Investigating Switchable Nanostructures in Shape Memory Process for

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Investigating Switchable Nanostructures in Shape Memory Process for Amphipathic Janus Nanoparticles Bingyun Yan, Xiaotong Zheng, Pandeng Tang, Huikai Yang, Jing He, and Shaobing Zhou ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b11276 • Publication Date (Web): 26 Sep 2018 Downloaded from http://pubs.acs.org on September 27, 2018

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ACS Applied Materials & Interfaces

Investigating Switchable Nanostructures in Shape Memory Process for Amphipathic Janus Nanoparticles Bingyun Yan, Xiaotong Zheng,* Pandeng Tang, Huikai Yang, Jing He, Shaobing Zhou

School of Materials Science and Engineering, Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu 610031, China * Corresponding author: Tel: 86-28-87600896, E-mail: [email protected], [email protected]

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ABSTRACT Janus particles (JPs) have attracted increasing attention from the communities of materials science, chemistry, physics and biology. However, the nanoscale JPs that can switch shapes in response to an environmental stimulus is a significant challenge. In this article, we have demonstrated a simple procedure to fabricate the amphipathic Janus nanoparticles (JNPs) composed of hydrophilic body and hydrophobic lobe via using sudden negative pressure technique. Moreover, in response to temperature, the nanoparticles can recover to their initial nanosphere state by a switchable process, showing promising shape memory effect. Here, we can monitor the switchable nanostructures with hydrophilic and hydrophobic changes in the shape memory process of the JNPs by transmission electron microscope (TEM), dynamic light scattering (DLS) and water contact angle (WCA). Furthermore, we successfully compare the differences of shape deformation ratio and shape recovery ratio using the three test methods by the statistical analysis of Student's t test for independent samples. In addition, we also develop a hybrid magnetic Janus nanoparticles changed from the amphipathic JNPs by the selective attachment of magnetic nanoparticles with hydrophobic molecules, which shows new Janus nanostructure and shape memory property. Keywords: JNPs, shape memory, nanostructures, amphipathic, statistical analysis


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INTRODUCTION JNPs with two incompatible compositions onto the opposite sides have gained growing interests.1 −4 They are featured in flexibility, versatility, and controllable asymmetric structures.5−7 A key characteristic is that each particle features a specific property that is opposing in nature, for example, one side being hydrophilic while the other side is hydrophobic.8,9 Polymeric JNPs, acting as building blocks, which make them attractive novel units for self-assembly of complex structures.10−12 Meanwhile, they can also serve as solid surfactants.13,14 Numerous strategies have been developed to synthesize polymeric Janus particles. Synthesis processes reported for producing asymmetrical particles include surface templates and area selective modification,15 template-assisted self-assembly,16 emulsion/phase separation,17 surface-controlled nucleation and growth,18,19 and microfluidic techniques.20 Shape memory polymers (SMPs), due to their special ability to remember deformed shapes and recover these original shapes in response to external stimuli, such as temperature, electricity, magnetism, light and solution are attractive in a wide array of fields.21-26 More and more researchers are attracted by microscopic shape memory polymers due to the strong trend toward miniaturization in all technical fields.27-29 Block copolymers are good candidates due to their ability to form uniform scale domains.30-32 Multicompartment micelles (MCMs) are easily formed by self-assembly of block copolymers in selective solvents,33,34 which can further derive JNPs. However, the JNPs cannot respond to the external stimulation. Recently, we have developed shape switchable micrometer-sized particles based on a cross-linked



polymer

network

including

glycol)-poly(ε-caprolactone)

(6A

biocompatible

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six-arm

PEG-PCL)

poly-(ethylene

copolymers35

or

sucrose-poly(ε-caprolactone) (SU-PCL) copolymers.36 These particles have the ability of switching their shapes with a shape memory effect of the polymer matrix. The results illustrate that the cross-linked polymer network could show microscopic shape memory effect. Clearly, it would be attractive and challenge to combine the microscopic shape memory effect and Janus-shaped particle.37,38 Herein, in this study, we present a facile strategy towards the design and fabrication of the asymmetric JNPs with shape memory property on the basis of the cross-linked amphipathic polymer network. These amphipathic JNPs with a special structured shape composed of a hydrophilic body and hydrophobic lobe can switch their shape in response to an temperature stimulus. Moreover, we monitor the shape memory effect by TEM test, LDS test and WCA test, and compare the difference for the shape deformation ratio and shape recovery ratio each other among the test groups by Student's t test for independent samples. Furthermore, we also present the hybrid magnetic Janus nanoparticles (MJNPs) with a new Janus shape changing from the amphipathic JNPs possessing shape memory property.

