Latex Particle Size Distribution Research Articles

In-Line and In Situ Monitoring of Ionic Surfactant Dynamics in Latex Reactors Using Conductivity Measurements and Ion-Selective Electrodes

In an emulsion polymerization process, surfactant type and concentration play an important role in the stability, appearance, reaction kinetics, and particle size distribution of latexes. The possibility of carrying out in-line evaluation of the distribution of free surfactant molecules in the media is of interest in polymer reaction engineering, because this would provide information about the rates of nucleation and particle stabilization. Both ion-selective electrodes and conductimetry seem to be very promising techniques for this objective. Ion-specific electrodes are able to determine the concentration of several substances, in a quantitative and specific manner, and may also be a good way of monitoring ionic surfactant. Conductivity measurements offer a means of monitoring the evolution of concentrations of different species in the latex. The objective of this work is to evaluate the use of ion-selective electrodes as a tool for the on-line monitoring of an emulsion polymerization reaction and to compare this method to conductivity. Ion-selective electrodes were prepared for two ionic surfactant species: dodecyl sulfate and dodecyltrimethylammonium, coming from SDS (sodium dodecyl sulfate) and DTAB (dodecyl trimethylammonium bromide), respectively. To do so, a glass electrode was coated with polymeric membranes specific for each surfactant. It is demonstrated that ion-selective electrodes can provide insight into the evolution of the colloidal surface in the latex, even when temperature and composition drifts are present.

Preparation of polystyrene particles with narrow particle size distribution by γ-ray initiated miniemulsion polymerization stabilized by polymeric surfactant

Co-60 γ-ray initiated miniemulsion polymerization of styrene stabilized by an alkali soluble polymeric surfactant (ASPS) was studied in this work. The affecting factors, including absorbed dose, dose rate, surfactant concentration, and hexadecane (HD) concentration, were systematically studied. The particle size and particle size distribution (PSD) of final latexes was determined by transmission electron microscope (TEM). The results indicated that polystyrene (PS) particles with narrow PSD could be easily prepared by this method, and the particle size could be controlled from 50 nm to 250 nm by adjusting the concentration of HD and ASPS. HD concentration, surfactant concentration, dose rate and total absorbed dose strongly affected the particle size and PSD of PS latexes.

Determination of Latex Particle Size Distribution by Transmission Electron Microscopy (TEM) and Image Analysis: Standardized Procedures and Key Factors

The factors that affect the determination of latex particle size distribution (PSD) using transmission electron microscopy (TEM) and image analysis were studied. It has been found that suitable TEM magnification is in inverse proportion to particle size. Moreover, a linear functional relationship between uniformity ratio (U) of particle size and the minimum number of particles analyzed (N min ) is obtained by the two-sample Kolmogorov-Smirnov statistical test. Based on a two-step thresholding and image split technique, a standardized procedure is proposed to process the image of latex particles. The proposed method has significantly improved accuracy.

Kinetics of the batch cationic emulsion polymerization of styrene: A comparative study with the anionic case

AbstractAn in‐depth study on the kinetics of the cationic emulsion polymerization of styrene in a batch reactor is presented. This study is focused on the effect of the amount of the cationic surfactant dodecyltrimethylammonium bromide (DTAB), using two different cationic initiators: 2,2′‐azobisisobutyramidine dihydrochloride (AIBA), 2,2′‐azobis (N,N′‐dimethyleneisobutyramidine) dihydrochloride (ADIBA), on kinetics and colloidal features such as conversion, number of particles, number average of radicals per particle, mean particle diameter, and particle size distribution (PSD) of the polystyrene latices obtained by emulsion polymerization in a batch reactor. Furthermore, the results of the cationic emulsion polymerization were compared with its homologous anionic case. Using DTAB as cationic surfactant an expected increase in the total rate of polymerization was observed when the DTAB concentration increased. However, the total number of particles increased much more than in the anionic system. On the other hand, a dependence on the particle size of the rate of polymerization per particle together with the average number of radicals per particle was found. These differences between cationic and anionic emulsion polymerizations were explained taking into account the limited particle coagulation observed with cationic surfactants, and the high rate of radical formation of cationic initiators. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4461–4478, 2006

