Abstract
Time-resolved small-angle X-ray scattering (SAXS) was used to probe the assembly of cellulose nanocrystals (CNC) and montmorillonite (MNT) over a wide concentration range in aqueous levitating droplets. Analysis of the SAXS curves of the one-component and mixed dispersions shows that co-assembly of rod-like CNC and MNT nanoplatelets is dominated by the interactions between the dispersed CNC particles and that MNT promotes gelation and assembly of CNC, which occurred at lower total volume fractions in the CNC:MNT than in the CNC-only dispersions. The CNC dispersions displayed a d ∝ φ-1/2 scaling and a low-q power-law exponent of 2.0-2.2 for volume fractions up to 35%, which indicates that liquid crystal assembly co-exists and competes with gelation.
Highlights
The thickness of the Cellulose nanocrystals (CNC) particles derived from small-angle X-ray scattering (SAXS) (34 Å) is slightly lower than that obtained
The absence of a Guinier region in the SAXS patterns indicates that the characteristic dimension of the CNC particles is at least partially outside of the investigated q range
The low-q slope gradually diverged from a qÀ1 dependence, which is characteristic of rod-like objects, to higher negative exponents as the volume fraction increased; this trend is attributed to the transition from essentially non-interacting to strongly interacting CNC particles with increasing volume fraction in the shrinking levitating droplet.[44]
Summary
Cellulose nanomaterials (CNM) can be isolated from naturally abundant and renewable sources, e.g. wood, cotton, bacteria.[6,7] The high strength, low density and chemical versatility make CNM excellent candidates for functional nanomaterials and nanocomposites.[8,9,10] Cellulose nanocrystals (CNC) obtained by sulfuric acid hydrolysis are rigid rod-like particles that can form chiral nematic liquid-crystalline phases in aqueous dispersions[11] and yield materials with high specific mechanical strength and toughness[12] and useful optical[13,14,15] properties, making CNC interesting for a range of high-performance applications.[16]. CNM-based composite and hybrid coatings, films and aerogels containing various inorganic components can have favourable mechanical properties.[21,22,23,24,25] materials consisting of CNM with nanoclays, especially montmorillonite (MNT), have displayed combinations of high strength with heat tolerance,[26] fire retardancy,[27] dye adsorption,[28] and low oxygen[29] and water– vapour[30] permeability. While self-assembly has been studied in single-component CNC and MNT dispersions,[11,31,32,33] including, in the case of CNC, in confined geometries such as sessile,[34] emulsion[35] and levitating[36] droplets, studies of multicomponent CNC:MNT systems are sparse.[28,37] Exploring and probing how CNC and inorganic nanoparticles such as clays assemble in aqueous dispersions is important for the development of processing routes and new classes of sustainable materials
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