Syringe Pump

Just like the maximum and minimum dispense rates, the accuracy of dispensing depends on the accuracy of both the syringe pump and the syringe being used. The Ossila syringe pump has a stepping accuracy of 0.16% which gives a rate accuracy of 19 nm.s^-1. However different syringes will have manufacturing tolerances on the internal diameter, the type of syringe used therefore will have a strong impact on the accuracy of flow rates.

Plastic disposable syringes commonly used due to their ease have the lowest tolerances with diameters that can vary by up to 3% depending upon the manufacturer, this can result in up to a 6% error in your dispense rate. Glass and stainless steel syringes have a higher tolerance with a maximum of 0.5% variation in the internal diameter, this results in a volume error of up to 1%.

The maximum applicable force can be varied in the system for use as an additional safety feature. At its maximum the pump can apply over 500N of linear force to the syringe. For a 50ml syringe this equates to a pressure of 4.37 bar placed upon the piston, while for a 5ml syringe this becomes as high as 47 bar. Most syringes are rated up to a certain maximum pressure, for plastic syringes this is 10 bar, glass syringes this can be as low as 1.5 bar or as high as 30 bar depending upon the make. Therefore setting maximum limitations within the software based upon the syringe manufacturers recommendations protects your syringes against damage.

As it has been designed to be a completely self-contained unit, no external controls are required in order to operate the system. With its built-in memory, up to 20 programmes each with 100 individual steps can be stored. This allows for the programming of complex processes, such as sequential deposition of multilayered structures.

The exit of the syringe can be connected to the spin coater via the use of PTFE tubing with female/male Luer lock adapters fitted at the ends. The diameter and length of the tubing used is dependent upon the total volume of solution you have as well as the viscosity of the solution. For highly viscous solutions we recommend a wider diameter pipe to maintain a lower overall pressure within the system.

At the exit of the tubing, we recommend using a blunt needle with a Luer lock adapter for the actual dispensing of solution into the spin coater. By selecting a specific gauge of needle the minimum droplet size can be varied for your experimental needs. The blunt ending also reduces the chances of injury or damage to equipment if used within a glovebox.

The ends of the needles can be positioned directly above the spin coater entrance by using clamps or other similar equipment. Alternatively a rubber stopper with a single hole in the middle can be used to hold the needle in position, we recommend a stopper size of 0 or 1 for the Ossila spin coater to get a tight fit within the lids hole.

The cause of solution dripping can be due to several factors, including: the syringe type being used, the presence of air bubbles, the viscosity of the solution, the density of solution, and the surface tension.

The most common cause of this occurrence is when a pressure difference between the inside of the syringe and the outside remains after the solution has been dispensed. This can happen when air bubbles are trapped inside the solution, resulting in a compression of the gasses during dispensing. After the pump has stopped, the compressed air expands and pushes solution out of the syringe. Similarly, for plastic syringes and pipes, elastic deformation. Over time, this can result in dripping of the solution.

This can be avoided by removing bubbles within the syringe before loading, using tubing and syringes that show limited amounts of elastic deformation, and reducing the overall pressures within the syringe. To avoid a build-up build up in the syringe lower dispense rates should be used, the viscosity of solution can be reduced, or the velocity of the solution can be reduced by increasing the diameter of pipes and needles.

Sometimes, dripping can be due to the use of dense solutions with low surface tensions and viscosities. The adhesive forces between i) the molecules in the solution, and ii) the surface of the needle and tubing can become lower than the gravitational force acting upon the solution within the tube. This results in the continuous dripping of solution, until the gravitational force acting on the solution in the tubing becomes lower than the combined adhesive forces of the solution and the increasing pressure difference due to the displaced volume.

To reduce the effects of dripping from dense, low surface tension solutions, a lower diameter of tubing and needles should be used. Alternatively, the tubing and needle can be tilted horizontally to reduce the gravitational force being exerted in the direction of the tubing.