Polymers exhibit a rich range of properties in almost any physical aspect. Electrical properties are no exception, and whereas some polymers may conduct electricity, most are considered good insulators (they do not readily conduct electrical current). Recent developments have created families of polymers with enhanced conductivity and these innovative materials allow the partial replacement of traditional conductors, such as copper, with flexible polymer conductors. CPG can assist with developing these advanced materials.
The more conventional use of polymers remains as insulators, where low conductivity is important and their role is to isolate two conductors from each other. However, as is often the case, this simple picture is not adequate to describe the behavior or an insulator in the electrical field. Low conductivity alone is not sufficient to describe the performance of these materials. Another critical parameter (amongst others!) strongly influences the possible end-use of these materials is the permittivity of the material.
Relative Permittivity: Energy Storage in a Polymer
When an insulator is placed in an electric field, the field can induce polarization in the molecules of the material. This polarization results in stored energy that can be leveraged for various uses. For most polymers, this polarization is negligible and the polymer does not change the behavior of the field relative to vacuum. In such cases, the material is said to have a relative permittivity (or the dielectric constant, a legacy term, but still in common usage) of 1.
However, a high permittivity material is key to the success of capacitors and transformers since this parameter describes the additional energy stored by the material in an electric field. Understanding the nature of this process is critical because if storage of energy is not required (just insulation), accidental charge build up in an unintentional capacitor can have profound consequences. Further, because the polarization induced is not instantaneous, the permittivity, and thus the manner in which materials interact with oscillating fields, is frequency dependent. In healthcare, these parameters are important in sensors or tool that utilize electrical energy, such as microwave and radiowave telemetry, ablation tools and even MRI.
Measuring Relative Permittivity
ASTM D150 outlines the standard practices for measuring the relative permittivity of a material. The standard assumes these materials are solids and describes several methods of measuring this property, depending on the nature and form of the material through the measurement of the capacitance of the material within a carefully constructed fixture. At CPG, we use the Keysight 16451B fixture.
Cambridge Polymer Group also possesses the means to measure the permittivity of liquids using the Keysight 16452A fixture. The measurement is based on the same principles but fills the capacitor with the liquid sample. We have also developed techniques to measure this property in weakly conducting materials where the conventional method using parallel conducting plates is not adequate. This final measurement is important in areas of healthcare where radio or microwaves interact with tissue because tissues generally are filled with salts that make them conductive.
Dielectric Breakdown Testing
Another closely related property is dielectric breakdown, which describes the point at which an insulating material transitions to a conductor under high voltage stress. Cambridge Polymer Group can also assist in measuring this parameter.
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Whether you are exploring advanced conductive polymers or optimizing traditional insulating materials, Cambridge Polymer Group offers tailored solutions and state-of-the-art testing to support your innovation needs.