In situ preparation and properties of high-solid-content and low-viscosity poly(methyl methacrylate/n-butyl acrylate/acrylic acid)/poly(styrene/acrylic acid) composite latexes

With monodispersed poly(methyl methacrylate/n-butyl acrylate/acrylic acid) [P(MMA/BA/AA)] seeded latex with a particle size of 485 nm and a solid content of 50 wt % as a medium, a series of stable P(MMA/BA/AA)/poly(styrene/acrylic acid) composite latexes with a high solid content (70 wt %) and low viscosities (500–1000 mPa · s when the shear rate was 21 s−1) was prepared in situ via simple two-step semicontinuous monomer adding technology. The coagulum ratio of polymerization was about 0.05 wt %. The particle size distribution of such latexes was bimodal, in which the large particle was about 589 nm and the small one was about 80 nm. The latexes combined good mechanical properties with good film-forming properties. Differential scanning calorimetry showed that the corresponding latex film had a two-phase structure. The morphology of the latex film was characterized with atomic force microscopy and scanning electron microscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1815–1825, 2007

Preparation of crosslinked composite nanoparticles

AbstractCrosslinked composite nanoparticles were prepared by adding a trifunctional monomer (trimethyol propane trimethacrylate) or a difunctional monomer (divinyl benzene) as a crosslinker into the emulsion polymerization system of styrene in the presence of inorganic nanosilica. A coupling agent, 3‐methacryloxypropyltrimethoxysilane (MPS), was added along with the monomer, crosslinker, and silica to improve the interfacial interaction between silica and polymer and thus to obtain high binding efficiency. The role of MPS was examined. The effects of crosslinkers on the kinetics of emulsion polymerization, monomer conversion, and yield were investigated. The morphology of the composite particles was observed by TEM. The particle size and size distribution of composite latex particles were measured by the dynamic light scattering method. The binding efficiency and swelling ratio were determined by reluxing the sample in xylene using a Soxhlet extraction apparatus. FTIR spectra and TGA verified the participation of crosslinker and silica. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1538–1544, 2005

Synthesis of cationic poly(methyl methacrylate)-poly( N-isopropyl acrylamide) core-shell latexes via two-stage emulsion copolymerization

Thermally sensitive poly(methyl methacrylate (MMA))-poly( N-isopropylacrylamide (NIPAM)) core-shell particles were prepared via a two-stage emulsion copolymerization process. Methylene bisacrylamide (MBA), 2,2′-azobis (2-amidinopropane) dihydrochloride (V50) and dodecylethyl dimethyl ammonium bromide (DEDAB) were used as crosslinker, cationic initiator and surfactant, respectively. Functional core-shell particles were prepared using aminoethyl methacrylate hydrochloride (AEMH) as cationic co-monomer to increase the surface charge density. The influences of the crosslinker and co-monomer concentrations on the thickness and swelling capacity of the PNIPAM-based shell layer were studied. The latex particle size and particle size distribution were determined both by dynamic light scattering (DLS) and scanning electron microscopy (SEM). Monodisperse particles were produced with diameters between 150–250 nm (at 25 °C) and 140–190 nm (at 50 °C). The surface charge density was determined by chemical titration and higher values (∼10 μmol/g) were obtained for the functional core-shell particles. The electrokinetic properties of the dispersions at several pH and temperature values confirm the presence of the shell layer and cationic surface charges.

Assessing the effect of latex particle size and distribution on the rheological and adhesive properties of model waterborne acrylic pressure-sensitive adhesives films

The adhesive and rheological properties of model acrylic pressure-sensitive adhesive (PSA) films prepared from high solid emulsions with different particle sizes and distributions have been investigated with a customized probe tack apparatus. For each emulsion, the monomer composition and gel content were kept constant but different average particle sizes and distributions were used. Adhesive films 100 μm thick were then prepared from these emulsions and their rheological properties in the linear regime and adhesive properties were systematically characterized. Surprisingly, both the rheological and adhesive properties were found to be very dependent on the initial latex particle size distribution. A series of experiments were carried out to assess the adhesive properties of films made from blends of small- and large-particle-size latexes. Using the probe tack test, a maximum in adhesion energy of the dry films was found for 60% of small particles in the blend, a composition clearly different from that giving a minimum viscosity of the latex implying that optimizing for properties may not be equivalent to optimizing for processing in these adhesive applications. Finally, the adhesive properties of two multimodal latexes with different particle size distributions were investigated. Both gave significantly higher adhesion energies and clear evidence of a fibrillar detachment process. This important result suggests that the spatial distribution of gel domains in the dry film and the molecular connectivity between those gel domains also play an important role in controlling its adhesive properties.

