Glycerol-silicone foams – Tunable 3-phase elastomeric porous materials

Enhanced Low-Density Silicone Foams Blown by Water-Hydroxyl Blends

Water, alcohols, diols, and glycerol are low-cost blowing agents that can be used to create the desired silicone foam structures. Although their combined use can be beneficial, it remains unclear how it affects the physical properties of the resulting materials. We conducted a comparative study of these hydroxyl-bearing blowing agents in fumed silica- and mica-filled polymer composite systems for simultaneous blowing and crosslinking to obtain a low-density, uniform porosity and superior mechanical properties. The foams were optimized for a uniform open-pore structure with densities ranging from 75 to 150 kg‧m-3. Varying the diol chain length (Cn) from one to seven carbons can alter the foam density and structure, thereby enhancing the foam tensile strength while maintaining a low density. Replacing 10 mol% of water with 1,4-butanediol decreased the density by 26%, while increasing the specific strength by 5%. By combining glycerol and water blowing, the resulting foams exhibited a 30% lower apparent density than their water-blown analogs. The results further showed that Cn > 4 alkane chain diols had an odd-even effect on the apparent density and cell wall thickness. All foamable compositions had viscosities of approximately 7000 cSt and curing times below 2 min, allowing for quick dispensing and sufficient time for the foam to cure in semi-industrial volumes.

A Super-Amphiphilic 3D Silicone Sponge with High Porosity for the Efficient Adsorption of Various Pollutants

Silicone sponge, which is nontoxic, highly flexible, insulated, and chemically inert, has great promise in the aerospace, electronics, and health care industries. However, the inherent surface properties and the harsh synthesis method limit its application. A super-amphiphilic 3D silicone sponge is designed by a thiol-ene click reaction for the first time. The sponge possesses high porosity, low density, excellent adsorption ability, and reusability for water, oil, emulsions, and Hg²⁺ or dyes or suspended solids in them. The sponge can selectively adsorb a very high amount (941.3 mg g^-1 ) of Hg²⁺ from solutions (water, oil, emulsions) containing various ions at a nearly 100% removal efficiency. Cation dyes can also be selectively captured by the sponge. Furthermore, the sponge is designed as a filter element for a filtration system, and the content of the pollutants in the filtrate reaches drinkable levels after the Hg²⁺ and dye solutions are processed. The filter can be reused with almost unchanged filtration efficiency after a simple washing process. The successful treatment of actual/artificial polluted water proves its practical value.

Interdigitated Sensor Based on a Silicone Foam for Subtle Robotic Manipulation

In this contribution, a soft sensor configuration based on silicone foam is developed to measure compressive forces in the range of 50 N with the aim of providing proprioceptive capabilities to conventional robotic manipulators based on hard materials. This then makes them capable of interacting with soft and fragile objects without damage. The concept relies on interdigitated electrodes that are patterned on the backside of the sensor to generate a fringing electric field into a soft compressible polymeric foam. The deformation of the foam causes changes to relative permittivity as the air-filled cells compress. The model in this article shows how the different parameters of the foam, such as air volume fraction, permittivity, and Young's modulus, affect the stiffness and electrical sensitivity of the sensor, and how controlling the porosity of the foam is key to optimizing the sensitivity of the sensor. This sensor is easy to fabricate and does not require compliant electrodes, while exhibiting high sensitivity values of 33% capacitance change for as little as 10 N applied force.