Polytetrafluoroethylene, adsorption

Dekker A, Reitsma K, Beugeling T, Bant]es A, Fei]en J and van Aken W G 1991 Adhesion of endothelial-oells and adsorption of serum-proteins on gas plasma-treated polytetrafluoroethylene S/omaferfa/s 12 130-8... 

Some authors have suggested the use of fluorene polymers for this kind of chromatography. Fluorinated polymers have attracted attention due to their unique adsorption properties. Polytetrafluoroethylene (PTFE) is antiadhesive, thus adsorption of hydrophobic as well as hydrophilic molecules is low. Such adsorbents possess extremely low adsorption activity and nonspecific sorption towards many compounds [109 111]. Fluorene polymers as sorbents were first suggested by Hjerten [112] in 1978 and were tested by desalting and concentration of tRN A [113]. Recently Williams et al. [114] presented a new fluorocarbon sorbent (Poly F Column, Du Pont, USA) for reversed-phase HPLC of peptides and proteins. The sorbent has 20 pm in diameter particles (pore size 30 nm, specific surface area 5 m2/g) and withstands pressure of eluent up to 135 bar. There is no limitation of pH range, however, low specific area and capacity (1.1 mg tRNA/g) and relatively low limits of working pressure do not allow the use of this sorbent for preparative chromatography. 

In starting a residue analysis in foods, the choice of proper vials for sample preparation is very important. Available vials are made of either glass or polymeric materials such as polyethylene, polypropylene, or polytetrafluoroethylene. The choice of the proper material depends strongly on the physicochemical properties of the analyte. For a number of compounds that have the tendency to irreversible adsorption onto glass surfaces, the polymer-based vials are obviously the best choice. However, the surface of the polymer-based vials may contain phthalates or plasticizers that can dissolve in certain solvents and may interfere with the identification of analytes. When using dichloromethane, for example, phthalates may be the reason for the appearance of a series of unexpected peaks in the mass spectra of the samples. Plasticizers, on the other hand, fluoresce and may interfere with the detection of fluorescence analytes. Thus, for handling of troublesome analytes, use of vials made of polytetrafluoroethylene is recommended. This material does not contain any plasticizers or organic acids, can withstand temperatures up to 500 K, and lacks active sites that could adsorb polar compounds on its surface. 

The parfait-distillation method uses a sequential series of adsorbents to remove contaminants from water and vacuum distillation to recover unadsorbed materials. This method recovers a wide range of neutral, cationic, anionic, and hydrophobic contaminants. The first adsorbent, porous polytetrafluoroethylene (PTFE), removed humic acid and a broad range of hydrophobic compounds. PTFE was followed by Dowex MSC-1 and then Duolite A-162 ion-exchange resins. A synthetic hard water spiked parts-per-billion concentrations with 20 model compounds was used to evaluate the method. Poorly volatile, neutral, water-soluble species (glucose) cationic aromatics and most hydro-phobic compounds were recovered quantitatively. Model ampho-terics were removed from the influent but were not recovered from the adsorption beds. The recovery of model acids and bases ranged from 22% to 70% of the amount applied. 

There are various kinds of polytetrafluoroethylene. One is granular polymer consisting of spongy, white particles having a median size of about 600/l The specific surface of this polymer is on the order of 2 m2/g (determined by nitrogen adsorption and calculations by the method of Brunauer, Emmett, and Teller). Since this specific surface area is about 1700 times the observed outer surface of the particles, these measurements confirm the porous, spongelike structure that can be seen in the photomicrograph of a cross section of several particles in Fig. la. 

Ottewill and Ranee (29) using well-dialysed PTFE latices obtained the results shown in Figure 6. The change in c.c.c. with pH is clearly defined but the c.c.c. above pH 5 is at a fairly high concentration of electrolyte and insufficient positive charge is built up to stabilise the dispersion. It is also possible with this system that the very hydrophobic polytetrafluoroethylene parts of the surface do not adsorb the hydrolysed species and in the well-dialysed system adsorption can only occur on the sparse charged sites. 

In developing a method that requires filtration, adsorption of the analyte onto the filter must be taken into account. For dilute solutions of adriamycin, >95% is adsorbed to cellulose ester membranes and about 40% to polytetrafluoroethylene membranes [19]. For more concentrated solutions, as would be encountered in bulk formulation testing, filter ad-... 

