Piezoelectric droplet generators

What was said about the state of knowledge on collisions of different miscible liquid drops applies to the case of immiscible liquids also. We find the work by Chen and Chen [49], who investigated the collision of equal-sized droplets of water and Diesel oil. The dynamic viscosities and surface tensions of the two liquids against air at the temperature of the experiments are different by a factor of 3.1 and 2.6, respectively. Drop sizes, produced with the same piezoelectric droplet generators as in Gao et al. [45], ranged between 700 and 800 pm. The result of an experimental survey of the outcome fi om the collisions for varying impact Weber number and non-dimensional impact parameter is a flow chart similar to that in Fig. 7.5a, where the Weber number is defined with the relative velocity of the colliding drops and the liquid properties of Diesel oU. The boundaries between the... 

Keywords Droplet-on-demand (DOD) droplet generators Electrohydrodynamics (EHD) droplet generators Microfluidic droplet generators Piezoelectric droplet generators Pneumatic droplet generators Thermal or bubble jet droplet generators... 

Fig. 25.5 (a) Schematic of a piezoelectric droplet generator, (b) sequences of droplet ejectiOTi liom the droplet generator (Reproduced from [36]. With permission. Copyright 2008 Elsevier)... 

H. Ulmke, T. Wriedt, and K. Bauckhage Piezoelectric droplet generator for the calibration of particle-sizing instruments. Chemical Engineering and Technology, 24(3), 265-268 (2001). 

A complete description of droplet generator and of several atomization methods appears in a previous paper [8]. Simple air-stripping or piezoelectric drop generators were employed. The core liquid typically consisted of a polyanion solution, while the receiving bath contained a polycation(s) solution and, in many instances, a divalent cation. 

A. Bransky, N. Korin, M. Khoury, and S. Levenberg, A microfluidic droplet generator based on a piezoelectric actuator, Lab on a Chip, 9, 516-520,... 

Abstract This chapter provides information on different types of drop-on-demand drop generators. It starts with thermal or bubble jets, in which a nucleation bubble is used to eject a droplet out of an orifice. This is followed by piezoelectric, pneumatic, microfluidic, electrohydrodynamics (EHD) and aerodynamic droplet generators. For each droplet generator, the principle of operation and major features and characteristics are described. 

Droplet Generators that Use Disk-Type Piezoelectric Ceramics... 

A disk-type piezoelectric ceramic and some sequential pictures of droplet ejection from this droplet generator are shown in Fig. 25.5 [36]. The piezoelectric buzzer is constructed of a 0.2 mm piezoelectric ceramic layer, which sticks on a vibration diaphragm with a 27 mm diameter. It is fixed within the main body and bends when a voltage pulse is applied. The pressure is generated in the liquid flow channel and pushes the liquid out of the glass nozzle. 

Microfluidic generation of droplets is a method of droplet formation in microfluidic channels. It works by combining two or more streams of immiscible fluids and generating a shear force on the discontinuous phase causing it to break up into discrete droplets. In contrast to piezoelectric, pneumatic and acoustic forms of droplet generation, in this method, there is no need for an actuator to impose instabilities on the liquid jet. In the absence of an actuator, the size and polydisper-sity of the droplets are determined by the dimensions of microchannels, the flow rates of liquids, wetting properties of microchannels, etc. 

The piezoelectric chip generating the SAW is coupled to microfluidic devices. The flow actuated by the SAWs is nonintrusive. There are no mechanical moving parts inside. It can comprise sealed containers without external plumbing. SAWs have been used to manipulate droplets [2-4] and to mix and pump liquids [5-10]. 

Droplet generator Piezoelectric drop on demand Piezoelectric ink jet Piezoelectric micro-/ nanoliter droplet dispenser... 

A rotating-wheel interface has been devised to couple LC and CE with MS [57]. The LC effluent premixed with the MALDI matrix flows through a fused-silica capillary at the rate of 100 to 400 nLmin . The tip of the separation capillary is in contact with the rotating wheel. The solution deposited is dried rapidly in vacuum of the MALDI source, leaving a narrow trace of cocrystallized analyte-matrix mixture. The wheel is transported to the repeller, where laser desorption-ionization of the analyte-matrix mixture occurs. A similar system that uses a rotating ball coated with matrix for deposition of a single drop is also available for online LC/MALDI-MS [58]. The droplet deposition is controlled by a piezoelectric-actuated droplet generator. 

In the mid-1970s the piezoelectric ink-jet (PIJ) DoD system was developed (Figure 3(c)). The first piezoelectric DoD printer on the market was the serial character printer Siemens PT80 in 1977. Generally, four different modes for droplet generation by means of a piezoelectnc device were developed squeeze, bend, push, and shear. 

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