No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

The surface force apparatus (SFA) has been an important technique for making direct force measurements and has contributed enormously to our understanding of colloidal interactions. The conventional SFA has been limited to measuring forces between solid surfaces, until recently when a modified SFA was developed at the Ian Wark Research Institute [1]. A fluid drop (mercury) is introduced into the apparatus which allows a range of deformable surfaces to be studied in the SFA. This project is an extension of this technique. Interactions between a mica sheet and a mercury drop are studied, including the modification of mercury with self-assembled monolayers (SAMs) of thiol surfactants, and the drop deformation due to non-equilibrium adsorption effects and hydrodynamic forces.

The surface force apparatus (SFA) has been an important technique for making direct force measurements and has contributed enormously to our understanding of colloidal interactions. The conventional SFA has been limited to measuring forces between solid surfaces, until recently when a modified SFA was developed at the Ian Wark Research Institute [1]. A fluid drop (mercury) is introduced into the apparatus which allows a range of deformable surfaces to be studied in the SFA. This project is an extension of this technique. Interactions between a mica sheet and a mercury drop are studied, including the modification of mercury with self-assembled monolayers (SAMs) of thiol surfactants, and the drop deformation due to non-equilibrium adsorption effects and hydrodynamic forces.

<p dir="ltr">There is a plethora of applications that require chemical patterning on the molecular scale. While the surface science community has made tremendous progress in achieving this level of control on hard, crystalline interfaces, significant challenges are associated with extending this progress to less “perfect” systems such as soft, amorphous interfaces. Applications ranging from soft robotics and wearable electronics to regenerative medicine often utilize polymeric materials such as polydimethylsiloxane (PDMS) and hydrogels. These materials have advantageous properties, including biocompatibility and mechanical tunability. Biological applications, for example, often require the display of functional groups with precise spatial resolution. Cellular behavior is dictated by biochemical and biophysical cues in the extracellular matrix; therefore, substrate properties, including stiffness and ligand density, must be independently tunable. Soft, polymeric materials are highly heterogenous with pore sizes ranging from 10 nm to 1 µm and hence, particularly difficult to pattern below the length scale of substrate heterogeneity. Furthermore, deconvolving mechanical properties such as elastic modulus from the density of surface-active functional groups is especially challenging, with softer materials typically corresponding is lower ligand densities. Additionally, many traditional surface science characterization and patterning methods are incompatible with soft interfaces (e.g. amorphous surface structure, low mechanical strength, hydrated environment). Recently, we have reported a method capable of achieving high-resolution chemical patterning of PDMS and hydrogels. Long studied within the scanning probe community, amphiphiles with long alkyl chains self-assemble into lying down stripe phases on highly ordered pyrolytic graphite (HOPG), generating 1-nm-wide stripes of functional headgroups between 5-nmwide stripes of exposed alkyl chains. Stripe phases of functional diacetylenes (DA) are photopolymerized, producing a polydiacetylene backbone that tethers together adjacent molecules, generating a PDA film on HOPG (sPDA). We have shown that PDA films on HOPG can be transferred to PDMS as well as polyacrylamide hydrogels. When PDMS is cured in contact with sPDAs, the PDA backbones can act as a site for hydrosilylation, the same reaction responsible for PDMS curing, covalently linking sPDAs to the PDMS mesh. Careful exfoliation reveals nm-scale functional patterns on the surface layer of PDMS. 10 Here, we examine the impact of PDMS structural components on the efficiency of interfacial reactions between sPDAs and the PDMS network. We also illustrate the impact of PDAfunctionalized PDMS on the adhesion and spreading behavior of C2C12 murine myoblasts.</p>

Various aspects of the surface chemistry of a ruthenium (1010) single crystal have been investigated under ultra-high vacuum conditions, employing the techniques of Auger Electron Spectroscopy, Low Energy Electron Diffraction, Multimass Thermal Desorption Spectroscopy, photoemission spectroscopies and work function measurements. The studies were undertaken with a view towards the applicability of ruthenium and iron-ruthenium alloys to the ammonia synthesis, though work relevant to the Fischer-Tropsch synthesis was also performed. The interactions of the gases nitrogen, hydrogen and ammonia with the clean surface were all explored. Molecular nitrogen was found to have an extremely low sticking probability of less than 10<SUP>-9</SUP> at room temperature, but surface nitrogen atoms were deposited via two separate means, using either a mixture of nitrogen ions or nitrogen atoms themselves as the impinging species. Both chemisorbed and bulk implanted states were thereby observed. Hydrogen uptake at 310 K saturated at small doses but an estimate of 256 kJ mol<SUP>-1</SUP> was made for the Ru-H bond strength from thermal desorption traces. Ammonia readily adsorbed at and above room temperature. Partial dissociation occurred at 300 K, the extent of fragmentation increasing as the crystal temperature was raised. Strong electron beam perturbations of the adlayer occurred, accelerating the rate of adsorption and resulting in the appearance of otherwise unobservable LEED patterns. The behaviour of the model promoter potassium was relatively typical of alkali metal/transition metal systems, though the anisotropic substrate potential was found to induce a series of interesting one dimensionally incoherent compressed overlayer structures. A further striking observation was the occurrence of substantial bulk dissolution of potassium following small doses at 430 K. The promoting effects of potassium on CO adsorption were investigated and interpreted interms of a recent modification of the Blyholder model, which combines indirect, through metal and direct, through space interactions. Finally, the deposition of iron on Ru(10bar 10) was studied. At 300 K the iron film grew in a metastable layer by layer mode, which rapidly rearranged on heating to either an alloy phase or a regime of 3D crystallites lying above one or two iron monolayers. Adsorption at elevated temperatures produced essentially the same results as heating layers deposited at room temperature.