Scanning electric potential microscopy images were acquired from coalesced poly (styrene-butyl acrylateacrylic acid) latex films having a Tg equal to 15.9 °C. The micrographs show the boundaries between particles even in transparent films (transmittance > 99%), and the boundaries appear as positive domains, relative to the particle cores. Large local electric potential gradients are observed, ca. 1 V/10 nm, but these are smeared when the latex is dialyzed prior to film formation. Electric domain patterns are modified by aging, annealing and exposure to toluene or chloroform vapors. Completely independent patterns are obtained, in each case. The significance of charge distribution to latex cohesion, adhesion and swelling behavior is discussed.

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Submonocamadas de látex estireno-acrílico preparado usando um tensoativo sulfonato reativo e um tensoativo fosfato não-reativo foram examinadas em um microscópio de transmissão equipado com um espectrômetro de perda de energia de elétrons, para a aquisição de mapas de distribuição elementar. P está ausente do centro das partículas mas é encontrado em uma casca espessa, no fundo da imagem e em estruturas incomuns com um baixo teor de carbono, enquanto S está uniformemente distribuído nas partículas. Os mapas elementares de Na e N mostram que os respectivos cátions (Na + , NH 4 +) têm diferentes distribuições: o sinal de Na é mais intenso nas partículas do que no fundo, enquanto N se acumula nas bordas das partículas. As distribuições de tensoativos e contraíons são portanto diferentes de algumas suposições correntes, mas elas estão de acordo com resultados recentes sobre a distribuição de constituintes iônicos em látex, obtidas por microscopia de varredura de potencial elétrico. Styrene-butyl acrylate-acrylic acid latex submonolayers prepared using a non-reactive phosphate surfactant together with a reactive sulfonate surfactant were examined in a transmission microscope using electron energy loss spectroscopy imaging (ESI-TEM). Phosphorus is nearly absent from the particles core but it is detected in a thick shell and in unusual, strongly scattering structures with a low carbon content, and largely made out of inorganic phosphate. P is also dispersed outside the particles, while S is uniformly distributed within then. The Na and N elemental maps show that the respective monovalent ions (Na + and NH 4 +) have different distributions, in the latex: Na signal within the particles is stronger than in the background, while N is accumulated at the particle borders. The distributions of surfactant and counter-ions are thus different from some current assumptions, but they support recent results on the distribution of ionic constituents in latex films, by scanning electric potential microscopy.

This work reviews new probe and electron microscopy approaches for the detection of charged domains in insulating polymers, as well as for the identification of the charge‐bearing species: scanning electric potential microscopy (SEPM), electric force microscopy (EFM) and energy‐loss spectroscopy imaging in the transmission electron microscope (ESI‐TEM). The SEPM and EFM micrographs show patterned domains bearing excess electric charges and extending for tens of nanometers, in polymer latex particles and films. The charged species are identified by ESI‐TEM as emulsion polymerization initiator and surfactant residues, as well as the associated counter‐ions. Charged domains are also observed in common thermoplastic polymers, producing unexpectedly large electric potential gradients.

ABSTRACT:Film formation by a surfactant-stabilized, peroxide-initiated styrene/butyl acrylate latex was followed in situ by ultramicroscopy. The effects of latex serum components on film formation were observed first by the subjection of the latex to extensive dialysis and then by the separate addition of salt and surfactants. Domains of different particle concentrations were observed in the latex dispersion during liquid evaporation, and their positions were related to those of defects in the dry film. Films obtained with the dialyzed latex showed macroscopic defects, which were not seen in the as-prepared latex. Partially reconstituted latex (dialyzed, with the later addition of salt but not surfactant) behaved like the as-prepared latex.