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RESEARCH

The research group is interested in understanding fundamental interactions in soft materials from the molecular level and relating them to the bulk state properties. The specialty of the group is to characterize the colloidal dispersions/microstructures in details with extensive scattering techniques and to relate them to dynamics at the interface and physical properties in bulk.

The current interests include dispersions of colloids and polymers in non-equilibrium states, interfacial properties of block copolymers and polymer nanocomposites, and dispersions of 2D colloids.

Polymer Nanocomposites

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While nanoparticles and polymers are widely used materials in industrial/daily products, it can exhibit unique properties when they are combined. Our research group is interested in understanding of particle-polymer interactions and controlling the structures to produce desired properties in complex nanoparticle-polymer composites. Upon the deep understanding of structural behavior of polymer composite materials, versatile thin film and novel 3-D nanostructures can be created; a special interest lies on block copolymer related composites.

Currently, the following topics are being investigated

  • Colloids and polymer mixtures in non-equilibrium state
  • Block copolymer related nanocomposites
  • Functionalized particle-polymer composites

Graphene Oxide as Two-Dimensional Colloid

Graphene oxide (GO) is often referred as a 2D colloid, which can be dispersed in water and form nematic liquid crystal (LC) phase. The good dispersity and the ability to form the LC phase enables the solution processing of GO; thus, GO LC has been actively employed in high-performance graphene-based fibers or films applications through solution processing. While GO LC exhibits extraordinary physical properties of high mechanical strength, tunable bandgap or good electrical/thermal conductivity, the performance of GO LC applications can be dependent on their colloidal properties in solution. In this regard, we systematically study the stable dispersion of GO in polymer solutions and examine how polymer influence the microstructure and rheological properties of GO suspension.

a. Graphene Oxide Liquid Crystallinity in Polymer Solutions

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b. The Correlation of Rheological Properties and Microstructure of GO using Rheo-SAXS

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c. polymer crystallization on Graphene Oxide surface

Graphene oxide (GO) can be employed as fillers in polymer-based applications. The liquid crystallinity (LC) of GO and good dispersity in polar solvent make GO more attractive than any other materials, expecting to improve the physical property of neat polymers. While GO can certainly retain their LC or alignments even in very dense polymer solutions, the degree of GO LC may compete with the possible polymer crystallization. We aim to correlate the GO LC with polymer crystallization to build a stronger structure-property relationship.

 

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Nanopatterning with Block Copolymers

Based on fundamental soft matter physics, we are interested in showing how soft materials can be employed in nanofabrication. More specifically, nanopatterning with block copolymers will be one of the promising applications. Since the characteristic size and spacing of block copolymer domains are on the order of 10- 100 nm, the range required by next-generation electronic and functional devices, nanopatterning with block copolymer thin films has emerged as a favorable technique. Furthermore, its distinct advantages in cost, fabrication and areal coverage are expected to overcome the shortcomings of conventional lithographic techniques.

Our focus was on

  • Film structure of Block copolymers in a confined space
  • Block Copolymer Interfacial Self-Assembly (ISA)
  • Multilayer structure with nanoparticles
  • Nano-contact printing system
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Surface and Interface

a. interfacial self-assembly

Amphiphilic block copolymers (BCPs) can self-assemble at air/water interfaces exhibiting interesting periodic structures. Using Langmuir-Blodgett method, these periodic structures can be finely tuned with a few nm resolutions and easily transferred to other substrates Our group is interested in employing these structures as a platform to build new nanostructures in thin films.

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b. drying in thin films

Many soft matter processings in film industry require a continuous process of coating and drying. While desired nanostructures expecting to convey a certain physical property need to keep their original structures, a rapid and dynamic drying/annealing process can deform the structures. We are interested in revealing how the drying process can deform the nanostructures of polymer nanocomposites in bulk and films.

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Colloids… and beyond

Based on an understanding on the relationship between polymer and particle interactions, we investigate how the microstructure of the colloidal system correlates to physical properties such as optical, mechanical, and electrical properties.

we are focused on

– dispersion stability of particles/polymers

– microstructure of dispersed particles/polymers

– rheological properties of polymer nanocomposites/suspension

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Going into Details for Micro- Nano- structures

We use small angle scatterings extensively to study the microstructure of soft matter systems listed above. Small angle x-ray scattering (SAXS), small angle neutron scattering (SANS), Grazing Incidence SAXS (GI-SAXS) and light scattering (LS) are good experimental tools to study particle interactions and polymer microstructures. We are also interested in seeing their physical properties; rheological properties are examined with conventional rheometer and Diffusing Wave Spectroscopy (DWS).

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