Self-Assembly of Charged Nanoparticles by an Autocatalytic Reaction

Subscriber access provided by NEW YORK MED COLL

Article

Self-assembly of charged nanoparticles by an autocatalytic reaction front Biborka Bohner, Gabor Schuszter, Hideyuki Nakanishi, Dániel Zámbó, András Deák, Dezsö Horváth, Agota Toth, and Istvan Lagzi Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.5b03219 • Publication Date (Web): 19 Oct 2015 Downloaded from http://pubs.acs.org on October 26, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Self-assembly of charged nanoparticles by an autocatalytic reaction front Bíborka Bohner1a, Gábor Schuszter1a, Hideyuki Nakanishi2, Dániel Zámbó3, András Deák3, Dezső Horváth4, Ágota Tóth1, István Lagzi5* a

1

2

3

contributed equally to the work

Department of Physical Chemistry and Materials Science, University of Szeged, Szeged, Hungary

Department of Macromolecular Science and Engineering, Kyoto Institute of Technology, Kyoto, Japan

Institute for Technical Physics and Materials Science, Centre for Energy Research, Hungarian Academy of Sciences, Budapest, Hungary 4

5

Department of Applied and Environmental Chemistry, University of Szeged, Szeged, Hungary

Department of Physics, Budapest University of Technology and Economics, H-1111 Budapest, Budafoki út 8, Hungary

AUTHOR EMAIL ADDRESS: [email protected]

RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to)

TITLE RUNNING HEAD ACS Paragon Plus Environment

1

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 22

Self-assembly of charged nanoparticles

CORRESPONDING AUTHOR FOOTNOTE *Correspondence to: István Lagzi. Department of Physics, Budapest University of Technology and Economics, H-1111 Budapest, Budafoki út 8, Hungary. E-mail: [email protected], Tel.:+361-463-1341, Fax:+ 361-463-4180.

Abstract In this work we present that aggregation of charged and pH sensitive nanoparticles can be spatiotemporally controlled by an autonomous way using the chlorite–tetrathionate autocatalytic front, where the front regulates the electrostatic interaction between nanoparticles due to protonation of the capping – carboxylate-terminated – ligand. We found that the aggregation and sedimentation of nanoparticles in liquid phase with the effect of reversible binding of the autocatalyst (H+) play important roles in changing the front stability (mixing length) and the velocity of the front in both cases when the fronts propagate upwards and downwards. Calculation of interparticle interactions (electrostatic and van der Waals) with the measurement of front velocity revealed that the aggregation process occurs fast (within a few seconds) at the front position.

KEYWORDS self-assembly, nanoparticles, autocatalytic front, fronts, autocatalysis

INTRODUCTION Self-assembly of nanoparticles (NPs) into nanostructured materials has gained considerable interest in the past decades due to their unique optical, electrical and magnetic properties1-9 and their potential applications in material science, physics, chemistry and medicine.7,8,10-13 There are several powerful methods that control the assembly of NPs in the bulk.1,4,6 In the past few years successful realizations of ACS Paragon Plus Environment

2

Page 3 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

temporal control of reversible assembly and disassembly of nanoparticles and transformation of micelles and vesicles have been achieved and presented.14-18 The main idea is that an autonomous chemical subsystem operating at molecular level, namely a pH oscillator, can control the interaction between nanoscopic parts, and thus driving the self-assembly of building blocks. However, spatiotemporal control of the self-assembly of nanoscopic objects is challenging. It should be noted that the lightinduced spatiotemporal self-assembly of AgCl colloids with a typical size of 1µm due to selfdiffusiophoresis has been reported.19 Additionally, system containing Ag/AgCl particles can selfgenerate a front and it can interact with these particles.20 One of the examples of spatiotemporal patterns is the autocatalytic front, in which an autocatalytic reaction is coupled to the transport phenomena of involved reactants.21 In this case the front propagates with a finite velocity and the chemical front can be considered as a thin zone where the autocatalytic reaction takes place at considerable rate and spatially separates the reactants from the products. The chlorite–tetrathionate (CT) autocatalytic reaction22 is one of the model reactions which has been extensively studied in the last 20 years. This reaction provides a rich variety of spatiotemporal patterns in case of pure diffusion of the reagents (in gels23-25), in the presence of either convection26-29 (e.g., due to density difference in a liquid phase) or an electric field.30-31 In this reaction the hydrogen ion is the autocatalyst,32-33 and the net reaction in slight excess of chlorite can be written in a form 7ClO 2− + 2S4 O 62− + 6H 2 O → 7Cl − + 8SO 24 − + 12H + ,

