Morphologies, growth rates, and melting of isothermally crystallized ultrathin (200-1 nm) poly( -caprolactone) (PCL) films have been investigated in real time by atomic force microscopy. The flat-on orientation of the lamellar crystals relative to the substrate was determined by electron diffraction. The truncated lozenge-shaped PCL crystals observed at low undercooling become distorted for films of thicknesses equal to or thinner than the lamellar thickness, which depends on the crystallization temperature but not on the initial film thickness. The melting behavior of distorted crystals differs from that of undistorted ones, and their growth is slower and nonlinear. The crystal growth rate decreases greatly with the film thickness. All these observations are discussed in terms of the diffusion of the polymer chains from the melt to the crystal growth front.

Silica (SiO2) nanoparticles (NPs) were functionalized by silanization to produce a surface covered with organosiloxanes. Information about the surface coverage and the nature, if any, of organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear (29)Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of (29)Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of ∼625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D (29)Si-(29)Si correlation experiments, it is shown that the required reaction conditions favor lateral polymerization and domain growth. Moreover, the natural abundance correlation experiments permitted the estimation of (2)J(Si-O-Si)-couplings (13.8 ± 1.4 Hz for surface silica) and interatomic distances (3.04 ± 0.08 Å for surface silica) since complications associated with many-spin systems and also sensitivity were avoided. The work detailed herein not only demonstrates the possibility of using MAS-DNP to greatly facilitate the acquisition of 2D (29)Si-(29)Si correlation spectra but also shows that this technique can be used in a routine fashion to characterize surface grafting networks and gain structural constraints, which can be related to a system's chemical and physical properties.

Operando Raman spectroscopy and synchrotron X-ray diffraction were combined to probe the evolution of strain in Li-ion battery anodes made of crystalline silicon nanoparticles. The internal structure of the nanoparticles during two discharge/charge cycles was evaluated by analyzing the intensity and position of Si diffraction peaks and Raman TO-LO phonons. Lithiation/delithiation of the silicon under limited capacity conditions triggers the formation of "crystalline core-amorphous shell" particles, which we evidenced as a stepwise decrease in core size, as well as sequences of compressive/tensile strain due to the stress applied by the shell. In particular, we showed that different sequences occur in the first and the second cycle, due to different lithiation processes. We further evidenced critical experimental conditions for accurate operando Raman spectroscopy measurements due to the different heat conductivity of lithiated and delithiated Si. Values of the stress extracted from both operando XRD and Raman are in excellent agreement. Long-term ex situ measurements confirmed the continuous increase of the internal compressive strain, unfavorable to the Si lithiation and contributing to the capacity fading. Finally, a simple mechanical model was used to estimate the sub-nanometer thickness of the interfacial shell applying the stress on the crystalline core. Our complete operando diagnosis of the strain and stress in SiNPs provides both a detailed scenario of the mechanical consequences of lithiation/delithiation in SiNP and also experimental values that are much needed for the benchmarking of theoretical models and for the further rational design of SiNP-based electrodes.

Growth rates and morphologies of thin (0.1-2 µm) and thick (30 µm) films of miscible poly-( -caprolactone)/poly(vinyl chloride) (PCL/PVC) blends have been investigated. Under isothermal crystallization, PCL growth rates decrease in blend films thinner than 1 µm. However, in pure PCL films, no growth rate dependence is seen at the same thicknesses. In thick films of blends isothermally crystallized at a slow growth rate, two types of spherulites are observed with different growth rates and morphologies. One type of spherulites develops at the free surface of the film whereas the other is located in the bulk. The surface enrichment of the blend in PCL appears to be a key factor explaining the crystallization and morphological behavior of this system.

Morphology of grain boundaries observed during order-order transition at the perforated layer (PL)/gyroid interface was investigated by electron tomography in a polystyrene-block-polyisoprene (SI)/polystyrene (hS) blend. As a general result, 3D analysis shows the nonrelated orientation of the growing gyroid phase relative to the consumed PL grain: a nonepitaxial transition. This is a predictable result due to the nucleation of PL and gyroid grains in the sponge phase, with random orientation. In few cases, however, epitaxy was observed with part of the PL phase orientation conserved by the growing gyroid, a rare situation potentially resulting from the nucleation of the gyroid grain into the PL phase, or from the lucky match between both grain orientations. For both epitaxial and nonepitaxial grain boundaries, the PI and PS phases were found continuous through the grain boundary. For nonepitaxial transitions, connections were observed at the grain boundary between the otherwise independent PI gyroid networks. These networks remain independent through epitaxial transitions, each of them being connected, with a regular pattern, to one out of two perforated layers. With clarification of these complex morphologies, electron tomography demonstrates again its usefulness for polymer science.

No abstract

No abstract

The structure of a commercial sulfonated poly(ether ether ketone) (sPEEK) membrane was analyzed by Small-Angle X-Ray Scattering (SAXS) for different water uptakes obtained after immersion in liquid water at various temperatures. For low membrane swelling, the SAXS profile displays only a wide-angle peak in the 0.2-0.3 Å(-1) region. As the membrane swells, two supplementary correlation peaks arise and shift towards small angles, which are the signature of a structural evolution of the membrane, whereas the wide angle peak remains stable. The SAXS spectra of sPEEK membranes can thus display three correlation peaks simultaneously. Therefore we propose a new interpretation of these SAXS spectra which conclude that the two small angle peaks are attributed to the so-called matrix and ionomer peaks and the wide-angle peak is ascribed to the mean separation distance between sulfonic acid groups grafted onto the polymer backbone. This peak attribution implies that the sPEEK nano-phase separation is triggered by an immersion in hot water (ionomer peak apparition). Our new peak attribution was confirmed by studying the impact of temperature, electron density contrast and ionic exchange capacity.