Dispersions Of Colloidal Particles Research Articles

Electrochemical Synthesis of Self-Doped Poly(3,4-ethylenedioxythiophene) and Application to Flexible Biosensors

Wet-processable and highly conductive polymers are promising candidates for key materials in organic electronics. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), commercially available as a water dispersion of colloidal particles, has potential applications to organic electronics because of its high electrical conductivity, transparency and thermal stability 1). However, the PEDOT:PSS has some technical issues owing to the PSS: The ultra-thin layers thinner than the colloidal particle size is difficult; The PEDOT:PSS colloids aggregate and precipitate when stored for an extended period; The pristine PEDOT:PSS exhibits poor electrical conductivity without secondary dopants such as ethylene glycol and DMSO. Recently, we have developed a novel fully soluble self-doped PEDOT (S-PEDOT) by chemical oxidative polymerization having a high conductivity without secondary dopants 2).This presentation deals with the first study on synthesis of the S-PEDOT by a facile electrochemical polymerization and characterization by means of cyclic voltammetry (CV), reflection spectroscopy, X-ray diffraction analysis (XRD), and the four-point technique.The S-PEDOT was electrochemically synthesized at different current densities ranging from 0.5 to 5 mA/cm2. It was found that the electrical conductivity increased with increasing current density and attained as high as 427 S/cm at 5 mA/cm2 which was one order of magnitude higher than those so far reported in the literature. Further investigation has been made to clarify the role and effect of current density on molecular weight, crystallinity, and carrier transport properties in more detail.For the application to biosensors, flexible organic electronic circuits consisting of working, counter, and reference electrodes were fabricated by line-patterning 3) the S-PEDOT water solution as a conductive ink on a Kapton film as a flexible substrate. The flexible glucose sensor was then fabricated by coating the bioink containing glucose oxidase, ferrocene, and chitosan on the working electrode. It was found that the flexible biosensor successfully worked where the electric current during the CV measurement increased with increasing the glucose concentration.1) H. Okuzaki ed., PEDOT: Materials Properties and Device Applications, S&T (2012).2) H. Yano, K. Kudo, K. Marumo, H. Okuzaki, Sci. Adv., 5, eaav9492 (2019).3) D. Hohnholz, H. Okuzaki, and A. G. MacDiarmid, Adv. Funct. Mater., 15, 51 (2005).

Molecular-Level Relation between the Intraparticle Glass Transition Temperature and the Stability of Colloidal Suspensions.

In many colloidal suspensions, the dispersed colloidal particles are amorphous solids, resulting from vitrification. A crucial open problem is understanding how colloidal stability is affected by the intraparticle glass transition. By dealing with the latter process from a solid-state perspective, we estabilish a proportionality relation between the intraparticle glass transition temperature, Tg, and the Hamaker constant, AH, of a generic suspension of nanoparticles. It follows that Tg can be used as a convenient parameter (alternative to AH) for controlling the stability of colloidal systems. Within the Derjaguin-Landau-Verwey-Overbeek theory, we show that the novel relationship, connecting Tg to AH, implies the critical coagulation ionic strength to be a monotonically decreasing function of Tg. We connect our predictions to recent experimental findings.

Heterostructure particles enable omnidispersible in water and oil towards organic dye recycle

Dispersion of colloidal particles in water or oil is extensively desired for industrial and environmental applications. However, it often strongly depends on indispensable assistance of chemical surfactants or introduction of nanoprotrusions onto the particle surface. Here we demonstrate the omnidispersity of hydrophilic-hydrophobic heterostructure particles (HL-HBPs), synthesized by a surface heterogeneous nanostructuring strategy. Photo-induced force microscopy (PiFM) and adhesion force images both indicate the heterogeneous distribution of hydrophilic domains and hydrophobic domains on the particle surface. These alternating domains allow HL-HBPs to be dispersed in various solvents with different polarity and boiling point. The HL-HBPs can efficiently adsorb organic dyes from water and release them into organic solvents within several seconds. The surface heterogeneous nanostructuring strategy provides an unconventional approach to achieve omnidispersion of colloidal particles beyond surface modification, and the omnidispersible HL-HBPs demonstrate superior capability for dye recycle merely by solvent exchange. These omnidispersible HL-HBPs show great potentials in industrial process and environmental protection.

