Search results for "Lamellar structure"
showing 10 items of 85 documents
Direct evaluation of the electron density correlation function of partially crystalline polymers
1980
A discussion of the general properties of the one-dimensional electron density correlation function K(z) of a partially crystalline polymer with lamellar structure shows that application of a graphical extrapolation procedure permits direct determination of the crystallinity, the specific inner surface, and the electron density difference ηc − ηa. The procedure is based upon the occurrence of a straight section in the “self-correlation” range of K(z). Curved and nonparallel lamellae do not invalidate the concept. In the case of heterogeneous samples composed of partially crystalline and totally amorphous regions, some of the parameters of the experimentally obtained correlation function, as…
A study of the enolization of some alkyl ketones in lyomesophases formed by alkylammonium surfactants
1988
The kinetics of enolization of acetone, 3-pentanone, and 6-undecanone have been studied in lyotropic systems in the isotropic, nematic, and lamellar phases. The data, analysed in terms of spontaneous and acid-catalyzed rate constants, do not show any relevant influence of the physical nature of the phase. Effects are instead observed in relation to the length of the alkyl chains of the ketones and the type of the amphiphilic molecule. 6-undecanone has a surprising effect in stabilizing ordered mesophases.
Influence of the modification, induced by zirconia nanoparticles, on the structure and properties of polycarbonate
2013
Melt compounding was used to prepare polycarbonate (PC)–zirconia nanocomposites with different amounts of zirconia. The effect of the zirconia loading, in the range of 1–5 wt.%, on the structure, mechanical properties and thermal degradation kinetics was investigated. The zirconia nanoparticle aggregates were well dispersed in the PC matrix and induced the appearance of a local lamellar order in the polycarbonate as inferred by SAXS findings. This order could be a consequence of the intermolecular interactions between zirconia and the polymer, in particular with the quaternary carbon bonded to the methyl groups and the methyl carbon as inferred from the NMR results. The presence of zirconia…
Ferroelectric block copolymers
1997
A block copolymer consisting of polystyrene and a side chain ferroelectric liquid crystalline polymer was synthesized using polymer analogous chemistry on a monodisperse poly(styrene-b-isoprene). Composition was adjusted to give lamellar microstructure after addition of the mesogenic side groups. If placed in an LC cell without orientation of domains, no ferroelectric response was observed. After shearing the thin film, presumably due to alignment of lamellae, a bistable ferroelectric switching could be detected.
Rapid small-angle and wide-angle x-ray studies of crystallization behavior in polymers
1976
Small-angle and wide-angle x-ray scattering measurements, using a position-sensitive detector, were made during melt-crystallization of linear polyethylenes and PEO–PS–PEO triblock copolymer. The scattering measurements indicated that the triblock copolymer grew by the enlargement of regions in which lamellae are regularly stacked. During primary crystallization at higher temperatures similar behavior is observed in two linear polyethylenes. At lower temperatures, changes in the shape of small-angle scattering curves during the primary stage of crystallization indicate that amorphous gaps within the lamellar stacking become filled in. During secondary crystallization at higher temperatures …
Prediction of the morphology of polymer-clay nanocomposites
2015
Abstract Polymer nanocomposites have continually attracted increasing interest over the last decade, due to significant improvements they can offer compared to neat polymer matrices. However, the final morphology of a nanocomposite, determined by several variables, can significantly influence the macroscopic properties of the final product. Therefore, it is important to study the interactions between processing, morphology, structure and rheological properties, and the suitability of existing models in order to predict the system's behaviour with change of the main processing variables. In this work, the applicability of a predictive theory based on the Wu model was formulated and proposed …
Cooperative formation of inorganic-organic interfaces in the synthesis of silicate mesostructures.
1993
A model is presented to explain the formation and morphologies of surfactant-silicate mesostructures. Three processes are identified: multidentate binding of silicate oligomers to the cationic surfactant, preferential silicate polymerization in the interface region, and charge density matching between the surfactant and the silicate. The model explains present experimental data, including the transformation between lamellar and hexagonal mesophases, and provides a guide for predicting conditions that favor the formation of lamellar, hexagonal, or cubic mesostructures. Model Q(230) proposed by Mariani and his co-workers satisfactorily fits the x-ray data collected on the cubic mesostructure …
Effect of the orientation and rheological behaviour of biodegradable polymer nanocomposites
2014
Abstract The recent increasing interest towards biodegradable polymers has favoured the investigation on these systems, showing also their limits. On the other hand, the success achieved by nanocomposites has fostered the search for new systems where the polymer matrix is biodegradable. The final properties can depend on a number of factors, including the biodegradable polymer used as well as the nanosized filler, their mutual compatibility, the filler dispersion and the processing conditions. In this work, nanocomposites based on a starch-derived matrix and three different lamellar silicates were prepared, and the effects of the elongational flow on the dispersion, the improvement of inter…
Calculation of the Phase Behavior of Lipids
1998
The self-assembly of monoacyl lipids in solution is studied employing a model in which the lipid's hydrocarbon tail is described within the Rotational Isomeric State framework and is attached to a simple hydrophilic head. Mean-field theory is employed, and the necessary partition function of a single lipid is obtained via a partial enumeration over a large sample of molecular conformations. The influence of the lipid architecture on the transition between the lamellar and inverted-hexagonal phases is calculated, and qualitative agreement with experiment is found.
Elastic properties of polymer interfaces: Aggregation of pure diblock, mixed diblock, and triblock copolymers
2002
Block copolymers adsorbing to an interface between two immiscible homopolymers modify the elastic constants of this interface. Within self-consistent field calculations for Gaussian chains, we determine how the bending constants vary in dependence on the block copolymer concentration and architecture. Four phenomena are discussed. (i) When a tricritical or isotropic Lifshitz critical point is approached in a ternary mixture by varying the concentration of diblock copolymers or changing temperature, the elastic constants vanish. We determine the corresponding power laws, and show that the de Gennes--Taupin criterium for the stability of lamellar phases against undulations and the Ginzburg-La…