“Liquid, gel and soft glass” phase transitions and rheology of nanocrystalline cellulose suspensions as a function of concentration and salinity

Abstract

The colloidal size and rod morphology of nanocrystalline cellulose (NCC) lead to suspensions with useful phase and gelation behaviours as well as complex rheologies. However, these have not been comprehensively evaluated previously. Here we report the detailed phase behaviour of sulphonated NCC aqueous suspensions as a function of concentration and salinity. Four phases - liquid, viscoelastic, repulsive glass and attractive glass/gel - are identified in terms of their distinct rheological behaviours. The liquid-solid transitions (LSTs) are determined rheologically, and these are supported by a simplified model based on the DLVO theory that indicates the importance of charge in determining the phase behaviour. Rheology is also used to investigate the solid-solid transition from a repulsive glass to an attractive gel with increasing salt at high NCC concentrations. A time-dependent aging phenomenon is observed in suspensions with a composition just below the LSTs, and the implications of this on the dynamics occurring during gelation processes are discussed. This work can be directly applied to the development of structure-function relationships and the expanding utilisation of NCC suspensions, whilst also providing a basis for the study of charged colloidal rods more generally and evaluation of theoretical models.

Arrested dynamics in a model peptide hydrogel system

“…the entanglement density due to the increase of hydrophobic contacts when the electrostatic repulsion gets screened. 22,69 A similar increase in network stiffness is also observed in a-synuclein hydrogels when decreasing the fibril charge density by pH. 70 Moreover, similar salt effects are observed for nanocrystalline cellulose.…”

“…70 Moreover, similar salt effects are observed for nanocrystalline cellulose. 69 Frequency sweeps were also performed with the samples containing salt, and the results are presented in Fig. S2 (ESI †).…”

Shear melting and recovery of crosslinkable cellulose nanocrystal–polymer gels

“…The polyamine curing agent is also polar (Lewis base) and has a structure of the form (R-NH 2 ) 2 SO 2 , where R is a hydrocarbon group. The polar curing agents in the UV-curable gels cause an analogous charge screening effect to that of sodium chloride in aqueous CNC suspensions [35,55]. Note that the reference composite gels do not show an increase in G after a sequence of high shear rate, i.e.…”

“…The rod-like shape of CNCs and the presence of surface charges also favor the formation of liquid crystal phases, which can give the gels a local crystalline order [35,53,54]. The case of aqueous CNC gels has been the most documented: the addition of charge-screening ions results in attractive van der Waals interparticle interactions leading to a broad range of rheological behavior depending on whether the gel is dominated by repulsive or attractive interactions [55][56][57]. Under external shear, the storage modulus of aqueous CNC gels decreases irreversibly as the gel is subject to increasing strain amplitude, and the CNCs are irreversibly rearranged [58].…”

Cellulose Nanocrystals as a Sustainable Raw Material: Cytotoxicity and Applications on Healthcare Technology

“…Moreover, the high organization of cellulosic molecules in crystalline regions is reflected in the inaccessibility of the acids and their consequent insolubility . Thus, when attacked by acids, they cleave, leading to the formation of small bundles of crystalline cellulosic nanoparticles, usually called whiskers, crystallites, or nanocrystalline cellulose—so called due to the physical characteristics of stiffness, thickness, and length …”