Stability Of Latex Particles Research Articles

Fabrication of dual-functional cellulose nanocrystals/fluorinated polyacrylate containing coumarin derivatives by RAFT-assisted Pickering emulsion polymerization for self-healing application

Polymeric coatings are easy to be damaged by harsh environment condition, which causes cracks and loss of function. Inspired by the natural self-healing phenomenon, we successfully synthesized dual-functional cellulose nanocrystals/fluorinated polyacrylate containing coumarin derivatives by RAFT-assisted Pickering emulsion polymerization. The amphiphilic and photo-responsive copolymer, PDMAEMA-b-PGMA-b-P(HFBA-co-VBMC) was synthesized by RAFT process, followed by characterization using FT-IR, SEC, 1H NMR and UV–vis. The cellulose nanocrystals were modified by the copolymer, which were confirmed via XPS, UV–vis and so on. Besides, the droplet size of Pickering emulsion gradually increased and the creaming layer gradually decreased as the pH value increased. The TEM result showed that the modified cellulose nanocrystals were effectively anchored on the outside of latex particles. The size of the spherical-like latex particles increased and the stability of latex particles was worse with increasing pH value. Finally, the finished fabric had excellent water resistance due to the combination of micro- or nanoscale hierarchical structure and low surface energy. Moreover, the latex film exhibited excellent repeatability of self-healing ability. The fabric coating achieved the intrinsic and superficial dual-functional self-healing performance by the reversible [2 + 2] cycloaddition of coumarin groups. This strategy provides a powerful guide for preparing the high-performance waterborne fluorinated polyacrylate coating.

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.

Stability of nanoparticles during semibatch emulsion polymerization of butyl methacrylate, in the presence of methacrylic acid via RSM

AbstractThe size and stability of latex particles in the semibatch emulsion polymerization of butyl methacrylate (BMA), in the presence of 0–10% methacrylic acid (MAA), were investigated. Response surface methodology (RSM), as a design of experiment, was used to obtain a more systematic understanding of the role of emulsifier and MAA in the stability of the particles. The amount of coagulum can be greatly reduced by increasing the concentration of sodium lauryl sulfate (SLS) in the monomer emulsion feed (MEF) and initial reactor charge (IRC). On the other hand, increasing the concentration of SLS in the IRC can result in a decrease of the particles size. According to the experimental data, the yield of reaction can be improved with incorporation of MAA into the emulsion polymers. The size and morphology of particles were obtained by scanning electron microscopy (SEM). FTIR and titration were used to determine the percentage of MAA in the copolymer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Mechanisms involved in the stabilization of latex particles by adsorbed block copolymers in emulsion polymerization process

The efficiency of amphiphilic block copolymers composed of butyl methacrylate and methacrylic acid (PBMA-b-MAA) of various compositions was evaluated in terms of colloidal stability. These copolymers were adsorbed on a PBMA latex in quantities inferred from adsorption isotherm and their colloidal stability was investigated through the determination of the critical coagulation concentration CCC, by addition of either electrolyte or acid. The latexes covered with block copolymers were very stable against addition of either electrolyte or acid compared to the bare latex. The colloidal stability as evaluated by the CCC, increased with the relative coverage. The results were discussed in relation with the behavior obtained in emulsion polymerization. The overall trends were sorted correctly since a better coverage yielded a better colloidal stability and a smaller size at the end of emulsion polymerization. But no direct correlation could be found out between adsorption, colloidal stability and emulsion polymerization. Influence of stirring during the flocculation test was also evaluated.

Characterization of colloidal polymer particles through stability ratio measurements

We propose a general methodology for the estimation of the doublet formation rate constant (proportional to the stability ratio of primary particles) in colloidal dispersions from measurements obtained by common optical techniques, such as dynamic light scattering, static light scattering (nephelometry) or turbidimetry. In contrast to previous approaches relying on the initial slopes of the measured quantities, such as the mean hydrodynamic radius, scattered light intensity or turbidity, we introduce a transformation of the measurables to properly scaled quantities, which grow linearly in time with a slope proportional to the doublet formation rate. Analysis of systematic and random errors allows one to control the error in the estimated value of the aggregation rate. Using this approach, we measured the aggregation rate constant of colloidal polymer particles prepared by surfactant-free emulsion copolymerization of styrene and 2-hydroxyethyl methacrylate (HEMA). It was found that the stability ratio at constant ionic strength decreases with increasing dilution of the original polymer latex. This can be explained by the presence of non-reacted stabilizing species (most likely oxidized HEMA) that desorb from the particle surface upon latex dilution and thus diminish the repulsive interactions between particles. In order to check if the stability of latex particles is influenced by reversibly adsorbed species it is always necessary to perform aggregation experiments at various dilutions.

