Eyal Zussman

Electrostatic field-assisted alignment of electrospun nanofibres

This paper describes an electrostatic field-assisted assembly technique combined with an electrospinning process used to position and align individual nanofibres (NFs) on a tapered and grounded wheel-like bobbin. The bobbin is able to wind a continuously as-spun nanofibre at its tip-like edge. The alignment approach has resulted in polyethylene oxide-based NFs with diameters ranging from 100-300 nm and lengths of up to hundreds of microns. The results demonstrate the effectiveness of this new approach for assembling NFs in parallel arrays while being able to control the average separation between the fibres.

Effect of supramolecular structure on polymer nanofibre elasticity

Polymer materials of reduced size and dimensionality, such as thin films, polymer nanofibres and nanotubes, exhibit exceptional mechanical properties compared with those of their macroscopic counterparts. We discuss here the abrupt increase in Youngs modulus in polymer nanofibres. Using scaling estimation we show that this effect occurs when, in the amorphous (non-crystalline) part of the nanofibres, the transversal size of regions consisting of orientation-correlated macromolecules is comparable to the nanofibre diameter, thereby resulting in confinement of the supramolecular structure. We suggest that in polymer nanofibres the resulting supramolecular microstructure plays a more dominant role in the deformation process than previously thought, challenging the commonly held view that surface effects are most significant. The concept we develop also provides a way to interpret the observed--but not yet understood--temperature dependence of Youngs modulus in nanofibres of different diameters.

Formation of nanofiber crossbars in electrospinning

In this letter, we report on a technique for the hierarchical assembly of nanofibers into crossbar nanostructures. An electrospinning process is used to create polymer-based nanofibers with diameters ranging from 10–180 nm and lengths of up to several centimeters. By controlling the electrostatic field and the polymer rheology, the nanofibers can be assembled into parallel periodic arrays. We also propose a theoretical model for the process.

Assembly of microsystems

In the microworld, as well as in the macroworld, assembly is a crucial operation in the genesis of a product. This keynote paper focusses on the assembly problems occurring in the manufacturing cycle of microsystems. Scaling effects make that the assembly problems are different in the microworld. The different assembly operations and techniques, like manipulation by physical contact, non-contact manipulation, smart assembly techniques, and joining methods are thoroughly discussed. Finally, some relevant examples of micro-assembly systems and of assembled microproducts are given.

Nanofiber garlands of polycaprolactone by electrospinning

Abstract Over a period of time, the typical path of a single jet of polymer solution, in the electrospinning process follows the nearly straight electric field lines for a certain distance away from the tip, and then develops a series of electrically driven bending instabilities that cause the path of the jet to explore a cone shaped envelope as the jet elongates and dries into a nanofiber. The multitudes of open loops that are formed are rarely observed to come into contact with each other until the dry nanofiber is collected at the end of the process. A new phenomenon is reported in this paper. Electrospinning a solution of polycaprolactone in acetone caused the dramatic appearance of a fluffy, columnar network of fibers that moved slowly in large loops and long curves. The name ‘garland’ was given to the columnar network. Open loops of the single jet came into contact just after the onset of the bending instability and then merged into a cross-linked network that created and maintained the garland. Contacts between loops occurred when the plane of some of the leading loops of the jet rotated around a radius of the loop. Then a small following loop, expanding in a different plane, intersected a leading loop that was as many as several turns ahead. Mechanical forces overcame the repulsive forces from the charge carried by the jet, the open loops in flight made contact and merged at the contact point, to form closed loops. The closed loops constrained the motion to form a fluffy network that stretched and became a long roughly cylindrical column a few millimeters in diameter. This garland, which was electrically charged, developed a path of large open loops that are characteristic of a large-scale electrically driven bending instability. Over a long period of time, the fluffy garland never traveled outside a conical envelope similar to, but larger than the conical envelope associated with the bending instability of a single jet.

