Suspensions Of Colloidal Particles Research Articles

Phase‐Change Materials for Controlled Release and Related Applications

Phase-change materials (PCMs) have emerged as a novel class of thermo-responsive materials for controlled release, where the payloads encapsulated in a solid matrix are released only upon melting the PCM to trigger a solid-to-liquid phase transition. Herein, the advances over the past 10 years in utilizing PCMs as a versatile platform for the encapsulation and release of various types of therapeutic agents and biological effectors are highlighted. A brief introduction to PCMs in the context of desired properties for controlled release and related applications is provided. Among the various types of PCMs, a specific focus is placed on fatty acids and fatty alcohols for their natural availability, low toxicity, biodegradability, diversity, high abundance, and low cost. Then, various methods capable of processing PCMs, and their mixtures with payloads, into stable suspensions of colloidal particles, and the different means for triggering the solid-to-liquid phase transition are discussed. Finally, a range of applications enabled by the controlled release system based on PCMs are presented together with some perspectives on future directions.

Viscoplastic drop impact on thin films

We use high-speed imaging to study the effect of thixotropic aging in drop impact of yield-stress fluids on pre-coated substrates. Our results reveal that drop splashing is suppressed for "aged" compared to "unaged" samples, indicating that thixotropic breakdown timescales during impact are long enough to affect the dynamics. We propose and test several hypotheses for modifying the dimensionless group ${\rm IF}(D/t)$ [1,2] to account for thixotropic aging. The main challenge is that the steady flow properties (Herschel-Bulkley model parameters) used in the current dimensionless group cannot be defined or measured for thixotropically aged samples, because any deformation inherently rejuvenates and breaks down the microstructure. We find the most suitable hypothesis is to only increase the yield stress ($\sigma_{\rm y}$, plastic component) based on the storage modulus of aged samples, while keeping the viscous parameters ($K$ or $\eta_{\infty}$) constant. The work reveals fundamental insight into rarely studied short-timescale flow conditions with thixotropic effects. These results are important for applications such as fire suppression or spray coating that involve complex fluids of varying degrees of thixotropic aging.

Enhanced fabrication of silicon carbide membranes for wastewater treatment: From laboratory to industrial scale

An environmental-friendly procedure has been developed for the fabrication of pure silicon carbide membranes on macroporous SiC support via ceramic processing. Water dispersions of α-SiC powders were used for deposition of membrane layers by dip-coating. The influence of the fine/coarse powder mixing ratio, solid loading, use of α-SiC powders with different particle sizes as well as sintering temperature on the structural morphology of the membranes were investigated in order to obtain uniform, homogeneous, and defect-free SiC membrane layers. The optimized protocol was up-scaled on industrial SiC tubular supports with high reproducibility, reducing the sintering temperature compared to conventional SiC membrane synthesis. The new SiC membranes were used for the treatment of a secondary effluent from Biofos wastewater treatment plant in Avedøre, Denmark, and their performances evaluated in terms of removal of the suspended solids, colloidal particles and reduction of chemical oxygen demand. According to filtration results, the new SiC membranes showed high removal of suspended solids (99.4%) and colloidal particles (96%) along with significant reduction of chemical oxygen demand (83%). The pure SiC membranes developed in this study have a potential to be applied in the wastewater treatment since they combine the robustness of SiC with high selectivity.

A facile two-step approach to synthesize monodisperse and high-magnetization Fe3O4@PS composite colloidal particles for constructing dual-response photonic crystals

Monodisperse Fe3O4@PS colloidal particles with hollow core/shell structure and high saturation magnetization were successfully fabricated by a facile chemical approach. Owing to magnetic nature of iron oxide core and positively charged polystyrene shell, the colloidal particles in suspension assembled into ordered array and showed dual-response behavior to magnetic and electric field. When the cooperation between magnetic and electric field matched well, the photonic crystals showed better structural color and higher reflectivity. Consequently, as-synthesized Fe3O4@PS colloids have great potentials in some high-tech fields such as color sensors, color display, camouflage, electronic papers, and so on.

