טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSalalha Wael
SubjectFluidic Assembly of Rod-like Nano Particles
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Eyal Zussman


Abstract

Nanowires are common building blocks for the bottom-up assembly of electronic and photonic devices. A significant challenge is to introduce a single nanowire into an oriented assembly in order to express its unique anisotropic properties or to fabricate a nano-device. In this work we focused on the alignment of inertialless and non-Brownian rod-like particles (e.g., nanowires) by means of different flows. First, the alignment of rod-like particles was studied by manipulating a micro-scale droplet composed of a dilute nanowires suspension within a micro-channel using thermocapillary motion. The droplet motion creates several flow patterns which are responsible for the alignment of the nanowires. Real-time observations show that the nanowires found in the middle region of the droplet, between the rear and the front contact lines, were aligned most of the time with the Poiseuille flow, but they did 'flip-over' occasionally. Nanowires which reach the front meniscus move together with the displacing fluid which undergoes a 'rolling'' type motion, and are finally adsorbed to the surface of the micro-channel. The adsorbed nanowires were found in most cases to align with the droplet’s flow direction. However, in certain cases nanowires may become re-oriented by the passage of the rear-contact line. The second study dealt with the alignment of nanowires dispersed in a polymer solution. The nanowires were aligned by sink-like, and subsequently by elongation flow, via an electrospinning process and were eventually embedded in the nanofibers. In this process we found that the nanowires are initially randomly oriented, but due to the sink-like flow they are gradually oriented mainly along the stream lines, so that straight nanowires are sucked into the electrospun jet almost oriented. The high elongation flow during the fiber stretching enhanced the alignment. Experimental and theoretical investigation of fluidic assembly of nanowires will be presented.