Latex film morphology

Feng J, Winnik MA, Shivers RR, Clubb B. Polymer blend latex films morphology and transparency. Macromolecules 1995 28 7671-7682. 

Emulsion copolymerizations can be carried out using batch, semi-continuous, or continuous processes. The copolymers made by these processes differ according to the process used, the copoly-meriztion reactivity ratios of the monomers, and the monomer solubilities in the aqueous phase. To show the difference between batch and semi-continuous polymerization, the latex particle size, surface characteristics, latex stability, copolymer properties, and latex film morphology were investigated for the vinyl acetate-butyl acrylate system (37). The water solubilities are 290 mM and llmM for vinyl acetate and butyl acrylate, respectively, and the copoly-merization reactivity ratios of = 0-0.04 and r 2 show... 

Scanning electron microscopy was used to probe the film morphology of the two-stage latex particles. Figure 9A is a surface photograph of the 65//35 (St//BA) latex showing a uniform packing... 

The morphological characterization of structured latexes is a fundamental aspect of their study, because (1) it provides very useful information on the nature of the mechanisms that regulate the formation of the particle, and (2) knowledge of the organization of the polymer within the particle is the essential foundation for the theoretical interpretation of the behavior of the resulting latex films (mechanical properties, permeability, etc.). From this perspective, there are a great many techniques that require examination to eliminate artifacts and incorrect conclusions deduced from their use. 

Processes of mechanical and dielectrical relaxation as well as structural-morphological self-organization in these systems under vibrowave treatment have been already described in our previous work [8]. In the presented work the major attention is paid to an estimation of elastic-strenght properties of latex films and their IR-spectra. Figures 1 and 2 illustrate the dependence of physicomechanical properties of films on their composition, and also change of these dependences at simple mechanical influence (stirring of a latex by means of a mechanical stirrer) and under vibrowave treatment. 

E. Ruckenstein, Emulsion pathways to composite polymeric membranes for separation processes, Colloid Polym. Sci., 1989, 267, 792-797 J.P. Cohen-Addad and C. Bogonuk and V Granier, Gel-like behavior of pH dependent latex films, Macromolecules, 1994, 27, 5032-5036 T.-H. Young, L.-W. Chen and L.-P. Cheng, Membranes with a microparticulate morphology, Polymer, 1996, 37, 1305-1310. 

El-Aasser M.S, Makgawmata T, VanderHoff J.W (1983) Batch and Semicontinuous Emulsion Copolymerization of Vinyl Acetate-Butyl Acrylate, n. Morphological and Mechanical Properties of Copolymer Latex Films. J. Pol)nn. Sci. 21 2383-2395. 

Latex with hydroxyl functionalised cores of a methyl methacrylate/butyl acrylate/2-hydroxyethyl methacrylate copolymer, and carboxyl functionalised shells of a methyl methacrylate/butyl acrylate/methacrylic acid copolymer was prepared by free radical polymerisation. The latex was crosslinked using a cycloaliphatic diepoxide added by three alternative modes with the monomers during synthesis dissolved in the solvent and added after latex preparation and emulsified separately, then added. The latex film properties, including viscoelasticity, hardness, tensile properties, and water adsorption were evaluated as functions of crosslinker addition mode. Latex morphology was studied by transmission electron and atomic force microscopy. Optimum results were achieved by introducing half the epoxide by two-step emulsion polymerisation, the balance being added to the latex either in solution or as an emulsion. 8 refs. 

Atomic force microscopy has also been used to investigate the morphology of natural rubber blended films. The natural rubber and poly(methyl methacrylate) particles in the latex films can be easily distinguished and are clearly... 

The removal of direct carbon replicas is dependent upon the polymer. Boiling xylene vapor was used to remove drawn PE from replicas [296] in work on drawn polymer morphology. Hobbs and Pratt [297] described a direct carbon replica method for replication of a PBT impact fracture surface by evaporation of platinum at 20° and PBT removal in hexafluor-oisopropanol (HFIP). Latex film coalescence in poly(vinyl acrylate) homopolymer and vinyl acrylic copolymer latexes was studied using direct replicas [298]. As the latex films have a low glass transition temperature, they were cooled by liquid nitrogen to about -150°C in the vacuum evaporator and shadowed with Pt/ Pd at 45° followed by deposition of a carbon support film at 90° to the specimen surface. The latex films were dissolved in methyl acetate/ methanol. TEM micrographs of the latex films show the difference between films aged for various times (Section 5.5.2). 

Since process and properties are so closely linked in the production of emulsion polymers, a variety of processes have been devised as efforts to design and control the microstructure of latex particles have intensified. The central issue is whether, as a general rule, particle growth is better represented in terms of a surface growth model or of a bulk polymerization model. Results obtained by a variety of methods developed to study particle and film morphology will be reviewed, and the special case of water-soluble monomers will be considered along with descriptions of process techniques designed to control particle structure. 

Marchessault R H, Monasterios C J, Lepoutre P (1990), Properties of poly(/3-hydroxyalkanoate) latex nascent morphology, film formation and surface chemistry , in Dawes E A, Novel Biodegradable Microbial Polymers, Dordrecht, Kluwer, 97-112. 

Mechanical Properties of the Latex Films. Figure 13.18 shows a noteworthy effect of the addition of Laponite on the mechanical properties of the nanocomposite film. A remarkable increase in the storage modulus at the rubbery plateau was observed with the addition of only 5 wt% Laponite. This improvement of the mechanical properties of the poly(styrene-co-butyl acry-late)-Laponite film was expected, considering the good dispersion of the clay platelets inside the polymeric matrix and the armored morphology of the hybrid particles. It is worth remembering here that similar results were reported by Ruggerone and co-workers" and Faucheu et al. for PS-Laponite films obtained from latexes prepared by emulsion and miniemulsion polymerization, respectively (see Sections 13.3.2.1 and 13.3.2.2). 

Emulsion homopolymers and copolymers (latexes) are widely used in architectural interior and exterior paints, adhesives, and textile industries [2-4]. Colloidal stabilizators in the emulsion polymerization strongly affect not only the colloidal properties of latexes but also the film and mechanical properties, in general. Additionally, the properties of polymer/copolymer latexes depend on the copolymer composition, polymer morphology, initiator, polymerization medium and colloidal characteristics of copolymer particles. 

This is truly reflected in the morphology of the uncured clay preexfoliated rubber nanocomposite films (NLu NA) prepared by the latex blending method (Fig. 7a). Curing the NR/NA nanocomposites in situ prevulcanization (No>NA) does not alter the arrangements of dispersed clay layers greatly, as seen from the... 

Transmission and scanning electron microscopy, differential scanning calorimetry and minimum film temperature analysis supports a core/shell morphology for the two-stage latex polymers, consisting predominantly of a polystyrene rich core surrounded by a soft acrylic rich shell. 

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