Modification surface

Surface modification is widely used to change the properties of a surface to suit specific applications. It has found increasing use in biotechnology applications. Our discussion on this topic is limited to the modification of surface hydrophilicity and hydrophobicity. As discussed in Chapter 2, they are very important factors in the creation of liquid microlenses. 

The first way of modifying the surface hydrophilicity and hydrophobicity is to apply an ultrathin monolayer of chemical onto the surface. This is often referred to as a self-assembled monolayer (SAM). One example in photolithography is to coat hexamethyldisilazane (HMDS) onto the substrate surface to enhance the adhesion of PR. Another example is applying octa-decyltricholorosilane (OTS) onto a glass substrate to make it hydrophobic. 

The second method involves plasma treatment of the surface. For example, when two plasma oxidized PDMS surfaces are brought into conformal contact, an irreversible seal forms between them. This technique can be used to bond two PDMS layers [15,16]. Oxygen plasma treatment of PDMS also enables the bonding of PDMS to other materials such as glass [17]. Plasma oxidation of a PDMS surface makes it more hydrophilic from its native hydrophobic state [15,16]. 

The third approach is modifying the surface morphology. For example, super-hydrophobicity (contact angle approaching 180 degrees) may be accomplished when a surface is covered wi nanoscale fabricated structures [18]. 

Coextrusion compound modification is the process in which a number of extruders are used to produce different molten material flows individually, which are then gathered in a complex head sink to obtain multilayer composite products. The procedure can combine multilayer materials with different 

In addition, coextrusion compound modification can greatly reduce product cost, simplify processes, and reduce equipment investment. The composite process does not use solvents and therefore will not produce waste gas, waste water, and industrial residue. For these reasons, coextrusion composite modification is widely used in the production of compound fibers, films, plates, pipes, profiles, wires, and cables. 

Polymers can also be used to prevent the adsorption of proteins to surfaces. For example, polyvinylpyrrolidone can prevent protein adsorbing onto a variety of surfaces and it can also displace adsorbed protein [ 18]. This has led, for example, to its application in the coating of filtration membranes in order to reduce biofouling. Polymers are also used to inhibit the adhesion of bacteria or water-borne micro-organisms onto siufaces [19,20]. Bacteria are usually surrounded by exoceUular polysaccharides that can aid adhesion to clean surfaces. Thus prosthetic devices and vascular implants carrying blood suffer from the build up of biofilms, leading to blockages and infection. This build up can be markedly reduced 

A conceptually simple example of surface modification for lithographic imaging was based on the use of focused ion beam to write a pattern onto the sub- 

Silicon oxide formation at the near surface of UV irradiated polymers was applied to surface imaging [476]. For example, a photosensitive polymer 

In this chapter we discuss how solid surfaces can be modified. Surface modification is essential for many applications, for example, to reduce friction and wear, to make implants biocompatible, or to coat sensors [405,406], Solid surfaces can be changed by various means such as adsorption, thin film deposition, chemical reactions, or removal of material. Some of these topics have already been discussed, for example in the chapter on adsorption. Therefore, we focus on the remaining methods. Even then we can only give examples because there are so many different techniques reflecting diverse applications in different communities. 

Before we focus on chemical vapor deposition let us briefly mention other methods for thin film deposition. Films with thicknesses from 1 /zm to several 10 /zm play a fundamental role in everyday life, for example as paints and coatings. Processes during film formation are complex and a discussion would exceed the scope of this book. Introductions are Refs. [407,408], 

Different techniques to deposit thin layers of material have already been described spin and dip coating in Section 7.5.2, evaporation, sputtering, and molecular beam epitaxy in Section 8.3. Film thicknesses are in the 20 nm to 10 /zm range. 

As described above, the resistances to oxygen permeation in perovskite membranes may be from the bulk diffusion and the surface exchange reactions. 

Therefore, the membrane surface areas for exchange reactions are increased noticeably while the effective membrane thickness for bulk diffusion is also decreased (only limited to the central dense layer). As a consequence, the oxygen permeation flux can be improved greatly, e.g. a maximum improvement factor of 18.6 can be obtained at 800 °C for the H2S04-modified membranes.  

It is noted that the flux improvement decreases with increasing temperature because the relative limiting effect of the bulk diffusion gradually becomes more noticeable at higher temperatures. 

