Surfactant Behavior of Amphiphilic Polymer-Tethered Nanoparticles

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Surfactant Behaviors of Amphiphilic Polymer-Tethered Nanoparticles Yue Zhang, and Hanying Zhao Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b00267 • Publication Date (Web): 28 Mar 2016 Downloaded from http://pubs.acs.org on April 4, 2016

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Surfactant Behaviors of Amphiphilic PolymerTethered Nanoparticles Yue Zhang1, and Hanying Zhao1,2* 1

Key Laboratory of Functional Polymer Materials, Ministry of Education, College of Chemistry,

Nankai University, Tianjin 300071, China 2

Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin

300071, China

ABSTRACT: In these years, an emerging research area is the surfactant behaviors of polymertethered nanoparticles. In this feature article, we have provided a general introduction to the synthesis, self-assembly and interfacial activity of polymer-tethered inorganic nanoparticles, polymer-tethered organic nanoparticles and polymer-tethered natural nanoparticles. In addition, applications of the polymer-tethered nanoparticles in colloidal and materials science are briefly reviewed. All the researches demonstrate that amphiphilic polymer-tethered nanoparticles present surfactant behaviors, and can be used as elemental building blocks for the fabrication of advanced structures by self-assembly approach. The polymer-tethered nanoparticles provide new

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opportunities to engineer materials and biomaterials possessing specific functionality and physical properties.

Introduction A surfactant is a substance that has the property of adsorbing onto the surfaces or interfaces of a system and of changing the surface or interfacial free energies significantly.1 Usually, a surfactant molecule is composed of a polar head that is compatible with aqueous phase and a hydrophobic tail that is compatible with oil phase. The amphiphilic surfactant molecules present unique solution and interfacial characteristics, among which the surface or interfacial properties and the self-assembly behaviors are the two most noteworthies. Surfactant molecules at oil-water interface make an arrangement with the polar heads in water phase and the hydrophobic species dissolved in oil phase, and thus the interfacial tension is decreased. In aqueous solutions above critical micelle concentrations (CMCs), the surfactant molecules self-assemble into aggregates with various morphologies, including spherical micelles, rodlike micelles and bilayer vesicles (Scheme 1a).2-4 Understanding the solution properties and self-assembly behaviors of surfactants enables us to develop their new practical applications in industry and academic science. Amphiphilic polymers including block copolymers, graft copolymers and random copolymers, also present surfactant behaviors in aqueous solutions. With the rapid development of controlled/living radical polymerizations (CRP), amphiphilic polymers with well-defined structures and precisely controlled molecular weights, have been synthesized.5,6 In comparison with small molecular surfactants the amphiphilic polymers are able to reduce interfacial or


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surficial tension with lower CMC and diffusion coefficient, which make them more efficient surfactants. The surfactant behaviors of the amphiphilic polymers are not only affected by the chemical components but also by the topological structures.7 Like small molecular surfactants, amphiphilic copolymers can make spontaneous arrangements into micelles of various morphologies in aqueous solutions, such as spheres,8 vesicles,9 bowls,10 and discs (Scheme 1).11 Comparing with the aggregates of small molecular surfactants, the self-assemblies of amphiphilic polymers possess larger sizes, tunable stimuli-responsiveness and robust structures. Replacing the hydrophilic or hydrophobic part of an amphiphilic polymer chain with a hydrophobic or hydrophilic nanoparticle offers us amphiphilic polymer-tethered nanoparticles. The introduction of nanoparticles to polymer chains not only endows the hybrid particles combined properties of polymers and nanoparticles but also creates a type of new surfactants. The amphiphilic polymer-tethered nanoparticles, which are composed of hydrophobic (or hydrophilic) polymer chains and hydrophilic (or hydrophobic) nanoparticles, can be used as surfactants to reduce the oil-water interfacial tension, and as building blocks for the fabrication of advanced structures by self-assembly approach. Nanoparticles possess many distinctive properties, which enable the self-assembled structures with additional practical functions. For example, gold nanoparticles can be used for surface enhanced Raman scattering applications,12 Fe3O4 nanoparticles find applications in magnetic resonance imaging13 and proteins as natural nanoparticles have multiple functions involving catalysis, immunity and recognition.14 There are researches on amphiphilic polymer-conjugated particles where hydrophilic and hydrophobic components are both polymers, while nanoparticles are only used as units. The self-assembly properties of the hybrid nanoparticles are mainly determined by the polymer chains.15 What we discuss in this paper are the amphiphiles, where the nanoparticles are the only hydrophilic


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components (Scheme 1c) and the polymers are hydrophobic. The nanoparticles play key roles in the interfacial activities and the self-assembly of the amphiphiles. Based on the type of nanoparticles, the hybrid amphiphiles are catalogued into polymer-tethered inorganic nanoparticles, polymer-tethered orgainc nanoparticles and polymer-tethered natural nanoparticles. In our researches, we are interested in the interfacial activities and the self-assembled structures of the amphiphilic polymer-tethered nanoparticles.

Scheme 1. Surfactant behaviors of small molecular surfactants, amphiphilic polymers and amphiphilic polymer-tethered nanoparticles.


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Polymer-tethered inorganic nanoparticles A variety of inorganic nanoparticles were employed to prepare polymer-tethered amphiphiles, among which polyoxometalate and polyhedral oligomeric silsesquioxanes (POSS) were ideal model particles for the synthesis of polymer-tethered nanoparticles due to the well-defined structures. Cheng and coworkers synthesized polymer-tethered POSS16-18 and they found that driven by chemical incompatibility and geometric incommensurateness, the hybrid amphiphiles are able to self-assemble into ordered structures. The self-assembled morphology can be tuned from vesicles, to wormlike cylinders, and to spherical micelles. They called the amphiphiles “giant surfactants”.19 Polymer-tethered gold nanoparticles (AuNPs) also present surfactant behaviors and are able to self-assemble into ordered structures. Duan and coworkers prepared plasmonic vesicles assembled from amphiphilic AuNPs with mixed polymer brush coatings and they used the hybrid vesicles for cancer cell targeting and traceable intracellular drug delivery.20,21 Nie and coworkers fabricated vesicles and tubular nanostructures by self-assembly of AuNPs tethered with amphiphilic linear block copolymer chains.22 The self-assembly processes of the above polymer-modified AuNPs are driven by the conformation change of the polymer chains on the AuNPs. In our group, we are interested in the role of hydrophilicity of AuNPs in the self-assembly process. In an approach, polystyrene (PS) chains with known number of pendant AuNPs (PS-g-AuNPs) were synthesized by free-radical polymerization.23 As shown in Figure 1a, 11-mercaptoundecyl methacrylate monomer was grafted to the citratecapped AuNPs via ligand exchange, and AuNPs monomer with mono-vinyl groups were obtained. In an emulsion, the AuNP monomers located at the interface between toluene and water. The free-radical copolymerization between styrene and AuNPs monomers was conducted at toluene-water interface. In the amphiphiles, the citrate-capped AuNPs are hydrophilic and PS


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is hydrophobic. The amphiphilic PS-g-AuNPs molecules were directly observed on a transmission electron microscope (TEM). The confined AuNPs in the PS coil structures demonstrated the synthesis of the amphiphilic PS-g-AuNPs (Figure 1b). In aqueous solution, the hybrid copolymer with five pendant AuNPs on each chain (PS-g-AuNP5) were able to selfassemble into micelles with collapsed PS in the cores and AuNPs in the coronae.