RESULTS AND DISCUSSION Amphipathic Nanostructure with Shape Memory Property The polymeric nanoparticles are precisely achieved through using a solvent evaporation method as shown in Figure 1. Amphipathic SU-PCL molecules can be assembled to form nanoscale micelles with the hydrophobic PCL segment gathering


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in the center and the hydroxyl groups of sucrose toward the outside in water. Additionally, in order to fabricate the cross-linked polymeric nanoparticles (CPNPs) with well-defined network, benzophenone (BP) was used to cross-link PCL segment under UV irradiation. Consequently, the PCL segment of the CPNPs would be endowed with shape memory effect due to the chemical cross-linking points as shape-fixed phase of molecular chains.39 FT-IR was performed to demonstrate the cross-linked results of the CPNPs, as shown in Figure S1. The sucrose characteristic peaks -OH (3431 cm-1) and the PCL characteristic peaks O=C-O (1726 cm-1) are observed in all the samples, indicating the successful of sucrose ring-opening polymerization of ε-caprolactone.36 The enhanced peak at 1665 cm-1 in the spectrum of uncross-linked polymer nanoparticles (UPNPs) attributes to the characteristic peak C=O of added BP (Figure S1b). From spectrum of the CPNPs shown in Figure S1c, the BP characteristic peak is disappeared and ester peak (1726 cm-1) is much bigger than the UPNPs, which should be caused by the cross-linking reaction after UV irradiation. It may verify that the polymeric nanoparticles with cross-linked network structure are formed successfully. The molecular mechanism showing the effect of cross-linking reaction on the crystallinity of the polymeric nanoparticles is schematically illustrated in Figure 2a. The PCL molecular chain can cross-link with each other to form a cross-linking network structure under the UV light. Moreover, this polymeric network structure consists of two different units: the cross-linked PCL molecular chains and free PCL molecular chains. Therefore, the CPNPs with network structures are endowed with



shape memory property. The chemical cross-linking points as fixable phase determine the permanent shape of the polymeric network and the free molecular chains as reversible phase decide molecular switching. In addition, the PCL molecular chains are semi-crystalline structure at room temperature. Cross-linking points can inhibit the orderly motion of molecular chains so that the crystallization behavior of PCL becomes hard.39 Accordingly, the crystallization area of the PCL molecular chains decrease and the active molecular chains increase. Figure 2b,c show the XRD patterns and the degrees of crystallinity of the UPNPs and the CPNPs. The crystalline peaks at 2θ =21.3° (110) and 23.6° (200) ascribe to the PCL segments for both UPNPs and CPNPs. For the UPNPs, the diffraction peaks (2θ=21.3° and 23.6°) are higher and wider than the CPNPs. The degrees of crystallization of UPNPs and CPNPs are 42.69 % and 28.86 %, respectively. This could be attributed to the happened cross-linking which results in the decreasing crystallinity of the polymeric nanoparticles. In contrast to the influence of the cross-linking on the thermal properties, we can find that the melting points (Tm) of UPNPs and CPNPs are determined as 60.2 ̊C and 56.3 ̊C, respectively (Figure 2d). The UPNPs polymer shows the higher values of Tm than the CPNPs.40-42 This result also indicates that the existence of the cross-linking points limits the folding and ordering of the polymeric chains, leading to the increase of the activity of the PCL molecular chains. The degree of crystallinity and Tm of CPNPs decreased significantly because of the cross-linking structure indicate the potential shape memory effect and the broad application.


