Direct measurement of self-diffusiophoretic force generated by active colloids of different patch coverage using optical tweezers.

Hypothesis: Synthetic micro/nanomotors are gaining extensive attention for various biomedical applications (especially in drug delivery) due to their ability to mimic the motion of biological micro/nanoscale swimmers. The feasibility of these applications relies on tight control of propulsion speed, direction, and type of motion (translation, circular, etc.) along with the exerted self-propulsive force.

Development of Hematite Nano Ellipsoids/Pectin Composite Films for Green Packaging Applications.

Synthetic packaging materials are known to cause serious environmental and human health problems. Among the eco-friendly biopolymers from nonfood sources that are suitable for packaging applications, pectin is a promising candidate. However, native pectin films (NPF) exhibit poor mechanical strength, high hydrophilicity, and poor gas diffusion barrier properties.

Drying-Induced Flash Nanoprecipitation in a Sessile Drop: A Route to Synthesize Polymeric Nanoparticles.

Flash nanoprecipitation is a simple and scalable method to produce nanoparticles by rapid mixing of a polymer solution with an antisolvent. High-speed mixing devices for the continuous synthesis of polymeric nanoparticles and drug-encapsulated nanoparticles have been designed. In this work, we demonstrate a different approach to induce flash nanoprecipitation using the differential evaporation of solvents in a sessile drop.

Contact Angle Modulation: In Situ Polymer Deposition during Sessile Drop Evaporation.

The drying kinetics of a sessile drop on a solid surface are a widely studied phenomenon because of their relevance to various fields such as coating, printing, medical diagnostics, sensing, and microfluidic technology. Typically, the drop undergoes drying either at a constant contact radius () with a decrease in the three-phase contact angle or at a constant contact angle (θ) with a reduction in the radius with time. These two drying modes are referred to as CCR and CCA, respectively.

Demulsification of Pickering Emulsions by Chemical Dissolution of Stabilizers.

Demulsification of particle-stabilized oil-in-water emulsions is crucial in diverse fields such as treatment of produce water, recovery of valuable products of Pickering emulsion catalysis, and so on. In this work, we investigated a facile method for destabilizing emulsions by dissolving stabilizer particles by the introduction of acid or base. Nanoellipsoidal hematite-stabilized decane-in-water emulsions are destabilized by dissolving hematite with oxalic or hydrochloric acid in situ.

Liquid-Liquid Phase Separation (LLPS)-Driven Fibrilization of Amyloid-β Protein.

Amyloid-β [Aβ(1-40)] aggregation into a fibrillar network is one of the major hallmarks of Alzheimer's disease (AD). Recently, a few studies reported that polyphosphate (polyP), an anionic biopolymer that participates in various cellular physiological processes in humans, induces fibrilization in many amyloidogenic proteins [ ; John Wiley and Sons Inc., 2020; Tanzi, R.

Oil-in-Water Emulsions Stabilized by Hydrophilic Homopolymers.

Most of the polymeric emulsifiers have diblock and triblock copolymer architecture containing hydrophilic and hydrophobic domains. In this work, we show that hydrophilic homopolymers can be effective stabilizers of oil-in-water emulsions. Using polyethelyne oxide and poly(vinylpyrrolidone) as model hydrophilic homopolymers and n-decane and n-hexane as model nonpolar phases, we show that high-molecular weight polymers can stabilize emulsions over 24 h beyond a threshold concentration.

Brownian dynamics simulations of telechelic polymer - latex suspensions under steady shear.

We carry out coarse-grained Brownian dynamics simulations of shearing flow of a colloidal suspension bridged by telechelic polymers with "sticky" end groups and vary sticker strength over a range from 3 to 12 in units of , motivated by an interest in simulating the rheology of latex paints. The most extensive results are obtained for dumbbells, but the trends are confirmed for 3-bead trumbbells and chains of up to 11 beads. The numbers of colloids and of polymers are also varied over a wide range to confirm trends established for smaller, more computationally affordable, systems.

