Surface coatings durability testing

Once the durability testing of the fuel cells is finalized, the internal components are then characterized. For diffusion layers, some of these characterization techniques include SEM to visualize surface changes, porosimetry measurements to analyze any changes in porosity within the DL and MPL, IGC (inverse gas chromatography) to identify relative humidity effects on the hydrophobic properties of the DLs, contact angle measurements to observe any changes in the hydrophobic/hydrophilic coatings of the DL, etc. [254,255]. 

We speculate that contact of this surface with the atmosphere prior to coating with test polymer or mirror backing paint could be related to mirror durability. Regardless, improved polymer additives and particularly mirror backings must be found before durable polymer/mirror assemblies can be developed. The backings must be flexible, Impermeable and light-stable, and they must not contain solvents that will swell the polymer or disrupt the polymer/mlrror Interface. Thus, these backings may have to be polymer specific. 

The performance and durability of a surface coating will not only depend on the attributes of the coating but will also be determined by the particular chemistry created at the interface. This chapter also reviews how scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and antimicrobial testing (growth inhibition and kill rate) can provide practical information about the effectiveness of a surface treatment applied to biotextiles or antimicrobial textiles. As the demand for such bioactive products increases, such tests help to ensure that products meet essential safety criteria and achieve an appropriate level of performance and durability. 

Zhang et al. [58] developed superhydrophobic aluminum alloys by one-step spray coating of an alcohol solution consisting of hydrophobic silica nanoparticles (15-40 nm) and methyl silicate precursor on etched aluminum alloy with pitted morphology. The as-sprayed metal surface showed APCA of 155° and ROA of 4°. In their study they used many different mechanical durability tests that we will describe in the next section and... 

EMMA devices are successfully used by many manufacturers, particularly in the surface-coating industry, who wish to evaluate rapidly the durability of their products outdoors. However, these devices are also used in the study of accelerated weathering of almost all polymeric materials and plastics. One of the largest testing stations in the world is Heraeus DSET Laboratory Inc. (45601N, 47 Ave., Phoenix, AZ 85027-7042, USA) it employs hundreds of EMMA and EMMAQUA devices. 

Table 1 Surface energies (by the Owens-Wendt method) of two different SIGRACET gas diffusion layer (GDL) types before and after accelerated durability testing (different catalyst-coated membranes were used in the cells)...

It is evident in Figures 30.18 and 30.19 that, after the accelerated adhesion test, the primer-coated air LPCAT treated TPOs showed poor adhesion performance as compared to argon and methane LPCAT-treated TPOs. This is a clear indication that air-plasma treatment can achieve the paintable surface but cannot provide the treated surface that can be painted in a durable manner. The poor durability can be attributed to (1) the water-sensitive nature of adhesion and (2) the excessive degradation of polypropylene that causes weaker boundary layer. 

The use of XPS for the assessment of the UV durability of polymeric coatings has met with little success, the reason for this is, ironically, associated with the sensitivity of the XPS technique. XPS is surface sensitive, and the rate of detection of photoelectrons emitted from a depth of greater than 5 nm into the polymer material is too low to give a useful signal. This causes a problem with the reproducibility of the test conditions, as the slightest loss of degradation products from the surface can be detected and this makes the job of obtaining reproducible quantita-... 

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