Control of Nanomaterial Self-Assembly in Ultrasonically Levitated Droplets

Seddon, Annela M.; Richardson, S. J.; Rastogi, Kunal; Plivelic, Tomás S.; Squires, Adam M.; Pfrang, Christian

doi:10.1021/acs.jpclett.6b00449

Cited by 50 publications

(47 citation statements)

References 37 publications

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“…Self-assembly thus may play a significant role in the kinetic behaviour of surfactant molecules in the atmosphere. We are currently carrying out experimental studies on oleic-acid-based aerosol proxies with complementary techniques (Seddon et al, 2016) to further investigate the importance of complex self-assembly in atmospheric aerosols .…”

Section: Atmospheric Implicationsmentioning

confidence: 99%

Nighttime oxidation of surfactants at the air–water interface: effects of chain length, head group and saturation

et al. 2018

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Reactions of the key atmospheric nighttime oxidant NO 3 with organic monolayers at the air-water interface are used as proxies for the ageing of organic-coated aqueous aerosols. The surfactant molecules chosen for this study are oleic acid (OA), palmitoleic acid (POA), methyl oleate (MO) and stearic acid (SA) to investigate the effects of chain length, head group and degree of unsaturation on the reaction kinetics and products formed. Fully and partially deuterated surfactants were studied using neutron reflectometry (NR) to determine the reaction kinetics of organic monolayers with NO 3 at the air-water interface for the first time. Kinetic modelling allowed us to determine the rate coefficients for the oxidation of OA, POA and MO monolayers to be (2.8 ± 0.7) × 10 −8 , (2.4 ± 0.5) × 10 −8 and (3.3 ± 0.6) × 10 −8 cm 2 molecule −1 s −1 for fitted initial desorption lifetimes of NO 3 at the closely packed organic monolayers, τ d,NO 3 ,1 , of 8.1 ± 4.0, 16 ± 4.0 and 8.1 ± 3.0 ns, respectively. The approximately doubled desorption lifetime found in the best fit for POA compared to OA and MO is consistent with a more accessible double bond associated with the shorter alkyl chain of POA facilitating initial NO 3 attack at the double bond in a closely packed monolayer. The corresponding uptake coefficients for OA, POA and MO were found to be (2.1±0.5)×10 −3 , (1.7±0.3)×10 −3 and (2.1±0.4)×10 −3 , respectively. For the much slower NO 3 -initiated oxidation of the saturated surfactant SA we estimated a loss rate of approximately (5 ± 1) × 10 −12 cm 2 molecule −1 s −1 , which we consider to be an upper limit for the reactive loss, and estimated an uptake coefficient of ca. (5 ± 1) × 10 −7 . Our investigations demonstrate that NO 3 will contribute substantially to the processing of unsaturated surfactants at the air-water interface during nighttime given its reactivity is ca. 2 orders of magnitude higher than that of O 3 . Furthermore, the relative contributions of NO 3 and O 3 to the oxidative losses vary massively between species that are closely related in structure: NO 3 reacts ca. 400 times faster than O 3 with the common model surfactant oleic acid, but only ca. 60 times faster with its methyl ester MO. It is therefore necessary to perform a case-by-case assessment of the relative contributions of the different degradation routes for any specific surfactant. The overall impact of NO 3 on the fate of saturated surfactants is slightly less clear given the lack of prior kinetic data for comparison, but NO 3 is likely to contribute significantly to the loss of saturated species and dominate their loss during nighttime. The retention of the organic character at the air-water interface differs fundamentally between the different surfactant species: the fatty acids studied (OA and POA) form products with a yield of ∼ 20 % that are stable at the interface while NO 3 -initiated oxidation of the methyl ester MO rapidly and effectively removes the organic character (≤ 3 % surface-active products). The film-forming potential of r...

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Section: Atmospheric Implicationsmentioning

confidence: 99%

Nighttime oxidation of surfactants at the air–water interface: effects of chain length, head group and saturation

et al. 2018

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“…27 Acoustic levitation of aqueous drops is a convenient approach which has been used to study the crystallization and agglomeration of proteins as well as the assembly of nanoparticles. [28][29][30] Levitating drops that slowly shrink as the water evaporates constitute a system that does not require the addition of surfactants and allows assembly to be studied without the presence of a solid substrate. Here, we have quantified the nanoscale assembly of cellulose nanocrystals in an acoustically levitating drop by time-resolved small angle X-ray scattering (SAXS).…”

Section: Introductionmentioning

confidence: 99%

Assembly of cellulose nanocrystals in a levitating drop probed by time-resolved small angle X-ray scattering

et al. 2018

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Assembly of bio-based nano-sized particles into complex architectures and morphologies is an area of fundamental interest and technical importance. We have investigated the assembly of sulfonated cellulose nanocrystals (CNC) dispersed in a shrinking levitating aqueous drop using time-resolved small angle X-ray scattering (SAXS). Analysis of the scaling of the particle separation distance (d) with particle concentration (c) was used to follow the transition of CNC dispersions from an isotropic state at 1-2 vol% to a compressed nematic state at particle concentrations above 30 vol%. Comparison with SAXS measurements on CNC dispersions at near equilibrium conditions shows that evaporation-induced assembly of CNC in large levitating drops is comparable to bulk systems. Colloidal states with d vs. c scalings intermediate between isotropic dispersions and unidirectional compression of the nematic structure could be related to the biphasic region and gelation of CNC. Nanoscale structural information of CNC assembly up to very high particle concentrations can help to fabricate nanocellulose-based materials by evaporative methods.

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“…Acoustic methods have distinct advantages over other levitation methods, for example, optical, magnetic, or electrostatic levitation, particularly in their ability to levitate a wider range of materials in different host fluids. Consequently, acoustic trapping is a fundamental tool in chemistry [19], blood analysis [20], the study of organisms in microgravity [21,22], control of nanomaterial self-assembly [23], and x-ray crystallography [24]. At the same time, contactless rotation has proven invaluable for understanding planetary formation [25] and acoustic streaming has been used to rotate microorganisms for microscopy [26].…”

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confidence: 99%

Acoustic Virtual Vortices with Tunable Orbital Angular Momentum for Trapping of Mie Particles

2018

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Acoustic vortices can transfer angular momentum and trap particles. Here, we show that particles trapped in airborne acoustic vortices orbit at high speeds, leading to dynamic instability and ejection. We demonstrate stable trapping inside acoustic vortices by generating sequences of short-pulsed vortices of equal helicity but opposite chirality. This produces a "virtual vortex" with an orbital angular momentum that can be tuned independently of the trapping force. We use this method to adjust the rotational speed of particles inside a vortex beam and, for the first time, create three-dimensional acoustics traps for particles of wavelength order (i.e., Mie particles).

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Control of Nanomaterial Self-Assembly in Ultrasonically Levitated Droplets

Cited by 50 publications

References 37 publications

Nighttime oxidation of surfactants at the air–water interface: effects of chain length, head group and saturation

Nighttime oxidation of surfactants at the air–water interface: effects of chain length, head group and saturation

Assembly of cellulose nanocrystals in a levitating drop probed by time-resolved small angle X-ray scattering

Acoustic Virtual Vortices with Tunable Orbital Angular Momentum for Trapping of Mie Particles

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