10 research outputs found
Deformation Behavior of Foam Laser Targets Fabricated by Two-Photon Polymerization
Two-photon polymerization (2PP), which is a three-dimensional micro/nano-scale additive manufacturing process, is used to fabricate component for small custom experimental packages (ātargetsā) to support laser-driven, high-energy-density physics research. Of particular interest is the use of 2PP to deterministically print millimeter-scale, low-density, and low atomic number (CHO) polymer matrices (āfoamsā). Deformation during development and drying of the foam structures remains a challenge when using certain commercial acrylic photo-resins. Acrylic resins were chosen in order to meet the low atomic number requirement for the foam; that requirement precludes the use of low-shrinkage organic/inorganic hybrid resins. Here, we compare the use of acrylic resins IP-S and IP-Dip. Infrared and Raman spectroscopy are used to quantify the extent of the polymerization during 2PP vs. UV curing. The mechanical strength of beam and foam structures is examined, particularly the degree of deformation that occurs during the development and drying processes. The magnitude of the shrinkage is quantified, and finite element analysis is used in order to simulate the resulting deformation. Capillary drying forces during development are shown to be small and are likely below the elastic limit of the foam log-pile structures. In contrast, the substantial shrinkage in IP-Dip (~5ā10%) causes large shear stresses and associated plastic deformation, particularly near constrained boundaries and locations with sharp density transitions. Use of IP-S with an improved writing procedure results in a marked reduction in deformation with a minor loss of resolution
Surface deposition and encapsulation of metallic clusters
In this work metallic clusters are produced by both encapsulation in an aerogel matrix and deposition on a surface. Entrapment of metal clusters inside aerogels is accomplished through synthesis of a hydrogel precursor, washing it with an aqueous metal salt solution, and controlled reduction of the metal. Although the aerogel matrix stabilizes and prevents subsequent loss or aggregation of the clusters once they are produced, controlling the rate of reduction is key to the size and morphology of the clusters. In order to do this, both radiolytic and chemical reduction methods are used --Abstract, page iv
Deformation Behavior of Foam Laser Targets Fabricated by Two-Photon Polymerization
Two-photon polymerization (2PP), which is a three-dimensional micro/nano-scale additive manufacturing process, is used to fabricate component for small custom experimental packages (ātargetsā) to support laser-driven, high-energy-density physics research. Of particular interest is the use of 2PP to deterministically print millimeter-scale, low-density, and low atomic number (CHO) polymer matrices (āfoamsā). Deformation during development and drying of the foam structures remains a challenge when using certain commercial acrylic photo-resins. Acrylic resins were chosen in order to meet the low atomic number requirement for the foam; that requirement precludes the use of low-shrinkage organic/inorganic hybrid resins. Here, we compare the use of acrylic resins IP-S and IP-Dip. Infrared and Raman spectroscopy are used to quantify the extent of the polymerization during 2PP vs. UV curing. The mechanical strength of beam and foam structures is examined, particularly the degree of deformation that occurs during the development and drying processes. The magnitude of the shrinkage is quantified, and finite element analysis is used in order to simulate the resulting deformation. Capillary drying forces during development are shown to be small and are likely below the elastic limit of the foam log-pile structures. In contrast, the substantial shrinkage in IP-Dip (~5ā10%) causes large shear stresses and associated plastic deformation, particularly near constrained boundaries and locations with sharp density transitions. Use of IP-S with an improved writing procedure results in a marked reduction in deformation with a minor loss of resolution
Synthesis of Homogeneous Alloy Metal Nanoparticles in Slica Aerogels
Homogeneous alloy nanoparticles of the noble metals gold and silver were formed in silica aerogels. In our synthesis procedure, silica aquogels were first prepared with a standard base-catalyzed route, washed several times with distilled water, and then bathed in an aqueous solution with a total metal ion concentration of 3 Ć 10ā4 M. Formaldehyde (0.5 M) was then added as a reducing agent, with NaOH, in a typical concentration of 1-2 mM, employed to control the velocity of reduction. After reduction, the gels were washed, and then dried supercritically (from CO2) to yield aerogels. The optical absorption of the gels exhibits a single plasmon peak that shifts linearly to higher wavelengths when the Au mole ratio is increased. These results indicate that bimetallic nanoparticles are formed, and that the metals are homogeneously alloyed. Transmission electron microscopy shows that the diameter of the metal nanoparticles depends on the molar ratio of metals used in the bathing solution of the aquogel precursor, and ranges from a minimum of not, vert, similar20 nm (100% Au sample) to a maximum of 70-80 nm (25 at.% Au). Energy-dispersive X-ray analysis confirms that the nanoparticles are bimetallic, with a mean mole ratio within 15% of the bathing solutio