A method for measuring the size distribution of latex particles by scanning force microscopy

A methodology has been developed to accurately determine the size distribution of latex particles using the scanning force microscope (SFM). Unlike other workers, who have generally measured the lateral dimensions of monolayers of latex particles using a global quantification method, we have measured the heights of individual latex particles located at the edges of latex monolayers that were immobilised onto mica substrates. In agreement with other work, we noted that the edges of monolayers of latex particles provided stable and reproducible scanning force imaging. Whilst SFM imaging noise, image processing artifacts, tip/sample forces and variations in the mica substrate are sources of measurement error that should not be overlooked, our experience has been that the variation over time of the sensitivity of the Z actuator is the greatest potential uncertainty in determining the heights of latex particles. The methodology that we used requires frequent calibration of the Z actuator of the SFM, typically before and after two or three images, in order to ensure that the uncertainties in the Z sensitivity are known and minimised. This methodology was developed for an SFM instrument that was equipped with open loop piezoelectric actuators following a careful study of the behaviour of those actuators. Using this methodology, we have measured the size distributions of populations of 300–400 latex particles from each of several different latex samples, with the maximum variation in the Z-actuator calibration experienced during the measurement of a sample being less than 2%, often about 1% and occasionally better still. In so doing, we have demonstrated that SFMs equipped with open loop actuators can be used for high confidence quantitative measurements of step heights.

Particle Size Distribution by Combined Elastic Light Scattering and Turbidity Measurements. A Novel Method to Estimate the Required Normalization Factor

AbstractTurbidity (T) and Elastic Light Scattering (ELS) measurements can be combined to estimate the particle size distribution (PSD) of a polymer latex. To this effect a “normalization factor” must be employed to adequately scale both measurements. In a real application, such factor is a priori unknown, and it must be estimated for determining the PSD. In a previous publication, a method was proposed to simultaneously estimate the normalization factor and the PSD by solving an inverse nonlinear problem. In this work, a simpler technique is presented which estimates the normalization factor and the PSD by sequentially solving two inverse linear problems. To evaluate the proposed technique, a synthetic example based on a polystyrene latex sample with a bimodal PSD was solved. It is shown that, for slight noise measurements, the errors in the estimation of the normalization factor are quite small and have a low effect on the PSD recovery.

Latex particle size distribution by dynamic light scattering: novel data processing for multiangle measurements

Multiangle dynamic light scattering (DLS) provides a better estimate of particle size distributions (PSD) than single-angle DLS. However, multiangle data treatment requires appropriate weighting of each autocorrelation measurement prior to calculation of the PSD. The weighting coefficients may be directly obtained from (i) the autocorrelation baselines or (ii) independent measurement of the average light intensity by elastic light scattering. However, the propagation of errors associated with such procedures may intolerably corrupt the PSD estimate. In this work, an alternative recursive least-squares calculation is proposed that estimates the weighting coefficients on the basis of the complete autocorrelation measurement. The method was validated through a numerical example that simulates the analysis of a polystyrene latex with a bimodal PSD and with “measurements” taken at 10 detection angles. The ill-conditioned nature of the problem determines that the “true” PSD cannot be recovered, even in the absence of errors. A sensitivity analysis was carried out to determine the effect of errors in the weighting coefficients on the PSD recoveries.

Novel Operating Method for Controlling Latex Particle Size Distribution in Emulsion Polymerization of Vinyl Acetate

This paper presented a non-steady-state operation for controlling latex particle size distribution by using continuous emulsion polymerization of vinyl acetate. The experiment was conducted in a CSTR under conditions below the critical micelle concentration of the emulsifier. The monomer conversion attained in the time-independent steady-state operation showed a dramatic rise from nearly 0 to over 60% at the mean residence time of the continuously stirred tank reactor (CSTR), τ c = 22 min. The mean residence time was switched alternately between two values in the non-steady-state operation, one giving zero monomer conversion and the other a high monomer conversion in the usual steady-state operation. The periodic-switching operation induced oscillations in monomer conversion in time. When the switching interval was sufficiently long as compared with the mean residence time, the particle size distribution (PSD) varied synchronously with the switching operation. The present work showed the possibility of controlling the temporal PSD by adjusting the frequency and/or the amplitude of the temporal variation of the mean residence time.

