Surface chemical modification polymeric materials, plasma

Plasma treatment and plasma deposition polymerization provides a unique and powerful method for the surface chemical modification of polymeric materials without altering their bulk properties. (7-5) These techniques offer the possibility to improve the performance of existing biomaterials and medical devices and for developing new biomaterials-(- -6)... 

Surface modification of a contact lens can be grouped into physical and chemical types of treatment. Physical treatments include plasma treatments with water vapor (siUcone lens) and oxygen (176) and plasma polymerization for which the material surface is exposed to the plasma in the presence of a reactive monomer (177). Surfaces are also altered with exposure to uv radiation (178) or bombardment with oxides of nitrogen (179). Ion implantation (qv) of RGP plastics (180) can greatiy increase the surface hardness and hence the scratch resistance without seriously affecting the transmission of light. 

A wide array of surface modification techniques, ranging from simple to sophisticated, wet to dry, and vacuum to nonvacuum, are available for a host of polymeric materials. They include plasma surface treatment laser surface treatment corona, flame, UV, ozone, UV/ozone, photochemical, photografting, chemical grafting, and chemical methods of stuface modification and modification of polyamide surfaces by microorganisms [7]. 

It is well known that the surface chemical and physical properties play a dominant role in the separation characteristics of a membrane. Most of the currently used membranes are made of polymers because they have excellent bulk physical and chemical properties, they are inexpensive, and are easy to process. However, the surface properties of polymers, their hydrophobicity, and their lack of functional groups stand in the way of many other applications (Chan et al. 1996). So far, various polymers have been used for membrane fabrication. However, due to the limited number of polymeric materials on the market, one cannot expect any significant increase in the variety of the membranes offered. What is more, large-scale production of brand-new polymers has not been commercialized during the last decade, nor is it expected to be launched in the near future. These observations have forced material scientists to search for alternative methods to increase the number and variety of membranes being prepared. There are two directions for new membrane manufacturing (i) to modify a polymer in bulk and then prepare the membrane from it or (ii) to prepare the membrane from a standard polymer and then modify its surface. The first method needs the optimization of the membrane formation for the particular derivative separately. The second seems to be less complicated and less expensive, and it can offer a wide variety of new membranes based on one starting matrix. The authors intention is to present the plasma methods for membrane modification and tailor them based on the end-user requests. 

Chapter 7 examines the use of plasma treatment for the modification of polymeric membranes. Plasma treatment is carried out at the manbrane surface so that the beneficial properties of the bulk material remain unchanged. Surface properties such as roughness and functionality can be altered to improve the performance of the membrane. All these processes are very quick and the time taken for modification is usually a few seconds up to a few minutes. The method uses chemicals in the gaseous form and produces very small amounts of wastes. Among all techniques of membrane surface modification, plasma treatment seems to be the most versatile and environment-friendly. The authors of Chapter 7 discuss how these benefits impact on membrane modification strategies. 

Polymer Suiface Modifications The growing need of polymeric materials with specific properties for sophisticated applications has led to the development of new polymer surfaces, which can be created by traditional polymerization processes or by the modification of existing surfaces. Surface modification of polymers is used to improve their chemical, physical, mechanical, and tribological properties. Many techniques have been applied to produce the desired surface properties, ranging from thermal treatments, chemical and electrochemical modifications, metallization, and electrical treatments, to plasma treatments and particle beam irradiation techniques. The literature shows that SIMS is a method of choice to characterize the results of such treatments. Hereafter we introduce some examples taken from published studies. 

Surface modification refers to the modification that occurs only on the surface of a polymer material without further internal modification. Surface modifications of polymeric materials include surface chemical oxidation, corona surface treatment, surface flame treatment, surface heat treatment, surface plasma treatment, surface metallization processing, ion implantation, and surface grafting polymerization. Because surface modification occurs only on the surface of materials, the performance does not change uniformly. 

The surface modification of biomaterials is also frequently achieved using plasmas. The physico-chemical properties of the material surface may be modified using plasma discharge in different gases, or a polymer coating may be deposited using plasma polymerization (cf. the section on Data Interpretation Through Simulation). A well-known example of the first approach is tissue-culture polystyrene (TCPS), which is commonly used to culture cells in vitro (Fig. 19). XPS shows that plasma... 

Above all of these requirements, SAIE must produce products that are superior to the conventional products. In other words, low-pressure plasma SAIE is not an alternative process it should be a new approach to create superior composite materials that could not be obtained by other means, which is of utmost importance with respect to the use of LCVD. It is often mentioned that plasma polymerization was successfully used in the surface modification but that a conventional, more economical, wet chemical process later replaced it. Such an attempt to use LCVD process based only on the laboratory curiosity is an absolutely wrong approach. This aspect is explored in Chapter 12. 

This modification could be made by plasma polymerization wherein a thin, highly cross-linked and pin hole free film of filler free silicone polymer could be added onto a variety of substrate materials in order to prepare improved blood compatible surfaces (1). Alternatively, gaseous plasma could be used to add new chemical groups to a material surface which could then be used for attaching a variety of biomolecules. By anhydrous ammonia plasma, amino groups can be added to the surface of polypropylene membranes or to the surface of polypropylene beads. These amino groups can then be employed to bind albumin to polypropylene as was done in our previous work in which a quantitative measure of bound protein was... 

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