Evolution of colloidal coatings due to a wetting and drying process

Paints and coatings are usually made by depositing a volatile liquid containing dispersed colloidal particles. The dry film is obtained through the evaporation of the volatile liquid. Depending on the ability of the particles to deform under capillary effect, we show that the drying can yield continuous coatings with no porosity, uniform porous coatings, or the formation of singularities, such as cracks causing the final film to be non-uniform. The evolution of the resulting coatings is then subjected to a wetting and drying process. Wetting leads to an increase in the water content of the unsaturated porous coating while drying results in water reduction. The response of the coatings to such a process can exhibit slight or significant changes in the morphology of the coatings that are related to their rheological properties. In particular, the growth of blisters is reported during the wetting and drying process.

Enhanced dispersion in an oscillating array of harmonic traps.

Experiment, theory, and simulation are employed to understand the dispersion of colloidal particles in a periodic array of oscillating harmonic traps generated by optical tweezers. In the presence of trap oscillation, a nonmonotonic and anisotropic dispersion is observed. Surprisingly, the stiffest traps produce the largest dispersion at a critical frequency, and the particles diffuse significantly faster in the direction of oscillation than those undergoing passive Stokes-Einstein-Sutherland diffusion. Theoretical predictions for the effective diffusivity of the particles as a function of trap stiffness and oscillation frequency are developed using generalized Taylor dispersion theory and Brownian dynamics simulations. Both theory and simulation demonstrate excellent agreement with the experiments, and reveal a "slingshot" mechanism that predicts a significant enhancement of colloidal diffusion in dynamic external fields.

Continuous resin refilling and hydrogen bond synergistically assisted 3D structural color printing

3D photonic crystals (PCs) have attracted extensive attention due to their unique optical properties. However, fabricating 3D PCs structure by 3D printing colloidal particles is limited by control of assembly under a fast-printing speed. Here, we employ continuous digital light processing (DLP) 3D printing strategy with hydrogen bonds assisted colloidal inks for fabricating well-assembled 3D PCs structures. Stable dispersion of colloidal particles inside UV-curable system induced by hydrogen bonding and suction force induced by continuous curing manner cooperatively realize the simultaneous macroscopic printing and microscopic particle assembly, which endows volumetric color property. Structural color can be well regulated by controlling the particle diameter and printing speed, through which various complex 3D structures with desired structural color distribution and optical light-guide properties are acquired. This 3D color construction approach shows great potential in customized jewelry accessories, decoration and optical device preparation, and will innovate the development of structural color.

Study of the physico-chemical, structural, microbiological properties and volatile flavour compounds profile of kefir supplemented with electro-activated whey

The physico-chemical, microbiological, structural properties, and the volatile flavour compounds of kefir supplemented with electro-activated whey (EAW) at 3–9% level were studied. Fermentation kinetics showed a delayed time to reach pH 4.6 in kefir with electro-activated whey. Syneresis was absent in the kefir with electro-activated whey. Kefir with 3% EAW showed non-Newtonian pseudoplastic behaviour with shear thinning characteristics, whereas the 9% supplemented kefir had Newtonian pseudoplastic behaviour. The mineral profile showed higher K+ content in kefir with EAW, which was due to its high content in this ingredient. Electron scanning microscopy revealed a homogeneous fine structure of kefir with EAW compared with the control or whey supplemented kefir. This structure indicated entrapment of EAW particles in the kefir matrix which is a liquid dairy product with dispersed colloidal particles. GC analysis showed rich volatile aromatic profile of kefir with electro-activated whey.

