A technical note on large normal-stress differences observed in a novel self-assembling functionalized dipeptide surfactant solution



Maklad, Osama M, McAulay, Kate, Lerouge, Sandra, Adams, Dave J and Poole, Robert J ORCID: 0000-0001-6686-4301
(2022) A technical note on large normal-stress differences observed in a novel self-assembling functionalized dipeptide surfactant solution. Rheologica Acta.

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Abstract

<jats:title>Abstract</jats:title><jats:p>A number of functionalised dipeptides self-assemble in water under specific conditions to give micellar aggregates. The micellar aggregates formed depend on the exact molecular structure and are important to understand as they control the properties both of the micellar phase and also of the gel phase which can be formed from these precursor solutions. Here, we investigate the rheological properties of a functionalised dipeptide which behaves as a surfactant at high pH. This solution has been shown previously to exhibit very “stringy” behaviour, and this has previously been characterised using capillary breakup extensional rheometry (CaBER). In the current technical note, we extend the rheological characterisation of an exemplar precursor solution via small-amplitude oscillatory shear and steady shear. Using a cone-and-plate geometry and a dedicated protocol, we can measure the first normal-stress difference <jats:italic>N</jats:italic><jats:sub>1</jats:sub> and using a parallel-plate geometry to also measure (<jats:italic>N</jats:italic><jats:sub>1</jats:sub>-<jats:italic>N</jats:italic><jats:sub>2</jats:sub>), subsequently determining the second normal-stress difference <jats:italic>N</jats:italic><jats:sub>2</jats:sub>. In so doing, we confirm that these systems are highly elastic, e.g. for shear rates greater than ~ 30 s<jats:sup>−1</jats:sup>, corresponding to a Weissenberg number based on the longest relaxation time ~ 330, <jats:italic>N</jats:italic><jats:sub>1</jats:sub> &gt; 10τ where τ is the shear stress, and also, we find that <jats:italic>N</jats:italic><jats:sub>2</jats:sub> can be significant, is negative and approximately equal in magnitude to ~ 0.36 ± 0.05 <jats:italic>N</jats:italic><jats:sub>1</jats:sub>. Significant uncertainties associated with the normal-stress difference data led to us using a range of different rheometers (and geometries) and highlight the issues with determining <jats:italic>N</jats:italic><jats:sub>2</jats:sub> using this two-measurement approach. Despite these uncertainties, the non-negligible value of the second-normal stress difference is demonstrated for these fluids.</jats:p>

Item Type: Article
Depositing User: Symplectic Admin
Date Deposited: 23 Sep 2022 09:23
Last Modified: 12 Oct 2022 02:46
DOI: 10.1007/s00397-022-01368-7
Open Access URL: https://trebuchet.public.springernature.app/get_co...
URI: https://livrepository.liverpool.ac.uk/id/eprint/3164966