Figure 1. (a) Outline for the copolymerization of styrene and AuNPs monomer at the interface of toluene and water. (b) TEM image of polystyrene with pendant AuNPs showing the structure of the hybrid copolymer prepared from THF solution. Reproduced from ref 23. Copyright 2008 Royal Society of Chemistry.


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Figure 2. Schematic illustrations and TEM images of (a) self-assembly of PS with five pendant AuNPs, (b) self-assembly of PS with two pendant AuNPs, and (c) co-assembly of PS-g-AuNPs and PS-coated Fe3O4 nanoparticles. All the self-assemblies were performed in aqueous solutions. Reproduced from ref 26. Copyright 2011 Royal Society of Chemistry.

It is well known that for an amphiphilic block copolymer in aqueous solution the morphology of the self-assemblies changes from spherical micelle to hollow vesicle with an increase in the hydrophobic chain length or a decrease in the hydrophilic chain length.24,25 The number of hydrophilic AuNPs grafted to the PS main chain exerts a significant effect on the self-assembly of PS-g-AuNPs. A decrease in the number of pendant AuNPs results in a transition from


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spherical micellar structure to hollow vesicular structure.26 As shown in Fig. 2a, PS-g-AuNP5 hybrid copolymer self-assembles into micelles; however, PS-g-AuNP2, a hybrid copolymer with two pendant AuNPs on the main chain, self-assembles into vesicles in aqueous solution (Fig. 2b), indicating a decrease in hydrophilicity of PS-g-AuNPs hybrid copolymer leads to a morphology change from spherical micellar structure to vesicular structure. In order to investigate the effect of the hydrophobic components on the self-assembled structure of the hybrid copolymer, amphiphilic PS-g-AuNP5 was used to make co-assembly with PS coated Fe3O4 nanoparticles, and it turned out that the co-assembly of PS-g-AuNP5 and hydrophobic Fe3O4 nanoparticles also resulted in a morphology change from spherical micelles to hollow vesicles.27 As shown in Figure 2c, the collapsed PS chains on PS–g-AuNP5 and PS coated Fe3O4 nanoparticles stay in the hydrophobic walls of the vesicles to avoid unfavorable interaction with water, while the negatively charged AuNPs locate at the surfaces to stabilize the aggregates. In many cases, it is difficult to find a solvent to dissolve both the hydrophilic and hydrophobic components, so the preparation of amphiphilic polymer-tethered nanoparticles in homogeneous solutions is difficult. The amphiphilic AuNPs are able to undergo directed self-assembly onto liquid-liquid interface, which enhances the stability of the interface.28 We reported in-situ synthesis of amphiphilic AuNPs at oil-water interface by ligand exchange and fabrication of advanced hybrid structures. In a previous research, citrate-stabilized AuNPs were dispersed in aqueous solution, and PS with thiol terminal groups (PS-SH) was dissolved in toluene.29 Due to the in situ formation of amphiphilic PS-tethered AuNPs at oil-water interface, a stable emulsion was obtained upon mixing the two solutions. AuNPs aggregated together after the evaporation of toluene and no individual nanoparticles were observed outside of the oil droplets (Fig. 3). In the emulsion, the interfacial tension was reduced and the average size of toluene droplets was


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decreased. The decrease in the interfacial tension was attributed to the formation of amphiphilic AuNPs at liquid-liquid interface. Colloidal particles with collapsed PS cores and AuNPs coronae were obtained by adding the emulsion to methanol, a solvent which is miscible with toluene and water (Fig. 3). The surface of a typical AuNP in the corona was divided into two parts, the hydrophobic part composed of PS chains grafted to the nanoparticles and the citrate-protected part exposing to the medium (Fig. 3).

Figure 3. Schematic illustrations and TEM images of emulsions with PS-tethered AuNPs at the liquid-liquid interface and colloidal particles with PS cores and AuNP coronae prepared by adding the emulsions into excess methanol. Reproduced from ref 29. Copyright 2010 American Chemical Society. In this decade, the synthesis of Janus particles have been studied extensively.30-32 The amphiphilic Janus particles present very interesting surfactant behaviors. Most of the previous


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researches focused on Janus particles with sizes in the range from one hundred nanometers to a few micrometers. Efficient synthesis of Janus nanoparticles with sub-10 nm size is still a big challenge. Li and coworkers prepared asymmetric AuNPs with bicompartment polymer brushes by using the immobilization of the AuNPs on the thiolate surface followed by “grafting from” method.33 In our research, the PS-AuNP core-corona colloidal particles were used as templates for the preparation of Janus AuNPs. The AuNPs on a colloidal particle are partially embedded in the PS phase and the citrate-protected regions of the AuNPs are exposed to the medium, so the AuNPs can be functionalized with atom transfer radical polymerization (ATRP) initiator by ligand exchange. After surface-initiated ATRP of 2-(dimethamino)ethyl methacrylate (DMAEMA), Janus AuNPs with PS and PDMAEMA on two hemispheres were prepared (Fig. 4).34 The Janus structure of AuNPs was demonstrated by labeling the PDMAEMA brushes with Pt nanoparticles. TEM image and energy dispersive X-ray (EDX) spectrum of the labeled Janus AuNPs are shown in Figure 4. In methanol-THF mixture the Janus AuNPs self-assembled into bilayer structures with collapsed PS in the interiors and the solvated PDMAEMA brushes at the exteriors stabilizing the aggregated structures (Fig. 4).


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Figure 4. Outline for the synthesis and self-assembly of Janus AuNPs prepared by surfaceinitiated Atom Transfer Radical Polymerization, and TEM image and energy dispersive X-ray (EDX) spectrum of the Pt-labelled Janus AuNPs. Reproduced from ref 34. Copyright 2014 Wiley-VCH Verlag GmbH & Co. KGaA.


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Figure 5. Synthetic outline and TEM results of colloidal particles with PS-coated Fe3O4NP cores and AuNP coronae. As shown in the TEM image and cartoon picture, AuNPs form complexes with PS-coated Fe3O4NPs in THF solution. Reproduced from ref 35. Copyright 2011 American Chemical Society.

