Text Box: Stoykovich Research Group:  Self-assembly and nanofabrication laboratory

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Molecular-level interactions in polymer flocculants

The separation and concentration of biomass from dilute cultures is often achieved at commercial scales through the use of an aggregating agent or flocculant.  Flocculation provides an attractive dewatering option for cellular suspensions, yet commercial flocculants may contaminate downstream processes and are expensive.  We have developed a novel approach for the dewatering and harvesting of microalgae using polymer flocculants that can be recovered and recycled.  Polyampholytes (polymers with both negative and positive charges) with pH-dependent charge character are used as a model flocculant system and provide reversible electrostatic interactions with negatively-charged cells.  The flocculants are recovered with >90% yields after biomass dewatering, can be recycled more than 5 times for flocculation, and are broadly applicable to a variety of cellular suspensions in biotechnological or pharmaceutical processes (for example, yeast or wastewater). 

Selected Publications: 

1.  Biotech. Bioeng., 2015, 112(1), 74-83 (PDF).




1.  JACS, 2013, 135, 6669-6676 (PDF).

Block copolymer self-assembly and directed self-assembly

Diblock copolymers (A-block-B or AB) spontaneously microphase separate and self-assemble into ordered lamellar, cylindrical, spherical, or network nanostructures with tunable dimensions from 5 to 50 nm.  Such self-assembling materials are attractive for nanofabrication because the nanostructures 1) are spontaneously assembled in dense, periodic arrangements with length scales below those accessible to conventional top-down fabrication processes, 2) have molecular-level control over the interfaces and surfaces, and 3) can be simultaneously generated over large areas.  Nanostructures of diblock copolymers in thin films have therefore attracted significant attention as a next generation lithographic technique, and have been demonstrated to be suitable masks for pattern transfer by etching or deposition and as templates for the synthesis of inorganic structures.  We are currently exploring:

Topology of two-dimensional block copolymer networks:  The lamellar morphology in thin films looks like a ’fingerprint’, as shown in the SEM image at the left.    The topology (i.e., connectivity and continuity) of the lamellar network is a function of the types of defects and defect density formed during self-assembly, and thus, as we have recently discovered, is a function of the composition of the copolymer system and the processing conditions.  Our current research considers how the topology of these two-dimensional networks in thin films impacts in-plane transport in devices fabricated with such patterns and the effects of structural confinement on the transport pathways. 

Selected Publications: 

1.  ACS Nano, 2015, in press (PDF).

2.  ACS Macro Letters, 2013, 2, 918-923 (PDF).

3. Macromolecules, 2012, 45(3), 1587-1594 (PDF).

Interfaces:  Polymer-polymer interfaces are often generated spontaneously through phase separation processes in copolymers or polymer blends, and dominate the structural, mechanical, optical, and transport properties of such systems.  These interfaces are relatively soft/flexible and therefore their shape is influenced by the interface bending rigidity, capillary waves, and thermal fluctuations.  We study the interfaces between lamellar block copolymer domains focusing upon their impact as line edge roughness (LER) in the resulting nanopatterns.

Selected Publications: 

1.  Macromolecules, 2010, 43, 2334-2342 (PDF).

3D structures through multilayer assembly:  We are developing systems for the ‘layer-by-layer’ self-assembly of block copolymers, where each ‘layer’ is 25~100 nm thick, to achieve nanostructured multilayer films.  The process involves initially self-assembling the block copolymer nanostructures in an individual layer and then locking-in the nanostructured morphology by cross-linking the polymer domains in response to thermal- or UV-stimuli to become more chemically, thermally, and mechanically robust.

Selected Publications: 

1.   Small, 2015, in press (PDF).

2.   Adv. Func. Mater., 2014, 24, 7078-7084 (PDF).


Nano- / micro-structured functional materials

Our group also works to fabricate, synthesize, and characterize novel materials structured from the nanoscale to the microscale.  The ability to structure materials across these scales often leads to  unique properties and functions.  Some examples of our research includes:

Biomimetic fishskin material:  Natural and man-made materials are often designed to perform the same functions, for example for structural support, robustness, protection, or being lightweight.  Nature is therefore a significant source of inspiration for new and alternative designs for engineered materials, even for cutting-edge technologies such as flexible/stretchable electronics.  Scaled skins in nature have remarkable mechanical properties including being compliant, resistant to penetration, and lightweight, all of which is achieved within an ultrathin membrane structure.  With collaborators in Mechanical Engineering (Prof. Franck Vernerey), we are investigating the mechanics in scales and scaled skins in order to design and microfabricate a new bio-inspired material that can serve as a deformable, damage resistant, and robust protective coating. 

Selected Publications:

1.  ACS Applied Materials & Interfaces, 2015, in press (PDF).

Nanocrystal synthesis:  We are also broadly interested in the chemical synthesis of inorganic nanocrystals in solution.  Of particular interest has been the synthesis of copper nanocrystals, and the optical and kinetic characterization of the rapid oxidation of these  Cu nanomaterials to

cuprous oxide(Cu2O).  We have also discovered a synthetic route based on seed-mediated growth to generate CdSe nanocrystals with unique shapes (e.g., cubes and platelets of wurtzite-CdSe).

Selected Publications: 

1.  JACS, 2013, 135, 6669-6676 (PDF).

2.  J. Physical Chemistry C, 2011, 115(5), 1793-1799 (PDF).

Materials characterization:  Characterization of the topography, shape, and crystal structure of materials at the nano– and micro-scales is important, but often can be a challenging task.  For much of our research, we use conventional tools like scanning electron microscopy, optical microscopy, and x-ray diffraction.  We also have worked to develop new characterization tools and approaches to study materials structured at these length scales.  One example is our work to use complex Fourier descriptors as a quantitative and high-throughput approach for automatically classifying the shape of colloidal nanocrystals.  Similarly, with collaborators at NIST, we have been advancing transmission electron backscatter detection (EBSD) by using Monte Carlo simulations of electron trajectories (image at left) through thin films.  Codes for these analyses were written in-house and are available upon request.

Selected Publications: 

1.  Journal of Microscopy, 2014, , (PDF).

2.  Crystal Growth & Design, 2012, 12(2), 825-831 (PDF).

National Science Foundation - Where Discoveries Begin

Materials for optical biosensing

Protein kinases are a critical family of enzymes involved in cell signaling pathways that regulate cell differentiation, growth, and death.  Poor kinase function has been implicated in cancer and other degenerative and inflammatory diseases, and although kinases are the second largest therapeutic drug target, there is a lack of robust, high-throughput techniques available for screening compounds that modulate kinase activity.  In collaboration with Prof. Joel Kaar, we are developing biosensors capable of quantifying kinase activity using a rapid and simple optical approach.  The biosensors developed here consist of hydrogel-encapsulated colloidal crystal arrays:  1) the hydrogels detect kinase activity and swell in response and 2) the colloidal crystal array displays this response as a visible color change.  The developed biosensors have shown potential for investigating other post-translational modifications such as dephosphorylation, sulfidation or acetylation, as well as for detecting the presence of specific DNA sequences or other biomolecules.

Selected Publications: 

1.  JACS, 2013, 135, 6669-6676 (PDF).

2.  Analytical Chemistry, 2015, in press (PDF).