Poly(3-hydroxybutyrate-co-10%3-hydroxyhexanoate)(PHBHHx) thin films were prepared by means of spin-coating PHBHHx/chloroform solutions on the silicon substrate. The crystalline morphologies of PHBHHx thin films were observed by atomic force microscopy(AFM) at room temperature. A novel crystalline morphology, that is like sunflower was found when the film is very thin and named as sunflower-like crystalline morphology. Compared with usual PHBHHx spherulites, there are obvious differences in aspects of nucleation, crystal growth process and crystalline morphology for the sunflowers. The PHBHHx/chloroform solution properties and the substrate have great effects on the formation of the sunflower. A circular boundary that may result from a liquid-liquid phase separation in PHBHHx solution first formed in the thin film during the spin-coating process, then it induced the formation of the sunflowers.
The crystallization of poly(vinylcyclohexane)-b-poly(ethylene)-b-poly(vinylcyclohexane)(PVCH-PE-PVCH) triblock copolymer/chloroform solution was investigated. The solvent of the solution system was evaporated at various temperatures. It was found that the crystallinity was decreased with increasing the solvent evaporating temperature. This indicated that the crystallinity depends on the crystallization time because the higher the evaporating temperature, the faster the speed of the solvent evaporating is. However, the melting temperature(T_m) of the block copolymer was found to depend on the competition between the crystallization and the microphase separation. When the evaporating temperature is lower(below 333 K), i.e. the speed of the solvent-evaporating is slow, the PE block crystallized freely and the T_m increased with increasing the solvent evaporating temperature, implying that the T_m only depends on the crystalline temperature. On the other hand, with the increasing temperature up to above 343 K for solvent evaporating, two melting peaks at 356 and 377 K were observed for the crystallization of PVCH-PE-PVCH in the solution. It resulted in that the crystallization and the microphase separation of the block copolymer occurred simultaneously. And the confined and unconfined crystallization coexisted for the samples. The competition of the crystallization and the microphase separation can be controlled through changing the solvent evaporating speed.
A network of 3719 tRNA gene sequences was constructed using simplest alignment. Its topology, degree distribution and clustering coefficient were studied. The behaviors of the network shift from fluctuated distribution to scale-free distribution when the similarity degree of the tRNA gene sequences increases. The tRNA gene sequences with the same anticodon identity are more self-organized than those with different anticodon identities and form local clusters in the network. Some vertices of the local cluster have a high connection with other local clusters, and the probable reason was given. Moreover, a network constructed by the same number of random tRNA sequences was used to make comparisons. The relationships between the properties of the tRNA similarity network and the characters of tRNA evolutionary history were discussed.
