Imperial College London

ProfessorJoaoCabral

Faculty of EngineeringDepartment of Chemical Engineering

Professor of Soft Matter
 
 
 
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Contact

 

+44 (0)20 7594 5571j.cabral Website

 
 
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Assistant

 

Mrs Sarah Payne +44 (0)20 7594 5567

 
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Location

 

517AACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

131 results found

Khodaparast S, Sharratt WN, Dalgliesh RM, Cabral JTet al., 2021, Growth of Myelin Figures from Parent Multilamellar Vesicles, LANGMUIR, Vol: 37, Pages: 12512-12517, ISSN: 0743-7463

Journal article

Donina L, Rafique A, Khodaparast S, Porcar L, Cabral JTet al., 2021, Lamellar-to-MLV transformation in SDS/octanol/brine examined by microfluidic-SANS and polarised microscopy, SOFT MATTER, Vol: 17, Pages: 10053-10062, ISSN: 1744-683X

Journal article

Tan A, Pellegrino L, Cabral JT, 2021, Tunable Phase Gratings by Wrinkling of Plasma-Oxidized PDMS: Gradient Skins and Multiaxial Patterns, ACS APPLIED POLYMER MATERIALS, Vol: 3, Pages: 5162-5170, ISSN: 2637-6105

Journal article

Sharratt WN, Lee VE, Priestley RD, Cabral JTet al., 2021, Precision Polymer Particles by Flash Nanoprecipitation and Microfluidic Droplet Extraction, ACS APPLIED POLYMER MATERIALS, Vol: 3, Pages: 4746-4768, ISSN: 2637-6105

Journal article

Sharratt WN, Lopez CG, Sarkis M, Tyagi G, O'Connell R, Rogers SE, Cabral JTet al., 2021, Ionotropic Gelation Fronts in Sodium Carboxymethyl Cellulose for Hydrogel Particle Formation, GELS, Vol: 7

Journal article

Khodaparast S, Sharratt WN, Tyagi G, Dalgliesh RM, Robles ESJ, Cabral JTet al., 2021, Pure and mixed aqueous micellar solutions of Sodium Dodecyl sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO): Role of temperature and composition, JOURNAL OF COLLOID AND INTERFACE SCIENCE, Vol: 582, Pages: 1116-1127, ISSN: 0021-9797

Journal article

Khodaparast S, Marcos J, Sharratt WN, Tyagi G, Cabral JTet al., 2021, Surface-Induced Crystallization of Sodium Dodecyl Sulfate (SDS) Micellar Solutions in Confinement, LANGMUIR, Vol: 37, Pages: 230-239, ISSN: 0743-7463

Journal article

Wong HC, Wang Q, Speller EM, Li Z, Cabral JT, Low HYet al., 2020, Photoswitchable solubility of fullerene-doped polymer thin films., ACS Nano, Vol: 14, Pages: 11352-11362, ISSN: 1936-0851

Controlling polymer film solubility is of fundamental and practical interest and is typically achieved by synthetically modifying the polymer structure to insert reactive groups. Here, we demonstrate that the addition of fullerenes or its derivatives (C60 or phenyl-C61-butyric acid methyl ester, PCBM) to polymers, followed by ultraviolet (UV) illumination can change the film solubility. Contrary to most synthetic polymers, which dissolve in organic solvents but not in water, the fullerene-doped polymer films (such as polystyrene) can dissolve in water yet remain stable in organic solvents. This photoswitchable solubility effect is not observed in either film constituents individually and is derived from a synergy of photochemistries. First, polymer photooxidation generates macroradicals which cross-link with radical-scavenging PCBM, thereby contributing to the films' insolubility in organic solvents. Second, light exposure enhances polymer photooxidation in the presence of PCBM via the singlet oxygen pathway. This results in polymer backbone scission and formation of photooxidized products which can form hydrogen bonds with water, both contributing to water solubility. Nevertheless, the illuminated doped polymer thin films are mechanically robust, exhibiting significantly increased modulus and density compared to their pristine counterpart, such that they can remain intact even upon sonication in conventional organic solvents. We further demonstrate the application of this solubility-switching effect in dual tone photolithography, via a facile, economical, and environmentally benign solution-processing route made possible by the photoactive nature of polymer-PCBM thin films.

