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Nanoparticles are used in large quantities for very different applications. A precise determination of the diameter and the particle size distribution which is responsible for the application properties is therefore essential. Reliable methods for measuring the above mentioned quantities are photometric measurements and analytical ultracentrifugation with an UV optics detector. Both methods are ruled by the Mie effect, that is scattering and absorption of the particles as function of the diameter, the wavelength, and the shape of the particles. The extinction coefficients ε=τ/c for spheres, rods, and core shell particles have been calculated and plotted over a wide range of the size parameter πd/λ. Two examples for multimodal latex particles and core shell particles have been given and demonstrate the applicability of the method.

Sedimentation velocity runs were carried out on two standard polystyrene polymers and their 1:1 mixture in an analytical ultracentrifuge as a function of polymer concentration. Schlieren optics was used for the detection and self-developed VelXLS data analysis program was used for the evaluation of sedimentation data. The generated mean molecular weight for the single component polymer solutions using VelXLS program was similar as the values from dynamic light scattering. The molecular weight distributions from VelXLS also matched with the distributions generated by using interference optics and VelXLAI data analysis program. The sedimentation coefficient was observed to have a concentration dependency as the sedimentation coefficient values shifted to lower values as a function of polymer concentration. The relative amount of polymer fractions in a polymer mixture detected by the analysis programs was also compared. VelXLS program led to the computation of better detection of the amount of polymer fractions, thus, indicating the application potential of VelXLS program for the colloid characterization. [ABSTRACT FROM PUBLISHER]

Summary. The stability of turnip yellow mosaic virus (TYMV) was investigated under pressure, using solution neutron small angle scattering. Dissociation products were characterized by analytical ultracentrifugation and electron microscopy. At pH 6.0, TYMV remained unaffected by pressure, up to 260 Megapascals (MPa), the highest pressure reached in these experiments. At pH 8.0, TYMV remained unaffected by pressure up to 160 MPa, but decapsidated irreversibly above 200 MPa, giving rise to more and more empty shells upon increasing pressure. The organization of these empty shells was similar to that of the capsid of native virions, apart from the presence of a hole corresponding to the loss of a group of 5–8 coat protein subunits, through which the RNA may have escaped. At variance with other small isometric viruses, the capsid of TYMV never dissociated under pressure into subunits or small aggregates of subunits. This exceptional behavior of TYMV is probably due to the importance of van der Waals contacts and hydrogen bonds in the stability of its capsid. [ABSTRACT FROM AUTHOR]

The process of determining a critical DS to a polymer''s gelation is a key link in identifying degradable polymers'' cross-linking behaviors. A feasible method was developed from the rheological technique. In principle, it was a new application of gel point, tg, in an overlapping field of polymers'' modification and characterization, by which the gelling properties of carboxyl methylated guar gum (CMGG) and locust bean gum (CMLBG) were dynamically investigated by identifying their tg. Differing from the routine research in rheology or synthesis chemistry, the present study focused on neither pure tg nor pure DS but on their interrelation. The results demonstrated that CMGG/CMLBG''s gel points could be observed only when their DS were 0.2. However, it was not guaranteed to yield the tested polymers'' gel points unless the investigation was performed on a plateau region. Two preconditions, DS≤0.2 and ω=3–60 rad s-1, must be satisfied simultaneously besides γ of 0.5% was maintained in order to obtain the expected gel point. Since DS was regarded as a contradictory focus related to the polymers'' hydrophilicity and cross-linking behavior, the value DS=0.2 was exactly the upper limit of CMGG/CMLBG''s gelation. The significance of the present study rests not only in the first successful attempt in determining galactomannan-based derivatives'' DScritical but also in its universal application for other polysaccharide-based derivatives because of a similarity in structure. [Copyright &y& Elsevier]