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We have demonstrated the formation of the cross-linked network structure through measuring the CMC of the polymeric nanoparticles. Fluorescence measurements were carried out using pyrene as a fluorescent probe to determine the CMC of UPNPs and CPNPs. It can be observed from Figure 2e,f that as the concentration of the relevant polymers increases, the fluorescence intensity of pyrene abruptly increases at a certain concentration. The CMC values of these micelles are 5.623×10-3 mg/L for UPNPs and 0.759×10-3 mg/L for CPNPs, respectively. The CPNPs are much more stable in a dilute aqueous environment than the UPNPs.43 The results further demonstrate that the cross-linking reaction have happened in the polymeric nanoparticles. Janus Nanostructure as Temporary Shape The preparing procedure of the JNPs using a sudden negative pressure technique is illustrated in Figure 3a. When the environment temperature is higher than Tm (T > Tm), the crystalline region of PCL molecular chains of the CPNPs would melt (Figure 3b). Meanwhile, the CPNPs have been exposed to a sudden negative pressure environment (P < 0.1 MPa). Consequently, because the pressure of the surrounding environment is far below the pressure at the core of CPNPs (POUT-Particle < PIN-Particle), a large amount of solvent THF molecules would escape from the center of the CPNPs. According to the forming mechanism of the microspheres by solvent evaporation and negative air pressure,44,45 we believe that the surface of nanoparticles would be perforated to form one open hole because of the rapid solvent evaporation under sudden negative pressure. Therefore, the melted PCL segment can easily gush through the hole in the



hydrophilic surface following with the violently volatilizing THF and forms a hydrophobic lobe on the open surface of the particle. When the environment temperature is immediately cooled to 0 ℃ (below Tm), the cross-linked PCL molecular chains switching the Janus shape (temporary shape) could be fixed temporally. As a result, the JNPs with the nanoscale shape memory property are obtained by the novel method. To investigate the changed nanostructure of the JNPs, TEM test was used though a solvent evaporation method. From Figure 3c, it is clear that the CPNPs possess a well-defined spherical shape and their average particle size is 64 nm. The size distribution of the CPNPs (measured by DLS) is depicted in Figure 3d. However, the CPNPs have an average diameter of 110 nm, indicating that here the particle diameter is bigger than measured from TEM image. We believe TEM method measuring the particle size in the dry state under vacuum can cause the shrinkage of the particle due to the removal of water molecules, while DLS method measures the intensity-average size of nanoparticles in the emulsion which contains the contribution from the swollen corona.46 In addition, the CPNPs possess a good dispersibility in water, indicating that the surfaces of the CPNPs are hydrophilic. As shown in Figure 3e, we found the structure of JNPs with two parts: a sucrose nanosphere as a body at one side and a cross-linked PCL segment as a lobe on the other side. Because the CPNPs have the well cross-linking structure, the spherical part of the JNPs still keep hydrophilic SU surface and the PCL molecules on the open surface of the microsphere form a new hydrophobic lobe. Furthermore, few hydrophobic PCL segments of the JNPs adsorb


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with each other. Figure 3f explains the size distribution of the JNPs, which shows that the average particle size is about 220 nm. Compared with CPNPs, the size increase of the JNPs may attribute to the part of cross-linked molecular chains breaking from the surface of the initial nanospheres and the low dispersibility of the hydrophobic PCL molecules in aqueous solution. Moreover, from Figure S2 we can see that the chemical structures were not changed from the CPNPs to the JNPs during the sudden negative pressure, indicating that only molecular state took place during the shape deformation process. Gushed hydrophobic cross-linked PCL segment makes the hydrophobicity of nanoparticles increase. To investigate the hydrophilic/hydrophobic change from the spherical CPNPs to the JNPs in the shape memory process, WCA was successfully used to monitor the switched nanostructures. Due to the high hydrophilicity of the surfaces of the CPNPs, the water droplet could not stay on the surface of the CPNPs and was absorbed immediately. Figure S3a shows the contact angles of a sessile water droplet placed on the surface of the coatings. The WCA values of the water dropped on the CPNPs reduce quickly from 80° to 30° within 15s, suggesting a perfect hydrophilic performance of the CPNPs. Interestingly, the water droplet permeates into the interior of the film quickly rather than spreading on the film, which demonstrates that the CPNPs possess strong water-absorbing capability. This phenomenon is attributed to the hydroxyl groups coming from the surface of the CPNPs. In contrast, the surface performance of the JNPs behaves differently, that is, the water droplet stays on it for a