Journal article

Rafique AS, Khodaparast S, Poulos AS, Sharratt WN, Robles ESJ, Cabral JTet al., 2020, Micellar structure and transformations in sodium alkylbenzenesulfonate (NaLAS) aqueous solutions: effects of concentration, temperature, and salt, Soft Matter, Vol: 16, Pages: 7835-7844, ISSN: 1744-683X

We investigate the shape, dimensions, and transformation pathways of micelles of linear sodium alkylbenzenesulfonate (NaLAS), a common anionic surfactant, in aqueous solution. Employing Small Angle Neutron Scattering (SANS) and surface tensiometry, we quantify the effects of surfactant concentration (0.6–15 wt%), temperature (5–40 °C) and added salt (≤0.35 M Na2SO4). Spherical micelles form at low NaLAS (≤2.6 wt%) concentration in water, and become elongated with increasing concentration and decreasing temperature. Addition of salt reduces the critical micelle concentration (CMC) and thus promotes the formation of micelles. At fixed NaLAS concentration, salt addition causes spherical micelles to grow into cylindrical micelles, and then multilamellar vesicles (MLVs), which we examine by SANS and cryo-TEM. Above a threshold salt concentration, the MLVs reach diameters of 100 s of nm to few μm, eventually causing precipitation. While the salt concentrations associated with the micelle-to-cylinder transformation increase only slightly with temperature, those required for the cylinder-to-MLV transformation exhibit a pronounced, linear temperature dependence, which we examine in detail. Our study establishes a solution structure map for this model anionic surfactant in water, quantifying the combined roles of concentration, temperature and salt, at practically relevant conditions.

Journal article

White RP, Aoki Y, Higgins JS, Keddie JL, Lipson JEG, Cabral JTet al., 2020, Thermodynamics of model PαMSAN/dPMMA blend: a combined study by SANS, ellipsometry, and locally correlated lattice (LCL) theory, Macromolecules, Vol: 53, Pages: 7084-7095, ISSN: 0024-9297

We combine experiment and theory to elucidate how small, local, structural changes can impact miscibility in polymer blends. Small-angle neutron scattering (SANS) experiments yield both the phase boundaries and the temperature dependence of the second derivative of the free energy of mixing. We demonstrate here, for the first time, that a fundamental characterization of pure component properties can be achieved through ellipsometry measurements on films of pure polymers (thickness ∼200 nm) to provide key data on the volume (or thickness)–temperature relationships; this development is significant given the scarcity of precise pressure–volume–temperature (PVT) data on pure polymers and blends. The experimental measurements allow us to undertake a detailed thermodynamic analysis of mixing using the locally correlated lattice (LCL) theory, which has been shown to be effective in rationalizing blend miscibility in terms of the pure component properties. We focus here on polymer blends of poly(α-methyl styrene-co-acrylonitrile) (PαMSAN) with deuterated poly(methyl methacrylate) (dPMMA), which differ in the degree of tacticity in the dPMMA component (atactic or syndiotactic), leading to an increase in miscibility for the latter. By combining LCL analysis of pure and mixed systems, we are able to connect tacticity changes to shifts in local nonbonded interactions, in free volume, and in thermal expansion coefficients, which in turn impact the thermodynamic compatibility of the blend components.