Improving tribological properties of oil-based lubricants using hybrid colloidal additives

Colloidal particles and ionic liquids (ILs) are emerging as potential additives for enhancing lubricant performance. We examine a hybrid system containing colloidal suspensions of hairy silica particles (HSPs) in an IL and motor oil. HSPs swollen in IL lower the sliding friction between steel ball-plate tribopairs at room temperature, while the addition of HSP/IL into motor oil at 100 °C dramatically impacts wear and lubrication. This included prevention of significant noise and scuffing from occurring in the tribometer when using motor oil alone. The outstanding performance of the HSP/IL to modulate friction and wear suggests such hybrid lubricants have potential to be the basis for a new class of tuneable friction modifiers to low-viscosity ‘energy efficient’ lubricants.

Dispersion of praseodymium-doped zirconium silicate pigment in aqueous suspension by modified hydroxyl copolymer

Water-based copolymer dispersants, i.e., sodium polyacrylic acid-co-2-acrylamide-2-methylpropanesulfonic acid-co-glycerol monomethacrylate (PASGS), were synthesized for dispersion of praseodymium-doped zirconium silicate pigment in aqueous suspension with polyacrylic acid-co-2-acrylamido-2-methylpropanesulfonic acid (PAS). Effects of different parameters on the dispersion behavior of colloidal particles were investigated via sedimentation tests. The samples were characterized by particle size analysis, Fourier transform infrared spectroscopy, and electrokinetic potential measurement. The interparticle potential energy at different pH values and dispersant types was calculated. The results show that PASG1 at 3wt.% addition effectively disperses the colloidal particles in the denser suspension of 35wt.% at pH 7.0, compared to PAS. Dispersant PASG1 provides greater steric hindrance and electrostatic repulsive energies than dispersant PAS. The dispersion/aggregation behavior of colloidal particles in the suspension under different conditions was also predicted by a modified population balance model (PBM). The predicted data are similar to the experimental results.

Simple Method for Rheological Determination of Surfactant Layer Thickness, Adsorbed on Soft Rubber Particles.

Natural rubber latex is a colloidal suspension of particles, which is very important for many industrial applications. These latex particles are not only polydispersed but also very soft and deformable, which makes the prediction of rheological properties much difficult. Herein, the rheology of natural rubber latex has been studied at high particle concentrations, analyzing the effects of surfactant addition on colloidal stability. A hydrophobically modified inulin surfactant (INUTEC NRA) was selected for this study since previous works had shown that this inulin surfactant imparts good colloidal stability to polystyrene latex particles. The most important objective was studying the influence of the surfactant on the particle adsorbed layer and determining the thickness of the adsorbed surfactant layer. The results showed that the relative viscosity increased as a function of latex volume fraction, and this increase became extremely sharp as the volume fraction approached the maximum packing volume fraction, as expected. This variation in viscosity with the volume fraction has a complex behavior, which could not be analyzed using conventional models based on hard rigid spheres, such as Krieger-Dougherty (K-D) or Maron-Pierce (M-P). Herein, we describe a simple semiempirical method to determine the surfactant adsorbed layer thickness, based on the linear dependence of intrinsic viscosity with 1/(ϕmax - ϕ)2, where ϕ is the volume fraction of rubber particles and ϕmax is the maximum volume fraction at which viscosity tends to infinity. The difference in the maximum packing fraction, with and without the surfactant, allows the calculation of the adsorbed layer thickness, δ ≈ 2.8 nm, which is a good estimate for the thickness of surfactant molecules adsorbed on latex particles. This surfactant thickness has been confirmed by direct measurements using dynamic light scattering (DLS), which gave a value of 3.1 nm. Viscoelastic oscillatory measurements have also been performed, showing that natural rubber particle suspensions are predominantly elastic above ϕ = 0.63 latex volume fractions. The elastic modulus has been analyzed as a function of surfactant concentration, confirming that the stability of latex particles is mainly controlled by the surfactant concentration.

Intrinsic viscosities of non-spherical colloids by Brownian dynamics simulations.