Differentiation among dairy products by combination of fast field cycling NMR relaxometry data and chemometrics.

A set of commercial milk and Sicilian cheeses was analysed by a combination of fast field cycling (FFC) nuclear magnetic resonance (NMR) relaxometry and chemometrics. The NMR dispersion (NMRD) curves were successfully analysed with a mathematical model applied on Parmigiano-Reggiano (PR) cheese. Regression parameters were led back to the molecular components of cheeses (water trapped in casein micelles, proteins and fats) and milk samples (water belonging to hydration shells around dispersed colloidal particles of different sizes and bulk water). The application of chemometric analysis on relaxometric data enabled differentiating milk from cheeses and revealing differences within the two sample groups of either cheeses or milk samples. Marked differences among cheeses were evidenced by statistical analysis of the sole quadrupolar peaks parameters, suggesting that these contain information on the nature of the milk used during cheese production. Hence, combination of FFC NMR and chemometrics represents a powerful tool to investigate alterations in dairy products.

Colloidal assembly by directional ice templating.

We investigate directional ice templating of dilute aqueous colloidal particle dispersions and examine the nature of the assemblies that result. We coat micron-size polystyrene colloids with cross-linkable polymer (polyethyleneimine, PEI), add cross-linker, and subject this dispersion to unidirectional freezing. We work at sufficiently low colloid concentrations, such that the particles do not percolate on freezing. When the aqueous dispersion freezes, ice crystals force polymer-coated particles and cross-linker into close proximity. This results in the formation of cross-linked clusters of particles at ice crystal boundaries. We vary the particle volume fraction from φ ∼ 2.5 × 10-3 to φ ∼ 5.0 × 10-2 and observe that there is a transition from isolated single particles to increasingly large sized clusters. Most of the clusters formed under these conditions are either linear, two-particle wide chains, or sheet-like aggregates. The probability (Pn) of clusters containing n particles (n > 2) obeys a power law Pn ∼ n-η, where η strongly depends on the particle concentration in the dispersion, varying from 2.10 (for φ ∼ 5.0 × 10-2) to 3.03 (for φ ∼ 2.5 × 10-3). This change in η is qualitatively different from the case of isotropic freezing, where η is particle concentration-independent and depends only on the ice nucleation density. To understand the differences between isotropic and directional ice templating, we performed lattice simulations of a highly simplified model, where ice crystals grow at a constant rate to force clustering. We ignore hydrodynamic interactions and ice growth instabilities. Despite ignoring these experimental details, the simulations capture the experimental results, nearly quantitatively. As the ice crystals grow and the space available to the colloids "closes up" so that the particles cluster to form aggregates, crystallization protocol-induced differences in the geometry of these "closed up" spaces determine the scaling behaviour of Pn.

Effect of gum arabic or sodium alginate incorporation on the physicochemical and curcumin retention properties of liposomes

Natural biopolymers such as food gums can be effective in improving the physical stability of colloidal particle dispersions. To improve the loading stability of curcumin in liposomes, liposomes with gum arabic (GA) or sodium alginate (SA) (0–2% w/v) were prepared and their physicochemical properties evaluated. Results showed that GA, which has a high surface activity, interacted more with the liposome surface resulting in smaller liposome size and polydispersity. However GA disrupted the internal lamellar structure of the liposomes at low concentrations, resulting in increased flocculation and was associated with poor retention of encapsulated curcumin. In contrast, SA formed a viscious continuous phase due to the gum network which reduced particle mobility and sedimentation, and increased curcumin retention, although this was associated with an increase in particle size and polydispersity index.

