Single Molecule Study on PolymerâNanoparticle Interactions: The

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Single molecule study on polymer-nanoparticle interactions: the particle shape matters Zhandong Li, Bin Zhang, Yu Song, Yurui Xue, Lixin Wu, and Wenke Zhang Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b01698 • Publication Date (Web): 18 Jul 2017 Downloaded from http://pubs.acs.org on July 20, 2017

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Single molecule study on polymer-nanoparticle interactions: the particle shape matters Zhandong Li†, Bin Zhang†, Yu Song†, Yurui Xue†,‡, Lixin Wu†,* and Wenke Zhang†,* †

State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin

University, Changchun 130012, China. ‡

Institute of Chemistry, Chinese Academy of Science, Beijing, 100190, China.

E-mail: [email protected] or [email protected]

KEYWORDS: nanoparticle-polymer interactions, nanocomposite, SMFS, POM, particle shape, electrostatic interactions

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ABSTRACT: The study on the nanoparticle-polymer interactions is very important for the design/preparation of high performance polymer nanocomposite. Here we present a method to quantify the polymer-particle interaction at single molecule level by using AFM-based single molecule force spectroscopy (SMFS). As a proof-of-concept study, we choose Poly-L-Lysine (PLL) as the polymer and several different types of polyoxometalates (POM) as the model particles to construct several different polymer nanocomposites and to reveal the binding mode and quantify the binding strength in these systems. Our results reveal that the shape of the nanoparticle and the binding geometry in the composite have significantly influenced the binding strength of the PLL/POM complexes. Our dynamic force spectroscopy studies indicate that the disk-like geometry facilitate the unbinding of PLL/AlMo6 complexes in shearing mode, while the unzipping mode becomes dominate in spherical PLL-P8W48 system. We have also systematically investigated the effects of charge numbers, particle size and ionic strength on the binding strength and binding mode of PLL/POM, respectively. Our results show that electrostatic interactions dominate the stability of PLL/POM complexes. These findings provide a way for tuning the mechanical properties of polyelectrolyte-nanoparticle composites.

INTRODUCTION The studies on polymer nanocomposites have drawn great attention of a broad range of researchers due to their unique properties, such as optical,1,2 mechanical,3,4 electronic5,6 and antimicrobial properties.7 The compatibility (dispersion) of the nano-filler with (in) the polymer matrix turns to be essential for these enhanced properties.8,9 Polymer-particle interactions, however, dominate the compatibility of the nanocomposites.10,11 Therefore, it is of pretty importance to explore polymer-particle interaction and study the effects of particle property such as particle size, particle shape and charge numbers on the binding mode and


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binding strength of nanocomposite at molecular level. Such studies are critical for the design/preparation of high performance polymer nanocomposites. Theoretical simulations, such as atomistic and coarse-grained molecular simulations,12,13 have made significant progress in studying polymer-particle interactions. However, with the limitation of the computational environment required, these studies have been mostly restricted to the context of single and two-particle systems.14 Other methods, like atomic force microscopy (AFM) for studying modulus strength and the friction,15,16 FTIR for the characterization of polymers/nanoparticles interactions,17 even though are successful in probing average interactions. It is quite difficult to derive the binding mode and quantify the stability of polymer/particle complexes directly from those ensemble measurements. The investigation on polymer−particle interactions as well as the factors that can affect such interactions at the single molecule level will reveal the nature of the interaction, and eventually provide means for tuning the interactions and the rational design of high performance nanomaterials, such as the design of functional quantum dots for efficient biolabelling.18 AFM-based single molecule force spectroscopy (SMFS),19,20 as a rapidly developed practical technique, has been utilized to reveal many significant problems by the direct single-molecule level measurement of both specific/nonspecific and intra/intermolecular interactions.21-27 From the investigation on melting of double strand DNA,24, polysaccharides,30,31

28-29

conformation transition of

proteins unfolding mechanism32-34 to polymer interactions in their

condensed states (e.g., polymer crystals),35,36 thiol-gold interactions in self-assembled monolayer,37 AFM-based SMFS has helped us gain deep insights into the nature of these processes/interactions, which is difficult to realize by using traditional methods.


