Self-Assembling Nanocomposite Tectons

Article abstract of DOI:10.1021/jacs.6b11052

The physical characteristics of composite materials are dictated by both the chemical composition and spatial configuration of each constituent phase. A major challenge in nanoparticle-based composites is developing methods to precisely dictate particle positions at the nanometer length scale, as this would allow complete control over nanocomposite structure-property relationships. In this work, we present a new class of building blocks called nanocomposite tectons (NCTs), which consist of inorganic nanoparticles grafted with a dense layer of polymer chains that terminate in molecular recognition units capable of programmed supramolecular bonding. By tuning various design factors, including the particle size and polymer length, we can use the supramolecular interactions between NCTs to controllably alter their assembly behavior, enabling the formation of well-ordered body-centered cubic superlattices consisting of inorganic nanoparticles surrounded by polymer chains. NCTs therefore present a modular platform that enables the construction of composite materials where the composition and three-dimensional arrangement of different constituents within the composite can be independently controlled.

Full text of DOI:10.1021/jacs.6b11052

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Self-Assembling Nanocomposite Tectons
Jianyuan Zhang, Peter J Santos, Paul A. Gabrys, Sangho Lee, Caroline Liu, and Robert J. Macfarlane
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b11052 • Publication Date (Web): 07 Dec 2016
Downloaded from http://pubs.acs.org on December 9, 2016
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Jianyuan Zhang, Peter J. Santos, Paul A. Gabrys, Sangho Lee, Caroline Liu and Robert J.
Macfarlane*
Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts
Avenue, Cambridge, MA 02139
Supporting Information Placeholder
ABSTRACT: The physical characteristics of composite materials
are dictated by both the chemical composition and spatial
configuration of each constituent phase. A major challenge in
nanoparticle-based composites is developing methods to precisely
dictate particle positions at the nanometer length scale, as this
would allow for complete control over nanocomposite structure-
property relationships. In this work, we present a new class of
building blocks called nanocomposite tectons (NCTs), which
consist of inorganic nanoparticles grafted with a dense layer of
polymer chains that terminate in molecular recognition units
capable of programmed supramolecular bonding. By tuning
various design factors including particle size and polymer length,
Figure 1. Nanocomposite tectons (left) use supramolecular
we can use the supramolecular interactions between NCTs to
controllably alter their assembly behavior, enabling the formation
of well-ordered body centered cubic superlattices consisting of
inorganic nanoparticles surrounded by polymer chains. NCTs
therefore present a modular platform enabling the construction of
composite materials where the composition and three-dimensional
arrangement of different constituents within the composite can be
independently controlled.
binding interactions to form nanocomposite materials with spatial
control over particle placement in three dimensions.
either 1) focus on ensuring compatibility of the different phases
but lack hierarchical structural organization of all constituent
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components,
or 2) utilize directing agents or processing
conditions that are not amenable to functional composite
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architectures.
developing a class of nanocomposite “tectons”
irreducible nanocomposite building blocks that are themselves
Here, we circumvent these challenges by
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(NCTs, Fig. 1)
–
composite materials. An NCT consists of a nanoparticle grafted
with polymer chains that terminate in functional groups capable of
supramolecular binding, where supramolecular interactions
between polymers grafted to different particles enable
programmable bonding that drives particle assembly (Fig. 1).
Importantly, these interactions can be manipulated separately
from the structure of the organic or inorganic components of the
NCT, allowing for independent control over the chemical
composition and spatial organization of all phases in the
nanocomposite via a single design concept.
Nanocomposites are an important class of materials based on
integrating two or more disparate phases to achieve physical
characteristics that cannot be realized with a single-phase
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material. The properties of these composites are dictated by
their chemical compositions, as well as the relative three-
dimensional arrangements of each component. While structure
control in macroscopic composites can be easily achieved via
direct approaches like mechanical processing, top-down methods
to control nanoscale composite structure either provide limited
spatial resolution or are undesirably inefficient. Alternatively,
self-assembly can produce nanocomposite materials with well-
defined geometries in a parallelizable manner that is amenable to
scale-up. Indeed, many sophisticated nanoscale assembly
techniques have been developed to synthesize materials with
unique photonic, plasmonic, electronic, and mechanical
NCTs represent
a versatile class of building blocks for
nanocomposite synthesis, as the inorganic nanoparticle core
provides a basic scaffold that dictates the size and shape of the
NCT, while the polymeric ligands define its solubility, the
stiffness of its corona, and the interparticle distances in the final
structure; together, these two components also dictate the overall
chemical composition of the NCT. Conversely, the assembly
process, and thus the final mesoscale ordering of particles within
the composite, are dictated by the interactions between
supramolecular binding groups. Indeed, the unique aspect of the
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properties, making use of multiple types of nanoscale building
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blocks including polymers,
inorganic nanocrystals.