Highly-efficient and easy separation of hexahedral sodium dodecyl sulfonate/δ-FeOOH colloidal particles for enhanced removal of aqueous thallium and uranium ions: Synergistic effect and mechanism study

Thallium (Tl) and uranium (U) contaminants pose serious threats to the ecological environment and human health. In this research, a cost-effective feroxyhite (δ-FeOOH) dispersed with sodium dodecyl sulfonate (SDS) was prepared and a series of experiments were optimized to explore the removal mechanism of Tl+ and UO22+ from the effluent. The SDS/δ-FeOOH exhibited highly dispersed colloidal particles and showed significantly enhanced adsorption performance on the removal of Tl and U in the presence of H2O2 and pH of 7.0. Equilibrium uptakes of 99.5% and 99.7% were rapidly achieved for Tl+ and UO22+ within 10 min, respectively. The Freundlich isotherm model fitted well with the adsorption data of Tl and U. The maximum isotherm sorption capacity of SDS/δ-FeOOH for Tl+ and UO22+ was 182.9 and 359.6 mg/g, respectively. The sorption of Tl followed the pseudo-second-order kinetic model, whereas the sorption of U followed the pseudo-first-order kinetic model. The uptake of Tl and U by SDS/δ-FeOOH was notably inhibited at Na+, K+ concentrations over 5.0 mM, and a high content of dissolved organic matter (over 0.5 mg/L). The mechanistic study revealed that ion exchange, precipitation, and surface complexation were main mechanisms for the removal of Tl and U. The findings of this study indicate that stabilizer dispersion may serve as an effective strategy to facilitate the treatment of wastewater containing Tl and U by using δ-FeOOH.

Evaporation and particle deposition of bi-component colloidal droplets on a superhydrophobic surface

Droplet evaporation is not only a natural phenomenon occurring on a daily basis, but also a novel approach to pattern microscopic structures using small colloids via the evaporative self-assembly. In this work, we carry out a comparative investigation of the evaporation kinetics and particle deposition dynamics of diverse bi-component colloidal droplets on a superhydrophobic surface. We found that the evaporation modes of a drying droplet are determined by both the added volatile component and dispersed colloidal particles, which affect the droplet-surface interactions and thus the contact line motion. While increasing the concentration of the volatile component significantly accelerates the evaporation, no apparent influence was observed for the presence of colloidal particles on droplet lifetime, and the evaporation rate of bi-component droplets in the constant contact angle and constant contact radius modes can still be described by their classical theories for single component droplets. Three types of deposition patterns, namely, a thin disk, a three-dimensional cap and a circular ring, were obtained after evaporation. By direct visualizing the particle aggregation process and analyzing the evaporation flux distribution around sessile droplets, we demonstrate that the residual colloidal structures are regulated by the capillary flows developed in the evaporating droplets.

Thermoresponsive Stiffening with Microgel Particles in a Semiflexible Fibrin Network

We report temperature-responsive soft composites of semiflexible biopolymer networks (fibrin) containing dispersed microgel colloidal particles of poly(N-isopropylacrylamide) (pNIPAM) that undergo a thermodynamically driven de-swelling transition above a Lower Critical Solution Temperature (LCST). Unlike standard polymer-particle composites, decreasing the inclusion volume of the particles (by increasing temperature)is concomitant with a striking increase of the overall elastic stiffness of the composite. We observe such a behavior over a wide composition space. The composite elastic shear modulus reversibly stiffens by up to 10-fold over a small change in temperature from 25-35{\deg}C. In isolation, the fibrin network and microgel suspension both soften with increased temperature, making the stiffening of the composites particularly significant. We hypothesize that stiffening is caused by contracting microgel particles adsorbing on the fibrin filaments and modifying the structure of the semiflexible network. We develop two phenomenological models that quantify this hypothesis in physically distinct manners, and the derived predictions are qualitatively consistent with our experimental data

Fully soluble self-doped poly(3,4-ethylenedioxythiophene) with an electrical conductivity greater than 1000 S cm-1.

