Latex Particles Research Articles

Remarkable potential of Na-montmorillonite as a sustainable and eco-friendly material for flocculant studied in the standardized mixing flow

This present study focuses on the ability of montmorillonite, a ubiquitous and non-toxic clay which can be used as an eco-friendly flocculant. For this purpose, coagulation behavior of Polystyrene Amidine Latex (AL) particles with Na-montmorillonite was investigated by the application of standardized mixing method. The flocculation rate of AL particles was assessed as a function of Na-montmorillonite concentration, considering ionic strength and pH. The results showed an enhancement factor (β) ranging from 2 to 5 at an optimal concentration of Na-montmorillonite (∅9.8×10−7). The obtained enhanced rate is attributed to the adsorbing conformation of montmorillonite onto AL particles detected by the combined experiment of electrophoretic mobility and measurement of hydrodynamic layer thickness of clay on AL particles. The finding and established method will be ultimately useful to assess the effect of bio-surfactants or biopolymers which are usually present in microbial extracellular polymeric substances (EPS) interacting with environmental colloidal particles.

Evaluation of chemical mechanical planarization slurry dispersion using a combined scanning mobility particle sizer-optical particle sizer system

A combined scanning mobility particle sizer-optical particle sizer (SMPS-OPS) system was evaluated for measuring the dispersion of a chemical mechanical planarization (CMP) slurry. The dilution rate of one particle per droplet was confirmed to minimize agglomeration. The SMPS and OPS measurements showed similar particle size distributions of 400 nm polystyrene latex particles. The particle size distributions of settled ceria and silica slurries were measured using the SMPS-OPS system. The settled commercial ceria slurry showed a decrease in the number concentration in the top layer. In the bottom layer, increases in the concentration of active particles and in the number of large particles were observed. This indicates that large particles were formed during settling of the slurry. In the silica slurry, there was a change in concentration with depth and little change in number of large particles with settling time. The SMPS-OPS system was able to analyze CMP slurries across a wide range of particle diameters for both active and large particles. Therefore, this system can be helpful for analysis of CMP slurry size.

Film formation of high poly(vinyl chloride) content latex particles

Although poly(vinyl chloride) (PVC) is produced on a large scale industrially by emulsion and suspension polymerization, it is usually processed from the dry state and is seldom directly used as an aqueous polymer dispersion. In this work we demonstrate that by control of particle morphology and particle size distribution it is possible to produce latexes with high PVC content from which polymer films can be cast directly. A series of hybrid PVC/acrylic latexes with a core-shell structure are produced by semi-batch emulsion polymerization using a preformed PVC latex as a seed. Although monomodal particles of this type have a minimum film formation temperature in excess of 80 °C when the content of PVC is high, it is shown that through the use of a bimodal particle size distribution the packing efficiency of the spherical PVC domains is increased such that room temperature film formation is possible with PVC content up to 80 wt%.

Advances in Organic-Inorganic Hybrid Latex Particles via In Situ Emulsion Polymerization.

Hybrid latex particles combine the unique properties of inorganic nano/micro particles with the inherent properties of polymers, exhibiting tremendous potential for a variety of applications. Recent years have witnessed an increased interest in the design and preparation of hybrid latex particles with well-defined size, structure and morphology. Due to its simplicity, versatility and environmental friendliness, the in situ (Pickering) emulsion polymerization has been demonstrated to be a powerful approach for the large-scale preparation of hybrid latex particles. In this review, the strategies and applications of in situ (Pickering) emulsion polymerization for the preparation of hybrid latex particles are systematically summarized. A particular focus is placed on the strategies for the preparation of hybrid latex particles with enhanced properties and well-defined core-shell, yolk-shell, multinuclear, raspberry-like, dumbbell-shaped, multipod-like or armored morphologies. We hope that the considerable advances, examples and principles presented in this review can motivate future contributions to provide a deeper understanding of current preparation technologies, develop new processes, and enable further exploitation of hybrid latex particles with outstanding characteristics and properties.

Preparation and Characterization of fluorinated copolymer emulsion for concrete protection

Emulsifier-free copolymerizations of 2,2,2-trifluoroethyl 2-methylpropanoate (TFMPA) and methyl acrylate in the presence of surface-active commoner, undecylenic acid (UA), were carried out using potassium persulfate (KPS) as initiator. The prepared copolymer emulsions were characterized and analyzed by FT-IR, 1H and 19F NMR spectra, TEM, dynamic light scattering (DLS), and contact angle testing. The results showed that the average particle size of copolymer latex particles was 200-300 nm with a relatively uniform particle size distribution. The glass transition temperature was controlled with the monomer feed ratios. After copolymer emulsions coating on the concrete surface, the contact angle was significantly increased, and the water absorption of the concrete was significantly reduced.

