The rheological properties of liquid polybutadiene rubber/organo-clay nanocomposite gels were
investigated by rheological experiments, focusing on the effects of clay exfoliation and orientation−disorientation
as well as polymer−clay interaction and temperature. Both irreversible and reversible viscosity transitions were
observed in the temperature range from 26 to 136 °C in steady shear experiments on as-prepared and exfoliated
samples. These transitions depend strongly on the end groups, molecular weight of the liquid rubber, and the
shear field. The irreversible transition is attributed to the exfoliation of the clay, and the reversible transition can
be understood as a shear-induced orientation−disorientation transition of the clay sheets. Polymer−clay interaction
is confirmed to be a key controlling factor of the orientation−disorientation transition, whereas the shear field
plays a critical role to induce such a transition. To our knowledge, this is the first rheological observation of the
in-situ exfoliation process and the shear-induced orientation−disorientation transition of layered silicate in polymer/organo-clay nanocomposites. A tentative model was suggested on the basis of the clay exfoliation and orientation−disorientation transition, and the model is used to explain the observed unique rheological behavior.
The mobility and glass transition temperature (T g ) for polymers under nanoscale confinement differ substantially from the bulk. Whereas many studies have focused on the one-dimensional confinement, it has great significance to extend studies to higher geometries. Here, we systematically investigate the mobility by dipolar-filter sequence in solid-state NMR and T g by DSC for thiolated polystyrene (PS-SH) on gold nanoparticles. The increase in T g and signal suppression in NMR spectra clearly indicate that the surface confinement dominates molecular mobility as well as T g . The molecular weight of PS-SH and nanoparticles size show significant influence on the immobilization and T g . Our results can be fitted with a core−two shell model; the inner shell is under strong constraints while the outer shell with less confinement. This work is essential to better understand the confinement effect and also provides a step toward the ultimate desire to tailor the properties of nanomaterials.
Incorporation of hydroxyapatite (HA) into the matrix of collagen (Col) and chitosan (Chi) by in situ synthesis was introduced to prepare nanocomposites. Structural investigations of the pure Col-Chi mixture validated the influence of Chi on Col assembly, but the molecular interactions between Col and Chi was partially depressed during the intervention of in situ HA synthesis, as revealed by FTIR and DSC analyses. A series of Col-Chi-HA (CCHA) nanocomposites with varying HA content were thereby prepared by a sequential method, involving in situ synthesis in the Col-Chi system, then gelling at 25 degrees C and subsequently washing the resultant elastic gel followed by dehydration consolidation. The structural characteristics and biological properties of the dehydrated CCHA nanocomposites were further evaluated by using XRD, FTIR, TG, and SEM analyses and the osteoblast culture experiment. Formation of a well integrated microstructure of organic fibers (ca. 90 nm in size) and dense matrix including inorganic aggregates (less than 30 nm in size) was found in these nanocomposites. Rat Ros 17/2.8 Osteoblasts proliferated and attached well on the surface of both CCHA nanocomposite and Col-Chi mixture. These results indicated that in situ HA synthesis in the Col-Chi system provided a feasible route for bone grafting nanocomposites.
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