of and find that for 1200 EW polymer R = 1.4 ± 0.2 nm (22) for -1 < KJKg < 0. This value is in agreement with the value of 1.2-1.3 nm deduced from water transport experiments.2 The change in free energy that results from the formation of the channel is only -11 J/cm3; thus our elastic theory suggests the channels are continually forming and unforming at ambient temperatures. This is consistent with the previously proposed cluster-network model. V. ConclusionWe have derived a semiphenomenological expression for the diameter of ionic clusters in ionomers and demonstrated that this expression correctly describes the variation in cluster diameter in one perfluorinated ionomer with water content, equivalent weight, and cation form. We find the cluster diameter is dominated by a balance between hydrophilic surface interactions with the ion exchange sites and the energy of elastic deformation. The model also predicts that short channels connecting adjacent clusters are thermodynamically stable, in support of the clusternetwork model proposed by us earlier. The current elastic theory should generally apply to other ionomers, including hydrocarbon analogues and a comparison of the phenomenological parameters Kt and Kl for various ionomers should be instructive and interesting. References and Notes(1) Gierke, T.

The glass transition temperatures (Tg) and related properties of the styrene (S) and butadiene (B) microphases in styrene-butadiene (S-B) diblock and styrene-butadiene-styrene (S-B-S) triblock copolymers with low molecular weight S blocks were examined by refractive index-temperature (n-T) and differential scanning calorimetry (DSC) measurements. In all block copolymers investigated, having S block molecular weights <2.2 X 104, the S-phase TVs obtained by either n-T or DSC measurements were at least 18 K less than those of S homopolymers with molecular weights comparable to those of the S blocks. The change in specific heat at the Tg of the S microphase (ACps) was always equal to or greater than that of S homopolymer. These results suggest that some B segments are mixed into most of the S microphases examined, in contrast to earlier results on styrene-dimethylsiloxane (S-DMS) diblock copolymers, where mixing was postulated only at S block molecular weights <0.82 X 104.

No abstract

Oil spills and oily wastewater have become a major environmental problem in recent years, directly impacting the environment and biodiversity. Several techniques have been developed to solve this problem, including biological degradation, chemicals, controlled burning, physical absorption and membrane separation. Recently, biopolymeric aerogels have been proposed as a green solution for this problem, and they possess superior selective oil absorption capacity compared with other approaches. Several modification strategies have been applied to nanocellulose-based aerogel to enhance its poor hydrophobicity, increase its oil absorption capacity, improve its selectivity of oils and make it a compressible and elastic magnetically responsive aerogel, which will ease its recovery after use. This review presents an introduction to nanocellulose-based aerogel and its fabrication approaches. Different applications of nanocellulose aerogel in environmental, medical and industrial fields are presented. Different strategies for the modification of nanocellulose-based aerogel are critically discussed in this review, presenting the most recent works in terms of enhancing the aerogel performance in oil absorption in addition to the potential of these materials in near future.

No abstract