Cellulose nanocrystal/polymer nanocomposite latex via surfactant-free emulsion polymerization

Polar cellulose nanocrystals (CNCs) are difficult to disperse well in hydrophobic polymer matrices, and usually surfactants or expensive and time-consuming functionalization of the reinforcement or matrix have been attempted to improve dispersion. Here, we report a new, facile method to prepare CNC/polymer nanocomposite latices directly via surfactant-free emulsion polymerization of vinyl monomers and CNCs initiated by a cationic, water-soluble, free-radical initiator. The distribution of CNCs in the latex particles can be tailored through controlling the reaction procedures, namely, whether the monomers are added before or after preheating the CNCs with the initiator and has been confirmed by scanning electron microscopy (SEM) and scanning transmission X-ray microscopy (STXM) studies. CNCs distribute inside the latex particles if the monomers are added after the preheating step, and owing to the more even distribution of CNCs, such nanocomposite latices exhibit better mechanical properties than those prepared without preheating or via physically mixing CNCs with emulsions polymerized using conventional surfactant system. A latex particle formation mechanism is proposed based on these phenomena and polymerization kinetics studied in this work. Unlike typical CNC-based Pickering emulsion polymerization, our process can be operated without the need for intense mechanical shearing and provide an industrially scalable approach to prepare stable CNC/polymer nanocomposite latices that can be melt processed or used directly in a variety of applications, such as paints and coatings, adhesives, or cosmetics.

Technical note: Characterization of polystyrene latex spheres 300 nm in diameter with a singularly narrow size distribution

We have recently combined improved polystyrene latex (PSL) particle synthesis methods and new high resolution differential mobility analyzers (DMAs) covering the viral size range (up to about 300 nm) to demonstrate the availability of ∼200 nm PSL spheres with unusually narrow mobility distributions, with relative full width at half maximum (FWHM) as small as 1/60. By similar techniques we now report on the synthesis and analysis of PSL particles with diameters of about 300 nm achieving FWHM as small as 1/80. This is as narrow as the narrowest mobility peaks previously found with all but one of the viral particle so far studied with high resolution DMAs. The electrosprayed 300 nm particles produce two resolvable peaks, with the least mobile one being apparently an artifact of the electrospraying or charge reduction process. We conclude that future PSL synthesis improvements should be able to provide particles yielding mobility peaks with FWHM as small as 1/100.

Excellent hydrophobic, superior ozone and UV resistant, and high thermal stable films from bio‐based natural rubber latex via fluorinating under mild conditions

AbstractAs a renewable and widely applied bio‐based material, the relatively weak resistance of natural rubber (NR) resulting from the inherent unsaturated structure to the harsh environments limits their further applications in some special areas. Thus, the fluorinated natural rubber (FNR) latex was prepared with fluorinated acrylate as the monomer in aqueous emulsion system at ambient temperature. The fluorinating reaction, the structure and morphology of NR latex were examined. It was demonstrated that as the intrinsic surface layer of NR latex particles, the non‐rubber component hindered the penetrating of fluorinated monomer or initiator radicals into the inner NR Latex particles and reduce the grafting reactivity. The fluorination renders the resultant FNR latex film strong hydrophobicity and superior environmental resistance to UV, ozone, and heat. The defective time of the FNR latex film improved 65 times as long as the net NR latex film via ozone aging. The thermal decomposition temperature increased by 37.0°C compared with net NR latex film. This work provides a facile way for preparation of FNR with excellent stability under extreme environments such as high ozone concentration, high UV intensity and high temperature.

Diffusiophoresis of latex driven by anionic nanoparticles and their counterions

HypothesisDiffusiophoresis of colloidal latex particles has been reported for molecular anions and cations of comparable size. In the present study, this phenomenon is observed for two types of charged colloids acting as multivalent electrolyte: (i) anionic charge-stabilised silica nanoparticles or (ii) minimally-charged sterically-stabilised diblock copolymer nanoparticles. ExperimentsUsing a Hele-Shaw cell, a thin layer of relatively large latex particles is established within a sharp concentration gradient of nanoparticles by sequential filling with water, latex particles and nanoparticles. Asymmetric diffusion is observed, which provides strong evidence for diffusiophoresis. Quantification involves turbidity measurements from backlit images. FindingsThe latex particles diffuse across a concentration gradient of charged nanoparticles and the latex concentration front scales approximately with time1/2. Moreover, the latex particle flux is inversely proportional to the concentration of background salt, confirming electrostatically-driven motion. These observations are consistent with theory recently developed to account for diffusiophoretic motion driven by multivalent ions.

