Mechanically invisible encapsulations

Research into dielectric elastomers has intensified within the last two decades, due to the realisation that these materials undergo significant deformations when subjected to high electric fields. High efficiency, lightweight, low-cost and simple working principles are the main advantages of this technology.

A major part of the research on dielectric transducers is dedicated to the development of elastomeric membranes that create a basis for each potential application. It has been recognised that higher energy density and more durable materials need to be created in order to enable the commercialisation of such devices.

Therefore, this project was dedicated to exploring the possibility of using polar liquids as high dielectric constant fillers for dielectric PDMS-based elastomers. Incorporating polar liquids in the form of discrete droplets into nonpolar membrane swas expected to produce a two-fold improvement with respect to a reference material.

Firstly, dielectric constant enhancement and, secondly, a Young’s modulus decrease were anticipated. In the first approach a flow-focusing microfluidic technique was employed, in order to encapsulate polar liquids within a soft elastomeric shell. The produced core-shell microspheres served as a carrier for liquids, enabling the uniform dispersion of the filler droplets within PDMS prepolymer.

The dielectric constant of the prepared water-PDMS composite was proven to be enhanced by 30% following the incorporation of 4.5 wt.% of water. Due to the favourable structure of the capsules, mechanical properties remained unaffected. Importantly, the approach substantiated the high potential of liquid-PDMS composites for dielectric transducers.

In the second part of the study a new method for producing liquid-PDMS composites was developed and thoroughly investigated. Applying very high shear forces to mixtures of PDMS preelastomers and polar liquids facilitated the preparation of stable and uniform emulsions. Upon crosslinking the PDMS (which formed the continuous phase of the emulsions), stable hybridelastomers were obtained.

The method allowed for incorporating up to 50% by volume of various liquids, which resulted in significant improvements to the dielectric constant of the composites. An incorporation of 120 wt.% of glycerol increased the dielectric constant of a commercial PDMS composition by 380%. Additionally a three-fold decrease in the elastic modulus was observed.

Although the dielectric properties of the composites were very promising, the materials exhibited leakage current at high electric fields. Therefore, further study on improving high-voltage performance was conducted, exhibiting the high potential of the material. The second approach brought a breakthrough in the research on liquid-PDMS composites.

The developed technique proved to be very versatile, thereby allowing for the preparation of multiplehybrid materials with very distinct properties – an attractive proposition from the point of view of multiple scientific fields.