When magnetic nanoparticles coated with thiol-group functionalized polymer chains were employed in the interfacial exchange with AuNPs, colloidal particles with hydrophobic magnetic nanoparticle cores and hydrophilic AuNP coronae were prepared.35 As shown in Figure 5, PS brushes on Fe3O4 nanoparticles (PS-Fe3O4NPs) were prepared by surface reversible additionfragmentation chain transfer (RAFT) polymerization, and thiol-terminated PS brushes (PS-SH) were obtained after reduction reaction. HS-PS-Fe3O4NPs in toluene were added into aqueous solution of citrate-stabilized AuNPs. The AuNPs interacted with HS-PS-Fe3O4-NPs through ligand exchange at liquid-liquid interface resulting in the formation of amphiphilic nanoparticle complexes AuNPs-PS-Fe3O4NPs (Fig. 5). Upon addition of the emulsion into methanol, the complexes self-assembled into spherical structures with hydrophobic Fe3O4NP cores and hydrophilic AuNP coronae. TEM image of the structures is shown in Fig. 5. The weight ratio of HS-PS-Fe3O4NPs to AuNPs exerted a significant influence on the size of the core-shell structures. With an increase in the weight ratio, there were less AuNPs in the amphiphilic complexes resulting in poor stability and large sizes of the colloidal particles. In THF, a good solvent for PS, the nanostructures with Fe3O4NPs cores and AuNPs bonded to the magnetic cores through Au-S bonds were observed (Fig. 5).


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The method to prepare polymer-tethered AuNP amphiphiles at liquid-liquid interface can be applied in the fabrication of amphiphilic hybrid hollow capsules.36,37 Poly(ethylene glycol dimethacrylate) with a disulfide group at the mid-point (DS-PEGDMA) was synthesized by ATRP. The hydrophobic DS-PEGDMA was dissolved in toluene, and the solution was mixed with aqueous solution of citrate-stabilized AuNPs. Amphiphilic PEGDMA-tethered AuNPs were synthesized at liquid-liquid interface through ligand exchange between disulfides on the polymer chains and citrate groups on AuNPs. Cross-linked hollow capsules with AuNPs on the surfaces and PEGDMA on the inner walls were prepared after interfacial free radical polymerization (Fig. 6).36 In this strategy, amphiphilic PEGDMA-tethered AuNPs produced at liquid−liquid interface were used as surfactants, and toluene droplets in continuous water phase were used as templates. Free radical copolymerization of PEGDMA-tethered AuNPs and acrylamide (AM) at liquidliquid interface resulted in the production of multicomponent hollow capsules, a type of capsules with PAM-rich phases and AuNP-rich phases on the surfaces (Fig. 6). The formation of the two phases is attributed to the phase separation between PEGDMA and PAM. In addition to in situ free-radical polymerization, other cross-linking reactions were also able to be employed in the synthesis of hybrid hollow capsules. For example, hybrid hollow capsules with AuNPs on the surfaces were prepared by anthracene photodimerization at liquid–liquid interface.37


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Figure 6. Synthetic outline and TEM images of one-component (left) and multi-component hollow capsules (right) produced by interfacial free-radical polymerization. Reproduced from ref 36. Copyright 2012 American Chemical Society.


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The researches on polymer-conjugated AuNPs surfactant are not limited to spherical AuNPs. AuNPs with different shapes, such as gold nanorods, can be used to prepare polymer-tethered nanoparticles. The position of the tethered polymer plays an important role in the self-assembly of amphiphiles. Kumacheva and coworkers prepared hydrophilic gold nanorods with hydrophobic PS conjugated at both ends. The hybrid nanoparticles self-assembled into various structures including rings, chains, side to side aggregated bundles, nanospheres and bundled nanorod chains in selective solvents.38

Polymer-tethered organic nanoparticles Usually, precise control of the number and the type of tethered polymer chains on inorganic nanoparticles is difficult. For example, it is quite difficult to synthesize AuNPs with only one chain on a particle. However, well defined polymer-tethered organic nanoparticles can be fabricated by efficient coupling reactions. Fullerenes (also known as buckyballs) are consist of carbon atoms, and can be treated as organic nanoparticles. C60 is the smallest stable fullerene and frequently used as model organic nanoparticles. Cheng and coworkers synthesized polymertethered C60 by click chemistry and studied solution self-assembly of the amphiphiles,39 They found the molecular topology and the initial molecular concentration exerted influences on the self-assembled morphology. Recent advances in polymerization methodologies and the application of efficient and orthogonal coupling reactions have enabled the synthesis of polymers with different topological structures and functionalities, among which single-chain nanoparticles (SCNPs) prepared by intramolecular cross-linking of polymer chains have well-defined structures and varied


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functionalities,40,41 and can be used as an ideal platform for the study of surfactant behaviors of polymer-tethered nanoparticles. There have been extensive researches on the synthesis of SCNPs.40-45 In the synthesis of SCNPs, the intramolecular crosslinking reactions need to be conducted in dilute solutions at concentrations below the overlap concentration to avoid intermolecular reaction. It is required that the crosslinking reactions are highly effective and efficient. There are three strategies frequently used in the preparation of SCNPs.41 The first one is to introduce functional groups to polymer chains which can undergo self-cross-linking reactions. For example, Hawker and coworkers synthesized benzocyclobutene monomer and made a copolymerization of the monomer with styrene.46 At an elevated temperature, the benzocyclobutene groups on the polymer chains underwent irreversible dimerization reaction resulting in the formation of SCNPs. The second method is to introduce two different functional groups to the same polymer chains and make them react with each other under dilute conditions.47 In the third method, cross-linking molecules are used to bind functional groups on the polymer chains.42 By choosing different monomers or conducting postpolymerization functionalization, hydrophobic or hydrophilic SCNPs have been prepared. In the structure, amphiphilic mono-tethered SCNPs with tadpole-like structure are very similar to small molecular surfactants, and the polymer-tethered SCNPs present very interesting surfactant behaviors. In a previous research, we synthesized poly(2-(dimethylamino)ethyl methacrylate)-block-polystyrene

(PDMAEMA-b-PS)

diblock

copolymer

by

RAFT

polymerization. The PDMAEMA blocks were intramolecularly crosslinked by 1,4-diiodobutane (DIB) under dilute conditions, resulting in the formation of tadpole-like PS-tethered SCNPs (NPPDMAEMA-b-PS) (Fig. 7a).48 After quartenization of the dimethylamino groups, the PDMAEMA blocks turned into positively charged PDMAEMA nanoparticles. By controlling the


