Latex films, polarity

An average of eight measurements was taken as the contact angle. Water and methylene iodide were used as test liquids. Polarity of the dried latex films were estimated according to the method of Kaelble (10). 

Polarity of Vinyl Acrylic Latex and Surfactant Adsorption Contact angle measurements, dispersion and polar contribution to latex film surface tension and polarity of polymer calculated according to the method of Kaelble (10) of the three latex films are whown in Table V. It is seen that the polarity of the latex film decreases with increase in butyl acrylate content of the vinyl acrylic co-polymer. The polarity of the 70/30 (VA/BA) latex is very similar to that of the polybutyl acrylate homopolymer estimated to be about 0.21 (1). ... 

The polarity and adsorption data discussed above reveal some interesting aspects of the surface chemistry of vinyl acrylic latex surfaces. It is quite likely that the polarity of the latex films, expecially of the two co-polymers, determined by contact angle measurements may not correspond exactly with their respective latex surfaces in the dispersed state due to reorientation of polymer chains during film formation. But the surfactant adsorption data shows clearly that the three latex surfaces in their dispersed state do exhibit varying polarity paralleling the trend found from contact angle measurements. The result also shows that the surface of the co-polymer latex surface is a mixture of vinyl acetate and acrylate units. This result is somewhat unexpected in a vinyl acrylic latex, prepared by a batch... 

In these studies, the stronger and more compact structure of the latex films was attributed to intermolecular interactions between the polar functional groups. This conclusion implies that the polar groups were oriented at the polymer/water interface of the latex particles but were randomly distributed in the solution polymers. 

One feature which distinguishes latex film formation from other polymer sintering processes is that latex microspheres have polar groups at the particle surface. These groups are introduced during the emulsion polymerization process used to prepare the particles, and they serve to provide colloidal stability for the particle dispersion. When the dispersion... 

The second important observation for the data in Figure 1 is that interdiffusion occurs even at the early stages of annealing time, in the all films. This result is very different from that reported by Joanicot et al. b for a different latex film. They found that polyacrylic acid [PAA] at the surface of a poly(styrene-co-butyl acrylate) latex effectively suppressed interdiffusion until the film temperature exceeded the Tg of the PAA, at which point the polar membranes ruptured. The essential difference in... 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

The parameters K1/ K2/ and K3 are defined by the refractive indices of the crystal and sample and by the incidence angle [32]. If the sample has uniaxial symmetry, only two polarized spectra are necessary to characterize the orientation. If the optical axis is along the plane of the sample, such as for stretched polymer films, only the two s-polarized spectra are needed to determine kz and kx. These are then used to calculate a dichroic ratio or a P2) value with Equation (25) (replacing absorbance with absorption index). In contrast, a uniaxial sample with its optical axis perpendicular to the crystal surface requires the acquisition of spectra with both p- and s-polarizations, but the Z- and X-axes are now equivalent. This approach was used, through dichroic ratio measurements, to monitor the orientation of polymer chains at various depths during the drying of latex [33]. This type of symmetry is often encountered in non-polymeric samples, for instance, in ultrathin films of lipids or self-assembled monolayers. 

We were able to reveal the structure of latex particles and films of polar polymers (acrylate latexes) using a special technique for preparing samples... 

A number of issues and challenges will be of particular interest in the future. Up to now, little data is available regarding latex properties, such as stability and film formation, and on the properties of the resulting films (such as adhesion to substrates of varying polarity). In aqueous olefin polymerizations, these properties... 

Fig. 4 A Schematic cross section of metal film growth and corresponding scanning electron micrographs (below) of the gold nanocavities fabricated with a = 350 nm latex spheres of thickness t for (a) ajl, (b) a, and (c) 2.1a [91]. B Measured energy dispersion of the reflectivity for TM polarized light as a function of the in-plane wave vector for increasing relative void depth, i=t/(2a) (a-c). Log color scale white dotted lines show a zone-folded plasmon dispersion, sample orientations of 4> = 30° in all cases, (i-iv) k space cuts through dispersion relation at (i) (i,E) = (0.25,2.2 eV) (ii) (i,E) = (0.4,2.2 eV) (in) (i,E) = (0.4,1.7 eV) (iv) (f, ) = (0.6,2.2 eV), symmetry shown above (i). Light shade corresponds to absorption features [93]...

One of the most important bulk property variables of polymers is the glass transition temperature 7g, which must be well below the use temperature to allow the interdiffusion and entanglement of polymer chains when the particles get in contact, once the aqueous phase has been evaporated. Thus, the monomer(s) used have to be selected such that the desired is obtained. Useful tables showing Tg and other physical and chemical properties of homopolymers are available in the literature [66-68]. The well-known Fox equation [69] can be used to estimate the Tg of a copolymer as a function of monomer composition and TgS of the component monomers. It is important to take into account that polar polymers tend to hydroplasticize, reducing the in the film formation process [70]. Several commercial latexes are terpolymers that contain two of the monomers present in major amounts to grossly obtain the basic desired properties, with the third monomer present in a minor amount for fine tuning of a special property [71-73]. 

The suggestion of this model, that the last stages of drying involve diffusion of water through a continuous polymer layer, may be correct only under certain circumstances. For example, there is some evidence that near the end of the drying process the rate of water loss is consistent with Fickian diffusion of water through the solid polymer [9]. On the other hand, when the latex has sufficient polar material in its shell that it forms a continuous membrane in the film as it dries, water loss through the membrane may predominate. 

Latex (emulsion) adhesives. In contact with water, adhesive bonds with latex adhesives may release surfactants, which will have the effect of lowering surface tension and changing the thermodynamic work of adhesion. Some latices based on copolymers of vinyl acetate were dried to give films which were then immersed in small quantities of water. The surface tensions (/w) fell from 72.8 mN m to values in the range 39-53 mN m in the first hour and then remained fairly static [76]. Measurements of interfacial tensions against n-hexadecane showed the dispersion components of surface tension remained essentially constant but polar components were reduced into the range 6-20 mN m ... 

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