(1)

and the empirical rate law for the reaction is second-order with respect to the autocatalyst hydrogen ion. This reaction has a complicated multi-step mechanism34 with supercatalytic characteristics because it is second order with respect to hydrogen ion in the empirical rate law in the early stages of the reaction, which determines the velocity of front propagation. Here we show a concept how an autonomous molecular-scale subsystem can couple to and control self-assembly of nanoscopic part. Namely, we present that an autocatalytic front propagating

ACS Paragon Plus Environment

3

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 22

with a finite velocity can spatially drive the aggregation of pH sensitive gold NPs in liquid phase. Aggregation of NPs can have a dramatic effect on the front characteristics depending on the orientation of the motion of the front relative to the horizontal plane (upwards and downwards) due to induced convection by the gravitational sedimentation of formed aggregated NPs clusters.

EXPERIMENTAL SECTION Reagent grade chemicals were used to prepare initial aqueous solutions of the CT reaction, which were mixed in a specific order: deionized water, tetramethylammonium hydroxide solution (Sigma Aldrich, liquid), either a pH sensitive dye solution or gold NPs solution, polymethacrylic acid solution (40%, Sigma Aldrich, liquid), potassium tetrathionate solution (Sigma Aldrich, solid) and sodium chlorite solution (80%, Sigma Aldrich, solid). Tetramethylammonium hydroxide was added to the system to adjust the pH to alkaline (pH = 10.50), thus preventing the mixture of reactants from self-initialization and ensuring the stability of NPs. Preparation of the high viscosity polymethacrylic acid solution was based on its mass. Potassium tetrathionate solution was stored in the refrigerator at 11 ºC; sodium chlorite solution was protected from light. To visualize the front propagation and investigate the characteristics of the front, we used negatively charged gold NPs (average metal core diameter 6.5 nm and standard deviations σ = 15%) stabilized with self-assembled monolayers of mercaptoundecanoic acid (AuMUA), and for the control experiments we used bromophenol blue dye solution (Reanal). These solutions change their color within the same pH range therefore, replacing them does not affect the determination of the pattern characteristics. The reactant solution with composition summarized in Table I was injected into a 13 × 15 × 0.05 cm Plexiglas Hele-Shaw (HS) cell with 6 mm thick walls that eliminates the heat effect caused by the reaction. Figure 1 shows the sketch of the experimental setup. The reaction area was 8 × 10 cm with a 0.05 cm wide spacer; and the cell was closed using an adhesive tape. The HS cell was positioned ACS Paragon Plus Environment

4

Page 5 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

vertically and reaction fronts – both upwards and downwards – were initiated electrochemically by applying a 3.0 V potential difference between two Pt wires (diameter of 0.25 mm) for 10 s in case of using the pH dye and for 30-60 s when the AuMUA solution was applied. Front propagation was monitored using a digital camera (Unibrain 1394), color images (1024 × 768 pixels) were captured in 15 s intervals with a computer controlled imaging system. LED light source was applied to enhance the brightness. The images were analyzed by in-house software. The density of the reactant and the product solutions were measured three times using an Anton Paar DMA 500 compact digital density meter with a 10−5 g/mL precision.

Tetramethylammonium Hydroxide Polymethacrylic Acid Potassium Tetrathionate Sodium Chlorite Bromophenol Blue dye OR AuMUA nanoparticles

2.5 mM 20 mM 5 mM 20 mM 0.08 mM 1.2 mM (in terms of gold atoms)

Table I. The initial composition of the CT solution.