Transient and steady shapes of droplets attached to a surface in a strong electric field

The shape evolution of small droplets attached to a conducting surface and subjected to relatively strong electric fields is studied both experimentally and numerically. The problem is motivated by the phenomena characteristic of the electrospinning of nanofibres. Three different scenarios of droplet shape evolution are distinguished, based on numerical solution of the Stokes equations for perfectly conducting droplets. (i) In sufficiently weak (subcritical) electric fields the droplets are stretched by the electric Maxwell stresses and acquire steady-state shapes where equilibrium is achieved by means of the surface tension. (ii) In stronger (supercritical) electric fields the Maxwell stresses overcome the surface tension, and jetting is initiated from the droplet tip if the static (initial) contact angle of the droplet with the conducting electrode is αs < 0.8π; in this case the jet base acquires a quasi-steady, nearly conical shape with vertical semi-angle β 30 ◦ , which is significantly smaller than that of the Taylor cone (βT =4 9.3 ◦ ). (iii) In supercritical electric fields acting on droplets with contact angle in the range 0.8π <α s < π there is no jetting and almost the whole droplet jumps off, similar to the gravity or drop-on-demand dripping. The droplet–jet transitional region and the jet region proper are studied in detail for the second case, using the quasi-one-dimensional equations with inertial effects and such additional features as the dielectric properties of the liquid (leaky dielectrics) taken into account. The flow in the transitional and jet region is matched to that in the droplet. By this means, the current–voltage characteristic I = I (U ) and the volumetric flow rate Q in electrospun viscous jets are predicted, given the potential difference applied. The predicted dependence I = I (U ) is nonlinear due to the convective mechanism of charge redistribution superimposed on the conductive (ohmic) one. For U = O(10kV ) and fluid conductivity σ =1 0 −4 Sm −1 , realistic current values I = O(10 2 nA )w ere predicted.

Material encapsulation and transport in core–shell micro/nanofibers, polymer and carbon nanotubes and micro/nanochannels

In this article, we review recent work on the co-electrospinning of polymer core–shell nanofibers and the manufacture of hollow nanotubes. The encapsulation and release of bioactive compounds from co-electrospun core–shell fibers is considered next, bearing in mind such applications as sensors and drug release. Then, nanofluidic phenomena in nanotubes made via co-electrospinning (as well as via the other processes) are discussed. We also consider dielectrophoresis in microchannels as a possible tool for the separation of viruses, nanoparticles and macromolecules.

A methodology for modeling and adaptive planning of disassembly processes

A principal process during the remanufacturing of worn-out or malfunctioning products is disassembly that enables the dumping, cleaning, repair or replacement of components as desired. Products subjected to disassembly exhibit uncertainty in the product structure and component conditions. Hence the termination goal (the level of disassembly) is subject to change, and the disassembly plan must be adapted. This paper proposes a mathematically sound disassembly Petri net (DPN) for the modeling and adaptive planning of disassembly processes. The planning algorithm guarantees the optimal remanufacturing value when each nodes utility function (benefit of a subassembly or part and cost of a disassembly operation) is fixed. It can be modified to deal with the cases when the disassembly operation success rates vary with the product condition and reliability of resources performing the operations. The proposed methodology and algorithms are demonstrated through the sample disassembly of a telephone.

Mechanics of hydrogenated amorphous carbon deposits from electron-beam-induced deposition of a paraffin precursor

Many experiments on the mechanics of nanostructures require the creation of rigid clamps at specific locations. In this work, electron-beam-induced deposition (EBID) has been used to deposit carbon films that are similar to those that have recently been used for clamping nanostructures. The film deposition rate was accelerated by placing a paraffin source of hydrocarbon near the area where the EBID deposits were made. High-resolution transmission electron microscopy, electron-energy-loss spectroscopy, Raman spectroscopy, secondary-ion-mass spectrometry, and nanoindentation were used to characterize the chemical composition and the mechanics of the carbonaceous deposits. The typical EBID deposit was found to be hydrogenated amorphous carbon (a-C:H) having more sp2- than sp3-bonded carbon. Nanoindentation tests revealed a hardness of ∼4GPa and an elastic modulus of 30–60GPa, depending on the accelerating voltage. This reflects a relatively soft film, which is built out of precursor molecular ions impacting ...

Biohybrid nanosystems with polymer nanofibers and nanotubes

Advanced techniques for the preparation of nanofibers, core shell fibers, hollow fibers, and rods and tubes from natural and synthetic polymers with diameters down to a few nanometers have recently been established. These techniques, among them electro- and co-electrospinning and specific template methods, allow the incorporation not only of semiconductor or catalytic nanoparticles or chromophores but also enzymes, proteins, microorganism, etc., directly during the preparation process into these nanostructures in a very gentle way. One particular advantage is that biological objects such as, for instance, proteins can be immobilized in a fluid environment within these polymer-based nano-objects in such a way that they keep their native conformation and the corresponding functions. The range of applications of such biohybrid nanosystems is extremely broad, for instance, in the areas of biosensorics, catalysis, drug delivery, or optoelectronics.