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Instruments / Technical Area	Publication Details	Published
I22-Small angle scattering & Diffraction	Acoustic levitation with polarising optical microscopy (AL-POM): water uptake in a nanostructured atmospheric aerosol proxy Adam Milsom , Adam M. Squires , Christopher Brasnett , William N. Sharratt , Annela M. Seddon , Christian Pfrang Environmental Science: Atmospheres 88 DOI: 10.1039/D3EA00083D Diamond Proposal Number(s): [23852, 17791] Open Access Show Abstract ▼ Abstract: Laboratory studies on levitated particles of atmospheric aerosol proxies have provided significant contributions to our understanding of aerosol processes. We present an experimental method combining acoustic levitation with polarising optical microscopy (AL-POM) to probe optically birefringent particles, such as the nanostructured surfactant atmospheric aerosol proxy studied here. Birefringent particles were subjected to a step increase in humidity. A decrease in birefringence was measured over time as a result of a nanostructure change, confirmed by complementary synchrotron X-ray scattering. A multi-layer water uptake model was created and fitted to the experimental data, revealing a water diffusion coefficient increase by ca. 5–6 orders of magnitude upon phase transition. This has implications for the timescale of water uptake in surfactant-containing aerosols and their atmospheric lifetimes. This experimental setup has strong potential to be used in conjunction with other levitation methods and in different contexts concerning birefringent materials such as crystallisation.	Sep 2023
B21-High Throughput SAXS	Light responsiveness and assembly of arylazopyrazole-based surfactants in neat and mixed CTAB micelles Gunjan Tyagi , Jake L. Greenfield , Beatrice E. Jones , William N. Sharratt , Kasim Khan , Dale Seddon , Lorna A. Malone , Nathan Cowieson , Rachel C. Evans , Matthew J. Fuchter , Joao T. Cabral Jacs Au DOI: 10.1021/jacsau.2c00453 Diamond Proposal Number(s): [98433, 28884] Open Access Show Abstract ▼ Abstract: The self-assembly of an arylazopyrazole-based photosurfactant (PS), based on cetyltrimethylammonium bromide (CTAB), and its mixed micelle formation with CTAB in aqueous solution was investigated by small angle neutron and X-ray scattering (SANS/SAXS) and UV–vis absorption spectroscopy. Upon UV light exposure, PS photoisomerizes from E-PS (trans) to Z-PS (cis), which transforms oblate ellipsoidal micelles into smaller, spherical micelles with larger shell thickness. Doping PS with CTAB resulted in mixed micelle formation at all stoichiometries and conditions investigated; employing selectively deuterated PS, a monotonic variation in scattering length density and dimensions of the micellar core and shell is observed for all contrasts. The concentration- and irradiance-dependence of the E to Z configurational transition was established in both neat and mixed micelles. A liposome dye release assay establishes the enhanced efficacy of photosurfactants at membrane disruption, with E-PS exhibiting a 4-fold and Z-PS a 10-fold increase in fluorescence signal with respect to pure CTAB. Our findings pave the way for external triggering and modulation of the wide range of CTAB-based biomedical and material applications.	Oct 2022
B21-High Throughput SAXS	Conformation and phase behavior of sodium carboxymethyl cellulose in the presence of mono- and divalent salts William N. Sharratt , Róisín O’connell , Sarah E. Rogers , Carlos G. Lopez , Joao T. Cabral Macromolecules DOI: 10.1021/acs.macromol.9b02228 Diamond Proposal Number(s): [21035] Show Abstract ▼ Abstract: We report a small-angle neutron scattering (SANS) study of semidilute aqueous solutions of sodium carboxymethyl cellulose (NaCMC), in the presence of mono- (Na+) and divalent salts (Mg2+, Ca2+, Zn2+, and Ba2+). A degree of substitution of 1.3 is selected to ensure that, in salt-free solution, the polymer is molecularly dissolved. We find that Na+ and Mg2+ salt addition yields H-type phase behavior, while Ca2+, Zn2+, and Ba2+ instead yield a mixed H/L-type phase behavior dependent on the NaCMC concentration (cp), in the decreasing order of the salt concentration required to induce turbidity (at a fixed cp). Charge screening by addition of NaCl induces the disappearance of the characteristic polyelectrolyte correlation peak and eventually yields scattering profiles with a q–1 dependence over nearly 3 decades in the wavenumber q. By fitting a descriptive model to data with excess Na+, we obtain a correlation length ξ′ = 1030 cp–0.72 Å with cp in g L–1. Addition of Mg2+, which does not interact specifically with NaCMC carboxylate groups, yields an analogous screening behavior to that of Na+, albeit at lower salt concentrations, in line with its higher ionic strength. At low salt concentration, addition of specifically interacting Ca2+, Zn2+, and Ba2+ yields a comparatively greater screening of the polyelectrolyte correlation peak, and at concentrations above the phase boundary, results in excess scattering at low-q, compatible with the formation of 20–40 nm clusters. This behavior is interpreted as due to the reduction in charge density along the chain, promoting interchain association and multichain domain formation resulting in visible turbidity. Overall, drawing analogies with NaCMC at a lower degree of substitution, where hydrophobic association takes place, our findings provide a framework to describe the solution structure and phase behavior of NaCMC in salt-free and salt solutions.	Feb 2020

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