The effect of oxygen and silicon impurities on the structural and physicochemical properties of the nickel melts is studied in performing evaluations based on the density and surface tension ...parameters. The behavior of the impurity elements is considered in studying the liquid state of pure nickel and nickel containing 0.005–0.01% silicon and oxygen in the course of refining these melts, in which the compression effect and negative deviations from Raoult’s law are formed. The surface tension of the silicon-containing nickel melt is found to increase with the oxygen concentration. The absorption parameters of a solution abruptly decrease in accordance with the increase in interparticle interaction in the volume and the formation of a strong cluster.
The combined effect of oxygen and antimony impurities on the structural and physicochemical properties of the nickel melt as the base of high-temperature alloys is investigated. A compression effect ...in the form of a density increment is observed on the density polytherms of the nickel melts containing oxygen and antimony. The maximum compression effect is found to correspond to the chemical composition with 0.01–0.02 wt % oxygen and 0.01 wt % antimony.
The 2-fold thermoresponsive diblock copolymer PSPP498-b-PNIPMAM144, which consists of a zwitterionic polysulfobetaine (PSPP) block and a nonionic poly(N-isopropylmethacrylamide) (PNIPMAM) block, is ...prepared by consecutive RAFT polymerizations. It combines the upper and lower critical solution temperature (UCST and LCST) behaviors, respectively, of the constitutive homopolymers in aqueous solution. We investigate the temperature-dependent phase behavior and the self-assembled structures of the block copolymer in D2O by turbidimetry and by small-angle neutron scattering (SANS) in salt-free solution and in the presence of small amounts of NaCl and NaBr. For comparison, solutions of PNIPMAM homopolymer in D2O are studied as well. Turbidimetry indicates thermally induced “schizophrenic” aggregation behavior for PSPP498-b-PNIPMAM144. SANS reveals that conventional star-like core–shell micellar structures are formed above the LCST transition, whereas below the UCST-transition, structure formation is much less pronounced. This is attributed to the different types of interactions, namely hydrophobic and ionic ones, dominating in the different regimes. Despite the increased polarity contrast between the zwitterionic and the nonionic blocks, and the much wider separation of the UCST- and LCST-based cloud points, CPUCST and CPLCST, the structural features of the new PSPP498-b-PNIPMAM144 resemble the ones found previously for the also 2-fold thermoresponsive analogue PSPP432-b-PNIPAM200, for which both phase transition temperatures nearly coincide. Remarkably, the addition of small amounts of NaBr or NaCl to the solution of PSPP498-b-PNIPMAM144 causes a significant increase of CPUCST, as well as minor but notable changes in the self–assembled structures, but no gross alterations of the phase behavior.
Structural changes occurring on a millisecond time scale during uptake of DNA by cationic lipid nanocarriers are monitored by time-resolved small-angle X-ray scattering (SAXS) coupled to a ...rapid-mixing stopped-flow technique. Nanoparticles (NPs) of nanochannel organization are formed by PEGylation, hydration, and dispersion of a lipid film of the fusogenic lipid monoolein in a mixture with positively charged (DOMA) and PEGylated (DOPE-PEG2000) amphiphiles and are characterized by the inner cubic structure of very large nanochannels favorable for DNA upload. Ultrafast structural dynamics of complexation and assembly of these cubosome particles with neurotrophic plasmid DNA (pDNA) is revealed thanks to the high brightness of the employed synchrotron X-ray beam. The rate constant of the pDNA/lipid NP complexation is estimated from dynamic roentgenograms recorded at 4 ms time resolution. pDNA upload into the vastly hydrated channels of the cubosome carriers leads to a fast nanoparticle–nanoparticle structural transition and lipoplex formation involving tightly packed pDNA.
In this study, we report detailed information on the internal structure of PNIPAM-b-PEG-b-PNIPAM nanoparticles formed from self-assembly in aqueous solutions upon increase in temperature. NMR ...spectroscopy, light scattering, and small-angle neutron scattering (SANS) were used to monitor different stages of nanoparticle formation as a function of temperature, providing insight into the fundamental processes involved. The presence of PEG in a copolymer structure significantly affects the formation of nanoparticles, making their transition to occur over a broader temperature range. The crucial parameter that controls the transition is the ratio of PEG/PNIPAM. For pure PNIPAM, the transition is sharp; the higher the PEG/PNIPAM ratio results in a broader transition. This behavior is explained by different mechanisms of PNIPAM block incorporation during nanoparticle formation at different PEG/PNIPAM ratios. Contrast variation experiments using SANS show that the structure of nanoparticles above cloud point temperatures for PNIPAM-b-PEG-b-PNIPAM copolymers is drastically different from the structure of PNIPAM mesoglobules. In contrast with pure PNIPAM mesoglobules, where solidlike particles and chain network with a mesh size of 1–3 nm are present, nanoparticles formed from PNIPAM-b-PEG-b-PNIPAM copolymers have nonuniform structure with “frozen” areas interconnected by single chains in Gaussian conformation. SANS data with deuterated “invisible” PEG blocks imply that PEG is uniformly distributed inside of a nanoparticle. It is kinetically flexible PEG blocks which affect the nanoparticle formation by prevention of PNIPAM microphase separation.
