Latex Particle Size Distribution Research Articles

Role of the nonionic surfactant Triton X-405 in emulsion polymerization. I. Homopolymerization of styrene

The emulsion polymerization of styrene was studied using the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol). Two separate nucleation periods were noted in these polymerizations resulting in bimodal final latex particle size distributions. The partitioning of the surfactant between the phases was found to play the major role in determining the nucleation mechanism(s) in these polymerizations. Although the total concentration of the emulsifier was always added at a level above its critical micelle concentration (CMC) based on the water phase in the recipe, it was found that the portion of the surfactant initially present in the aqueous phase was below its CMC due to the partitioning. This CMC was also found to increase with increasing total surfactant because the distribution of the surfactant (varying ethylene oxide chain length) depended on the partitioning between the phases. Under these conditions, the first of the two nucleation periods was attributed to homogeneous nucleation, while the second was attributed to micellar nucleation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3813–3825, 1997

Role of the nonionic surfactant Triton X‐405 in emulsion polymerization. I. Homopolymerization of styrene

The emulsion polymerization of styrene was studied using the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol). Two separate nucleation periods were noted in these polymerizations resulting in bimodal final latex particle size distributions. The partitioning of the surfactant between the phases was found to play the major role in determining the nucleation mechanism(s) in these polymerizations. Although the total concentration of the emulsifier was always added at a level above its critical micelle concentration (CMC) based on the water phase in the recipe, it was found that the portion of the surfactant initially present in the aqueous phase was below its CMC due to the partitioning. This CMC was also found to increase with increasing total surfactant because the distribution of the surfactant (varying ethylene oxide chain length) depended on the partitioning between the phases. Under these conditions, the first of the two nucleation periods was attributed to homogeneous nucleation, while the second was attributed to micellar nucleation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3813–3825, 1997

Role of the nonionic surfactant Triton X-405 in emulsion polymerization. II. Homopolymerization ofn-butyl acrylate

In the emulsion polymerization of n-butyl acrylate, the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol) partitions primarily into the aqueous phase leading to nucleation in the presence of micelles and unimodal final latex particle size distributions. Nucleation is accompanied by limited aggregation in the early stages of the reactions with particles being formed in some cases past 50% conversion depending on the experimental conditions. High values of the average number of radicals per particle (n > 10) are observed during these reactions which explains a secondary increase in the heat of reaction. This increase was not observed when the initiator (K2S2O8) concentration was reduced from 6.4 to 0.6 mM or the temperature was decreased from 70°C to 60°C; contrary to what was expected, an inverse relationship was observed between the rate of polymerization and the final number of particles for these experiments. This was attributed to more extensive limited aggregation at the higher temperature and initiator concentration. Limited aggregation is thus shown to be an important mechanism in these polymerizations. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3827–3835, 1997

Semibatch Seeded Emulsion Polymerization of Acrylic Monomers: Bimodal Particle Size Distribution

Injecting sodium dodecyl sulfate (SDS) into the reaction medium induces a second crop of tiny primary particles (i.e., secondary nucleation) in semibatch seeded emulsion polymerization. Secondary nucleation may thus result in latex products with a bimodal particle size distribution (BPSD-Latices). The concentration of seed particles ([Seed]) is the most important variable for controlling the particle-size-distribution-related parameter (P), followed by the time when the surfactant is injected into the reactor (t s). The resultant latex particle size (d p) is not sensitive to changes in the concentration of injected SDS ([SDS]). Parameter P decreases with increasing [Seed] or t s. This implies retarded secondary nucleation during monomer addition when [Seed] or t s increases. An experiment with smaller values of [Seed] and t s favors formation of BPSD-Latices. The data clearly show a bimodal particle size distribution when P is greater than approximate 70%. Parameter P correlates well with the total seed particle surface area (A s) regardless of the seed particle size, and P (%) is proportional to A s (cm2) to the -0.319 power. Thus, A s is a very useful parameter for manipulation of the resultant latex particle size and particle size distribution.