A numerical study is presented on the intrinsic viscosities of sheared dilute suspensions of nonspherical Brownian colloidal particles. The simulations confirm theoretical predictions on the intrinsic viscosities of highly oblate and highly prolate spheroids in the limits of weak and strong Brownian noise (i.e., for low and high Péclet numbers). Numerical data and fit functions are provided covering the entire shear-thinning regime, for spheroids ranging from highly oblate to highly prolate. The tumbling motion and intrinsic viscosities of a hemispherical cap and a helix are briefly discussed.

Special Issue on Nanofluids and Their Applications

Nanofluids can be considered as engineered colloidal suspensions of nanometer-sized particles in a base fluid of water, ethylene glycol, or oil [...]

Effect of Alumina Addition on the Rheological Behavior of Shear Thickening Fluids

Shear thickening fluids (STF) have attracted much attention in many applications including body armor. In this study, suspensions of silica colloidal particles and polyethylene glycol fluid were prepared at varying volume fractions φ = 0.3 to 0.52 and their rheological behavior was investigated. It was found that the suspensions exhibited a Newtonian behavior for φ < 0.4, whilst a shear thinning followed by a thickening behavior could clearly be observed for φ > 0.4. Furthermore, the critical shear rates for the onset of shear thickening was found to decrease with increasing silica volume fraction but the corresponding critical shear stresses were independent of the volume fraction. To improve the ballistic protective performance, small amount of hard material particles, such as alumina, were added into the silica suspension of φ = 0.5. It was shown that the critical shear rates of the reinforced-STFs decreased with increasing volume fraction and decreasing alumina particle size. However, higher thickening ratio was observed for the alumina additive with agglomerated structure and this ratio increased with increasing alumina volume fraction.

Carbon-based electronic textiles: materials, fabrication processes and applications

Electronic textiles (E-textiles) impart the conductive functionality in textiles without altering the intrinsic properties of textile materials. The growth of E-textiles requires the development of functional materials and the scaling-up of their production methods. Since textile is a porous, and anisotropic three-dimensional material, it is crucial to develop the scalable methods to apply these functional materials on textiles efficiently that can impart added functionality to the pristine textile materials. Organic carbon-based functional materials are being widely used for the comparative low-cost manufacturing process and the availability of their raw materials. Thus, the overview of the different carbonaceous conductive materials and their application methods on textiles is very important to understand and compare for utilizing these materials efficiently in numerous E-textile applications. This paper reviews the fabrication procedures of the common carbon-based electronic materials, the methods of formulating colloidal suspensions of different carbonaceous particles in the liquid solvent to develop conductive inks, the methods to apply the inks on textile substrates, and relevant use cases. A critical review has been discussed to compare and select appropriate materials and their application methods on textiles for the scalable manufacturing process and desired electrical characteristics.

Adsorptive removal of C.I. Direct Yellow 142 from textile baths using nanosized silica-titanium oxide

.The adsorption properties of the silica-titanium mixed oxide consisting of 80 wt.% SiO2 and 20 wt.% TiO2 (ST20) in relation to C.I. Direct Yellow 142 (DY142) were examined. The experimental adsorption capacity of ST20 for DY142 determined at room temperature equals 104.8 mg/g. The equilibrium data were fitted by means of the Freundlich, Langmuir and Tempkin isotherm models. The values of determination coefficients (r2) confirmed applicability of the Langmuir ( r^{2}=0.990) isotherm model, the monolayer capacity was found to be 106.5 mg/g. The kinetic parameters calculated from the pseudo-first-order (PFO) and pseudo-second-order (PSO) equations as well as the intraparticle diffusion (IPD) model revealed that the chemisorption is the rate limiting step as the r2 value obtained for the pseudo-second-order model equals 0.999. The PSO adsorption rate constant was found to be 0.070 g/mg min. The presence of additives such as electrolytes (Na2SO4 and Na2CO3) and surface active agents (anionic SDS, cationic CTAB and non-ionic Triton X-100) reduce dye retention compared to systems that do not contain these additives. The presence of the dye with the anionic character in the colloidal suspension of ST20 oxide particles results in considerable increase of the solid surface charge density. In the systems of mixed adsorbates (dye-surfactant and dye-salt) the specific changes in surface properties were obtained --the cationic surfactant has the greatest effect on the solid surface groups type and its concentration.