Effect of substrate charge density on the adsorption of intrinsically disordered protein amyloid β40: a molecular dynamics study.

The inhibitory effect of negatively charged gold nanoparticles (AuNPs) on amyloidogenic protein fibrillation has been established from experiments and computer simulations. Here, we investigate the effect of the charge density () of gold (Au) surfaces on the adsorption of the intrinsically disordered amyloid β40 (Aβ40) monomer using molecular dynamics (MD) simulations. On the basis of the binding free energy, some key residues (ARG5, LYS16, LYS28, LEU17-ALA21, ILE31-VAL38) were found to be responsible for preventing the β-sheet formation, which is known to be a precursor for fibrillation.

Electrostatic Heteroaggregation: Fundamentals and Applications in Interfacial Engineering.

The aggregation of oppositely charged soft materials (particles, surfactants, polyelectrolytes, etc.) that differ in one or more physical or chemical attributes, broadly referred to as electrostatic heteroaggregation, has been an active area of research for several decades now. While electrostatic heteroaggregation (EHA) is relevant to diverse fields such as environmental engineering, food technology, and pharmaceutical formulations, more recently there has been a resurgence to explore various aspects of this phenomenon in the context of interface stabilization and the development of functional materials.

Collective behavior of passive and active circle swimming particle mixtures.

We present a numerical study on a binary mixture of passive and circle swimming, self-propelling particles which interact the Lennard-Jones (LJ) potential in two dimensions. Using Brownian Dynamics (BD) simulations, we present state diagrams using the control parameters such as attraction strength, angular velocity, self-propulsion velocity and composition. In a symmetric mixture, the system undergoes a transition from a mixed gel to a rotating passive cluster state and finally to a homogeneous fluid state as translational activity increases.

Light-induced destabilisation of oil-in-water emulsions using light-active bolaform surfactants.

External stimuli-induced destabilisation of oil-in-water emulsions is of both fundamental and technological importance. In this work we synthesize light-active bolaform-type surfactants (LABSs) and show the preparation of decane-in-water emulsions over a range of surfactant and salt concentrations. Under ultraviolet (UV) illumination, LABSs undergo to isomerization affecting their interfacial activity.

Destabilization of Pickering emulsions by interfacial transport of mutually soluble solute.

Hypothesis: Pickering emulsions (PEs) once formed are highly stable because of very high desorption energies (∼10 kT) associated with particles adsorbed to the interfaces. The destabilization of PEs is required in many instances for recovery of valuable chemicals, products and active compounds. We propose to exploit interfacial instabilities develop by the addition of different types of solutes to PEs as a route to engineer their destabilization.

Self-assembly of a CTAB surfactant on gold nanoparticles: a united-atom molecular dynamics study.

Self-assembly of a cetyltrimethyl ammonium bromide (CTAB) surfactant on gold nanoparticles (AuNPs) is studied using united-atom molecular dynamics (MD) simulations. For AuNPs in the size range of 1-3 nm, CTAB self-assembles such that the tail groups adsorb on the AuNP surface while the ionic head group is exposed to water, giving a net negative charge to the AuNPs. Near the AuNP surface, water molecules are depleted.

Collective dynamics of active circle-swimming Lennard-Jones particles.

We report a numerical study on the collective dynamics of self-propelling and circle-swimming Lennard-Jones (LJ) particles in two dimensions using Brownian dynamics simulations. We investigate the combined role of attraction, self-propulsion and rotation in their phase behavior. At a low rotational speed, the system shows re-entrant phase behavior as a function of self-propulsion similar to active Brownian particles (ABPs).

Exploiting Heteroaggregation to Quantify the Contact Angle of Charged Colloids at Interfaces.

