these properties depends on the detachment mode, being deformability more important in shear mode and hydrophobicity more relevant in tensile mode. In addition, oil infusion further reduces ice adhesion due to the interfacial slippage. From an optimal balance between deformability and hydrophobicity, we were able to identify surfaces with super-low ice adhesion.


Subject(s)
Ice , Hydrophobic and Hydrophilic Interactions , Physical Phenomena , Surface Properties
5.
Kardiologiia ; 59(8): 5-14, 2019 Aug 08.
Article in Russian | MEDLINE | ID: mdl-31397225

ABSTRACT

BACKGROUND: Recently lung ultrasound (LUS) based on B-lines measurement has been proposed as an effective tool for assessment of pulmonary congestion (PC) in patients with decompensated heart failure (DHF). OBJECTIVE: to assess the incidence, in-hospital changes and prognostic significance of PC assessed by LUS in DHF patients. MATERIALS AND METHODS: Routine clinical assessment and eight-zone LUS were performed in 162 patients with DHF (men 66%, mean age 68±12 years, hypertension 97%, history of myocardial infarction 44%, atrial fibrillation 60%, ejection fraction [EF] 40±14%, EF<40% 46%, baseline NT-proBNP 4 246 [1741; 6 837] pg/ml). Sum of B-lines ≤5 was considered as normal, 6-15, 16-30 and >30 - as mild, moderate and severe PC, respectively. RESULTS: Using LUS on admission PC was diagnosed in all patients (moderate and severe in 31.5 and 67.3%, respectively). At discharge normal LUS profile was observed in 48.2% of patients. In 33.3, 14.8 and 3.7% of patients PC was mild, moderate, and severe, respectively. According to multivariable Cox regression analysis including age, sex, EF, NYHA functional class, and jugular venous distension sum of B-lines >5 at discharge was associated with higher probability of 12-month all-cause death (hazard ratio [HR] 2.86, 95% confidence interval [CI] 1.15-7.13, p=0.024), sum of B-lines >15 - with higher probability of HF readmission (HR 2.83, 95%CI 1.41-5.67, p=0.003). CONCLUSION: During hospital stay the incidence of PC as assessed by LUS decreased from 100 to 52% of patients. Sum of B-lines >5 at discharge was independently associated with higher risk of 12-month all-cause death, >15 - with higher risk of 12-month HF readmission.


Subject(s)
Heart Failure , Pulmonary Edema , Aged , Aged, 80 and over , Female , Humans , Lung , Male , Middle Aged , Natriuretic Peptide, Brain , Prognosis , Pulmonary Edema/diagnostic imaging , Ultrasonography
6.
J Colloid Interface Sci ; 539: 448-456, 2019 Mar 15.
Article in English | MEDLINE | ID: mdl-30605814

ABSTRACT

HYPOTHESIS: Wettability of solid surfaces is mostly probed with sessile drops rather than bubbles because this method is readily followed out. This recurrent use may lead to a misleading connection of certain phenomena to the hydrophobicity/hydrophilicity of materials. For instance, the Cassie-Baxter regime and the wicking effect are generally associated only to hydrophobic and hydrophilic surfaces, respectively. However, the same phenomenology should be observed when air bubbles (underwater conditions) in contact with solid surfaces are used instead. In particular, one might expect that rough-hydrophilic surfaces become superaerophobic due to the appearance of a hybrid dewetting regime, like the Cassie-Baxter regime described for rough-hydrophobic surfaces. Otherwise, rough-hydrophobic surfaces might become superaerophilic due to air-wicking. EXPERIMENTS: To elucidate this issue, in this work, we analyzed the wettability of surfaces with very different intrinsic contact angle and roughness degree. The analysis was performed with both Sessile Drop and Captive Bubble methods. FINDINGS: Our results with captive bubbles for rough-hydrophilic surfaces revealed phenomena only explained by the occurrence of a transition from the Wenzel regime to an "inverse" Cassie-Baxter regime. In addition, our results with captive bubbles for rough-hydrophobic surfaces showed evidences of air percolation through the interconnected asperities. This effect reminds the wicking effect reproduced on rough-hydrophilic surfaces, responsible for superhydrophilicity.

7.
J Vis Exp ; (138)2018 08 15.
Article in English | MEDLINE | ID: mdl-30175989

ABSTRACT

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in industry. The wettability of the produced surface was analyzed by bouncing drop experiments and the topography was analyzed by confocal microscopy. In addition, we show various methodologies to measure its durability and anti-icing properties. Superhydrophobic surfaces hold a special texture that must be preserved to keep their water-repellency. To fabricate durable surfaces, we followed two strategies to incorporate a resistant texture. The first strategy is a direct incorporation of roughness to the metal substrate by acid etching. After this surface texturization, the surface energy was decreased by silanization or fluoropolymer deposition. The second strategy is the growth of a ceria layer (after surface texturization) that should enhance the surface hardness and corrosion resistance. The surface energy was decreased with a stearic acid film. The durability of the superhydrophobic surfaces was examined by a particle impact test, mechanical wear by lateral abrasion, and UV-ozone resistance. The anti-icing properties were explored by studying the ability to repeal subcooled water, freezing delay, and ice adhesion.


