Aqueous solutions of HEC and hmHEC: effects of molecular mass versus hydrophobic associations on hydrodynamic and thermodynamic parameters

Abstract

Aqueous solutions of amphiphilic polymers usually comprise of inter-and intramolecular associations of hydrophobic groups often leading to a formation of a rheologically significant reversible network at low concentrations that can be identified using techniques such as static light scattering and rheometry. However, in most studies published till date comparing water soluble polymers with their respective amphiphilic derivatives, it has been very difficult to distinguish between the effects of molecular mass versus hydrophobic associations on hydrodynamic (intrinsic viscosity [g]) and thermodynamic parameters (second virial coefficient A 2 ), owing to the differences between their degrees of polymerization. This study focuses on the dilute and semi-dilute solutions of hydroxyethyl cellulose (HEC) and its amphiphilic derivatives (hmHEC) of the same molecular mass, along with other samples having a different molecular mass using capillary viscometry, rheometry and static light scattering. The weight average molecular masses (M W ) and their distributions for the nonassociative HEC were determined using size exclusion chromatography. Various empirical approaches developed by past authors to determine [g] from dilute solution viscometry data have been discussed. hmHEC with a sufficiently high degree of hydrophobic modification was found to be forming a rheologically significant network in dilute solutions at very low concentrations as opposed to the hmHEC with a much lower degree of hydrophobic modification which also enveloped the hydrophobic groups inside the supramolecular cluster as shown by their [g] and A 2 . The ratio A 2 M W /[g], which takes into account hydrodynamic as well as thermodynamic parameters, was observed to be less for associative polymers compared to that of the non-associative polymers.

Diffusion of rod-like nanoparticles in non-adhesive and adhesive porous polymeric gels

“…Furthermore, a rapid decrease in diffusivity was observed when the AR increases to 4 and 8, suggesting the existence of an optimal AR ( ∼3) for the maximum transport rate in adhesive mucus. To test whether the high affinity between NPs and mucin fibers is a key factor that leads to the observed anomalous diffusion behaviors, we also investigated the diffusivity of MSNs in hydroxyethyl cellulose (HEC, 0.5%, w/w), a hydrophilic and non-ionic gel without hydrophobic regions ( Vadodaria and English, 2016 ). HEC has been used to mimic the mesh structure of mucus, and its porous structure has also been confirmed via cryogenic scanning EM (cryo-SEM) ( Kirch et al, 2012 ).…”

Association of κ‐carrageenan subjected to deep alkaline hydrolysis

“…The concentration dependence of η rd (the Huggins ordinate) is slightly concave whereas the concentration dependence of η inh (the Kraemer ordinate) is linear. Similar differences between the Kraemer and Huggins extrapolations were observed for associative hydrophobically modified polysaccharides . Molecular masses M η presented in Table were calculated by a Mark‐Kuhn equation [ η ] = 0.003 M η 0.95 established in Ref.…”

“…The A 2 M w /[η] ratio that takes into account both thermodynamic and hydrodynamic interactions, also decreases with T h from 0.74 (κCG‐60) to 0.23 (κCG‐75). Such behavior of A 2 M w /[η] is typical for associative polymers …”

The rheological behaviour of a water-soluble polymer (HEC) used in drilling fluids

“…This geometry was employed in all rheological experiments. The same geometry was used by Vadodaria and English [30], to measure the shear-rate-dependent viscosity of HEC and hmHEC solutions with different concentrations at low and high shear rates. Kang et al [18] had also used microchannel and RFS II rheometer with Couette tool sets, to measure the rheological properties of HEC solutions at low and high shear rates; as a result, no degradation, vortices, or flow instability were observed in these experiments.…”

“…The importance of the overlap concentration (C*) cannot be neglected because the changes in the rheological properties including the mechanism of viscosification are seen at concentrations greater than (C*). For C \ C*, the curvature of the flow lines around the individual polymer coils is responsible for the increase in viscosity, as opposed to C [ C* when the network composed of overlapping coils resists the flow [30].…”