5

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 22

Figure 1 The sketch of the experimental setup.

RESULTS AND DISCUSSION We investigated front propagation in two orientations, namely when the front moved downwards and upwards. After initialization of the CT reaction mixture in HS cell by generation of H+ ions electrochemically at the planar orientation, the autocatalytic process evolved in the vicinity of the platinum wire. The reaction in Equation 1 produces more H+ ions so that the pH changes locally from alkaline (pH ~ 10.5) to acidic (pH ~ 2). Hydrogen ions diffuse farther from the platinum wire due to their high concentration gradient, and initiate the autocatalytic reaction there as well. This process continues repeatedly and a planar 2D front evolves and propagates through the reactant solution. Shortly after initialization of the reaction front, not only diffusion can be responsible for the mass transport of the autocatalyst, but convection, induced by density difference between the reactant and product solution, can drive the pattern formation. The position of the front, defined as a point with the highest


6

Page 7 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

pH change, can be detected by a pH sensitive dye. The density of the liquid increases from 1.00073 ± 0.00006 g/mL to 1.00083 ± 0.00006 g/mL in the course of the reaction due to the change in composition, therefore, in thin solutions the upward propagating planar fronts creating horizontal interfaces perpendicular to the gravity field are hydrodynamically stable as illustrated in Fig. 2(a). It should be noted that even though the reaction is highly exothermic, the produced heat of reaction is efficiently dissipated in the environment because of the very thin solution layer. We repeated the experiments with the same initial conditions (Table I) but replacing the bromophenol blue dye by AuMUA NPs which resulted in a density change from 1.00093 ± 0.00006 g/mL to 1.00100 ± 0.00001 g/mL.

Figure 2 Upwardly propagating autocatalytic fronts with (a) bromophenol blue dye where the reactant solution on top is blue and (b) AuMUA NPs with red colors representing the upper reactant solution layer. ACS Paragon Plus Environment

7

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 22

The pH change of the medium has a profound effect on the AuMUA NP system as well, since the extent of surface grafted MUA dissociation depends on the pH as Γ=Γ0/(1+10pKa(MUA)−pH),14 where Γ0 is the surface coverage of the AuNPs (4.7 nm−2)35 and pKa(MUA) = 7.36 The surface charge density (σ) of the NPs is then obtained from the total charge on the NP divided by the outer surface of the ligand shell. The double layer repulsion can be then calculated as

U EDL ( D ) k BT

 a 2  −κ D =   Ze ,  2a 

where κ is the reciprocal Debye length, Z is the interaction constant, kB is the Boltzmann constant (1.38064×10−23 m2 kg s−2 K−1 ), T is the thermodynamic temperature, a is the radius of the particle and

D is the separation distance between the particles' surfaces. The interaction constant in the expression can be calculated as follows 2

 zeψ 0  k T  Z = 64πε 0ε  B  tanh 2  ,  e   4 k BT  where ε0 is the vacuum permittivity (8.854×10−12 F/m), ε is the relative permittivity for water (80.1 at 20 °C), z is the valence of ions, ψ0 is the surface potential of NP and e is the elementary charge, which is related to the surface charge density by

  2 k BT σ −1   sinh ψ0 = 1 ,  ze  ( 8 RT ε 0ε c∞ ) 2  with c∞ being the electrolyte concentration (set to 0.05 M in the specific case) and R is the Regnault constant. The van der Waals (vdW) attraction, however, is not affected by the pH and can be obtained from


8

Page 9 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

U vdW ( D ) k BT

 D 2 + 4aD   A  2a 2 2a 2   =− + + ln  1 −  ( 2a + D )2   , 6  D 2 + 4aD ( 2a + D )2   

where A is the Hamaker constant for AuMUA system (4.52×10−19 J).37 The radius of the NP was calculated as a sum of the gold core’s radius (4.85 nm) and the thickness of the MUA layer (1.60 nm). The stability of the NPs will hence depend on the sum of these interactions:38 U total ( D ) k BT