Particle Size Distribution of SBR and NBR Latexes by UV-VIS Turbidimetry near the Rayleigh Region

Abstract This paper deals with data treatment problems that arise when turbidimetry is employed to estimate the particle size distribution (PSD) of soft polymer latexes with low diameter limits around 40 nm. Scanning electron microscopy and dynamic light scattering were used as comparison techniques. Industrial latexes of styrene-butadiene rubber (SBR) and of acrylonitrile-butadiene rubber (NBR) were investigated. The data treatment involved the use of Mie's Model to obtain an average diameter and/or the complete PSD. For estimating the complete PSD, a least squares optimization (with an imposed distribution shape) and a numerical deconvolution procedure (without assumptions on the distribution shape) were attempted. A synthetic example was solved to investigate the limits of the applied numerical methods. For the polymer refractive index functions, Cauchy's Law was used — and its adequate adjustment proved essential for good turbidimetric estimations. A reasonable agreement between the turbidity measurements and the other independent estimations was verified. For the SEM observations, the soft latexes were hardened by irradiation before observation, but negligible diameter variations were detected.

Determination of the Particle Size Distribution of Latex Using a Combination of Elastic Light Scattering and Turbidimetry: A Simulation Study

Turbidimetry at several wavelengths and elastic light scattering (ELS) at several angles can be used to determine particle size distributions (PSDs) of suspended particles using Mie scattering theory. The limited range of measurement in reciprocal space and the measurement noise always cause both techniques to have their own limitations. In this work, a way to combine turbidimetry and ELS data to be processed together is proposed. In order to investigate the convenience of simultaneous versus individual processing, a set of computationally generated experiments performed on suspensions of polystyrene particles is analyzed. The results clearly show that when the data are jointly processed the quality of the PSDs obtained is highly superior. This fact can be explained by the complementary characteristics of both techniques. Turbidimetry is more accurate at larger sizes, whereas ELS gives more precise estimations at smaller sizes. This work shows that simultaneous processing of experimental data from different sources seems to be a valid alternative for improving the quality of indirect measurements.

Determination of Mean Diameter and Particle Size Distribution of Acrylate Latex Using Flow Field-Flow Fractionation, Photon Correlation Spectroscopy, and Electron Microscopy

Flow field-flow fractionation (flow FFF) was employed to determine the mean diameter and the size distribution of acrylate latex materials having diameters ranging from 0.05 to 1 μm. Mean diameters of the samples determined by flow FFF are in good agreement with those obtained from photon correlation spectroscopy (PCS). Scanning electron microscopy (SEM) yielded a mean diameter that is about 20% lower than those obtained from flow FFF or PCS, probably due to the shrinkage of particles during sample drying and high-vacuum measurements. It was found that flow FFF is particularly useful for the determination of particle size distributions of latex materials having broad size distributions. Flow FFF separates particles according to their sizes and yields an elution curve that directly represents the particle size distribution of the sample. In PCS, measurements had to be repeated at more than one scattering angle to obtain an accurate mean diameter for the latex having a broad size distribution. Flow FFF was fast (less than 12 min of run time) and showed an excellent repeatability in measuring the mean diameter with ±5% relative error.

Preparation of poly(vinyl chloride) latexes by polymerization of stabilized monomer droplets

AbstractPoly(vinyl chloride) latexes have been prepared by polymerization in micron and submicron sized monomer droplets. Monomer emulsions with excellent long time stability were obtained by diffusional swelling of vinyl chloride monomer into preformed, stable polydisperse pre‐emulsions of water‐insoluble oils or monodisperse, oligomer styrene seed particles. It was found that the size and size distribution of the final latex particles were determined by those of the parent monomer emulsions. Except for the secondary particles formed during polymerization, the size and size distributions of the latex particles were found to be com‐parable to those of the monomer emulsions employed, indicating a complete nucleation of the parent emulsion droplets. The extent of secondary particle formation was found to be very dependent upon the emulsifier concentration as well as on the type and amount of initiator used. © 1995 John Wiley & Sons, Inc.

Emulsion copolymerization of tribromophenyl maleimide with styrene

AbstractEmulsion copolymerization of Tribromophenyl Maleimide (TBPMI) and styrene was conducted by semi‐batch and batch processes. The effects of monomer composition and copolymerization method on copolymerization rate, molecular weight and molecular weight distribution, latex particle size and size distribution, glass transition temperature (Tg), thermal stability and mechanical properties were investigated. A kinetic study has shown that the rate of copolymerization in the batch process increased with increasing TBPMI content in the monomer feed. For the semi‐batch polymerized samples, molecular weight decreased and molecular weight distribution increased with increasing TBPMI content in the monomer feed. For the batch polymerized samples, molecular weight also decreased but no obvious tendency was observed for the molecular weight distribution when TBPMI content increased. Compared with the batch copolymers, the semi‐batch copolymers have a higher molecular weight at the same initial monomer mixture composition. Latex particle size decreased, while particle size distribution slightly increased with increasing TBPMI content in both semi‐batch and batch latices. The semi‐batch samples exhibit only a single Tg, the value of which increses linearly with increasing TBPMI content. For the batch copolymers, two Tgs were found, reflecting a mixture of styrene‐rich and TBPMI‐rich copolymer chains. TGA results indicate that the thermal stability of the semi‐batch copolymers increased with increasing TBPMI concentration. Young's and flexural moduli increased, while tensile and flexural strengths decreased by increasing the TBPMI content for both the semi‐batch and batch specimens. The semi‐batch specimens have higher tensile and flexural strenghts than the batch ones.

