The effect of clay on the morphology of multiphase latex particles

The effect of montmorrilonite clay (MMT) platelets on the morphology of polystyrene/poly(methyl methacrylate) (PMMA) composite latex particles prepared via PMMA-seeded (semi-) batch emulsion polymerization of styrene was studied. It was found that the particle morphology obtained greatly depended on the ability of the clay platelets to diffuse through the polymer particle. Indeed, when the reactions were strictly under kinetic control, i.e., where the clay platelets were unable to diffuse during polymerization, anisotropic core-shell-like morphologies with split core were observed. A better mobility of the clay platelets could more or less restrict the diffusion of the second-stage polymers within the host polymer, leading to original kinetically controlled morphologies. In the case of a full migration of the clay platelets to the particle surface, the penetration of the second-stage polymer species in the seed latex was found to be more limited, enhancing the formation of secondary particles.     

Dynamic mechanical spectrometry for the study of multiphase polymer materials

The dynamic mechanical behaviour of multiphase polymer materials depends on two factors: (i) properties of each phase and (ii) geometric arrangement of these phases (so-called morphology). Analysis of experimental results has been performed in order to separate these two factors; it leads to informations about morphology, presence of interphase between main phases, chemical composition of different domains and possible changes in physical properties of one phase, induced by its neighbours. The interest in such an analysis based on mechanical spectrometry appears important because of difficulties in direct investigations (low contrast in Electron Microscopy, poor information provided by X-ray measurements on amorphous polymers … )     

Dynamic modeling of the morphology of latex particles with in situ formation of graft copolymer

Modification of the polymer–polymer interfacial tension is a way to tailor‐make particle morphology of waterborne polymer–polymer hybrids. This allows achieving a broader spectrum of application properties and maximizing the synergy of the positive properties of both polymers, avoiding their drawbacks. In situ formation of graft copolymer during polymerization is an efficient way to modify the polymer–polymer interfacial tension. Currently, no dynamic model is available for polymer–polymer hybrids in which a graft copolymer is generated during polymerization. In this article, a novel model based on stochastic dynamics is developed for predicting the dynamics of the development of particle morphology for composite waterborne systems in which a graft copolymer is produced in situ during the process. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Practical methods to control morphology of heterogeneous polymer particles

This review focusses on processes in which emulsion polymerizations are carried out in stages so that previously formed particles are either overcoated in subsequent polymerization stages or engulf the second and later stage polymers. These products are often called “core-shell” particles. Basically, the most stable state of the final system is the one with the lowest net interfacial energy. In the case of a two-stage emulsion polymerization there can be three interfacial tensions to consider. Several mutually consistent, effective thermodynamic treatments have been published. At present, they serve primarily to predict when the morphology of multi-stage polymerization products may not be a simple reflection of the synthesis sequences. It is possible, and frequently desirable, however to produce particle structures that appear at first glance to be thermodynamically forbidden. This is achieved either by changing the surface characteristics of a polymer from those of the bulk material or by employing kinetic factors to anchor energetically unprofitable morphologies. This paper summarizes methods of both types that have been reported to control the texture of structured latex particles in order to produce designed morphologies.     

Revisiting the morphology development of solvent-swollen composite polymer particles at thermodynamic equilibrium

Morphology of polystyrene (PS)/poly(methyl methacrylate) (PMMA)/toluene droplets, in which phase separation proceeds, dispersed in SDS aqueous solution was examined. It changed from ex-centered PS-core/PMMA-shell to hemisphere with increasing SDS concentration. At low polymer weight fraction (wp), PS and PMMA phases contained non-negligible amount of PMMA and PS, respectively. The small amount of PS and PMMA in PMMA and PS phases, respectively, affected significantly the interfacial tension between polymer/toluene and aqueous solutions. Interfacial tension between PS and PMMA phases at low wp was measured by the spinning drop method, showing a quite low value ( approximately 10-2 mN/m). Predicted morphology obtained from calculation of minimum total interfacial free energy of the droplets using the interfacial tensions agreed well with the experimental observation.     

Estimation of morphology of composite polymer emulsion particles by the soap titration method

The occupied area (A_m) of a sodium dodecyl benzene sulfonate molecule adsorbed on particles was measured by the soap titration method. The A_m values are 214, 133, and 53 Ų for poly(methyl acrylate) (I), poly(methyl methacrylate) (II), and polystyrene (III), respectively. For methyl metharylate-styrene copolymer emulsions the additivity was established between the A_m value and copolymer composition. Composite emulsion particles consisting of I/II, I/III, and II/III were prepared by seeded emulsion polymerization. For these emulsions the relationship between polymer composition at the surface layer calculated from the A_m value and that in a particle calculated from the polymerization process was investigated. This relationship is remarkably affected by the order of polymerization, the hydrophilicity of polymer, the flexibility of the seed polymer, and the monomer addition method. The models of the morphology of these composite particles explain the results successfully.     

