Novel and simple design of nanostructured, super-insulative and flexible hybrid silica aerogel with a new macromolecular polyether-based precursor.

This study reports a new strategy to fabricate a thermally super-insulative and flexible hybrid silica aerogel. A new generation of polymeric precursors was first synthesized for hybrid organic/inorganic silica aerogels from an epoxide ring containing a silica precursor. Ring opening polymerization (ROP) was used so as to insert flexible ether groups into the main chain. It has been demonstrated that the particulate structure of the polyether-based silica aerogel could be changed to a novel non-particulate and continuous one, by meticulous control of the thermodynamics, namely, through variations of the molecular weight of the polymeric precursor, the amount of the non-solvent, and the temperature. The study presents a new strategy to manufacture a polyether-based hybrid silica aerogel, which is fast and scalable, and also eliminates the aging process while accelerating the gelation time. This new strategy reduces the wet gel preparation time, including gelation, aging and solvent exchange, from several days to just a few seconds. However, this structure suffers from a low void fraction and wide pore size distribution. These drawbacks are then removed by chemically incorporating pre-polymerized vinyl trimethoxysilane chains. The resultant aerogels exhibit thermal superinsulation (λ = 15.9 mW·m-1·K-1) while providing good mechanical properties and flexibility. The polyether-based aerogels also demonstrated good performance as adsorbent material to remove organic solvents from water.

Robust, ultra-insulative and transparent polyethylene-based hybrid silica aerogel with a novel non-particulate structure.

Aerogels derived from pre-polymerized vinyl trimethoxy silane (VTMS) precursor with nano-size particles are known to exhibit outstanding mechanical and insulation properties. However, the density reduction has been limited by the poor connectivity. This paper presents an innovative technology to generate a new class of VTMS-based hybrid silica aerogels that possess outstanding non-particulate, reticulated structure and superior properties. This technology relies on spinodal decomposition instead of conventionally exploited binodal decomposition, which leads to a particulate structure. This new aerogel technology has significantly increased the void fraction of the pre-polymerized VTMS-based aerogel, which could not be achieved previously using binodal decomposition. The increased void fraction in the form of nano-pores with an average pore size of 21.75 nm nullifies the gas thermal conductivity effectively. Another consequence of the non-particulate structure is decreased processing time by removing the aging step. These improvements are due to the non-particulate structure's increased connectivity produced by spinodal decomposition. This novel structure was then compared to a particulate counterpart aerogel of the same material derived from the conventional binodal decomposition of the pre-polymerized VTMS precursor. To further decrease the processing cost, a lower molecular-weight polymeric precursor was synthesized under milder polymerization conditions. The effects of the polymeric precursor's molecular weight on the mechanical and thermal properties of the aerogel created via spinodal decomposition were also investigated.

Partial to complete wetting transitions in immiscible ternary blends with PLA: the influence of interfacial confinement.

In this study it is shown that the three different intermediate phases in melt blended ternary PLA/PHBV/PBS, PLA/PBAT/PE and PLA/PE/PBAT systems all demonstrate partial wetting, but have very different wetting behaviors as a function of composition and annealing. The interfacial tension of the various components, their spreading coefficients and the contact angles of the confined partially wet droplets at the interface are examined in detail. A wetting transition from partially wet droplets to a complete layer at the interface is observed for both PHBV and PBAT by increasing the concentration and also by annealing. In contrast, in PLA/PE/PBAT, the partially wet droplets of PE at the interface of PLA/PBAT coalesce and grow in size, but remain partially wet even at a high PE concentration of 20% and after 30 min of quiescent annealing. The dewetting speed of the intermediate phase is found to be the principal factor controlling these wetting transitions. This work shows the significant potential for controlled wetting and structuring in ternary polymer systems.

Partial and Complete Wetting in Ultralow Interfacial Tension Multiphase Blends with Polylactide.

The control of phase structuring in multiphase blends of polylactide (PLA) with other polymers is a viable approach to promote its broader implementation. In this article, ternary and quaternary blends of PLA with poly(butylene succinate) (PBS), poly(butylene adipate-co-terephthalate) (PBAT), and poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) are prepared by melt blending. The interfacial tensions between components are measured using three different techniques, and a Fourier transform infrared imaging technique is developed for the purpose of unambiguous phase identification. A tricontinuous complete wetting behavior is observed for the ternary 33PLA/33PBS/33PBAT blend before and after quiescent annealing, which correlates closely with spreading theory analysis. In the quaternary PLA/PBS/PBAT/PHBV blend, a concentration-dependent wetting behavior is found. At 10 vol % PBAT, self-assembled partially wet droplets of PBAT are observed at the interface of PBS and PHBV, and they remain stable after quiescent annealing as predicted by spreading theory. In contrast, at 25 vol % PBAT, a quadruple continuous system is observed after mixing, which only transforms to partially wet PBAT droplets after subsequent annealing. These results clearly indicate the potential of composition control during the mixing of multiphase systems to result in a complete change of spreading behavior.