Separation thousand-fold faster

Separation thousand-fold faster

12:56 PM, 18th July 2011
Separation thousand-fold faster
The separation of components in inhomogeneous blends can be accelerated even thousand-fold with an alternating electric field of adequately tuned frequency. The effect is presented by Natalia Ziebacz, a PhD student at the Institute of Physical Chemistry of the Polish Academy of Sciences.

WARSAW, POLAND: Numerous industrial processes make use of blends. Researchers from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) have studied how the external electric field affects the rate of component separation in blends composed of polymers and liquid crystals and those composed of various types of polymers. The observations gathered open interesting opportunities, eg, for the development of new composite materials.

Inhomogeneous blends of polymers with other polymers or liquid crystals are widely used in industrial applications - in LCD displays, gas-flow sensors, optical memories and other devices. Researchers from IPC PAS in Warsaw analysed the behaviour of such blends in alternating external electric field. “We managed to determine precisely the conditions permitting even a thousand-fold acceleration of component separation process in the blends under study,” said Prof Robert Holyst.

With time, many blends separate spontaneously into their components, usually at a low rate. The researchers from IPC PAS studied blends of a polymer with another polymer or liquid crystal. In the presence of an alternating electric field with the strength of several million volts per metre the ions of the component with higher conductivity start to move freely towards the electrode with the opposite charge. “Under these conditions, an additional force appears at the interface. With electric field alternating at appropriate frequency the ions start to yank the interface. Due to the yanking, the droplets of a component merge with each other significantly more efficiently than in the normal case, thus leading to a faster separation of both phases,” said Natalia Ziebacz, a PhD student, IPC PAS.

The separation efficiency of studied blends into their components is strongly dependent on the frequency of the applied electric field. Optical measurements carried out at the IPC PAS have shown that under optimal conditions, at frequencies up to the kilohertz range, the separation takes place even thousand-fold faster. The physical mechanism of the phenomenon suggests that similar effect can be expected in all blends contaminated with ions and containing components with different charge conductivities.

Controlling the rate of separation process over so long time range, extending over three orders of magnitude, opens the way to interesting applications. The separation process can be carried out quickly and then virtually stopped at a precisely selected stage. The structure of the blend so obtained can be then fixed, for instance by changing the temperature. Thus, the method to control separations of blends of polymers and liquid crystals using electric field turned out to be an excellent tool for the development of new materials. A patent application for the method has been filed.

© Institute of Physical Chemistry of the Polish Academy of Sciences News




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