Journal article

Higgins JS, Cabral JT, 2020, A thorny problem? spinodal decomposition in polymer blends, Macromolecules, Vol: 53, Pages: 4137-4140, ISSN: 0024-9297

Journal article

McGilvery CM, Abellan P, Klosowski MM, Livingston AG, Cabral JT, Ramasse QM, Porter AEet al., 2020, Nanoscale chemical heterogeneity in aromatic polyamide membranes for reverse osmosis applications, ACS Applied Materials & Interfaces, Vol: 12, Pages: 19890-19902, ISSN: 1944-8244

Reverse osmosis membranes are used within the oil and gas industry for seawater desalination on off-shore oilrigs. The membranes consist of three layers of material: a polyester backing layer, a polysulfone support and a polyamide (PA) thin film separating layer. It is generally thought that the PA layer controls ion selectivity within the membrane but little is understood about its structure or chemistry at the molecular scale. This active polyamide layer is synthesized by interfacial polymerization at an organic/aqueous interface between m-phenylenediamine and trimesoyl chloride, producing a highly cross-linked PA polymer. It has been speculated that the distribution of functional chemistry within this layer could play a role in solute filtration. The only technique potentially capable of probing the distribution of functional chemistry within the active PA layer with sufficient spatial and energy resolution is scanning transmission electron microscopy combined with electron energy-loss spectroscopy (STEM-EELS). Its use is a challenge because organic materials suffer beam-induced damage at relatively modest electron doses. Here we show that it is possible to use the N K-edge to map the active layer of a PA film using monochromated EELS spectrum imaging. The active PA layer is 12 nm thick, which supports previous neutron reflectivity data. Clear changes in the fine structure of the C K-edge across the PA films are measured and we use machine learning to assign fine structure at this edge. Using this method, we map highly heterogeneous intensity variations in functional chemistry attributed to N—C═C bonds within the PA. Similarities are found with previous molecular dynamics simulations of PA showing regions with a higher density of amide bonding as a result of the aggregation process at similar length scales. The chemical pathways that can be deduced may offer a clearer understanding of the transport mechanisms through the membrane.

Journal article

Wang H, Khodaparast S, Carroll J, Kelly C, Robles ESJ, Cabral JTet al., 2020, A microfluidic-multiwell platform for rapid phase mapping of surfactant solutions, Review of Scientific Instruments, Vol: 91, Pages: 1-11, ISSN: 0034-6748

Measurement of the phase behavior and (meta)stability of liquid formulations, including surfactant solutions, is required for the understanding of mixture thermodynamics, as well as their practical utilization. We report a microfluidic platform with a stepped temperature profile, imposed by a dual Peltier module, connected to an automated multiwell plate injector and optical setup, for rapid solution phase mapping. The measurement protocol is defined by the temperature step ΔT ≡ T1 − T2 (≲100 °C), volumetric flow rate Q ≡ ΔV/Δt (≲50 μl/min), which implicitly set the thermal gradient ΔT/Δt (≃0.1–50 °C/min), and measurement time (which must exceed the intrinsic timescale of the relevant phase transformation). Furthermore, U-shaped microchannels can assess the reversibility of such transformations, yielding a facile measurement of the metastable zone width of the phase diagram. By contrast with traditional approaches, the platform precisely controls the cooling and heating rates by tuning the flow rate, and the absolute temperature excursion by the hot and cold thermal profile, which remain stationary during operation, thus allowing the sequential and reproducible screening of large sample arrays. As a model system, we examined the transition from the micellar (L1) to the liquid crystalline lamellar phase (Lα), upon cooling, of aqueous solutions of sodium linear alkylbenzene sulfonate, a biodegradable anionic surfactant extensively employed in industry. Our findings are validated with quiescent optical microscopy and small angle neutron scattering data.

Journal article

Sharratt WN, OConnell R, Rogers SE, Lopez CG, Cabral JTet al., 2020, Conformation and phase behavior of sodium carboxymethyl cellulose in the presence of mono- and divalent salts, Macromolecules, Vol: 53, Pages: 1451-1463, ISSN: 0024-9297

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.

