The properties of many functional materials depend critically on the spatial distribution of an active phase within a support. In the case of solid catalysts, controlling the spatial distribution of metal (oxide) nanoparticles at the mesoscopic scale offers new strategies to tune their performance and enhance their lifetimes. However, such advanced control requires suitable characterization methods, which are currently scarce. Here, we show how the background in small-angle X-ray scattering patterns can be analyzed to quantitatively access the mesoscale distribution of nanoparticles within supports displaying hierarchical porosity. This is illustrated for copper catalysts supported on meso- and microporous silica displaying distinctly different metal distributions. Results derived from X-ray scattering are in excellent agreement with electron tomography. Our strategy opens unprecedented prospects for understanding the properties and to guide the synthesis of a wide array of functional nanomaterials.

Abstract:In industry, rapid crystallization is often required. At present, the crystallization rate of poly(lactic acid) (PLA) is too low compared to industrial needs. In this paper, amino acids such as glycine and L-alanine and poly(amino acids) like polyglycine and poly-DL-alanine are considered as heterogeneous crystallization nucleating agents. The impact of adding these bio-based additives on the isothermal crystallization behavior of PLA was quantified and compared at different concentrations by using the so-called Lotz efficiency scale, which here is based on isothermal DSC measurements. In addition, rheological and rheo-optical techniques were used to monitor the isothermal crystallization. Our results indicate that polyglycine possesses a significant nucleating ability (60.5%) which is comparable to the industrially used talc (81.1%).

High-performance, biobased materials can potentially be manufactured from polymerized α-amino acids (α-polypeptides). This paper reports on the synthesis, structure, and properties of both polyalanine enantiomers (PLAla and PDAla). The molecular structure of the polypeptide chains, their molecular weight, and polydispersity were investigated by (1)H NMR, MALDI-TOF, and size-exclusion chromatography. The secondary structure and crystalline order were probed via Fourier transform infrared spectroscopy, circular dichroism, and (synchrotron) wide-angle X-ray diffraction. The phase behavior and thermal stability were assessed by differential scanning calorimetry and thermogravimetric analysis. The kinetically trapped PAla chain conformation in the solid state, after synthesis or solvent treatments, is the α-helical shape. Upon heating, crystals from the α-helices convert into more stable crystals from β-sheets at a temperature higher than 210 °C. This temperature is close to where polymer degradation sets in. The β-sheet crystals combine melting with thermal degradation at temperatures above 330 °C. In the presence of superheated water, the conversion from α-helices to β-sheets happens at lower temperatures, allowing for a conversion without degradation.

The properties of many functional materials depend critically on the spatial distribution of an active phase within as upport. In the case of solid catalysts,c ontrolling the spatial distribution of metal (oxide) nanoparticles at the mesoscopic scale offers new strategies to tune their performance and enhance their lifetimes.H owever,s uch advanced control requires suitable characterization methods,which are currently scarce.H ere,w es howh ow the background in small-angle Xray scattering patterns can be analyzed to quantitatively access the mesoscale distribution of nanoparticles within supports displaying hierarchical porosity.T his is illustrated for copper catalysts supported on meso-and microporous silica displaying distinctly different metal distributions.Results derived from X-ray scattering are in excellent agreement with electron tomography.O ur strategy opens unprecedented prospects for understanding the properties and to guide the synthesis of aw ide arrayoff unctional nanomaterials.Nanoparticles find countless applications in heterogeneous catalysis, [1] in energy storage and conversion devices, [2] in biology and medicine, [3] among others. [4] In many applications the nanoparticles are dispersed on ap orous support or embedded in am atrix for the purpose of improving their stability,o rt oe xploit synergistic effects.U nderstanding the relation between the structure and properties of such complex materials is particularly challenging,f irst of all from the standpoint of structure characterization at nanometer scale. Thep roperties of nanoparticulate materials depend largely on the characteristics of the particles taken individually.T his is the case for their size and shape,which endow the materials with unique thermodynamic, [5] chemical, [6,7] optical, [8] and magnetic [9] properties.I na ddition, many functionalities are controlled also by collective characteristics of ensembles of nanoparticles.O ne such characteristic is their spatial distribution at the mesoscopic scale,that is,over distances smaller than about 100 nm, which is attracting an increasing attention in various fields. [10,11] Aw ide array of phenomena depend critically on distances between particles.T his is the case for electromagnetic properties because they generally depend on interference conditions or on the possibility of charge transfer between particles. [12,13] Theinterparticle distance controls also the stability of nanoparticles towards growth by coalescence or diffusion-limited Ostwald ripening.[11] It was also found that activity and selectivity of avariety of catalysts depend on the spatial distribution of the active nanoparticles at the nanometer scale. [14][15][16][17] Understanding all these phenomena, and developing functional nanomaterials that exploit them for specific applications requires the development of efficient and reliable characterization methods.Experimental methods that can be used to characterize the spatial distribution of nanoparticles at the mesoscopic scale are scarce.The only method ...