Colloidal Density Research Articles

Easy Cell Detachment and Spheroid Formation of Induced Pluripotent Stem Cells Using Two-Dimensional Colloidal Arrays

Induced pluripotent stem cells (iPSCs) may develop into any form of cell and are being intensively investigated. The influence on iPSCs of nanostructures generated using two-dimensional colloidal arrays was examined in this study. Colloidal arrays were formed using the following procedure. First, core–shell colloids were adsorbed onto a glass substrate using a layer-by-layer method. Second, the colloids were immobilized via thermal fusion. Third, the surface of the colloids was modified by plasma treatment. By adjusting the number density of colloids, cultured iPSCs were easily detached from the substrate without manual cell scraping. In addition to planar culture, cell aggregation of iPSCs attached to the substrate was achieved by combining hydrophilic surface patterning on the colloidal array. Multilayered cell aggregates with approximately four layers were able be cultured. These findings imply that colloidal arrays might be an effective tool for controlling the strength of cell adhesion.

How Dimensionality Affects the Structural Anomaly in a Core-Softened Colloid

The interaction between hard core–soft shell colloids are characterized by having two characteristic distances: one associated with the penetrable, soft corona and another one corresponding to the impenetrable core. Isotropic core-softened potentials with two characteristic length scales have long been applied to understand the properties of such colloids. Those potentials usually show water-like anomalies, and recent findings have indicated the existence of multiple anomalous regions in the 2D limit under compression, while in 3D, only one anomalous region is observed. In this direction, we perform molecular dynamics simulations to unveil the details about the structural behavior in the quasi-2D limit of a core-softened colloid. The fluid was confined between highly repulsive solvophobic walls, and the behavior at distinct wall separations and colloid densities was analyzed. Our results indicated a straight relation between the 2D- or 3D-like behavior and layer separation. We can relate that if the system behaves as independent 2D-layers, it will have a 2D-like behavior. However, for some separations, the layers are connected, with colloids hopping from one layer to another, thus having a 3D-like structural behavior. These findings fill the gap in the depiction of the anomalous behavior from 2D to 3D.

High density deposits of binary colloids

Colloids are essential materials for modern inkjet printing and coating technology. For printing and coating, it is desirable to have a high density of colloids with uniformity. Binary colloids, which consist of different size colloidal particles, have the potential to achieve high coating density and uniformity from size effects. We report a strategy to attain high-density deposits of binary colloids with uniform, crack-free, and symmetric deposits through droplet evaporation on micropillar arrays. We modify surfaces of micropillar arrays with plasma treatment to control their surface energy and investigate how binary colloidal fluids turn into well-controlled deposits during evaporation with X-ray microscopic and tomographic characterizations. We attribute temporary surface energy modification of micropillar arrays to the well-controlled high-density final deposits. This simple, low-cost, and scalable strategy would provide a viable way to get high-quality, high-density deposits of colloids for various applications.

Active responsive colloids driven by intrinsic dichotomous noise.

We study the influence of intrinsic noise on the structure and dynamics of responsive colloids (RCs), which actively change their size and mutual interactions. The colloidal size is explicitly resolved in our RC model as an internal degree of freedom (DOF) in addition to the particle translation. A Hertzian pair potential between the RCs leads to repulsion and shrinking of the particles, resulting in an explicit responsiveness of the system to self-crowding. To render the colloids active, their size is internally driven by a dichotomous noise, randomly switching ("breathing") between growing and shrinking states with a predefined rate, as motivated by recent experiments on synthetic active colloids. The polydispersity of this dichotomous active responsive colloid (D-ARC) model can be tuned by the parameters of the noise. Utilizing stochastic computer simulations, we study crowding effects on the spatial distributions, relaxation times, and self-diffusion of dense suspensions of the D-ARCs. We find a substantial influence of the "built-in" intrinsic noise on the system's behavior, in particular, transitions from unimodal to bimodal size distributions for an increasing colloid density as well as intrinsic noise-modified diffusive translational dynamics. We conclude that controlling the noise of internal DOFs of a macromolecule or cell is a powerful tool for active colloidal materials to enable autonomous changes in the system's collective structure and dynamics towards the adaptation of macroscopic properties to external perturbations.

