Porous metals colloidal templates

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Include any more information that will help us locate the issue and fix it faster for you. Macroporous metals with strong diffractive properties at visible wavelengths can be synthesized from colloidal crystal templates.

The synthesis, characterization, and potential applications of macroporous metals created in this manner are summarized in this article. Advanced Materials — Wiley. Continue with Facebook. Sign up with Google. Log in with Microsoft. Bookmark this article. You can see your Bookmarks on your DeepDyve Library.

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They were placed on your computer when you launched this website. You can change your cookie settings through your browser. The present invention eliminated or sufficiently reduced this problem by laying down a very thin layer e. This effectively insulates the tin plating-bath electrolyte from the catalytic platinum surface and avoids bubble formation. There are many published methods of assembling colloidal spheres into a film layer.

Two alternate methods of assembling colloidal spheres into a film layer were selected for their convenience and simplicity. Other methods of assembling colloidal spheres into a film layer can be substituted by one skilled in the art. The first method is to immerse the substrate vertically in an aqueous-alcoholic dispersion of colloidal-sized e.

In each case, capillary forces between the particles will cause them to assemble into a crystalline, amorphous, or mixed crystalline-amorphous arranged film. As described above, the sphere arrangement depends on the size distribution of the sphere population used. Once the film is dry the spheres may optionally be slightly sintered together by heating the template below the melting point of the material composing the spheres e.

This procedure serves to assure that the spheres will interconnect and provide windows between the pores of templated materials; however, this interconnected pore structure is often obtained without heat-treating the template.

Once prepared, the template film was immersed in a suitable tin or tin alloy electroplating solution with proper counter and reference electrodes in a suitable configuration known to those versed in the art of high-quality metal electroplating.

Either potentiostatic metal deposition or any manner of pulsed potential profile may be used to electroplate the metal throughout the template. Preferably the plating process is stopped before the thickness of the metal film reaches the top of the sphere template. If metal plating is continued beyond this point, non-porous bulk metal will be formed and the template may be physically isolated from being extracted. The metal-sphere composite was then rinsed off in an appropriate wash solution e.

After thoroughly rinsing and drying, thermally and or by using negative pressure, the porous metal films are ready to be interfaced with a suitable lithium-ion containing electrolyte and a cathode material, as part of a lithium-ion secondary battery assembly process. Both Pt and Au were used in different samples. A plastic mask was fashioned out of a strip of Teflon, such that only certain areas of the slide were exposed to the conductive metal.

These slides were cut into smaller strips for use as substrates. Strips of indium tin oxide ITO coated glass, which were cut to about 1 cm wide, were also used as substrates after cleaning with isopropanol, dilute HCl, and deionized DI water. Vertical deposition was carried out by suspending substrates in vials containing dispersions of polystyrene spheres and allowing the solvent to evaporate.

A glass crystallization dish was used to slow the evaporation rate and to prevent contamination and convection currents. The goal was to determine quantitatively the relationships between concentration and thickness and between thickness and the degree of cracking. Non-functionalized polystyrene spheres contain negatively charged sulfate groups on the surface due to their synthesis method. Negatively charged polystyrene template may tend to delaminate from an electrode that is also negatively charged during the electrochemical reduction of tin ions.

In such a case, deposition of tin metal could occur between the template and the electrode, pushing the template forward with the metal formation. Thus, use of a positively charged PS template that would adhere more strongly with the applied bias during the tin electrodeposition process was described. These positively charged spheres flocculated from dispersions diluted with methanol or ethanol, so aqueous dispersions of these spheres, as well as the standard negatively charged spheres were used.

Deposition studies were made using ITO coated glass substrates in aqueous dispersions with sphere concentrations ranging from about 0. Dried films were examined by optical and electron microscopy.

Electron beam evaporated metal substrates offer several advantages over previously used copper foil tape, including: minimal interfacial effects, easily controlled geometry, greater uniformity, and smoothness. Results from polystyrene-film depositions using these substrates were indistinguishable from those using cleaned ITO-coated glass.

However, in either case, when negatively charged spheres from methanol dispersions were deposited, the film quality varied significantly. Some samples exhibited iridescence red transmission, green reflection which is characteristic of ordered sphere arrays, while others showed no iridescence and uneven coverage of films. Although the iridescent films exhibited a dense network of cracks, it was clear that the film appeared the same on the metallized portion of the substrate and the uncoated glass.

This result confirms that the edge between the Pt layer and the glass substrate did not significantly disrupt the structure of the polystyrene template. Polystyrene films prepared from positively charged spheres appeared quite different from the films acquired from the non-functionalized negatively charged spheres from methanol or water dispersions.

The positively charged films did not exhibit iridescence, but rather appeared hazy white in color. Also, samples from positively charged spheres exhibited much more uniform and smooth coverage than the substrates with negatively charged spheres. Optical and scanning electron microscopy also revealed several differences between films prepared from positive and negative spheres.

Both techniques showed that the positively charged templates exhibited less or no cracking compared to those from negative spheres. In addition, SEM showed the positively charged templates to be disordered while the negative templates are close packed into ordered face-centered cubic arrays.

