A simple but novel thermodynamic model is presented, based upon van't Hoff analysis, for the reversible swelling behavior of colloidal microgels. The swelling, as a function of temperature, of poly(N-isopropylacrylamide/N,N'-methylenebisacrylamide) as well as poly(N-isopropylacrylamide/vinylpyridine/N,N'-methylenebisacrylamide) and poly(N-isopropylacrylamide/acrylic acid/N,N'-methylenebisacrylamide) microgel dispersions in H2O and D2O has been studied by photon correlation spectroscopy (PCS). PCS data was used to obtain the hydrodynamic diameter and hence the volume of the microgels (before and after reconstitution following freeze-drying) as a function of temperature. The choice of standard reference states, for analyzing the data attained, is discussed, and the one selected is that of the volume of the microgels at 333 K in H2O. For all microgels examined the volume, at this temperature, is shown to be independent of solvent (H2O, D2O). The derived data has allowed the exploration of a novel thermodynamic approach to the study of the swelling behavior of the microgels. The constant volume, at 333 K, for each of the polymer systems constituting the microgels is suggested to be an intrinsic property of the polymers themselves.
In the partition of some resorcinol alkyl ethers between water and 1-octanol, the values of delta Gtrs do not increase in a regular way. Odd and even chain alkyl compounds show different, regular increases in delta Gtrs for addition of each methylene group. The unrecognized occurrence of this phenomenon in earlier data is pointed out, and its possible significance in medicinal chemistry is discussed.
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