The Effect of POSS Type on the Shape Memory Properties of Epoxy-Based Nanocomposites

POSS and SSQ Materials in Dental Applications: Recent Advances and Future Outlooks

Recently, silsesquioxanes (SSQ) and polyhedral oligomeric silsesquioxanes (POSS) have gained much interest in the area of biomaterials, mainly due to their intrinsic properties such as biocompatibility, complete non-toxicity, the ability to self-assemble and to form a porous structure, facilitating cell proliferation, creating a superhydrophobic surface, osteoinductivity, and ability to bind hydroxyapatite. All the above has resulted in new developments in medicine. However, the application of POSS-containing materials in dentistry is still at initial stage and deserves a systematic description to ensure future development. Significant problems, such as reduction of polymerization shrinkage, water absorption, hydrolysis rate, poor adhesion and strength, unsatisfactory biocompatibility, and corrosion resistance of dental alloys, can be addressed by the design of multifunctional POSS-containing materials. Because of the presence of silsesquioxanes, it is possible to obtain smart materials that allow the stimulation of phosphates deposition and repairing of micro-cracks in dental fillings. Hybrid composites result in materials exhibiting shape memory, as well as antibacterial, self-cleaning, and self-healing properties. Moreover, introducing POSS into polymer matrix allows for materials for bone reconstruction, and wound healing. This review covers the recent developments in the field of POSS application in dental materials and gives the future perspectives within a promising field of biomedical material science and chemical engineering.

Novel axial dynamic mechanical analysis setup for thermo-analytical study and curing kinetics optimization of thermoset adhesives

Thermo-analytical studies of thermoset adhesives, either during research and development or in quality assurance activities, involve the application of various analytical equipment for adhesive characterization, from initial mixing to final product decomposition. Gelation is usually measured with rheometers or dynamic mechanical analyzers (DMAs); curing, post-curing, and curing kinetics are often studied using differential scanning calorimetry (DSC). Glass transition temperature (T_g) is measured via DSC or DMA, and finally, thermal decomposition measurements are done using thermal gravimetric analysis. Here, we present a new curing kinetics optimization module (C-KOM), an extension to an axial DMA, and a protocol for its usage, which combines elements from all of the above thermo-analytical techniques into one tool. As a case study, we apply C-KOM to investigate the effect of the curing temperature on the physical properties of an epoxy adhesive including gelation and end of cure points as well as its T_g. The data collected via C-KOM were used to extract the adhesive's curing reaction rates and its activation energy. Our research allowed us to compare and evaluate previously suggested curing procedures and assess their validity. As a final step, the thermal decomposition temperature of the epoxy adhesive was also identified via C-KOM. The newly suggested C-KOM setup provides a fast path toward characterization and optimization of the curing processes of thermoset materials in a way that was not available before.

Influence of POSS Type on the Space Environment Durability of Epoxy-POSS Nanocomposites

In order to use polymers at low Earth orbit (LEO) environment, they must be protected against atomic oxygen (AO) erosion. A promising protection strategy is to incorporate polyhedral oligomeric silsesquioxane (POSS) molecules into the polymer backbone. In this study, the space durability of epoxy-POSS (EPOSS) nanocomposites was investigated. Two types of POSS molecules were incorporated separately—amine-based and epoxy-based. The outgassing properties of the EPOSS, in terms of total mass loss, collected volatile condensable material, and water vapor regain were measured as a function of POSS type and content. The AO durability was studied using a ground-based AO simulation system. Surface compositions of EPOSS were studied using high-resolution scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that with respect to the outgassing properties, only some of the EPOSS compositions were suitable for the ultrahigh vacuum space environment, and that the POSS type and content had a strong effect on their outgassing properties. Regardless of the POSS type being used, the AO durability improved significantly. This improvement is attributed to the formation of a self-passivated AO durable SiO₂ layer, and demonstrates the potential use of EPOSS as a qualified nanocomposite for space applications.