In Vitro Evaluating Antimicrobial Activity for MgO Nanoparticles Prepared by PLAL

Pulsed laser ablation in liquid (PLAL) of metallic magnesium was used in this work to manufacture magnesium nanoparticles with varying average sizes (10–90[Formula: see text]nm). (2.07–3.44) [Formula: see text] 108[Formula: see text]W/cm2 of laser intensity and pulse rates of 100 pulses were used to create the nanoparticles. Laser power increased the number of nanoparticles in magnesium oxide (MgO) at 204[Formula: see text]nm absorption spectroscopic absorbance linearly. When the UV–Vis absorbance of nanoparticles rose, so did their colloidal density (measured in mg/mL). Nanoparticles are more likely to be produced at higher laser scanning rates: UV–Vis absorbance and nanoparticle diameters. Field emission scanning electron microscopy (FESEM) revealed that nanoparticles created dendritic patterns when put upon metal foil. The nanoparticles were measured using dynamic light scattering. When MgO particles were used in antibacterial activity against (in vitro) various gram-positive and gram-negative strains of bacteria, they had a demonstrable impact on some strains of bacteria. MgO has been shown to have antibacterial properties.

Coarse-grained Hamiltonian and effective one component theory of colloidal suspensions

We develop a theory to trace out the solvent degrees of freedom from the grand partition function of colloid-solvent mixtures. Our approach to coarse-graining is based on density functional formalism of density profile and the grand thermodynamic potential of solvent. The solvent-induced interaction which is many-body in character is expressed in terms of two functionals; one that couples the solvent to the colloidal density distribution and the second represents the density–density correlation function of the solvent. The nature, strength, and range of the potential depend on these functionals and therefore on the thermodynamic state of the solvent. The solvent-induced contribution to free energy functional is also derived. A self-consistent procedure is developed to calculate the effective potential between colloidal particles, colloid-solvent, and colloid-colloid correlation functions. The theory is used to investigate both additive and nonadditive binary hard-sphere mixtures. Results are reported for the two systems for several values of packing fractions ηb and ηs and particles diameter ratio q=σsσb where symbols b and s refer to colloid and solvent, respectively. Several interesting features are found: The short-range attractive part of the potential shows non-monotonic dependence on ηb; when ηb is increased from zero, initially the potential becomes more attractive but beyond a certain value of ηb that depends on q, the attraction starts weakening. The repulsive peaks formed at R∼(1+12nq) where R is a distance between centers of colloidal particles expressed in units of σb and n is an integer, become stronger on increasing ηb. These results show that many-body contribution to the effective potential depends in a subtle way on packing fractions ηb,ηs, size ratio q, and on nature of the interaction model and makes a non-negligible contribution to the coarse-grained Hamiltonian.

Magnesium nanoparticle synthesis from powders via LASIS – Effects of liquid medium, laser pulse width and ageing on nanoparticle size, concentration, stability and electrical properties

Mg nanoparticles (NPs) in a range of sizes (20–213 nm) were fabricated via LASIS from powders within two different liquid mediums, namely DI water and isopropyl alcohol for the first time. The effect of laser pulse width (0.60, 0.92 and 1.24 ns) and liquid medium on the UV–Visible and Fourier-transform infra-red spectra, zeta potentials, concentration (particles/ml), colloidal density, mean NP size and electrical properties were investigated. Nanoparticle ageing experiments were conducted whereby the NP size was analysed soon after fabrication and then again after 9-months of shelf life at room temperature. The effect of the colloid storage temperature after fabrication (−17, 4 and 20 °C) on the NP concentration was investigated. DI water-synthesised Mg NPs tend to be larger (89 ± 4 nm) than IPA-synthesised Mg NPs (52 ± 6 nm). IPA-synthesised NPs provided better colloidal stability (zeta potential = +158.7 ± 13.5 mV) than DI water (zeta potential = +16.6 ± 3.1 mV). Mg NPs reduced the resistivity of glass from 102 to 92 Ω/square which gave them a potential application in electronics. Mg NPs have versatile applications including surface coating, printed electronics, battery technology and antibacterial agents.

