Smart ultra-stable foams stabilized using cellulose nanocrystal (CNC) gels via noncovalent bonding

Cellulose Nanocrystal (CNC) Gels: A Review

The aim of this article is to review the research conducted in the field of aqueous and polymer composites cellulose nanocrystal (CNC) gels. The experimental techniques employed to characterize the rheological behavior of these materials will be summarized, and the main advantages of using CNC gels will also be addressed in this review. In addition, research devoted to the use of numerical simulation methodologies to describe the production of CNC-based materials, e.g., in 3D printing, is also discussed. Finally, this paper also discusses the application of CNC gels along with additives such as cross-linking agents, which can represent an enormous opportunity to develop improved materials for manufacturing processes.

CO2-responsive gels

CO₂-responsive materials undergo a change in chemical or physical properties in response to the introduction or removal of CO₂. The use of CO₂ as a stimulus is advantageous as it is abundant, benign, inexpensive, and it does not accumulate in a system. Many CO₂-responsive materials have already been explored including polymers, latexes, surfactants, and catalysts. As a sub-set of CO₂-responsive polymers, the study of CO₂-responsive gels (insoluble, cross-linked polymers) is a unique discipline due to the unique set of changes in the gels brought about by CO₂ such as swelling or a transformed morphology. In the past 15 years, CO₂-responsive gels and self-assembled gels have been investigated for a variety of emerging potential applications, reported in 90 peer-reviewed publications. The two most widely exploited properties include the control of flow (fluids) via CO₂-triggered aggregation and their capacity for reversible CO₂ absorption-desorption, leading to applications in Enhanced Oil Recovery (EOR) and CO₂ sequestration, respectively. In this paper, we review the preparation, properties, and applications of these CO₂-responsive gels, broadly classified by particle size as nanogels, microgels, aerogels, and macrogels. We have included a section on CO₂-induced self-assembled gels (including poly(ionic liquid) gels).

Behaviour of polymer-coated composite nanoparticles at bubble-stabilizing interfaces during bubble coarsening and accelerated coalescence: A Cryo-SEM study

HYPOTHESIS

Dynamics of polymer-coated silica composite nanoparticles (CPs) during bubble coarsening is highly dominated by the behaviour of the polymer layer, while in-situ particle aggregation would lead to accelerated bubble coalescence.

EXPERIMENTS

CPs-stabilized foams were prepared in 0.1 M and 0.55 M Na₂SO₄ solution, referring to the 0.1 M and 0.55 M foam/bubble respectively. The 0.1 M to 0.55 M transition foam was also prepared. High resolution Cryo-SEM was originally used to investigate the CPs behaviour at the bubble-stabilizing interface during bubble coarsening and accelerated coalescence.

FINDINGS

The 0.1 M bubble-stabilizing interface buckles in uniaxial compression due to coarsening, with the CPs being observed to desorb from the interface. While the CPs were visualized to rearrange into crumpled particle multi-layers surrounding the shrinking 0.55 M bubbles, due to the adhesion between interpenetrating polymer chains and the unique lubrication effect of the PVP layers. The 0.1 M to 0.55 M transition foaming behaviour was also studied. Cracks and voids were observed at interfaces surrounding the transition bubbles driven by in-situ particle aggregation, resulting in accelerated bubble coalescence during the transition process.

Liquid Foam Stabilized by a CO2-Responsive Surfactant and Similarly Charged Cellulose Nanofibers for Reversibly Plugging in Porous Media

CO₂ foams are of great importance in oil recovery but challenging in some aspects like long-term stabilization and time-separated conflict. In this work, a stability-enhanced switchable foam was fabricated using bis-(2-hydroxyethoxy) olefine amine (BOA) and trace amounts (0.05 wt %) of cationic-modified cellulose nanofibers (CCNFs). The CCNF was developed using sequentially functionalized CNF with diamine groups, which were essential to promote the aqueous dispersibility and a key for strengthening the stabilization of foam. The combination of similarly charged CCNFs and BOA in the presence of CO₂ contributed to both surface activity and viscoelasticity. It was demonstrated that CCNFs were entangled and stacked to form the compact films and possessed the ability to costabilize the lamellae, as observed by microscopic studies. In addition, the intermolecular H-bonds were promoted in the binary system after being protonated by CO₂ and thus balancing the electrostatic forces, as explored by spectroscopy characterizations. The soft fibrous structure of the CCNF was also capable of wrapping gas bubbles in the form of a functional membrane with both low gas permeability and high surface potential, which slowed down the coarsening and coalescence. Of particular interest is that the reversible protonation state of CCNF-BOA complexes upon the alternate treatment with CO₂/N₂ led to reversible fast foaming/defoaming, which would be beneficial to construct the steerable plugging in the sand pack. This work is expected to provide a new direction and application of the CO₂ responsive foam stabilized by similarly charged nanocellulose fibers in oilfield development.