Just Add Water

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Science  08 Feb 2002:
Vol. 295, Issue 5557, pp. 931
DOI: 10.1126/science.295.5557.931c

In polymer and biological gels, water affects both the mechanical properties of the gel and the ordering of the macromolecules, which in turn affect properties such as solute diffusion. For a series of block copolymers, Miyazaki et al. show that the water can also cause a localized phase transition. The authors reacted n-alkyl acrylate, which is hydrophobic, with acrylic acid, which is hydrophilic, to form a block copolymer. In the dry state, the alkyl segments formed a disordered bilayered structure. The addition of even a small amount of water caused the alkyl segments to crystallize and increased the melting point of the copolymer. It is possible that the water preferentially hydrates the acrylic acid segments, which lowers the glass transition temperature of the copolymer and raises the mobility of the alkyl segments. Thus, when water was first added to the copolymer, the mechanical strength of the gel increased, although above 5% water content, the strength decreased, which is typical of most hydrogels when additional water is added. — MSL

Langmuir 10.1021/la010922v.

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