Browsing by Author "Pang, Bo"

Abstract The self-assembly of cellulose nanowhiskers (CNWs) in confined geometries provides a powerful method for the fabrication of novel structures. Herein, ordered honeycomb microporous films were first prepared with surface-acylated CNWs (CNWs-SU) through the breath figure method. Resulting films showed highly porous order over large regions and the iridescent color was only displayed by their rims, which is different from traditional dish-cast CNW films showing the iridescent color over the whole area. This is mainly due to the condensation of water droplets forming three-dimensional (3D) geometry, which forced CNWs-SU to self-assemble into cholesteric architectures in confined geometry and resulted in the iridescent color of the rims after drying. The mechanism was further studied by investigating the critical influencing factors, primarily the concentration of CNW-SU suspensions, the relative humidity of the atmosphere and the surface-attached moieties. In particular, CNW-SU suspensions with a concentration of 3 mg/mL at the relative humidity of 75% preferentially formed honeycomb films with uniform pores. Too low or too high concentrations of CNW-SU suspensions or relative humidity are not preferable for uniform porous films. CNWs-SU with further immobilized octadecane or fluoroalkyl groups on their surface strongly affected the formation of uniform porous films because of higher hydrophobicity and accompanying inhomogeneous condensation of water droplets. This work provides a novel method to study the interactions of CNWs beyond the planar geometry and the formation of uniform porous films solely with CNWs with structural colors open up interesting possibilities for broad application in photonic nanomaterials. Graphic abstract

Highlights Preparation strategies of cellulose nanopaper were elaborated. Functionalization of cellulose nanopaper and its advanced applications were summarized. Prospects and challenges of cellulose nanopaper were discussed.

Many efforts have been made to isolate native nanocrystals from raw materials in the last two decades, such as cellulose nanocrystals (CNCs), but existing methods still suffer from low yields, complicated synthesis processes, and nonuniform sizes of obtained CNCs. This study concerns a facile, self-terminating, and efficient method for the formation of uniform CNCs in high yields during the periodate oxidation process within Pickering emulsions. A biphasic system containing hexane with dissolved hexylamine and an aqueous solution of sodium periodate (NaIO4 ) was used as the reaction medium. Regulated by hexylamine, owing to its limited solubility in water, the pH value of the aqueous phase was enhanced to around 9.8, leading to the precipitation of sodium orthoperiodate (Na2 H3 IO6 ) nanoplates and thus the formation of the initial Pickering emulsions. During the gradual formation of cellulose nanofibers and then CNCs, CNCs were attracted to stabilize the interface of the Pickering emulsions, which prevented further decomposition of CNCs by the oxidizing agent in aqueous suspensions. Thus, this isolation strategy secured the efficient separation of CNCs based on their own particular amphiphilic properties and achieved a high yield of up to 56 wt %.

A controllable drug delivery system demonstrates a promising tool for diverse biomedical applications. In this work, a group of amphiphilic macromolecules was designed and prepared via Schiff base reactions between 2,3-dialdehyde cellulose (DAC) with oleylamine and amino-containing compounds. Benefiting from the self-assemble process of these amphiphilic macromolecules in the poor solvent, a group of novel pH-responsive nanoparticles (NPs) were facilely fabricated by using nanoprecipitation dropping technique. The high amount of aldehyde groups on DAC chains enabled immobilization of tunable amounts of amine compounds (up to 1.67 mmol/g) in the NPs. Furthermore, the Schiff base bonds in NPs allowed the efficient release of the drug in acidic tumor microenvironment by cleaving the Schiff base linkages. This study demonstrates the formation of a group of novel pH-sensitive and drug-loadable NPs, which provide a simple and efficient drug delivery system for the potential application for cancer treatment.

Many natural materials have helical or twisting shapes. Herein, we show the formation of helical fibers with the lengths of micrometers by the evaporation-driven self-assembly on silicon wafers of functionalized cellulose nanowhiskers (CNWs) with surface-attached acyl chains. The self-assembly process and the final helical structures were affected by parameters including the wettability of substrates, dispersing solvents, the amount of 10-undecenoyl groups, the crystallinity, the dimension of CNWs, and the length of acyl chains. In particular, surface-acylated CNWs with a certain amount of 10-undecenoyl groups (ca. 3.52 mmol g-1 ), an appropriate crystallinity (ca. 40 %), a length of about 135 nm, and a diameter of around 4 nm, preferentially self-assembled into explicit left-handed helical fibers from their THF suspensions on wafers. Thus, we showed novel particular self-assembly behaviors of surface-acylated CNWs, and we expanded the materials spectrum for the construction of helical structures.

Many natural materials have helical or twisting shapes. Herein, we show the formation of helical fibers with the lengths of micrometers by the evaporation‐driven self‐assembly on silicon wafers of functionalized cellulose nanowhiskers (CNWs) with surface‐attached acyl chains. The self‐assembly process and the final helical structures were affected by parameters including the wettability of substrates, dispersing solvents, the amount of 10‐undecenoyl groups, the crystallinity, the dimension of CNWs, and the length of acyl chains. In particular, surface‐acylated CNWs with a certain amount of 10‐undecenoyl groups (ca. 3.52 mmol g−1), an appropriate crystallinity (ca. 40 %), a length of about 135 nm, and a diameter of around 4 nm, preferentially self‐assembled into explicit left‐handed helical fibers from their THF suspensions on wafers. Thus, we showed novel particular self‐assembly behaviors of surface‐acylated CNWs, and we expanded the materials spectrum for the construction of helical structures.