Semi-Batch Emulsion Copolymerization of Vinyl Acetate and Butyl Acrylate Using Oligomeric Nonionic Surfactants

Detailed kinetic studies on semi-batch emulsion copolymerization of vinyl acetate/butyl acrylate (VAc/BuA) (80 : 20) at 80°C were carried out using alkyl polyglucoside nonionic surfactants and ammonium persulfate as initiator. The polymerization recipe was varied with respect to the amount of initiator initially charged and continuously fed to the reactor, the surfactant concentration, the electrolyte concentration, and the monomer addition rate. Various types of alkyl polyglucosides with different hydrophilic and hydrophobic chain lengths were tested. Latex particle stabilization was shown to depend significantly on the surfactant structure and its adsorption characteristics. In general, the latex particle size distribution evolved from a bimodal to a unimodal distribution while latex destabilization was observed at high surfactant or/and high initiator concentrations. Based on experimental observations it was found that the most important factor for imparting particle stability was the hydrophilic/hydrophobic chain length ratio of the surfactant which actually controlled the balance between surface coverage and stabilizing capability.

Nonconventional Emulsion Polymerization of Styrene with Mixed Anionic and Nonionic Emulsifiers

Emulsion polymerization of styrene (St) in the presence of mixed anionic/nonionic emulsifiers (SDS/NP 40) has been investigated. The polymerization rate (R p ) vs. conversion (X) curves show a relatively constant R p region (Smith-Ewart Interval 2) in the range ofX=20-40% and a shoulder at X=ca. 75%. R p is independent of the emulsifier charge composition except the run with SDS or NP 40 as the sole emulsifier. The latex particle size (d w ) increases with increasing X and the degree of the increased d w is more pronounced at low X. The number of latex particles strongly increases up to ca. 20% conversion and then remains relatively constant toward the end of polymerization. The particle size distribution of latex particles is quite narrow. The average number of free radicals per particle (n) is below or close to 0.5 for the polymerization system with SDS alone and mixed SDS/NP 40 emulsifiers before the system experiences the gel effect at high X. On the contrary, for the system with NP 40 alone, n increases significantly with increasing X and it is well above 0.5 throughout the reaction. The colloidal and kinetic data obtained from this work are discussed in terms of the hairy or close-packed particle (droplet) surface layer, the decreased entry and exit rates of radicals, the relatively high oil-solubility of NP 40, accumulation of polystyrene and NP 40 within the monomer droplets, preservation of monomer droplets during polymerization and formation of double emulsion droplets. The increased uniformity and stability of the initial emulsion may promote the monomer-starved condition even at a relatively low level ofX.

Latex Particle Size Distribution by Dynamic Light Scattering: Computer Evaluation of Two Alternative Calculation Paths

Two calculation paths for estimating the particle size distribution (PSD) of a polymer latex from single-angle dynamic light scattering (DLS) measurements are evaluated on the basis of a numerical example. In the more common “double-step method,” two calculation steps are applied, with the intermediate estimation of the particle light intensity distribution (PLID). In the “single-step method,” the calculation is performed in one operation. From the specification of several PSDs, a mathematical model is used to produce the synthetic measurements. An iterative procedure was applied for determining the diameter range and the number of PSD points. The inversion operations were carried out using a regularization technique. For narrow distributions with diameters in the range 100–1000 nm, the PSD and the PLID are similar in shape, and both calculation paths produce similar results. For broad PSDs in the range 100–1000 nm, and for arbitrary PSDs in the range 10–100 nm (i.e., in the Rayleigh region), the single-step method proved preferable.

