Two-step replica

Electron microscopy represents the only direct method that permits to see with our own eyes the interior of a sample with a resolution of a few nanometers. To characterize the texture of hypercrosslinked polystyrenes both transmission and scanning electron microscopy have been appfied. In the former case, ultrathin sections with a thickness of about 600 A were cut firom a sample fixed in epoxy resin, and then directly examined in transmission mode. Alternatively, two-step replicas have been prepared firom the cleavage face. To prepare the repfica the surface was first coated with a collodion film appfied from amyl acetate solution, and then with a carbon—platinum film. Finally, the collodion support was dissolved and the free carbon—platinum repfica examined under a transmission microscope. 

Figure 7.30 Electron macrographs of the networks prepared by post-crosslinking linear polystyrene (/M = 300,000 Da) with (a, b) p-xylylene dichloride (a) X=100%, (b) X=43% and (c, d) monochlorodimethyl ether (c) X=100%, (d) X=5% (a, b) two-step replicas, transmission electron microscopy, 46,600x (c, d) scanning electron microscopy, (c) 40,000x, (d) 100,000x. (After [198]).

Zhou et al. obtained nitrogen-doped titanium dioxide replicas via a two-step infiltration process with natural leaves as templates [220]. The replicas inherited the hierarchical structures of the natural leaf at the macro-, micro-, and nanoscales. These materials showed enhanced light-harvesting and photocatalytic hydrogen evolution activities. The photocatalytic water splitting activity of the artificial leaf structures was eight times higher than that of titanium dioxide synthesized without templates. 

Mord eux F, Kazanji M, Gabet AS, de Thoisy B, Wattel E (2001) Two-step nature of human T-cell leukemia virus type 1 replica don in experimentally infected squirrel morrkeys (Saimiri sciureus). J Virol 75 1083-1089. 

Transmission electron micrographs of two-step PS-carbon replicas taken from the surfaces of gold decorated samples deformed to the various values of draw ratio and containing 40 wt.% of modified chalk are presented in Fig. 6. Fig. 6a) shows a void around a filler particle in the early stage of deformation, the intermediate stage of deformation is shown in Fig. 6b), while the situation just before the sample fracture is presented in Fig. 6c). Presence of unoriented fraction of polymer matrix at the pole sides of voids and its decrease with the draw ratio, being in agreement with the theoretical predictions, is well documented by the above data. 

Fig, 6. Transmission electron micrographs of two-step PS-carbon replicas from the surfaces of gold decorated samples, a) initial, b) intermediate, c) final stages of deformation, Modified filler contents - 40 wt.%. 

Replica molding is a method to reproduce the desired structures by filling the mold with the particular material. It is used to create structures on the materials that are not easy to have patterns created. It has the advantages of low cost and the capability of mass production. Replica molding involves two steps 3D mold fabrication and mold transfer. 

Two stage, or double, replicas provide positive impressions of the specimen surface, although they require more time to prepare. The steps involved in formation of a two stage replica are ... 

For the 648-atom structure, the initial coordinates of the 648-atom sample were obtained from a previous computer-aided deposition simulation [25], The size of the cubic box was reduced in two steps from 27.736 A (amorphous density) to 27.150 A (density 0.0324 atoms/A ), which is incommensurate with the rock salt stmcture with this number of atoms. Complete crystallization was not expected and was not found at 600 K (see Fig. 17.13f), but the crystallite grew until making contact with its replica at the simulation cell boundaries. 

Thirty-two replicas were used, and exchanges were attempted every 0.2 ps (100MD steps). The temperatures (in K) were, respectively, 292.9, 300.0, 307.3, 314.8, 322.4,... 

Incubate the cultures at 37°C with shaking overnight. These strains will be used on Day 3 to isolate plasmid DNA. Place the two replica plates produced in step 3, agar side up, in the 37°C incubator overnight. 

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