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Large-scale self-assembled α-ZrP nanoplatelet/polymer layers with tunable gas permeability via a simple spray-coating process

Release Date
08 Apr, 2014
  • BL40B2 (Structural Biology II)

Kyushu University

Nanoparticles*4 are commonly used to modify the mechanical and physical properties of polymers for high-performance applications. One of the most significant challenges is to develop techniques to control the organization of nanoparticles*4 in the polymer, which is desired to optimize performance and address difficult applications, such as sensors, membranes, or photovoltaics. Most current methods to control nanostructure are based on complex techniques such as layer-by-layer or patterning approaches, which are highly energy intensive, limited in scale, and often have poor stability. An international team of researchers working at I2CNER, IMCE and Texas A&M University has developed an approach to functionalize the surface of nanoplatelets (a kind of flat and thin nanoparticle*4) with oligomers and demonstrated that the particles spontaneously organize to form a nano-wall structure. An extremely simple and efficient spray-coating method is used to create a coating on a surface, whereby the nano-walls self-assembled within the coating. The nano-walls act as rigid barriers that prevent oxygen gas from reaching the surface, and are effective at low and high humidity levels. Using this scalable and simple processing method, researchers have achieved extremely fine and highly ordered nano-scale features that are usually achieved with complex and energy intensive manufacturing techniques. This new technology is expected to be immediately useful in any application where blocking oxygen molecules is important, such as anti-corrosion paints for metal surfaces. The technique is simple and should be easily extended to other functional nanosheets.
This research is published in Nature Communications (DOI: 10.1038/ncomms4589).

<<Background information>>
The exceptional combination of mechanical and functional properties shown by natural materials, such as sea-shells, bone, and enamel, are due to multiple levels of structure (hierarchical structure*2) with extremely high degrees of order.  Nanoparticles may potentially be used as artificial building blocks to create complex, multi-level structures with unique properties that are not currently possible with synthetic materials.  There has been some success in achieving complex structures, but the methods are highly complex and energy intensive, and often very limited in scale and stability.  One potential approach to control structure in a more efficient way is to take advantage of nanoparticle shape.  For rod-like and plate-like nanoparticles, that shape can be conveniently summarized by the aspect ratio, which is the ratio of the largest and smallest dimensions of the particle.  Materials with large aspect ratio (including 1-dimensional nano-rods or nanotubes and 2-dimensional nanosheets) show a natural tendency to self-assemble into highly ordered phases.  In most cases, factors such as particle curvature, size distribution, and interactions between particles will disrupt the transition to a highly-ordered liquid crystalline*3 phase and result in disordered structures.  This limits the efficiency of the nanoparticles, and often significantly degrades the properties of the composite material.  If the particle structure and surface interactions can be sufficiently controlled, it is possible to create materials with multiple levels of organization.

Dr. Minhao Wong, a former graduate student at the Polymer Technology Center, Texas A&M University prepared coatings on polyimide*6 films where the nanoplatelets are aligned almost perfectly parallel to the polyimide*6 surface. Dr. Ryohei Ishige, formerly a research assistant professor working in Professor Atsushi Takahara’s group at I<sup>2</sup>CNER and IMCE, confirmed the smectic arrangement*7 of the nanoplatelets using the high intensity X-ray source at the Japan Synchrotron Radiation Research Institute SPring-8 facility located in Hyogo, Japan. The smectic arrangement*7 of nanoplatelets allows them to act like a wall to block oxygen gas. The most exciting aspect of this technology is that a spray-coating method can be used to create the highly ordered nano-wall structure. The nanoplatelets are dispersed in a solution filled with epoxy*1, which is then sprayed onto a surface that can be of any shape. A nano-wall coating forms naturally as the solution slowly evaporates. The coating is then heated up to cure or harden the epoxy*1. To understand this process, imagine a bricklayer who dumps a barrow of bricks and the bricks spontaneously build up into a wall on their own.  A similar process of “self-assembly” occurs to the nanoplatelets to create nano-walls that increase the barrier efficiency of the film by over twenty times.

<<Benefit or positive impact>>
The advantage of the spray-coating method is its simplicity. It is now possible to achieve very fine and highly ordered nanoscale features that are usually seen only through the use of photolithographic manufacturing techniques. This means that the same degree of order can be achieved without the need for expensive clean room facilities. All that is needed is a common spray-gun that can be bought at any local art store. This new technology is expected to be immediately useful in any application where blocking oxygen molecules are important, such as anti-corrosion paint for metal surfaces.

chematic representation of large-scale self-assembled

chematic representation of large-scale self-assembled α-ZrP nanoplatelet/polymer layers with tunable gas permeability prepared via a simple spray-coating process

<<Future plan>>
In the future, researchers hope to adjust the composition of the nanoplatelets to control the type of gas molecules that can pass through the nano-wall. This would allow for inexpensive, yet efficient, gas separation membranes that will be useful in many industrial processes. They are also interested in introducing new functionalities such as electrical conductivity or sensitivity to magnetic fields, so that large-area smart nano-walls can be fabricated. Many different kinds of nanoplatelets may potentially be used with this technology, so there are potentially countless possibilities for applications. In addition, incorporating different nanoplatelets to create hierarchical structures with improved properties is seen as another promising application for this technology.

1 Epoxy

A type of polymer that is often used in glues and adhesives.

2 Hierarchical structure
A structure that is composed of highly ordered arrangements of structural elements at different length scales.

3 Liquid crystal
A phase of matter that shows a degree of order intermediate between a crystal and a random structure.

4 Nanoparticle
A particle with at least one dimension in the range of 1 to 100 nanometers.

5 Photolithography
An advanced manufacturing technique used in the manufacturing of computer chips.

6 Polyimide
A kind of polymer often used in flexible electronic parts.

7 Smectic arrangement
A kind of liquid crystal phase where the nanoplatelets are lined up in layers in the same direction and the distance between each layer is constant.

For more information, please contact:
(About Research)
  Kyushu University
  International Institute for Carbon-Neutral Energy Research
  Division/ Name:Hydrogen Production/Atsushi Takahara
  Phone:+81-(0)92-802-2517 FAX:+81-(0)92-802-2518
    E-mail : mail1

(About I2CNER)
  Kyushu University
  International Institute for Carbon-Neutral Energy Research
  Administrative Office PR Group:Masumoto, Takada, Aitani
  Phone:+81-(0)92-802-6935 FAX:+81-(0)92-802-6939 

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