Polymer-Based Soft-Template Processes

A similar approach was also used in the case of poly(vinyl alcohol) (PVA). In 1999, Wang et al. used a soft-template method based on PVA/isopropanol/ water micelles, and operated the Cu reduction by means of borohydride [203] more recently, Khanna et al. obtained Cu NPs in PVA/water emulsions, by employing hydrazine hydrate or sodium formaldehyde sulfoxylate as reducing agents [204]. 

It should be noted here that the use of polymer/surfactant complex mixtures such as those proposed in Ref. [202] seems particularly promising, due to some additional advantages. Surfactants associated with a polymeric additive may form micelles at concentrations considerably lower than those required by the surfactant alone. Moreover, in the case of polymer/surfactant mixtures, stabilization of the inorganic crystals may benefit from synergetic capping effects that improve both morphological stabihty and homogeneity [202]. 

Poly(vinylpyrrolidone) (PVP) is certainly one of the most investigated polymeric additives for the template Cu NP synthesis, having been employed in aqueous [205-208], amide [209], polyol [210-214] and alcohol solvents [215, 216]. 

In the first of these cases, spherical NPs were easily obtained by conventional reduction of a Cu salt in the presence of alkaline borohydride [205, 207] or ascorbic acid [206] aqueous reducing solutions. Recently, a continuous and steady-flow reactor was proposed, in which a metal displacement reaction occurred. Basically, this involved a spontaneous redox reaction between Cu ions and an 

Interestingly, processes involving the use of polyol/alcohol solvents appear as a form of modified/improved version of the polyol method, in which the polyol/ alcohol solvent is assisted by a specific (and generally stronger) reducing agent, such as hydrazine [215, 216), sodium phosphinate monohydrate [212] or ascorbic acid [210, 211). The simultaneous presence of PVP and solvents with alcoholic moiehes made it possible to obtain monodisperse copper nanocubes [211], nanoparhcle arrays and aggregates [216] or nanorods [216], as a function of the experimental conditions. 

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For all forms of DNA, hydrogen bonding between the two spiral chains stabilizes the double helix. Replication of DNA occurs when the hydrogen bonds are broken, and the two strands are separated. These form the templates that are used to make identical copies, via enzymes called DNA polymerases. In fact, the second strand of the double helix is complementary to the first, it contains no extra information but is involved in replication. Ribonucleic acid (RNA) is also found in cells. It has a similar structure to DNA, but the sugar is instead D-ribose and uracil bases replace thymine bases. RNA is important in the synthesis of proteins. It is produced from DNA templates via the process of transcription. Further details of protein biochemistry can be found elsewhere (e.g. Voet and Voet, 1995). Here we simply emphasize that life itself is created from that special class of soft material called polymers. 

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