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In this study, Poly-L-Lysine/polyoxometalates (PLL/POMs) complex is chosen as a simplified model system for the study of polymer-particle interaction. An AFM-based method has been established for quantifying the interactions between a positively charged PLL and negatively charged POMs.38,39 The formation and disruption of the PLL/POMs complexes were monitored by repeatedly stretching and relaxation of a single PLL polymer chain in the presence of POMs. The effects of particle shape, particle size, charge density, and solvent quality on the PLL/POMs interactions have been investigated systematically. Experimental results show that the particle shape has greatly influenced the binding mode and strength between polymers and POM particles. Compared with particle shape/geometry, charge density and particle size are not crucial for the unbinding strength.

EXPERIMENTAL SECTION Chemicals and reagents. 3-Aminopropyldimethylmethoxysilane (APDMMS) was obtained from Fluorochem (UK). Poly-L-Lysine hydrobromide (Mw≥300,000 da), Oxalic acid, Nhydroxy-succinimide(NHS), 1-(3-Dimethylaminopropyl)-3-ethylcarbodi-imide hydrochloride (EDC) were purchased from Sigma-Aldrich. The PBS solution (pH 7.4) was prepared by dissolving one PBS tablet (Sigma) in 200 ml of deionized water and filtered. High-purity deionized water (dH2O＞18 MΩ cm) purified with a Millipore System was adopted to prepare all aqueous solutions in this work. Amino-silanization of Si substrate and AFM tips. Silicon wafer was first cut into small slides (10 × 10 mm) ，and followed by treating with freshly prepared piranha solution (H2SO4 (98 %)/H2O2(30 %) 7:3 in volume) for 30 minutes. After rinsing with high-purity deionized water, the slides were dried in an oven at 115 ℃ for 90 min to remove any remaining water.


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Then, the cleaned hydroxyl-group activated slides were put into a pre-dried desiccator filled with 3-aminopropyldimethylmethoxysilane vapor for 1 h at 20 ℃. After this vapor phase silanization ， the slides were rinsed thrice with methanol and subsequently placed in an oven at 110 ℃ for 10 min. The AFM tip (MSCT, Bruker Nano, Santa Barbara, CA), was treated in the same way to obtain the amino-group modified tip. NHS activation. Immediately before use, amino-terminated tip and substrate were activated by a mixture of EDC/NHS/oxalic acid in PBS (pH 7.4) solution, then washed with PBS solution. The NHS activated substrate and AFM tip are ready for the coupling of PLL molecule via the formation of amide bond. Synthesis

of

POMs.

Five

different

kinds

of

POM

particles

(Table

S1)

Na3(H2O)6[Al(OH)6Mo6O18] (AlMo6),40,41 (NH4)14[NaP5W30O110] (P5W30),42 H3[PW12O40] [PW12],43 (NH4)6[P2W18O62] (P2W18),44 and K28Li5[H7P8W48O184] (P8W48),45 were synthesized according to the published procedures.40-45 FTIR was employed to characterize these particles. The appearance of characteristic peaks indicate that these five particles have been successfully synthesized (more details can be found in Figure S5). Preparation of PLL/POM composites. Poly-L-Lysine was dissolved in water for at least 72 h to obtain its dilute solution (0.1 mg/ml). All the polyoxometalates were dissolved in water to obtain a solution of 10 mg/ml. To form PLL/POM complexes, 80 μl of the PLL solution was mixed with 20 μl POM solution in an Eppendorf tube on a vertex mixer for at least 30 s, to form a solution containing 0.08 mg/ml of PLL and excess amount of POM.


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SMFS experiments. Force spectroscopy experiments on both isolated single molecules and PLL/POM composite were carried out on a ForceRobot 300 (JPK Instrument AG, Berlin, Germany) in contact mode. Operating details for AFM-based SMFS has been described in previous wok.14,35 Spring constant of AFM tips (MSCT, Bruker Nano, Santa Barbara, CA) were calibrated by thermal noise method, and the measured values were between 0.02-0.03 N/m. The NHS activated Si was incubated with a drop of PLL or PLL-POM solutions, followed by rinsing thrice with PBS solution. PLL chain was coupled to the Si substrate via amide bond. During the pulling experiment, NHS-activated AFM tip was brought to contact with the PLL-modified substrate (at 1 nN for 3 s) to allow the formation of amide bond (or multipoint physical adsorption) between the AFM tip and PLL chain. The extending speed was set to 1 µm/s in all experiments except for the dynamic force spectroscopy experiment. The loading rate was obtained by multiplying the retract velocity by apparent elasticity of the molecular bridge, which was determined from the slope of the F-E curves on the last several data points before the dissociation events.46 Data analysis. All data analysis on AFM experiment was performed by using custom software written in Igor Pro (Wavemetrics). The histogram of length increment and rupture force of sawtooth pattern were fitted by Gaussian function to obtain the most probable value. XPS spectra were collected by using an electron spectrometer (ESCALAB 250) equipped with monochromatized Al Kα radiation source with pass energy of 30 eV. The binding energies were corrected by referencing the C (1 s) to 284.6 eV.