=

U EDL ( D ) U vdW ( D ) + . k BT k BT

The calculated net interaction energy curves are shown in Figure 3 for selected, characteristic pH values. It can be expected, that the gold NPs will undergo rapid, diffusion limited aggregation upon decreasing the pH of the solution form ~10.5 to ~2. Although the autocatalytic reaction leads to an increase of the ionic strength of the medium, this is accompanied by a quick pH decrease. Even assuming 100% conversion of the tetrathionate to sulphate (equaling to a salt concentration increase of 15 mM based on Eq. 1), the interaction energy curves are identical, hence the pH-dependent surface charge change of the NPs is the main factor determining the stability of the present system.

Figure 3 Calculated net interaction energy curves at different pH as a function of nanoparticle separation distance ‘D’.


9

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 22

In the initial reaction mixture the pH is ~ 10.5, at which MUA is fully (99.9%) deprotonated thus all head groups are negatively charged with zeta potential being ~ −45 mV. Charge-charge interparticle repulsion overcomes the attractive van der Waals interaction. Therefore, AuMUA NPs are disaggregated and the solution has characteristic red color owing to the localised surface plasmon resonance of spherical gold NPs, as shown in Fig. 2(b). In the wake of the front, the pH rapidly decreases and hence the ratio of deprotonation MUA molecules decreases. MUA is practically fully protonated at acidic pH (pH ~ 2) corresponding to the product solution. Therefore, the electrostatic repulsions between the NPs are weak, and the interparticle interactions are dominated by vdW attractions, thus the NPs aggregate and their color becomes bluish due to plasmon coupling. The front propagation manifests itself in a pronounced color change from red to blue, allowing the monitoring of front evolution visually, hence, Fig. 2(b) illustrates not only the propagation of an autocatalytic chemical front but also the front induced aggregation of NPs. In the opposite scenario, when chemical fronts propagate downwards, different pattern formation is observed: since the product solution has greater density, the propagating planar fronts are hydrodynamically unstable resulting in a cellular structure. Figure 4(a) shows the spatiotemporal pattern formation that has been studied and understood in the past years both experimentally26-28 and theoretically.39-44 These structures can be characterized by their wavelength (λ) and their amplitude or mixing length (Lm) defined as the standard deviation of the front position in the direction of front propagation. At glance, we can find that the wavelength increases in time while the change in the mixing length is not that obvious. When the dye is replaced by the gold NPs, the evolving structure (see Fig. 4(b)) is clearly different. The number of cells appears similar but the mixing lengths are distinctly larger. It is also undoubtedly seen that behind the front (regions where front passed) the aggregation is so intense that after several minutes millimeter-sized clusters are formed and those aggregates change the characteristics of the front due to the gravitational sedimentation of clusters.


10

Page 11 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 4 Downward propagating autocatalytic fronts with (a) bromophenol blue dye and (b) AuMUA NPs.

The characteristics of the front have also been determined for all four cases. The velocities for the upward propagating fronts correspond to those of reaction-diffusion fronts, however slower propagation (17.7 ± 0.6 µm/s) is observed with NPs compared to the system with bromophenol blue (28.6 ± 1.0 µm/s). This is a result of the larger hydrogen ion binding capacity of NPs (due to carboxyl end-group of MUA), which in effect represents a reversible removal of the autocatalyst, leading to slower propagation.23 Considering the stability of the planar front for the upward propagating case, the front geometry does not change significantly, hence the mixing length remains approximately the same for both cases as shown in Fig. 5, since with NPs the aggregated particles sediment downwards and do not interfere with the upward propagating front. In case of downward propagating fronts, the ACS Paragon Plus Environment

