Confined Crystallization of Ethylene Oxide-Butadiene Diblock Copolymers in Lamellar Films

ABSTRACT: The isothermal crystallization of a semicrystalline poly(ethylene oxide-b-ethylene/butylene) diblock copolymer (PEO-b-PBh) in uniform lamellar films has been investigated by X-ray reflectivity, optical microscopy, and atomic force microscopy. Crystallization of the PEO block leads to an increase in the lamellar thickness of both blocks. As the density of PEO increases upon crystallization, this effect is accompanied by a contraction in the lateral direction, which results in cracking of the film. The combination of the different techniques allows construction of a complete model with an integer or half-integer number of folds in the vertically oriented crystalline stems

Basic X-ray scattering for soft matter

X-ray scattering is a well-established technique in materials science. Several excellent textbooks exist in the field, typically written by physicists who use mathematics to make things clear. Often these books do not reach students and scientists in the field of soft matter (polymers, liquid crystals, colloids, and self-assembled organic systems), who usually have a chemical-oriented background with limited mathematics. Moreover, often these people like to know more about x-ray scattering as a technique to be used, but do not necessarily intend to become an expert. This volume is unique in trying to accommodate both points. The aim of the book is to explain basic principles and applications of x-ray scattering in a simple way. The intention is a paperback of limited size that people will like to have on hand rather than on a shelf. Second, it includes a large variety of examples of x-ray scattering of soft matter with, at the end of each chapter, a more elaborate case study. Third, the book contains a separate chapter on the different types of order/disorder in soft matter that play such an important role in modern self-assembling systems. Finally, the last chapter treats soft matter surfaces and thin film that are increasingly used in coatings and in many technological applications (liquid crystal displays, nanostructured block copolymer films). There is a niche for a book of this type that potentially addresses a large group of (soft matter) students and scientists

Difference in critical behaviour of the phase transitions nematic-smectic A1\mathsf{_1} and nematic-smectic Ad_{\rm d}

A high resolution X-ray study is presented of the nematic to smectic A$_1$ phase transition in 8OPCBOB and of the nematic to smectic A$_{\rm d}$ phase transition in a binary mixture of 7CB and 8CB (7.6CB). The known critical exponents of the heat capacity of both these systems agree with the predictions for the 3D XY model. For 8OPCBOB we find values for the susceptibility $\gamma$ and the parallel correlation length $\nu_{\parallel}$ that also agree with the 3D XY model, thus confirming the predictions of de Gennes. However, the values $\gamma$ and $\nu_{\parallel}$ of 7.6CB are larger than the 3D XY values. This indicates a possible difference in the critical behaviour of the nematic-smectic A$_1$ and the nematic-smectic A$_{\rm d}$ phase transition. In all cases $\nu_{\parallel}$ is larger than $\nu_{\perp}$. Furthermore it is shown how the values for the critical exponents depend on the specific form chosen for the structure factor.
A l'aide de la diffusion de rayons X à haute résolution, nous avons étudié les transitions de phase nématique-smectique A$_1$ dans le 8OPCBOB et nématique-smectique A$_{\rm d}$ dans un mélange binaire de 7CB et 8CB (7,6CB). Les valeurs connues de l'exposant critique de la chaleur spécifique pour ces deux systèmes sont en accord avec les prédictions pour le modèle 3D XY. Pour le 8OPCBOB nous trouvons des valeurs de la susceptibilité $\gamma$ et de la longueur de corrélation longitudinale $\nu_{\parallel}$ qui sont aussi en accord avec le modèle 3D XY, ce qui confirme les prédictions de de Gennes. Cependant les valeurs de $\gamma$ et de $\nu_{\parallel}$ obtenues pour le 7,6CB sont plus grandes que les valeurs du modèle 3D XY. Ceci suggère l'existence d'une différence dans le comportement critique des transitions de phase nématique-smectique A$_1$ et nématique-smectique A$_{\rm d}$. Dans tous les cas, $\nu_{\parallel}$ est supérieur à $\nu_{\perp}$. De plus, nous analysons la dépendance des valeurs obtenues pour les exposants critiques avec la forme spécifique du facteur de structure utilisée