Rafal Klajn

Personal info:

hometown:
Czestochowa, Poland

degree:
M.Sc. in Chemistry, Warsaw University (summa cum laude)

awards:
2000 Research Science Institute, Cambridge, MA
2001 London International Youth Science Forum, London, U.K.
2003 Goldman Sachs Global Leaders Award, London, U.K.
2003 Undergraduate Research Program, CSHL, Cold Spring Harbor, NY
2006 NU Materials Research Science & Engineering Center Fellowship


Research areas:

Nanoscience. Organic chemistry.


Current research projects:

Light-controlled self-assembly (LISA) of nanoparticles

Light is a very attractive means to guide self-assembly of metal nanoparticles (NPs) because of several reasons: it can be delivered instantaneously, into a precise location, and using light of different wavelenghts might potentially lead to adaptive materials, which can build themselves and fall apart depending on light stimulus. Our approach to LISA is based on NPs decorated with ligands combining a photoresponsive azobenzene moiety with thiol groups at two ends. NPs are first covered with a desired amount of trans-azobenzene (these NPs are stable and do not aggregate in toluene when stabilized with surfactant), and then irradiated with UV light. UV induces molecular dipoles on the surface of NPs and as a result, the NPs start to "feel" each other and interact by attractive forces. Importantly, we can modulate the strength of these interactions by (1) adjusting the number of dipoles on NPs, and (2) dielectric contsant of the solvent. As a result, this light-initiated approach allows us to get a good control over superstructure (ad. 1) size and (ad. 2) morphology. (ad. 1). NPs to not interact below a critical number of azobenzenes per NP. Above threshold, a small number of nuclei form and superstructures grow big. Finally, increasing azobenzene surface coverage results in decreasing structure size. (ad. 2) In a hydrophobic solvent (pure toluene), the cis-azobenzene NPs "collapse" and spherical aggregates (supraspheres) form. When the dielectric constant of the solvent is increased (by the addition of methanol), the NPs crystallize into micron-size supracrystals. We found that at a low azobenzene surface coverages, the crystals that form are metastable and disassemble into free NPs once UV is turned off.

References: R. Klajn, K.J.M. Bishop, B.A. Grzybowski, Proc. Natl. Acad. Sci. U.S.A. 2007 , 104, 10305-10309.

 

 

 

 

 

 

 

 

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Novel nanomaterials derived from supraspheres.

Nanomaterials - structures assembled from nanosized building blocks - represent an interesting class of materials with novel optical, electrical and mechanical properties. A lot of effort has been devoted to sizing up nanomaterials to the macroscale - that is, to bridging the six orders of magnitude between the two scales. In our two-step approach to the problem, we first assemble nanocrystals (etc. Au, Ag, Pt, Pd) into well-defined, size-uniform spherical aggregates (supraspheres). These supraspheres have two important characteristics: (1) they are sticky with respect to one another (because their surface is partially covered with thiol groups), and (2) they readily undergo plastic deformation (because their nanocrystal components are connected by flexible alkyl chains). These molecular characteristics translate into a macroscale in a way that a macroscopic sample of supraspheres has mechanical properties of a plastic (and can be molded like clay or Play-doh), yet it displays some properties characteristic of a metal, such as color and moderate electrical conductivity. When molded into a desired structure, this "metal wax" can be turned into a robust piece of porous metal by gentle heating (5O oC), which desorbs organic coatings.

References: R. Klajn et al., Science 2007, 316, 261-264.

 

 

 

 

 

 

 

Publications:

  1. M. Makosza, J. Przyborowski, R. Klajn, A. Kwast, “Simple synthesis of 2-substituted tetra-hydrofuran-3-carbonitriles”, Synlett 2000, 12, 1773-1774.
  2. A. Michrowska, M. Bieniek, M. Kim, R. Klajn, K. Grela, “Cross-metathesis reaction of vinyl sulfones and sulfoxides”, Tetrahedron 2003, 59, 4525-4531.
  3. R. Klajn, M. Fialkowski, I.T. Bensemann, A. Bitner, C.J. Campbell, K. Bishop, S. Smoukov, B.A. Grzybowski, “Microcolour micropatterning of thin films of dry gels”, Nat. Mater. 2004, 3, 729-735.
  4. C.J. Campbell, M. Fialkowski, R. Klajn, I.T. Bensemann, B.A. Grzybowski, “Color micro- and nanopatterning with counter-propagating RD fronts”, Adv. Mater. 2004, 16, 1912-1917.
  5. D. Witt, R. Klajn, P. Barski, B.A. Grzybowski, “Applications, properties, and synthesis of omega-functionalized n-alkanethiols and disulfides – the building blocks of self-assembled monolayers”, Curr. Org. Chem. 2004, 8, 1763-1797.
  6. C.J. Campbell, R. Klajn, M. Fialkowski, B.A. Grzybowski, “One-step multilevel microfabrication by reaction-diffusion”, Langmuir 2005, 21, 418-423.
  7. S.K. Smoukov, C.J. Campbell, R. Klajn, K.J.M. Bishop, B.A. Grzybowski, “Surface microstructuring by wet stamping”, Adv. Mater. 2005, 17, 1361-1365.
  8. M. Fialkowski, K.J.M. Bishop, R. Klajn, S.K. Smoukov, C.J. Campbell, B.A. Grzybowski, "Principles and imprementations of dissipative (dynamic) self-assembly", J. Phys. Chem. B 2006, 110, 2482-2496.
  9. K.J.M. Bishop, R. Klajn, B.A. Grzybowski, “The core and the most useful molecules of organic chemistry”, Angew. Chem. Int. Ed. 2006, 45, 5348-5354.
  10. A.M. Kalsin, B. Kowalczyk, S.K. Smoukov, R. Klajn, B.A. Grzybowski, "Ionic-like behavior of oppositely charged nanoparticles", J. Am. Chem. Soc. 2006, 128, 15046-15047.
  11. M. Paszewski, S.K. Smoukov, R. Klajn, B.A. Grzybowski, “Multilevel surface nano- and microstructuring via sequential photoswelling of dichromated gelatin”, Langmuir 2007, 23, 5419-5422.
  12. R. Klajn, K.J.M. Bishop, M. Fialkowski, M. Paszewski, C.J. Campbell, T.P. Gray, B.A. Grzybowski, “Plastic and moldable metals by self-assembly of “sticky” nanoparticle aggregates”, Science 2007, 316, 261-264.
  13. R. Klajn, K.J.M. Bishop, B.A. Grzybowski, “Light-controlled self-assembly of reversible and irreversible nanoparticle suprastructures”, Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 10305-10309.
  14. R. Klajn, A.O. Pinchuk, G.C. Schatz, B.A. Grzybowski, “Synthesis of heterodimeric sphere-prism nanostructures via metastable gold supraspheres”, Angew. Chem. Int. Ed. 2007, accepted.
  15. R. Klajn, T.P. Gray, P.J. Wesson, S.K. Smoukov, B.A. Grzybowski, “Synthesis of nanoporous metal foams via self-assembly and thermal annealing”, Nat. Mater. 2007, submitted.

 

 

 

 

Heterodimeric nanostructures via a controlled decomposition of supraspheres

In a way similar to isomerization reactions, nanostructures undergo transformations in a one-to-one stoichiometry. This work demonstrates that supraspheres - spherical, internally disordered nanoparticle (NP) aggregates - thermally decompose into heterodimeric nanostructures comprising connected spherical and flat hexagonal domains (well, "decompose" may not be an accurate word as it implies disintegration, whereas here the process leads to much more complex structures). Further heating results in growth and transformation of the hexagons into triangles and dodecagons at the expense of the spherical NP aggregate. Remarkably, the supraspheres remain attached to the prisms at every stage of the process, until they finally vanish. By quenching the reaction at various time intervals, a continuum of heterodimers (analogous to molecular structures that appear along the reaction coordinate on the way to products) can be isolated. These results raise several interesting questions, e.g., how are the spherical and prismatic domains connected at the atomic level? How would a mixed suprasphere (composed of nanoparticles of two different metals) react? Are other (e.g., two-to-one, one-to-two) "reaction" stoichiometries possible?

R. Klajn, A.O. Pinchuk, G.C. Schatz, B.A. Grzybowski, Angew. Chem. Int. Ed. 2007, accepted.