Prediction of collector contact efficiency for colloid transport in porous media using Pore-Network and Neural-Network models

Conventional colloid filtration theory (CFT) uses the single collector contact efficiency (η) to describe the mass transfer of colloids to a collector surface. However, this approach neglects the full complexity of the pore structure and flow field of real porous media. In this study, the porous medium geometry, flow field, and colloid mass transfer are quantified using a pore-network model (PNM). A database of pore scale η is established by finite-element method to train a Neural-network model (NNM). The reasonable prediction of η indicates the potential of using the developed NNMs as an alternative to correlation equations, which can free the users from repeated numerical simulation. In contrast to the prediction by conventional CFT, the value of η in the PNM occurs as a distribution, which is dependent upon the geometry parameters of the PNM. The mean value of η increases with the standard deviation of pore radius and decreases with the curvature number, but the dependency on coordination number is more complex. Upscaled values of the deposition rate coefficient (kd) corresponding to the distribution of η are calculated by the breakthrough curves by PNMs. The prediction of kd by PNM is then compared with that by CFT. Results show that kd predicted by PNM shows more significant response to velocity change, and less remarkable response to colloid density change than kd predicted by CFT. The comparison between the flow velocity distribution between PNM and CFT shows that the high-velocity region of the flow field in the porous media has been neglected in CFT, which can lead to insufficient consideration of convection. The results of this work imply that it is necessary to consider the influence of the complex pore structure of porous media on the collection of colloids.

Magnesium Nanoparticle Synthesis from Powders via Pulsed Laser Ablation in Liquid for Nanocolloid Production

Magnesium nanoparticles of various mean diameters (53–239 nm) were synthesised in this study via pulsed laser ablation in liquid (PLAL) from millimetre sized magnesium powders within isopropyl alcohol. It was observed via a 3 × 3 full factorial design of experiments that the processing parameters can control the nanoparticle distribution to produce three size-distribution types (bimodal, skewed and normal). Ablation times of 2, 5, and 25 min where investigated. An ablation time of 2 min produced a bimodal distribution with the other types seen at higher periods of processing. Mg nanoparticle Ultraviolet–Visible spectroscopy (UV–Vis) absorbance at 204 nm increased linearly with increasing ablation time, indicating an increase in nanoparticle count. The colloidal density (mg/mL) generally increased with increasing nanoparticle mean diameter as noted via increasing UV–Vis absorbance. High laser scan speeds (within the studied range of 3000–3500 mm/s) tend to increase the nanoparticle count/yield. For the first time, the effect of scan speed on colloidal density, UV–Vis absorbance and nanoparticle diameter from metallic powder ablation was investigated and is reported herein. The nanoparticles formed dendritic structures after being drop cast on aluminium foil as observed via field emission scanning electron microscope analysis. Dynamic light scattering was used to measure the size of the nanoparticles. Magnesium nanoparticle inks show promise for use in the fabrication conductive tracks or thermal insulation in electronics.

Colloidal Crystal Thin Films with Square Lattice Nanoprotrusions Formed by Self‐Assembly via Spin‐Coating and Heating

AbstractColloidal crystals with non‐close‐packed structures, such as body‐centered cubic (bcc) structures, are of high interest. Nanosized protrusions, prepared from colloidal crystals, are interesting for biomimetic applications. Herein, self‐assembly approaches for synthesizing colloidal crystals with square lattice nanoprotrusions are presented. In the first approach, spin‐coating and subsequent heating of colloidal silica and acrylic monomer results in a bcc‐like arrangement; the number of stacked colloid layers and the colloid density of these compounds are important in the formation of this structure. Moreover, prolonged heating exposes colloids from acrylic monomer, with square lattice nanoprotrusions formed. In the second approach, the protrusions are fabricated in a shorter time by replacing some of the acrylic monomer with volatile media. Only certain volatile media, such as a solvent with a structure similar to diethylene glycol, exhibit the formation of square lattice protrusions. These bottom‐up approaches contribute toward high‐throughput techniques for fabricating metastable square lattice colloidal arrangements.

