Additive manufacturing (AM) of aerogels increases the achievable geometric complexity, and affords fabrication of hierarchically porous structures. In this work, a custom heated material extrusion (MEX) device prints aerogels of poly(phenylene sulfide) (PPS), an engineering thermoplastic, via in situ thermally induced phase separation (TIPS). First, pre‐prepared solid gel inks are dissolved at high temperatures in the heated extruder barrel to form a homogeneous polymer solution. Solutions are then extruded onto a room‐temperature substrate, where printed roads maintain their bead shape and rapidly solidify via TIPS, thus enabling layer‐wise MEX AM. Printed gels are converted to aerogels via postprocessing solvent exchange and freeze‐drying. This work explores the effect of ink composition on printed aerogel morphology and thermomechanical properties. Scanning electron microscopy micrographs reveal complex hierarchical microstructures that are compositionally dependent. Printed aerogels demonstrate tailorable porosities (50.0–74.8%) and densities (0.345–0.684 g cm−3), which align well with cast aerogel analogs. Differential scanning calorimetry thermograms indicate printed aerogels are highly crystalline (≈43%), suggesting that printing does not inhibit the solidification process occurring during TIPS (polymer crystallization). Uniaxial compression testing reveals that compositionally dependent microstructure governs aerogel mechanical behavior, with compressive moduli ranging from 33.0 to 106.5 MPa.
Fresnel lens arrays are widely employed in concentrator photovoltaics, photonic devices, and integral imaging systems. In this study, a rapid non-isothermal imprinting process for Fresnel lens arrays was proposed. In this process, a heated mold with microstructures was momentarily pressed onto a thermoplastic polymer surface that was initially kept at room temperature. The microstructures of the mold can be copied completely to the polymer substrate by imprinting consecutively until a continuous surface Fresnel lens array is obtained. Different from more traditional molding processes, the substrate does not need to be heated and cooled repeatedly in the replicating process. In addition, the imprinting process is carried out at room temperature, which can greatly reduce the thermal cycle time and energy consumption. Generally speaking, the material flow and stress distribution of the substrate need to be monitored so that the microlenses with a high precision surface finish can be produced in the non-isothermal imprinting process. To verify this, the finite element method (FEM) model for the non-isothermal process was established, and the feasibility of this process was analyzed. A hexagonal continuous surface Fresnel lens array was then fabricated, and its geometrical contour and imaging performance were tested. The experimental results showed this new process could be an effective and low-cost optical fabrication technology for high-quality production of Fresnel lens arrays.
more » « less- NSF-PAR ID:
- 10208854
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Applied Optics
- Volume:
- 60
- Issue:
- 2
- ISSN:
- 1559-128X; APOPAI
- Page Range / eLocation ID:
- Article No. 351
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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