An official website of the United States government
Polystyrene‐Silica Colloidal Janus Particles with Uniform Shapes and Complex Structures
Abstract Colloidal Janus particles with well‐controlled parameters are sought for a range of applications in mesoscale self‐assembly, stabilization of Pickering emulsion, and development of multifunctional devices, among others. Herein, a versatile method for fabricating polystyrene‐silica (PS‐SiO2) Janus particles featuring complex shapes and structures is developed by swelling PS@SiO2core–shell spheroids. When the PS encapsulated in a rigid SiO2shell is swollen by a good solvent for PS, the swelling‐induced pressure will result in an uneven distribution of stress acting on the SiO2shell, as determined by the intrinsic symmetry of a spheroid. When the stress reaches a threshold value, the swollen PS will preferentially poke out from equatorial sites on the SiO2shell to form T‐shaped Janus particles comprised of PS and SiO2compartments. The size of the PS portion can be controlled by varying the extent of swelling, while the size, shape, and shell thickness of the SiO2portion are determined by the original PS spheroids and the SiO2coating. This solution‐phase method holds promise to produce Janus particles with diverse shapes, structures, and compositions for various applications. The T‐shaped Janus particles can serve as an emulsifier to effectively stabilize an oil‐in‐water (O/W) Pickering emulsion for at least 35 days.
more »
« less
- Award ID(s):
- 2137669
- PAR ID:
- 10444550
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Particle & Particle Systems Characterization
- Volume:
- 39
- Issue:
- 8
- ISSN:
- 0934-0866
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract Macromolecules exhibit rich phase behavior that may be exploited for advanced material design. In particular, the volume phase transition in certain crosslinked hydrogels is a key property controlling the transition between a collapsed/dehydrated and a swollen/hydrated state, thereby regulating the release and absorption of water via a temperature change. In this work, a simple and tunable system exhibiting a carbon dioxide (CO2)‐switchable volume phase transition is introduced, which displays isothermal swelling‐shrinking behavior that is activated by addition and removal of CO2,respectively. Through systematic compositional studies, shifts in phase transition temperatures of up to 8.6 °C are measured upon CO2exposure, which enables pronounced isothermal swelling in response to CO2, reaching up to a fivefold increase in mass. The shift in transition temperature and the extent of swelling are controlled by the hydrogel composition, thus enabling the transition temperature and swelling degree to be tuned a priori for a particular application. Controlled release experiments from these gels upon a CO2‐induced phase transition suggest viability for drug delivery applications. It is anticipated that this work will motivate and expand efforts to exploit phase behavior for smart material development.more » « less
-
The effect of nanoscale defects on nanoparticle dynamics in defective tetra-poly(ethylene glycol) (tetra-PEG) hydrogels is investigated using single particle tracking. In a swollen nearly homogeneous hydrogel, PEG-functionalized quantum dot (QD) probes with a similar hydrodynamic diameter ( d h = 15.1 nm) to the mesh size (〈 ξ s 〉 = 16.3 nm), are primarily immobile. As defects are introduced to the network by reaction-tuning, both the percentage of mobile QDs and the size of displacements increase as the number and size of the defects increase with hydrolysis time, although a large portion of the QDs remain immobile. To probe the effect of nanoparticle size on dynamics in defective networks, the transport of d h = 47.1 nm fluorescent polystyrene (PS) and d h = 9.6 nm PEG-functionalized QDs is investigated. The PS nanoparticles are immobile in all hydrogels, even in highly defective networks with an open structure. Conversely, the smaller QDs are more sensitive to perturbations in the network structure with an increased percentage of mobile particles and larger diffusion coefficients compared to the larger QDs and PS nanoparticles. The differences in nanoparticle mobility as a function of size suggests that particles of different sizes probe different length scales of the defects, indicating that metrics such as the confinement ratio alone cannot predict bulk dynamics in these systems. This study provides insight into designing hydrogels with controlled transport properties, with particular importance for degradable hydrogels for drug delivery applications.more » « less
-
null (Ed.)The use of the Janus motif in colloidal particles, i.e., anisotropic surface properties on opposite faces, has gained significant attention in the bottom-up assembly of novel functional structures, design of active nanomotors, biological sensing and imaging, and polymer blend compatibilization. This review is focused on the behavior of Janus particles in interfacial systems, such as particle-stabilized (i.e., Pickering) emulsions and foams, where stabilization is achieved through the binding of particles to fluid interfaces. In many such applications, the interface could be subjected to deformations, producing compression and shear stresses. Besides the physicochemical properties of the particle, their behavior under flow will also impact the performance of the resulting system. This review article provides a synopsis of interfacial stability and rheology in particle-laden interfaces to highlight the role of the Janus motif, and how particle anisotropy affects interfacial mechanics.more » « less
-
Microgels are spherical particles suspended in solution, comprised of crosslinked polymer chains. Due to the amphiphilic property of the parent polymer, microgels display a temperature dependent volume phase transition (de-swelling), and thus have the potential to be used for drug delivery. Previous studies suggest that increasing the concentrations of the chemical cross-linker reduces the hydrodynamic radius (Rh) and the de-swelling ability, thus primary experiments focused on the variation of cross-linker to polymer ratios. Microgels were synthesized using the polysaccharide polymer hydroxypropyl cellulose (HPC) and chemical cross-linker divinyl sulfone (DVS), in a surfactant solution. Synthesized particles were characterized using dynamic light scattering (DLS) for temperature and angular dependence to study their shape and determine the apparent Rh of the swollen and de-swollen states. Initial microgel synthesis revealed a dependence of Rh on microgel concentration in samples, requiring a correction for infinite sample dilution during analysis. Increasing DVS:HPC ratio from 1 to 30 causes Rh to decrease from 150 to 190 nm at 25 °C, and from 65 to 95 nm at 50 °C. Ratios from 40 to 50 resulted in swelling from 70 nm at 25 °C to 165 nm at 50 °C. At a ratio of 60, an apparent bulk gelation occurred. The increase in DVS:HPC ratio allowed for the controlled synthesis of more compact microgels that display reversible temperature controlled deswelling. However, at ratios above 30, particles were found to grow in size above the transition temperature.more » « less