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Results and discussion Dissociation of AlMo6 particles from PLL. We used Poly-L-Lysine consisted of amide bond backbone and N-butyl amine side chains, as a probe to monitor polymer-particle interactions. PLL chain was covalently attached in between the Si substrate and AFM tip (Figure 1a) symmetrically by employing EDC/NHS chemistry (XPS characterization on surface chemistry of PLL immobilization is shown in Figure S1). Force spectroscopy mode of AFM was used to extend individual PLL chains in the absence or presence of POMs at constant speed.


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Figure 1. (a) Covalent attachment of Poly-L-Lysine to amino-functionalized surfaces. The preamino-silanized Si3N4 tip and Si substrate were activated by EDC/NHS chemistry. (b) Typical force-extension curves of individual PLL molecules with different contour lengths in water and superposition of the normalized F-E curves (inset). (c) Schematic of SMFS on PLL/AlMo6


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complexes. (d) Comparison of typical F-E curves of PLL obtained in the absence (line in black) and presence (line in red) of POM particles. There is a marked sawtooth pattern appeared in the presence of AlMo6 (inset, an enlarged view of the sawtooth pattern). (e), (f) Estimation of distance between adjacent sawtooth peaks in the stretching curves of PLL chain in the presence of AlMo6 particles. The solid red curve is the Gaussian fit on the distribution of length increment. The black traces in the inset are worm-like chain fits (with a persistence length of 0.37 nm). Inset, schematic of the length increment (∆L) during the rupturing of PLL/AlMo6 complexes. In the absence of POMs, the stretching curves obtained on PLL are smooth and the force increases monotonically with the extension before the rupture event, as shown in Figure 1b. These smooth force-extension (F-E) curves can be normalized and superimposed very well, which indicate that the elastic behavior of single polymer chain has been obtained.26 Quantitative analysis of the rupture force is shown in Figure S2, the most probable rupture force derived from the Gaussian fit is ~1.2 nN indicative of the strong attachment of PLL chain in between the AFM tip and substrate. The smooth curves also show that apart from the covalent attachment point there is no obvious interactions between PLL and the substrate. In the presence of AlMo6 nanoparticles, sawtooth pattern (see Figure 1d) can be observed in the low force region of F-E curves. According to literature, such sawtooth peaks may come from the rupture of multiple molecule with different length, the desorption of PLL chain from the substrate, or the disruption of PLL/AlMo6 complexes.26,47 Considering the fact that there is no obvious PLL-substrate interactions in the absence of POMs, such sawtooth pattern should not come from the desorption of PLL from the substrate. In addition, the good superposition of normalized F-E curve obtained on PLL at longer extension (normalized length > 0.8, as shown in


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Figure 1d) in the absence and presence of POMs indicate that the multiple molecule stretching can be excluded. The sawtooth patterns in the F-E curves thus come from the disruption of PLL/AlMo6 complexes. Considering the size of the nanoparticle and dimension of the polymer chain, PLL may bind to the nanoparticles and form multiple polymer loops on the particle surface or the PLL chain wraps around the nanoparticle forming the structure that is similar to histone/DNA complexes.48 To further identify the binding mode, we conduct statistical analysis on the length increment between adjacent sawtooth peaks. To do that we use worm like chain model21 to fit those sawtooth peaks (with a persistence length of 0.37 nm) and measure the contour length increment (∆L), as shown in Figure 1e, f. From this Figure we can derive the most probable length increment of 15 ± 4 nm by the Gaussian fitting of the histogram. Considering the fact that the particle size of AlMo6 is about 1 nm (in diameter), the 15-nm length increment is far more beyond the wrapping perimeter of PLL on POM, which implies that PLL chains attach to AlMo6 particles surface via multiple adsorption points, resulting in the formation of some polymer loops. To test the reversibility for the formation of the PLL-AlMo6 complexes, we manipulated the same PLL molecule in the presence of AlMo6 repeatedly. In such an experiment PLL molecule was stretched to break the binding sites within the PLL-AlMo6 complexes while avoiding detaching the molecule from either the AFM tip or the substrate (Figure S3). Then the molecule was relaxed to a position ~ 50 nm away from the surface (to further minimize the PLL-substrate interaction) and stayed there for 3 s to allow the reformation of complexes. The representative force-extension curves show that the PLL-AlMo6 complexes can reform during relaxation, since similar sawtooth patterns appeared in the subsequent stretching curves, as shown in Figure S3b.


