Supramolecular structures in nanocomposite multilayered films

Tunable viscosity modification with diluted particles: when particles decrease the viscosity of complex fluids

While spherical particles are the most studied viscosity modifiers, they are well known only to increase viscosities, in particular at low concentrations of approx. 1%. Extended studies and theories on non-spherical particles in simple fluids find a more complicated behavior, but still a steady increase with increasing concentration. Involving platelets in combination with complex fluids—in our case, a bicontinuous microemulsion—displays an even more complex scenario that we analyze experimentally and theoretically as a function of platelet diameter using small angle neutron scattering, rheology, and the theory of the lubrication effect, to find the underlying concepts. The clay particles effectively form membranes in the medium that itself may have lamellar aligned domains and surfactant films in the case of the microemulsion. The two-stage structure of clay and surfactant membranes explains the findings using the theory of the lubrication effect. This confirms that layered domain structures serve for lowest viscosities. Starting from these findings and transferring the condition for low viscosities to other complex fluids, namely crude oils, even lowered viscosities with respect to the pure crude oil were observed. This strengthens our belief that also here layered domains are formed as well. This apparent contradiction of a viscosity reduction by solid particles could lead to a wider range of applications where low viscosities are desired. The same concepts of two-stage layered structures also explain the observed conditions for extremely enhanced viscosities at particle concentrations of 1% that may be interesting for the food industry.

Facile access to large-scale, self-assembled, nacre-inspired, high-performance materials with tunable nanoscale periodicities

Although advances have been reported to mimic the mechanically excellent structure of natural nacre, larger-scale applications are still limited due to time and energy-intensive preparation pathways. Herein, we demonstrate that simple high-shear homogenization of dispersions containing biobased high molecular weight sodium carboxymethyl cellulose (700 kg/mol, CMC) and natural sodium montmorillonite (MTM), serving as the soft energy-dissipating phase and reinforcing platelets, respectively, can be used to prepare large-area and thick films with well-aligned hard/soft nacre-mimetic mesostructure. During this process, core-shell nanoplatelets with intrinsic hard/soft structure form, which then self-assemble into a layered nanocomposite during water removal. The nanoscale periodicities of the alternating hard/soft layers can be precisely tuned by changing the ratio of CMC to MTM, which allows studying the evolution of mechanical properties as a function of the lamellar nanoscale periodicity and fractions of hard to soft material. Remarkable mechanical stiffness (25 GPa) and strength (320 MPa) can be obtained placing these materials among the top end of nacre-inspired materials reported so far. Mechanical homogenization also allows direct preparation of concentrated, yet homogeneous, gel-like dispersions of high nanoclay content, suited to doctor-blade large-area and thick films with essentially the same properties as films cast from dilute dispersions. In terms of functional properties, we report high-transparency, shape-persistent fire-blocking and the ability to surface-pattern via inkjet printing. Considering the simple, fully scalable, waterborne preparation pathway, and the use of nature-based components, we foresee applications as ecofriendly, bioinspired materials to promote sustainable engineering materials and novel types of functional barrier coatings and substrates.

Assessment of using laponite cross-linked poly(ethylene oxide) for controlled cell adhesion and mineralization

The in vitro cytocompatibility of silicate (Laponite clay) cross-linked poly(ethylene oxide) (PEO) nanocomposite films using MC3T3-E1 mouse preosteoblast cells was investigated while cell adhesion, spreading, proliferation and mineralization were assessed as a function of film composition. By combining the advantageous characteristics of PEO polymer (hydrophilic, prevents protein and cell adhesion) with those of a synthetic and layered silicate (charged, degradable and potentially bioactive) some of the physical and chemical properties of the resulting polymer nanocomposites could be controlled. Hydration, dissolution and mechanical properties were examined and related to cell adhesion. Overall, this feasibility study demonstrates the ability of using model Laponite cross-linked PEO nanocomposites to create bioactive scaffolds.

Insight into the Broad Field of Polymer Nanocomposites: From Carbon Nanotubes to Clay Nanoplatelets, via Metal Nanoparticles

Highly ordered polymer nanocomposites are complex materials that display a rich morphological behavior owing to variations in composition, structure, and properties on a nanometer length scale. Metal-polymer nanocomposite materials are becoming more popular for applications requiring low cost, high metal surface areas. Catalytic systems seem to be the most prevalent application for a wide range of metals used in polymer nanocomposites, particularly for metals like Pt, Ni, Co, and Au, with known catalytic activities. On the other hand, among the most frequently utilized techniques to prepare polymer/CNT and/or polymer/clay nanocomposites are approaches like melt mixing, solution casting, electrospinning and solid-state shear pulverization. Additionally, some of the current and potential applications of polymer/CNT and/or polymer/clay nanocomposites include photovoltaic devices, optical switches, electromagnetic interference (EMI) shielding, aerospace and automotive materials, packaging, adhesives and coatings. This extensive review covers a broad range of articles, typically from high impact-factor journals, on most of the polymer-nanocomposites known to date: polymer/carbon nanotubes, polymer/metal nanospheres, and polymer/clay nanoplatelets composites. The various types of nanocomposites are described form the preparation stages to performance and applications. Comparisons of the various types of nanocomposites are conducted and conclusions are formulated.