Modeling multiphase latex particle equilibrium morphology

Multiphase waterborne polymer particles provide advantages in more demanding applications and their performance depends on particle morphology. Currently, no general approach to predict the morphology of multiphase latex particles is available. In this work, a model based on Monte Carlo methods was developed for the prediction of equilibrium morphologies of multiphase waterborne systems, such as polymer‐polymer and polymer‐polymer‐inorganic hybrids. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2579–2583, 2010     

Influence of particle diameter on the morphology of micron-sized, monodispersed composite polymer particles produced by seeded polymerization for the dispersion of highly monomer-swollen polymer particles

 Micron-sized, monodispersed polystyrene (PS)/poly (n-butyl methacrylate) (PBMA) composite particles, in which the PS domain(s) were dispersed in a PBMA continuous phase, were produced by seeded polymerization for dispersions of n-butyl methacrylate (BMA) swollen PS particles in a wide range of PS/BMA ratios in the presence of NaNO₂ as a water-soluble inhibitor. Moreover, in order to change the diameter of the composite particles at same PS/BMA ratio, PS/PBMA (1/150 w/w) composite particles were produced using five kinds of PS particles in a range of diameters from 0.64 to 3.27 μm as seeds. The percentages of the PS/PBMA composite particles having double and triple and over PS domains, which were thermodynamically unstable morphologies, increased with the increase in the diameter of BMA swollen PS particles. There was a clear influence of the size of the swollen particles on the morphology of the PS/PBMA composite particles produced. Received: 30 September 1999/Accepted: 18 April 2000     

Pore morphology of porous polymer particles probed by NMR relaxometry and NMR cryoporometry

The pore size distribution (PSD) and pore connectivity (PC) within porous polymer particles are probed by combining NMR cryoporometry and NMR relaxometry (spin-spin relaxation). With water as a probe molecule, the constant K in the so-called Gibbs-Thompson equation and the surface relaxivity (rho2) were determined to be K = (420 +/- 50) KA and rho2 = (0.44 +/- 0.01) x 10(-6) ms(-1), respectively. Also, the thickness of the interface layer was estimated to be of the order of one monolayer of water molecules. A detailed analysis of the complete set of NMR data enabled the morphology or pore structure to be probed, and is thoroughly discussed in the text.     

The morphology of composite polymer particles produced by multistage soapless seeded emulsion polymerization

 Composite polymer particles which contain poly(methyl methacrylate) (PMMA) and polystyrene (PS) components (PMMA/PS composite particle) were synthesized by the method of multistage soapless seeded emulsion polymerization. In this study, the process of multistage soapless seeded emulsion polymerization included two-stage polymerization, three-stage polymerization or four-stage polymerization. The morphologies of the PMMA/PS composite particles were studied. The kinetic factor was the main force to control the morphology of the linear PMMA–PS composite particles which were synthesized by the method of two-stage reaction. Both the kinetic factor and the thermodynamic factor decide the morphology of the linear composite particles which were synthesized by the method of either three-stage or four-stage reaction. However, the thermodynamic factor cannot influence the morphology of the PMMA/PS composite particles with a cross-linked structure which were synthesized by the method of three-stage reaction. The cross-linked composite polymer particles had the morphology of a multilayer structure, which showed that the polymer layers accumulated in their order of production. Received: 9 January 2001 Accepted: 14 June 2001     

Fabrication and morphology control of hollow polymer particles by altering core particle size

Particles with various morphologies were fabricated by changing the size of carboxyl-containing core particles and performing seeded emulsion polymerization as well as alkali posttreatment. The distribution of carboxyl groups, size, and morphology of the resultant particles were characterized with conductometric titration, dynamic light scattering (DLS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Results indicated that the size of carboxyl-containing core latex particles could be varied from 95 to 240 nm by adjusting the concentration of sodium dodecyl sulfate (SDS). The percentage of carboxyl groups buried inside particles increased clearly along with the encapsulation of core by interlayer and shell polymers, and seeded emulsion copolymerization performed smoothly except the system using core particles with size less than 99 nm. After alkali posttreatment, the morphologies of corresponding particles showed porous, hollow, and bowl-like structure, respectively. Moreover, the relationship between core particle size and alkali-treated particle morphology was elucidated briefly.     