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Effect of particle properties on the stability of PLL/POM complexes. To explore the effect of particle property on the stability of PLL/POM complex, we compared the force-extension curves of PLL in the presence of five different kinds of POM particles (Figure S4), AlMo6, P5W30, PW12, P2W18, and P8W48, respectively. These POM particles show different size, charge number, particle shape (more detailed properties are listed in Table S1). Unbinding force in the sawtooth patterns obtained on these POM systems were compared quantitatively. To make sure that the single molecule unbinding force is measured, only sawtooth peaks that are followed by a single rupture event at longer extension (Figure 2a) were used for statistical analysis. The charge number effect on the stability of PLL/POM was quantified by measuring the unbinding force in PLL/PW12, PLL/P2W18, PLL/P8W48, where the particles are of the same size and shape but with different charge numbers (i.e., 3, 6 and 33, respectively). The disruption of PLL/PW12, PLL/P2W18 and PLL/P8W48 complexes produced an unbinding force of 34 ± 5, 32 ± 7, and 34 ± 4 pN, respectively (Figure 2b). The barely changed force value for these three PLL/POM system indicate that the unbinding strength was not affected by the charge number of POM particles. This is reasonable since it was reported before that the desorption force of a positively charged polyelectrolyte string from a negatively charged substrate was determined by both the surface charge density and polymer line charge density.49,50 In our current system, the linear charge density of PLL chain remains unchanged and the total negatively charged surface sites on all the POM particles that bind to PLL chain are equal to the number of positive charges. As a result, the unbinding forces of these binding sites are almost the same.


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Figure 2. Charge number, particle size and shape effects on the stability of PLL/POM. (a) A typical F-E curve obtained on PLL/POM complexes. The sawtooth force peaks were used for statistical analysis. (b) Superposition of force distribution of the sawtooth peaks obtained on PLL/PW12 (yellow trace), PLL/P2W18 (blue trace), and PLL/P8W48 (black trace), respectively. (c) Comparison of force distribution of the sawtooth peaks for PLL/PW12 (yellow bar) and PLL/P5W30 (blue bar). (d) Comparison of force distribution of the sawtooth peaks for PLL/AlMo6 (green bar); PLL/PW12 (yellow bar). F = 81 ± 16 pN for AlMo6, F = 34 ± 5 pN for PLL/PW12, F = 34 ± 5 pN for PLL/P2W18, F = 32 ± 7 pN for PLL/P5W30 and F = 34 ± 4 pN for PLL/P8W48.

To explore the dominant factor for the stability of PLL-POM complexes, we also analyzed the particle-size effect on the unbinding force. PW12 and P5W30 have similar shape but different


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particle size of 1 nm and 2 nm, respectively. The most probable force to unbind PLL from P5W30 and PW12 were 32 ± 7 pN and 34 ± 5 pN, respectively (as shown in Figure 2c). It seems that there is no obvious particle size effect on the stability of PLL-POM complexes since the most probable force in these two system are quite similar. Furthermore, the shape effect on the binding strength was also investigated. PW12 and AlMo6 have the same charge numbers and similar particle size, but the force required to disassemble PLL chain from disk-like AlMo6 was markedly higher than that of spherical PW12 system. As shown in Figure 2d, the most probable force required to unbind PLL from AlMo6 (disk-like shape) was 81 ± 16 pN, while for PW12 the force was 34 ± 5 pN. According to our results, particle shape, rather than particle size or charge numbers dominates the mechanical stability of PLL-POM complexes. The issue of how disk-like particle can result in such great apparent mechanical strength is a question of critical importance to understanding the enhancement of a broader class of polymer nanocomposite materials. From previous studies we know that the force loading direction can affect a lot on the apparent mechanical stability of biological systems, such as protein and DNA.51 For example, in double strand DNA system, the unzipping force (force is loaded onto one base pair a time) is much smaller than that of shearing force (force is loaded onto all base pairs in parallel). The significantly high unbinding force for disk-like POM/PLL chain system may come from the shear force to unbind the polymer chain trapped in between two "disks” (Figure 3d). However, the lower force to unbind spherical POM particle from PLL chains could be mainly ascribed to the fact that the polymer chain on spherical particles can adjust the torsion angle into an unzipping geometry during stretching. To further prove this hypothesis, we investigate the unbinding process of PLL-POM complexes under different loading rate. To do that, the unbinding experiment were performed on


