Silicone thinner

Room temperature liquid alloy galinstan, GaInSn (68.5 wt% gallium, 21.5 wt% indium, 10 wt% tin, with viscosity of 2.4 × 10⁻³ Pa∙s, from Geratherm Medical AG, Geschwenda, Germany) was used as the inner flow. It was used without any pre-processing and post-processing [30 (link),31 (link)].
A silicone (polydimethylsiloxane, PDMS) kit, Elastosil RT601 A and B (mixed at a weight ratio of 9:1, Wacker Chemie, Munchen, Germany) was used as outer channel flow. The diluted PDMS was prepared by adding 3 wt% thinner (Silicone Thinner, Smooth-On, Macungie, PA, USA) to the mixed PDMS. To tune the surface tension, a 0.33 wt% surfactant Silwet L-77 (GE, Boston, MA, USA) was added to the PDMS mixture. Afterwards, the whole mixtures were put in vacuum for 10 min to eliminate bubbles. Ecoflex 0030 (Smooth-On, Macungie, PA, USA), another kind of silicone kit (mixed at a weight ratio of 1:1), was used to improve the stretchability of printed devices.
The viscosities of pure PDMS, diluted PDMS and surfactant added PDMS are 4.73 Pa∙s, 4.39 Pa∙s and 13.2 Pa∙s, respectively, which are measured by a rheometer (DHR-1, TA, New Castle, DE, USA) after the silicones were prepared for 10 min. All measurements were conducted at 20 °C with preliminary equilibration time of 1 min.

The deposited material was the UV-curable silicone elastomer Silopren UV Electro 225 (hereafter referred to as UV Electro; Momentive Performance Materials, Inc., Waterford, NY). Different ratios of Silicone Thinner (Smooth-On, Inc., Macungie, PA) were mixed with UV Electro to achieve the desired material stiffness, that is, adding thinner resulted in lower cured stiffness. The silicone was prepared by first pouring 1 g of thinner into a small mixing container to ensure that the more viscous silicone components that would be subsequently added would not be as susceptible to sticking to the bottom of the container.
Next, the base and catalyst of UV Electro with a 1:20 ratio (base:catalyst by weight) were added, followed by the desired quantity of remaining thinner (discussed below). For visual analysis, pigment (Silc Pig; Smooth-On, Inc.) was occasionally added to provide a color gradient when printing. These components were mixed for 2 min at 2350 rpm using a planetary centrifugal mixer (DAC 150.1 FVZ-K SpeedMixer; FlackTek, Landrum, SC), poured into a syringe, and degassed as needed.