The present study aims to investigate the structure-morphology-rheology relationships for cellulose nanoparticles (CNPs), including cellulose nanofibers (CNFs), and cellulose nanocrystals (CNCs). CNCs were extracted from never dried CNFs using sulfuric acid with controlled hydrolysis time. The crystalline structure, surface charge, morphology and rheological behavior of the CNPs were measured and contrasted. The CNF suspensions exhibited rigid solid-like viscoelastic behavior even at a low concentration due to the formation of highly entangled network.Upon the acid hydrolysis, the network of rigid, long and highly entangled nanofibers was eliminated, resulting in a significant loss of viscoelastic properties. Both steady-state and dynamic rheological measurements showed that the rheological behavior of the CNC suspensions was strongly dependent on the concentration and acid hydrolysis time. The CNC suspensions exhibited elastic gel-like rheological behavior at high concentrations, but viscous liquid-like rheological behavior at low concentrations. Longer acid hydrolysis time produced CNCs with lower aspect ratio, leading to higher critical transition concentration for the formation of anisotropic phase. The aspect ratio of CNCs was predicted from the intrinsic viscosity using the Simha's equation. The theoretically predicted aspect ratio values corresponded well with the transmission electron microscopy results. Finally, the network of CNF and CNC suspensions were schematically proposed. and immobilized water molecules mainly existed. The differences in the physiochemical characteristics (e.g., aspect ratio, surface properties, flexibility) among CNPs resulted in distinctive network in the CNP suspensions.The mechanical disintegrated CNFs showed inactive surface characteristic (e.g., low zeta potential value and fewer hydroxyl groups), larger aspect ratio (> 80), and high flexibility, as observed previously. It is believed that the chemical interactions between CNFs, and the hydrogen bonds between CNF and water molecule were very weak, whereas the physical entanglements between CNFs were quite strong. Therefore, the network of CNF suspension mainly contained physical entanglements between CNFs ( Figure 8a). The physical entanglements between CNFs could be easily created due to the large aspect ratio and high flexibility of CNFs even at a very low concentration. This is the reason for the observed phenomenon that the CNF suspensions at any concentration level displayed solid-like viscoelastic properties (i.e., ′ ≈ 0 , ′ ≫ ′′ , and tan < 1). By contrast, the sulfuric acid-hydrolyzed CNCs carried negatively charged sulfate groups and a large number of hydroxyl groups on the surface. These highly active groups enabled the CNCs to greatly interact with each other as well as the adjacent water molecules. On the other hand, the needle-like CNCs with relatively low aspect ratio and high crystallinity had worse flexibility than CNFs, leading to the less possibility of formation of physically entangled network between CNCs...

Rheological and filtration characteristics of drilling fluids are considered as two critical aspects to ensure the success of a drilling operation. This research demonstrates the effectiveness of cellulose nanoparticles (CNPs), including microfibrillated cellulose (MFC) and cellulose nanocrystals (CNCs) in enhancing the rheological and filtration performances of bentonite (BT) water-based drilling fluids (WDFs). CNCs were isolated from MFC through sulfuric acid hydrolysis. In comparison with MFC, the resultant CNCs had much smaller dimensions, more negative surface charge, higher stability in aqueous solutions, lower viscosity, and less evident shear thinning behavior. These differences resulted in the distinctive microstructures between MFC/BT- and CNC/BT-WDFs. A typical "core-shell" structure was created in CNC/BT-WDFs due to the strong surface interactions among BT layers, CNCs, and immobilized water molecules. However, a similar structure was not formed in MFC/BT-WDFs. As a result, CNC/BT-WDFs had superior rheological properties, higher temperature stability, less fluid loss volume, and thinner filter cakes than BT and MFC/BT-WDFs. Moreover, the presence of polyanionic cellulose (PAC) further improved the rheological and filtration performances of CNC/BT-WDFs, suggesting a synergistic effect between PAC and CNCs.

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Exploring high‐efficiency, stable, and cost‐effective bifunctional electrocatalysts for overall water splitting is greatly desirable and challenging. Herein, a newly designed hybrid catalyst with Cr‐doped FeNi–P nanoparticles encapsulated into N‐doped carbon nanotubes (Cr‐doped FeNi–P/NCN) with unprecedented electrocatalytic activity is developed by a simple one‐step heating treatment. The as‐synthesized Cr‐doped FeNi–P/NCN with moderate Cr doping exhibits admirable oxygen evolution reaction and hydrogen evolution reaction activities with overpotentials of 240 and 190 mV to reach a current density of 10 mA cm−2 in 1 m KOH solution. When used in overall water splitting as a bifunctional catalyst, it needs only 1.50 V to give a current density of 10 mA cm−2, which is superior to its typically integrated Pt/C and RuO2 counterparts (1.54 V @ 10 mA cm−2). Density functional theory calculation confirms that Cr doping into a FeNi‐host can effectively alter the relative Gibbs adsorption energy and reduces the theoretical overpotential. Additionally, the synergetic effects between Cr‐doped FeNi–P nanoparticles and NCNs are regarded as significant contributors to accelerate charge transfer and promote electrocatalytic activity in hybrid catalysts.

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