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PLL/AlMo6 (disk-like POM) and PLL/P8W48 (spherical POM) at different stretching velocities, which vary from 100 nm/s to 3000 nm/s. Statistical analysis have been performed on the unbinding force at each stretching speed. Figure 3a, b show the unbinding force distributions obtained on PLL/AlMo6 and PLL/P8W48 system at different speed (i.e., 0.1, 0.2, 0.5, 1, 2, and 3 µm/s), respectively. From Figure 3a and 3b, we can see that for PLL/AlMo6 system, the melting forces increase with the increase of stretching speed. While for PLL/P8W48 system the melting force remains almost unchanged at different stretching speed. We then carried out further analysis by plotting the unbinding force as a function of loading rate. The relationship between the most probable rupture force and the corresponding loading rate in a logarithmical scale is given in Figure 3c. The independence of unbinding force on the force loading rate for PLL/P8W48 system suggests that the unbinding process was performed under equilibrium condition. And the unbinding process corresponds to the unzipping of multiple PLL loops from the spherical nanoparticle surface, which is similar to previous findings in other systems.52-56 However, the unbinding force of PLL/AlMo6 complexes increase linearly with the increase of loading rate (as shown in Figure 3c), indicative of non-equilibrium unbinding process, supporting our hypothesis that disk-like AlMo6 may bind with PLL in a "sandwich" mode and the unbinding process is dominated by shearing mode (see Figure 3d). Our findings are useful for the rational design of high performance polymer nanocomposites.57 For example, by changing the shape of the nanoparticle, which has the same chemical composition, the apparent mechanical properties of the polymer nanocomposite can be tuned.


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Figure 3. Effect of stretching speed on unbinding forces of (a) PLL/AlMo6 and (b) PLL/P8W48 complexes, respectively. (c) Most probable unbinding forces are plotted logarithmically against the corresponding force loading rates. Each data set is subjected to a linear ﬁt (PLL/AlMo6, solid red line; PLL/P8W48, solid blue line). For P8W48 (spherical POM), the most probable rupture force are: 33 ± 3 pN at 0.1 µm/s, 33 ± 3 pN at 0.2 µm/s, 34 ± 4 pN at 1 µm/s, 33 ± 3 pN at 2 µm/s, 34 ± 4 pN at 3 µm/s. For AlMo6 (disk-like POM), the most probable rupture force are: 44 ± 9 pN at 0.1 µm/s, 56 ± 9 pN at 0.2 µm/s, 71 ± 15 pN at 0.5 µm/s, 81 ± 16 pN at 1 µm/s, 93 ± 10 pN at 2 µm/s, 97 ± 13 pN at 3 µm/s. (d) Possible unbinding mode for disk-like (shearing) and spherical (unzipping) POMs. For disk-like system, the PLL fragment may be trapped in between


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two disk-like particles, while for the spherical system the PLL chain can form multiple loops on the nanoparticle surface.