Developing green and sustainable micro/nanoparticles that can be used to stabilize high-internal-phase Pickering emulsions (HIPPEs) via simple methods is of great significance. Herein, polymeric nanoparticles, fabricated via a facile one-step interfacial Schiff base reaction between dialdehyde cellulose (DAC) and aniline, were successfully used to stabilize oil-in-water HIPPEs. The ratio between aldehyde groups in DAC and aniline demonstrated a great effect on the emulsifying performance of the resultant dialdehyde cellulose-aniline nanoparticles (DANPs). DANPs prepared with suitable high ratios of aldehyde groups to aniline (from 20:1 to 6:1) were able to stabilize oil-in-water HIPPEs with various oil types, such as toluene, hexadecane, styrene, and even viscous edible sunflower oil. In comparison, DANPs fabricated with the ratios of aldehyde groups in DAC to aniline of 4:1 and lower were unable to stabilize HIPPEs. In addition, HIPPEs stabilized by DANPs prepared with higher ratios of aldehyde groups to aniline have smaller droplets, higher storage modulus, and better thermal stability. In particular, DANP-stabilized HIPPEs had good stability at diverse environmental conditions, e.g., higher temperatures (of up to 80 °C) and higher electrolyte concentrations (of at least 50 mM NaCl). Although phase separation occurred to all DANP-stabilized HIPPEs after a freeze–thaw treatment, gel-like HIPPEs could be easily refabricated by handshaking, for at least five cycles of the freeze–thaw treatment. In addition, macroporous poly(melamine-formaldehyde) (PMF) foams were prepared using DANP-stabilized HIPPEs as a template. Therefore, this study further advances the design of stable HIPPEs using polysaccharide-based nanoparticles and the potential of HIPPEs in practical applications.

Polymers or small molecules with functional groups were always employed to synthesize two-dimensional (2D) silver nanostructures, but the polysaccharides and derivatives have rarely been used for their preparation, let alone of uniform quadrilateral shapes. Herein, amylopectin derivatives containing concentrated carboxyl groups were first used for the synthesis of uniform 2D quadrilateral silver nanoplates (QAgNPs) with lamellar structure. As a native hyperbranched polysaccharide, amylopectin was esterified with 10-undecenoyl chloride and then modified via thiol–ene click chemistry to introduce high amount and high density of carboxyl groups. Then, QAgNPs were synthesized via UV photoreduction in the presence of the resultant amylopectin 11-((3-carboxyl)ethylthio)undecanoate (APUE3-MPA) in water–tetrahydrofuran binary system. QAgNPs showed novel uniform quadrilateral shapes with lamellar structure, as verified by their wide-angle X-ray scattering patterns. The average interlayer distance was around 1.3 nm, whereas the average edge lengths of QAgNPs varied between 0.29 ± 0.07 and 1.09 ± 0.25 μm. The concentration of APUE3-MPA and the amount of water in the reaction system strongly affected the shapes of QAgNPs. Thus, the reaction system and the arrangement of numerous carboxyl groups were the key factors for the formation of lamellar-structured QAgNPs.

Biodegradable nanoparticles (NPs) have shown great promise as intracellular imaging probes, nanocarriers and drug delivery vehicles. In this study, we designed and prepared amphiphilic cellulose derivatives via Schiff base reactions between 2,3-dialdehyde cellulose (DAC) and amino compounds. Polymeric NPs were facilely fabricated via the self-assembly of the as-synthesized amphiphilic macromolecules. The size distribution of the obtained NPs can be tuned by changing the amount and length of the grafted hydrophobic side-chains. Anticancer drugs (DOX) were encapsulated in the NPs and the drug-loaded NPs based on cellulose derivatives were stable in neutral and alkaline environments for at least a month. They rapidly decomposed with the efficient release of the drug in acidic tumor microenvironments. These drug-loaded NPs have the potential for application in cancer treatment.

Facile and low‐cost methods for the fabrication of superhydrophobic and superoleophilic materials to effectively separate oil/water mixtures are of great interest and significance. Especially, those with robust surfaces for the separation under harsh conditions including corrosive solutions and hot water are still very challenging. In this paper, Cu(OH)2 nanoneedles and CuO nanoplates are controllably generated on copper meshes by simply changing the oxidization time. After hydrophobic coating with polydimethylsiloxane, the as‐prepared copper meshes not only possess superhydrophobicity with static water contact angle up to 160.2° ± 2.6° and superoleophilicity but also exhibit high resistance against peeling and abrasion cycles. The superhydrophobic/superoleophilic meshes are also utilized to separate various oil/water mixtures with a high separation efficiency up to 98.89%. Moreover, a high separation efficiency of over 97% can be maintained after at least 30 separation cycles and a slight decrease in the flux caused by oil contamination is easily recoverable after rinsing with ethanol. In addition, these meshes demonstrate high separation efficiency for separating mixtures of diesel and diverse corrosive solutions or hot water (above 97 °C). These combined advantages make the meshes promising candidates for practical applications.