Ink-Jet Printing of Colored Latex Inks with a “Soft” Core–“Hard” Shell Structure

Colored latex particles (CLPs) as a novel colorant have been widely applied to salt-free dyeing and printing due to their adjustable composition, brilliant colors, excellent durability, and small particle size. In this paper, the effects of glass-transition temperatures (Tg) on the filterability of CLP inks were first studied, and the results showed that the CLP inks can be successfully filtered and ejected when the Tg’s of CLP inks exceeded 48 °C. Based on our previous research, CLP (Tg = 25 °C)-printed fabrics had excellent color fastness and a soft hand feel, while a stiff hand feel occurred with the increase of the Tg. Herein, the CLPs with a core–shell structure (CLP@PS) were designed using CLPs (Tg = 25 °C) as a “soft” core for ensuring the color fastness of printed fabrics and PS as a “hard” core for ensuring excellent filterability of inks. Transmission electron microscopy and dynamic light scattering indicated that the prepared particles had an obvious core–shell structure, and the particle size was 96 nm. To balance the filterability of inks and color fastness of printed fabrics, the encapsulated thickness was optimized at 20 nm by adjusting the amounts of styrene (St) and 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AIBA). The flow rate and filtration time of CLP@PS inks were 8.9 mL/s, and 11 s, respectively. Finally, the CLP@PS inks were applied to ink-jet printing of cotton fabric. Compared with pigment ink-jet printing, CLP@PS-printed fabrics had a softer hand feel and better rubbing and washing fastness.

Quantification of Very Low Concentrations of Colloids with Light Scattering Applied to Micro(Nano)Plastics in Seawater

The detection and quantification of micro(nano)plastics in the marine environment are essential requirements to understand the full impacts of plastic pollution on the ecosystem and human health. Here, static light scattering (SLS) and dynamic (DLS) light scattering techniques are assessed for their capacity to detect colloidal particles with diameters between d = 0.1 and 0.8 µm at very low concentrations in seawater. The detection limit of the apparatus was determined using model monodisperse spherical polystyrene latex particles with diameters of 0.2 µm and 0.5 µm. It is shown that the concentration and size of colloids can be determined down to about 10−6 g/L. Light scattering measurements on seawater obtained from different locations in Western Europe show that colloidal particles were detected with DLS in seawater filtered through 0.8 µm pore size filters. The concentration of these particles was not higher than 1 µg/L, with an average diameter of about 0.6 µm. We stress that these particles are not necessarily plastic. No particles were detected after filtration through 0.45 µm pore size filters.

Synthesis and Characterization of Charge-Stabilized Poly(4-hydroxybutyl acrylate) Latex by RAFT Aqueous Dispersion Polymerization: A New Precursor for Reverse Sequence Polymerization-Induced Self-Assembly.

The reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 4-hydroxybutyl acrylate (HBA) is conducted using a water-soluble RAFT agent bearing a carboxylic acid group. This confers charge stabilization when such syntheses are conducted at pH 8, which leads to the formation of polydisperse anionic PHBA latex particles of approximately 200 nm diameter. The weakly hydrophobic nature of the PHBA chains confers stimulus-responsive behavior on such latexes, which are characterized by transmission electron microscopy, dynamic light scattering, aqueous electrophoresis, and 1H NMR spectroscopy. Addition of a suitable water-miscible hydrophilic monomer such as 2-(N-(acryloyloxy)ethyl pyrrolidone) (NAEP) leads to in situ molecular dissolution of the PHBA latex, with subsequent RAFT polymerization leading to the formation of sterically stabilized PHBA-PNAEP diblock copolymer nanoparticles of approximately 57 nm diameter. Such formulations constitute a new approach to reverse sequence polymerization-induced self-assembly, whereby the hydrophobic block is prepared first in aqueous media.