Multiple Technique Characterization of the Physical and Chemical Properties of Silica Abrasives Used in Chemical-Mechanical Planarization

The performance of chemical-mechanical planarization (CMP) slurries in the commercial fabrication of integrated circuits depends critically on the physical and chemical properties of abrasive particles used in CMP slurries. A host of analytical methods are used for characterizing the properties of CMP abrasive particles including spectroscopic,1,2 sedimentation,3 viscometric4 and fractionation5 techniques. One particular method, fluorescence correlation spectroscopy (FCS),1 has demonstrated significant versatility in this application due to its ability to simultaneously analyze the particle size distribution and the surface chemistry of abrasive particles in aqueous mixture containing small molecule CMP additives. The need for further characterization of these properties, especially the surface chemistry, is the product of the increasing use of nano-abrasives with reduced hydrodynamic diameters (< 20 nm) in CMP slurries in order to minimize surface defect creation during CMP processes. Incorporation of nano-abrasives in CMP slurries will promote surface chemistry-driven CMP additive adsorption on abrasive particles due to the increase in the total particle surface area as the hydrodynamic diameters of nano-abrasives decrease. The use of FCS in conjunction with the application of complementary techniques, such as dynamic light scattering and fluorescence lifetime analysis, is described in the presentation for the comprehensive characterization of the physical and chemical properties of representative silica abrasives used in CMP slurries.1. Jacobson, L.M.; Turner, D.K.; Wayman, A.; Rawat, A.; Carver, C.T..; Moinpour, M.; Remsen, E.E. “Characterization of Particle Size and Surface Adsorption for SiO2 Abrasives Used in Chemical Mechanical Planarization via Fluorescence Correlation Spectroscopy”, ECS J. Solid State Sci. Tech. 2015, 4, P5053-P5057.2. Marsh, J.L.; Wayman, A.E.; Smiddy, N.M.; Campbell, D.J.; Parker, J.C.; Bosma, W.B.; Remsen, E.E. “Infrared Spectroscopic Analysis of the Adsorption of Pyridine Carboxylic Acids on Colloidal Ceria”, Langmuir 2017, 33 , 13224-13233.3. Kamiti, M.; Boldridge, D.; Ndoping, L.M.; Remsen, E.E. “Simultaneous Absolute Determination of Particle Size and Effective Density of sub-Micron Colloids by Disc Centrifuge Photosedimentometry”, Anal. Chem. 2012, 84, 10526−10530. 4. Boldridge, D.; Kamiti, M.; Remsen, E.E. “Avoiding the Spherical Particle Assumption: Fractal Particle Density, Size and Structure Characterization through Combined Sedimentation and Viscometry Measurements”, Anal. Chem. 2020, 92, 15034-15041.5. Williams, S.K.R.; Park, I.; Remsen, E.E.; Moinpour, M. “New Particle Metrology for CMP Slurries”, Mater. Res. Soc. Symp. Proc. 2007, 991, 249-251.

Electrical conductivity of dilute colloid electrolytes

We discuss the mechanism of the influence of the multiply-charged colloidal clusters on linear electric transport in diluted polyelectrolytes. The structure of these colloids has well known form. They are effectively neutral and cannot participate in the transfer of charges in the solution. Nevertheless, there is a linear increase in the conductivity of colloidal polyelectrolyte with an increase in the density of colloids. This phenomenon is observed experimentally. It is shown that this happens due to the change of electric field in the polyelectrolyte under the effect of colloidal particle polarization.

Формирование структуры каолина, обработанного давлением

To form the technological properties of clays, various methods of their activation have been developed, the essence of which is that when processing clays, their structure (defectiveness) changes, which forms the energy potential of clay particles, and the latter is realized in the form of "specified" physicochemical properties of clays. In this regard, the effect of stress pressure on the change in the defectiveness of structural elements of kaolin was studied. Experimental studies showed that the pressure value P = 150 MPa was the boundary value at which different conditions for the formation of defectiveness of structural elements of kaolin were observed. High pressure has a multidirectional effect on the defectiveness formation of the kaolin structural elements: a package, a mineral, a colloid and an aggregate. In a package of kaolinite mineral, the defectiveness increases with increasing pressure. Defects are formed due to the removal of Al, Fe, Mg, Si ions from the octahedral and tetrahedral sheets. Al ions are the most sensitive to pressure. The removal of ions entails deformation of the packet and the formation of "hole" energy centers. Pressure up to 0–150 MPa has a greater effect on the formation of defectiveness (calculated correlation coefficient rс = 0.86) than in the range 150–800 MPa (rс = 0.82). In the kaolinite mineral at pressures up to 150 MPa, a decrease in defectiveness is observed due to the ordering of the structure under pressure (rс = 0.67). At pressures above 150 MPa, an increase in the defectiveness of the kaolinite mineral (rс = –0.72) is observed due to the destruction of hydrogen bonds between the packets, which entails the sliding and rotation of the structural packets among themselves. In a colloid (particle), with an increase in pressure to 150 MPa, the structural defect decreases due to an increase in the colloid density (rс = 0.67). In the pressure range of 150–800 MPa, it is rather difficult to reveal the effect of pressure on the formation of defectiveness (rс = 0.37). In the aggregate, with an increase in pressure to 150 MPa, the defectiveness of the structure increases due to crushing of particles, sliding and displacement of particles among themselves (rс = 0.95). In the pressure range of 150–800 MPa, it is rather difficult to reveal the influence of pressure on the formation of defectiveness (rс = 0.58), although the tendency increases with increasing pressure, the defectiveness of the aggregate remains.

