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

https://cyberleninka.org/article/n/1018032.pdf

Polymer nanotechnology: Nanocomposites

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/App%20Cla%20Sci15,%2011.pdf

Polymer-layered silicate nanocomposites: an overview

the kinetics of polystyrene melt intercalation in organically modified mica-type silicates were studied using X-ray diffraction and transmission electron microscopy. By monitoring the change in the integrated intensity of the basal reflection of the silicate host, the rate of conversion from unintercalated to intercalated silicate was determined at various temperatures and for various molecular weights of polystyrene. Hybrid formation is limited by mass transport into the primary particles of the host silicate and not specifically by diffusion of the polymer chains within the silicate galleries. The activation energy of hybrid formation is similar to that previously measured for polystyrene self-diffusion in the melt, implying that the mobility of the polymer chains within the host galleries is at least comparable to that in the melt.

Kinetics of polymer melt intercalation

The microstructure of various (ordered and disordered) polymer−organically modified layered silicate hybrids, synthesized via static polymer melt intercalation, is examined with X-ray diffraction and transmission electron microscopy. The ordered intercalates exhibit microstructures very similar to the unintercalated organically modified layered silicate (OLS). Polymer intercalation occurs as a front which penetrates the primary OLS particle from the external edge. The disordered hybrids, on the other hand, exhibit heterogeneous microstructures with increased layer disorder and spacing toward the polymer−primary particle boundary. In these hybrids, individual silicate layers are observed near the edge, whereas small coherent layer packets separated by polymer-filled gaps are prevalent toward the interior of the primary particle. The heterogeneous microstructure indicates that the formation of these disordered hybrids occur by a more complex process than simple sequential separation of individual layers sta...

Microstructural Evolution of Melt Intercalated Polymer−Organically Modified Layered Silicates Nanocomposites

Objectives To test the hypothesis that a blue light emitting diode (LED) light curing unit (LCU) can produce an equal dental composite depth of cure to a halogen LCU adjusted to give an irradiance of 300 mWcm–2 and to characterise the LCU's light outputs. Materials and methods Depth of cure for three popular composites was determined using a penetrometer. The Student's t test was used to analyse the depth of cure results. A power meter and a spectrometer measured the light output. Results The spectral distribution of the LCUs differed strongly. The irradiance for the LED and halogen LCUs were 290 mWcm–2 and 455 mWcm–2, when calculated from the scientific power meter measurements. The LED LCU cured all three dental composites to a significantly greater (P < 0.05) depth than the halogen LCU. Conclusions An LED LCU with an irradiance 64% of a halogen LCU achieved a significantly greater depth of cure. The LCU's spectral distribution of emitted light should be considered in addition to irradiance as a performance indicator. LED LCUs may have a potential for use in dental practice because their performance does not significantly reduce with time as do conventional halogen LCUs.

/pdf/restorative-dentistry-dental-composite-depth-of-cure-with-2byacc42qv.pdf

Restorative Dentistry: Dental composite depth of cure with halogen and blue light emitting diode technology

Does the nanometre scale topography of titanium influence protein adsorption and cell proliferation

The material most commonly used for the fabrication of complete dentures is poly (methyl methacrylate) (PMMA). This material is not ideal in every respect and it is the combination of virtues rather than one single desirable property that accounts for its popularity and usage. Despite its popularity in satisfying aesthetic demands it is still far from ideal in fulfilling the mechanical requirements of a prosthesis. The fracture of dentures may be due to the mechanical properties of the acrylic resin or may be due to a multiplicity of factors leading to failure of the denture base material. Generally, there are three routes which have been investigated to improve the impact properties of PMMA: the search for, or development of, an alternative material to PMMA; the chemical modification of PMMA such as by the addition of a rubber graft copolymer; and the reinforcement of PMMA with other materials such as carbon fibres, glass fibres and ultra-high modulus polyethylene. The following review of attempts to improve the mechanical properties of denture base material takes account of papers published during the last 30 years.

Klaus D. Jandt

Papers

Kinetics of polymer melt intercalation

Microstructural Evolution of Melt Intercalated Polymer−Organically Modified Layered Silicates Nanocomposites

Restorative Dentistry: Dental composite depth of cure with halogen and blue light emitting diode technology

Does the nanometre scale topography of titanium influence protein adsorption and cell proliferation

The reinforcement of dentures