Light-induced reversible destabilization of responsive latex particles prepared via high solids content emulsion polymerization

Light-induced reversible destabilization of responsive latex particles prepared via high solids content emulsion polymerization

Mechanical Properties and Blocking Resistance of Films Cast from Core–Shell Latex Particles

AbstractThe mechanical properties and blocking resistance of films cast from latex particles can be improved by addition of a reinforcing polymer of high modulus that acts as a “hard” phase. This work demonstrates that blocking resistance, a key performance parameter for use in coatings, of such films can be understood in terms of the relative contribution of the “hard” and “soft” components to the rheological properties of the material. In order to do so, representative latexes that contain a semicrystalline core of poly(stearyl acrylate) as a reinforcing phase and a shell of amorphous poly(styrene‐co‐butyl acrylate) are synthesized. By varying the composition of the amorphous phase (glass transition temperature, molar mass) and the relative amorphous/semicrystalline fraction, it is demonstrated that the improvement in blocking resistance is strongly correlated with the increase in the modulus of the material but is also affected by the dynamics of polymer diffusion of chains in the soft phase. This work allows to establish design rules for polymer and colloidal structures that can be targeted to maximize blocking resistance.

Extraordinary Destabilization of Silica Nanocolloids by Filtration

After silica nanoparticles in solutions were filtered by a syringe filter with a much larger pore size than the particle diameter Dp, the filtrated effects on the rapid coagulation rate in 1 M KCl solution, the dynamic light scattering diameter, and the zeta potential at pH ∼ 6 were investigated by employing the particles of two different sizes: S particles (Dp ∼ 50 nm) of silica and latex and L particles (Dp ∼ 300 nm) of silica. It was found that the hydrodynamic diameters of silica particles became a little smaller and the absolute values of their zeta potentials decreased significantly by filtration, but that is not the case for latex particles. As for the rapid coagulation rate, the value of silica S particles increased more than 2 orders of magnitude by filtration, but no significant difference was found in the case of silica L and latex S particles. From these data, it was postulated that the gel-like layer was removed from the surface of silica S particles by filtration and the existence of the gel-like layer resulted into about 2 orders of magnitude reduction of the rapid coagulation rate. The extraordinary reduction of rapid coagulation of silica particles at Dp < 150 nm was successfully estimated by the revised Smoluchowski theory, which we call the Higashitani-Mori (HM) model. It was also found that the rapid coagulation rate of filtrated particles decreased slowly with a decreasing particle size at Dp < ca. 250 nm, which was also estimated properly by the HM model, neglecting the contribution of the redispersion of coagulated particles. Another finding in this study was that the gel-like layers were recovered with time even if they were removed by filtration, although the detailed mechanism of this recovering is not known at present and left as a future problem.

DIAGNOSTIC UTILITY OF QUANTITATIVE D-DIMER TESTING IN CORRELATION WITH CT ANGIOGRAPHY IN RULING OUT THROMBOEMBOLISM- A PROSPECTIVE STUDY AT A TERTIARY CARE CENTRE

Background: Vascular Thromboembolism (VTE)- blockage of a blood vessel by the broken components of a blood clot, is commonly caused by Thromboembolism Deep venous thrombosis (DVT) and Pulmonary embolism (PE). It can also be caused by various other conditions, and have overlapping features. VTE's have signicant morbidity and mortality, treatment carries signicant side effects, hence, objective testing becomes must to establish or exclude the presence of thromboembolism. D-Dimer, a brin degradation product (FDP), appears in blood after degradation of blood clot by brinolysis. It is normally undetectable or detectable at a very low level, unless the body is forming and breaking down blood clots as in VTE. Materials and Methods: Quantitative D-Dimer test was performed using fully automated technique, on patient's serum. Latex particles coated with anti D-dimer monoclonal antibodies were mixed with the test plasma. In the presence of D-dimer, the latex particles agglutinate, the suspension claries and translates in low turbidimetric readings. All results were further correlated with their CT Angiography ndings.Results: Most patients had D-Dimer value in range of 1.0 to 2.0 µg/ml. High (96.77%) Sensitivity shows that the test can be used safely to detect Thromboembolism even in early stages, whereas, High Negative Predictive value (93.54%), suggests safe exclusion in suspected cases. Conclusion: D-Dimer is highly sensitive, accurate and rapid test, but alone cannot conclude diagnosis. It is advisable to correlate with combination of Radiological investigations (CT Angiography) and clinical probability- Revised Geneva score and to establish a nal diagnosis and plan an appropriate treatment.

Particle counting immunoassay system using a low-aspect-ratio pore

We have developed a new particle counting immunoassay system integrated with a resistive-pulse sensor with a low-aspect-ratio pore. The particle counting immunoassay is based on the principle of latex aggregation. The target single-molecule concentration is measured by counting aggregated latex particles that form multimers over the reaction time. To enable highly accurate identification of the number of aggregated particles, we designed and fabricated a low-aspect-ratio pore device to perform quantitative structural analysis of particles. The aggregation numbers of the conjugated particles were classified based on blockade current profiles when the particles translocated through the pore. Time-dependent agglutination reaction monitoring demonstrated that the reaction speed increased for a solution containing a higher concentration of antigens. The results prove the feasibility of using the proposed immunoassay system to count particles while determining the aggregation number based on their current profiles.

