Polymer/layered silicate nanocomposites: a review from preparation to processing

This review aims at reporting on very recent developments in syntheses, properties and (future) applications of polymer-layered silicate nanocomposites. This new type of materials, based on smectite clays usually rendered hydrophobic through ionic exchange of the sodium interlayer cation with an onium cation, may be prepared via various synthetic routes comprising exfoliation adsorption, in situ intercalative polymerization and melt intercalation. The whole range of polymer matrices is covered, i.e. thermoplastics, thermosets and elastomers. Two types of structure may be obtained, namely intercalated nanocomposites where the polymer chains are sandwiched in between silicate layers and exfoliated nanocomposites where the separated, individual silicate layers are more or less uniformly dispersed in the polymer matrix. This new family of materials exhibits enhanced properties at very low filler level, usually inferior to 5 wt.%, such as increased Young’s modulus and storage modulus, increase in thermal stability and gas barrier properties and good flame retardancy.

Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials

Responsive polymer materials can adapt to surrounding environments, regulate transport of ions and molecules, change wettability and adhesion of different species on external stimuli, or convert chemical and biochemical signals into optical, electrical, thermal and mechanical signals, and vice versa. These materials are playing an increasingly important part in a diverse range of applications, such as drug delivery, diagnostics, tissue engineering and 'smart' optical systems, as well as biosensors, microelectromechanical systems, coatings and textiles. We review recent advances and challenges in the developments towards applications of stimuli-responsive polymeric materials that are self-assembled from nanostructured building blocks. We also provide a critical outline of emerging developments.

Emerging applications of stimuli-responsive polymer materials

A wide variety of media can be used in learning, including distance learning, such as print, lectures, conference sections, tutors, pictures, video, sound, and computers. Any one instance of distance learning will make choices among these media, perhaps using several.

Multimedia in Learning

With digital equipment becoming increasingly networked, either on wired or wireless networks, for personal and professional use alike, distributed software systems have become a crucial element in information and communications technologies. The study of these systems forms the core of the ARLES' work, which is specifically concerned with defining new system software architectures, based on the use of emerging networking technologies. In this context, we concentrate on the study of distributed systems which bring to life the vision of ubiquitous computing systems, also known as ambient intelligence.

반도체 공정 overview

Using numerical self-consistent field (SCF) calculations, we investigate the interactions between two closely spaced surfaces and the surrounding polymer melt. Short chains (surfactants) are terminally anchored to each of the surfaces. The coated substrates model organically modified clay crystallites (sheets). Through the calculations, we vary the characteristics of the surfactants and polymers to isolate conditions that drive the polymer to penetrate the gap between the surfaces. We also consider the effect of employing end-functionalized chains to promote the dispersion of bare clay sheets within the polymer matrix. We find that this scheme provides a robust method for exfoliating the sheets. To consider this case in greater depth, we develop an analytical SCF theory to model the interactions among the functionalized chains, nonfunctionalized polymers, and the clay sheets. The results from the numerical and analytical SCF models show good agreement on the behavior of the system. The results indicate th...

Modeling the Interactions between Polymers and Clay Surfaces through Self-Consistent Field Theory

We investigate the difficulties of advanced undergraduate students toward the end of a full year upper-level quantum mechanics course with concepts related to quantum measurements and time development. Our analysis is based upon a test administered to 89 students from six universities and interviews with 9 students. Strikingly, most students shared the same difficulties despite variations in background, teaching styles, and textbooks. Concepts related to stationary states, eigenstates, and time dependence of expectation values were found to be particularly difficult. An analysis of written tests and interviews suggests that widespread misconceptions originate from an inability to discriminate between related concepts and a tendency to overgeneralize.

https://www.if.ufrj.br/~pef/aulas_seminarios/notas_de_aula/carlos_2011_1/ensinoMQ/Singh_QM_test.pdf

Student understanding of quantum mechanics

We combine a density functional theory (DFT) with a self-consistent field model (SCF) to calculate the phase behavior of thin, oblate colloidal particles that are coated with surfactants and dispersed in a polymer melt. These coated particles represent organically modified clay sheets. By integrating the two methods, we can investigate the effect of the surfactants' characteristics (grafting density ρgr and length Ngr) and the polymer−surfactant interaction energy on the polymer−clay phase diagram. Depending on the values of these critical parameters and the clay volume fraction, φ, the system can be in an isotropic or nematic phase (which corresponds to an exfoliated composite). The system can also form a smectic, crystal, columnar, or “house-of-cards” plastic solid, as well as a two-phase (immiscible) mixture. Using this model, we isolate conditions that lead to the stabilization of the homogeneous, exfoliated phases (the isotropic and nematic regions) and to the narrowing of the immiscible two-phase re...

Theoretical Phase Diagrams of Polymer/Clay Composites: The Role of Grafted Organic Modifiers

To model the phase behavior of polymer−clay composites, we develop a free energy expression for a mixture of polymers and solid, thin disks. The free energy expression is adopted from the Onsager model for the equilibrium behavior of rigid rods. Thus, our theory takes into account the possible nematic ordering of the disks within the polymer matrix. By minimizing this free energy and calculating the chemical potentials, we construct phase diagrams for the polymer−disk mixtures. The findings provide guidelines for tailoring the polymer molecular weight and the volume fraction of the different components to fabricate thermodynamically stable mixtures with the desired morphology.

Modeling the Phase Behavior of Polymer/Clay Nanocomposites

To address the misconceptions that students typically hold concerning quantum mechanics, instructors should couple computer-based visualizations with research-based pedagogical strategies.

/pdf/improving-students-understanding-of-quantum-mechanics-4iceg387a0.pdf

Chandralekha Singh

Papers

Modeling the Interactions between Polymers and Clay Surfaces through Self-Consistent Field Theory

Student understanding of quantum mechanics

Theoretical Phase Diagrams of Polymer/Clay Composites: The Role of Grafted Organic Modifiers

Modeling the Phase Behavior of Polymer/Clay Nanocomposites

Improving students’ understanding of quantum mechanics