Layer-by-Layer Synthesis of Multilayer Core−Shell Latex and the Film Formation Properties

Abstract

Polymer latex particles were synthesized with multilayer core-shell structure via surface cross-linking emulsion polymerization. The latex core is coated with a five-layer shell. The polymerization was done in a semicontinuous fashion monitored by a dynamic laser scattering (DLS). The copolymer in each layer is designed with alternating high and low glass transition temperature (T(g)). Divinylbenzene (DVB) was added as the cross-linking agent in the synthesis of the "hard" layers to prevent the molecular diffusion from the adjacent "soft" layers. The layer-by-layer increment on the latex core is proved by the alternating changes on the film-formation capabilities of different latex emulsions at room temperature in correspondence with the variance in the T(g) of the outermost polymer layer. The detailed morphologies of the films formed by the latex with different number of layers were characterized by atom force microscopy (AFM). The deformation of the latex particles is largely depended on the nature of the polymer in the outermost layer of the latex particles. Further characterization carried out by multifrequency temperature-modulated differential scanning calorimetry (TOPEM-DSC) confirmed the layer-by-layer structure of the particles, although the molecular redistribution and the interlayer structures were observed. The work provides a routine toward the synthesis of multilayer polymer latexes.

Stress development and film formation in multiphase composite latexes

“…1,4,5,24,25 While a measurement of the MFFT is useful, the MFFT is only a criterion for bulk film formation and cannot provide information on the microscopic behavior of the latex particles. Combining MFFT measurements with other experimental techniques, like cryoSEM and AFM, provides a more complete picture of film formation.…”

“…4,5,25 The effect of shell ratio is clearly illustrated by comparing AL25, AL35, and AL50. For a shell ratio of 25% (AL25), the MFFT is close to the measured core T g (see Table 1); however, as shell ratio increases, the MFFT approaches the measured shell T g (AL50).…”

“…These results are consistent with others using AFM to explore film formation and coalescence for composite latex particles. 25,30,31 The influence of the shell ratio on particle deformation and the MFFT is clear when the difference between the T g of the core and shell polymers (DT g ) is large. However, when the DT g is smaller, the relationship is less defined.…”

Characterization methods of polymer core–shell particles

“…Mu et al used TOPEM-DSC to demonstrate a multilayered structure for core-shell particles composed of five types of copolymers by revealing the presence of interfaces in a single scan over a range of frequencies without quantitative details [86]. Apart from the signals attributed to each component, two additional signals were present that related to the presence of the two interfacial regions.…”

Self film‐forming and opaque hollow latexes fabricated via seeded emulsion polymerization followed by alkali post‐treatment

“…1 However, because the shell is too hard to deform under interfacial surface tension and capillary forces with the evaporation of water, and diffusion of copolymer chains across particle boundaries and further coalescence of particles are also limited by cross-link network and high T g , the current hollow latexes cannot form a continuous and intact film by themselves at room temperature, which only can be used as white pigments. [20][21][22][23] For obtaining opaque coatings at ambient condition, hollow latexes must be applied together with other film-forming resins, hinders, or coalescents. 24,25 In this work, based on the osmotic swelling method and the previous research on the three-layer core/shell latex, 18,19 a four-layer core/ shell polymer latex with an outermost soft film-forming layer was designed to prepare the hollow latex with both opaque and self film-forming properties, and effects of the BA/St mass ratio, DVB content, and the core/film-forming layer mass ratio in the film-forming layer preparation on the four-layer core/shell latex and the final hollow latex were investigated.…”