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molecular weight of the linear precursor and the cross-linking degree, SCNPs in the range from a couple of nanometers to 20 nm were synthesized. The amphiphilic tadpole-like structures with hydrophilic nanoparticle heads and hydrophobic linear tails were able to self-assemble into aggregates with different morphologies in selective solvents. In aqueous solutions, the NPPDMAEMA74-b-PS297 with 10% and 20% crosslinking degrees self-assembled into strawberrylike micelles with collapsed PS in the cores and hydrophilic PDMAEMA nanoparticles in the corona (Fig. 7b). However, NP-PDMAEMA15-b-PS151 with smaller hydrophilic nanoparticle heads self-assembled into vesicles in water. The hydrophobic PS chains collapsed forming the walls of the vesicles and the hydrophilic SCNPs distributed at the inner and outer surfaces to stabilize the structures (Fig. 7c). The morphology change of the PS-tethered SCNPs was attributed to the decreases in PDMAEMA block length and the hydrophilicity of the SCNPs. In cyclohexane, a good solvent for PS tails and a precipitant for the nanoparticle heads, the tadpolelike structures self-assembled into bunchy micelles with SCNPs in the cores and linear PS in the coronae (Fig. 7d). This result is consistent with a previous theoretical study conducted by Marques that micellization of macrosurfactants with a soluble long polymer chain tethered to an insoluble solid spherical particle results in aggregates with molten cores and swollen polymer shells.49 The surface charge density on the SCNPs exerts a significant effect on the size and selfassembly of the tadpole-like structures.50 The charge density can be controlled by controlling the degree of quaternization of PDMAEMA. NP-PDMAEMA74-b-PS100 with 20%, 44% and 68% quaternized PDMAEMA self-assembled into micelles in water and the average size of the micelles increased with charge density. In order to reduce the unfavorable interaction between the neighboring positively charged nanoparticles in the coronae, the PS-tethered SCNPs with


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higher quaternization degree favored larger micelles to minimize the free energy of the system. The effect of charge density on the morphology of the assemblies of NP-PDMAEMA30-b-PS169 in water was also investigated. As shown in Figure 8, with an increase in the degree of quaternization from 20% to 44%, to 68%, the morphology of self-assemblies changed from spherical micelle (Fig. 8a) to hollow vesicles (Fig. 8b) and to a mixture of worm-like cylinders and vesicles (Fig. 8c). Magnified TEM images showing structural details of a vesicle and a cylinder structure are shown in Fig. 8d,e. The free energy of the assembled aggregates increased with the surface charge density on the SCNPs. In order to minimize the free energy, the PStethered SCNPs self-assembled into aggregates with larger surface and lower charge density. Therefore, with an increase in the quaternization degree, the morphology changed from spherical micelles to vesicles, and to a mix of cylinders and vesicles.


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Figure 7. (a) Outline for the synthesis and self-assemblies of tadpole-like structures with poly(2(dimethylamino)ethyl methacrylate) (PDMAEMA) single-chain nanoparticles (SCNPs) and PS tails, (b) TEM image of micelles self-assembled by NP-PDMAEMA74-b-PS297 in aqueous solution, (c) TEM image of hollow vesicles formed by NP-PDMAEMA15-b-PS151 in aqueous solution, (d) TEM image of bunchy micelles with SCNPs in the cores and linear PS in the coronae self-assembled by NP-PDMAEMA74-b-PS297 in cyclohexane. Reproduced from ref 48. Copyright 2013 American Chemical Society.


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Figure 8. TEM images of self-assembled aggregates made from (a) NP0.2-PDMAEMA30-bPS169, (b) NP0.44-PDMAEMA30-b-PS169 and (c) NP0.68-PDMAEMA30-b-PS169 in aqueous solutions, and magnified TEM images showing the structures of (d) a vesicle and (e) a worm-like cylinder self-assembled by NP0.68-PDMAEMA30-b-PS169. Reproduced from ref 50. Copyright 2014 Royal Society of Chemistry.

Synthesis and self-assembly of amphiphiles based on single-chain nanoparticles were also reported by other groups. Chen and coworkers synthesized amphiphilic mono-tethered SCNPs by intramolecular photo-cross-linking reaction.51 The tadpole-like nanoparticles are able to make self-assembly in a selective solvent. They made investigations on the stability of the assemblies under ultrasonic treatment. He and coworkers prepared mono-tethered and dual-tethered SCNPs by silane chemistry. They found that the intramolecular cross-linking resulted in morphological changes and the conformation of tail chains was critical for the self-assembly of polymertethered SCNPs.52 The amphiphilic mono-tethered SCNPs were applied in the synthesis and stabilization of surface-tunable polystyrene colloidal particles.53 A linear block copolymer consisting of poly(εcaprolactone) (PCL) and PDMAEMA linked by a redox-responsive disulfide linkage was synthesized

by

ring-opening

polymerization

and

ATRP.

PDMAEMA

blocks

were

intramolecularly crosslinked by quaternization reaction and PCL-tethered SCNPs were obtained (Fig. 9a). The hydrophobic PCL chains and the hydrophilic PDMAEMA nanoparticles were connected by disulfide bonds, which could be cleaved by a reducing agent. The amphiphilic tadpole-like nanoparticles showed surfactant-like properties in water. Both the quaternized linear


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diblock copolymer and the PCL-tethered SCNPs were able to lower the surface tension of water, and the mono-tethered SCNPs exhibited a relatively higher CMC value (0.022 mg/mL) compared to the linear block copolymer (0.014 mg/mL) due to the repulsion of positively charged SCNPs (Fig. 9b). The CMC value increased with the quaternization degree of the SCNPs. The PCL-tethered SCNPs could be used as stabilizers for the suspension polymerization of styrene. The average size of the polystyrene colloidal particles decreased with increasing amount of stabilizers. The cleavage of the disulfides between the PCL tails and the SCNPs using n-tributylphosphine afforded reactive thiol functional groups on the surface of the colloidal particles and the cleaved SCNPs (Fig. 9c). The thiol groups on the surface were further modified by thiol-disulfide exchange reaction with 2,2′-dipyridyl disulfide and pyridyl disulfide-modified colloidal particles were obtained, which could be used as a platform for further functionalization.


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Figure 9. (a) Outline for the synthesis of cleavable mono-tethered SCNPs, (b) plots of surface tensions of water vs concentrations of partly quaternized PCL79-S-S-PDMAEMA63 linear diblock copolymer (curve a), mono-tethered single-chain nanoparticles with a quaternization degree of 15% (curve b), and mono-tethered SCNPs with a quaternization degree of 60% (curve c), (c) TEM image of PS colloidal particles after cleavage reaction. Reproduced from ref 53. Copyright 2015 Elsevier Ltd.