Effect of ionic strength on PLL–POM interactions. Considering the fact that PLL molecules have positive charges, while the POM particles shows negative charges at neutral pH, electrostatic interactions may thus play important roles on these PLL-POM interactions. We then investigated the effect of ionic strength on PLL/POM interaction by stretching the complexes in aqueous solutions with various concentrations of phosphate buffer saline (PBS). As can be seen from Figure 4a and 4b, the height of sawtooth peaks get decreased as the PBS concentration is increased from 10% to 100% in the typical F-E curves. Statistical analysis shows the most probable unbinding force of 73 ± 12, 45 ± 10, and 24 ± 9 pN for PLL-AlMo6 complex in 10%, 50% and 100% PBS solution, respectively (Figure 4c). Similar trend has been found also in PLL/PW12 system, where unbinding force of 26 ± 7 pN, 18 ± 6 pN and 10 ± 6 pN pN was obtained in 10%, 50% and 100% PBS solution, respectively, as shown in Figure 4d. These results show that PLL-POM interaction can be weakened by high ionic strength, which indicates that PLL binds to POM mainly via electrostatic interaction. The biopolymer-nanoparticle interactions can lead to some important biological process such as particle wrapping, biocatalysis, which might be related to biological toxicity or biocompatibility.58 Our finding may be helpful for regulating and controlling these processes. For example, charged toxic nanoparticles that adsorbed on the cell or tissue surface can be removed by washing with salty water.


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Figure 4. Effect of ionic strength on the mechanical stability of PLL/POM complexes. The SMFS experiment was performed in 10% PBS, I = 0.015; 50% PBS, I = 0.075; 100% PBS, I = 0.15, respectively. (a), (b) Typical F-E curve obtained on PLL/AlMo6 and PLL/PW12 complexes in 10% PBS, I = 0.015 (red trace); 50% PBS, I = 0.075 (blue trace); 100% PBS, I = 0.15 (black trace), respectively. (c), (d) Corresponding unbinding force distributions for PLL/AlMo6 and PLL/PW12 complexes in 10% (red trace), 50% (blue trace), and 100% (black trace) PBS. For PLL/AlMo6 system, the most probable rupture forces are 73 ± 12 pN（I=0.015), 45 ± 10 pN （I=0.075), and 24 ±9 pN（I=0.15), respectively. For PLL/PW12 system, the unbinding forces are 26 ± 7 pN（I=0.015), 18 ± 6 pN（I=0.075), and 10 ± 6 pN（I=0.15).


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Conclusions In conclusion, by using a long polymer chain (PLL) as a probe, a single molecule method based on AFM has been established for the study of polymer-nanoparticle interactions. Our results show that the particle shape has greatly influenced the apparent interactions between PLL and POMs particles. Disk-like particle-PLL complex exhibit a higher unbinding force, which can be ascribed to the multipoint shear unbinding mode during stretching. While for spherical nanoparticle, the unzipping mode can be dominated during the disruption of PLL/POM complex. Charge numbers show no obvious effect on the unbinding strength under our experimental condition. The ionic strength dependence of the unbinding force in PLL/POM systems indicates that electrostatic interaction is the major driving force for the stabilization of PLL/POM complexes. Our research provides a way for tuning the mechanical properties of polyelectrolytenanoparticle composites. Furthermore, the established single-molecule method can be used to study many other polymer-nanoparticle interactions. Supporting Information. Characterization on the covalent immobilization of PLL; statistical analysis on the rupture force of PLL bridge; binding-rebinding experiments of PLL-AlMo6 complexes; typical F-E curves of five PLL/POMs systems; properties of five POMs used in current research and other experimental details; FTIR characterization of POM particles. This material is available free of charge via the internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] or [email protected]


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Notes The authors declare no competing ﬁnancial interest.