Synthesis and Physical Properties of the Crosslinking Poly(butyl acrylate)/ Polystyrene Core-Shell Composite Latex

Butyl acrylate and styrene were used as monomers in the first stage and second stage respectively, and potassium persulfate (K 2 S 2 O 8 ), as the initiator to synthesize the polymer/polymer composite latex by two-stage soapless emulsion polymerization. In the first stage, the poly(butyl acrylate) with crosslinking structure (PBA(XL)) was synthesized to be the seed latex. In the second stage, the styrene was polymerized in the presence of PBA(XL) seeds to form the PBA(XL) / PS composite latex. The morphology of the composite latex was observed by transmission electron microscopy (TEM) and showed that composite latex particles were with core-shell structure. The particle size distribution of the composite latex was very uniform. The kinetics of reaction of the second stage polymerization were investigated. The results showed that the reaction rate would be influenced by the degree of crosslinking of the PBA(XL) seeds, initiator concentration and agitation speed. The components of the PBA(XL)/PS composite polymers were measured by thin-layer chromatographic (TLC) analysis. The results showed a thin layer of PBA-graft-PS copolymer between the core (PBA) and shell (PS) region. The morphology of the PBA(XL)/PS composite polymers, processed under heat and pressure, was observed by transmission electron microscope (TEM). The morphology may change gradually with increase of processing time. The mechanical properties and rheological properties of the composite polymers were investigated.

A novel methodology to estimate the particle size distribution of latex using relative measurements of elastic light scattering and turbidimetry

A novel methodology to estimate the particle size distribution of latex using relative measurements of elastic light scattering and turbidimetry

A novel methodology to estimate the particle size distribution of latex using relative measurements of elastic light scattering and turbidimetry

In a previous publication, turbidimetry and elastic light scattering (ELS) were shown to be two techniques that, combined, can be used to determine particle size distributions (PSDs) of suspended particles. The proposed method, consisting in the solution of a linear inverse problem, was based on the assumption that absolute measurements of both turbidimetry and ELS were available. However, such measurements are normally difficult to obtain in practice, whereas relative measurements can be easily made. The technique proposed in this paper relaxes the assumption of absolute measurements by including an unknown parameter in the combined model. In this form the inverse problem to be solved under the new assumptions becomes a non-linear one. Since the problem can be solved semi-analytically, in all cases the results are exact and not linked to issues such as lack of convergence or other similar types of complications sometimes encountered in purely numerical solutions. Three synthetic examples of PSD estimation of polymer latex are used to show how the proposed methodology works in practice. The approach proposed here avoids the use of any type of calibration of the instruments used to measure turbidity and ELS, and makes the technique based on the combination of these two measurements a more powerful alternative than it was before. Copyright © 2000 John Wiley & Sons, Ltd.

Inversion of turbidity measurements of polymer latex using wavelet functions

The determination of the particle size distribution (PSD) of latex from turbidimetry at several wavelength may be considered as an inverse problem. Classical regularization methods to solve ill conditioned linear inverse problems have been applied to this problem previously. Poor quality results were obtained when the range of the particle sizes is wide and the particles are small. The wavelet-based approach investigated in this work considers the expansion of the solution in wavelet series with selective regularization of each component of the expansion. The results achieved from simulated experiments show that the solutions obtained by classical regularization methods can be improved by means of wavelet-based regularization. The method is developed so that good initial values for the regularization parameters can be selected using different techniques.

Soap-free emulsion polymerization ofn-butyl acrylate: Copolymerization with 1,1-(dimethyl)-1- (3-methacryloxyethyl)-1-(sulfopropyl)ammonium betaine

Emulsifier-free emulsion polymerization of n-butyl acrylate has been performed in the presence of a polymerizable sulfobetaine monomer, 1,1-(dimethyl)-1-(3-methacryloxyethyl)-1-(sulfopropyl)ammonium betaine (SPE). An investigation of the effect of various salts (NaCl, NaHCO3, Na2CO3, and NaH2PO4) on the emulsifier-free emulsion polymerization of n-butyl acrylate revealed that the type and quantity of salt is important in determining the size and size distribution of the final latex particles. In the case of the copolymerizations, control of the monomer feeding protocol (batch vs. semicontinuous and unseeded vs. seeded reactions) and of the ionic strength of the reaction mixture via addition of electrolytes allowed the preparation of stable latexes at 10% solids content with controllable particle size distributions. The results indicate that the amphiphilic sulfobetaine is able to stabilize the latex in much the same way as a polymerizable surfactant or an ionic comonomer. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 227–236, 1998