CO₂ Separation in Nanocomposite Membranes by the Addition of Amidine and Lactamide Functionalized POSS® Nanoparticles into a PVA Layer

Self-Healing of Poly(vinyl Alcohol)/Poly(acrylic Acid)-Polytetrahydrofuran-Poly(acrylic Acid) Blend Boosted via Shape Memory

The self-healable polymers that can repair physical damage autonomously to extend their lifetime and reduce maintenance costs are promising intelligent materials. However, utilizing shape memory to facilitate self-repair is unusual at present. In this work, a series of poly(acrylic acid)-polytetrahydrofuran-poly(acrylic acid) polymers (PAA-PTMG-PAA, diPAA-PTMG) are synthesized as a switching phase and healing accelerator to blend into poly(vinyl alcohol) (PVA). The water swelling rate of the blend is up to 400.0% at 1/1 molecular weight ratio of PTMG/PAA and 20.0 wt % blend ratio of diPAA-PTMG to PVA, and its crystallization is changed significantly under wet conditions. The blend membrane exhibits not only a good hydrothermal-response shape memory effect but also a favorable self-healing behavior. The tensile strength and elongation at break are 12.4 MPa and 320.0% after healing at 25 °C, respectively. In particular, the wound membrane can achieve a better self-healing effect with the assistance of shape memory at 37 °C, and the elongation at the break increased to 515.9% after healing. The membrane is not cytotoxic, so it will be a promising biomedical material.

Multiple Amine-Contained POSS-Functionalized Organosilica Membranes for Gas Separation

A new polyhedral oligomeric silsesquioxane (POSS) designed with eight –(CH₂)₃–NH–(CH₂)₂–NH₂ groups (PNEN) at its apexes was used as nanocomposite uploading into 1,2-bis(triethoxysilyl)ethane (BTESE)-derived organosilica to prepare mixed matrix membranes (MMMs) for gas separation. The mixtures of BTESE-PNEN were uniform with particle size of around 31 nm, which is larger than that of pure BTESE sols. The characterization of thermogravimetric (TG) and gas permeance indicates good thermal stability. A similar amine-contained material of 3-aminopropyltriethoxysilane (APTES) was doped into BTESE to prepare hybrid membranes through a copolymerized strategy as comparison. The pore size of the BTESE-PNEN membrane evaluated through a modified gas-translation model was larger than that of the BTESE-APTES hybrid membrane at the same concentration of additions, which resulted in different separation performance. The low values of E_p(CO₂)-E_p(N₂) and E_p(N₂) for the BTESE-PNEN membrane at a low concentration of PNEN were close to those of copolymerized BTESE-APTES-related hybrid membranes, which illustrates a potential CO₂ separation performance by using a mixed matrix membrane strategy with multiple amine POSS as particles.

Mixed Matrix Membranes

In recent decades, mixed matrix membranes (MMMs) have attracted considerable interest in research laboratories worldwide, motivated by the gap between the growing interest in developing novel mixed matrix membranes by various research groups and the lack of large-scale implementation. This Special Issue contains six publications dealing with the current opportunities and challenges of mixed matrix membranes development and applications as solutions for the environmental and health challenges of 21st century society.

Study of Gases Permeation in Necklace-Shaped Dimethylsiloxane Polymers Bearing POSS Cages

The transport of small gases (H₂, CO₂, N₂, O₂) through a series of novel membranes based on necklace-shaped inorganic polymers (DMS@POSS), in which a polyhedral oligomeric silsesquioxane (POSS) cage unit and soft chains of oligo-dimethyl siloxane (DMS) were alternately connected, was investigated. The influence of the DMS chain length and crosslinking density of the DMS@POSS on membrane properties were studied. The membranes revealed characteristic structure-property relation towards both glass transition and gases transport. Specifically, clear dependence of properties from the length of DMS units (or overall siloxane content) was revealed. Gas transport properties, when compared to state-of-art polydimethylsiloxane and commercial silicone rubber, demonstrated significantly higher selectivity of DMS@POSS for carbon dioxide (in CO₂/N₂), hydrogen (in H₂/N₂) and oxygen (in O₂/N₂) but lowered permeability, proportional to the amount of POSS in the material. With a precise control over mechanical and thermal properties compared to conventional silicone rubbers, described materials could be considered as materials of choice in niche gas separation or other applications.