Adsorption of Surface-Modified Silica Nanoparticles to the Interface of Melt Poly(lactic acid) and Supercritical Carbon Dioxide

Interfacial Assembly of Bacterial Microcompartment Shell Proteins in Aqueous Multiphase Systems

Compartments are a fundamental feature of life, based variously on lipid membranes, protein shells, or biopolymer phase separation. Here, this combines self-assembling bacterial microcompartment (BMC) shell proteins and liquid-liquid phase separation (LLPS) to develop new forms of compartmentalization. It is found that BMC shell proteins assemble at the liquid-liquid interfaces between either 1) the dextran-rich droplets and PEG-rich continuous phase of a poly(ethyleneglycol)(PEG)/dextran aqueous two-phase system, or 2) the polypeptide-rich coacervate droplets and continuous dilute phase of a polylysine/polyaspartate complex coacervate system. Interfacial protein assemblies in the coacervate system are sensitive to the ratio of cationic to anionic polypeptides, consistent with electrostatically-driven assembly. In both systems, interfacial protein assembly competes with aggregation, with protein concentration and polycation availability impacting coating. These two LLPS systems are then combined to form a three-phase system wherein coacervate droplets are contained within dextran-rich phase droplets. Interfacial localization of BMC hexameric shell proteins is tunable in a three-phase system by changing the polyelectrolyte charge ratio. The tens-of-micron scale BMC shell protein-coated droplets introduced here can accommodate bioactive cargo such as enzymes or RNA and represent a new synthetic cell strategy for organizing biomimetic functionality.

Synthesis and Characterization of Thermosensitive P(NIPAAm-co-AAc)-Grafted Silica Nanocomposites for Smart Architectural Coatings

In this study, a new class of thermosensitive poly(N-isopropylacrylamide)-co-poly(acrylic acid) (P(NIPAAm-co-AAc))-grafted modified silica (m-silica) nanocomposites was prepared using a sol-gel technique. The addition of silica to P(NIPAAm-co-AAc) copolymer hydrogel has the potential to open up new applications in the development of thermosensitive building materials by leveraging the favorable thermal characteristics of P(NIPAAm-co-AAc). The silica was prepared using 3-aminopropyltriethoxysilane and 4,4'-azobis(4-cyanovaleric acid) to form the m-silica powder, which increased the adhesion between the organic and inorganic hybrid materials. The P(NIPAAm-co-AAc) copolymer hydrogel was mixed with the m-silica to form the P(NIPAAm-co-AAc)-grafted m-silica nanocomposites. Scanning electron microscopy, X-ray diffraction analysis, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and thermosensitive measurement were conducted to evaluate the structure and water-holding capacity of the nanocomposites. The results indicated that the P(NIPAAm-co-AAc)-grafted m-silica nanocomposites could retain water for more than 300 min at temperatures higher than the lower critical solution temperature. The P(NIPAAm-co-AAc)-grafted m-silica nanocomposites exhibited favorable thermosensitive properties and may therefore be applied in smart architectural coatings.

A Review on Synthesis, Properties, and Applications of Polylactic Acid/Silica Composites

Polylactic acid (PLA)/silica composites as multifunctional high-performance materials have been extensively examined in the past few years by virtue of their outstanding properties relative to neat PLA. The fabrication methods, such as melt-mixing, sol–gel, and in situ polymerization, as well as the surface functionalization of silica, used to improve the dispersion of silica in the polymer matrix are outlined. The rheological, thermal, mechanical, and biodegradation properties of PLA/silica nanocomposites are highlighted. The potential applications arising from the addition of silica nanoparticles into the PLA matrix are also described. Finally, we believe that a better understanding of the role of silica additive with current improvement strategies in the dispersion of this additive in the polymer matrix is the key for successful utilization of PLA/silica nanocomposites and to maximize their fit with industrial applications needs.

Surface-assisted assembly of a histidine-rich lipidated peptide for simultaneous exfoliation of graphite and functionalization of graphene nanosheets

Biological molecules have promising potential to exfoliate graphite and produce biocompatible graphene nano-materials for biomedical applications. Here, a systematic design of a histidine-rich lipidated peptide sequence is presented that simultaneously exfoliates graphite flakes and functionalizes the resulting graphene nanosheets (∼150 nm lateral size) with long-term dispersion stability in aqueous solution (>8 months). The details of peptide/peptide and peptide/graphite interactions are probed using various microscopy, spectroscopy and molecular dynamics simulation methods. The results show that histidine and stearic acid interact with the graphite surface through π-π stacking and hydrophobic forces, respectively. Surface-assisted assembly of peptide molecules is then initiated via hydrogen bonds between deprotonated histidine segments, and a textured peptide nano-structure is formed. The work of adhesion between the peptide and graphite is found to be high enough to promote exfoliation of graphite flakes through layer-by-layer peeling of graphene nanosheets. The positively charged arginine in the peptide is exposed outward, and is responsible for the stable dispersion. The peptide molecules are sufficiently small, presenting the possibility to insert into and increase the spacing between the graphitic layers for enhanced exfoliation. The peptide-functionalized graphene nanosheets not only show great biocompatibility with cells in vitro, but also enhance cancer drug uptake by the cells.

Stability Mechanism of Nitrogen Foam in Porous Media with Silica Nanoparticles Modified by Cationic Surfactants

This work aims at studying the effect of electrostatic interactions between cationic surfactants and silica nanoparticles (NPs) on foam stability in porous media. The physio-chemical property of NPs, the gas-liquid interface properties, the foam flow characteristics, together with the stability under different concentrations of surfactant and NPs were investigated and compared. It was found that the affinity of silica NPs to the surface is tunable by variation of surfactant concentrations. NPs and surfactants as a whole assembling at the surface substantially improve the foam stability in static and dynamic tests. These surfactant-modified NPs accumulate at the bubble surface and remain stable under dilution of brine, providing a barrier effectively preventing coalescence. In addition, foam stability is enhanced since the layer of NPs significantly reduces the mass transfer rate, consequently mitigating the Ostwald ripening.

From micro/nano structured isotactic polypropylene to a multifunctional low-density nanoporous medium

A homogeneous low-density nano-porous medium of isotactic polypropylene (iPP) with a low thermal conductivity was fabricated using supercritical carbon dioxide (scCO₂).