Poly plasma treatment method

An alternative photo-SIP approach was described by Kang and coworkers, where they used an argon plasma to oxidize alkylthiolate SAMs on planar gold [55]. The plasma treatment oxidized carboxy-terminated SAMs to peroxide moieties. UV irradiation in the presence of acryhc acid and allylpentafluorobenzene yielded ultra-thin graft layers of 6-7nm. The poly(acrylic acid) layers were found to adsorb Fe " ions from solution. This particular photoinitiation method yields low-density polymer brush films. 

All the work described above has established XPS firmly as a flexible method for the evaluation of the acid-base properties of homopolymers, but the technologically more important advantage of XPS is its ability to analyze thin modified or segregated layers not amenable to traditional forms of analysis [129]. The molecular probe technique has been used to good effect by Shahidzadeh et al. in the study of the plasma treatment of poly(propylene) film [130-132]. Their work identified the need to select basic probe molecules for the assessment of acidic surfaces, and dimethyl sulfoxide was shown to be a good choice, although the photoelectron cross section for sulfur is low, as it is for the Cl 2p core level used for trichloromethane this puts an effective limit on the detectability of the molecular probe, i.e., the number (but not the strength) of the acid-base pairs detectable. 

The substrate for the microfluidic device should be selected with consideration of the end application. Substrates used to fabricate the microchip device should not interact with target analytes, and must be compatible with the detection method employed (i.e., should not exhibit background fluorescence, BGF.). For the analysis of nonpolar compounds, it should be kept in mind that substrates such as poly(dimethyl)siloxane (PDMS) can adsorb hydrophobic analytes such as peptides and proteins. Plasma oxidation or treatment of the surface can sometimes be useful to minimize these interactions [34,35]. For perfusates containing organic solvents, compatibility with polymer substrates can also be an issue. Substrates to be used for the fabrication of electrophoresis-based separation devices should be capable of supporting a stable electroomostic flow (EOF). The use of a low cost material and standard processing procedures can permit mass fabrication of devices. 

Another method to study the contact mechanics and adhesion behavior of soft solids is the so-called JKR test using elastomeric poly(dimethylsiloxane) (PDMS) lenses that are brought in contact with flat surfaces or with each other [884]. The soft PDMS ensures almost ideal JKR behavior of the contacting surfaces. Apphed load, indentation and contact radius, and neck shape can be determined simultaneously, which allows comparison with the JKR predictions. The surfaces of the lenses can easily be modified by treatment with an oxygen plasma to induce a silica-like surface that can then be modified using silane chemistry. As long as these layers are kept thin, the mechanical properties will still be dominated by the bulk PDMS. This type of experiments have been used extensively to study the influence of separation rate on adhesion (for a review, see Ref. [885]). 

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