11

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 22

hydrodynamics due to density difference is the major driving force for the system with the bromophenol blue dye resulting in an increased velocity of propagation (33.1 ± 1.3 µm/s), while for the NPs the sedimentation of aggregates also plays a role leading to a somewhat larger increase in the front velocity to 21.0 ± 2.1 µm/s. Although, we have found that there is no difference between the wavelength of the cellular structures appearing initially (λ = 12 mm), NPs can significantly influence the instability of the front. This effect is also observed in Fig. 5 where the mixing lengths increase monotonically and differ increasingly from each other in time in case of dye and NPs. The strength of the hydrodynamic instability is proportional to the density difference of the solution of reactants and products at the front interface, which is 10−4 g/mL in the case of bromophenol blue and 7×10−5 g/mL in the case of NPs, respectively. Based on the measured data one could expect higher instability and higher mixing length in case of the dye. However, the actual trend is opposite, namely the mixing length of fronts with NPs is almost twice higher compared to that with dye after 30 min (Fig. 5). This can be explained by the intense aggregation dynamics due to the pH decrease behind the front because the aggregated particles sediment and increase the hydrodynamic instability of the front.


12

Page 13 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 5 Temporal evolution of the mixing length (the measure of instability) in reaction fronts moving upwards (red lines) and downwards (blue lines) containing NPs (solid lines) and bromophenol blue dye (dashed lines).

Another important aspect of the front dynamics is how fast pH changes at a given spatial location. Figure 6 depicts an averaged intensity profile measured perpendicularly to front propagation. This intensity is proportional to pH, so the characteristic time scale for pH change can be obtained from the calculated width of the front, which is ~ 150 µm, and knowing that the front propagation velocity is ~ 20 µm/s, we can get ~ 8 s. This means that within this time the front passes fully through a given location, ACS Paragon Plus Environment

13

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 22

and pH decreases from 10.5 to 2. Based on net interaction energy (Fig. 3), the NPs system becomes unstable and start to aggregate between pH 5 and pH 4, where the overall energy is a few kBT. In other words, the whole aggregation process occurs very fast at the front position.

Figure 6 Profile of the front along the direction of propagation corresponding to the middle picture of 2(a). Solid line corresponds to the fitting of a Gaussian with FWHM = 148 μm.

CONCLUSIONS In this study we have shown a concept for spatiotemporal control of aggregation of NPs. We successfully coupled an autonomously propagating autocatalytic front operating at molecular scales to a system of nanoscopic components by fine-tuning the electrostatic interaction between NPs utilizing the front property. We found that NPs due to their aggregation can dramatically change the front stability (mixing length) when the front propagated downwards, however, no effect was observed in upwardly propagating fronts. Aggregation process seemed not to affect the initial wavelength of the appeared ACS Paragon Plus Environment

14

Page 15 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

cellular pattern, but both the aggregation of NPs and reversible binding of the autocatalyst to the protecting ligand (MUA) affect and change the velocity of the fronts, when fronts moved downwards and upwards. The characteristics of a front, namely front velocity and its stability, depend on the initial concentration of the reagents, the size of the reaction domain, and temperature, which give us a simple and versatile way to drive and control the spatiotemporal assembly of nanoscopic objects.

ACKNOWLEDGMENT Authors acknowledge the financial support of the Hungarian Scientific Research Fund (OTKA K104666 and OTKA-PD-105173). A. D. acknowledges the support of the János Bolyai Research Fellowship from the Hungarian Academy of Sciences. Á. T. and D. H. thanks the support of TÁMOP 4.2.1/B09/1/KONV-2010-0005. H. N. and I. L. acknowledge support from the Project for Enhancing Research and Education in Polymer and Fiber Science at KIT and the National Research, Development and Innovation Office of Hungary (TÉT_12_JP-1-2014-0005).

The authors declare no competing financial interest.


15

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 22

FIGURE CAPTIONS Figure 1 The sketch of the experimental setup.

Figure 2 Upwardly propagating autocatalytic fronts with (a) bromophenol blue dye where the reactant solution on top is blue and (b) AuMUA NPs with red colors representing the upper reactant solution layer.

