Local Measurement of Janus Particle Cap Thickness

Rashidi, Aidin; Issa, Marola W.; Martin, Ina T.; Avishai, Amir; Razavi, Sepideh; Wirth, Christopher L.

doi:10.1021/acsami.8b11011

Cited by 22 publications

(24 citation statements)

References 25 publications

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“…The figure illustrates a set of pressure isotherms for 7.5 mg of each particle type dispersed from 200 μL of spreading solution onto the interface. On the basis of the estimated density of Janus particles (2.3 g/cm 3 ), this quantity of particles amounts to ∼6.1 × 10 9 Janus particles assuming the Janus cap is crescent-shaped . It roughly corresponds to 1.27 μm 2 /particle at the interface in the open-barrier state.…”

Section: Resultsmentioning

confidence: 99%

“…Details of the fabrication of Janus particles using the physical vapor deposition technique are provided in the Supporting Information. Using the density values for silica (2.0 g/cm 3 ), titanium (4.5 g/cm 3 ), and gold (19.2 g/cm 3 ), and assuming that the Janus cap is crecent-shaped, 75 we estimate the density of a Janus particle to be 2.3 g/cm 3 . All glassware used in the study is thoroughly cleaned using a sulfuric acid (Certified ACS Plus, Fisher Scientific) and NOCHROMIX (Godax Laboratories, Inc.) mixture, followed by rinsing with copious amounts of ultrapure water and drying under vacuum.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

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Impact of Surface Amphiphilicity on the Interfacial Behavior of Janus Particle Layers under Compression

et al. 2019

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Langmuir monolayers of silica/gold Janus particles with two different degrees of amphiphilicity have been examined to study the significance of particle surface amphiphilicity on the structure and mechanical properties of the interfacial layers. The response of the layers to the applied compression provides insight into the nature and strength of the interparticle interactions. Different collapse modes observed for the interfacial layers are linked to the amphiphilicity of Janus particles and their configuration at the interface. Molecular dynamics simulations on nanoparticles with similar contact angles provide insight on the arrangement of particles at the interface and support our conclusion that the interfacial configuration and collapse of anisotropic particles at the air/water interface are controlled by particle amphiphilicity.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Materials and Methodsmentioning

confidence: 99%

Impact of Surface Amphiphilicity on the Interfacial Behavior of Janus Particle Layers under Compression

et al. 2019

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“…Janus particles are fabricated by coating one hemisphere of a spherical colloid particle with another material, usually a metal such as gold [30,31]. The cap typically has some nominal thickness from a few to tens of nanometers, but direct measurement of the coating thickness has shown the cap to be non-uniform across the contour of the particle [32]. Tracking translational and rotational displacement of Janus particles at the various boundary, physiochemical, and rheological conditions could help with predicting the dynamics of these particles [33][34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Influence of cap weight on the motion of a Janus particle very near a wall

2020

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The dynamics of anisotropic nano-to microscale 'colloidal' particles in confined environments, either near neighboring particles or boundaries, is relevant to a wide range of applications. We utilized Brownian dynamics simulations to predict the translational and rotational fluctuations of a Janus sphere with a cap of non-matching density. The presence of the cap significantly impacted the rotational dynamics of the particle as a consequence of gravitational torque at experimentally relevant conditions. Gravitational torque dominated stochastic torque for a particle > 1 m in diameter and with a 20 nm thick gold cap. Janus particles at these conditions sampled mostly cap-down or 'quenched' orientations. Although the results summarized herein showed that particles of smaller diameter (< 1 m) with a thin gold coating (< 5 nm) behave similar to an isotropic particle, small increases in either particle diameter or coating thickness drastically quenched the polar rotation of the particle. Histogram landscapes of the separation distance from the boundary and orientation observations of particles with larger diameters or thicker gold coatings were mostly populated with quenched configurations. Finally, the histogram landscapes were inverted to obtain the potential energy landscapes, providing a path for experimental data to be interpreted. 3 I. INTRODUCTION. Colloidal particles dispersed in a liquid interact via surface forces that play a critical role in dictating the properties and performance of complex fluid. Over the past decade, the dynamics and interactions of anisotropic colloidal particles have gained attention [1] because of potential applications in various fields such as optical displays [2], magnetorheological system [3], controlling interfacial microstructure [4], self-assembly [5,6], microfluidic devices [7], tuning interparticle interactions [8,9], and biomaterials or drug delivery [10].Supporting these efforts have been a variety of new techniques for the synthesis of anisotropic colloidal particles [5,[10][11][12][13][14][15][16][17][18][19][20][21]. Newly developed fabrication techniques provided the ability to tune the shape and the surface properties of these materials. Janus particles are one class of anisotropic colloid, typically with some property difference in the hemispherical domain. Each hemispherical domain of a Janus particle may have its own surface chemistry, shape, or other properties [22].Predicting the dynamics of anisotropic colloids is important for applications in real systems, for example during processing when complex fluids are often not at equilibrium [23,24].Various parameters influence the dynamics of anisotropic colloids [25][26][27][28]. Particle confinement will strongly impact the hydrodynamic interactions between the colloid and boundary, thereby strongly influencing particle mobility. Brownian motion and conservative (i.e. path independent) forces, such as electrostatic double layer repulsion and gravity, will also impact the dynamics of a confined spherical Janus part...

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“…Physical vapor deposition (PVD) (DV-502A Turbo High Vacuum Evaporator) was used to deposit a cap of 20 nm nominal thickness at a rate of 1 Å/s. We expect particles to have a nominal thickness of 20 nm cap at the 'north pole', but a thickness that decays to 0 nm at the particle equator 27 . After coating, Janus particles were removed from the silicon substrate via bath sonication and stored in ultra-pure water.…”

Section: Methodsmentioning

confidence: 99%