The structural and physicochemical properties (density and surface tension parameters) of the nickel melt containing a detrimental impurity (oxygen) in an amount of 0.01, 0.02, and 0.03 wt % of the ...pure nickel content are studied. The temperature dependences of the density of melts of the Ni–O system are characterized by higher values relative to the pure solvent and compression effect formation. Oxygen in the nickel melts possesses a high surface activity and also affects an increase in the surface tension under the heating conditions. The amount of oxygen adsorbed on the surface depends on the temperature and melting conditions. Under the heating and cooling conditions, the amount of the adsorbed substance at low temperatures is approximately twofold higher than that at high temperatures. In a content range of 0.018 wt % oxygen, the surface tension isotherms contain a minimum, the adsorption isotherms contain a maximum, and the density isotherms exhibit inflection points of the function. The appearance of specific points in the curves of the structure-sensitive properties makes it possible to predict the possibility of a structural transition caused by the decomposition of an oxygen-saturated γ-like liquid solution to a γ solution and microgroups of NiO oxide.
A 2-fold thermoresponsive diblock copolymer PSPP430-b-PNIPAM200 consisting of a zwitterionic polysulfobetaine (PSPP) block and a nonionic poly(N-isopropylacrylamide) (PNIPAM) block is prepared by ...successive RAFT polymerizations. In aqueous solution, the corresponding homopolymers PSPP and PNIPAM feature both upper and lower critical solution temperature (UCST and LCST) behavior, respectively. The diblock copolymer exhibits thermally induced “schizophrenic” aggregation behavior in aqueous solutions. Moreover, the ion sensitivity of the cloud point of the zwitterionic PSPP block to both the ionic strength and the nature of the salt offers the possibility to create switchable systems which respond sensitively to changes of the temperature and of the electrolyte type and concentration. The diblock copolymer solutions in D2O are investigated by means of turbidimetry and small-angle neutron scattering (SANS) with respect to the phase behavior and the self-assembled structures in dependence on temperature and electrolyte content. Marked differences of the aggregation below the UCST-type and above the LCST-type transition are observed. The addition of a small amount of NaBr (0.004 M) does not affect the overall behavior, and only the UCST-type transition and aggregate structures are slightly altered, reflecting the well-known ion sensitivity of the zwitterionic PSPP block.
This work focuses on the synthesis and self-assembly of triphilic poly(2-oxazoline) triblock copolymers with high fluorine content toward our future aim of developing poly(2-oxazoline) magnetic ...resonance imaging (MRI) contrast agents. A highly fluorinated 2-substituted-2-oxazoline monomer, namely 2-(1H,1H,2H,2H-perfluorooctyl)-2-oxazoline, was synthesized using the Grignard reaction. The polymerization kinetics of the synthesized monomer was studied, and it was used for the preparation of triblock copolymers with hydrophilic 2-methyl-2-oxazoline, hydrophobic 2-octyl-2-oxazoline, and fluorophilic blocks by cationic ring-opening polymerization yielding polymers with low relatively dispersity (1.2–1.4). The presence of the blocks with the different nature in one copolymer structure facilitated self-assembly of the copolymers in water and dimethyl sulfoxide as observed by dynamic light scattering, cryo-transmission electron microscopy, and small-angle neutron scattering. The nanoparticle morphology is strongly influenced by the order and length of each block and the nature of solvent, leading to nanoparticles with core–shell structure as confirmed by small-angle neutron scattering. The reported poly(2-oxazoline) block copolymers with high fluorine content have high potential for future development of MRI contrast agents.
A decrease in the detrimental effect of an antimony impurity in nickel is considered using structure-sensitive parameters, namely, density and surface tension. Samples of experimental heats ...containing 0.01–0.05 wt % Sb are prepared from a preliminarily cast master alloy. Antimony additions are found to increase the density of the nickel melt substantially. A negative density hysteresis appears in the temperature dependences recorded upon cooling. Antimony in the nickel melt is found to have a high surface activity and to decrease its surface tension strongly. When the melt is heated, its surface tension increases, which is accompanied by the passage of antimony into the volume and by changes in the volume and surface solution compositions.
Amphiphilic poly(N-(2-hydroxypropyl)methacrylamide) copolymers (pHPMA) bearing cholesterol side groups in phosphate buffer saline self-assemble into nanoparticles (NPs) which can be used as ...tumor-targeted drug carriers. It was previously shown by us that human serum albumin (HSA) interacts weakly with the NPs. However, the mechanism of this binding could not be resolved due to overlapping of signals from the complex system. Here, we use fluorescence labeling to distinguish the components and to characterize the binding: On the one hand, a fluorescent dye was attached to pHPMA, so that the diffusion behavior of the NPs could be studied in the presence of HSA using fluorescence lifetime correlation spectroscopy. On the other hand, quenching of the intrinsic fluorescence of HSA revealed the origin of the binding, which is mainly the complexation between HSA and cholesterol side groups. Furthermore, a binding constant was obtained.
PDF