Thin Film Formation and Morphology of Electrosprayed Polydimethylsiloxane

Abstract

Low-voltage dielectric actuators (DEAs) can be fabricated using submicrometer-thin polydimethylsiloxane (PDMS) films. The two established techniques, namely spin coating and molecular beam deposition, however, are inappropriate to produce multistack DEAs in an efficient way. Therefore, we propose an alternative deposition technique, i.e., the alternating current electrospray deposition (ACESD) of 5 vol % PDMS in ethyl acetate solution and subsequent ultraviolet light curing. Atomic force microscopy makes possible the three-dimensional analysis of cured droplet-like islands. These circular islands, prepared on 2 in. Si(100) wafers from four polymers with molecular masses between 800 and 62,700 g/mol, reveal a characteristic morphology with an increasing height-to-diameter ratio. Using the 6000 g/mol polymer for ACESD, the film morphology evolution was tracked by applying conventional optical microscopy and spectroscopic ellipsometry. When the deposition was terminated after 13 s, circular islands with a mean height of 30 nm were found, while terminating the deposition after about 155 s led to a confluent layer with a mean height of 91 ± 10 nm. Potential electrostatic interactions between the droplets could not be identified through the analysis of spatial island distribution. Nevertheless, ACESD is a budget-priced and competitive deposition technique that can be employed to fabricate submicrometer-thin PDMS films with true nanometer roughness.

Polar Elastomers as Novel Materials for Electromechanical Actuator Applications

“…Despite of the very low driving voltage of 12 V with actuation strains of 10%, the rather complex set‐up and the required ultrahigh vacuum (10 −8 mbar) conditions needed for film formation make this process less attractive for large‐scale production, but may be attractive for high end‐applications . Contrary to MBD, thin film formation by electrospraying is rather fast, cheap, and has a high potential for industrial implementation …”

Electrospraying and ultraviolet light curing of nanometer-thin polydimethylsiloxane membranes for low-voltage dielectric elastomer transducers

“…The evaporation of liquid PDMS pre-polymers is limited to oligomers at low deposition rates, due to the thermal degradation of the used polymer [12]. As shown recently, electro-spraying of vinyl-terminated PDMS with an average molecular weight of 6,000 g/mol leads initially to a partially coalescent drop-like film with an average thickness of about 150 nm [13]. The confluent layers shown here were covered only by 75 %.…”

“…The elastic modulus of these layers can be tuned between 165 and 1'300 kPa. Compared to previous studies, the stable single-cone jet enabled us to produce a film that fully covered the substrate in less than one minute [13]. Subsequent UV-polymerization, without applying any photoinitiators, allowed us to form a homogenously crosslinked thin film.…”

Electro-spraying and ultra-violet light curing of polydimethylsiloxane to fabricate thin films for low-voltage dielectric elastomer actuators

“…Innumerable investigations were conducted on the materials permittivity [11]. Conversely, only a few studies on film thickness reduction are known [13][14][15]. To compensate for the low forces, which Here, we propose the ac electrospray method as an approach for future fabrication of nanometer-thin elastomer layers in low-voltage DEAs with the aim to realize artificial muscles for incontinence treatment [16,17].…”