Preparation and application of polyaluminum chloride for demulsification of colloidal biliquid aphron and density modification for DNAPLs

The preparation and application of suitable demulsifiers in the process of density control of DNPALs is in urgent demand. In this study, we prepared a demulsifier -polyaluminum chloride (PACl), for density modifier -colloidal biliquid aphron (CBLA). We found that PACl2 (PACl with [OH]/[Al] = 2) can make CBLA to completely release light organic liquids within 30 min. The prepared PACl was characterized by SEM, XRD, the reaction curve of PACl with ferron reagent, 27Al NMR and charge density test in order to identify the reactive groups and elucidate the demulsification mechanisms. The system achieved 95% demlusification efficiency in acidic environment (pH < 4). The demulsification process followed pseudo-second-order kinetics model. A small amount of aquifer material could promote demulsification due to natural demulsifiers. We also used PACl2 to break CBLA and modify the density of two DNPALs, trichloroethylene (from 1.464 g/cm3 to 0.980 g/cm3), and nitrobenzene (from 1.197 g/cm3 to 0.921 g/cm3). The results show that the density of DNAPL can be reduced to less than that of water, which effectively prevents the downward migration of DNAPLs during remediation process. The findings will improve our understanding of the mechanism of CBLA demulsification and its density modification of DNAPLs for enhanced groundwater remediation.

Quantification of the Structure of Colloidal Gas-Liquid Interfaces.

We have quantified the structure of the colloidal gas–liquid interface using synchrotron X-ray reflectivity measurements on a model colloid–polymer mixture. The interfacial width shows mean-field scaling with the colloid density difference, and the density profiles appear to be monotonic. Furthermore, our measurements allow us to distinguish between different theoretical polymer descriptions commonly used to model colloid–polymer mixtures. Our results highlight the importance of capturing the correct polymer physics in obtaining a quantitative theoretical description of the colloidal gas–liquid interface.

Origin of Laser-Induced Colloidal Gold Surface Oxidation and Charge Density, and Its Role in Oxidation Catalysis

Laser fragmentation in liquids (LFL) allows the synthesis of fully inorganic, ultrasmall gold nanoparticles, usAu NPs (<3 nm). Although the general method is well established, there is a lack of un...

Modelling the fate and transport of colloidal particles in association with BPA in river water

A simplified modelling approach for illustrating the fate of emerging pollutants can improve risk assessment of these chemicals. Once released into aquatic environments, these pollutants will interact with various substances including suspended particles, colloidal or nano particles, which will greatly influence their distribution and ultimate fate. Understanding these interactions in aquatic environments continues to be an important issue because of their possible risk. In this study, bisphenol A (BPA) in the water column of Bentong River, Malaysia, was investigated in both its soluble and colloidal phase. A spatially explicit hydrological model was established to illustrate the associated dispersion processes of colloidal-bound BPA. Modelling results demonstrated the significance of spatial detail in predicting hot spots or peak concentrations of colloidal-bound BPA in the sediment and water columns as well. The magnitude and setting of such spots were system based and depended mainly on flow conditions. The results highlighted the effects of colloidal particles' concentration and density on BPA's removal from the water column. It also demonstrated the tendency of colloidal particles to aggregate and the impact all these processes had on BPA's transport potential and fate in a river water. All scenarios showed that after 7.5–10 km mark BPA's concentration started to reach a steady state with very low concentrations which indicated that a downstream transport of colloidal-bound BPA was less likely due to minute BPA levels.

