skip to main content


Search for: All records

Creators/Authors contains: "Russell, Thomas P."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    Janus structures have unique properties due to their distinct functionalities on opposing faces, but have yet to be realized with flowing liquids. We demonstrate such Janus liquids with a customizable distribution of nanoparticles (NPs) throughout their structures by joining two aqueous streams of NP dispersions in an apolar liquid. Using this anisotropic integration platform, different magnetic, conductive, or non-responsive NPs can be spatially confined to opposite sides of the original interface using magnetic graphene oxide (mGO)/GO, Ti3C2Tx/GO, or GO suspensions. The resultant Janus liquids can be used as templates for versatile, responsive, and mechanically robust aerogels suitable for piezoresistive sensing, human motion monitoring, and electromagnetic interference (EMI) shielding with a tuned absorption mechanism. The EMI shields outperform their current counterparts in terms of wave absorption, i.e., SET ≈ 51 dB, SER ≈ 0.4 dB, and A = 0.91, due to their high porosity ranging from micro- to macro-scales along with non-interfering magnetic and conductive networks imparted by the Janus architecture.

     
    more » « less
    Free, publicly-accessible full text available December 1, 2024
  2. Research involving polymer zwitterions typically involves the preparation of ammonium-based structures and their study as coatings or gels that impart hydrophilicity and/or antifouling properties to substrates and materials. More recent synthetic advances have produced a significant expansion in polymer zwitterion chemistry, especially with respect to the composition of the cationic moieties that open new possibilities to examine polymer zwitterions as amphiphiles, functional surfactants, and components of complex emulsions. This article describes the synthesis of new zwitterionic sulfonium sulfonate monomers and their use as starting materials in controlled free radical polymerization to yield the corresponding polymers. These novel polymer zwitterions bear sulfonium sulfonate groups, that possess an inverted dipole directionality relative to prior examples that yields different and unexpected physical and chemical properties. For example, the polymer zwitterions described here are soluble in a wide range of nonaqueous solvents and possess significantly greater stability against nucleophiles relative to their dipole-inverted counterparts. Additionally, the amphiphilic character of these sulfonium sulfonate polymers makes them amenable to use as surfactants for stabilizing oil-in-water emulsions, a feature that is not possible using conventional ultrahydrophilic polymer zwitterions. 
    more » « less
  3. Abstract

    By combining the unique characteristics of molecular bottlebrushes (MBBs) and the properties of stimuli‐responsive polymers, we show that MBBs with randomly grafted poly(n‐butyl acrylate) and pH‐responsive poly(2‐(N,N‐diethylamino)ethyl methacrylate) (PDEAEMA) side chains are efficient and robust pH‐responsive emulsifiers. Water‐in‐toluene emulsions were formed at pH 4.0 and disrupted by increasing the pH to 10.0. The emulsion generation and disruption was reversible over the ten cycles investigated, and the bottlebrushes remained intact. The exceptional emulsion stability stemmed from the high interfacial binding energy of MBBs, imparted by their large molecular size and Janus architecture at the interface, as evidenced by the interfacial jamming and wrinkling of the assemblies upon reducing the interfacial area. At pH 10.0, PDEAEMA became water‐insoluble, and the MBBs desorbed from the interface, causing de‐emulsification. Consequently, we have shown that the judicious design of MBBs can generate properties of particle emulsifiers from their large size, while the responsiveness of the MBBs enables more potential applications.

     
    more » « less
  4. Abstract

    By combining the unique characteristics of molecular bottlebrushes (MBBs) and the properties of stimuli‐responsive polymers, we show that MBBs with randomly grafted poly(n‐butyl acrylate) and pH‐responsive poly(2‐(N,N‐diethylamino)ethyl methacrylate) (PDEAEMA) side chains are efficient and robust pH‐responsive emulsifiers. Water‐in‐toluene emulsions were formed at pH 4.0 and disrupted by increasing the pH to 10.0. The emulsion generation and disruption was reversible over the ten cycles investigated, and the bottlebrushes remained intact. The exceptional emulsion stability stemmed from the high interfacial binding energy of MBBs, imparted by their large molecular size and Janus architecture at the interface, as evidenced by the interfacial jamming and wrinkling of the assemblies upon reducing the interfacial area. At pH 10.0, PDEAEMA became water‐insoluble, and the MBBs desorbed from the interface, causing de‐emulsification. Consequently, we have shown that the judicious design of MBBs can generate properties of particle emulsifiers from their large size, while the responsiveness of the MBBs enables more potential applications.

     
    more » « less
  5. Abstract

    It has been shown both theoretically and experimentally that amphiphilic Janus particles are the most effective solid surfactants to stabilize interfaces. In most cases, the Janus particles investigated have uniform morphologies with Janus boundaries dividing the particle into halves. However, there are many examples of Janus particles where the hydrophilic and hydrophobic domains are not equally distributed. The effects of this uneven domain distribution on the mechanism and kinetics of Janus particle assembly, and final equilibrium state are not well‐understood. Dynamic pendant drop tensiometry offers a means to probe both the equilibrium assembly and the kinetics and mechanism of assembly. Here, the interfacial kinetics and assembly of spherical anisotropic Janus particles are investigated using dynamic pendant drop tensiometry. Systematic studies quantifying the time‐dependent interfacial behavior as a function of Janus particle morphology, chemical composition, particle concentration, and NaOH and HCl concentration are performed. These studies shed light on the assembly mechanism of more complex Janus particle morphologies and highlight their effectiveness as interface stabilizers.

     
    more » « less
  6. Abstract

    An active droplet system, programmed to repeatedly move autonomously at a specific velocity in a well‐defined direction, is demonstrated. Coulombic energy is stored in oversaturated interfacial assemblies of charged nanoparticle‐surfactants by an applied DC electric field and can be released on demand. Spontaneous emulsification is suppressed by an increase in the stiffness of the oversaturated assemblies. Rapidly removing the field releases the stored energy in an explosive event that propels the droplet, where thousands of charged microdroplets are ballistically ejected from the surface of the parent droplet. The ejection is made directional by a symmetry breaking of the interfacial assembly, and the combined interaction force of the microdroplet plume on one side of the droplet propels the droplet distances tens of times its size, making the droplet active. The propulsion is autonomous, repeatable, and agnostic to the chemical composition of the nanoparticles. The symmetry‐breaking in the nanoparticle assembly controls the microdroplet velocity and direction of propulsion. This mechanism of droplet propulsion will advance soft micro‐robotics, establishes a new type of active matter, and introduces new vehicles for compartmentalized delivery.

     
    more » « less
  7. null (Ed.)
  8. null (Ed.)