Non-porous Surfaces

Figure 6.8 The generalised effect of molecular weight and cationicity on adsorption of cationic polyelectrolytes on non-porous surfaces.

Until now we have mainly treated adsorption onto non-porous surfaces. In reality, most industrial and many natural materials are porous Textiles, paper, bricks, sand, porous rocks, food products, zeolites etc. We start our discussion with a classification of pores according to their size, which is recommended by IUPAC ... 

Figure 7.42 Types of gas sorption isotherm - microporous solids are characterised by a type I isotherm. Type II corresponds to macroporous materials with point B being the point at which monolayer coverage is complete. Type III is similar to type II but with adsorbate-adsorbate interactions playing an important role. Type IV corresponds to mesoporous industrial materials with the hysteresis arising from capillary condensation. The limiting adsorption at high P/P0 is a characteristic feature. Type V is uncommon. It is related to type III with weak adsorbent-adsorbate interactions. Type VI represents multilayer adsorption onto a uniform, non-porous surface with each step size representing the layer capacity (reproduced by permission of IUPAC).

In 40 CRF Section 761 Subpart O, the TSCA specifically addresses the requirements for verification of self-implementing cleanup by defining the numbers and locations of samples to be collected from bulk PCB remediation waste and porous surfaces. Section 761 Subpart P specifies the requirements for non-porous surfaces cleanup verification. These regulation-prescribed sampling designs are discussed in detail in Chapter 3.5.2. 

We use wipe sampling to detect contaminants on non-porous surfaces, such as the surfaces of plastic or metal drums transformer casings various heavy equipment walls floors ceilings laboratory benches. Sampling with wipes allows transferring contaminants from a surface area of a known size onto the wipe material. The wipes are then analyzed, and the amounts of contaminants found on the wipe are related to the surface area. 

Cleanup Level for Non-Porous Surfaces in Contact with Liquid PCBs ... 

Current research involves the use of radioimmunoassay to quantitate testosterone and estrogen in dried blood samples (22, 24). The ultimate goal of this research will be to determine the sexual origin of the stains. In the past, researchers have attempted this by identifying Barr bodies and Y chromosomes using differential fluorescence staining with quinacine however, these tests required a substantial amount of blood deposited as a thin film on a non-porous surface and are therefore limited in their application (19, 20, 21). The sensitivity and basic technique of radioimmunoassay will permit the analysis of bloodstains on virtually any surface and should also be applicable to very small ones. 

Alon (nonporous) surface area 100 m2/g Si02, Cab-o-Sil (non-porous) surface area 200 m2/g Si02 Al2C>3, W. R. Grace grade 160 % AI2O3 = 13, surface area 425 m2/g. The oxide was either used directly as supplied or activated by heating in vacuo to 400°C for 4 hours. 

The physisorption isotherm on a mesoporous or macroporous adsorbent follows the same monolayer-multilayer path as on the corresponding non-porous surface until the secondary process of capillary condensation occurs. In the case of a macro-porous solid, the deviation from the standard monolayer-multilayer isotherm does not take place until very high relative pressures are attained (with nitrogen adsorption at 77 K, this would be at p)p° > 0.99). 

The deviations from linearity shown by the as-plots on gels B and C in Figure 10.11 confirm the respective mesoporous and microporous nature of these silica gels. Thus, the as-plot on gel B is linear up to pjp° = 0.4 (i.e. as = 1). This indicates that the argon monolayer has formed on the mesopore surface in the same manner as on the non-porous surface. The upward deviation is clearly due to the onset of capillary condensation. 

The onset of capillary condensation is indicated by an upward departure of the isotherm from the standard curve determined on the same area of a non-porous surface of similar composition. The mesopore capacity is the amount adsorbed at the plateau of the Type IV isotherm to obtain the mesopore volume, it is assumed that the condensate has the same density as the liquid adsorptive at the operational temperature. 

Approach I Reactants in two adjacent colors This approach is aimed at eliminating intercolor bleeding phenomenon which takes place at the border of two adjacent colors when printed on a non-porous surface. Interaction between reactants which are present in two adjacent colors will cause either a viscosity increase in the ink ("jellation") or fixing of the colorants present in the droplet by converting them to insoluble compounds. The methods taken in this approach are summarized in Table 3. 

This lack of micropores is further confirmed by SAXS and nitrogen adsorption data. Again a very helpful concept is fractality, in this case the surface fractal dimension D. A smooth, non-porous surface is described by a surface fractal dimension of = 2.0, but a totally porous body will reach a of up to nearly 3. SAXS and adsorption measurements on fumed silica result in a surface fractal dimension very close to 2.0 [6j. The fact of a nonporous smooth surface of the fumed silica particles is a most... 

The stepwise isotherms of type VI are only observed under a number of idealized conditions for uniform non-porous surfaces. Ideally, the step-height represents monolayer capacity In the simplest case, it remains constant for two or three layers. Argon or krypton adsorption on graphltized carbon blacks at liquid nitrogen temperature are amongst the best examples. 

Values of t are obtained from adsorption data of the same adsorptive on a non-porous surface of the same nature, as in fig. 1.28. Substituting bulk values for y and, the pore size distribution a(p) or d(p) is obtainable. The occurrence of hysteresis implies that this gives different results for the two branches (ascending and descending) of the curve. In fact, the difference between the two metastable states is a characteristic of the type of pores. For non-connected pores, usually the downward curve is analyzed, because then the menisci have already been formed but for connected networks the ascending one may be more appropriate. After each stepwise change of p, the radius is calculated and from that the exposed pore volume and pore area. This yields a cumulative distribution which, if so desired, can be differentiated. 

Mechanical adhesion, as the title implies, is achieved by the open or porous nature of the substrate(s), whereby the adhesive penetrates into the cracks, crevices or gaps in the surface(s) involved. Specific or chemical adhesion involves the bonding of nonabsorbent or non-porous surfaces such as found with glass, metals, including foil, and plastics. The bond achieved between these materials and the adhesive depends on molecular or electrical forces based on van der Waals forces. Polar and non-polar materials need to bond with like adhesives. 

ISO 22196 2011P Measurement of the Antibacterial Activity of Plastic and other Non-porous Surfaces. 

PCB-Contaminated is any non-Uquid material containing PCBs at concentrations >50 ppm but <500 ppm a Uquid material containing PCBs at concentrations > 50 ppm but <500 ppm or where insufficient liquid material is available for analysis, a non-porous surface having a surface concentration of >10 micrograms/100 cm but <100 micrograms/100 cm. The term PCB-Contaminated Electrical Equipment is defined in a similar fashion. 

The cleanup levels applicable in a self-implemented cleanup depend upon the category of remediation waste, i.e., bulk PCB remediation waste, non-porous surfaces, porous surfaces, and liquids, whether the location of the waste is a high occupancy area or low occupancy area, and whether an engineered control, such as a cap, is installed. For bulk remediation materials, such as soils and sediments, EPA allows self-implementing cleanup levels of 1 ppm in high occupancy areas and 25 ppm in low occupancy areas. ... 

Violations involving PCB disposal are treated as more serious, and the penalties are based on the cost of cleanup and proper disposal of the PCBs. The extent of violations are minor if they involve disposal of less than 25 kilograms or 5 gallons of PCBs or less than 625 square feet of a non-porous surface, 60 square feet of soil, 20 square feet of a porous surface, or 60 cubic feet of other materials. The extent is significant if the quantities exceed the minor category but are less than 125 kilograms or 25 gallons of PCBs or less than 3125 square feet of a non-porous surface, 300 square feet of soil,... 

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