Journal article

Pellegrino L, Khodaparast S, Cabral JT, 2020, Orthogonal wave superposition of wrinkled, plasma-oxidised, polydimethylsiloxane surfaces, Soft Matter, Vol: 16, Pages: 595-603, ISSN: 1744-683X

We report a versatile approach to generate 2D dual-frequency patterns on soft substrates by superposition of 1D single-frequency wrinkles. Wave superposition is achieved by applying sequential orthogonal strains to elastomeric coupons, as opposed to the application of a (simultaneous) biaxial strain field. First, a 1D wrinkling pattern is induced by the well-known mechanical instability of a bilayer formed by oxygen plasma-oxidation of a (pre-strained) polydimethylsiloxane elastomer. The wrinkled surface formed upon strain release is then replicated to obtain a stress-free substrate, and stretched in the direction perpendicular to the first generation. Subsequent plasma exposure and mechanical relaxation (with independent process parameters) yield a prescribed second-generation wrinkling, whose profile and dependence on the first generation we examine in detail. By independently varying plasma oxidation and strain parameters in both directions, we demonstrate the formation of a wide array of topographies, including arrays of symmetric 2D checkerboard patterns with exceptional area coverage with respect to those formed by simultaneous 2D wrinkling. While the resulting topographies cannot be explained in terms of a simple orthogonal wave superposition, we show that, by accounting for the orthogonal prestrain experienced by the first wrinkling generation, the resulting 2D patterns can be readily calculated from 1D wrinkling behaviour.

Journal article

Aoki Y, Sharratt W, Wang H, O'Connell R, Pellegrino L, Rogers S, Dalgliesh RM, Higgins JS, Cabral JTet al., 2020, Effect of tacticity on the phase behavior and demixing of p alpha MSAN/dPMMA blends investigated by SANS, Macromolecules, Vol: 53, Pages: 445-457, ISSN: 0024-9297

We investigate the effect of polymer tacticity on the phase behavior and phase separation of polymer mixtures by small-angle neutron scattering (SANS). Poly(α-methyl styrene-co-acrylonitrile) (PαMSAN) and deuterated poly(methyl methacrylate) (dPMMA) with two degrees of syndiotacticity were selected as a model partially miscible blend, as one of the most highly interacting systems known (defined by the temperature dependence of the blend’s interaction parameter). One-phase (equilibrium) and time-resolved, spinodal demixing experiments were analyzed by de Gennes’ random phase approximation (RPA) and Cahn–Hilliard–Cook (CHC) theory, respectively. The second derivative of the Gibbs free energy of mixing with respect to composition (G″ ≡ ∂2ΔGm/∂ϕ2) and corresponding χ parameter were obtained from both RPA and CHC analysis and found to correlate well across the phase boundary. We find that blends with higher PMMA syndiotacticity exhibit greater miscibility and a steeper G″ temperature dependence by ∼40%. The segment length of dPMMA with higher syndiotacticity was found to be a = 7.4 Å, slightly larger than 6.9 Å reported for lower syndiotacticity dPMMA. Consideration of thermal fluctuations is required for the self-consistent analysis of the nontrivial evolution of the spinodal peak position q* over time, corroborated by CHC model calculations. The temperature dependence of the mobility parameter, M, can be described by a “fast-mode” average of the diffusion coefficients of the blend constituents, except for quenches originating near the glass transition. A minimum demixing length scale of Λ ≈ 40 nm is obtained, in agreement with the theory for deeper quenches, but deviates at shallower quenches, whose origin we discuss. CHC correctly describes demixing length and time scales, except for quenches into the vicinity of the spinodal boundary. Our data demonstrat

Journal article

Sharratt WN, Cabral JT, 2020, Design and fabrication of polymer microparticles and capsules using microfluidics, Polymer Colloids: Formation, Characterization and Applications, Editors: Priestley, Prud'homme, Pages: 100-147

Since the advent of microfluidics in the late 1990s, microfluidic approaches to polymer microparticle and capsule formation have become widespread. They benefit from the precise spatio-temporal control attainable over single and multi-phase channel flows, coupled with a range of solidification strategies, which enable the predictive and reproducible design and manufacture of unprecedented polymeric and composite particles. The control over particle shape, microstructure and architecture, monodispersity and regularity, provides unique chemical, biological, bio-medical and physical opportunities for the complex assembly and functionality of these materials. In this chapter, we summarise recent developments of the use of microfluidics for particle and capsule formation, providing an overview of the main approaches available for their manufacture. We describe key mechanistic and design considerations, including system compatibility and demonstrated capability, seeking to establish limitations and identify unexplored opportunities for these methods. We conclude with an outlook on future directions in terms of scalability, functionality, phase space mapping and commercial and societal impact, of this creative and rapidly evolving soft matter field.