Subject(s)
Surface Properties , Freezing , Hydrophobic and Hydrophilic Interactions
8.
J Environ Manage ; 227: 256-266, 2018 Dec 01.
Article in English | MEDLINE | ID: mdl-30199721

ABSTRACT

Forest fires are one of the main environmental problems in Mediterranean environments and different fire prevention policies have been applied: livestock grazing, prescribed fires and a combination of both. However, none present satisfactory results. In that context, in 1986 the Regional Government of La Rioja started the Plan for Shrub Clearing (PSC), combining shrub clearings and livestock grazing to control fires and improve the land management of abandoned mountain areas. Our study aims to analyse the effects of shrub clearings on forest fires in La Rioja and to compare the main results with those observed in Spain in the last 30 years. We apply an interdisciplinary methodology based on the analysis of the evolution of cleared areas, the evolution of wildfires in La Rioja and Spain, mapping land use and land cover changes, and quantifying the combustibility. Results obtained in La Rioja are very positive compared with the evolution of Spain, both in the reduction of the number of fires and the burned areas. Decreases in the combustible material, fuel load and biomass and in the occurrence of fires (>1 ha) were observed. In addition, clearing shrubland and extensive livestock provided other environmental benefits (i.e. mosaic landscapes, ecosystem services). Finally, this study suggested that they are good and sustainable techniques to prevent and control wildfires and they could be used as a land management strategy in other Mediterranean areas.


Subject(s)
Agriculture , Livestock , Wildfires , Animals , Ecosystem , Fires , Spain
10.
J Colloid Interface Sci ; 508: 129-136, 2017 Dec 15.
Article in English | MEDLINE | ID: mdl-28822862

ABSTRACT

The analysis of wetting properties of superhydrophobic surfaces may be a difficult task due to the restless behavior of drops on this type of surfaces and the limitations of goniometry for high contact angles. A method to validate the performance of superhydrophobic surfaces, rather than standard goniometry, is required. In this work, we used bouncing drop dynamics as a useful tool to predict the water repellency of different superhydrophobic surfaces. From bouncing drop experiments conducted over a wide range of superhydrophobic surfaces, we found that those surfaces with a proper roughness degree and homogeneous chemical composition showed higher water-repellency. We also conducted a drop condensation study at saturating conditions aimed to determine whether there is direct correlation between water repellency and condensation delay. We found that the drop condensation process is strongly related to the surface topography, as well as the intrinsic wettability. The condensation is promoted on rough surfaces but it is delayed on intrinsically hydrophobic surfaces. However, the differences found in condensation delay between the superhydrophobic surfaces explored in this study cannot be justified by their chemical homogeneity nor their efficiency as water repellent surfaces, separately.

11.
Microsc Res Tech ; 80(1): 144-152, 2017 Jan.
Article in English | MEDLINE | ID: mdl-26999314

ABSTRACT

In this article, a compilation of results on direct force measurements between colloidal particles in monovalent salts carried out with the colloidal probe technique based on Atomic Force Microscopy was presented. The interaction forces between similar and dissimilar particles was studied and it was concluded that, in general, these force profiles may be satisfactorily quantified by the DLVO theory down to distances of few nanometers. However, in the specific case where the charge of one of the involved particle is close to neutral, it was found that the surface potential of this particle may change its sign depending on the sign of charge of the opposite particle. In this respect, the assumption that the surface potential of a particle is a property only related to the particle surface features and the bulk properties is called into question. Microsc. Res. Tech. 80:144-152, 2017. © 2016 Wiley Periodicals, Inc.

