Structured latex films

Film formation from poljmer latexes is a complicated, multi-stage phenomenon and has been the subject of much theoretical and experimental attention. Many studies of the individual stages, utilising a variety of different techniques, have been published. The use of latex films to investigate 

The other interesting method utilises fluorescence measurements. This approach has been mainly applied to latex film formation by Winnik and Wang [90]. In this technique, latex is prepared in two different batches. In one batch, the chains contain a donor group, while in the other, an acceptor group is attached. The interdiffusion of polymer chains between neighbouring latex particles is then studied by direct non-radiative energy transfer measurements. 

Molecular interdiflfusion in a core (poly(butyl methacrylate)-shell (poly(butyl methacrylate-co-butyl acrylate) latex, which exhibits miscibility between the core and shell polymers, has been studied [93]. The volume fraction of mixing and the inter-particle penetration distance increased with annealing time [93]. In other core-shell latex films, phase separation can occur upon annealing, because of immiscibility of the core and shell phases. 

As has already been made clear, interdiffusion is of great importance for the development of the physical properties of latex films [94]. In order to learn how to optimise the performance of a wide variety of coatings formulations, a deeper understanding of the coalescence process is needed. The essential feature that one needs to understand is the role of inter-particle polymer diffusion once the water has evaporated and the nascent film has formed. Although, as reported above, latex film coalescence processes have been studied [90-94], a much better understanding of these processes is needed. In this section, the process of core-shell latex film coalescence and the dynamics of surface structure development of latex films will be discussed in the light of recent MTDSC studies by the authors. 

It has already been shown above that the dCp/dT signal readily provides fruitful information about multi-phase polymer materials. Measurement of the ACp values of the pure shell and core phases at their TgS leads to 

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Journal of Polymer Science Polymer Physics Edition 39, No.14, 15th July 2001, p.1659-64 EFFECT OF RESIDUAL WATER AND FREE VOLUME ON THE GLASS-TRANSITION TEMPERATURE AND HEAT CAPACITY IN POLYSTYRENE/POLYVINYL ACETATE-CO-BUTYL ACRYLATE STRUCTURED LATEX FILMS... 

The dynamic heat capacity and Tg of PS/vinyl acetate-butyl acrylate copolymer latex films as a function of annealing time were examined with modulated-temperature DSC. The mean free volume and relative concentration of holes at room temperature as a function of time were obtained using positron annihilation lifetime spectroscopy. The effect of residual water in the structured latex films on thermal properties is discussed. 33 refs. 

From the electron micrographs, assuming that PVAc particles in the latex are the same size, the formation model of the porous film from the latex film can be illustrated as in Fig. 3 [19]. When the latex forms a dried film over minimum film-forming temperature, it is concluded that PVA coexisted in the latex and is not excluded to the outside of the film during filming, but is kept in spaces produced by the close-packed structure of PVAc particles. 

In the same year, Fulda and Tieke [75] reported on Langmuir films of monodisperse, 0.5-pm spherical polymer particles with hydrophobic polystyrene cores and hydrophilic shells containing polyacrylic acid or polyacrylamide. Measurement of ir-A curves and scanning electron microscopy (SEM) were used to determine the structure of the monolayers. In subsequent work, Fulda et al. [76] studied a variety of particles with different hydrophilic shells for their ability to form Langmuir films. Fulda and Tieke [77] investigated the influence of subphase conditions (pH, ionic strength) on monolayer formation of cationic and anionic particles as well as the structure of films made from bidisperse mixtures of anionic latex particles. 

These ortho-linked compounds have also shown considerable promise in emulsion and solution SBR and are particularly valuable in carboxyl-ated SBR latex films combining good activity with excellent color—i.e., no pinking. The results of resinification tests on films laid from cafboxyl-ated SBR latex shown in Table VI demonstrate that the polycyclic nature of these compounds contributes significantly to their stabilizing activity, monocyclic compounds of similar structure being markedly poorer in activity. 

Nikolov, A.D. et al.. Ordered structures in thinning micellar foam and latex films, in Ordering and Organisation in Ionic Solutions, Ise, N. and Sogami, I., Eds., World Scientific, Singapore, 1988. 

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. 

Reduction of the vapor transmittance of latex films as a result of vibrowave influences on the latex, measured by diffusion method, also confirms the change of a film structure under the influence of nonlinear vibrations [8], It is necessary to emphasize, that the influence of vibrowave treatment observed already at a stage of synthesis of polymers [14] is efficient at the subsequent stages of formation of a complex of properties of polymeric composite materials. 

Ihe effect of composition drift and the resulting particle stmeture was studied by Zosel et al. [194]. They used dynamic medianical testing to study the properties of latex films and tensile bars. In a comparison of the mamic mechanic propoties of films of solution-polymmzed copolymers of BA and acrylic acid (AA), of bloids of a PBA latex and PAA homopolymer, and of copolymer latexes, they noted a pronounced difleraice in the properties, with those of the emulsion copolymer intermediate to the other products. The structure of the films, as determined 1 TEM, cemfirmed the differmces. The structure of the films and the resulting properties of various mulsion copolymer systems could be traced back to mtXKMner reactivity and water solubility, but also to process mode and ccHiditions. 

As noted in Section 6.5.2, the hydrolysis resistance of latex films from emulsion polymers prepared from the vinyl acetate (VA) monomer is marginal for ontdoor use. In Europe and recently in the United States, vinyl versatate (II) (Ri = —CH2CH2CH2CH2CH2CH2CH3 and R2 = R3 = —CH3) has been introduced for use along with vinyl acetate for improved outdoor performance of latex coatings. Vinyl versatate is the vinyl ester of versatic acid, a 10-carbon carboxylic acid of the highly branched structure sometimes called neo ... 

International Journal of Adhesion Adhesives 17, No.2, May 1997, p. 169-76 EFFECTS OF FILM STRUCTURE ON MECHANICAL AND ADHESION PROPERTIES OF LATEX FILMS... 

In all of these applications the particles are soft and must be capable of forming a film at temperatures close to room temperature. In addition, they must display favorable interactions with the surface of the substrate on which they are applied. In this respect, a review of recent publications and patents showed that structured latex particles still represent an active area of research, the principal objective being to improve the performances of the coating formulation. Indeed, as will be illustrated below in the case of organic/inorganic colloids, structured latexes represent a possible means to overcome the usual compromises between a good film quality and optimal properties. 

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