Latex characterization by atomic force microscopy

AbstractWays, benefits and limitations of extracting the form and size of single latex particles or particle size distributions out of the surface topography of non‐coalesced latex films obtained by atomic force microscopy (AFM) are discussed. The general ways to generate the desired information out of topographical information in terms of height, surface curvature and lateral extensions are shown for idealized particles and measurement conditions. The different sources of information are evaluated for practical use and the analysis of particle size distributions is demonstrated by practical examples. The information content in lateral particle dimensions is shown to be the most advantageous for practical use.Determination of latex particle size distributions by AFM is shown to be an interesting alternative to the arsenal of available methods with respect to exactness of results, time consummation and instrumentation costs.

Miniemulsion polymerization of styrene: Evolution of the particle size distribution

AbstractThe mechanism of the miniemulsion polymerization of styrene was investiaged through a combination of calorimetry to monitor the polymerization rate and transmission electron microscopy (TEM) to follow the evolution of the particle size distribution. These techniques proved to be a powerful combination for gaining detailed mechanistic information regarding these polymerizations. Particle size analysis of the latexes withdrawn during the course of the reaction revealed that most of the polymer particles were formed by a relatively low conversion (i.e., 10% conversion). However, nucleation continued well past this point (to 40‐60% conversion). In fact, it was observed that nucleation in miniemulsion polymerizations using cetyl alcohol continued past the maximum in the rate of polymerization. As a result of these long nucleation periods, the latex particle size distributions produced from these miniemulsion polymerizations were broader than their conventional emulsion polymerization counterparts, and were negatively skewed with a tail of small particles. The amount of negative skewing of the particle size distributions was found to decrease with increasing initiator (potassium persulfate) concentration. Finally, a correlation was observed between the length of time to the maximum polymerization rate and the breadth of the particle size distribution as reflected in the standard deviation. © 1995 John Wiley & Sons, Inc.

Emulsion polymerization of styrene in a continuous Taylor vortex flow reactor

A continuous emulsion polymerization of styrene was tried in a Taylor vortex flow reactor which has characteristics of a plug flow reactor. The Taylor vortex flow reactor has the mixing characteristics appropriate for this reaction system. The steady-state conversion, the average molecular weight and the size distribution of latex particles can be controlled by the flow condition as well as by the reaction temperature.

Synthesis of polystyrene suspensions with an arrow size distribution of latex particles

Synthesis of polystyrene suspensions with an arrow size distribution of latex particles

A comparison of some methods for measuring the size distribution of two-dimensionally clustered latex particles in TEM images using mathematical morphology

SUMMARY The particle size distribution of polymer latexes of, for example, polybutadiene can be measured on transmission electron micrographs using image analysis methods. By taking suitable measures in preparing the sample it can be ensured that the image only consists of projections of two-dimensional clusters of adhering latex spheres. For the deagglomeration of these clusters a number of methods based on mathematical morphology are discussed. Speed and accuracy of the methods were tested on a personal-computer-based image analysis system and compared to manual measurements. Repeated openings or erosions applied to a binary image are relatively fast global methods with a low accuracy due to the fact that particle diameters are measured in whole numbers of pixels; only the horizontal diameters of rectangular pixels are measured. With an iterative method the individual components of the clusters are found by repeated conditional thickening of the erosion kernels. The method is accurate but very slow due to the large number of processing steps. The watershed method as applied to the original grey-scale transmission electron micrograph makes use of the sharp local maxima which arise at the interface of the projection of two adhering particles. This method is as accurate as the iterative method, but about eight times as fast.

The dispersed composition of monomer emulsions and its effect on the mechanism of polymer-monomer particle formation

Conditions for the formation of highly dispersed monomer emulsions containing a large amount of a microemulsion have been investigated. It is shown that in these systems polymer-monomer particle formation takes place from monomer microdrops. The latex particle size distribution and the MMD of the polymers grow narrower in the course of polymer-monomer particle formation from monomer microdrops.