Figure 3 Calculated net interaction energy curves at different pH as a function of nanoparticle separation distance ‘D’.

Figure 4 Downward propagating autocatalytic fronts with (a) bromophenol blue dye and (b) AuMUA NPs.

Figure 5 Temporal evolution of the mixing length (the measure of instability) in reaction fronts moving upwards (red lines) and downwards (blue lines) containing NPs (solid lines) and bromophenol blue dye (dashed lines).

Figure 6 Profile of the front along the direction of propagation corresponding to the middle picture of 2(a). Solid line corresponds to the fitting of a Gaussian with FWHM = 148 μm.


16

Page 17 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

REFERENCES (1) Fendler, J. H. Self-Assembled Nanostructured Materials. Chem. Mater. 1996, 8, 1616–1624. (2) Mirkin, C. A.; Letsinger, R. L.; Mucic, R. C.; Storhoff, J. J. DNA-based Method for Rationally

Assembling Nanoparticles into Macroscopic Materials. Nature 1996, 382, 607–609. (3) Brinker, C. J.; Lu, Y.; Sellinger, A. Evaporation-Induced Self-Assembly: Nanostructures Made

Easy. Adv. Mater. 1999, 11, 579–585. (4) Lin, Y.; Böker, A.; He, J.; Sill, K.; Xiang, H.; Abetz, C.; Li, X.; Wang, J.; Emrick, T.; Long, S.;

Wang, Q.; Balazs, A.; Russell, T. P. Self-directed Self-assembly of Nanoparticle/Copolymer Mixtures. Nature 2005, 434, 55–59. (5) Grzelczak, M.; Vermant, J.; Furst, E. M.; Liz-Marzán. L. M., Directed Self-Assembly of

Nanoparticles. ACS Nano 2010, 4, 3591–3605. (6) Singh, G.; Chan, H.; Baskin, A.; Gelman, E.; Repnin, N.; Král, P.; Klajn, R. Self-Assembly of

Magnetite Nanocubes into Helical Superstructures. Science 2014, 345, 1149–1153. (7) Ray, P. C. Size and Shape Dependent Second Order Nonlinear Optical Properties of Nanomaterials

and Its Application in Biological and Chemical Sensing. Chem. Rev. 2010, 110, 5332–5365. (8) Nakanishi, H.; Bishop, K. J. M.; Kowalczyk, B.; Nitzan, A.; Weiss, E. A.; Tretiakov, K. V.;

Apodaca, M. M.; Klajn, R.; Stoddart, J. F.; Grzybowski, B. A. Photoconductance and Inverse Photoconductance in Films of Functionalized Metal Nanoparticles. Nature 2009, 460, 371–375. (9) Song, Q.; Zhang, Z. J. Shape Control and Associated Magnetic Properties of Spinel Cobalt Ferrite

Nanocrystals. J. Am. Chem. Soc. 2004, 126, 6164–6168. (10) Arico, A. S.; Bruce, P.; Scrosati, B.; Tarascon, J. M.; van Schalkwijk, W. Nanostructured Materials

for Advanced Energy Conversion and Storage Devices. Nat. Mater. 2005, 4, 366–377. (11) Jiang, P. Large-Scale Fabrication of Periodic Nanostructured Materials by Using Hexagonal Non-

Close-Packed Colloidal Crystals as Templates. Langmuir 2006, 22, 3955–3958. ACS Paragon Plus Environment

17

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 22

(12) Goldberg, M.; Langer, R.; Jia, X. Nanostructured Materials for Applications in Drug Delivery and

Tissue Engineering. J. Biomater. Sci. Polym. Ed. 2007, 18, 241–268. (13) Hu, X.; Li. G.; Yu, J. C. Design, Fabrication, and Modification of Nanostructured Semiconductor

