The viscosities of aqueous sodium alginate solutions were measured in different NaCl concentrations (C s ) at 298 K. Based on the Odijk±Skolnick±Fixman theories, the electrostatic persistence lengths were calculated for various ionic strengths. The intrinsic persistence length of sodium alginate in solution was determined to be 125 A Ê by the method suggested by Odijk. In the region of C À1=2 S > 6:5, the increase in intrinsic viscosity, [], for sodium alginate on decreasing the C s is due to the larger contribution of electrostatic persistence length to the total persistence length, and the departure of [] calc from [] expl is attributed to the variation of the Flory Φ constant with ionic strength. A peak was observed in the plot of reduced viscosity v. sodium alginate concentration at a constant low ionic strength. As in the treatment of Rinaudo et al., this maximum in reduced viscosity is attributed to a preferential intermolecular distance. The roles of electrostatic persistence length, the critical interrod spacing and the effect of added salt concentration on this maximum are discussed.
:In this paper, biomedical Mg-Zn-Ca alloy was processed by high pressure torsion (HPT) up to a maximum of 5 revolutions at room temperature and 7.5GPa. The microstructures of as-received material and HPT material were studied, as well as the corrosion properties and degradation mechanism of the alloy immersed in simulation body fluid (SBF). It revealed that the average grain size of as-received material was 11μm and most of the second phases distributed along the grain boundaries. The corrosion pits formed near the grain boundaries where the corrosion rate was much faster than that of other areas. After HPT processing for 5 revolutions, not only the grain size was significantly refined to 130-150nm, but also the second phases distributed uniformly. These microstructural variations caused the entire surface of the alloy corroded almost at the same corrosion rate. The corrosion interface of the center region and the edge region presented the uniform and gentle profile curve without any obvious corrosion pits. The HPT material in SBF tended to degrade by uniform corrosion mode.
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The great improvement in electrical conduction of PbS films is still critical for the application of PbS-infrared detectors and solar cells so far. The incorporation of certain ions to PbS is proved effective for the improvement in electrical conduction. Herein a series of face-centered cubic Al3+-incorporated PbS (PbS:Al3+) films with improved electrical conduction are synthesized on p-type Si(100) substrates from an alkaline chemical bath. The impact of Al3+ molar concentration (CAl) is intensively studied on the microstructural pattern, optical and electrical behaviors of the films. The mechanism of the formation of highly crystallized PbS:Al3+ in alkaline chemical bath is also proposed. All the PbS:Al3+ films are slightly rich in Pb. The strong coordination between Pb2+ and organic triethanolamine molecules plays a key role in the formation of highly crystallized PbS:Al3+. The incorporated Al3+ weakens and even destroys the preferred 〈200〉 orientation of the films due to the enhanced crystal lattice distortion. The film’s resistivity is firstly reduced and then increased with increase in CAl, and the near-infrared optical absorption edge slightly blueshifts and then redshifts. The change in resistivity with increase in CAl can be explained by the substitution of Pb2+ by Al3+ and the change in crystallite size, and the slight blue and red shift in optical edge with increase of CAl is mainly attributed to the increase and the decrease in tensile stress of the films caused by the Al3+ incorporation into PbS, respectively.
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