much longer time, with the WCA decreasing progressively (Figure S3b). This is an indication of the enhanced hydrophobic nature resulting from the exposed cross-linked PCL segment. During the sudden negative pressure, the cross-linked PCL segment gushes with the THF forms a hydrophobic lobe on the surface of spherical CPNPs and provides more hydrophobic properties. In detail, it can be observed from Figure S3c that the WCA value increases to 116° compared to the spherical CPNPs. Furthermore, the WCA values of the water dropped on the JNPs film progressively reduce from 116° to 96° within 15s. The changes further demonstrate that the formed Janus-shape nanoparticles are featured in amphipathic asymmetric structure. Monitoring Nanostructure in Shape Recovery Process Figure 4 shows the change of the morphology, the size distribution and the surface properties of the nanoparticles in the shape deformation and shape recovery process. Under the sudden negative pressure, we obtain the JNPs with increased contact angle and particle size. When heated to above Tm again, the hydrophobic lobe almost disappears and the JNPs recover to hydrophilic spherical state (Figure 4b). Meanwhile, the increased contact angle (Figure 4c) and particle size (Figure 4d) almost reduce to the original values. Here, the cross-linking points and crystallization area of the PCL molecular chains and the self-assembly micelle structure of microspheres are considered as the stationary phase during shape switching process. The uncross-linking molecular chains in PCL segment are movable and defined as reversible phase. Thus, during the shape memory, the hydrophobic PCL segment gathering in the center of the micelle is


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forced to obtain the amphipathic Janus particle under the sudden negative pressure. Then, the uncross-linking molecular chains in PCL segment are reversible and move into the cavity of the nanoparticle because of the recovery force of the stationary phase during the shape recovery. Figure S4 shows the TEM images of the recovered nanospheres showing the reproducibility of shape memroy property on multiple cycles using sudden negative pressure technique. From the second shape memory cycle (Figure S4a), the cross-linked SU-PCL nanoparticles could easily deform to the Janus structure (temporary shape) and recover their initial nanosphere structure (permanent shape). Furthermore, the shape memory and recovery process could also reproduce in the third shape memory cycle (Figure S4b). Hence, we can believe that the nanoparticles have a promising shape meory effect based on the result. We further investigated the relationship between the recovery temperature and shape recovery property of the JNPs. Accordingly, a series of shape recovery behaviors at different recovery temperature ranging from 40 ̊C to 70 ̊C were performed to obtain a direct contrast. When the recovery temperatures are 40 ̊C and 50 ̊C (lower than Tm), the molecular movement of cross-linked PCL chains is restrained so that the recovery force is weak. The volumes of hydrophobic lobe of the JNPs decrease slightly (Figure S5a,b). In contrast, when the JNPs recover at 60 ̊C, the activity of the molecular chain increases obviously and the JNPs can show an obvious shape memory effect (Figure S5c). When recovery temperature reach 70 C ̊ , the JNPs almost completely recover to their initial spherical shape (Figure S5d).



Figure S6a,b show the changing data of DLS and WCA with the increase of the recovery temperature. When the recovery temperatures are 40 ̊C and 50 ̊C, the average particle sizes of the JNPs decrease slightly to 205 nm and 193 nm, and the WCA values of the JNPs decrease slightly to 109° and 106°, respectively. In contrast, when the recovery temperature is heated gradually to 60 ̊C (just above the Tm), the average particle sizes of the JNPs decreases to 132 nm and the contact angle of the JNPs decreases to 95°, respectively. When recovery temperature reaches 70 ̊C, the average particle size of the JNPs decreases to 117 nm and the contact angle of the JNPs decreases to 83°, respectively. These results are explained by the fact that the mobility of PCL molecular chain becomes more flexible and soft when the recovery temperature is higher than Tm. Based on above analysis, in order to further explore the shape recovery speed for the amphipathic nanostructures in the recovery process, we investigated the relationship between the recovery shape of the JNPs and recovery time at a recovery temperature of 70 C ̊ . Figure S7 shows the shape recovery morphology at different recovery time. It is clearly seen that the volume of the hydrophobic segments of the JNPs decrease slightly in the first 30 seconds (Figure S7a,b). However, when the recovery time increases to 60 seconds, the hydrophobic lobes decrease drastically (Figure S7c). Moreover, after 120 seconds, the hydrophobic lobes almost disappear and the JNPs completely recover to their initial spherical shape (Figure S7d). Figure S8a,b show the quantitative change of DLS and WCA with the increase of recovery time. In the beginning 30 seconds, the average particle size of the JNPs