Book chapter

O'Connell RA, Porter AE, Higgins JS, Cabral JTet al., 2019, Phase behaviour of poly(2, 6-diphenyl-p-phenylene oxide) (PPPO) in mixed solvents, Polymer, Vol: 180, ISSN: 0032-3861

The solution phase behaviour of poly(2, 6-diphenyl-p-phenylene oxide) (PPPO) is investigated by a combination of turbidimetry, infrared spectroscopy, dynamic light scattering and densitometry, combined with calorimetry and X-ray scattering. We select dichloromethane (DCM) and heptane as, respectively, representative good and poor solvents for the polymer. This ternary system results in a miscibility gap which can be utilised for the design and fabrication of PPPO porous materials, membranes and scaffolds via phase inversion. We establish the phase diagram and resolve the kinetic solidification condition arising from the intersection between the coexistence and glass transition curves. PPPO exhibits a high 230 ∘C and is found to crystallise at 336 ∘C, and melt at 423, 445 ∘C with a double endotherm. The kinetics of demixing and (buoyancy-driven) stratification are quantified by optical imaging and the PPPO-rich phase analysed by SAXS/WAXS to resolve both amorphous and crystalline phases. Equipped with this knowledge, we demonstrate the controlled formation of nodular, bicontinuous and cellular morphologies by non-solvent induced demixing.

Journal article

Hynes EL, Cabral JT, Parnell AJ, Gutfreund P, Welbourn RJL, Dunbar ADF, Mon D, Higgins AMet al., 2019, Interfacial width and phase equilibrium in polymer-fullerene thin-films, Communications Physics, Vol: 2, ISSN: 2399-3650

Domain composition and interfacial structure are critical factors in organic photovoltaic performance. Here, we report neutron reflectivity, grazing-incidence X-ray diffraction and atomic force microscopy measurements of polymer/fullerene thin-films to test a hypothesis that these partially miscible blends rapidly develop composition profiles consisting of co-existing phases in liquid-liquid equilibrium. We study a range of polymer molecular weights between 2 and 300 kg mol−1, annealing temperatures between 120 and 170 oC, and timescales up to 10 min, yielding over 50 distinct measurement conditions. Model bilayers of fullerene-derivatives and polystyrene enable a rigorous examination of theoretical predictions of the effect of polymer mass and interaction parameter on the compositions, ϕ, and interfacial width, w, of the coexistent phases. We independently measure ϕ and w and find that both Flory-Huggins mean-field-theory and key aspects of self-consistent-field-theory are remarkably consistent with experiment. Our findings pave the way for predictive composition and interface design in organic photovoltaics based on simple experimental measurements and equilibrium thermodynamic theory.

Journal article

Pont S, Osella S, Smith A, Marsh AV, Li Z, Beljonne D, Cabral JT, Durrant JRet al., 2019, Evidence for strong and weak phenyl-C61-butyric acid methyl ester photodimer populations in organic solar cells, Chemistry of Materials, Vol: 31, Pages: 6076-6083, ISSN: 0897-4756

In polymer/fullerene organic solar cells, the photochemical dimerization of phenyl-C61-butyric acid methyl ester (PCBM) was reported to have either a beneficial or a detrimental effect on device performance and stability. In this work, we investigate the behavior of such dimers by measuring the temperature dependence of the kinetics of PCBM de-dimerization as a function of prior light intensity and duration. Our data reveal the presence of both “weakly” and “strongly” bound dimers, with higher light intensities preferentially generating the latter. DFT simulations corroborate our experimental findings and suggest a distribution of dimer binding energies, correlated with the orientation of the fullerene tail with respect to the dimer bonds on the cage. These results provide a framework to rationalize the double-edged effects of PCBM dimerization on the stability of organic solar cells.