Silica-Coated Micrometer-Sized Latex Particles.

A series of silica-coated micrometer-sized poly(methyl methacrylate) latex particles are prepared using a Stöber silica deposition protocol that employs tetraethyl orthosilicate (TEOS) as a soluble silica precursor. Given the relatively low specific surface area of the latex particles, silica deposition is best conducted at relatively high solids to ensure a sufficiently high surface area. Such conditions aid process intensification. Importantly, physical adsorption of chitosan onto the latex particles prior to silica deposition minimizes secondary nucleation and promotes the formation of silica shells: in the absence of chitosan, well-defined silica overlayers cannot be obtained. Thermogravimetry studies indicate that silica formation is complete within a few hours at 20 °C regardless of the presence or absence of chitosan. Kinetic data obtained using this technique suggest that the adsorbed chitosan chains promote surface deposition of silica onto the latex particles but do not catalyze its formation. Systematic variation of the TEOS/latex mass ratio enables the mean silica shell thickness to be tuned from 45 to 144 nm. Scanning electron microscopy (SEM) studies of silica-coated latex particles after calcination at 400 °C confirm the presence of hollow silica particles, which indicates the formation of relatively smooth (albeit brittle) silica shells under optimized conditions. Aqueous electrophoresis and X-ray photoelectron spectroscopy studies are also consistent with latex particles coated in a uniform silica overlayer. The silica deposition formulation reported herein is expected to be a useful generic strategy for the efficient coating of micrometer-sized particles at relatively high solids.

Hydroxyl Boron Nitrid e/Natural Rubber Composites with Enhanced Mechanical and Thermal Conduction Properties: Implications for Heat Dissipative Tires or Conveyor Belts

For its significant technological interest, a systematic investigation on mechanical and thermal conduction properties of natural rubber reinforced by functionalized hexagonal boron nitride nanosheets is highly desirable. We herein first demonstrate a unique synthesis of hydroxyl-functionalized boron nitride nanosheets (OH-BNNSs) via a simple one-pot reduction reaction. This involves negative charging by treating BNNSs with lithium in liquid ammonia and subsequent bubbling of oxygen into dispersion of BNNS salts. Subsequently, a series of functionalized boron nitride nanosheets/natural rubber (NR) composites were fabricated by latex mixing and co-coagulation. Co-coagulating a stable aqueous suspension of OH-BNNSs with natural rubber latex afforded a weblike morphology consisting of platelet networks between the latex particles. Compared to pure rubber, the tensile strength and storage modulus at 25 °C for OH-BNNSs/NR (5 wt %) are increased by 466% and 1 order of magnitude, respectively. Benefiting from the unique structure, the composite at 5 wt % shows a 40% improvement in thermal conductivity relative to pure rubber. This latex-based method provides a facile and effective strategy to design and fabricate advanced functional BNNS-based polymeric nanocomposites with a segregated filler network morphology and considerable property enhancements in direct competition with graphene sheets. The composites could be potentially used in heat dissipative tires or conveyor belts.

Silver Nanoparticles as Antifungal Agents in Acrylic Latexes: Influence of the Initiator Type on Nanoparticle Incorporation and Aureobasidium pullulans Resistance.

Discoloration of wood coatings due to fungal growth negatively affects the aesthetic properties of the coatings, and new ways to control fungal growth on coatings are needed. For this reason, silver nanoparticles (AgNPs) have been incorporated in acrylic latexes as antifungal agents. Using miniemulsion polymerization, latexes were prepared with two types of initiators (hydrophilic and hydrophobic) to assess the influence of the initiator type on AgNPs dispersion, both within the latex particles and the dry film. In addition, the impact of NP dispersion on resistance to black-stain fungi (Aureobasidium pullulans) was also evaluated. Inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis indicates that acrylic latexes prepared with azobisisobutyronitrile (AIBN) as the initiator contain more AgNPs than those prepared with potassium persulfate (KPS). Cryo-TEM and SEM analyses show that the distribution of the AgNPs within the polymer particles is influenced by the nature of the initiator. When AIBN, a hydrophobic initiator, is used, the AgNPs appear to be closer to the surface of the polymer particles and more evenly distributed. However, the antifungal efficiency of the AgNPs-embedded latexes against A. pullulans is found to be higher when KPS is used, despite this initiator leading to a smaller amount of incorporated AgNPs and a less uniform dispersion of the nanoparticles.