Wet-processable and highly conductive polymers are promising candidates for key materials in organic electronics. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is commercially available as a water dispersion of colloidal particles but has some technical issues with PSS. Here, we developed a novel fully soluble self-doped PEDOT (S-PEDOT) with an electrical conductivity as high as 1089 S cm-1 without additives (solvent effect). Our results indicate that the molecular weight of S-PEDOT is the critical parameter for increasing the number of nanocrystals, corresponding to the S-PEDOT crystallites evaluated by x-ray diffraction and conductive atomic force microscopic analyses as having high electrical conductivity, which reduced both the average distance between adjacent nanocrystals and the activation energy for the hopping of charge carriers, leading to the highest bulk conductivity.

Contribution of frictional contact during steady and oscillatory shear in the discontinuous shear thickening fluid

In the present work, an elastic-core-modified mesoscale dissipative particle dynamics model is proposed, so as to investigate the microstructural evolution dependency on the viscosity in shear thickening fluids. The characteristic of the microstructural evolution in the colloidal suspensions under steady shear deformation is studied. The dominant interaction in the system changes from the hydrodynamics to the strong frictional contacts during the discontinuous shear thickening (DST) stage. An oscillatory shear action is creatively taken to study the rheological properties of the suspension, as well as to investigate the microstructural evolution with dynamic response of the system. The exact formulation of the relative viscosity as a function of the effective volume fraction (EVF), which is obtained from the packaging of the frictional contact network, is proposed. It is confirmed that the formation of frictional contact network of dispersed colloidal particles is determined by the competition between construction and decomposition of the particle contacts. The influences of different factors, like particle size, volume fraction, and surface roughness, on the DST behavior are also explored to prove our mechanism. The relationship of shear rate, frictional contact network, EVF, and apparent viscosity is revealed clearly.

Correlative studies on the fabrication of poly(styrene-methyl-methacrylate-acrylic acid) colloidal crystal films

This research describes a one-step procedure for monodispersed poly(styrene-methyl-methacrylate-acrylic acid colloidal spheres [P(St-MMA-AA)] via soap-seeded emulsion polymerization. The effects ofreaction conditions such as temperature, stirring speed, initiation concentration, e.t.c. were examined. The results obtained showed that the spheres average particle diameter decreased with increase in initiator concentration, the reaction temperature and stirring speed and increased with an increase in monomer concentrations. The particles show stable mechanical properties within the transition and heating temperatures of 111.9 °C and 388 °C respectively. Zeta-potential values ranging from −31.8 mV to −36.5 mV which is indicative of stable dispersion of colloidal particles were obtained for all the prepared latexes. The assembled colloidal latex had periodic structures with mainly hexagonal three-dimensional structures with multi-facet arrangements. The latex also shows spherical shape of monodispersed core-shell particles.

Measurement of volume fraction distribution on a colloidal particle dispersion film in drying process

Measurement of volume fraction distribution on a colloidal particle dispersion film in drying process

Click-based thiol-ene photografting of COOH groups to SiO2 nanoparticles: Strategies comparison

We present the study of the anchoring of carboxylic groups on SiO2 nanoparticles from different approximations based on the photochemical radical thiol-ene addition (PRTEA) reaction: a photografting approach between mercaptosuccinic acid (MSA) and vinyl-modified SiO2 nanoparticles and the post-grafting on the surface of silica colloids of the silane precursor 2-((2-(trimethoxysilyl)ethyl)thio)succinic acid (TMSMSA), obtained from the PRTEA. These synthetic strategies were compared with a widely common derivatization methodology based on the nucleophilic attack of surface-anchored amino groups with succinic anhydride. The successful functionalization of the colloidal silica was confirmed by infrared spectroscopy (FTIR), zeta potential at different pH and contact angle measurements. We found that although these three approaches were valid for −COOH immobilization, they had a noticeable impact on the dispersability and agglomeration of the colloidal suspension at the end of the synthesis. Scanning electron microscopy, dynamic light scattering (DLS) and fluorescence correlation spectroscopy (FCS) measurements indicated that the PRTEA photografting between MSA and vinyl-modified SiO2 resulted in highly dispersed colloidal particles. On the other hand, the presence of surface −COOH groups was highly beneficial for redispersion of the colloidal material after lyophilization or freeze-drying procedures.