FIG. 2 Bovine serum albumin adsorption to different polymer surfaces at 37°C in phosphate-buffered solution. The initial albumin concentration is 3 mg/ml. PVA poly(vinyl alcohol), PMMA poly(methyl methacrylate), PET polyethylene therephthalate), PP polypropylene, HDPE high-density polyethylene, PTFE polytetrafluoroethylene. (From Ref. 1.)... 

As discussed above for simple adsorption, polymer sorption can be treated in both thermodynamic and kinetic contexts. The quantity of an analyte that is sorbed by a polymer at equilibrium is referred to as the solubility of the analyte, while the rate at which the analyte is transported through the polymer is referred to as permeability. Although high solubility is generally a prerequisite for high permeability (on any reasonable time scale), there are some notable exceptions. Poly-siloxanes and polytetrafluoroethylene (Teflon ), for example, are quite permeable to water, but the solubility of water is not particularly large in either material. 

In dishwashing, one must consider soil and surfactant adsorption to both polar and nonpolar surfaces. Metals (aluminum, stainless steel, carbon steel, cast iron, silver, and tin), siliceous surfaces (china, glass, and pottery), and organics (polyethylene, polypropylene, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), and wood) present a wide variety of surface characteristics. They span the range of high interfacial free energy (metals and many ceramics) to low interfacial free energy (hydrocarbon polymers) surfaces [27,28],... 

The various results quoted do not provide conclusive evidence as to the magnitudes of film pressures of highuciling liquids on low energy solids such as polyethylene and polytetrafluoroethylene. On the other hand, film pressures of the order of 10 dynes per cm., as obtained by use of the Bartell-Osterhof relation, do not seem unreasonable. Other adsorption studies in which film pressures have been reported and which support the arguments just presented are those of Harkins and coworkers [12,45,51]. 

Despite the excellent chemical and thermal stahihty of hydrophobic polymers (e.g., polytetrafluoroethylene (PTFE) and polyvinylfluoridine (PVDF) membranes are used in UF and MF of organic solutions), stable hydrophihc polymers are more effective as membrane materials because of their reduced adsorption tendencies. In general. 

AAS, atomic absorption spectrometry AdSV, adsorptive stripping voltammetry Amp, amperometric GC, gas chromatography LC, liquid chromatography MEKC, micellar electrokinetic chromatography PAR, 4-(2 -pyridylazo)-resorcinol phot, photometric PTFE, polytetrafluoroethylene PVDF, polyvinylidenedifluoride. 

DLC Supra 30, further named AC) and of electrodes with 80% AC, 10% conductivity additive and 10% polyvinylidene difluoride (PVdF) or polytetrafluoroethylene (PTFE) as binder, the porosity drops due to the binder implementation into the electrodes. The SSA is less reduced for electrodes incorporating PTFE (11% loss), as compared to PVdF containing electrodes, where a 25% decrease is observed. The PSD curve (Figure 8.6b) demonstrates that all pores are significantly blocked when PVdF is used this is especially emphasized for the micropores responsible of the adsorption of ions and charge accumulation in the EDL. The cumulative volume of pores <1 nm is 0.32 and 0.28 cm for electrodes with PTFE and PVdF... 

This book presents coverage of the dynamics, preparation, application and physico-chemical properties of polymer solutions and colloids. It also covers the adsorption characteristics at and the adhesion properties of polymer surfaces. It is written by 23 contemporary experts within their field. Main headings include Structural ordering in polymer solutions Influence of surface Structure on polymer surface behaviour Advances in preparations and appUcations of polymeric microspheres Latex particle heterogeneity origins, detection, and consequences Electrokinetic behaviour of polymer colloids Interaction of polymer latices with other inorganic colloids Thermodynamic and kinetic aspects of bridging flocculation Metal complexation in polymer systems Adsorption of quaternary ammonium compounds art polymer surfaces Adsorption onto polytetrafluoroethylene from aqueous solutions Adsorption from polymer mixtures at the interface with solids Polymer adsorption at oxide surface Preparation of oxide-coated cellulose fibre The evaluation of acid-base properties of polymer surfaces by wettability measurements. Each chapter is well referenced. 

Adsorption phenomena may also play an important role in fouling and hence it is important to the select an appropriate membrane material. Hydrophobic materials of the type mentioned above have a larger tendency to foul in general, especially in the case of proteins. Furthermore, such hydrophobic materials (e.g. polytetrafluoroethylene) are not wetted by water and no water will flow through the membrane at normal applied pressures. This non-wettability is another disadvantage and such membranes have to be pretreat, for example with alcohol, prior to use with aqueous solutions. 

---