12.
Langmuir ; 32(45): 11918-11927, 2016 11 15.
Article in English | MEDLINE | ID: mdl-27779881

ABSTRACT

Colloidal interactions have been extensively studied due to the wide number of applications where colloids are present. In general, the electric double layer force and the van der Waals interaction dominate the net force acting between two colloids at large separation distances. However, it is well accepted that some other phenomena, especially those acting at short separation distances, might be relevant and induce substantial changes in the force profiles. Within these phenomena, those related to the surface contact angle, the hydration degree of the ions, or the pH, may dominate the force profiles features, not only at short distances. In this paper, we analyzed the effect of the pH and counterion type on the long-range as well as short-range forces between polystyrene colloidal particles by using the colloidal probe technique based on AFM. Our results confirm that the features of the force profiles between polystyrene surfaces are strongly affected by the pH and hydration degree of the counterions in solution. Additionally, we performed a study of the role of the pH on the wettability properties of hydrated and nonhydrated polystyrene sheets to scan the wettability properties of this material with pH. Contact angle measurements confirmed that the polystyrene surface is hydrophobic in aqueous solutions over the entire range of pHs investigated. These results are in good agreement with the features observed in the force profiles at low pH. At high pH, a short-range repulsion similar to the one observed for hydrophilic materials is observed. This repulsion scales with the pH, and it also depends on the hydration degree of the ions in solution. This way, the short-range forces between polystyrene surfaces may be tunable with the pH, and its origin does not seem to be related to the hydrophobicity of the material.

13.
J Phys Chem B ; 119(25): 8184-93, 2015 Jun 25.
Article in English | MEDLINE | ID: mdl-26005063

ABSTRACT

Force profiles and aggregation rates involving positively and negatively charged polystyrene latex particles are investigated in monovalent electrolyte solutions, whereby the counterions are varied within the Hofmeister series. The force measurements are carried out with the colloidal probe technique, which is based on the atomic force microscope (AFM), while the aggregation rates are measured with time-resolved multiangle light scattering. The interaction force profiles cannot be described by classical DLVO theory, but an additional attractive short-ranged force must be included. An exponential force profile with a decay length of about 0.5 nm is consistent with the measured forces. Furthermore, the Hamaker constants extracted from the measured force profiles are substantially smaller than the theoretical values calculated from dielectric spectra. The small surface roughness of the latex particles (below 1 nm) is probably responsible for this deviation. Based on the measured force profiles, the aggregation rates can be predicted without adjustable parameters. The measured absolute aggregation rates in the fast regime are somewhat lower than the calculated ones. The critical coagulation concentration (CCC) agrees well with the experiment, including the respective shifts of the CCC within the Hofmeister series. These shifts are particularly pronounced for the positively charged particles. However, the consideration of the additional attractive short-ranged force is essential to quantify these shifts correctly. In the slow regime, the calculated rates are substantially smaller than the experimental ones. This disagreement is probably related to surface charge heterogeneities.

14.
Soft Matter ; 11(8): 1562-71, 2015 Feb 28.
Article in English | MEDLINE | ID: mdl-25590285

ABSTRACT

Forces between charged particles in aqueous solutions containing multivalent coions and monovalent counterions are studied by the colloidal probe technique. Here, the multivalent ions have the same charge as the particles, which must be contrasted to the frequently studied case where multivalent ions have the opposite sign as the substrate. In the present case, the forces remain repulsive and are dominated by the interactions of the double layers. The valence of the multivalent coion is found to have a profound influence on the shape of the force curve. While for monovalent coions the force profile is exponential down to separations of a few nanometers, the interaction is much softer and longer-ranged in the presence of multivalent coions. The force profiles in the presence of multivalent coions and in the mixtures of monovalent and multivalent coions can be accurately described by Poisson-Boltzmann theory. These results are accurate for different surfaces and even in the case of highly charged particles. This behavior can be explained by the fact that the force profile follows the near-field limit to much larger distances for multivalent coions than for monovalent ones. This limit corresponds to the conditions with no salt, where the coions are expelled between the two surfaces.


Subject(s)
Colloids/chemistry , Ions/chemistry , Latex/chemistry , Silicon Dioxide/chemistry , Static Electricity , Surface Properties
15.
Article in English | MEDLINE | ID: mdl-25122297

ABSTRACT

We show how the colloidal-probe technique, which is based on force measurements made with the atomic force microscope, can be used to accurately determine the charging parameters of water-solid interfaces. Besides yielding accurate values of the double-layer or diffuse-layer potential, the method also allows reliable determination of the charge regulation properties of the surfaces. The latter can be quantified with a regulation parameter, which is essential to properly describe forces between interfaces, especially in asymmetric situations when one of the interfaces is charged and the other one is close to neutral. The technique relies on a highly charged probe particle, for which the charging properties are accurately determined by interpreting the double-layer contribution of the measured force profiles in the symmetric sphere-sphere geometry with Poisson-Boltzmann (PB) theory. Once the probe particle is calibrated, this particle is used to measure the force profile between an unknown substrate in the asymmetric sphere-sphere or sphere-plane geometry. From this profile, the diffuse-layer potential and regulation parameter of the substrate can be again determined with PB theory. The technique is highly versatile, as it can be used for a wide variety of substrates, including colloidal particles and planar substrates. The technique is also applicable in salt solutions containing multivalent ions. The current drawbacks of the technique are that it can only be applied up to moderately high salt levels, typically to 10 mM, and only for relatively large particles, typically down to about 1 µm in diameter. How the technique could be extended to higher salt levels and smaller particle size is also briefly discussed.