Research progress of bicontinuous interfacially jammed emulsion gel (Bijel)

In 2005, a bicontinuous arrangement of domains was explored by large-scale computer simulations. In a binary liquid host, the behaviors of neutrally wetting particles were simulated following an instantaneous quench into the demixed region. As the two mutually immiscible liquids phase separate, particles can be swept up by the freshly created interface and jam together as the domains coarsen, forming a particle-stabilized interface between two continuous liquid phases. This type of material is known as “bicontinuous interfacially jammed emulsion gel” (Bijel), and has been demonstrated experimentally using water-lutidine mixture in 2007. It is believed that Bijels have rich potential applications in diverse areas including healthcare, food, energy and reaction engineering due to their unique structural, mechanical and transport properties.As a new class of soft materials, Bijels have received great attention in recent years, and have been developed by using different liquids and non-spherical particles. However, a wide gap remains between the experimental systems and the industrial applications. This short review will critically assess current progress of Bijels and relevant studies including the attempts and challenges to use them in industry; the creation of Bijels by direct mixing at room temperature will be highlighted specifically.Chapter 1 presents the theoretical background. For binary-liquid systems containing dispersed colloidal particles, arrested composites can be created via the stabilization of convoluted fluid-fluid interfaces. Based on this, different morphologies of Pickering emulsions would be obtained. Chapter 2 first focuses on some complex emulsions, including Janus droplets and multiple emulsions, and then induces the bi-continuous structures. Such structures were originally formed through spinodal decomposition, which catches the phase demixing of an initially single-phase liquid mixture containing a colloidal suspension, and normally needs to control the temperature carefully. In Chapter 3, the mechanism of spinodal decomposition is presented. Chapter 4 shows some recent research progress of Bijels, including the studies with different liquid systems, nonspherical particles and some chemical property measurements. This chapter also summarizes the challenges in using Bijels in industry. In Chapter 5, a new method of creating Bijels by direct mixing at room temperature is demonstrated. This method simply needs high viscosity liquids, nanoparticles and a surfactant; it not only bridges the gap between conventional Bijel production (see Chapter 3) and that of particle stabilized bicontinuous structures using bulk polymers, but also bypasses the careful particle modification and phase separation steps for conventional Bijels. In Chapter 6 some conclusions are drawn and a general outlook is also provided.

The second virial coefficient of bounded Mie potentials.

The second virial coefficient (SVC) of bounded generalizations of the Mie m:n potential ϕ(r)=λ[1/(aq+rq)m/q-1/(aq+rq)n/q], where λ, a, q, m, and n are constants (a ≥ 0), is explored. The particle separation distance is r. This potential could be used as an effective interaction between polymeric dispersed colloidal particles of various degrees of interpenetrability. The SVC is negative for all temperatures for a, greater than a critical value, ac, which coincides with the range of a, where the system is thermodynamically unstable. The Boyle temperature and the temperature at which the SVC is a maximum diverge to +∞ as a → ac from below. Various series expansion expressions for the SVC are derived following on from those derived for the Mie potential itself (i.e., a = 0) in the study of Heyes et al. [J. Chem. Phys. 145, 084505 (2016)]. Formulas based on an expansion of the exponential in the Mayer function definition of the SVC are formally convergent, but pose numerical problems for the useful range of a < 1. High temperature expansion (HTE) formulas extending those in the previous publication are derived, which in contrast converge rapidly for the full a range. The HTE formulas derived in this work could be useful in guiding the choice of nucleation and growth experimental conditions for dispersed soft polymeric particles. Inter alia, the SVC of the inverse power special case of the Bounded Mie potential, i.e., ϕ(r)=1/(aq+rq)m/q, are also derived.