Commercially available polyurethane open cell foams are readily coated with mussel-inspired polydopamine. The polydopamine film allows robust immobilisation of TiO2 nanoparticles at the surface of the three-dimensional material. The resulting catalyst is efficient for the photo-degradation of an azo dye, reusable and highly resistant to mechanical stress. A novel type of robust structured catalytic support, easily accessible via an inexpensive and green process, is thus described.
The origin and time evolution of heterogeneities in drying colloidal films is still a matter of debate. In this work, we studied the behaviour of horizontal drying fronts in a 1D configuration. The effects of hydrostatic pressure and collective diffusion of charged particles, neglected so far, were introduced. We made use of the new simulation tool based on cellular automata we recently presented (Langmuir 2015 & 2017). To check the simulation results, measurements of film profiles in the wet state and drying front velocities were performed with silica colloids. It was shown that taking hydrostatic pressure into account much improves agreement between theory and experiment. On the other hand, the simulation showed that collective diffusion slows down the drying fronts, even more when the Debye length is increased. This latter effect remains to be checked experimentally. This work opens the way to further improvements of theory and simulation, notably 2D and 3D simulations.
Thin films of as emi-fluorinated alkane cast onto solid substrates consist of well-formed two-dimensional non-birefringent ring-banded and/or radial spherulites. Controlling the experimental conditions allows orientation of the crystallization toward either radial-only or ring-banded-only morphologies. Intermediate states were also captured in which both radial and ring-banded spherulites coexist. Monitoring of the formation of these intermediate states broughte videncef or af irst crystallization modet hat sweeps radially outwards from ac entral nucleusu ntil the propagating fronte dge experiences a second crystallization mode that proceeds through ad iffusioncontrolled rhythmic crystallization mechanism that leads to high ( % 2 mm) concentricr idges. These 2D spherulites were investigated by optical and atomicf orce microscopies,i nterferometric profilometry,and off-specularn eutron scattering.Polycrystalline aggregatesw ith an essentially spherical outer boundary,c alled spherulites, are observed to form from al arge variety of compounds, includingo rganic compounds andm inerals.[1] Two-dimensional spherulites have been characterized in films resulting, for example, from solvent evaporation during casting of liquid drops of solutions of such materials on solid substrates. Concentric ring-banded spherulites constitute an intenselyi nvestigated sub-class of spherulites that usually possess chiroptical properties. Such ring-banded spherulites are formed by polymers (e.g. polyethylene and poly(ethylene adipate)), [2] but also by various small organic molecules (e.g. phthalic acid, [3] aspirin, [4] hippuric acid, [5] mannitol, [6] testosterone propionate [7] ), and by inorganic compounds( e.g. potassium dichromatea nd boric acid [8] ). Am ajor distinction needs to be made between spherulites that have at wisted crystal morphology, which is responsible for the "banded" optical texture, and spherulites that have ar eal wave-like topography with actual valleys separated by ridges. The former do not necessarily have a" real" relief, while the latter can exhibit extinction bands or not. Lately,s ubstantial interest has focusedo nn onbirefringent ring-banded spherulites.[9] The latter have only been observed with af ew polymers and never with small molecules. Improving control over the morphology of 2D spherulites and understanding their mechanisms of formation,w hich can involve at wisting of the crystal or ar hythmic crystallization process, both being able to act in interplay,a re neededi n order to tailor new materialc haracteristics.Here we report first that as imple semi-fluorinated alkane, C 10 F 21 C 16 H 33 (F10H16), when deposited as at hin film on solid surfaces (glass or silicon wafers), forms non-birefringent 2D spherulites. To the best of our knowledge,t his is one of the rare examples of non-birefringent 2D spherulites obtained with small organic molecules. Remarkably,depending on the experimental conditions, we could obtain radial-only, or ring-bandedonly spherulites. We attained control of the morpholo...
A covalent grafting strategy of molecular catalysts onto a polydopamine-coated flexible three dimensional macroscopic support is presented.
Understanding how the evolving molecular composition of an oil paint layer on its transition to an aged solid film affects its dimensional change and mechanical properties is fundamental to the assessment of material durability and more broadly risk of degradation of oil paintings. Tensile properties—modulus of elasticity and strain at break—as well as cumulative shrinkage were determined for a selection of oil paints from Mecklenburg’s Paint Reference Collection now after approximately 30 years of drying. The oil paints were found to get stiffer and more brittle with diminishing plastic deformation and increasingly elastic behaviour. For some paints, the increases in stiffness and decreases in the strain at break were dramatic during the late stage of drying. The observations modify the current physical model of paintings in which the mismatch in the response of glue-based ground layer and unrestrained wood or canvas support to variations in relative humidity (RH) has been identified as the worst-case condition for the fracturing of the entire pictorial layer. This study demonstrated that some paints were more brittle than the glue-based ground layer and as a consequence more vulnerable to cracking. The shrinkage of paints due to molecular relocation and/or evaporation of organic medium as they dry and age was measured. This shrinkage can exceed their strain at break and lead to fracturing of the oil paint layer if it is restrained by a dimensionally stable substrate. Consequently, after long-term drying, the cumulative shrinkage can cause oil paints to crack even in absence of fluctuations in RH or temperature. An example of cracking developed in an oil paint layer on the top of an undamaged ground layer in a historic panel painting was made evident by the X-ray microtomography.
Creep during loading and recovery phases after load removal are studied using a homemade experimental device that allows us to record in situ the evolution of the true contact area and of the residual imprint versus the time. Indentation tests are performed using a spherical indenter with a tip radius R 5 400 lm onto amorphous polymeric surface poly(methylmethacrylate) (PMMA) at different contact durations (10-10 5 s) and controlled temperatures varying between À20 and 100°C. Original experimental results are presented about the true evolution of the contact area during creep and recovery phases. An interesting experimental parameter, defined by the ratio a(t)/a 0 , (with a(t), evolution of the contact radius with creep or relaxation time, and a 0 , the initial value of the contact radius at the end of the loading phase or at the end of the creep phase) has been introduced to describe the evolution of imposed strain during indentation. As a function of the temperature and of the initial average strain imposed at the end of the loading phase, some nonlinear phenomena can be observed. Using two-dimensional axisymmetric finite element modeling, assuming only viscoelastic behavior, creep and recovering phases during indentation have been reproduced. The simulation results indicate that (i) the test is mainly controlled by the imposed strain and not by the contact pressure, and (ii) some plasticity could appear in the contact zone and as a function of the location and the size of the volume where the strain is maximal, the recovery is more or less limited.
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