Evaluation of effectiveness of antiandrogen treatments on cavernosal tissues in rats.

In this study, we aimed to compare changes in cavernosal tissues in rats with antiandrogen treatment and orchiectomy. A total of 42 Wistar albino rats were divided into four groups. Group I, control group,Group II, LH-RH was given for 1month, Group III-LH-RH+Bicalutamide was given for 1month, and Group IV was defined as orchiectomy and followed up for 1month. Measurements of intracavernosal pressure with different electrical stimuli and pathological findings of smooth muscle collagen in cavernosal tissues were examined. While the cavernosal pressure response in all the different electrical stimuli given in the control group and in all other groups was significantly lower than that in the other groups, it was statistically significant at 7.5 and 10V (p=.005, p<0001). According to the pathologic evaluation, the density of tissue collagen increased significantly in the other groups according to the control group. In groups 3 and 4, the density of 4+ collagen was found to be increased according to Groups 1 and 2. In the LH-RH alone group, it appears that there are no 4+ colloid density and less damage. According to these findings, the negative effect of LH-RH treatment on cavernosal tissues appears to be less.

Evaluation of selected properties of a gelatinized potato starch colloid by an ultrasonic method

The aim of the work was to provide accurate models for an evaluation of a potato starch colloid properties based on fast ultrasonic tests. All measurements were performed considering five temperatures (20, 25, 30, 35 and 40 °C) of colloids with a starch concentration from 1 to 5%. In these conditions, density of studied colloids was determined, and ultrasound signals transmitted through them were registered. Based on the ultrasonic measurement, the sound velocity was determined. Results of these measurements were used to derive several empirical models. These models allow, for example, to perform rapid calculations of potato starch colloid density at a given temperature based on the sound velocity measurement with a relative error of 0.15% or even 0.09% for specific frequency (10 MHz), which is the highest accuracy of considered methods. Findings of this work can be implemented in industrial devices used for real-time on-line monitoring of technological processes.

Формирование структуры каолина, обработанного давлением

To form the technological properties of clays, various methods of their activation have been developed, the essence of which is that when processing clays, their structure (defectiveness) changes, which forms the energy potential of clay particles, and the latter is realized in the form of "specified" physicochemical properties of clays. In this regard, the effect of stress pressure on the change in the defectiveness of structural elements of kaolin was studied. Experimental studies showed that the pressure value P = 150 MPa was the boundary value at which different conditions for the formation of defectiveness of structural elements of kaolin were observed. High pressure has a multidirectional effect on the defectiveness formation of the kaolin structural elements: a package, a mineral, a colloid and an aggregate. In a package of kaolinite mineral, the defectiveness increases with increasing pressure. Defects are formed due to the removal of Al, Fe, Mg, Si ions from the octahedral and tetrahedral sheets. Al ions are the most sensitive to pressure. The removal of ions entails deformation of the packet and the formation of "hole" energy centers. Pressure up to 0–150 MPa has a greater effect on the formation of defectiveness (calculated correlation coefficient rс = 0.86) than in the range 150–800 MPa (rс = 0.82). In the kaolinite mineral at pressures up to 150 MPa, a decrease in defectiveness is observed due to the ordering of the structure under pressure (rс = 0.67). At pressures above 150 MPa, an increase in the defectiveness of the kaolinite mineral (rс = –0.72) is observed due to the destruction of hydrogen bonds between the packets, which entails the sliding and rotation of the structural packets among themselves. In a colloid (particle), with an increase in pressure to 150 MPa, the structural defect decreases due to an increase in the colloid density (rс = 0.67). In the pressure range of 150–800 MPa, it is rather difficult to reveal the effect of pressure on the formation of defectiveness (rс = 0.37). In the aggregate, with an increase in pressure to 150 MPa, the defectiveness of the structure increases due to crushing of particles, sliding and displacement of particles among themselves (rс = 0.95). In the pressure range of 150–800 MPa, it is rather difficult to reveal the influence of pressure on the formation of defectiveness (rс = 0.58), although the tendency increases with increasing pressure, the defectiveness of the aggregate remains.