The shape and size distribution of crystalline nanoparticles resulting from the sulfuric acid hydrolysis of cellulose from cotton, Avicel, and tunicate were investigated using transmission electron microscopy (TEM) and atomic force microscopy (AFM) as well as small- and wide-angle X-ray scattering (SAXS and WAXS). Images of negatively stained and cryo-TEM specimens showed that the majority of cellulose particles were flat objects constituted by elementary crystallites whose lateral adhesion was resistant against hydrolysis and sonication treatments. Moreover, tunicin whiskers were described as twisted ribbons with an estimated pitch of 2.4-3.2 microm. Length and width distributions of all samples were generally well described by log-normal functions, with the exception of tunicin, which had less lateral aggregation. AFM observation confirmed that the thickness of the nanocrystals was almost constant for a given origin and corresponded to the crystallite size measured from peak broadening in WAXS spectra. Experimental SAXS profiles were numerically simulated, combining the dimensions and size distribution functions determined by the various techniques.

This work deals with the study of the mesomorphic form or mesophase induced by tensile drawing from the amorphous state of a polylactide material containing 4 mol % of d-stereoisomer units. Investigations have been carried out over the draw temperature domain 45−90 °C, i.e. an interval spanning roughly ±20 °C about the glass transition temperature. In situ WAXS experiments during drawing, stress relaxation, and/or heating of stretched samples invariably showed the strain-induced occurrence of the mesophase as far as temperature did not exceed 70 °C. This seems to be the upper stability temperature of the mesophase identified in a previous study. DSC traces upon heating of drawn samples exhibit a post glass transition endothermic peak similar to the enthalpy relaxation phenomenon observed for aged polymers. The amplitude of this strain-induced endotherm proved to be strongly dependent on draw temperature and draw ratio. Draw ratio also appeared to strongly influence the temperature domain of cold crystallization. The quite different structural evolution of the drawn samples as a function of temperature, depending whether cold crystallization occurred close or far from the strain-induced endotherm, led us to the conclusion that this endotherm results from neither physical aging nor orientation relaxation but from “melting” of the mesophase. This proposal is thoroughly supported by the insensitivity of the endotherm enthalpy to the DSC scanning rate that gives evidence of a first order thermodynamic transition in contrast to the case of aging-induced endotherm. WAXS as a function of temperature on drawn samples annealed with free ends enabled to probe the persistence of chain orientation and the stability of the strain-induced structural changes in relation to drawing conditions.

Block copolymers demonstrate potential for use in next-generation lithography due to their ability to self-assemble into well-ordered periodic arrays on the 3-100 nm length scale. The successful lithographic application of block copolymers relies on three critical conditions being met: high Flory-Huggins interaction parameters (χ), which enable formation of <10 nm features, etch selectivity between blocks for facile pattern transfer, and thin film self-assembly control. The present paper describes the synthesis and self-assembly of block copolymers composed of naturally derived oligosaccharides coupled to a silicon-containing polystyrene derivative synthesized by activators regenerated by electron transfer atom transfer radical polymerization. The block copolymers have a large χ and a low degree of polymerization (N) enabling formation of 5 nm feature diameters, incorporate silicon in one block for oxygen reactive ion etch contrast, and exhibit bulk and thin film self-assembly of hexagonally packed cylinders facilitated by a combination of spin coating and solvent annealing techniques. As observed by small angle X-ray scattering and atomic force microscopy, these materials exhibit some of the smallest block copolymer features in the bulk and in thin films reported to date.

The micellar state of Pluronic P123, which is a poly(ethylene oxide)-b-poly(propylene oxide)-b- poly(ethylene oxide) block polymer (EO(20)PO(70)EO(20)), has been investigated using SANS, SAXS, and differential scanning calorimetry under the conditions utilized in the synthesis of ordered mesoporous materials, such as SBA-15. The absolute intensity measurements, both with SANS and SAXS, have provided a detailed quantitative description of the P123 micelles in the framework of a simple core-shell spherical model. The model developed has been used to establish the structure of the copolymer micelles, including their size, shape, aggregation number and detailed composition, as well as the structural changes induced by varying reaction conditions. The effects of temperature, pH, acidic source and the addition of swelling agents (toluene and TMB) are reported and discussed.