Effect of the Emulsifier on the Dynamic Behavior of Particle Size Distribution in Continuous Emulsion Polymerization of Vinyl Acetate

The purpose of this research is to elucidate the effect of the emulsifier on the dynamic behavior of particle size distribution (PSD) in continuous emulsion polymerization. Emulsion polymerization of vinyl acetate was performed in a continuous stirred tank reactor. An anionic surfactant (sodium dodecyl sulfate: SDS) was used as an emulsifier. The initial emulsifier concentration in the reactor and that in the feed was varied as a control parameter. In order to vary the colloidal stability of latex particles, a nonionic surfactant (polyoxyethylene sorbitan monooleate: Tween80) was added in some cases. It has been found that PSD varies with time even while the constant monomer conversion is maintained at a steady state in all cases. Compared with the case of using only SDS, however, using a mixture of anionic surfactant and nonionic surfactant can effectively suppress this time-dependent behavior.

Polymer Latex Stability Modification by Exposure to Hydrophobic Solvents

The stability of latex particles toward coagulation in the presence of salt is modified by swelling the latex with toluene and chloroform vapors. Short-term stability was determined by turbidimetric titrations, and the long-term stability was evaluated by adding latex and salt solutions, allowing the mixture to age for 24 or 48 h and determining the characteristics of the supernatant and of the sediment. Nine different latexes were examined, with variable results: in some cases, both apolar solvents stabilize the latex; in other cases, increased stability is induced by only one of the solvents, either toluene or chloroform. There is also coherence, but not a strict correlation, between the solvent effects on short- and long-term stability. For instance, in the case of a core-and-shell styrene–butyl methacrylate latex, chloroform has a small stabilizing effect in the titration experiment, but it prevents the formation of a coagulated latex sediment even 48 h after mixing latex and salt. Two hypotheses are discussed to account for these observations: (i) swelling solvents decrease the particles ability to dissipate the collision kinetic energy, so that particles collide but without joining each other; (ii) the solvents induce the release of trapped charged groups from the particle interior to the interface, enhancing the usual (electrostatic, steric, hydration) stability factors.

Stability of carboxylated poly(butyl acrylate) latices during semibatch emulsion polymerization

The stability of latex particles in the semibatch emulsion polymerization of butyl acrylate (BA) in the presence of 0–10% acrylic acid (AA) was investigated. The amount of coagulum (i.e., large flocs caused by intensive coagulation) can be greatly reduced by an increase in the concentration of sodium lauryl sulfate (SLS) in the monomer emulsion feed. On the other hand, increasing the concentration of SLS in the initial reactor charge can result in an increase in the percentage of the particle volume change (i.e., a measure of the degree of limited flocculation) later in the process. Both the scrap and percentage of the particle volume change increase with an increase in the electrolyte concentration. Both the coagulation and secondary nucleation process can result in a significant deviation from the Novak model. Experimental data also show that latex particles comprising pure BA can lose their stability rapidly at higher total solids content because of the crowding effect. Incorporation of only 5% AA into the emulsion polymers greatly improves the latex stability. © 1996 John Wiley & Sons, Inc.

Features of latex copolymerization of acrylic monomers with methylol methacrylamide

As was shown in papers [1,2], colloidally-stable latices are obtainable by copolymerizing lower alkylacrylates with methylol methacrylamide (MMAA) in the absence of emulsifiers ann with ammonium persulphate as initiator. The physicochemical properties of these latices are similar to those of latices prepared in the usual way with emulsifiers. The colloidal properties of these latices are influenced by the monomer-metering procedure as well as by the molecular weight of the polymer and its functional group content (methylolamide groups). The addition of MMAA to the copolymer composition has a stabilizing effect on the latices, and the stability of the latter increases with increase in the MMAA content. In this investigation we studied the reaction kinetics and the mechanism of the rising, growth and stabilization of latex particles in the copolymerization of ethyl acrylate (EA) with MMAA in the aqueous phase.