Replication carbon replicas

Ordered porous carbons were synthesized by replication of colloidal templates made from 30 - 100 nm diameter silica spheres and removal of the silica templates using aqueous HP. To create the templates, the monodisperse particles were pressed into pellets and then sintered slightly at their points of contact. The silica template were filled with carbon precursor solution of divinylbenzene (DVB) and a free radical initiator, azobisisobutyronitrile (AIBN). Polymerization and carbonization of the precursor solution and subsequent dissolution of the silica templates leave a polycrystalline network of carbon with interconnected uniform pores. The degree of order of the silica template is faithfully reproduced in the carbon replicas. 

The removal of direct carbon replicas is dependent upon the polymer. Boiling xylene vapor was used to remove drawn PE from replicas [296] in work on drawn polymer morphology. Hobbs and Pratt [297] described a direct carbon replica method for replication of a PBT impact fracture surface by evaporation of platinum at 20° and PBT removal in hexafluor-oisopropanol (HFIP). Latex film coalescence in poly(vinyl acrylate) homopolymer and vinyl acrylic copolymer latexes was studied using direct replicas [298]. As the latex films have a low glass transition temperature, they were cooled by liquid nitrogen to about -150°C in the vacuum evaporator and shadowed with Pt/ Pd at 45° followed by deposition of a carbon support film at 90° to the specimen surface. The latex films were dissolved in methyl acetate/ methanol. TEM micrographs of the latex films show the difference between films aged for various times (Section 5.5.2). 

Several polymer studies have been reported where the specimens were prepared by freeze fracture techniques. A modification of the freeze fracture method was used by Singleton et ah [432] in the preparation of plasticized PVC. The sample was notched, cooled and fractured and then immediately replicated with platinum-carbon. Replicas were stripped after warming to room temperature. The authors noted that the preparation was not highly reproducible, perhaps due to nonuniform cooling of large specimens. The results of such a study must be compared with other characterizations for accurate analysis. 

Because of the nature of this templating synthesis, which involves introduction of a carbon precursor into pores of the template followed by carbonization and template dissolution, inverse carbon replicas of the OMS templates are obtained. Although carbon replicas of MCM-48 often undergo a symmetry change ° (Figure 12.7) and the MCM-41 replication results in disordered carbon rods, the SBA-15 replication permits exact inverse replicas (Figure 12.8). The observed differences in replication of the aforementioned OMSs are caused by structural differences of these templates. For instance, the MCM-41 and MCM-48 (P6 mm and Ia3d symmetry, respectively) OMSs are... 

Figure 10.19 (a) Replica of an etched surface of isotactic polystyrene crystallised at 215°C in the form of a thin film. Replication involved an extraction procedure whereby a thin film of crystalline material remained adhering to the carbon replica, (b) Electron diffraction pattern from the replica... 

Citrus pectin ( Polygalacturonic Acid Methyl Ester from Citrus Fruits, Grade I ) was obtained from the Sigma Chemical Company. It had a galacturonic acid content of 89% and a degree of esterification of 57. Separate aqueous solutions of citrus pectin were freeze-dried and air-dried in deionized water. These samples were replicated with 9.8A Pt/C and backed with 148A of carbon. The replicas for these samples were picked up without a carbon support film (38). 

The immunoreplica technique (14) is used when it is necessary to detect antigenic sites on the plasma membrane of cultured cells. The cells are cultured on coverslips, and are fixed as described above depending on the antibody in question, and immunolabeled in situ as described in Section 3.1.1.2., steps 3-9. After immunolabeling (Section 3.1.1.2., step 9), they are further fixed with 1% osmium tetroxide and are dehydrated in a graded series of ethanol (70, 90, 100%), critically point-dried, and replicated with a layer of carbon and platinum, The replicas are cleaned with sodium hypochlorite and chronic acid before examination with the transmission electron microscope. Large areas of the replicated plasma membrane remain intact for observation. Colloidal gold probes are probably the only probes of sufficient density that can be detected on these surfaces. 

A most useful technique for examining surface structure is that of replication. One method is to deposit the sample on a freshly cleaved mica surface on to which carbon (and, if desired, a heavy metal) is vacuum-evaporated. The resulting thin film, with the specimen particles still embedded, is floated off the mica on to a water surface. The particles are dissolved out with a suitable solvent and the resulting replica is mounted on a copper grid. 

Highly ordered mesoporous silica can be regenerated from a mesoporous carbon CMK-3 that is a negative replica of mesoporous silica SBA-15, indicating reversible replication between carbon and inorganic materials.[193] The advantage of this synthesis method is that it does not need to make the same silica material (template). This method is likely to be a valuable complement to the existing methods for the fabrication of new mesoporous silicas and other composition materials. 

The regenerated HUM-1 (T41/a),11941 a silica replica of mesoporous carbon, is a cubic mesoporous silica that is distinctly different from the original MCM-48 silica and represents a previously unreported new mesoporous silica material. HUM-1 does not possess the two noninterconnecting channel systems found in the starting MCM-48 framework. This new mesoporous silicate was prepared by a cyclic serial replication process and it may not be possible to make this material using the current conventional surfactant assembly methods employed for the synthesis of mesoporous silicas. 

Two kinds of template, viz. hard template and soft template, are usually available for nanocasting processes. The true liquid crystal templating synthesis can be considered a soft-template process. In general, the hard template means an inorganic solid. For example, mesoporous silica as a template to replicate other materials, such as carbon or metal oxides, by which the pore structure of the parent can be transferred to the generated porous materials. A 3-D pore network in the template is necessary to create a stable replica. Mesoporous silica and carbon are commonly used templates for nanocasting synthesis. 

Three different techniques, namely FFEM [20, 22], Cryo-Direct Imaging (Cryo-DI) [104] and freeze-fracture direct imaging (FFDI) [105], can be used to visualise the structure of micro emulsions. In FFEM the samples are prepared in a protected fashion in a sandwich. They are then rapidly frozen, fractured, shadowed with metal, and replicated with a thin carbon film. The replica of the fractured surface, the morphology of which is controlled by the sample s microstructure, is then studied by a TEM. In contrast to FFEM, in Cryo-DI thin films of the sample are rapidly frozen but immediately, without replication, trans-... 

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