The surfactant behaviors of the monotethered SCNPs are attributed to their amphiphilic properties and asymmetric structures. Other type of asymmetric polymer-tethered nanoparticles


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may also have surfactant behaviors. Polymer brushes refer to an assembly of polymer chains which are tethered by one end to a surface or interface.54 Block copolymer brushes have many interesting properties, among which one of the most important properties is their response to environmental conditions. After being treated with selective solvents, block copolymer brushes make rearrangements, and segregated nanoscopic domains on the surfaces are created.54-56 For example, if AB diblock copolymer brushes are tethered to the solid surface by the ends of A blocks, and treated by a selective solvent which is a good solvent for A block and a precipitant for B block, block copolymer brushes self-assemble into pinned micelles with collapsed B blocks in the cores and A blocks in the coronae. The pinned micelles have asymmetric structures with high densities of A block on one side. In our research, we prepared cleavable pinned micelles on the surfaces of silica particles based on phase separation of block copolymer brushes in a selective solvent, and studied self-assembly of the cleaved pinned micelles.57 Poly(tert-butyl acrylate-block-styrene) (PtBA-b-PS) diblock copolymer brushes grafted to the silica particles by the ends of PtBA blocks via disulfide bonds, were prepared by ATRP. In acetone, a good solvent for PtBA and a precipitant for PS, pinned micelles with PS cores and PtBA coronae were formed. Upon cleavage of the disulfide bonds by n-tributylphosphine in acetone, cleaved pinned micelles with thiol groups on the surfaces were obtained (Fig. 10). Due to the asymmetric structure, the pinned micelles self-assembled into vesicles. As shown in Figure 10, the solvophobic PS cores of the pinned micelles aggregated into the walls and the soluble PtBA chains were in the coronae. The oxidation of thiol groups on the surfaces of vesicles resulted in the formation of the disulfide bonds between two different vesicles and the fusion of the vesicles into bigger hollow structures. In the meanwhile, the oxidation of thiols and the formation of the disulfides inside the hollow structures caused the


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collapse of the membranes, so a transition from hollow vesicles to fused vesicles to fiber-like structures were observed. The process is schemed in Figure 11.

Figure 10. Schematic representation for the formation of pinned micelles and the self-assembly of the cleaved pinned micelles into vesicles in a selective solvent. Reproduced from ref 57. Copyright 2015 American Chemical Society.

Figure 11. Schematic depiction of the fusion of vesicles self-assembled by the cleaved pinned micelles into bigger hollow structures and fiber-like structures. Reproduced from ref 57. Copyright 2015 American Chemical Society.

Polymer-tethered natural nanoparticles


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Compared to inorganic and synthetic organic nanoparticles, natural nanoparticles such as proteins are more versatile and well-defined. Strategies for polymer conjugation to natural nanoparticles, especially proteins, have been studied extensively.58-61 There are two principal techniques to synthesize polymer-protein conjugates: (1) the “grafting to” method, where the polymers react with the functional groups on the proteins, and (2) the “grafting from” method, where initiators or RAFT agents are attached to proteins to form macro-initiators or macroRAFT agents, and followed by growing polymer chains from the proteins. A number of different bioconjugation reactions were employed to make bioconjugates of proteins and organic compounds (or polymer chains).59,60 Usually, the functional groups of lysine, glutamate, aspartate, and cysteine on the surfaces of proteins were involved in the bioconjugation reactions.59 In these years, controlled radical polymerizations including ATRP 62,63 and RAFT polymerization64,65 have been successfully used in the grafting from strategy. Polymer-tethered proteins have asymmetric structures, and present very interesting surfactant behaviors. Nolte and coworkers synthesized PS-conjugated lipase B by making use of disulfide bonds exposed on the outer surface of the native enzyme. After reduction of disulfide bonds into thiol groups, reduced lipase B was reacted with maleimide-funtionalized PS in mixture of THF and water. The amphiphilic PS-tethered lipase B self-assembled into well-defined fibers composed of micellar rods.66 Nolte and coworkers also reported the synthesis and self-assembly of biohybrid ABC triblock copolymers consisting of a protein and a synthetic diblock copolymer.67 Polystyrene-b-polyethylene glycol (PS-b-PEG) diblock copolymer was synthesized by ATRP and functionalized with the heme cofactor by click chemistry. The functionalized diblock copolymer was reconstituted with the apoprotein or the apoenzyme. Depending on the protein and the PS block length, the block copolymer self-assembled into aggregates with different


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morphologies, including micellar rods, vesicles, toroids, figure eight structures, octopus structures, and spheres. In these years, a new family of conjugates synthesized by attaching environmental responsive polymers to proteins has been prepared, and the bioconjugates are able to self-assemble into core-corona structures upon exerting external stimuli.68-70 O’Reilly and workers reported synthesis of poly[(oligo ethylene glycol) methyl ether methacrylate] (PEGMA) tethered superfolder green fluorescent protein (sfGFP).71 They prepared alkyne-terminated PEGMA by RAFT polymerization and incorporated the noncanonical azide-functional amino acid p-azidophenylalanine into sfGFP. PEGMA chains were coupled with sfGFP by click chemistry. The attachment of the polymer onto the protein exerted significant impact on the thermoresponsive behavior. The cloud points of the bioconjugates were higher than that of POEGMA. They attributed the temperature shift to the protein molecules serving as hydrophilic end groups. People in the same group synthesized PS and PNIPAM conjugated DNA strand taking advantage of click reaction between azide groups on the polymers and alkyne groups on DNA.72 The polymer-tethered DNA strand was capable of sequence-specific hybridization, which could self-assemble with other DNA strands to form a DNA tetrahedron with a polymer chain. Self-assembly of PNIPAM-tethered DNA tetrahedron in water at the temperature above LCST of PNIPAM resulted in micelles with collapsed PNIPAM cores and DNA tetrahedron coronae. Zare and coworkers synthesized denatured bovine serum albumin (BSA) with tethered poly(methyl methacrylate) (PMMA) chains by free-radical copolymerization of MMA and protein monomer.73 In aqueous solution the amphiphiles were able to self-assemble into coreshell structures, which could be used in drug delivery.74 Mann and coworkers synthesized PNIPAM-tethered BSA by coupling reactions between mercaptothiazoline-activated PNIPAM and amine groups on BSA (Fig. 12a).75 The bioconjugates located at the interface between oil


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and water in emulsions. After interfacial cross-linking reactions and removal of oil phase, hollow capsules with bioconjugates on the surface were prepared (Fig. 12b). The hollow structures may find applications in synthetic biology and biomaterials as micro-sized reactors. The studies on the synthesis and surfactant behaviors of polymer-tethered natural nanoparticles provide possibilities for the preparation of new biomaterials.

Figure 12. Schematic illustrations for (a) coupling of mercaptothiazoline-activated PNIPAM with amine groups on BSA in the synthesis of PNIPAM-tethered BSA, (b) self-assembly of polymer-protein bioconjugates at water-oil interface and preparation of hollow capsules with bioconjugates on the surface. Reproduced from ref 75. Copyright 2013 Nature Publishing Group.