biological materials,
However, the major limitations of
current nanocomposite self-assembly techniques are that they
and
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B), the particles redispersed and the original color intensity was
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regained, demonstrating the dynamicity and complete reversibility
of the DAP-Thy directed assembly process. NCTs were taken
through multiple heating and cooling cycles without any alteration
to assembly behavior or optical properties, signifying that they
remained stable at each of these thermal conditions (Fig. 2C).
A key feature of NCTs is that the sizes of their particle and
polymer components can be easily modified independent of the
supramolecular binding group’s molecular structure. However,
because this assembly process is driven via the collective
interaction of multiple DAP and Thy-terminated polymer chains,
alterations that affect the absolute number and relative density of
DAP or Thy groups on the NCT surface impact the net
thermodynamic stability of the assemblies. In other words, while
all constructs should be thermally reversible, the temperature
range over which particle assembly and disassembly occurs
should be affected by these variables. To better understand how
differences in NCT composition impact the assembly process,
NCTs were synthesized using different nanoparticle core
diameters (10-40 nm) and polymer spacer molecular weights
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Figure 2. (A) Normalized UV-vis spectra of NCT dispersions in
toluene (20 nm AuNPs, 11.0 kDa DAP-PS or Thy-PS). (B) UV-
vis spectra of mixtures of complementary NCT dispersions. The
three traces represent the spectrum 2 minutes after mixing, 20
minutes after mixing, and after heating at 55 ˚C for ~1-2 min. (C)
Normalized extinction at 520 nm for a mixture of complementary
NCTs undergoing multiple heat-cool cycles between 20 and 55
(3.7–11.0 kDa), and allowed to fully assemble at room
temperature (~22 ˚C) (Fig. 3). Particles were then monitored
using UV-Vis spectroscopy at 520 nm while slowly heating at a
rate of 0.25 ˚C/min, resulting in a curve that clearly shows a
˚
C (lower and upper data points, respectively, see SI for details).
characteristic disassembly temperature (melting temperature, T
m
)
Insets: optical images of a representative NCT mixture at the
given temperatures.
for each NCT composition.
From these data, two clear trends can be observed. First, when
holding polymer molecular weight constant, Tm increases with
increasing particle size (Fig. 3A). Conversely, when keeping
particle diameter constant, Tm drastically decreases with
increasing polymer length (Fig. 3B). To understand these trends,
it is important to note that NCT dissociation is governed by a
collective and dynamic dissociation of multiple individual DAP-
Thy bonds, which reside at the periphery of the polymer-grafted
nanoparticles. The enthalpic component of NCT bonding behavior
is therefore predominantly governed by the local concentration of
the supramolecular bond-forming DAP and Thy groups, while the
entropic component is dictated by differences in polymer
configuration in the bound versus unbound states.
NCT architecture is the use of these molecularly-programmed
interactions to enable more sophisticated control over particle
assembly in the macroscopic composite than previous polymer-
grafted nanoparticle systems.
Here, we demonstrate the first example of an NCT by grafting
gold nanoparticles (AuNPs) with polystyrene (PS) chains that
terminate in molecular recognition units with complementary
hydrogen bonding motifs (diaminopyridine, DAP, and thymine,
Thy). Gold nanoparticles provide a sensitive spectral probe for
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particle assembly and are easily functionalized via gold-thiol
chemistry, while polystyrene can be synthesized with a wide
range of molecular weights and low dispersity using controlled
radical polymerization techniques such as atom transfer radical
All NCTs in this study possess similar polymer grafting densities
(i.e. equivalent areal density of polymer chains at the inorganic
nanoparticle surface, fig. S3) regardless of particle size or
polymer length. However, the areal density of DAP and Thy
groups at the periphery of the NCTs is not constant as a function
of these two variables due to NCT geometry. When increasing
inorganic particle diameter, the decreased surface curvature of the
larger particle core forces the polymer chains into a tighter
packing configuration, resulting in an increased areal density of
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polymerization (ATRP). Complementary hydrogen bonding
via the DAP and Thy units provides a simple means of controlling
particle interactions by modulating temperature, as hydrogen
bonds break upon addition of heat.