Enhanced removal of suspended colloidal particles from turbid water using a modified microbial flocculant

Microbial flocculant (MBF), as an efficient, environmental friendly and biodegradable flocculant, has been widely studied in water treatment. The cationic modification of MBF would improve its charge neutralization and extend its application. In this study, the effect of mAM:mDMDAAC, mMBF:m(AM + DMDAAC), reaction temperature and initiator dosage on the molecular weight of modified MBF were investigated. The optimal synthesis condition was obtained. Modified MBF performed well in the removal of suspended colloidal particles from water. It possessed the potential application in the surface water treatment.

Long-wavelength fluctuations and static correlations in quasi-2D colloidal suspensions.

Dimensionality strongly affects thermal fluctuations and critical dynamics of equilibrium systems. These influences persist in amorphous systems going through the nonequilibrium glass transition. Here, we experimentally study the glass transition of quasi-2D suspensions of spherical and ellipsoidal particles under different degrees of circular confinement. We show that the strength of the long-wavelength fluctuations increases logarithmically with system sizes and displays the signature of the Mermin-Wagner fluctuations. Moreover, using confinement as a tool, we also measure static structural correlations and extract a growing static correlation length in 2D supercooled liquids. Finally, we explore the influence of the Mermin-Wagner fluctuations on the translational and orientational relaxations of 2D ellipsoidal suspensions, which leads to a new interpretation of the two-step glass transition and the orientational glass phase of anisotropic particles. Our study reveals the importance of long-wavelength fluctuations in 2D supercooled liquids and provides new insights into the role of dimensionality in the glass transition.

Biaxial nematics of hard cuboids in an external field.

By computer simulation, we model the phase behaviour of colloidal suspensions of board-like particles under the effect of an external field and assess the still disputed occurrence of the biaxial nematic (NB) liquid crystal phase. The external field promotes the rearrangement of the initial isotropic (I) or uniaxial nematic (NU) phase and the formation of the NB phase. In particular, very weak field strengths are sufficient to spark a direct I-NB or NU-NB phase transition at the self-dual shape, where prolate and oblate particle geometries fuse into one. By contrast, forming the NB phase at any other geometry requires stronger fields and thus reduces the energy efficiency of the phase transformation. Our simulation results show that self-dual shaped board-like particles with moderate anisotropy are able to form NB liquid crystals under the effect of a surprisingly weak external stimulus and suggest a path to exploit low-energy uniaxial-to-biaxial order switching.

Dynamic clustering and re-dispersion in concentrated colloid-active gel composites.

We study the dynamics of quasi-two-dimensional concentrated suspensions of colloidal particles in active gels by computer simulations. Remarkably, we find that activity induces a dynamic clustering of colloids even in the absence of any preferential anchoring of the active nematic director at the particle surface. When such an anchoring is present, active stresses instead compete with elastic forces and re-disperse the aggregates observed in passive colloid-liquid crystal composites. Our quasi-two-dimensional "inverse" dispersions of passive particles in active fluids (as opposed to the more common "direct" suspensions of active particles in passive fluids) provide a promising route towards the self-assembly of new soft materials.

Characterization of aqueous cellulose nanofiber dispersions from microscopy movie data of Brownian particles by trajectory analysis.

Cellulose nanofibers (CNFs) are promising for various applications such as substrates of flexible devices and reinforcement materials. Most of these applications require control of the drying process of the aqueous CNF dispersions. However, the existing reports examine the surface of dried materials because scanning electron microscopy (SEM) and atomic force microscopy (AFM) are not compatible with either the wet conditions or structure inside the materials. We report the characterization of these aqueous dispersions by the use of optical microscopy although it cannot be used directly to observe CNFs. We add a small portion of colloidal particles into the samples and obtain their trajectory data. The trajectories of Brownian motion include information on the surrounding environments. We analyze the microscopy movie data from the viewpoint of statistical mechanics, and reveal the mesoscale characteristics beyond viscosity. In particular, the possible non-uniformity of the dispersion is quantitatively examined through the framework of the generalized diffusion.

