“Corona” v. “Corona-free”

NH3+

NH3+

NH3+

+H3N

SO3-

SO3-

SO3-

-O3S

SO3-

SO3-

-O3S

-O3S

+H3N

+H3N

NH3+

NH3+

Short oligomers with charged groups are covalently attached to the surface.

NH3+

NH3+

NH3+

+H3N

O- O-

O-

O-

O-

O-

-O

-O

-O

NH3+ +H3N

+H3N NH3+

Charges are provided by intrinsic surface charge on the nanoparticles.

Advantages of the corona-free approach: • Very simple synthesis. No complicated purification steps,

and essentially no byproducts or waste materials. • Easily scalable for bulk production.

Disadvantages of the corona-free approach: • Relatively low “graft” density (σ ≈ 0.8 nm-2 as opposed to

about 5 nm-2 for corona-based approach) • Limited gallery of particles with appropriate surface

chemistry.

Nanoparticle hybrids for Energy Applications

Materials for energy applications are a major area of research, both for producing energy, and for using energy more efficiently.

Dispersion (and self-assembly) are persistent challenges for nanoparticle/polymer hybrids.

Nanoparticle-polymer hybrid materials combine the advantages of inorganic nanoparticles (band gaps, surface area, mechanical strength) with the properties of organic polymers (processability, biodegradability), as well as having unique properties of their own.

Applications include: • Lubricants • Electrolytes • Carbon-capture liquids • Photovoltaics • Water-filtration membranes

Nanoparticle Ionic Materials

Iron oxide2

Silica1

Gold3 Fullerenes4

Nanoparticle Ionic Materials consist of a charged nanoparticle core, and an oppositely charged organic canopy. This allows the properties of these materials to be tuned by varying the core and the canopy. The electrostatic interaction between the core and the canopy stabilizes the particles against aggregation by creating a shell of organic material around each particle.

1,2 A. B. Bourlinos et al., Advanced Materials 17, 234 (2005). 3 R. R. Bhattacharjee. et al., Journal of Materials Chemistry 19, 8728 (2009). 4 N. Fernandes et al., Nanoscale 2, 1653 (2010).

Core Corona

Canopy

Potential applications for this new platform include single-ion conductors for battery electrolytes, thermal fluids, and high-refractive-index liquids, among others, as well as providing a straightforward route to dispersion of nanoparticles in polymers in general.

Silica-based Corona-free Nanoparticle Ionic Materials

Nikhil J. Fernandesa, Antonios Kelerakisb, and Emmanuel P. Giannelisb aSchool of Applied and Engineering Physics, Cornell University ; bDepartment of Materials Science and Engineering, Cornell University

NIMs v. mixtures

Nanoparticle Ionic Materials • Well-dispersed particles • Dispersion stable on drying • Fluid • Ionic interactions improve stability.

Particle-Polymer mixtures • Poor dispersion • Phase separation on drying • Solid • No ionic interactions

SiO2

O-

O-

O-

O- -O O-

-O

-O

SiO2

O-Na+

O-Na+

O-Na+

O-Na+

O-Na+

Na+-O

Na+-O

Na+-O

500 nm

TEM image of a sample with a superimposed Voronoi diagram showing hexagonal packing, indicating spherical shells of polymer around the nanoparticle.

The spacing between the particles can be tuned by varying the canopy molecular weight. Aside from changing the physical properties of the materials, this could be a route to the assembly of nanoparticle-based metamaterials and functional materials.

Applications: Polymer Battery electrolytes

Polyethylene oxide (PEO) is a common electrolyte for Li-Polymer batteries, but has a number of disadvantages. • Typical systems use PEO mixed with a

lithium salt as an electrolyte. The anion in the lithium salt can collect at the anode of the battery, causing passivation of the anode, reducing battery performance over time.

• Crystallization of high molecular weight PEO reduces conductivity, but low molecular weight PEO lacks mechanical strength.

NH3+

NH3+

NH3+

+H3N

Li+ Li+

Li+ Li+

O- O-

O-

O-

O-

O-

-O

-O

-O

Nanoparticle cores provide mechanical strength and low mobility anions.

PEO canopy stabilizes particles and makes them compatible with the PEO matrix

PEO matrix provides conducting framework for Li+ ions.

Corona-free NIMs in electrolytes: • The nanoparticle acts as an anion with extremely low mobility, minimizing the amount of accumulation at the anode. •Nanoparticles provide mechanical strength to a low molecular weight PEO matrix, avoiding the crystallization issue. • The corona-free approach makes these materials easy to produce in bulk.

Applications: Nanoparticle-PAG lubricants

Polyalkylene Glycols (PAGs) are finding new applications as biodegradable lubricants for high-load applications. • Polar medium stabilizes degradation products and prevents aggregates from forming.

• Biodegradability and non-toxicity reduces cleanup cost in the event of a spill. •PAG-based lubricants retain their lubricating properties in the presence of water. • High thermal stability makes PAG-based lubricants good for industrial applications.

(From http://www.dow.com/ucon/tech/816-00047.pdf)

Nanoparticle additives for lubricants have been shown to improve lubrication qualities. • They improve thermal stability and

reduce temperature-dependent viscosity fluctuations.

• They have been shown to reduce interfacial friction.

• Nanoparticles deposit on the wear track, reducing wear.

Nanoparticle Ionic Materials as additives: • The PEO canopy makes them easily dispersable in PAG-based

lubricants. • The canopy stabilizes the particles against aggregation. • Previous work has already shown that silica particles improve the

properties of poly-olefin based lubricants.

Acknowledgement

This work supported in part by Award No. KUS-C1-018-02 made by King Abdullah University of Science and Technology (KAUST).

Anode (e.g. LiCoO2)

Polymer electrolyte

Porous membrane

Cathode (e.g. Li metal)