Functionalized PS polymers (DAP-PS and Thy-PS) were made
from DAP or Thy modified initiators via ATRP, followed by post-
functionalization to install a thiol group that allowed for particle
attachment (scheme S1). The polymers synthesized for the current
study had three different molecular weights (~3.7, ~6.0, and ~11.0
kDa, fig. S1) with narrow dispersity (Đ<1.10), and were grafted
to nanoparticles of different diameters (10, 15, 20, and 40 nm) via
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DAP and Thy groups at the NCT periphery; this increased
concentration of binding groups therefore results in an increased
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m
T , explaining the trend in Fig. 3A.
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a “grafting-to” approach modified from a previous report.
Once synthesized, NCTs functionalized with either DAP-PS or
Thy-PS were readily dispersed in common organic solvents such
as
tetrahydrofuran,
chloroform,
toluene,
and
N,N’-
dimethylformamide with a typical plasmonic resonance extinction
peak at 530-540 nm (Fig. 2A, fig. S2) that confirmed their
stability in these different solvents. Upon mixing, DAP-PS and
Thy-PS coated particles rapidly assembled and precipitated from
solution, resulting in noticeable red-shifting, diminishing, and
broadening of the extinction peak within 1-2 minutes (example
with 20 nm AuNPs and 11.0 kDa polymers, Fig. 2B). Within 20
minutes, the dispersion appeared nearly colorless, and large,
purple aggregates were visible at the bottom of the tube. After
moderate heating (~55 ˚C for ~1-2 minutes for the example in Fig.
Figure 3. Thermal study of complementary NCT mixtures with
A) constant polymer molecular weight (11.0 kDa) and varying
(
NP diameter; (B) constant particle diameter (10 nm) and varying
polymer molecular weights.
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Conversely, for a fixed inorganic particle diameter (and thus
particle spacings that would decrease the overall stability of the
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constant number of polymer chains per particle), increasing
polymer length decreases the areal density of DAP and Thy
groups at the NCT periphery due to the “splaying” of polymers as
assembled structure. However, the inherent flexibility of the
polymer chains should allow the NCTs to adopt a conformation
that compensates for these structural defects. As a result, an
ordered NCT arrangement would still be predicted to be stable if
it produced a larger number of DAP-Thy binding events than a
disordered structure and this increase in binding events
outweighed the entropic penalty of reduction in polymer chain
configurations.
m
they extend off of the particle surface, thereby decreasing T in a
manner consistent with the trend in Fig. 3B. Additionally,
increasing polymer length results in a greater decrease of system
entropy upon NCT assembly, due to the greater reduction of
polymer configurations once the polymer chains are linked via a
m
DAP-Thy bond; this would also be predicted to reduce T . While
To test this hypothesis, multiple sets of assembled NCTs were
thermally annealed at a temperature just below their T
m
, allowing
particles to reorganize via a series of binding and unbinding
events (experimental details in the SI) until they reached the
thermodynamically most stable conformation. The resulting
structures were analyzed with small angle X-ray scattering
a more quantitative study on the melting behavior of NCTs is
currently underway, we note that within the range tested, all
samples were easily assembled and disassembled via alterations in
temperature. Inorganic particle diameter and polymer length are
therefore both effective handles to control NCT assembly
behavior.
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SAXS), revealing the formation of highly ordered mesoscale
Importantly, because the NCT assembly process is based on
dynamic, reversible supramolecular binding, it should be possible
to drive the system to an ordered equilibrium state where the
maximum number of binding events can occur. We hypothesize
that, although the particle cores and polymer ligands are more
polydisperse (fig. S6, table S1) than the particles and small
molecule ligands used in prior studies to form nanoparticle
structures where the nanoparticles were arranged in body-centered
cubic (bcc) superlattices (Fig. 4, fig. S4). The bcc structure was
observed for multiple combinations of particle size and polymer
length (table S3), indicating that the nanoscopic structure of the
composites can be controlled as a function of either the organic
component (via polymer length), the inorganic component (via
particle size), or both, making this NCT scheme a highly
tailorable method for the design of future nanocomposites.