The different steps of the self-assembly in solution of several 2D-hexagonal silica nanostructured SBA-15 materials have been investigated by SAXS and SANS in situ experiments. Unique quantitative information about the shape and size evolution upon time of the micellar aggregates throughout the self-assembly process is obtained using a complete model that describes well the scattering data for the various synthesis conditions. In all cases, before the precipitation of the material, the micelles shape changes from spherical to rod-like, where the structure of the rod-like micelles is linked to the structure of the 2D-hexagonal precipitated material. In addition, the kinetics of hydrolysis of the inorganic precursor (TEOS) has been determined by in situ Raman spectroscopy. More specifically, by comparing synthesis made with different acids (HNO(3), HBr, HCl, H(2)SO(4), and H(3)PO(4)), it is found that materials prepared using the "salting-out" anions (SO(4)(2-) and H(2)PO(4)(-)) are much better ordered than with the "salting-in" anions (NO(3)(-) and Br(-)).

In this article, we present a general overview of the organization of colloidal charged clay particles in aqueous suspension by studying different natural samples with different structural charges and charge locations. Small-angle X-ray scattering experiments (SAXS) are first used to derive swelling laws that demonstrate the almost perfect exfoliation of clay sheets in suspension. Using a simple approach based on geometrical constraints, we show that these swelling laws can be fully modeled on the basis of morphological parameters only. The validity of this approach was further extended to other clay data from the literature, in particular, synthetic Laponite. For all of the investigated samples, experimental osmotic pressures can be properly described by a Poisson-Boltzmann approach for ionic strength up to 10(-3) M, which reveals that these systems are dominated by repulsive electrostatic interactions. However, a detailed analysis of the Poisson-Boltzmann treatment shows differences in the repulsive potential strength that are not directly linked to the structural charge of the minerals but rather to the charge location in the structure for tetrahedrally charged clays (beidellite and nontronites) undergoing stronger electrostatic repulsions than octahedrally charged samples (montmorillonites, laponite). Only minerals subjected to the strongest electrostatic repulsions present a true isotropic to nematic phase transition in their phase diagrams. The influence of ionic repulsions on the local order of clay platelets was then analyzed through a detailed investigation of the structure factors of the various clay samples. It appears that stronger electrostatic repulsions improve the liquidlike positional local order.

The phenomenon of cavitation generally appears close to yielding in the high-density polyethylene. It can affect the yield stress and the properties at large strains. The influence of the microstructural and molecular parameters on cavitation is not well established; it is not even clear whether the cavitation is a cause or a consequence of plasticity. In this work, we focus on the initiation of cavitation and on the nucleation rate. Various polyethylenes with a wide range of microstructural and molecular parameters have been obtained. The cavitation is followed up by SAXS in-situ tensile tests. It is found that, depending on the polyethylene, cavitation can be avoided or, on the contrary, appears before or after yielding. The stresses necessary to initiate cavitation and crystallite shearing have been relied respectively on stress transmitters (tie molecules, interphase, etc.) and crystallite thickness. Then the comparison between the materials has allowed predicting the various polyethylene behaviors. All of the latter have been explained by a simple model based on very few microstructural parameters. Surprisingly, our results have shown that all the scenarios of plasticity and cavitation are possible. One is the cause or the consequence of the other in accordance with the molecular topology and the microstructure.

The structure and morphology of a set of high hard block content (50% to 100% hard segment by weight) linear thermoplastic polyurethanes has been investigated mainly via small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). All the results obtained in this investigation have been correlated to our previous work on the thermodynamic properties of the same set of samples (Saiani et al. Macromolecules 2001, 34, 9059). The soft segment was based on a poly(propylene oxide) polyol end-capped with ethylene oxide and the hard segment on a 4,4‘-methylenediphenyleneisocyanate (MDI) chain extended by 2-methyl-1,3-propanediol (MP−Diol). Samples with a hard segment volume fraction higher than 65% are shown to have a morphology consisting in soft phase domains embedded in a hard phase matrix. Alignment of the soft phase domains could be observed under specific preparation conditions. From our SAXS results, the same average interdomain distance was found for all the samples (d i ≈ 15 nm). These results confirm our DSC results and suggest a two-phase structure for the melt-quenched samples:  “pure” hard segment phase + mixed phase (soft + hard segments) with a hard segment content of 65 wt %. The mixed phase then undergoes phase separation during the annealing at 120 °C. The dynamics of the phase separation was also investigated showing a strong correlation between the peak observed in the scattering curves and the so-called T MMT melting endotherm. The results confirm the assignment of this endotherm to the microphase mixing of the soft and hard segments. The rate of phase separation was found to be a function of the hard segment content of the samples, and a delay time was found before the start of the phase separation process for the high hard block content samples. The degree of phase separation was calculated and found to be the same for all the samples except the PU-50%HS sample, which showed a higher degree of phase separation. The interface thickness is found to increase with increasing hard segment content.