Dispersion Polymerization of Styrene by Initiation Within Monomer Phase with Lauroyl Peroxide

Abstract Dispersion polymerization kinetics of styrene was investigated in this study. A monomer phase soluble initiator, namely lauroyl peroxide, and a water phase soluble emulsifier, namely sodium dodecyl sulfate, were used. the polymerizations were carried out in a magnetic drive, sealed, cylindrical polymerization reactor, in nitrogen atmosphere. Two different fatty alcohols, cetyl and lauryl alcohols, were tried as particle size increasing agents. the effects of initiator, emulsifier concentrations, monomer/water ratio, and the weight ratio of particle size increasing agent to emulsifier on the total monomer conversion, average size, and size distribution of the large latex particles were studied. the agglomeration conditions were tested by changing the polymerization temperature, initiator, and emulsifier concentrations. the results indicated that the polymerization rate and the average size of the latex increased with increasing emulsifier concentration. the average size of the latex was also increased with increasing initiator concentration. the use of cetyl alcohol in the presence of emulsifier resulted in an appreciable increase in the polymerization rate and in the average size of the latex. the effect of fatty alcohols on the polymerization rate in the dispersion polymerization system was completely different than that in the swollen emulsion polymerization. the agglomeration of the large latex particles was increased with decreasing emulsifier and increasing initiator concentrations.

Polymer latex particle size measurement through high speed dielectric spectroscopy

AbstractDielectric techniques have been implemented to study aqueous colloidal suspensions. A four electrode cell was used in two configurations; the first, a sweep of frequencies using a sequence of standard single frequency null‐balance measurements, and the second relying on the dielectric response to a Fourier synthesized pseudo random white noise (FSPN) with measurements performed using correlation techniques in the time domain. Single frequency measurements, which take on the order of 5–10 min per spectrum, were performed on polymer latex standards of varying size, latex concentration, and electrolyte concentration and were extended from 0.02 to over 500 kHz. It was found that the central relaxation frequency fc was inversely propotional to the square of the particle size, consistent with previous experimental results. Experiments were performed at different particle concentration and ionic strengths, and the magnitude and breadth of the dielectric dispersion was analyzed in terms of current theories. The distribution of relaxation times was found to be in general qualitative agreement with those predicted by some existing theories. The results indicate that a wide range of conditions exist in terms of latex concentration and ionic environment where the rapid and accurate measurement of polymer latex particle size and size distribution is feasible. FSPN measurements, which take on the order of seconds, were shown to be accurate over a moderate frequency range for model electrical network studies but were only partially successful for aqueous suspensions of latex because of high frequency limitations in the electronics. Experimental details and difficulties concerning the application of this technique are discussed.

Emulsifier‐free emulsion copolymerization of styrene and butyl acrylate. I. Kinetic studies in the absence of surfactant

AbstractSoapless emulsion copolymerization of styrene (S) and n‐butyl acrylate (BuA) has been investigated using two types of initiator and different comonomer feed mixtures. When using K2S2O8 as initiator, the particle size and size distribution of the final latexes (500 nm and 1.003, respectively) is not significantly affected by the comonomer feed composition, whereas the molecular weight and surface characteristics were found to sharply change at high butyl acrylate content. Based on the most probable particle nucleation mechanism and type of chain termination in the monomer swollen particles, a tentative explanation of these results has been proposed. Replacing persulfate by a carboxylic initiator (4‐4′‐azobiscyanopentanoic acid) results in the formation of stable particles as α observed with the persulfate, provided the aqueous phase pH is fixed in between 6 and 7. Results on the initiator residue location as a function of the conversion point out that the particle flocculation mechanism is strongly significant in the preparation of such latexes.

Latex particle size distribution from turbidimetry using inversion techniques

A method is reported for estimation of the particle size distribution of latices from spectral turbidity data. The method is based on existing solutions to Fredholm integral equations and it is demonstrated through recovery of the particle size distribution of polystyrene latices. Unimodal and bimodal particle size distributions of varying breadth and mean particle diameters have been investigated. It is shown that in every case the particle size distribution can be adequately recovered.

Latex Particle Size Distributions from Multiwavelength Turbidity Spectra

AbstractAccuracy, range, noise tolerance and resolution of turbitidy spectra analysis as a particle sizing method are discussed with respect to simulated data and data on latex spheres. The fine structure in the turbidity spectra is used to measure multimodal distributions with no apriori assumptions about the distribution.