3D Printing of Viscoelastic Suspensions via Digital Light Synthesis for Tough Nanoparticle–Elastomer Composites
3D Printing of Viscoelastic Suspensions via Digital Light Synthesis for Tough Nanoparticle–Elastomer Composites
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The rheological parameters required to print viscoelastic nanoparticle suspensions toward tough elastomers via Digital Light Synthesis (DLS) (an inverted projection stereolithography system) are reported. With a model material of functionalized silica nanoparticles suspended in a poly(dimethylsiloxane) matrix, the rheological-parameters-guided DLS can print structures seven times tougher than those formed from the neat polymers. The large yield stress and high viscosity associated with these high concentration nanoparticle suspensions, however, may prevent pressure-driven flow, a mechanism essential to stereolithography-based printing. Thus, to better predict and evaluate the printability of high concentration nanoparticle suspensions, the boundary of rheological properties compatible with DLS is defined using a non-dimensional Peclet number (Pe). Based on the proposed analysis of rheological parameters, the border of printability at standard temperature and pressure (STP) is established by resin with a silica nanoparticle mass fraction (ϕsilica) of 0.15. Above this concentration, nanoparticle suspensions have Pe > 1 and are not printable. Beyond STP, the printability can be further extended to ϕsilica = 0.20 via a heating module with lower shear rate to reduce the Pe < 1. The printed rubber possesses even higher toughness (Γ ≈ 155 kJ m−3), which is 40% higher over that of ϕsilica = 0.15.
The rheological parameters required to print viscoelastic nanoparticle suspensions toward tough elastomers via Digital Light Synthesis (DLS) (an inverted projection stereolithography system) are reported. With a model material of functionalized silica nanoparticles suspended in a poly(dimethylsiloxane) matrix, the rheological-parameters-guided DLS can print structures seven times tougher than those formed from the neat polymers. The large yield stress and high viscosity associated with these high concentration nanoparticle suspensions, however, may prevent pressure-driven flow, a mechanism essential to stereolithography-based printing. Thus, to better predict and evaluate the printability of high concentration nanoparticle suspensions, the boundary of rheological properties compatible with DLS is defined using a non-dimensional Peclet number (Pe). Based on the proposed analysis of rheological parameters, the border of printability at standard temperature and pressure (STP) is established by resin with a silica nanoparticle mass fraction (ϕsilica) of 0.15. Above this concentration, nanoparticle suspensions have Pe > 1 and are not printable. Beyond STP, the printability can be further extended to ϕsilica = 0.20 via a heating module with lower shear rate to reduce the Pe < 1. The printed rubber possesses even higher toughness (Γ ≈ 155 kJ m−3), which is 40% higher over that of ϕsilica = 0.15.
Published 1 paper as the 3rd author on Advanced Materials
Printer setup and resin design. a) Schematic illustration of the continuous bottom-up stereolithography (DLS), with the arrow indicating motion directions of the build-head. b) Photochemistry of the 3D printable silicone nanocomposite, with TEM images of ϕR202 = 0.05 silicone. c) Photorheological comparison of the neat 5% VS6000 resin and different suspensions. d) Uniaxial tensile tests of the cured silicone nanocomposites. e) First cycle of silicone nanocomposites from cyclic tensile tests, where the strain range is 0 to 0.6 γult.
Rheological properties of silica suspensions. a) Shear viscosity of the silica-siloxane suspensions with inlet figure showing a resin demo of ϕR202 = 0.15. b) Oscillatory strain amplitude sweep measuring the storage modulus (G′-closed dots) and loss modulus (G″-open dots) versus shear stress of the silica suspensions. c) Yield stress (τy, defined as the stress when G′ = G″) as a function of silica content (ϕR202), with the solid red line showing the exponential fitting (τy ∝ ϕR202) of yield stress with increasing ϕR202. d) Frequency sweep of silica-siloxane suspensions, where closed dots represent G′ and open dots represent G″.
3D printed pyramid demos via DLS. The demos are printed from neat 5% VS6000 (a), ϕR202 = 0.05 (b) and ϕR202 = 0.15 (c) resins. The laser confocal microscopy (LCM) images showed the front views (FV) and top views (TV) of the stairs with different surface roughness, Sq. The scale bars in the optical images represent 10 mm. d) Contour of one single stair extracted from FV images of CAD (dashed line) and different ϕR202.
Heating assisted DLS. a) Schematic design of the heating-assisted DLS. b) A 3D printed silicone pyramid with ϕR202 = 0.20 through heating-assisted DLS. c) Uniaxial tensile tests of molded and printed ϕR202 = 0.20. d) Temperature sweep of the silica–silicone suspensions with different ϕR202 from 30 to 100 °C. e) G″/ω versus ω of ϕR202 = 0.20 under different temperatures. f) Calculated Peclet number (dashed line) with temperature for different printing speed. The parameter used for successful printing is indicated in the figure.
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