18 Charge transfer mediation at n-Si produced by chemical modification of the surface. 

Several studies have been made to optimize the properties of natural fiber-reinforced PLA composites from the point of view of fiber-matrix adhesion. Pretreatment of fibers, such as chemical modification, seems to be the most promising approach, in which covalent bonds are formed between the fiber and matrix. One of the most common and efficient methods is alkali treatment (for example, with 2% sodium hydroxide aqueous solution) of fibers, which has been used to 

TABLE 18.1 Chemical Modification Methods for Natural Fibers 

Alkali treatment Aqueous NaOH solution Kenaf fiber/PLA [10, 21] hemp fiber/PLA [26] abaca fiber/PLA [29] 

Esterification Acetic anhydride (or butyric anhydride)/ pyridine solution Abaca fiber/PLA [29] 

Silane treatment 3-Aminopropyltri- ethoxysilane Kenaf fiber/PLA [10] 

Polymer surface engineering may potentially be used to create materials to control cellular adhesion and maintain differentiated phenotypic expressions, merely by the introduction of nanoparticles within the polymer generating surface modifications that may affect both cell behaviour and the antibacterial character of the material. 

Surface modification of polymeric biomaterials is becoming an increasingly popular method to improve material multifunctional, biological 

Another technique is the biomacromolecules entrapment, as reported by Quirk et They used PEG and poly(L-lysine) (PLL) to improve bio- 

Silicon is highly unstable in aqueous electrolytes due to the formation of an insulating oxide film which prevents the use of n-Si as photoanode. On the other hand, the silicon electrode has poor kinetics for hydrogen evolution which is not desirable for its use as a photocathode. Many methods have been explored to stabilize Si electrodes in aqueous solutions for possible applications as photochemical cells. They include coating the surface with noble metals, metal oxides, metal silicides, or organic materials as shown in Table 6.6. Also, some redox species, the reduction of which can favorably compete with the oxidation of silicon, can be used to stabilize silicon anodes 

Material Coalings Solvent Redox couple Refs. 

The silicon surface can be stabilized using surface modification techniques which are divided into three categories (1) attachment of redox mediator which consumes the holes on the surface (2) attachment of electronically conducting polymer and (3) coating with thin metal or semiconducting films to create a buried semiconductor interface. Combinations of these approaches can also be used to stabilize the sihcon surface.  

FIGURE 6.29. Photocurrent-time behavior of bare -Si ferrocene/n-Si polypyrrole/n-Si and polypyrrole/ ferrocene/n-Si electrodes. (Reprinted from Malpas and Rushby. 1983, with permission from Elsevier Science.) 

Deposition of a small amount of noble metals such as Cu, Pt, and Au increases the kinetics of redox reactions on silicon electrodes as shown in Fig. 6.3. Deposition of equivalent of 1 to 10 monolayers of Pt on silicon surface results in a shift of about 0.2V of the onset potential for hydrogen evolution to the positive direction. Because the flatband potential does not change with the Pt deposition, the enhanced hydrogen reaction kinetics is due to the catalytic effect of the deposited metal. The energy levels of the deposited metal grains are considered to lie in the middle of the band gap and communicate favorably to the surface states both energetically and spatially. The photovoltage of n-Si coated with sparsely scattered Pt islands has been found to increase proportionally to the inaease in the potential of the redox couple. Noble metal islands effectively collect photoelectrons and thus prevent the oxidation of the silicon surface by the photoelectrons. 

The use of molecularly smooth mica surfaces is a conceptual strength of the SFA. At the same time, it is a severe limitation since it is the only surface that can be directly studied. There have heen several approaches to overcome this limitation and allow the use of different surfaces. Evaporation of thin metal layers onto mica leads to increased roughness of the surfaces even when template stripping [192-194] is used. Most simple, but less controlled, is surface modification by adsorption, preferentially, of molecules that self-assemhle into monomolecular layers. Alternatively, chemical modification of the mica surfaces hy silanes can be achieved. Finally, mica can be 

Most of the anticipated uses of upconversion Ln -based nanoparticles require dispersibility in biological media, with blood arguably being the most challenging medium, because of the presence of salts, protein, and so on that may lead to instabihty of the colloidal dispersion. It is thus no wonder that considerable effort has been devoted to surface modification of the oleate-stabilised nanoparticles. There are four basic strategies  

Silica coating by using a modified Stober process. The Stober process [24] is the controlled hydrolysis of tetraalkoxysilanes in aqueous medium. 

Ligand exchange processes that swap the oleates (and amines) for water dispersible ones, the latter including (small) proteins and polymers as well. 

Chemical conversion of the double bonds (of the oleates and/or oleyl amines) by oxidation to carboxylic acids or epoxides. 

