Porous Polymer Structures with Tunable Mechanical Properties Using a Water Emulsion Ink

Abstract

Recently, the manufacturing of porous polydimethylsiloxane (PDMS) with engineered porosity has gained considerable interest due to its tunable material properties and diverse applications. An innovative approach to control the porosity of PDMS is to use transient liquid phase water to improve its mechanical properties, which has been explored in this work. Adjusting the ratios of deionized water to the PDMS precursor during blending and subsequent curing processes allows for controlled porosity, yielding water emulsion foam with tailored properties. The PDMS-to-water weight ratios were engineered ranging from 100:0 to 10:90, with the 65:35 specimen exhibiting the best mechanical properties with a Young's Modulus of 1.17 MPa, energy absorption of 0.33 MPa, and compressive strength of 3.50 MPa. This led to a porous sample exhibiting a 31.46% increase in the modulus of elasticity over a bulk PDMS sample. Dowsil SE 1700 was then added, improving the storage capabilities of the precursor. The optimal storage temperature was probed, with -60 °C resulting in great pore stability throughout a three-week duration. The possibility of using these water emulsion foams for paste extrusion additive manufacturing (AM) was also analyzed by implementing a rheological modifier, fumed silica. Fumed silica's impact on viscosity was examined, revealing that 9 wt% of silica demonstrates optimal rheological behaviors for AM, bearing a viscosity of 10,290 Pa·s while demonstrating shear-thinning and thixotropic behavior. This study suggests that water can be used as pore-formers for PDMS in conjunction with AM to produce engineered materials and structures for aerospace, medical, and defense industries as sensors, microfluidic devices, and lightweight structures.

Keywords: 3D printing; foam; polydimethylsiloxane (PDMS); rheology; tunable mechanical properties.

Figure 1

Foam Preparations, (A) PDMS synthesis, (B) centrifugal mixing, (C) DIW printing, (D) mold preparation, (E) thermal curing.

Figure 2

50:50 PDMS-to-water sample.

Figure 3

SEM images of water emulsion foams with varying PDMS-to-Water ratios, (A) specimen A, (B) specimen B, and (C) specimen C as described in Table 1.

Figure 4

Stress-strain curves for specimens A, B, C, and bulk PDMS generated through compression testing.

Figure 5

SEM images of specimen B (A) immediately after curing, (B) after 48 h (C) after 7 days of refrigerated storage.

Figure 6

SEM images of water emulsion foams with varying Sylgard 184: SE 1700 ratios, (A) specimen D, (B) specimen E, (C) specimen F, and (D) specimen G, as described in Table 3.

Figure 7

SEM images of water emulsion foams with optimized storage procedure for specimen A (A) before and (B) after a 3-week storage life in freezing temperatures.

Figure 8

Effects of specimen porosity as a function of specimen precursor viscosity under conditions of −60 °C and 20 °C.

Figure 9

Rheological properties of water emulsion foams show (A) shear thinning and (B) shape retention behavior.

Figure 9

Rheological properties of water emulsion foams show (A) shear thinning and (B) shape retention behavior.