Conclusions and perspective With the rapid development of polymer science and nanoscience, the scope of surfactants has expanded dramatically from small molecular surfactants, to amphiphilic polymers, and to polymer-conjugated nanoparticle amphiphiles. The attachment of polymer chains to


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nanoparticles endows the conjugates with adaptive properties and surfactant behaviors. Similar to the ionic head in a small molecular surfactant, nanoparticle in a conjugate functionalize as an independent hydrophilic (or hydrophobic) component. In this decade great progresses have been made in this field, nevertheless, there are still many problems that need to be solved. (1) Precise controls of the location and number of polymer chains on the nanoparticles are crucial in the preparation of polymer-tethered nanoparticles. Only based on the well-defined conjugates, the relationship between the structural parameters and the surfactant behaviors can be established. (2) Until now only limited inorganic nanoparticles were employed in the synthesis of polymertethered nanoparticles. In order to endow the conjugates with functionalities and broaden the scope of applications, many different inorganic particles should be involved in the synthesis of the conjugates. (3) The synthesis of polymer-tethered SCNPs makes use of collapse and fold of single polymer chains. It is a big challenge to make exact arrangement of functional groups on the surfaces and interiors of the SCNPs. Fabrication of new functional materials based on selfassembly of the well-defined SCNPs will be possible. (4) In most previous researches, linear polymers were used in the fabrication of polymer-tethered nanoparticles. The architecture of the polymers exerts significant effect on the surfactant behaviors of the conjugates. The synthesis and self-assembly of the conjugates with different polymer topological structures will be very interesting research topics in the future.

Corresponding Author * Corresponding Author: Hanying Zhao, [email protected]


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Notes The authors declare no competing financial interest. Acknowledgments: This project was supported by the National Natural Science Foundation of China (NSFC) under contract 21174073 and the National Basic Research Program of China (973 Program, 2012CB821500).

REFERENCES 1.

Rosen, M. J. Surfactants and Interfacial Phenomena, 3rd.; John Wiley & Sons, Inc., Hoboken, New Jersey, 2004.

2. Nagarajan, R., Ruckenstein, E. Theory of surfactant self-assembly: a predictive molecular thermodynamic approach. Langmuir 1991, 7. 2934-2969. 3.

Drummond, C. J.; Fong, C. Surfactant self-assembly objects as novel drug delivery vehicles. Curr. Opin. Colloid Interface Sci. 2000, 4, 449-456.

4.

Svenson, S. Controlling surfactant self-assembly. Curr. Opin. Colloid Interface Sci. 2004, 9, 201-212.

5.

Lutz, J. Solution self-assembly of tailor-made macromolecular building blocks prepared by controlled radical polymerization techniques. Polym. Int. 2006, 55, 979−993.

6.

Mespouille, L.; Hedrick, J. L.; Dubois, P. Expanding the role of chemistry to produce new amphiphilic polymer (co)networks. Soft Matter 2009, 5, 4878-4892.


30

Page 31 of 41

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

7.

Gibanel, S.; Forcada, J.; Heroguez, V.; Schappacher, M.; Gnanou, Y. Novel gemini-type reactive dispersants based on PS/PEO block copolymers: Synthesis and application. Macromolecules 2001, 34, 4451−4458.

8.

Moffit, M.; Khougaz, K.; Eisenberg, A. Micellization of ionic block copolymers. Acc. Chem. Res. 1996, 29, 95–102.

9.

Discher, D. E.; Eisenberg, A. Polymer vesicles. Science 2002, 297, 967-973.

10. Liu, X.; Kim, J.; Wu, J.; Eisenberg, A. Bowl-shaped aggregates from the self-assembly of an amphiphilic random copolymer of poly(styrene-co-methacrylic acid). Macromolecules 2005, 38, 6749-6751. 11. Cui, H.; Chen, Z.; Zhong, S.; Wooley, K. L.; Pochan, D. J. Block copolymer assembly via kinetic control. Science 2007, 317, 647-650. 12. Talley, C. E.; Jackson, J. B.; Oubre, C.; Grady, N. K.; Hollars, C. W.; Lane, S. M.; Huser, T. R.; Nordlander, P.; Halas, N. J. Surface-enhanced Raman scattering from individual Au nanoparticles and nanoparticle dimer substrates. Nano Lett. 2005, 5, 1569-1574. 13. Pankhurst, Q. A.; Thanh, N. T. K.; Jones, S. K.; Dobson, J. Progress in applications of magnetic nanoparticles in biomedicine. J. Phys. D: Appl. Phys. 2009, 42, 224001. 14. Pieters, B. J. G. E.; van Eldijk, M, B.; Nolte, R. J. M.; Mecinovic, J. Natural supramolecular protein assemblies. Chem. Soc. Rev. 2016, 45, 24-39.


31

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 32 of 41

15. Hu, J.; Wu, T.; Zhang, G.; Liu, S. Efficient synthesis of single gold nanoparticle hybrid amphiphilic triblock copolymers and their controlled self-Assembly. J. Am. Chem. Soc. 2012, 134, 7624-7627. 16. Zhang, W.; Li, Y.; Li, X.; Dong, X.; Yu, X.; Wang, C.; Wesdemiotis, C.; Quirk, R. P.; Cheng, S. Z. D. Synthesis of shape amphiphiles based on functional polyhedral oligomeric silsesquioxane end-capped poly(L-Lactide) with diverse head surface chemistry. Macromolecules 2011, 44, 2589-2596. 17. Yu, X.; Zhong, S.; Li, X.; Tu, Y.; Yang, S.; Horn, R. M. V.; Ni, C.; Pochan, D. J.; Quirk, R. P.; Wesdemiotis, C.; Zheng, W.; Cheng, S. Z. D. A giant surfactant of polystyrene(carboxylic acid-functionalized polyhedral oligomeric silsesquioxane) amphiphile with highly stretched polystyrene tails in micellar assemblies. J. Am. Chem. Soc. 2010, 132, 16741-16744. 18. Li, Y.; Su, H.; Feng, X.; Wang, Z.; Guo, K.; Wesdemiotis, C.; Cheng, S. Z. D.; Zheng, W. Exploring shape amphiphiles beyond giant surfactants: molecular design and click synthesis. Polym. Chem. 2013, 4, 1056-1067. 19. Zhang, W.; Yu, X.; Wang, C.; Sun, H.; Hsieh, I.; Li, Y.; Dong, X.; Yue, K.; Horn, R. V.; Cheng, S. Z. D. Molecular nanoparticles are unique elements for macromolecular science: from “nanoatoms” to giant molecules. Macromolecules 2014, 47, 1221-1239. 20. Song, J.; Cheng, L.; Liu, A.; Yin, J.; Kuang, M.; Duan, H. Plasmonic vesicles of amphiphilic Gold nanocrystals: self-assembly and external-stimuli-triggered destruction. J. Am. Chem. Soc. 2011, 133, 10760-10763.