We exploit the aggregation between oppositely charged particles to visualize and quantify the equilibrium position of charged colloidal particles at the fluid-water interface. A dispersion of commercially available charge-stabilized nanoparticles was used as the aqueous phase to create oil-water and air-water interfaces. The colloidal particles whose charge was opposite that of the nanoparticles in the aqueous phase were deposited at the chosen fluid-water interface.

Competing effects of rotational diffusivity and activity on finite-sized clusters.

Colloidal particles interacting via short-range attraction and long-range repulsion are known to stabilize finite-sized clusters under equilibrium conditions. In this work, the effect of self-propulsion speed (activity) and rotational diffusivity () on the phase behavior of such particles is investigated using Brownian dynamics simulations. The system exhibits rich phase behavior consisting of clusters of different kinds.

Computer simulations of self-assembly of anisotropic colloids.

Computer simulations have played a significant role in understanding the physics of colloidal self-assembly, interpreting experimental observations, and predicting novel mesoscopic and crystalline structures. Recent advances in computer simulations of colloidal self-assembly driven by anisotropic or orientation-dependent inter-particle interactions are highlighted in this review. These interactions are broadly classified into two classes: entropic and enthalpic interactions.

Kinetics of aggregation of amyloid β under different shearing conditions: Experimental and modelling analyses.

Amyloid β (Aβ40) is a class of amyloidogenic proteins known to aggregate into a fibrillar network. The rate of aggregation and fibril yield is sensitive to external energy input, such as shear. In this work, simple shear and shaking experiments are performed on Aβ40 solution using a Couette cell and an orbital shaker, respectively.

Adsorption of the amyloid β40 monomer on charged gold nanoparticles and slabs: a molecular dynamics study.

Negatively charged nanoparticles are known to inhibit the fibrillation of amyloidogenic protein amyloid β (Aβ40), though the overall charge on the protein is negative. In this work a molecular dynamics study is reported to investigate the interaction of Aβ40 on negatively charged gold nanoparticles (3-5 nm) and charged (positive and negative) and neutral gold slabs. The equilibrium structures of Aβ40 on gold surfaces are characterized using residue-specific contacts on the gold surface, secondary structure analysis and binding free energy calculations.

Stabilizing ordered structures with single patch inverse patchy colloids in two dimensions.

Oppositely charged bipolar colloids or colloids decorated with complementary deoxyribonucleic acid (DNA) on their surfaces are special kinds of patchy particles where only patch and non-patch parts are attractive. These are classified as inverse patchy colloids (IPCs). In this work, equilibrium self-assembly of IPC in two-dimensions is reported using Monte Carlo simulations.

Self assembly of nanorods on microspheres at fluid-fluid interfaces.

The potential applications of metal nanoparticles require their assembly/deposition on different solid matrices. In this work, an experimental method is demonstrated to assemble gold nanorods (AuNRs) as a ring-like structure on polystyrene (PS) microspheres at the fluid-fluid interface via dip-coating followed by solvent evaporation. The effects of AuNR concentration, size and surface charge of PS particles and size of AuNRs on the formation of AuNR ring-like structures on templated PS particles are investigated.

Rapid Dissolution of Amyloid β Fibrils by Silver Nanoplates.

Plaques of amyloid beta (Aβ) protein are associated with neurodegenerative diseases, and preventing their formation and dissolution of plaques are essential to the development of therapeutics. In this study, silver triangular nanoplates (AgTNPs) are shown to dissolve mature Aβ fibrils because of their plasmonic photothermal property. Mature Aβ fibrils treated with AgTNPs under near-infrared (NIR)-illuminated conditions are dissolved in less than 1 h, while an equal concentration of silver spherical nanoparticles took about 70 h.

Transition from Linear to Circular Motion in Active Spherical-Cap Colloids.

Nonspherical self-propelling colloidal particles offer many possibilities for creating a variety of active motions. In this work, we report on the transition from linear to circular motion of active spherical-cap particles near a substrate. Self-propulsion is induced by self-diffusiophoresis by catalytic decomposition of hydrogen peroxide (HO) on one side of the particle.