Ultralight, reusable biopolymer aerogels: Formation mechanisms to applications in selective fluid sorption and oil spill remediation

Highly porous (99.7 %), ultra-light (4.3 mg/ml) and mechanically robust cellulose ester aerogels with tailored hydrophobicity are synthesized. The aerogels achieve maximum compression strain of 92 % without failure and reach a compressive stress of 350 kPa, which is 100 times higher than that reported for cellulosic aerogels. In its native, unmodified state, the aerogels are hydrophilic and display unprecedented water uptake (45-90 g/g) while affording wet strength. Further adjustment of the aerogels towards hydrophobicity and oleophilicity via chemical vapor deposition with an organo-silane species reveal them to exhibit high oil retention (20-30 g/g aerogel) while maintaining mechanical integrity for fast oil cleanup from aqueous media under marine conditions. The modified aerogels are reusable and durable as they retain their hydrophobicity for months under ambient conditions. The Zisman and Fowkes theoretical frameworks are used to identify the selectiveness of the aerogel and establish a criterion for separation of various non-polar fluids from water media

Self supporting Nanodiamond gels: Elucidating colloidal interactions through rheology

While ND represents a promising class of nanofiller due to its high surface area, superior mechanical strength, optical transparency, tailorable surface functionality and biocompatibility, much remains unknown about the behavior of ND dispersions and their responses to various processing conditions. We hypothesize that controlling interactions in ND dispersions will lead to highly functional systems with tunable modulus and shear response. Steady and dynamic rheology techniques are thus employed to systematically investigate nanodiamonds dispersed in model polar and non-polar media and examine the microstructure and concomitant rheological behavior. We find that low concentrations of ND form gels almost instantaneously in a non-polar media, the strength of which follow a power-law behavior. In contrast, ND’s in polar media show a time-dependent behavior with the modulus increasing with time. We attribute the difference in behavior to variations in inter-particle interactions as well as the interaction of the ND with the media. Large steady and oscillatory strains are applied to ND colloidal gels to investigate the role of shear in gel microstructure breakdown and recovery. For colloidal gels in non-polar medium, the incomplete recovery of elastic modulus at high strain amplitudes indicates dominance of particle-particle interactions; however, in polar media the complete recovery of elastic modulus even at high strain amplitudes indicates dominance of particle-solvent interactions. These results taken together provide a platform to develop self-supporting gels with tunable properties in terms of ND concentration, and solvent ty

Hydrogels Of Chiral–Nematic Cellulose Nanocrystals And Nanochitin

The mechanical strength of hydrogels and aerogels produced from inorganic nano- and microparticles has been out of limits for those based on organic counterparts. Control over the nanoscale architecture of such materials is a possible answer to this challenge, which can even expand properties and functions, including mechano-optical activity. Here we show unprecedented levels of strength by controlling the assembly architecture of cellulose nanocrystals (CNC) and nanochitin (NCh), nanoscaled building blocks presenting anisometry and high intrinsic strength. High yield (\u3e85%) and low-energy deconstruction of never-dried residual marine biomass is proposed following partial deacetylation and microfluidization. This process results in NCh of ultrahigh axial size that produce highly entangled networks upon pH shift. Viscoelastic and strong hydrogels are formed by ice templating upon freezing and thawing with simultaneous cross-linking. Slow supercooling and ice nucleation at −20 °C make ice crystals grow slowly and exclude nanochitin and cross-linkers, becoming spatially confined at the interface. At a NCh concentration as low as 0.4 wt %, highly viscoelastic hydrogels are formed, at least an order of magnitude larger compared to those measured for the strongest chitin-derived hydrogels reported so far. The water absorption capacity of the hydrogels reaches a value of 466 g/g. Moreover, our results demonstrate that chiral-nematically ordered hydrogels can lead to aerogels with controlled meso- and microstructures that replicate the liquid crystalline phase transitions of the hydrogels. The obtained architectures are feasible by systematically varying the long-range order of the aqueous CNC dispersions, from mostly isotropic to completely anisotropic. The resultant aerogels display strong coupling between the mesopore fraction and selective light reflection (iridescence) as a function of mechanical load. Specifically, we find that the mechanical performance associated with pore compression under load is greatly enhanced by chiral nematic ordering. These new limits in the mechanical properties of CNC- and NCh-based hydrogels and aerogels point to new structural considerations for the synthesis of porous constructs that exploit the inherent long-range order of such unique building blocks

