An improved approach composed of an oxidation reaction in acidic H2O2 solution and a sequential silanization reaction using neat silane reagents for surface modification of poly(dimethylsiloxane) (PDMS) substrates was developed. This solution-phase approach is simple and convenient for some routine analytical applications in chemistry and biology laboratories and is designed for intact PDMS-based microfluidic devices, with no device postassembly required. Using this improved approach, two different functional groups, poly(ethylene glycol) (PEG) and amine (NH2), were introduced onto PDMS surfaces for passivation of nonspecific protein absorption and attachment of biomolecules, respectively. X-ray electron spectroscopy and temporal contact angle experiments were employed to monitor functional group transformation and dynamic characteristics of the PEG-grafted PDMS substrates; fluorescent protein solutions were introduced into the PEG-grafted PDMS microchannels to test their protein repelling characteristics. These analytical data indicate that the PEG-grafted PDMS surfaces exhibit improved short-term surface dynamics and robust long-term stability. The amino-grafted PDMS microchannels are also relatively stable and can be further activated for modifications with peptide, DNA, and protein on the surfaces of microfluidic channels. The resulting biomolecule-grafted PDMS microchannels can be utilized for cell immobilization and incubation, semiquantitative DNA hybridization, and immunoassay.

The collapse of monolayers of 2-hydroxytetracosanoic acid at the air/water interface has been examined by measurements of surface pressure-area isotherms and imaging with light scattering microscopy. Topographic images of films transferred to mica by the Langmuir-Blodgett technique have also been obtained. At low pressures, the films undergo "slow collapse" by the formation of multilayer islands. Folding occurs at highpressure plateaus. At low compression rates, "giant folds" into the subphase arise at defects. They are composed of bilayers that remain suspended beneath the film and open reversibly during expansion. At higher rates of compression, the dominant collapse mechanism is by the formation of small-amplitude "multiple folds" that extend across the trough and are perpendicular to the compression direction.

The maximum pressure a two-dimensional surfactant monolayer is able to withstand is limited by the collapse instability towards formation of three-dimensional material. We propose a new description for reversible collapse based on a mathematical analogy between the formation of folds in surfactant monolayers and the formation of Griffith Cracks in solid plates under stress. The description, which is tested in a combined microscopy and rheology study of the collapse of a single-phase Langmuir monolayer (LM) of 2-hydroxy-tetracosanoic acid (2-OH TCA), provides a connection between the in-plane rheology of LMs and reversible folding.

From analyses of pressure−area isotherms and X-ray photoelectron spectra, we have demonstrated that redox-controllable molecular shuttles, in the shape of amphiphilic, bistable rotaxanes, are mechanically switchable in closely packed Langmuir films with chemical reagents. Additionally, mechanical switching has been proven to occur in closely packed Langmuir−Blodgett bilayers while mounted on solid substrates. The results not only constitute a proof of principle but they also provide the impetus to develop solid-state nanoelectromechanical systems that have the potential to reach up to the mesoscale.