A low cost, low temperature process for sealing microfluidic devices composed of at least one organic polymeric substrate is presented. The process is based on the surface modification of the organic substrate by means of a silane solution, resulting in irreversible bonding. It is a generic method of bonding polymeric/plastic substrates, bare or structured ones, such as poly(methylmethacrylate) (PMMA), polystyrene (PS) or epoxy-type polymers, to Si-containing substrates, such as poly(dimethylsiloxane) (PDMS), Si and glass. In the case that bonding between organic polymer (PMMA, PS, etc) substrates is desired, an intermediate thin PDMS layer is required.

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In this study, the effect of sorbed water on the tensile mechanical properties of noncrosslinked, thermally treated poly(vinyl alcohol) (PVA) films was studied. The Young's modulus, elongation at break, and tensile strength of the PVA films equilibrated at different relative humidities (0-86%) are reported, together with the depression of the glass transition of the polymer at each equilibrating humidity, as determined by temperature-modulated differential scanning calorimetry. The results indicate that drastic changes in the tensile properties were correlated with the transition of the hydrated polymer from the glassy to the rubbery state.

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Film blends of poly(3-butyltiophene-2,5-diyl) (PT) and polystyrene (PS; 1 : 1 w/w) were spin-coated onto silicon wafers from chloroform, tetrahydrofuran, and cyclohexanone at a controlled relative humidity between 4 and 86%. The film morphologies were determined with atomic and lateral force microscopy and mapping and depth profiling modes of dynamic secondary-ion mass spectroscopy. Independently, white light interferometry was used to examine the expansion and response time (t) of pure polymer layers exposed to solvent vapors and moisture. The higher PS solubility, in comparison with the PT solubility, in chloroform and tetrahydrofuran resulted in PS/PT//Si bilayers, which were the final structures for coatings from chloroform [with much larger t(PS)/t(PT) ratios]. For tetrahydrofuran, these bilayers were destroyed, most likely by surface and interface instabilities, yielding hierarchic lateral structures. For cyclohexanone (with the largest t values), a large-scale component of the lateral structures was absent, and this suggested the leveling of surface instabilities. The humidity changed the structural scales and thickness of the films cast from tetrahydrofuran (because it had the best solubility with water). The humidity effects of chloroform and cyclohexanone [reported earlier for polyaniline and poly(vinyl pyridine) blends] were practically absent. Moisture was not easily absorbed by PT and PS [in contrast to polyaniline and poly(vinyl pyridine)] and probably adsorbed merely at the surfaces of blend films rich in tetrahydrofuran.