Poly(butyl methacrylate) (PBMA) latex labeled with either phenanthrene or anthracene derivatives in low concentrations (1 or 2 mol %) was prepared by semicontinuous emulsion polymerization.The latex film formation process was studied by analysis of the nonradiative energy transfer from phenanthrene (donor) to anthracene (acceptor). Initially, when the latex film dries, there is little energy transfer, indicating that the particles conserve their individual identity. With increasing time at temperatures above the glass transition temperature of PBMA, the extent of energy transfer increases. This is a clear indication that interdiffusion of polymer chains across particle boundaries occurs. The diffusion coefficient D of the polymer was evaluated by using models based upon Pick's second law. In each sample, the magnitude of D decreases with time. Initial D values increase with increasing temperature, taking values between 1 X 10"14 to 1 X 10"18 cm2/s, yielding an apparent activation energy of 38 kcal/mol. The diffusion data also fit well to the Williams-Landel-Ferry equation. The results demonstrate the great potential of fluorescence techniques in the study of polymer diffusion processes during latex film formation.
Micelle formation in tetrahydrofuran-methanol, 1,2-dichloroethane-methanol, tetrahydrofuranwater, and water solutions by PS-PEO diblock copolymers was studied by the fluorescence spectroscopy. For this purpose, a series of PS-PEO copolymers was labeled by the phenanthrene or anthracene groups at the block junctions. The chromophore contents in copolymers were determined by the absorbance spectroscopy using suitable model compounds. When micelles were present, intramicellar nonradiative energy transfer could be observed. For the PS-PEO copolymer (M" = 114 000,93 weight % PEO) we find the onset of micelle formation in water in the range of 10 X 10-3 g/L (9 X -8 M).
The surface of isotactic polypropylene (iPP) films
modified by oxyfluorination was studied
by a combination of complementary techniques to elucidate the effect of
the modification on the chemical
composition, surface energy, and morphology. The elemental
composition was measured by X-ray
photoelectron spectroscopy (XPS), and the surface free energy was
characterized by contact angle
measurements with different liquids. Following the approach by
Good and co-workers, the acid−base
characteristics of the modified polymer surfaces were estimated.
Subsequently, the modified iPP films
were investigated by scanning force microscopy (SFM). In tapping
mode SFM, the sample topography
was imaged and the surface roughness was quantitatively determined.
Gold-covered SFM probes modified
with carboxylic acid and methyl terminated self-assembled monolayers of
thiols were used to determine
the pull-off force distributions in ethanol. The interaction of
the treated polymer film surfaces with
chemically functionalized SFM tips was shown to correlate with the
surface tensions obtained by contact
angle measurements. In particular, pull-off forces measured with
carboxylic acid functionalized tips in
ethanol depended approximately linearly on the basic part of the
surface free energy of the polymer film
surface.
The lateral distribution of functional groups at polymer surfaces was studied with high resolution using atomic force microscopy with chemically modified tips ("chemical force microscopy"). Pull-off force measurements carried out on oxyfluorinated films of isotactic polypropylene as a function of pH using OH-functionalized tips revealed a "force pK a" of 5.5-6.0. At pH values close to or slightly higher than the "force pKa", position-resolved maps of pull-off forces showed laterally inhomogeneous adhesive forces on a sub-50 nm scale. These variations, which can be related to variations of local pKa values, are attributed to locally different hydrophobicity and thus to inhomogeneous distribution of the functional groups introduced by the surface treatment.
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