32

Page 33 of 41

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

21. Song, J.; Zhou, J.; Duan, H. Self-assembled plasmonic vesicles of SERS-encoded amphiphilic gold nanoparticles for cancer cell targeting and traceable intracellular drug delivery. J. Am. Chem. Soc. 2012, 134, 13458-13469. 22. He, J.; Liu, Y.; Babu, T.; Wei, Z.; Nie, Z. Self-assembly of inorganic nanoparticle vesicles and tubules driven by tethered linear block copolymers. J. Am. Chem. Soc. 2012, 134, 11342-11345. 23. Zhang, X.; Liu, L.; Tian, J.; Zhang, J.; Zhao, H. Copolymers of styrene and gold nanoparticles. Chem. Commun. 2008, 6549-6551. 24. Zhang, L.; Eisenberg, A. Aggregates of polystyrene-b-poly(acrylic acid) block copolymers. Science 1995, 268, 1728-1731. 25. Zhang, L.; Eisenberg, A. Multiple morphologies and characteristics of “crew-cut” micellelike aggregates of polystyrene-b-poly(acrylic acid) diblock copolymers in aqueous solutions. J. Am. Chem. Soc. 1996, 118, 3168-3181. 26. Tian, J.; Zheng, F.; Duan, Q.; Zhao, H. Self-assembly of polystyrene with pendant hydrophilic gold nanoparticles: the influence of the hydrophilicity of the hybrid polymers. J. Mater. Chem., 2011, 21, 16928-16934. 27.

Zhang, X.; Yang, Y.; Tian, J.; Zhao. H. Vesicles fabricated by hybrid nanoparticles. Chem. Commun. 2009, 3807-3809.

28. Duan, H.; Wang, D.; Kurth, D. K.; Mohwald, H. Directing Self-Assembly of Nanoparticles at Water/Oil Interfaces. Angew. Chem. Int. Ed. 2004, 43, 5639-5642.


33

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 34 of 41

29. Tian, J.; Jin, J.; Zheng, F.; Zhao, H. Self-assembly of gold nanoparticles and polystyrene: a highly versatile approach to the preparation of colloidal particles with polystyrene cores and gold nanoparticle coronae. Langmuir 2010, 26, 8762-8768. 30. Walther, A.; Müller A. H. E. Janus particles: synthesis, self-assembly, physical properties, and applications. Chem. Rev. 2013, 113, 5194-5261. 31. Zhang, J.; Wang, X.; Wu, D.; Liu, L.; Zhao, H. Bioconjugated Janus particles prepared by in situ click chemistry. Chem. Mater. 2009, 21, 4012 – 4018. 32. Hu, J.; Zhou, S.; Sun, Y.; Fang, X.; Wu, L. Fabrication, properties and applications of Janus particles. Chem. Soc. Rev. 2012, 41, 4356-4378. 33. Wang, B.; Li, B.; Zhao, B.; Li, C. Y. Amphiphilic Janus gold nanoparticles via combining “solid-state grafting-to” and “grafting-from” Methods. J. Am. Chem. Soc. 2008, 130, 1159411595. 34. Liu, G.; Tian, J.; Zhang, X.; Zhao, H. Amphiphilic Janus gold nanoparticles prepared by interface-directed self-assembly: synthesis and self-Assembly. Chem. Asian J. 2014, 9, 2597-2603. 35. Tian, J.; Zheng, F.; Zhao, H. Nanoparticles with Fe3O4-nanoparticle cores and goldNanoparticle coronae prepared by self-assembly approach. J. Phys. Chem. C 2011, 115, 3304-3312.


34

Page 35 of 41

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

36. Tian, J.; Yuan, L.; Zhang, M.; Zheng, F.; Xiong, Q.; Zhao, H. Interfacial-directed selfassembly of gold nanoparticles and fabrication of hybrid hollow capsules by interfacial cross-linking polymerization. Langmuir 2012, 28, 9365-9371. 37. Tian, J.; Liu, G.; Guan, C.; Zhao, H. Amphiphilic gold nanoparticles formed at a liquidliquid interface and fabrication of hybrid nanocapsules based on interfacial UV photodimerization. Polym. Chem. 2013, 4, 1913-1920. 38. Nie, Z.; Fava, D.; Kumacheva, E.; Zou, S.; Walker, G. C.; Rubinstein, M. Self-assembly of metal-polymer analogues of amphiphilic triblock copolymers. Nature Mater. 2007, 6, 609614. 39. Yu, X.; Zhang, W.; Yue, K.; Li, X.; Liu, H.; Xin, Y.; Wang, C.; Wesdemiotis, C.; Cheng, S. Z. D. Giant Molecular shape amphiphiles based on polystyrene−hydrophilic [60] fullerene conjugates: click synthesis, solution self-assembly, and phase behavior. J. Am. Chem. Soc. 2012, 134, 7780-7787. 40. Gonzalez-Burgos, M.; Latorre-Sanchez, A.; Pomposo, J. A. Advances in single chain technology. Chem. Soc. Rev. 2015, 44, 6122-6142. 41. Mavila, S.; Eivgi, O.; Berkovich, I.; Lemcoff, N. G. Intramolecular cross-linking methodologies for the synthesis of polymer nanoparticles. Chem. Rev. 2016, 116, 878-961. 42. Murray, B. S.; Fulton, D. A. Dynamic covalent single-chain polymer nanoparticles. Macromolecules 2011, 44, 7242-7252.


35

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 36 of 41

43. Cherian, A. E.; Sun, F. C.; Sheiko, S. S.; Coates, G. W. Formation of nanoparticles by intramolecular crosslLinking: following the reaction progress of single polymer chains by atomic force microscopy. J. Am. Chem. Soc. 2007, 129, 11350-11351. 44. Jiang, J.; Thayumanavan, S. Synthesis and characterization of amine-functionalized polystyrene nanoparticles. Macromolecules 2005, 38, 5886-5891. 45. Mecerreyes, D.; Lee, V.; Hawker, C. J.; Hedrick, J. L.; Wursch, A.; Volksen, W.; Magbitang, T.; Huang, E.; Miller, R. D. A novel approach to functionalized nanoparticles: selfcrosslinking of macromolecules in ultradilute Solution. Adv. Mater. 2001, 13, 204-208. 46. Harth, E.; Horn, B. V.; Lee, V. Y.; Germack, D. S.; Gonzales, C. P.; Miller, R. D.; Hawker, C. J. A facile approach to architecturally defined nanoparticles via intramolecular chain collapse. J. Am. Chem. Soc. 2002, 124, 8653-8660. 47. Luzuriaga, A. R. D.; Ormategui, N.; Grande, H. J.; Odriozola, I.; Pomposo, J. A.; Loinaz, I. Intramolecular click cycloaddition: an efficient room-temperature route towards bioconjugable polymeric nanoparticles. Macromol. Rapid Commun. 2008, 29, 1156– 1160. 48. Wen, J.; Yuan, L.; Yang, Y.; Liu, L.; Zhao, H. Self-assembly of monotethered single-chain nanoparticle shape amphiphiles. ACS Macro Lett. 2013, 2, 100-106. 49. Marques, C. M. Bunchy micelles. Langmuir 1997, 13, 1430−1433. 50. Wen, J.; Zhang, J.; Zhang, Y.; Yang, Y.; Zhao, H. Controlled self-assembly of amphiphilic monotailed single-chain nanoparticles. Polym. Chem. 2014, 5, 4032.