Subject(s)
Colloids/chemistry , Electrons , Microscopy, Atomic Force , Hydrogen-Ion Concentration , Salts/chemistry , Surface Properties , Water/chemistry
16.
Cancer Gene Ther ; 21(8): 317-32, 2014 Aug.
Article in English | MEDLINE | ID: mdl-24971583

ABSTRACT

Optimal tumor cell surface expression of human leukocyte antigen (HLA) class I molecules is essential for the presentation of tumor-associated peptides to T-lymphocytes. However, a hallmark of many types of tumor is the loss or downregulation of HLA class I expression associated with ineffective tumor antigen presentation to T cells. Frequently, HLA loss can be caused by structural alterations in genes coding for HLA class I complex, including the light chain of the complex, ß2-microglobulin (ß2m). Its best-characterized function is to interact with HLA heavy chain and stabilize the complex leading to a formation of antigen-binding cleft recognized by T-cell receptor on CD8+ T cells. Our previous study demonstrated that alterations in the ß2m gene are frequently associated with cancer immune escape leading to metastatic progression and resistance to immunotherapy. These types of defects require genetic transfer strategies to recover normal expression of HLA genes. Here we characterize a replication-deficient adenoviral vector carrying human ß2m gene, which is efficient in recovering proper tumor cell surface HLA class I expression in ß2m-negative tumor cells without compromising the antigen presentation machinery. Tumor cells transduced with ß2m induced strong activation of T cells in a peptide-specific HLA-restricted manner. Gene therapy using recombinant adenoviral vectors encoding HLA genes increases tumor antigen presentation and represents a powerful tool for modulation of tumor cell immunogenicity by restoration of missing or altered HLA genes. It should be considered as part of cancer treatment in combination with immunotherapy.


Subject(s)
Adenoviridae/genetics , Gene Expression , Genetic Vectors/genetics , Histocompatibility Antigens Class I/genetics , Neoplasms/genetics , Neoplasms/immunology , T-Lymphocyte Subsets/immunology , beta 2-Microglobulin/genetics , Antigen Presentation/immunology , Apoptosis/genetics , Cell Line, Tumor , Cell Proliferation , Genetic Loci , Histocompatibility Antigens Class I/metabolism , Humans , Immunohistochemistry , Immunophenotyping , Melanoma/genetics , Melanoma/metabolism , T-Lymphocyte Subsets/metabolism , Transcription, Genetic , Transduction, Genetic , Transgenes , beta 2-Microglobulin/metabolism
19.
J Phys Chem B ; 118(23): 6346-55, 2014 Jun 12.
Article in English | MEDLINE | ID: mdl-24849534

ABSTRACT

Force profiles as well as aggregation and deposition rates are studied for asymmetrically charged particles and surfaces in aqueous electrolytes theoretically. Interactions are calculated within the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, whereby the electrostatic part is modeled at Poisson-Boltzmann (PB) level. Unequally charged surfaces are examined, from the symmetric system, where both surfaces are equally charged, to fully asymmetric systems, where the surfaces are oppositely charged. Charged-neutral systems, where one surface is charged and the other is neutral, emerge as an essential scenario. In this case, the choice of boundary conditions used for solving the PB equation is crucial, whereby constant charge and constant potential boundary conditions lead to either fully repulsive or fully attractive forces. Consequently, charge regulation has a major influence on particle aggregation and deposition rates too. In the charge-neutral case, substantial shifts in the critical coagulation concentration (CCC) are observed when the regulation properties are changed. In the presence of multivalent ions, these systems behave similarly to the symmetrically charged ones. The CCC decreases with the square of the valence in weakly charged systems, while unrealistically high charge densities are needed to recover the classical Schulze-Hardy limit, which predicts a sixth power dependence on valence.

20.
Langmuir ; 30(16): 4551-5, 2014 Apr 29.
Article in English | MEDLINE | ID: mdl-24735066

ABSTRACT

Forces between positively and negatively charged colloidal particles across aqueous salt solutions containing multivalent ions are measured directly with the atomic force microscope (AFM). The measurements are interpreted quantitatively with Poisson-Boltzmann (PB) theory. Thereby, the surface potentials and regulation properties of the particle surfaces are extracted from symmetric measurements between the same types of particles. This information is used to predict force profiles in the asymmetric situations involving different types of particles without any adjustable parameters. These predictions turn out to be very accurate, which demonstrates that the mean-field PB theory is reliable down to distances of about 5 nm. While various reports in the literature indicate that this theory should fail due to neglect of ion correlations, such effects seem important only at higher concentrations and smaller distances.

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