Polymer modification treatments, techniques

Conventional polymers do not always possess the combination of desired bulk and surface properties for a specific application. The polymer materials used for microfluidic devices are innately hydrophobic, low-surface-energy materials and thus do not adhere weU to other materials brought into contact with them. This necessitates their surface modification/treatment to render them adhesive. This has prompted the development of a variety of polymer modification techniques, with the aim of developing new materials from known and commercially available polymers that have desirable bulk properties (elasticity, thermal stability, permeability, etc.) in conjunction with newly tailored surface properties (adhesion, biocompatibUity, optical reflectivity, etc.). 

Physical modification involves thermal treatments such as plasma or nonthermal treatments like application of electric discharge, ultrasound, ultraviolet, or high-frequency cold plasma to the fiber surface. Stmctural and surface properties of the fibers are changed by these treatments, which result in improved mechanical bonding to polymers. These treatments are apphed to separate the fiber bundles into individual filaments and modify the fiber surface for more compatibility with the matrix in the composite [6]. If separation of the fiber bundles is desired, methods like steam explosion and thermomechanical processing are adopted. Methods like plasma (thermal) treatment, dielectric barrier techniques, or corona discharge (nonthermal) treatments (CDT) are anployed to modify the fiber surface. 

Plasma treatment is probably one of the most versatile surface treatment techniques. Regardless of the structure and chemical reactivity of polymers, excited species generated in gas plasma allow the surface modification of any type of polymer. So if one is not aware of which method is the best for modifying a particular... 

The chemical modification techniques refer to the treatments used to modify the chemical compositions of polymer surfaces. Those can also be divided into two categories modification by direct chemical reaction with a given solution (wet treatment) and modification by covalent bonding of suitable macromolecular chains to the polymer surface (grafting). Among these techniques, surface grafting has been widely used to modify the surface of PDMS. 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

The surface analytical techniques mentioned above provide wealth information on the composition and structure of polymer surfaee and changes resulting from modification by plasma discharge. It should be however stressed that, despite of broad spectrum of analytical techniques available, the information is not sufficient to understand all imderlying proeesses in their eomplexity. Espeeially, it is the case of plasma treatment when the interaetions of many plasma eonstituents with polymer surface may play a role. Existing theoretical models are restricted to some specific cases and they usually deseribe only some part of the proeess. 

The change in authors has not altered the basic concept of this 4th edition again we were not aimed at compiling a comprehensive collection of recipes. Instead, we attempted to reach a broader description of the general methods and techniques for the synthesis, modification, and characterization of macromolecules, supplemented by 105 selected and detailed experiments and by sufficient theoretical treatment so that no additional textbook be needed in order to understand the experiments. In addition to the preparative aspects we have also tried to give the reader an impression of the relation of chemical structure and morphology of polymers to their properties, as well as of areas of their appUcation. 

In the following section, a new technique of surface modification of fillers and curing agents will be discussed plasma polymerization. This technique allows for surface coating of powders, whereby the chemical structure of the coating is determined by the monomer used for the process. The morphology of the substrate is preserved, which is an important precondition for filler treatment. The polarity of the functional groups can be chosen to fit the matrix of the polymer wherein it will be applied. 

Flame is probably the oldest plasma known to humanity and flame treatment is one of the oldest methods used by industries for the modification of polymeric surfaces. Flame treatment is very often used to treat bulky objects. It is mainly employed to enhance the ink permeability on the polymer surface. Though a very simple set-up (comprising of a burner and a fuel tank) is required for this technique, a very high degree of craftsmanship is needed to produce consistent results. Oxidation at the polymer surface brought about by the flame treatment can be attributed to the high flame temperature range (1000-1500 °C) and its interaction with many exited species in the flame. For an efficient flame treatment, the variables like air-to-... 

The primary technique for the surface analysis of polymers (3-4), including biomaterials (5-6) over the last decade has been X-ray photoelectron spectroscopy (XPS or GSCA). The technique has been employed to study the interfacial orientation, contamination, modifications, eg plasma treatments (7) and protein deposition on biomedical polymers ( ). While XPS provides valuable multi-element (except hydrogen) and chemical state information, the limited range... 

Since it was observed that fluorine contamination was a possibility and had potentially detrimental effects as described in Chapter 10, the excellent primer adhesion achieved with Tfs/(Ar) and Tcs/(Ar), shown in Table 31.3, has significant importance in the practical application of the plasma technique without any of the potentially deleterious effects of fluorine-based systems. Argon plasma treatments on both flow system TMS (Tfs) and closed system TMS (Tcs) polymers were then investigated as an additional system modification that could provide strong adhesion without the incorporation of fluorine-containing monomers in the quest to produce chromate-free coatings systems. 

Other Methods Examples for other methods include co-casting of a hydrophobic and a hydrophilic polymer that contains amine, imine, hydroxyl, or carboxyl groups [61,89] surface modification by oxidation with ozone or by exposure to an electron or ion-beam ultrasonic etching and UV or laser irradiation [90-92]. A variety of functional groups have been also introduced onto the membrane surfaces by applying the gas discharge techniques (plasma treatment) operated at low or ambient pressure [93,94]. 

In the context of polymers in industrial applications a number of key issues can be identified that are amenable to direct investigation and analysis by AFM approaches. From the preceding chapters the potential of probe microscopic techniques to conveniently visualize for instance surface (or bulk) morphologies and filler distributions has become obvious. Different classes of polymer materials, such as for instance thermoplastics, latexes, porous materials for membranes or thin films are subjected to different types of processing and treatments. The impact of all these modifications and the dependence on the process parameters can hence be closely monitored and in many cases quantitatively characterized by AFM. 

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