Heterogeneous Acetylation of Plant Fibers into Micro- and Nanocelluloses for the Synthesis of Highly Stretchable, Tough, and Water-Resistant Co-continuous Filaments via Wet-Spinning

| openaire: EC/H2020/788489/EU//BioELCellHeterogeneous acetylation of wood fibers is proposed for weakening their interfibrillar hydrogen bonding, which facilitates their processing into micro- and nanocelluloses that can be further used to synthesize filaments via wet-spinning. The structural (SEM, WAXD), molecular (SEC), and chemical (FTIR, titration) properties of the system are used to propose the associated reaction mechanism. Unlike the homogeneous acetylation, this method does not alter the main morphological features of cellulose fibrils. Thus, we show for the first time, the exploitation of synergies of compositions simultaneously comprising dissolved cellulose esters and suspended cellulose micro- and nanofibrils. Such colloidal suspension forms a co-continuous assembly with a matrix that interacts strongly with the micro- and nanofibrils in the dispersed phase. This facilitates uninterrupted and defect-free wet-spinning. Upon contact with an antisolvent (water), filaments are easily formed and display a set of properties that set them apart from those reported so far for nanocelluloses: a remarkable stretchability (30% strain) and ultrahigh toughness (33 MJ/m3), both surpassing the values of all reported nanocellulose-based filaments. All the while, they also exhibit competitive stiffness and strength (6 GPa and 143 MPa, respectively). Most remarkably, they retain 90% of these properties after long-term immersion in water, solving the main challenge of the lack of wet strength that is otherwise observed for filaments synthesized from nanocelluloses.Peer reviewe

Featherlight, Mechanically Robust Cellulose Ester Aerogels for Environmental Remediation

A unique combination of well-established synthesis procedures involving chemical cross-linking, careful solvent exchange to water, and subsequent freeze drying is used to produce ultralight (4.3 mg/mL) and highly porous (99.7%) cellulose diacetate (CDA) aerogels with honeycomb morphology. This versatile synthesis approach is extended to other nonaqueous polymers with hydroxyl functionalities such as cellulose acetate propionate and cellulose acetate butyrate to produce a single component polymer aerogel. These aerogels demonstrate a maximum water and oil uptake of up to 92 and 112 g/g, respectively. The honeycomb morphology provides a maximum compression strain of 92% without failure and reaches a compressive stress of 350 kPa, for 4 w/v % CDA aerogels (4%), which is higher than that reported for cellulosic aerogels. The 4% CDA aerogel were rendered hydrophobic and oleophilic via chemical vapor deposition with organosilane. The modified CDA aerogel surpasses their counterparts in maintaining their mechanical integrity for fast oil cleanup and efficient oil retention from aqueous media under marine conditions. These aerogels are identified to be reusable and durable for a long period.Peer reviewe

Synthesis of organic aerogels with tailorable morphology and strength by controlled solvent swelling following Hansen solubility

We introduce a generalized approach to synthesize aerogels that allows remarkable control over its mechanical properties. The Hansen solubility parameters are used to predict and regulate the swelling properties of the precursor gels and, consequently, to achieve aerogels with tailored density and mechanical properties. As a demonstration, crosslinked organogels were synthesized from cellulose esters to generate aerogels. By determination of Hansen's Relative Energy Difference, it was possible to overcome the limitations of current approaches that solely rely on the choice of precursor polymer concentration to achieve a set of aerogel properties. Hence, from a given concentration, aerogels were produced in a range of mass densities, from 25 to 113 mg/cm3. Consequently, it was possible to tailor the stiffness, toughness and compressive strength of the aerogels, in the ranges between 14-340, 4-103 and 22-373 kPa, respectively. Additionally, unidirectional freeze-drying introduced pore alignment in aerogels withhoneycomb morphologies and anisotropy. Interestingly, when the swelling of the polymeric gel was arrested in a non-equilibrium state, it was possible to gain additional control of the property space. The proposed method is a novel and generic solution to achieving full control of aerogel development, which up to now has been an intractable challenge.Peer reviewe

Experimental and Predictive Description of the Morphology of Wet-Spun Fibers

| openaire: EC/H2020/788489/EU//BioELCellThe prediction of the morphology of wet-spun fibers has so far been only possible by complex and experimentally intensive approaches that include the construction of ternary phase diagrams. Ultimately, however, the available models give approximate information. Here we propose an alternative predictive approach that uses design principles based on the combination of (1) relative energy difference (RED) of Hansen solubility and (2) a kinetic parameter "T" that considers mass transfer effects. Such a model is applied and experimentally validated for a priori determination of the diameter and internal morphology of wet-spun fibers. Remarkably, only three. variables relevant to wet-spinning are needed, namely, the choice of polymer, solvent, and nonsolvent types. A combination of systems is tested, and the morphology of the obtained fibers is determined via electron microscopy. Aspects related to demixing, internal specific surface area (BET), and layer formation on the fibers are described qualitatively. The facile implementation of the design parameters is further confirmed through comparison with data published on the subject. Our proposed model is expected to accelerate future developments in nanomaterials, especially in the context of ongoing efforts related to fiber spinning with biopolymers.Peer reviewe

