Preparation of monodisperse latexes and study of their rheological properties

The synthesis of (monodisperse) poly(styrene) latexes was reexamined using sodiumdodecyl sulfate as emulsifier and potassium persulfate as initiator. It has been shown, that at fixed emulsifier concentration c_E the variation of persulfate amount produces similar particle size variations as changes of electrolyte (potassium sulfate) concentration at a given low initiator level. For c_E << cmc a maximum of particle size versus initiator or electrolyte concentrations has been found. Concentrated monodisperse poly(styrene) dispersions and carboxylated latexes up to 50% have been prepared by a carefully controlled seeding process using monomer feed. Particle size influence on steady shear viscosity has been studied for different kinds of polymer dispersions: for electrostatic stabilized poly(styrene) latexes at high ionic strengths, for electrostatic and sterically stabilized carboxylated latexes at different pH values and for steric stabilized dispersions of poly(vinyl chloride) in plasticizer (dioctyl phthalate). All three kinds of dispersions give pronounced particle size effects on viscosity, which is different from hard-sphere-behaviour. Simple model equations have been formulated to describe the concentration and shear rate dependence on viscosity. Particle size influence may be discussed on the basis of the effective hydrodynamic particle diameter. Causes for the increase of the hydrodynamic particle size are given either by surface swelling or by the formation of particle clusters which are formed and destroyed within the shear field.     

Copolymerization of 2,2-dimethyltrimethylene carbonate and cyclic esters

The anionic and/or insertion copolymerization of 2,2-dimethyltrimethylene carbonate (DTC) with ϵ-caprolactone (ECL), pivalolactone (PVL) and L-lactide (LLA) is presented with special emphasis on the copolymerization mechanism. Statistical copolymers are obtained by copolymerization of DTC with ECL and with LLA, while with PVL a block copolymer is obtained. The role of transesterification on the microstructure is discussed.     

A study of the interactions between carboplatin and blood plasma proteins using size exclusion chromatography coupled to inductively coupled plasma mass spectrometry

To study the carboplatin–protein interaction, a sensitive method using size exclusion chromatography coupled to inductively coupled plasma mass spectrometry (SEC–ICP–MS) was developed. The complexes formed between plasma proteins and carboplatin were monitored and identified with this method. Composite blood plasma samples from patients who were undergoing chemotherapy were analyzed, and carboplatin was found to bind plasma proteins. In addition, blank plasma samples were spiked with carboplatin and were analyzed as a time course study, and the results confirmed that carboplatin formed complexes with plasma proteins, primarily albumin and γ-globulin. To further substantiate the study, these two proteins were incubated with carboplatin. The binding between carboplatin and these proteins was then characterized qualitatively and quantitatively. In addition to a one-to-one binding of Pt to protein, protein aggregation was observed. The kinetics of the binding process of carboplatin to albumin and γ-globulin was also studied. The initial reaction rate constant of carboplatin binding to albumin was determined to be 0.74 M⁻¹ min⁻¹, while that for γ-globulin was 1.01 M⁻¹ min⁻¹, which are both lower than the rate constant of the cisplatin–albumin reaction previously reported.     

Mechanical properties of single motor molecules studied by three-dimensional thermal force probing in optical tweezers.

A new method combining three-dimensional (3D) force measurements in an optical trap with the analysis of thermally induced (Brownian) position fluctuations of a trapped probe was used to investigate the mechanical properties of a single molecule, the molecular motor kinesin. One kinesin molecule attached to the probe was bound in a rigorlike state to one microtubule. The optical trap was kept weak to measure the thermal forces acting on the probe, which were mainly counterbalanced by the kinesin tether. The stiffness of kinesin during stretching and compression with respect to its backbone axis were measured. Our results indicate that a section of kinesin close to the motor domain is the dominating element in the flexibility of the motor structure. The experiments demonstrate the power of 3D thermal fluctuation analysis to characterize mechanical properties of individual motor proteins and indicate its usefulness to study single molecule in general     

Transport behavior of humic acid-modified nano-hydroxyapatite in saturated packed column: effects of Cu, ionic strength, and ionic composition

The surfaces of nano-hydroxyapatite (nHAP) used for contaminated soil and groundwater remediation may be modified to render nHAP highly mobile in the subsurface. Humic acid (HA) is widely used to modify and stabilize colloid suspensions. In this work, column experiments were conducted to determine the effects of contaminant (e.g., Cu) concentration, ionic strength (IS), and ion composition (IC) on the transport behavior of HA-modified nHAP in saturated packed columns. IS and nature of the cation had strong effects on the deposition of nHAP, and the effect was greater for divalent than for monovalent cations. Divalent cations have a greater capacity to screen the surface charge of nHAP, and Ca(2+) bridges the HA-modified nHAP colloidal particles, which causes greater deposition. Moreover, Cu(2+) had a greater effect on the transport behavior than Ca(2+) due to their strong exchange with Ca(2+) of nHAP and its surface complexation with nHAP. The relative travel distance L(T), of the injected HA-modified nHAP colloids, ranges from less than one to several meters at varying Cu concentrations, ISs, and ICs in saturated packed columns. The results are crucial to evaluate the efficacy of nHAP on the remediation of contaminated soil and groundwater environments.     

Combined use of small-angle neutron scattering and atom probe tomography for the analysis of precipitates in a Fe-15 m% Co-25 m% Mo alloy

Atom probe tomography (APT) measurements were conducted to analyze nm-sized precipitates in a Fe-25 m% Co-15 m% Mo model alloy. Calculation of isoconcentration surfaces and application of cluster-search algorithms yielded the chemical compositions of matrix and precipitates. Small-angle neutron scattering (SANS) was performed in order to calculate the ratio of magnetic to nuclear scattering. This so-called A-ratio was compared with values calculated from the chemical information derived from the atom probe data. For this, the magnetism of the precipitates has to be taken into account. Ab-initio studies have been carried out to determine the magnetic moment of the precipitate phase. The results show that the extremely fine precipitates are ferromagnetic and exhibit near-equilibrium composition. In the very early stage of decomposition, however, the composition is different from near-equilibrium. The influences of the magnetism of the precipitates as well as of artifacts from atom probe measurements on the obtained results are discussed.