Interfacial friction of thin PDMS network films

This study focuses on developing dry, surface‐tethered polymeric lubricant coatings capable of significantly decreasing friction and wear of nano‐ and micrometer scale machines. Vinyl‐terminated polydimethylsiloxane chains are spin‐coated with a crosslinking agent and platinum catalyst onto silicon wafers functionalized with a self‐assembling monolayer containing reactive vinyl groups. Lateral force microscopy (LFM) measurements employing a bead probe are used to quantify the coefficient of friction (COF) and adhesion characteristics of the PDMS‐SAM surface tethered networks. The combined polymer network and SAM layer manifest extremely low friction coefficients, μ = 4 × 10^?3, which is nearly one order of magnitude lower than the friction coefficient of the bare silicon substrate. The lowest friction forces are measured using silicon substrates covered with nanometer thick, peroxide crosslinked PDMS networks; though poorly crosslinked, these networks display COFs as much as ten‐times lower than a solitary SAM coating layer. Micrometer thick end‐linked optimal networks also manifest attractive interfacial friction properties, with COFs approximately three times larger than the thinner, imperfect networks. These observations are discussed in terms of the structure of the polymer networks and the role of adhesion forces on interfacial friction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1773–1787, 2008     

A facile synthesis of optically pure valerolactone and β-hydroxy valerolactone from a common sugar-derived precursor

Both title compounds were obtained in four steps from 2R, 3R-dihydroxy-4R-valerolactone 5 readily available from D-ribonolactone.     

A Kummer-type construction of self-dual 4-manifolds

Supported in part by NSF grant DMS-9204093     

Biorthogonal polynomials and the bordering method for linear systems

First, the problem of solving a system of linear equations is shown to be equivalent to the computation of biorthogonal polynomials. The bordering method is a procedure for solving recursively a sequence of linear systems with increasing dimensions and it gave rise to a recurrence relationship between two adjacent families of biorthogonal polynomials. Of course, one relation is not sufficient for computing two families. However, in some particular cases, a second recurrence relationship exists between these biorthogonal polynomials thus leading to procedures for solving recursively such linear systems with increasing dimensions. The cases of Hankel and Toeplitz matrices are treated in details. Conferenza tenuta da C. Brezinski il 12 ottobre 1993     

Fattening complex manifolds: Curvature and Kodaira—Spencer maps

We present a calculus whereby the curvature of a geometry arising from any generalized twistor correspondence is related to an obstruction-theoretic classification of the infinitesimal neighborhoods of submanifolds of its twistor space. The crux of the argument involves a relation between Kodaira—Spencer maps and the Penrose transform.