Materials for Environmental and Energy Applications. Langmuir 2010, 26, 3031–3039. (14) Lagzi, I.; Kowalczyk, B.; Wang, D.; Grzybowski, B. A. Nanoparticle Oscillations and Fronts. Angew. Chem. Int. Ed. 2010, 49, 8616–8619. (15) Nabika, H.; Oikawa, T.; Iwasaki, K.; Murakoshi, K.; Unoura, K. Dynamics of Gold Nanoparticle

Assembly and Disassembly Induced by pH Oscillations. J. Phys. Chem. C 2012, 116, 6153–6158. (16) Nabika, H.; Inumata, Y.; Oikawa, T.; Unoura, K. Effect of Gold Nanoparticle Dispersion Solution

on the Oscillation Behavior of Nonlinear Chemical Reaction. Chem. Lett. 2012, 41, 1139–1141. (17) Nabika, H.; Inumata, T.; Kitahata, H.; Unoura, K. Effect of Gold Nanoparticles on Chemical

Oscillators: A Comparative Study of the Experimental and Simulated Results. Colloids Surf. A

2014, 460, 236–239. (18) Lagzi, I.; Wang, D.; Kowalczyk, B.; Grzybowski, B. A. Vesicle-to-Micelle Oscillations and Spatial

Patterns. Langmuir 2010, 26, 13770–13772. (19) Ibele, M. E.; Mallouk, T. E.; Sen, A. Schooling Behavior of Light-Powered Autonomous

Micromotors in Water. Angew. Chem. Int. Ed. 2009, 48, 3308–3312. (20) Ibele, M. E.; Lammert, P. E.; Crespi, V. H.; Sen, A. Emergent, Collective Oscillations of Self-

mobile Particles and Patterned Surfaces Under Redox Conditions. ACS Nano 2010, 4, 4845–4851. (21) Epstein, I. R.; Pojman, J. A. An Introduction to Nonlinear Chemical Dynamics: Oscillations,

Waves, Patterns, and Chaos, Oxford University Press: Oxford, 1998 (22) Szirovicza, L.; Nagypál, I.; Boga, E. An algorithm for the design of propagating acidity fronts. J. Am. Chem. Soc. 1989, 111, 2842–2845.


18

Page 19 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(23) Tóth, Á.; Lagzi, I.; Horváth, D. Pattern Formation in Reaction-Diffusion Systems: Cellular Acidity

Fronts. J. Phys. Chem. 1996, 100, 14837–14839. (24) Fuentes, M.; Kuperman, M. N.; De Kepper, P. Propagation and interaction of cellular fronts in a

closed system. J. Phys. Chem. A 2001, 105, 6769–6774. (25) Tóth-Szeles, E.; Tóth, Á., Horváth, D, Diffusive fingering in a precipitation reaction driven by

autocatalysis. Chem. Comm. 2014, 50, 4289–4291. (26) Horváth, D.; Bánsági, T.; Tóth, Á, Orientation-dependent density fingering in an acidity front. J. Chem. Phys. 2002, 117, 4399–4402. (27) Casado, G. G., Tofaletti, L., Müller, D., D'Onofrio, A. Rayleigh-Taylor instabilities in reaction-

diffusion systems inside Hele-Shaw cell modified by the action of temperature. J. Chem. Phys.

2007, 126, 114502. (28) Pópity-Tóth, É.; Horváth, D.; Tóth, Á. Horizontally Propagating Three-Dimensional Chemo-

Hydrodynamic Patterns in the Chlorite-Tetrathionate Reaction. Chaos, 2012, 22, 037105. (29) Almarcha, C.; Trevelyan, P. M. J.; Riolfo, L.; Zalts, A.; El Hasi, C.; D'Onofrio, A.; De Wit, A.