Acknowledgements This work was funded by National Natural Science Foundation of China (21525418, 21474041, 91127031), the National Basic Research Program (2013CB834503), the Program for New Century Excellent Talents in University (NCET). References (1) Dung, M. X.; Choi, J.-K.; Jeong, H.-D. Newly Synthesized Silicon Quantum Dot–Polystyrene Nanocomposite Having Thermally Robust Positive Charge Trapping. ACS Appl. Mater. Interfaces 2013, 5, 2400-2409. (2) Farmer, S. C.; Patten, T. E. Photoluminescent Polymer/Quantum Dot Composite Nanoparticles. Chem. Mater. 2001, 13, 3920-3926. (3) Akcora, P.; Kumar, S. K.; Moll, J.; Lewis, S.; Schadler, L. S.; Li, Y.; Benicewicz, B. C.; Sandy, A.; Narayanan, S.; Ilavsky, J.; Thiyagarajan, P.; Colby, R. H.; Douglas, J. F. “Gel-like” Mechanical Reinforcement in Polymer Nanocomposite Melts. Macromolecules 2010, 43, 1003-1010. (4) Yang, J.; Han, C.-R.; Duan, J.-F.; Xu, F.; Sun, R.-C. Mechanical and Viscoelastic Properties of Cellulose Nanocrystals Reinforced Poly(ethylene glycol) Nanocomposite Hydrogels. ACS Appl. Mater. Interfaces 2013, 5, 3199-3207. (5) Maliakal, A.; Katz, H.; Cotts, P. M.; Subramoney, S.; Mirau, P. Inorganic Oxide Core, Polymer Shell Nanocomposite as a High K Gate Dielectric for Flexible Electronics Applications. J. Am.Chem. Soc. 2005, 127, 14655-14662. (6) Toor, A.; So, H.; Pisano, A. P. Improved Dielectric Properties of Polyvinylidene Fluoride Nanocomposite Embedded with Poly(vinylpyrrolidone)-Coated Gold Nanoparticles. ACS Appl. Mater. Interfaces 2017, 9, 6369-6375. (7) Bogdanović, U.; Vodnik, V.; Mitrić, M.; Dimitrijević, S.; Škapin, S. D.; Žunič, V.; Budimir, M.; Stoiljković, M. Nanomaterial with High Antimicrobial Efficacy—Copper/Polyaniline Nanocomposite. ACS Appl. Mater. Interfaces 2015, 7, 1955-1966. (8) Yang, Z.; Zhou, C.; Yang, H.; Cai, T.; Cai, J.; Li, H.; Zhou, D.; Chen, B.; Li, A.; Cheng, R. Improvement of the Compatibilization of High-Impact Polystyrene/Magnesium Hydroxide Composites with Partially Sulfonated Polystyrene as Macromolecular Compatibilizers. Ind. Eng. Chem. 2012, 51, 9204-9212. (9) Niu, Y.; Bai, Y.; Yu, K.; Wang, Y.; Xiang, F.; Wang, H. Effect of the Modifier Structure on the Performance of Barium Titanate/Poly(vinylidene fluoride) Nanocomposites for Energy Storage Applications. ACS Appl. Mater. Interfaces 2015, 7, 2416824176. (10) Martínez-Sanz, M.; Lopez-Rubio, A.; Lagaron, J. M. Optimization of the Dispersion of Unmodified Bacterial Cellulose Nanowhiskers into Polylactide via Melt Compounding to Significantly Enhance Barrier and Mechanical Properties. Biomacromolecules 2012, 13, 3887-3899. (11) Khare, K. S.; Khabaz, F.; Khare, R. Effect of Carbon Nanotube Functionalization on Mechanical and Thermal Properties of Cross-Linked Epoxy–Carbon Nanotube Nanocomposites: Role of Strengthening the Interfacial Interactions. ACS Appl. Mater. Interfaces 2014, 6, 6098-6110. (12) Komarov, P. V.; Mikhailov, I. V.; Chiu, Y. T.; Chen, S. M.; Khalatur, P. G. Molecular Dynamics Study of Interface Structure in Composites Comprising Surface-Modified SiO2 Nanoparticles and a Polyimide Matrix. Macromol. Theory Simul. 2013, 22, 187-197. (13) Meng, D.; Kumar, S. K.; D. Lane, J. M.; Grest, G. S. Effective interactions between grafted nanoparticles in a polymer matrix. Soft Matter 2012, 8, 5002-5010. (14) Ganesan, V.; Jayaraman, A. Theory and simulation studies of effective interactions, phase behavior and morphology in polymer nanocomposites. Soft Matter 2014, 10, 13-38. (15) Stankovich, S.; Dikin, D. A.; Dommett, G. H.; Kohlhaas, K. M.; Zimney, E. J.; Stach, E. A.; Piner, R. D.; Nguyen, S. T.; Ruoff, R. S. Graphene-based composite materials. Nature 2006, 442, 282-286. (16) Aurbach, D.; Koltypin, M.; Teller, H. In Situ AFM Imaging of Surface Phenomena on Composite Graphite Electrodes during Lithium Insertion. Langmuir 2002, 18, 9000-9009. (17) Wang, J.; Yang, J.; Wan, C.; Du, K.; Xie, J.; Xu, N. Sulfur Composite Cathode Materials for Rechargeable Lithium Batteries. Adv. Funct. Mater. 2003, 13, 487-492. (18) Selvan, S. T.; Patra, P. K.; Ang, C. Y.; Ying, J. Y. Synthesis of Silica-Coated Semiconductor and Magnetic Quantum


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