Room Temperature Synthesis of Noble Metal Clusters in the Mesopores of Mechanically Strong Silica-Polymer Aerogel Composites
Clusters of Ag and Au have been formed in the bulk of mechanically strong silica-polymer aerogel composite monoliths. For that purpose, base-catalyzed silica hydrogels were washed with a 50% w/w acetone/diisocyanate (di-ISO) solution, and cured at 55Ā°C for 3 days. Unreacted di-ISO solution was washed off with acetone, and the gels were washed with a acetone solutions of Ag+ or AuCl- 4 (3 Ć 10-4 mol Ā· L-1), containing also 0.2 mol Ā· L-1 of 2-propanol as radical scavenger. Metal clusters were formed upon radiolytic reduction (gamma rays, 48-72 h, 7-7.5 kGy) of the precursor ions. After irradiation, the hydrogels were washed with acetone, and dried in supercritical CO2. The resulting aerogel monoliths had a density of 0.56 gĀ·cm-3, a surface area of about 160 m2 Ā· g-1, and an average pore diameter of about 200 nm. Transmission electron microscopy showed that the metal clusters are free of contamination, with a cubic face centered structure, and a narrow size distribution, centered around 10 nm. The elastic module, measured with a three-point flexural bending method, was in the 60-70 MPa range, and the load at rupture between 16 and 19 kg. Thermogravimetric analysis showed that the composites were stable up to about 300Ā°C. These results are in excellent agreement with results obtained previously for as-grown, di-ISO cross-linked silica aerogels, and show that addition of metal clusters and gamma irradiation to a dose corresponding to a permanence of several years in low earth orbit at high inclination did not affect the chemical identity, the mechanical strength, the porosity and the bulk density of the composite aerogel monoliths
Synthesis of Aerogel-Metal Cluster Composites by Gamma Radiolysis
Noble metal clusters (Ag, Au) were formed in a silica aerogel matrix by gamma irradiation of hydrogel precursors loaded with aqueous solutions containing Ag+ or [AuCl4]- ions. Hydrogels exposed to gamma rays assumed the color expected for colloidal suspensions of Ag (respectively Au) clusters. The hydrogels were subsequently washed and supercritically dried, without any evident change in color, indicating that the metal clusters were not removed during drying. Typical gamma ray doses were between 3 and 3.5 kGy, and achieved complete reduction of hydrogels containing metal ion concentrations in the 10-4-10-3 M range. Metal clusters in the aerogel monoliths were characterized with optical absorption, transmission electron microscopy, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. These techniques have shown that the clusters have a crystalline fee structure. Au clusters consist of pure Au, while surface oxidation of Ag clusters was observed with XPS
Formation and Entrapment of Noble Metal Clusters in Silica Aerogel Monoliths by Ī³-Radiolysis
Noble metal clusters (Ag, Au) were formed in a silica aerogel matrix by Ī³-irradiation of hydrogel precursors loaded with aqueous solutions containing Ag+ or [AuCl4]- ions. Hydrogels exposed to Ī³-rays assumed the color expected for colloidal suspensions of Ag (respectively Au) clusters. The hydrogels were subsequently washed and supercritically dried, without any evident change in color, indicating that the metal clusters were not removed during drying. Typical Ī³-ray doses were between 2 and 3.5 kGy, and achieved complete reduction of hydrogels containing ion concentrations in the 10-4ā10-3 M range. Reduction of solutions with higher metal ion concentrations was achieved by multiple irradiations. In the case of Ag+ reduction, we noticed that the radiolytic yield G was higher than that of the reducing radicals equal to G = 6 Ć 10-7 mol/L of reducing species per joule of absorbed energy. For example, a total dose of 3.5 kGy has led to a reduction of 5.7 Ć 10-2 M in a hydrogel with [Ag+] = 0.1 M. The high radiolytic yield has been attributed to radiation-induced oxide surface catalysis, or to autocatalysis, but the precise mechanism has not been determined. Metal clusters in the aerogel monoliths were characterized with optical absorption, transmission electron microscopy, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. These techniques have shown that the clusters have a crystalline fcc structure. Au clusters consist of pure Au, while surface oxidation of Ag clusters was observed with XPS
High Resolution Patterning of Silica Aerogels
Three-dimensional metallic structures are fabricated with high spatial resolution in silica aerogels. In our method, silica hydrogels are prepared with a standard base-catalyzed route, and exchanged with an aqueous solution typically containing Ag+ ions (1 M) and 2-propanol (0.2 M). The metal ions are reduced photolytically with a table-top ultraviolet lamp, or radiolytically, with a focused X-ray beam. We fabricated dots and lines as small as 30 Ć 70 Ī¼m, protruding for several mm into the bulk of the materials. The hydrogels are eventually supercritically dried to yield aerogels, without any measurable change in the shape and spatial resolution of the lithographed structures. Transmission electron microscopy shows that illuminated regions are composed by Ag clusters with a size of several Ī¼m, separated by thin layers of silica