Active role of a color indicator in buoyancy-driven instabilities of chemical fronts. J. Phys. Chem. Lett., 2010, 1, 752–757. (30) Virányi, Zs.; Szommer, A.; Tóth, Á.; Horváth, D. Lateral Instability Controlled by Constant Electric

Field in an Acid-Catalyzed Reaction. Phys. Chem. Chem. Phys. 2004, 6, 3396–3401. (31) Virányi, Zs.; Horváth, D.; Tóth, Á. Migration-Driven Instability in the Chlorite-Tetrathionate

Reaction. J. Phys. Chem. A, 2006, 110, 3614–3618. (32) Nagypál, I.; Epstein, I. R., Fluctuations and Stirring Rate Effects in the Chlorite-Thiosulfate

Reaction. J. Phys. Chem. 1986, 90, 6285–6292.


19

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 22

(33) Horváth, A. K.; Nagypál, I.; Epstein, I. R., Three autocatalysts and Self-Inhibition in a Single

Reaction: A Detailed Mechanism of the Chlorite-Tetrathionate Reaction. Inorg. Chem. 2006, 45, 9877–9883. (34) Horváth, A. K.; Nagypál, I.; Peintler, G.; Epstein, I. R. Autocatalysis and Self-inhibition: Coupled

Kinetic Phenomena in the Chlorite Tetrathionate Reaction J. Am. Chem. Soc. 2004, 126, 6246– 6247. (35) Leff, D. V.; Ohara, P. C.; Heath, J. R.; Gelbart, W. M. Thermodynamic Control of Gold

Nanocrystal Size: Experiment and Theory. J. Phys. Chem. 1995, 99, 7036–7041. (36) Wang, D.; Nap, R. J.; Lagzi, I.; Kowalczyk, B.; Han, S.; Grzybowski, B. A.; Szleifer, I. How and

why nanoparticle's curvature regulates the apparent pKa of the coating ligands. J. Am. Chem. Soc.

2011, 133, 2192–2197. (37) Laaksonen, T.; Ahonen, P.; Johans, C.; Kontturi, K. Stability and Electrostatics of

Mercaptoundecanoic

Acid-Capped

Gold

Nanoparticles

with

Varying

Counterion

Size.

ChemPhysChem 2006, 7, 2143–2149. (38) Prasad, B. L.; Sorensen, C. M.; Klabunde, K. J. Gold Nanoparticle Superlattices. Chem. Soc. Rev.

2008, 37, 1871–1883. (39) Yang, J.; D'Onofrio, A.; Kalliadasis, S.; De Wit, A. Rayleigh-Taylor Instability of Reaction-

Diffusion Acidity Fronts. J. Chem. Phys. 2002, 117, 9395–9408. (40) Coroian, D. I.; Vasquez, D. A. The Effect of the Order of Autocatalysis for Reaction Fronts in

Vertical Slabs. J. Chem. Phys. 2003, 119, 3354–3359. (41) Vasquez, D. A.; De Wit, A. Dispersion Relations for the Convective Instability of an Acidity Front

in Hele-Shaw cells. J. Chem. Phys. 2004, 121, 935–941.


20

Page 21 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(42) D'Hernoncourt, J.; Merkin, J. H.; De Wit, A. Interaction Between Buoyancy and Diffusion-Driven

Instabilities of Propagating Autocatalytic Reaction Fronts. I. Linear Stability Analysis. J. Chem. Phys. 2009, 130, 114502. (43) D'Hernoncourt, J.; Merkin, J. H.; De Wit, A. Interaction between buoyancy and diffusion-driven

instabilities of propagating autocatalytic reaction fronts. II. Nonlinear simulations. J. Chem. Phys.

2009, 130, 114503. (44) Gérard, T.; De Wit, A. Stability of Exothermic Autocatalytic Fronts with Regard to Buoyancy-

Driven Instabilities in Presence of Heat Losses. Wave Motion 2011, 66, 814–823.


21

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 22

For Table of Contents Use Only

MS title: Self-assembly of charged nanoparticles by an autocatalytic reaction front Authors: Bíborka Bohner, Gábor Schuszter, Hideyuki Nakanishi, Dániel Zámbó, András Deák, Dezső Horváth, Ágota Tóth, István Lagzi


22

Self-Assembly of Charged Nanoparticles by an Autocatalytic Reaction

Recommend Documents