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superlattices,
ordered arrangements still represent the
thermodynamically favored state for a set of assembled NCTs. It
is true that, when packing NCTs into an ordered lattice, deviations
in particle diameter would be expected to generate inconsistent
In conclusion, we have demonstrated the versatility and
programmability of NCTs as controllable nanocomposite building
blocks. The data presented here provide the first example of this
concept, and we predict that these NCTs should be amenable to
multiple different particle core and polymer ligand formulations,
as well as different supramolecular binding motifs. Together,
these design handles allow for nanocomposite structure control at
a level that is unrivaled by previous composite synthesis
techniques. Future investigations will both explore the
fundamental processes involved in NCT assembly, as well as
develop synthesis schemes for making solid and free-standing
architectures from NCT building blocks. These structures are
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predicted to possess unique optical, mechanical, chemical,
5
and electrical phenomena that will make them highly desirable in
multiple potential applications.
ASSOCIATED CONTENT
Supporting Information
Detailed experimental procedure, characterization of the
polystyrene ligands, TGA data of the NCTs, and representative
TEM images of the dried superlattice samples. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
Robert J. Macfarlane rmacfarl@mit.edu
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This work was supported by the following awards: AFOSR
FA9550-11-1-0275. This work made use of the MRSEC Shared
Experimental Facilities at MIT, supported by the National Science
Foundation under award number DMR-1419807. P.J.S.
acknowledges support by the National Science Foundation
Graduate Research Fellowship Program under Grant No.
Figure 4. SAXS data showing NCT assembly into ordered bcc
superlattices: (green trace) 20 nm AuNPs and 11.0 kDa PS; (blue
trace) 10 nm AuNPs and 11.0 kDa PS; (red trace) 10 nm AuNPs
and 6.0 kDa PS; (black traces) predicted SAXS patterns for
corresponding perfect bcc lattices. Insets show the unit cell for
each lattice drawn to scale.
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122374. S.L. acknowledges support from a scholarship from the
(19) Heo, K.; Miesch, C.; Emrick, T.; Hayward, R. C. Nano Lett. 2013,
3, 5297.
20) Hashemi, A.; Jouault, N.; Williams, G. A.; Zhao, D.; Cheng, K. J.;
Kysar, J. W.; Guan, Z. B.; Kumart, S. K. Nano Lett. 2015, 15, 5465.
21) Williams, G. A.; Ishige, R.; Cromwell, O. R.; Chung, J.; Takahara,
A.; Guan, Z. B. Adv. Mater. 2015, 27, 3934
22) Macfarlane, R. J.; Lee, B.; Jones, M. R.; Harris, N.; Schatz, G. C.;
Mirkin, C. A. Science 2011, 334, 204.
23) Macfarlane, R. J.; O'Brien, M. N.; Petrosko, S. H.; Mirkin, C. A.
Angew. Chem. Int. Ed. 2013, 52, 5688.
1
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5
5
5
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5
6
Kwanjeong Education Foundation under the award No.
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REFERENCES
(
(1) Balazs, A. C.; Emrick, T.; Russell, T. P. Science 2006, 314, 1107.
(
2
(
2) Kumar, S. K.; Jouault, N.; Benicewicz, B.; Neely, T. Macromolecules
013, 46, 3199.
3) Kango, S.; Kalia, S.; Celli, A.; Njuguna, J.; Habibi, Y.; Kumar, R.
(
(24) Ye, X.; Zhu, C.; Ercius, P.; Raja, S. N.; He, B.; Jones, M. R.;
Hauwiller, M. R.; Liu, Y.; Xu, T.; Alivisatos, A. P. Nature Commun.
Prog. Polym. Sci. 2013, 38, 1232.
(4) Kim, C. R.; Uemura, T.; Kitagawa, S. Chem. Soc. Rev. 2016, 45, 3828.
2
015, 6, 10052.