Journal article

Udoh CE, Garbin V, Cabral JT, 2019, Polymer nanocomposite capsules formed by droplet extraction: spontaneous stratification and tailored dissolution, Soft Matter, Vol: 15, Pages: 5287-5295, ISSN: 1744-683X

We report the formation of polymeric and nanocomposite capsules via droplet solvent extraction, focusing on the interplay between solvent exchange and removal, demixing and directional solidification kinetics. We investigate a model system of sodium poly(styrene sulfonate), NaPSS and silica nanoparticles in aqueous solution, whose phase behaviour is experimentally measured, and examine a series of selective extraction solvents (toluene, butyl acetate, ethyl acetate and methyl ethyl ketone), ranging from 0.04 to 11% v/v water solubility. Tuning the rate of solvent exchange is shown to provide an effective means of decoupling demixing and solidification timescales, and thereby tunes the internal microstructure of the capsule, including hollow, microporous, core–shell, and bicontinuous morphologies. In turn, these determine the capsule dissolution mechanism and kinetics, ranging from single to pulsed release profiles of nanoparticle clusters (at intermediate solubilities), to minimal dissolution (at either extremes). These findings provide facile design and assembly strategies for functional capsules with time-varying release profiles.

Journal article

Khodaparast S, Sharratt W, Wang H, Robles ESJ, Dalgliesh R, Cabral JTet al., 2019, Spontaneous formation of multilamellar vesicles from aqueous micellar solutions of sodium linear alkylbenzene sulfonate (NaLAS), Journal of Colloid and Interface Science, Vol: 546, Pages: 221-230, ISSN: 0021-9797

We report the spontaneous formation of multilamellar vesicles (MLVs) from low concentration (<30 wt%) aqueous micellar solutions of sodium linear alkylbenezene sulfonate (NaLAS) upon cooling, employing a combination of optical microscopy (OM), Small Angle Neutron Scattering (SANS), and Cryo-TEM. Upon cooling, MLVs grow from, and coexist with, the surfactant micelles, attaining diameters ranging from hundreds of nanometers to a few micrometers depending on the cooling rate, whilst the d-spacing of internal lamellae remains unchanged, at 3 nm. While microscale fluid and flow properties of the mixed MLVs and micellar phase depend on rate of cooling, the corresponding nanoscale structure of the surfactant aggregates, resolved by time-resolved SANS, remains unchanged. Our data indicate that the mixed MLV and micellar phases are in thermodynamic equilibrium with a fixed relative volume fraction determined by temperature and total surfactant concentration. Under flow, MLVs aggregate and consequently migrate away from the channel walls, thus reduce the overall hydrodynamic resistance. Our findings demonstrate that the molecular and mesoscopic structure of ubiquitous, low concentration NaLAS solutions, and in turn their flow properties, are dramatically influenced by temperature variation about ambient conditions.

Journal article

Pont S, Durrant JR, Cabral JT, 2019, Dynamic PCBM:dimer population in solar cells under light and temperature fluctuations, Advanced Energy Materials, Vol: 9, Pages: 1-9, ISSN: 1614-6832

Photoinduced dimerization of phenyl-C61-butyric acid methyl ester (PCBM) has a significant impact on the stability of polymer:PCBM organic solar cells (OSCs). This reaction is reversible, as dimers can be thermally decomposed at sufficiently elevated temperatures and both photodimerization and decomposition are temperature dependent. In operando conditions of OSCs evidently involve exposure to both light and heat, following periodic diurnal and seasonal profiles. In this work, the kinetics of dimer formation and decomposition are examined and quantified as a function of temperature, light intensity, blend composition, and time. The activation energy for photodimerization is estimated to be 0.021(3) eV, considerably smaller than that for decomposition (0.96 eV). The findings are benchmarked with a variety of conjugated polymer matrices to propose a descriptive dynamic model of PCBM:dimer population in OSCs, and a framework is proposed to rationalize its interplay with morphology evolution and charge quenching. The model and parameters enable the prediction of the dynamic and long-term PCBM:dimer populations, under variable temperature and light conditions, which impact the morphological stability of OSCs.