Intercalation of amphiphilic molecules or polymers into the alkenyl chains of the stabilising ligands. This approach is based on hydrophobic forces that force the lipophylic (= hydrophobic) part(s) of the amphiphilic molecule or polymer into the hydrophobic monolayer on the nanoparticles. The hydrophilic parts then make these nanoparticles water dispersible. This method has been reported using PEG-oleate [25] and derivatised PM AO [poly (maleic anhydride-afi-octadecene)] [26-29]. 

As in the case of normal chromatography both stationary and mobile phases are also required in NLC. On the other hand, in NCE hydrophilic channel walls with improved control over electroosmotic flow are required for better separation of biological samples. Briefly, the separation efficiencies and selec-tivities in NLC and NCE depend on the properties of the microchannels, and, therefore, surface modification of the microchannel is usually necessary to achieve good separation of a variety of analytes. Recently, Muck and Svatos 

The polymeric chips require special attention to their surface properties due to their poor compatibility with many samples and organic solvents used in forming a coating and in the composition of the mobile phases. Lee et al. 

We have described how a step-by-step addition of oppositely charged PEL can improve the quality of flocculation. A possible flocculation mechanism is described (Fig. 5) and is also shown for comparison in Fig. 6a. However, an increase in the PC amount can also lead to the formation of PEC in solution (Fig. 6b), which can be used as an additimial flocculant. In the case that the PC and PA are added at the same time, the complex formatimi is favored (Fig. 6c). 

The situation shown in Fig. 6b can also be applied for a strong surface modiflcation of particles or fibers [42-45]. As demmistrated [43], in the presence of cellulose the complex formatimi between the two PEL is favored in the solution, and this complex itself is adsorbed on the surface by electrostatic interactions, which also causes flocculation. Under the cmidition that a large quantity of PC is still in solutimi when the PA is added dropwise, it is possible that the incorporation of the PC into the expanded complex takes place. As shown in Fig. 7, the surface charge of flocculated 

Clay particles whose surfaces have been modified by the PC PDADMAC and the sodium salt of the weak PA poly(maleic acid-co-a-methylstyrene), P(MS-a-MeSty), were used as sorbents for removal of surfactants from aqueous solutions [46]. 

The cubic pyrochlore-based ceria-zirconia solid solution is a good material. However, it has been reported that the reduction temperature has become higher after the high-temperature oxidation. This is due to the transformation from pyrochlore-based-cubic to r -tetragonal phase which is more stable than k, and t  

Recently, one of the solutions to overcome this problem has been proposed.This does concern surface modification of the pyrochlore-based oxides. It is known that cerium and zirconium chlorides provide vapor phase complexes with aluminum chloride at elevated temperatures.The new surface modification technique utilizes the formation of these vapor complexes to remove and modify the top surface of the pyrochlore ceria-zirconia solid solution. This method is named chenucal filing . Application of the above complexes formation has already been demonstrated for the vapor phase extraction and mutual separation of rare earths based on the so-called chemical vapor transport (CVT).  

The chemical filing technique is very effective in modifying the redox property in the low temperature regions. The reduction temperatures of the chemically filed samples become lower than those of the non-filed ones without decreasing in the amount of the released oxygen. The redox activities of the chemically filed samples are maintained even after several reduction and reoxidation aging at 1273 K. The reasons for these better redox activities have been attributed to the formation of trace amounts of CeOj ultrafine particles with the evolution of zirconium and subsequent stabilization of the metastable k and phases.  

Kaspar J., Fornasiero P., and Graziani M. Catal. Today, 50 (1999), 285-298. Kaspar J., Graziani M., Fornasiero P., Ceria-Containing Three-Way Catalysts, in Handbook on the Physics and Chemistry of Rare Earths, Vol. 29, eds. Gshneidner, Jr. K.A. and Eyring L. (Elsevier, Ireland, 2000), 159-267. 

Omata T., Kishimoto H., Otsuka-Yao-Matsuo S., Ohtori N., and Umesaki N., /. Solid State Chem., 147 (1999), 573-583. 

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MAZAL,P.-DVOftACEK,J.- KOLAft,D. AET Utilisation for Pitting Observation of Grey Cast Iron with Heat Treated Sur ce. Surface Modif. Technologies XI, will be published 1998. 

It has also been shown that sufiBcient surface self-diflfiision can occur so that entire step edges move in a concerted maimer. Although it does not achieve atomic resolution, the low-energy electron microscopy (LEEM) technique allows for the observation of the movement of step edges in real time [H]. LEEM has also been usefiil for studies of epitaxial growth and surface modifications due to chemical reactions. 