(5) Talapin, D. V.; Lee, J.-S.; Kovalenko, M. V.; Shevchenko, E. V.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(25) Wang X.; Simard M.; Wuest J. D.; J. Am. Chem. Soc. 1994, 116,
Chem. Rev. 2010, 110, 389.
12119.
(6) Rybtchinski, B. ACS Nano 2011, 5, 6791.
(26) Hosseini, M. W. Acc. Chem. Res. 2005, 38, 313.
(7) Boles, M. A.; Engel, M.; Talapin, D. V. Chem. Rev. 2016, 116, 11220.
(
27) Storhoff, J. J.; Lazarides, A. A.; Mucic, R. C.; Mirkin, C. A.;
Letsinger, R. L.; Schatz, G. C. J. Am. Chem. Soc. 2000, 122, 4640.
28) Matyjaszewski, K. Macromolecules, 2012, 45, 4015.
(29) Bertrand, A.; Lortie, F.; Bernard, J. Macromol. Rapid Commun. 2012,
3, 2062.
30) Goulet, P. J. G.; Bourret, G. R.; Lennox, R. B. Langmuir 2012, 28,
909.
31) Jones, M. R.; Macfarlane, R. M.; Lee B.; Zhang, J.; Young, K. L.;
Senesi, A. J,; Mirkin C. A. Nat. Mater. 2010, 9, 913.
32) Macfarlane, R. J.; Jones, M. R.; Senesi, A. J.; Young, K. L,; Lee, B.;
Wu, J.; Mirkin, C. A. Angew. Chem. Int. Ed. 2010, 122, 4693.
33) Li, T. I. N. G.; Sknepnek, R.; Macfarlane, R. J.; Mirkin C. A.; Olvera
(8) Ghosh, S.; Maiyalagan, T.; Basu, R. N. Nanoscale 2016, 8, 6921.
9) Tang, C. B.; Lennon, E. M.; Fredrickson, G. H.; Kramer, E. J.;
Hawker, C. J. Science 2008, 322, 429.
10) Bates, C. M.; Seshimo, T.; Maher, M. J.; Durand, W. J.; Cushen, J.
D.; Dean, L. M.; Blachut, G.; Ellison, C. J.; Willson, C. G. Science 2012,
38, 775.
11) Sing, C. E.; Zwanikken J. W.; Olvera de la Cruz, M.; Nat. Mater.
014, 13, 694.
12) Adler-Abramovich, L.; Gazit, E. Chem. Soc. Rev. 2014, 43, 6881.
(13) Jones, M. R.; Seeman, N. C.; Mirkin, C. A. Science 2015, 347.
14) Shevchenko, E. V.; Talapin, D. V.; Kotov, N. A.; O'Brien, S.;
Murray, C. B. Nature 2006, 439, 55.
15) Talapin, D. V.; Nelson, J. H.; Shevchenko, E. V.; Aloni, S.; Sadtler,
(
(
(
3
(
2
(
3
(
2
(
(
(
(
de la Cruz, M.; J. Am. Chem. Soc. 2013, 135, 8535.
(34) Beaulieu, M. R.; Hendricks, N. R.; Watkins, J. J. ACS Photon. 2014,
(
B.; Alivisatos, A. P. Nano Lett. 2007, 7, 2951.
(16) Yan, W.; Xu, L.; Xu, C.; Ma, W.; Kuang, H.; Wang, L.; Kotov, N. A.
J. Am. Chem. Soc. 2012, 134, 15114.
1
, 799.
(35) Crosby, A. J.; Lee, J. Y. Polym. Rev. 2007, 47, 217.
(36) Hui, C. M.; Pietrasik, J.; Schmitt, M.; Mahoney, C.; Choi, J.;
(17) Paik, T.; Diroll, B. T.; Kagan, C. R.; Murray, C. B. J. Am. Chem. Soc.
Bockstaller, M. R.; Matyjaszewski, K. Chem. Mat. 2014, 26, 745.
2
015, 137, 6662.
(18) Zhao, Y.; Thorkelsson, K.; Mastroianni, A. J.; Schilling, T.; Luther, J.
M.; Rancatore, B. J.; Matsunaga, K.; Jinnai, H.; Wu, Y.; Poulsen, D.;
Frechet, J. M. J.; Alivisatos, A. P.; Xu, T. Nat. Mater. 2009, 8, 979.
Table of Contents Figure:
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