예술 및 음악과 융합할 수 있는 재료로서의 나노 유체에 대한 연구

Nano science and nanotechnology has convergence with sports, music, and arts beyond convergence with other scientific technologies, and comes to develop into a totally new area. Ferrofluids feature the creation of the magnetic field induced shape on the ferrofluid surface, combination of drops, and magnetic microconvection. Because of its small particles size, a ferrofluid has been developed as a promising new nanomaterial the beginning. Ferrofluids are more applied to diverse areas, such as dynamic loudspeakers, computer hardware, dynamic sealing, and bioengineering because of their unique properties. The research method is as follows.BR Firstly, introduction of the background and scope of the study. The basic theories for ferrofluid science and examples of convergent work with ferrofluids are known and published.BR Secondly, the classification of magnetic fields are introduced. There are generally two type of magnetic fields which are magnetorheological fluids and ferrofluids. A ferrofluid is a colloidal suspension of magnetic particles with a very tiny size in a liquid carrier. A ferrofluid is different from MRF with regard to its fluidity even if subjected to strong magnetic fields.BR Thirdly, A key to the application of ferrofluids is colloidal stability. The stability is determined by the balance of multiple types of energy (attractive and repulsive forces) which are the factors to prevent separation for a given time after the disappearance of exterior magnetic fields and thermal energy. If average thermal energy exceeds a total of interaction, negligible agglutination arises. There are two types of ferrofluid which are water-based ionic fluid and organic media based ferrofluid. To use ferrofluid to convergent with arts or other areas, important factors are low viscosity, low vapor pressure and chemical inertness of carrier liquids and surfactants.BR Finally, There are many areas which convergent with ferrofluid to invent totally new work and to sell fantastical products which never meet before. Those areas are arts, music, sculpture, and commercial products. According to the development the nanotechnology, the convergence of ferrofluid with arts or other areas will be accelerate and develop further and intensively.

Rheology of a colloidal suspension of carbon nanotube particles in a water-based drilling fluid

High-pressure and high-temperature rheology of a nanomud suspension is studied. The nanomud is prepared by dispersing a water-based drilling mud suspension with multi-walled carbon nanotubes (MWCNT). Effect of nanoparticle concentration, shear rate, pressure, and temperature are investigated. The pressure and temperature are independently varied from ambient conditions to 170 MPa and 180 °C respectively. The results presented show that the addition of CNT increases the viscosity of the drilling mud. A shear thinning non-Newtonian behavior is observed for the basemud and the nanomud samples at all pressures and temperatures. The basemud showed an increase in viscosity with an increase in pressure. However, with CNT particle addition this trend is observed to have reversed. For the basemud and the nanomud at lower concentrations, the viscosity values are observed to have initially increased with the increase in temperature and to have reduced beyond 100 °C. For a higher particle loading, a consistent decrease in viscosity with temperature is observed. The behavior of higher concentration nanomud samples with respect to pressure and temperature are seen to follow a similar trend to that of water. It is reasoned that an adequate addition of CNT nanoparticles helps retain the mud particles in a more homogenous and stable state, where they are held within the CNT chains. However, with further addition of CNT nanoparticles, the mud particles become agglomerated with the long chains of CNT, eventually separating water from the drilling fluid mixture.

Experimental observations of bands of suspended colloidal particles subject to shear flow and steady electric field

Manipulating suspended colloidal particles flowing through a microchannel is of interest in microfluidics and nanotechnology. However, the flow itself can affect the dynamics of these suspended particles via wall-normal “lift” forces. The near-wall dynamics of particles suspended in shear flow and subject to a dc electric field was quantified in combined Poiseuille and EO flow through a ~ 30 μm deep channel. When the two flows are in opposite directions, the particles are attracted to the wall. They then assemble into very high aspect ratio structures, or concentrated streamwise “bands,” above a minimum electric field magnitude, and, it appears, a minimum near-wall shear rate. These bands only exist over the few micrometers next to the wall and are roughly periodic in the cross-stream direction, although there are no external forces along this direction. Experimental observations and dimensional analysis of the time for the first band to form and the number of bands over a field of view of ~ 200 μm are presented for dilute suspensions of polystyrene particles over a range of particle radii, concentrations, and zeta potentials. To our knowledge, there is no theoretical explanation for band assembly, but the results presented here demonstrate that it occurs over a wide range of different particle and flow parameters.