Energetic particles interacting can also modify the structure and/or stimulate chemical processes on a surface. Absorbed particles excite electronic and/or vibrational (phonon) states in the near-surface region. Some surface scientists investigate the fiindamental details of particle-surface interactions, while others are concerned about monitormg the changes to the surface induced by such interactions. Because of the importance of these interactions, the physics involved in both surface analysis and surface modification are discussed in this section. 

One of the main uses of these wet cells is to investigate surface electrochemistry [94, 95]. In these experiments, a single-crystal surface is prepared by UFIV teclmiqiies and then transferred into an electrochemical cell. An electrochemical reaction is then run and characterized using cyclic voltaimnetry, with the sample itself being one of the electrodes. In order to be sure that the electrochemical measurements all involved the same crystal face, for some experiments a single-crystal cube was actually oriented and polished on all six sides Following surface modification by electrochemistry, the sample is returned to UFIV for... 

Staufer U 1995 Surface modification with a scanning proximity probe microscope Scanning Tunnelling Microscopy II ed R Wiesendanger and Fl-J Guntherodt (Beriin Springer) ch 8... 

Mizutani T, Dale C J, Chu W K and Mayer T M 1985 Surface modification in plasma-assisted etching of silicon Nucl. Instrum. Methods B 7 825-30... 

Surface free energy Surface lubricants Surface modification... 

Eactors that could potentiaHy affect microbial retention include filter type, eg, stmcture, base polymer, surface modification chemistry, pore size distribution, and thickness fluid components, eg, formulation, surfactants, and additives sterilization conditions, eg, temperature, pressure, and time fluid properties, eg, pH, viscosity, osmolarity, and ionic strength and process conditions, eg, temperature, pressure differential, flow rate, and time. 

Fig. 1. Fquilihrium isotherms for adsorption on activated carbon at 298 K showing the effect of surface modification (2). —, SO2 -...

Physically or chemically modifying the surface of PET fiber is another route to diversified products. Hydrophilicity, moisture absorption, moisture transport, soil release, color depth, tactile aesthetics, and comfort all can be affected by surface modification. Examples iaclude coatiag the surface with multiple hydroxyl groups (40), creatiag surface pores and cavities by adding a gas or gas-forming additive to the polymer melt (41), roughening the surface... 

B. D. Bauman, "Scrap The Reuse Through Surface-Modification Technology," paper presented at International Symposium on Research and Depelopment for Improping Solid Waste Management, Cincinnati, Ohio, Eeb. 7, 1991. 

Surface Modification. Plasma surface modification can include surface cleaning, surface activation, heat treatments, and plasma polymerization. Surface cleaning and surface activation are usually performed for enhanced joining of materials (see Metal SURFACE TREATMENTS). Plasma heat treatments are not, however, limited to high temperature equiUbrium plasmas on metals. Heat treatments of organic materials are also possible. Plasma polymerization crosses the boundaries between surface modification and materials production by producing materials often not available by any other method. In many cases these new materials can be appHed directly to a substrate, thus modifying the substrate in a novel way. 

Biomaterials with Low Thrombogenicity. Poly(ethylene oxide) exhibits extraordinary inertness toward most proteins and biological macromolecules. The polymer is therefore used in bulk and surface modification of biomaterials to develop antithrombogenic surfaces for blood contacting materials. Such modified surfaces result in reduced concentrations of ceU adhesion and protein adsorption when compared to the nonmodifted surfaces. 

Surface Modification. Reaction or adsorption at the soHd surface can alter its properties and lead to a surface charge or steric stabilization... 

Numerous schemes can be devised to classify deposition processes. The scheme used herein is based on the dimensions of the depositing species, ie, atoms and molecules, softened particles, Hquid droplets, bulk quantities, or the use of a surface-modification process (1,2). Coating methods are as foHow (2) ... 

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobihty of individual molecules is restricted. This lack of mobihty is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibihty problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quahty. Alkyl silanes remain, however, ideal materials for surface modification and functionalization apphcations, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

SAMs of OH-terrninated alkanethiols have been used in many surface modification reactions (Fig. 14). These reacted with OTS to yield a weU-ordered bdayer (322), with octadecyldimethylchlorosilane (323,324), with POCI3 (325—327), with trifluoroacetic anhydride (328), epichlorohydrin (329), with alkyhsothiocyanate (330), with glutaric anhydride (331), and with chlorosulfonic acid (327). 

Organic titanates perform three important functions for a variety of iadustrial appHcations. These are (/) catalysis, especially polyesterification and olefin polymerization (2) polymer cross-linking to enhance performance properties and (J) Surface modification for adhesion, lubricity, or pigment dispersion. 

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