Expanding the upper limits of robustness of cellulose nanocrystal aerogels

| openaire: EC/H2020/788489/EU//BioELCellControl over the nanoscale architecture of a material enables fine tuning of its physical characteristics and associated functions. Depending on the performance demands, properties such as active surface area, density, optical response, transport characteristics and mechanical resilience can be tailored by nanostructuring. Herein, we exploit the liquid crystalline phase transitions in aqueous dispersions of highly anisometric, nanoscaled and high strength (EA > 150 GPa) cellulose nanocrystals (CNCs) to afford chiral-nematic ordered aerogels with controlled meso- and microstructures. Unprecedented levels of specific strength and toughness were achieved by controlling CNC assembly and derived architectures. We determined that the specific strength, and toughness, of CNC aerogels are improved by up to 137% and 60%, respectively, compared with the highest reported values for aerogels formed solely from cellulose nanofibrils or nanocrystals. Our results demonstrate that chiral-nematic ordered aerogels with controlled meso- and microstructures replicate the liquid crystalline phase transitions of CNCs in aqueous dispersions. The obtained architectures are evaluated systematically by varying the long-range order of the aqueous CNC dispersion from mostly isotropic to completely anisotropic. The resulting aerogels display a strong relationship between the mesopore fraction and selective light reflection (iridescence) as a function of mechanical load. Specifically, we find that the mechanical performance associated with pore compression under load is greatly enhanced by chiral-nematic ordering. The new limits in the mechanical properties of CNC-based aerogels point to new structural considerations for the synthesis of next generation porous constructs that exploit the inherent long-range order of such building blocks.Peer reviewe

Effect of Anisotropy of Cellulose Nanocrystal Suspensions on Stratification, Domain Structure Formation, and Structural Colors

| openaire: EC/H2020/788489/EU//BioELCellOutstanding optical and mechanical properties can be obtained from hierarchical assemblies of nanoparticles. Herein, the formation of helically ordered, chiral nematic films obtained from aqueous suspensions of cellulose nanocrystals (CNCs) were studied as a function of the initial suspension state. Specifically, nanoparticle organization and the structural colors displayed by the resultant dry films were investigated as a function of the anisotropic volume fraction (AVF), which depended on the initial CNC concentration and equilibration time. The development of structural color and the extent of macroscopic stratification were studied by optical and scanning electron microscopy as well as UV–vis spectroscopy. Overall, suspensions above the critical threshold required for formation of liquid crystals resulted in CNC films assembled with longer ranged order, more homogeneous pitches along the cross sections, and narrower specific absorption bands. This effect was more pronounced for the suspensions that were closer to equilibrium prior to drying. Thus, we show that high AVF and more extensive phase separation in CNC suspensions resulted in large, long-range ordered chiral nematic domains in dried films. Additionally, the average CNC aspect ratio and size distribution in the two separated phases were measured and correlated to the formation of structured domains in the dried assemblies.Peer reviewe

High Axial Ratio Nanochitins for Ultrastrong and Shape-Recoverable Hydrogels and Cryogels via Ice Templating

| openaire: EC/H2020/788489/EU//BioELCellHigh yield (>85%) and low-energy deconstruction of never-dried residual marine biomass is proposed following partial deacetylation and microfluidization. This process results in chitin nanofibrils (nanochitin, NCh) of ultrahigh axial size (aspect ratios of up to 500), one of the largest for bioderived nanomaterials. The nanochitins are colloidally stable in water (ζ-potential = +95 mV) and produce highly entangled networks upon pH shift. Viscoelastic and strong hydrogels are formed by ice templating upon freezing and thawing with simultaneous cross-linking. Slow supercooling and ice nucleation at -20 °C make ice crystals grow slowly and exclude nanochitin and cross-linkers, becoming spatially confined at the interface. At a nanochitin concentration as low as 0.4 wt %, highly viscoelastic hydrogels are formed, with a storage modulus of ∼16 kPa, at least an order of magnitude larger compared to those measured for the strongest chitin-derived hydrogels reported so far. Moreover, the water absorption capacity of the hydrogels reaches a value of 466 g g -1 . Lyophilization is effective in producing cryogels with a density that can be tailored in a wide range of values, from 0.89 to 10.83 mg·cm -3 , and corresponding porosity, between 99.24 and 99.94%. Nitrogen adsorption results indicate reversible adsorption and desorption cycles of macroporous structures. A fast shape recovery is registered from compressive stress-strain hysteresis loops. After 80% compressive strain, the cryogels recovered fast and completely upon load release. The extreme values in these and other physical properties have not been achieved before for neither chitin nor nanocellulosic cryogels. They are explained to be the result of (a) the ultrahigh axial ratio of the fibrils and strong covalent interactions; (b) the avoidance of drying before and during processing, a subtle but critical aspect in nanomanufacturing with biobased materials; and (c) ice templating, which makes the hydrogels and cryogels suitable for advanced biobased materials.Peer reviewe