Polymer surfaces, methods

Madey and co-workers followed the reduction of titanium with XPS during the deposition of metal overlayers on TiOi [87]. This shows the reduction of surface TiOj molecules on adsorption of reactive metals. Film growth is readily monitored by the disappearance of the XPS signal from the underlying surface [88, 89]. This approach can be applied to polymer surfaces [90] and to determine the thickness of polymer layers on metals [91]. Because it is often used for chemical analysis, the method is sometimes referred to as electron spectroscopy for chemical analysis (ESCA). Since x-rays are very penetrating, a grazing incidence angle is often used to emphasize the contribution from the surface atoms. 

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

Among the techniques mentioned previously, XPS has the greatest impact on polymer surface analysis. A major additional source of chemical information from polymers comes from IR and Raman spectroscopy methods, These vibrational data can be obtained from the bulk and the surface region, although the information depth is much greater than with AES, XPS, or ISS. 

A very simple, though indirect, method of surface analysis is the measurement of the angle of contact that a liquid makes with the solid surface being analyzed. This method has been widely used to study changes introduced in a polymer surface by various treatments. 

Being sensitive to the chemical composition of the outermost layers of the surface, contact angle measurement is widely used for characterizing polymer surfaces. Surface characterization for polymers using contact angle measurement and XPS will now be described in detail, as these are the most widely used methods. 

A variety of other techniques have been used to investigate ion transport in conducting polymers. The concentrations of ions in the polymer or the solution phase have been monitored by a variety of in situ and ex situ techniques,8 such as radiotracer studies,188 X-ray photoelectron spectroscopy (XPS),189 potentiometry,154 and Rutherford backscatter-ing.190 The probe-beam deflection method, in which changes in the density of the solution close to the polymer surface are monitored, provides valuable data on transient ion transport.191 Rotating-disk voltammetry, using an electroactive probe ion, provides very direct and reliable data, but its utility is very limited.156,19 193 Scanning electrochemical microscopy has also been used.194... 

Covalent binding of peptides to polymer surfaces is now a standard method to improve their biocompatibility. The primary amino acid sequence of a peptide can be chosen to mimic the putative... 

The deposition-reduction (DR) method is based on the weak electrostatic interactions of polymer surfaces with the oppositely charged Au(III) complex ions, leading to the reduction of Au(III) exclusively on the polymer surfaces. Appropriate anionic or cationic Au(III) precursors are chosen based on the zeta potentials of polymer supports (Figure 3.6) [43]. 

HPLC methods of determining the amounts of different additives in polymeric materials are preceded by an extraction process or dissolution of the polymer matrix. Although extraction-HPLC is often observed to be superior to the traditional spectroscopic techniques (UV and IR) in analysing additives, it is frequently difficult to obtain reproducible results in view of the variability of the extraction yield. On the other hand, it is equally difficult to obtain quantitative data in the dissolution/reprecipitation-HPLC method because of entrapment of analytes in the polymer precipitate and the potential for high absorption of the additives on the polymer surface. 

UV light in a second step. In later work reported by Tazuke, Kimura et al. (6-8) successful photograftings on the polymer surface of thin films (polyethylene, polypropylene and polystyrene) were achieved with various monomers. In this work, grafting was induced by UV irradiation through the film which was in contact with a solution containing initiator and monomer. The method is slow and - in addition to surface grafting - large amounts of homopolymer are formed. 

Photoinduced free radical graft copolymerization onto a polymer surface can be accomplished by several different techniques. The simplest method is to expose the polymer surface (P-RH) to UV light in the presence of a vinyl monomer (M). Alkyl radicals formed, e.g. due to main chain scission or other reactions at the polymer surface can then initiate graft polymerization by addition of monomer (Scheme 1). Homopolymer is also initiated (HRM-). 

Two methods for modification of polymer surfaces by photoinitiated graft copolymerization have been developed a discontinuous method (1) with vapor phase transfer of initiator and monomer and a continuous method (2) with presoaking of a film strip or a fiber bundle in a solution of initiator and monomer. Both methods have been applied to polyelefins and linear polyester. 

Methods currently used for the hydrophilization of polymer surfaces include chemical modification (8), plasma modification (9),... 

The permeation technique is another commonly employed method for determining the mutual diffusion coefficient of a polymer-penetrant system. This technique involves a diffusion apparatus with the polymer membrane placed between two chambers. At time zero, the reservoir chamber is filled with the penetrant at a constant activity while the receptor chamber is maintained at zero activity. Therefore, the upstream surface of the polymer membrane is maintained at a concentration of c f. It is noted that c f is the concentration within the polymer surface layer, and this concentration can be related to the bulk concentration or vapor pressure through a partition coefficient or solubility constant. The amount... 

To investigate heparin release in response to an electric current, the swollen heparin-polymer matrix was attached to a woven platinum cathode in a continuously stirred PBS solution (pH 7.4), and an electric current of 20 mA was applied. When the electric current was on, the polymer surface facing the cathode dissolved, thereby releasing heparin. The amount of heparin released was assayed by the Azure II method at pH 11 to prevent complexation of the two dissolved polymers. The release pattern of heparin showed a complete on-off profile in response to the applied electric field, as shown in Figure 23 [50],... 

We employ two basic approaches to rate a polymer s wear resistance. In the first, we expose a polymer surface to a standard set of abrasive or erosive conditions and examine the surface for visual evidence of wear. We primarily use this method to qualitatively rank materials. In the second approach, we expose samples to wear inducing conditions and determine wear resistance in terms of weight loss as a function of time. 

Today, controlled polymer surface direct fluorination is used in a number of specific applications. According to Annand22 there are primarily two different methods by which elemental fluorine can be applied to the surfaces of polymeric materials ... 

Minko, S., Grafting on Solid Surfaces Grafting to and Grafting from Methods, in Polymer Surfaces and Interfaces, M. Stamm, Editor. 2008, Springer Berlin Heidelberg, p. 215-234. 

Aside from the use of polymers as supports for phase transfer catalyst centers, much excellent work has been reported on the use of PTC in polymer chemistry for pol)rmerization methods (28), for the chemical modification of already formed polymers(29). for the modification of polymer surfaces without change of the bulk polvmerOO). and for the preparation and purification of monomers(31). 

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