Although the difference in assembly behavior was initially thought to be related to the surface charges of the spheres, subsequent SEM examination revealed that the difference is caused by a higher polydispersity of diameters in the positive spheres. The SEM images of corresponding films showed a disordered assembly of spheres. Additional SEM analyses revealed a large range of sphere sizes present in these templates. Large crack-free areas were observed from these disordered templates.

Analysis of optical microscopy images revealed that negatively charged arrays having a low size-polydispersity typically exhibited greater than three times the degree of cracking compared with positively charged sphere arrays having a high size-polydispersity. Moreover, many templates made from positively charged spheres using a variety of assembly conditions i.

In order to assess the differences between positively charged sphere arrays deposited from different concentrations of sphere dispersions and different temperatures, cross-sectional SEM measurements were also made.

By fracturing samples using a diamond-scribe and examining the fractured surface, film thickness was measured. Table 2 shows thickness measurements from cross sectional SEM results from some representative samples. A clear correlation between ordered sphere packing and film cracking was found. Ordered structures inherently possess anisotropy, due to the distinct crystallographic nature of the face-centered cubic close-packed lattice.

Since disordered structures are isotropic, shrinkage stresses are distributed uniformly. Also, since the spheres are not completely close-packed there is additional free volume that may accommodate relaxational re-assembly during the final shrinkage of the template that occurs during complete drying.

Templates containing a mass ratio of about nm diameter negatively charged polystyrene spheres were prepared from dispersions ranging from about 0. The thickness, sphere arrangement, and degree of cracking were assessed by SEM. In addition to mass ratios, the present invention also provided other mixtures of large to small such as and ratios of about nm diameter spheres. Both templates, which were prepared from about 0. The sample prepared with a ratio appeared iridescent green upon reflection, similar to the cracked, crystalline templates derived from nm sphere dispersion.

However, all of the iridescent samples made had been severely cracked, due to the anisotropic shrinkage of the template caused by the high degree of crystalline order. The effect of introducing a small number of nm spheres was to provide a distribution of point defect sites.

These defects break the crystalline symmetry and cause a relaxing of the overall structure such that no cracking occurs upon drying, even though the spheres between the off-sized defects appear perfectly close-packed. It is this local ordering that gives rise to the green iridescence. Both the and templates were also well suited for use in tin deposition. Porous metal films from templates made prepared in the ratio are especially well suited for theoretical and experimental modeling due to the high degree of local order as well as the relatively uniform pore size.

A disadvantage of the vertical deposition method is that only a relatively small fraction of the polystyrene spheres used to prepare each dispersion actually contributes to the film. The formation of aggregated particles precludes the reuse of these slurries.

Thicker templates that lead to thicker porous tin films are desirable in the fabrication of commercially useful battery anodes e. Porous tin films of 3 microns thickness will have anode mass of less than 1 mg, making accurate measurement of anode capacity difficult. For these reasons, the present invention also provides a method of template formation that does not waste large quantities of spheres and that reliably produces thick films of high quality.

The method of spreading a small volume of a concentrated sphere dispersion e. After evaporation, which took only about minutes, a uniform film with good adherence to the substrate was obtained FIGS. Platinum-on-glass conductive substrates for use in sphere array and tin deposition experiments were prepared as described previously.

Polystyrene sphere arrays were prepared by the vertical deposition method. Polystyrene spheres having an average diameter of about nm with positively charged surface groups were obtained from Bangs Labs, Inc.

Template films were typically prepared from about 0. Tin was electroplated from two separate baths: tin tetrafluoroborate and tin sulfate. To prepare the tin sulfate bath, solid tin sulfate was dissolved in 0. In addition, nonionic triblock copolymer Pluronic L64 was added to some solutions for the purpose of hindering dendrite formation.

Potentiostatic depositions were performed from both baths, on bare Pt-on-glass substrates, and on substrates containing polystyrene sphere arrays. The results are shown in FIG. The pore structure is disordered, as expected from the disordered template FIG. Pores in this material range from about nm in diameter, which satisfies the structural needs of high surface areas and low diffusion distances through the metal for use as a high-performance lithium-ion anode.

A tin sulfate bath was used as described previously 0. Polystyrene templates were dissolved in toluene after the tin electrodeposition. However, the metal structure did not appear to represent the desired high-porosity inverse of the polystyrene. Significant morphological improvements in the structure of electrodeposited tin, including smaller grain size reduction and greater throwing power, were obtained through the use of pulsed electroplating instead of using direct current.

Using the pulsed deposition, the present invention provides a significant morphological improvement in the tin as compared to the direct current. Hot toluene was used in order to insure complete dissolution of all polystyrene. The present invention thus creates submicron porous metal electrodes with designed morphologies. The porosity provides a high surface area of interface between the anode and the electrolyte, as well as a significant free volume in which the lithium-tin alloy can expand.

Additionally, if diffusion distances in the metal are limited to the submicron size scale then the electrochemical insertion and extraction of lithium from tin occur more homogeneously. DeepDyve requires Javascript to function. Please enable Javascript on your browser to continue.

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