36

Page 37 of 41

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

51. Zhou, F.; Xie, M.; Chen, D. Structure and ultrasonic sensitivity of the superparticles formed by self-assembly of single chain Janus nanoparticles. Macromolecules 2014, 47, 365−372. 52. Li, W.; Thanneeru, S.; Kanyo, I.; Liu, B.; He, J. Amphiphilic hybrid nano building blocks with surfactant-mimicking structures. ACS Macro Lett. 2015, 4, 736−740. 53. Zhang, Y.; Zhao, H. Surface-tunable colloidal particles stabilized by mono-tethered singlechain nanoparticles. Polymer 2015, 64, 277−284. 54. Yin, Y.; Sun, P.; Li, B.; Chen, T.; Jin, Q.; Ding, D.; Shi, A. A simulated annealing study of diblock copolymer brushes in selective solvents. Macromolecules 2007, 40, 5161-5170. 55. Zhao, B.; Brittain, W. J.; Zhou, W.; Cheng, S. Z. D. Nanopattern formation from tethered PS-b-PMMA brushes upon treatment with selective solvents. J. Am. Chem. Soc. 2000, 122, 2407-2408. 56. Zhao, B.; Brittain, W. J. Synthesis, characterize, and properties of tethered polystyrene-bpolyacrylate brushes on flat silicate substrates. Macromolecules 2000, 33, 8813-8820. 57. Sun, L.; Zhao, H. Cleavage of diblock copolymer brushes in a selective solvent and fusion of vesicles self-assembled by pinned micelles. Langmuir 2015, 31, 1867-1873. 58. Velonia, K. Protein-polymer amphiphilic chimeras: recent advances and future challenges. Polym. Chem. 2010, 1, 944-952. 59. Obermeyer, A. C.; Olsen, B. D. Synthesis and application of protein-containing block copolymers. ACS Macro Lett. 2015, 4, 101-110.


37

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 38 of 41

60. Cobo, I.; Li, M.; Sumerlin, B. S.; Perrier, S. Smart hybrid materials by conjugation of responsive polymers to biomacromolecules. Nature Mater. 2015, 14, 143-159. 61. Zhao, W.; Liu, F.; Chen, Y.; Bai, J.; Gao, W. Synthesis of well-defined protein-polymer conjugates for biomedicine. Polymer 2015, 66, A1-A10. 62. Averick, S. E.; Simakova, A.; Park, S.; Konkolewicz, D.; Magenau, A. J. D.; Mehl, R. A.; Matyjaszewski, K. ATRP under biologically relevant conditions: Grafting from a protein. ACS Macro Lett. 2012, 1, 6-10. 63. Averick, S. E.; Magenau, A. J. D.; Simakova, A.; Woodman, B. F.; Seong, A.; Mehl, R. A.; Matyjaszewski, K. Covalently incorporated protein-nanogels using AGET ATRP in an inverse miniemulsion. Polym. Chem. 2011, 2, 1476-1478. 64. Bulmus, V. RAFT polymerization mediated bioconjugation strategies. Polym. Chem. 2011, 2, 1463-1472. 65. Li, H.; Li, M.; Yu, X.; Bapat, A. P.; Sumerlin, B. S. Block copolymer conjugates prepared by sequentially grafting from proteins via RAFT. Polym. Chem. 2011, 2, 1531-1535. 66. Velonia, K.; Rowan, A. E.; Nolte, R. J. M. Lipase polystyrene giant amphiphiles. J. Am. Chem. Soc. 2002, 124, 4224-4225. 67. Reynhout, I. C.; Cornelissen, J. J. M.; Nolte, R. J. M. Self-assmebled architectures from biohybrid triblock copolymers. J. Am. Chem. Soc. 2007, 129, 9315-9323.


38

Page 39 of 41

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

68. Heredia, K. L.; Tolstyka, Z. P.; Maynard, H. D. Aminooxy end-functionalized polymers synthesized by ATRP for chemoselective conjugation to proteins. Macromolecules 2007, 40, 4772-4779. 69. Vaquez-Dorbatt, V.; Tolstyka, Z. P.; Maynard, H. D. Synthesis of aminooxy endfunctionalized pNIPAAm by RAFT polymerization for protein and polysaccharide conjugation. Macromolecules 2009, 42, 7650-7656. 70. Li, H.; Bapat, A. P.; Li, M.; Sumerlin, B. S. Protein conjugation of thermoresponsive aminereactive polymers prepared by RAFT. Polym. Chem. 2011, 2, 323-327. 71. Moatsou, D. Li, J.; Ranji, A.; Pitto-Barry, A.; Ntai, I.; Jewett, M. C.; O'Reilly, R. K. Selfassembly of temperature-responsive protein-polymer bioconjugates. Bioconjugate Chem. 2015, 26, 1890-1899. 72. Wilks, T. R.; Bath, J.; de Varies J. W.; Raymond, J. E.; Herrmann, A.; Turberfield, A. J.; O'Reilly, R. K. “Giant Surfactants” created by the fast and efficient functionalization of a DNA tetrahedron with a temperature-responsive polymer. ACS Nano 2013, 7, 8561-8572. 73. Ge, J.; Lei, J.; Zare, R. N. Bovine serum albumin_poly(methyl methacrylate) nanoparticles: an example of frustrated phase separation. Nano Lett. 2011, 11, 2551–2554. 74. Ge, J.; Neofytou, E.; Lei, J.; Beygui, R. E.; Zare, R. N. Protein–polymer hybrid nanoparticles for drug delivery. Small 2012, 8, 3573–3578.


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75. Huang, X.; Li, M.; Green. D. C.; Williams, D. S.; Patil. A. J.; Mann. S. Interfacial assembly of protein–polymer nano-conjugates into stimulus-responsive biomimetic protocells. Nat. commun. 2013, 4, 2239.

Table of Contents

Surfactant Behaviors of Amphiphilic Polymer-Tethered Nanoparticles Yue Zhang, and Hanying Zhao*


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Langmuir

Biographies

Yue Zhang received her B.S. in chemistry from Nankai University in 2010. Then, she joined Prof. Zhao’s research group as a graduate student and received her Ph.D. degree in June 2015. Her research interests focus on the conjugation of proteins to various polymer scaffolds. She joined College of Chemical Engineering at Hebei University of Technology in 2015.

Hanying Zhao is a professor in the College of Chemistry, Nankai University. He received his Ph. D. in Macromolecular Chemistry and Physics from Changchun Institute of Applied Chemistry, Chinese Academy of Sciences in 1997 with Prof. Baotong Huang. During 1997-2003, he carried out post-doctoral researches at Fudan University, Institute of Polymer Research Dresden, University of Florida and Clarkson University. His research interests are in the synthesis and self-assembly of polymers with different topological structures, polymer brushes, polymer nanocomposites, and polymer bioconjugates design.


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Surfactant Behavior of Amphiphilic Polymer-Tethered Nanoparticles

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