Kinetics of nanoparticle reassembly mediated by UV-photolysis of surfactant.

Real-time reassembly of an ordered nanoparticle monolayer due to UV-photolysis of the surfactant shell of nanoparticles was observed. The technique of grazing-incidence small-angle X-ray scattering provided the possibility to track in situ the nanoparticle pair correlation function of the sample processed in a UV-ozone reactor. The analysis revealed a total shift of approximately 1 nm of the nanoparticle nearest-neighbor distance. The temporal evolution of the interparticle distance proved to be the first-order process governed by the UV-photolysis and described by a single-exponential decay function. The nanoparticles tend to agglomerate into a labyrinth-like structure with a typical length scale of some 30 nm.

A new device for high-temperature in situ GISAXS measurements.

A heating stage originally designed for diffraction experiments is implemented into a Bruker NANOSTAR instrument for in situ grazing incidence small-angle x-ray scattering experiments. A controlled atmosphere is provided by a dome separating the sample environment from the evacuated scattering instrument. This dome is double shelled in order to enable cooling water to flow through it. A mesoporous silica film templated by a self-assembled block copolymer system is investigated in situ during step-wise heating in air. The GISAXS pattern shows the structural development of the ordered lattice of parallel cylindrical pores. The deformation of the elliptical pore-cross section perpendicular to the film surface was studied with increasing temperature. Moreover, the performance of the setup was tested by controlled in situ heating of a copper surface under controlled oxygen containing atmosphere.

Electrochemistry of a carbon microfiber adsorbed by cobalt nanoparticles.

The adsorption of cobalt nanoparticles on a carbon microfiber surface has been electrochemicaly detected. The redox processes observed in an electrochemical cell filled with redistilled water and equipped with the carbon fiber microelectrode modified by cobalt nanoparticles have been compared to those observed in an aqueous solution of Co2+ cations. The movement of the adsorbed nanoparticles has been demonstrated by the feedback capacitance-potential method.

Kinetics and mechanism of the biodegradation of PLA/clay nanocomposites during thermophilic phase of composting process.

The degradation mechanism and kinetics of polylactic acid (PLA) nanocomposite films, containing various commercially available native or organo-modified montmorillonites (MMT) prepared by melt blending, were studied under composting conditions in thermophilic phase of process and during abiotic hydrolysis and compared to the pure polymer. Described first order kinetic models were applied on the data from individual experiments by using non-linear regression procedures to calculate parameters characterizing aerobic composting and abiotic hydrolysis, such as carbon mineralization, hydrolysis rate constants and the length of lag phase. The study showed that the addition of nanoclay enhanced the biodegradation of PLA nanocomposites under composting conditions, when compared with pure PLA, particularly by shortening the lag phase at the beginning of the process. Whereas the lag phase of pure PLA was observed within 27days, the onset of CO2 evolution for PLA with native MMT was detected after just 20days, and from 13 to 16days for PLA with organo-modified MMT. Similarly, the hydrolysis rate constants determined tended to be higher for PLA with organo-modified MMT, particularly for the sample PLA-10A with fastest degradation, in comparison with pure PLA. The acceleration of chain scission in PLA with nanoclays was confirmed by determining the resultant rate constants for the hydrolytical chain scission. The critical molecular weight for the hydrolysis of PLA was observed to be higher than the critical molecular weight for onset of PLA mineralization, suggesting that PLA chains must be further shortened so as to be assimilated by microorganisms. In conclusion, MMT fillers do not represent an obstacle to acceptance of the investigated materials in composting facilities.