Journal article

Khan H, Seddon JM, Law RV, Brooks NJ, Robles E, Cabral JT, Ces Oet al., 2019, Effect of glycerol with sodium chloride on the Krafft point of sodium dodecyl sulfate using surface tension, Journal of Colloid and Interface Science, Vol: 538, Pages: 75-82, ISSN: 0021-9797

The effect of glycerol with sodium chloride (NaCl) on the phase behaviour of sodium dodecyl sulfate (SDS) near the Krafft point was studied by surface tension analysis using the pendant drop method. The critical micelle concentration (CMC) and Krafft Temperature (TK) of SDS in water: glycerol mixtures, across the full composition range, and in NaCl solutions within 0.005–0.1 M were obtained. The pendant drop method successfully allowed us to determine the Krafft point of SDS in high glycerol systems where other traditional methods (e.g. conductivity) have been ineffective. Overall the addition of glycerol increases the CMC and the TK, thus shifting the Krafft point of SDS to higher temperatures (increasing crystallisation temperatures) and higher SDS content in the presence of glycerol, which is interpreted as a result of the reduction in solvent polarity which opposes micellization. The addition of NaCl to the SDS – water-glycerol systems brings the CMC back down, while having no significant effect on the TK. Our results establish a robust route for tuning the Krafft point of model surfactant SDS by adjusting solvent quality and salt content.

Journal article

Aoki Y, Wang H, Sharratt W, Dalgliesh R, Higgins J, Cabral Jet al., 2019, Small angle neutron scattering study of the thermodynamics of highly interacting PαMSAN/dPMMA blends, Macromolecules, Vol: 52, Pages: 1112-1124, ISSN: 0024-9297

Poly(methyl methacrylate) (PMMA) and poly(α-methyl styrene-co-acrylonitrile) (PαMSAN) form partially miscible blends with lower critical solution temperature (LCST) behaviour. We revisit this system using small angle neutron scattering (SANS), examining the effect of molecular weight (Mw) of deuterated PMMA (dPMMA), blend composition (φ) and temperature (T) in the homogeneous region. All data are well described by the Random Phase Approximation (RPA) theory, enabling us to determine thermodynamic and structural parameters, including the correlation length ξ, G00 (the second derivative of the free energy of mixing with respect to composition), and the statistical segment length a of each component. Phase boundaries are computed by extrapolation of G00 with temperature, to yield the spinodal, and inspection of Kratky plots to yield the binodal. For PαMSAN, a is determined to be 10.1±0.4 ˚A. Unsurprisingly, this system deviates strongly from Flory-Huggins expectations, exhibiting a minimal Mw dependence of the phase boundaries and φ-dependence of effective interaction parameter (˜χ). Comparison of G00 with values for other blend systems places PαMSAN/dPMMA in a class of highly interacting blends, expected from Cahn-Hilliard theory to yield small initial phase sizes upon spinodal demixing. This is confirmed experimentally, with an illustrative temperature jump resulting in an initial phase size of ' 30 nm.

Journal article

Beber A, Taveneau C, Nania M, Tsai F-C, Di Cicco A, Bassereau P, Levy D, Cabral JT, Isambert H, Mangenot S, Bertin Aet al., 2019, Membrane reshaping by micrometric curvature sensitive septin filaments, Nature Communications, Vol: 10, ISSN: 2041-1723

Septins are cytoskeletal filaments that assemble at the inner face of the plasma membrane. They are localized at constriction sites and impact membrane remodeling. We report in vitro tools to examine how yeast septins behave on curved and deformable membranes. Septins reshape the membranes of Giant Unilamellar Vesicles with the formation of periodic spikes, while flattening smaller vesicles. We show that membrane deformations are associated to preferential arrangement of septin filaments on specific curvatures. When binding to bilayers supported on custom-designed periodic wavy patterns displaying positive and negative micrometric radii of curvatures, septin filaments remain straight and perpendicular to the curvature of the convex parts, while bending negatively to follow concave geometries. Based on these results, we propose a theoretical model that describes the deformations and micrometric curvature sensitivity observed in vitro. The model captures the reorganizations of septin filaments throughout cytokinesis in vivo, providing mechanistic insights into cell division.

