This study illustrates the capabilities of a nanoindentation/nanoscratch tester to assess mechanical and tribological properties of coating films. Properties such as hardness, elastic modulus, mar and scratch resistance, and critical force for cracking can be accurately measured. Operation of the Nano-Indenter is described in detail. A scanning probe microscope (SPM) is shown to be a valuable supplement to the Nano-Indenter. Well-characterized thermoset acrylic clearcoats and thermoplastic latex films were studied. For the first time, operating parameters are described for measurement of relatively soft coatings, such as films cast from a latex with a glass transition temperature (T g ) of 8°C. Thus, the method is made available for study of most types of coatings. The method can easily discriminate between coatings with different T g s and crosslink densities. Once operating parameters are established, it takes about 10 minutes for an indentation test and 10 minutes for a scratch test with the Nano-Indenter, and with further automation this time could be reduced. Each indentation test accurately measures hardness and elastic modulus as a function of depth within the coating, and each scratch test provides additional insight into the material's behavior. The method is sensitive to small changes in polymer composition and formulation, and results are highly reproducible.
Latexes have many product applications including functioning as a binder in coatings. For many years, coatings researchers in industry as well as in academe have been exploring various modes of crosslinking latexes. Quite often, the goal of preparing crosslinked latexes is to upgrade film properties relative to the film properties of uncrosslinked latexes. In the present report, the synthesis and properties of crosslinkable acrylic latexes prepared with either an internal crosslinker (1,3-butylene glycol dimethacrylate)-''precoalescence crosslinking''-or an external crosslinker (adipic dihydrazide)-''postcoalescence crosslinking''-at various levels of crosslinking were studied. For postcoalescence crosslinking, diacetone acrylamide was copolymerized into the latex to provide sites for subsequent reaction with adipic dihydrazide. Fundamental properties of films cast from the two types of latexes were systematically compared. These properties included gel content, dynamic mechanical properties, nano-indenter hardness and modulus, stress-strain properties as well as the characterization of latex morphology by atomic force microscopy (AFM). In addition, some specific end-use properties were determined. This study assesses the effect of type (precoalescence or postcoalescence) and level of crosslinking on the film formation process and the resulting fundamental and end-use properties as well as resulting latex film morphology.
A much studied oil-soluble surfactant, bis[2-ethylhexyl]sulfosuccinate, sodium salt, was ion exchanged into the silver ion form and dissolved into microemulsions of immiscible polyurethane step monomers. Coating and curing of these microemulsions produced polyurethane coatings that exhibit bactericidal activity against representative Gram negative bacteria. After 24 h exposure, 0.006-0.012% weight Ag relative to coating weight (0.0013-0.0025 micromol Ag/cm2) results in the three-log reduction in Escherichia coli. A slightly higher level of 0.031% weight Ag relative to coating weight (0.006 micromol Ag/cm2) killed all of the E. coli after 12 h exposure. Similar results were obtained for Pseudomonas aeruginosa. Since the double-tail surfactant anion promotes reverse micelle formation in many different kinds of oils and solvents, it appears an excellent vector for incorporating low and effective amounts of silver ion into many industrial, hospital, and household coating formulations.
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