Fabrication and morphology of spongelike polymer material based on cross-linked sulfonated polystyrene particles

A novel spongelike polymer material has been fabricated by γ-ray induced polymerization of methylmethacrylate (MMA) in an emulsion containing cross-linked sulfonated polystyrene (CSP) particles. Scanning electron microscopy (SEM) images reveal that the spongelike structure is made up of interlinked nanosized PMMA particles with micrometer-sized CSP-PMMA particles embedded inside. The nitrogen adsorption isotherm discloses that the spongelike material has a high specific surface area of 29 m(2)/g and a narrow pore size distribution of 60-120 nm. The formation mechanism is discussed in this paper, which indicates that the key steps to form the spongelike material include a Pickering emulsion stabilized by the CSP particles, followed by the swelling process of MMA into these particles. This approach offers a more convenient alternative to prepare polymeric spongelike material without any etching procedure.     

Influence of viscosity within polymerizing particle on the morphology of micron-sized,monodisperse composite polymer particles produced by seeded polymerization for the dispersion of highly monomer-swollen polymer particles

Micron-sized, monodisperse polystyrene (PS)/poly( n-butyl methacrylate) (PBMA) composite particles, in which PS domain(s) were dispersed in a PBMA continuous phase, were produced by seeded polymerization for the dispersion of highly n-butyl methacrylate (BMA)-swollen PS particles (PS/BMA=1/150, w/w) using various concentrations of benzoyl peroxide as initiator in the absence/presence of sodium nitrite (NaNO ₂) as a water-soluble inhibitor. The percentages of the composite particles having double, triple and over PS domains, which were thermodynamically unstable morphologies, increased with a rapid increase of viscosity within the polymerizing particle.     

Influence of the swelling state of seed polymer particles with monomer on the morphology of micron-sized monodispersed composite polymer particles produced by seeded polymerization utilizing the dynamic swelling method

 Micron-sized mono-dispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles (PS/PBMA=2/1 by weight) having a heterogeneous structure in which many fine PBMA domains dispersed in a PS matrix near the particle surface were produced by seeded polymerization of n-butyl methacrylate (BMA) of which almost all had been absorbed by 1.8 μm-sized monodispersed PS seed particles utilizing the dynamic swelling method. The morphology was varied by changing the PS/BMA ratio and polymerization temperature. It was concluded that the swelling state of 2 μm-sized BMA-swollen PS particles in the seeded polymerization process is one of the important factors to control the morphology of the composite particles. Received: 27 November 1996 Accepted: 21 March 1997     

Reconstruction of morphology of micron-sized,monodisperse composite polymer particles by the solvent-absorbing/releasing method

Micron-sized, monodisperse polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) (2/1 w/w) composite particles having different morphologies were prepared by the solvent-absorbing/releasing method (SARM). There was an obvious influence of the releasing rate of toluene from the toluene-swollen composite particles on the reconstructed morphology by the SARM. In the case of fast release, the reconstructed morphology was a bicontinuous structure that is similar to that formed by spinodal decomposition. On the other hand, in the case of slow release, a hemispherical structure was formed that consisted of PS and PBMA phases.Part CCLIV of the series Studies on Suspension and Emulsion     

The effect of first-stage polymer Tg on the morphology and thermomechanical properties of structured polymer latex particles

A series of heterogeneous latexes having stage ratios of 40:60 between the first and second stage polymers were prepared by emulsion polymerization. The first-stage polymers were non-polar S-BuA with T_gs ranging from + 100 °C to + 20 °C and the second stage polymer was polar MMA–BuA–MAA having a T_g of 20 °C. The latex particle morphologies were studied using TEM and the thermomechanical properties of the resulting latex films were studied with DSC and DMA. Calculated diffusion rates for propagating species during the reactions were correlated to the observed morphologies and to the amount of interphase in the latex particles. To cite this article: O.J. Karlsson et al., C. R. Chimie 6 (2003).     

Estimation of surface morphology of composite polymer particles prepared by the stepwise heterocoagulation method with ζ-potential measurement

 Core-shell composite polymer particle was prepared by the stepwise heterocoagulation of cationic small polymer particles (SPs) onto an anionic large polymer particle (LP), following heat treatment at temperatures which were higher than glass transition temperature (T _g=18 °C) of SP. At pH 9 ζ-potential of the hetero-coagulated particle (HP) was negative, but it changed to positive by the heat treatment and increased with the treatment time and finally attained to that of SP. The treatment time to attain the ζ-potential of SP became short by elevating the treatment temperature. This indicates that during the heat treatment, SP continued to melt on the surface of LP and finally formed a continuous shell. Received: 3 September 1997 Accepted: 29 October 1997