Journal article

Wang H, Khodaparast S, Cabral J, 2019, Study of phase behavior and (meta)stability of model surfactant solutions by microfluidic thermal fluctuation platform, APS March Meeting 2019

Conference paper

Wang H, Aoki Y, Sharratt W, Rogers S, Dalgliesh R, Higgins J, Cabral Jet al., 2019, SANS study of the thermodynamics and demixing of highly interacting PaMSAN/dPMMA blends, APS March Meeting 2019

Conference paper

Miller RM, Cabral J, Robles E, Brooks N, Ces Oet al., 2018, Crystallisation of sodium dodecyl sulfate–water micellar solutions with structurally similar additives: counterion variation, CrystEngComm, Vol: 20, Pages: 6834-6843, ISSN: 1466-8033

The effects of a series of structurally similar sodium dodecyl sulfate (SDS) additives on the crystallisation of SDS–water micellar solutions were investigated using a combination of differential scanning calorimetry, dynamic light scattering, optical microscopy and inductively coupled plasma optical emission spectroscopy. Seven different counterions were chosen from groups 1 and 2 of the periodic table to replace the sodium on SDS: LDS, (SDS), KDS, RbDS, CsDS, Mg(DS)2, Ca(DS)2 and Sr(DS)2. Two representative temperature profileswere employed – linear cooling ramps at rate of 0.5 °C min−1 to determine near-equilibrium kinetics and transitions and isothermal holds at 6 °C to elucidate morphological changes. Crystallisation of the reference solution 20% SDS–H2O with 0.25, 1.0 and 2.5% additive was generally promoted or inhibited even at the lowest concentrations. Melting points however remained largely unchanged, suggesting that the additives predominantly had a kinetic rather than thermodynamic effect. ICP-OES measurements for the solutions containing 1% additive indicated that most of the additives were integrated into the SDS crystals which was reflected by morphological changes, including the formation of hexagonal and oval shaped crystals. Our results both quantify and provide a morphological insight into the effect of a series of additives on the crystallisation of micellar SDS solutions, which can readily form due to preferential Na exchange.

Journal article

Pont S, Foglia F, Higgins A, Durrant JR, Cabral JPet al., 2018, Stability of polymer:PCBM thin films under competitive illumination and thermal stress, Advanced Functional Materials, Vol: 28, ISSN: 1616-301X

The combined effects of illumination and thermal annealing on the morphological stability and photodimerization in polymer/fullerene thin films are examined. While illumination is known to cause fullerene dimerization and thermal stress their dedimerization, the operation of solar cells involves exposure to both. The competitive outcome of these factors with blends of phenyl‐C61‐butyric acid methyl ester (PCBM) and polystyrene (PS), supported on PEDOT:PSS is quantified. UV–vis spectroscopy is employed to quantify dimerization, time‐resolved neutron reflectivity to resolve the vertical composition stratification, and atomic force microscopy for demixing and coarsening in thin films. At the conventional thermal stress test temperature of 85 °C (and even up to the PS glass transition), photodimerization dominates, resulting in relative morphological stability. Prior illumination is found to result in improved stability upon high temperature annealing, compatible with the need for dedimerization to occur prior to structural relaxation. Modeling of the PCBM surface segregation data suggests that only PCBM monomers are able to diffuse and that illumination provides an effective means to control dimer population, and thus immobile fullerene fraction, in the timescales probed. The results provide a framework for understanding of the stability of organic solar cells under operating conditions.

Journal article

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