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decreases to 174 nm and the contact angle of the JNPs decreases to 98°, respectively. When the recovery time reaches to 60 seconds, the average particle size of the JNPs decreases to 123 nm and the contact angle of the JNPs decreases to 87°, respectively. When the recovery time reaches to 120 seconds, the average particle size of the JNPs decreases to 117 nm and the contact angle of the JNPs decreases to 83°, respectively. The result demonstrates that the cross-linked amphipathic nanoparticles have the capability to be fixed into a temporary shape and recover to their original shape due to the excellent entropic elasticity of the polymer when heated.47 We further compared the shape deformation ratio and shape recovery ratio of the switched nanostructure during shape memory process of the amphipathic polymer using the DLS test and the WCA test. As shown in Figure S9, we can clearly calculate that the shape deformation ratios of the TEM test, the DLS test and the WCA test are 45%, 101% and 45%, respectively. While shape recovery ratios of the TEM test, the DLS test and the WCA test are 93%, 94% and 92%, respectively. Student's t Test for Shape Memory Property To evaluate the accuracy and relativity of the TEM, DLS and WCA test methods monitoring the switchable nanostructures in the shape memory process of the JNPs, Student's t test for the independent samples from the three test groups were carried out by IBM Spass Statistics 22. Table S1 shows the results of t test about the average shape deformation ratio for the independent samples from the DLS test & the TEM test, the WCA test & the TEM test and the DLS test & the WCA test. Because the p-values of Levene's test are 0.952, 1.000 and 0.233, respectively, we can assume that



the variances of all coupled sample groups are the same. Since the p-values of t test for DLS test & the TEM test and DLS test & the WCA test are all low than 0.001, so there is significant difference on the average shape deformation ratio between the two compared tests. In contrast, because the p-value of t test for the WCA test & the TEM test is 1.000, there is no significant difference on the average shape deformation ratio of the independent samples between the two tests. Hence, we conclude that the WCA test and the TEM test can more accurately express the shape deformation ratio of the JNPs than the DLS test. Table S2 shows the results of t test about the shape recovery ratio for the independent samples from the DLS test & the TEM test, the WCA test & the TEM test and the DLS test & the WCA test. The p-values of Levene's test are 0.309, 0.366 and 0.803, respectively. Thus, we can assume that the variances of all coupled sample groups are the same. As shown in the Table S2, the p-values of t test for DLS test & the TEM test, the WCA test & the TEM test, and the DLS test & the WCA test are 0.247, 0.840, 0.159, respectively. So, there is no significant difference on the average shape recovery ratio of the independent samples between the compared tests. The result demonstrates that all of test methods can accurately monitor the shape recovery process by the expressed consistency of the shape recovery ratios. Switching Janus Nanostructure for Hybrid MJNPs To further investigate the amphipathic nanostructure of the JNPs, the oleic acid capped iron oxide nanoparticles (OACIONs) was used to adsorb the exposed hydrophobic molecules by the hydrophobic effect,48,49 as illustrated in Figure 5a.


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Subsequently, we obtained the hybrid MJNPs with a strong magnetic domain and a polymeric microsphere domain. As the TEM image and highresolution shown in Figure 5b,c, the average diameter of these monodisperse OACIONs is about 9 nm. From the Figure 5d, we clearly observe that the composite MJNPs are demonstrated as the asymmetrical hybrids with two parts: inorganic iron oxide nanoparticles adsorbing the exposed PCL on one side and the hydrophilic polymeric microsphere on the other side. Here, it is very interesting that the switchable nanoparticle may form new Janus nanostructure from the JNPs to MJNPs. These magnetic Janus particles are of interest for use in applications such as responsive materials and sensors due to their addressability by external fields.50,51 The magnetic properties of the MJNPs and the OACIONs have been investigated using VSM. As shown in Figure 5e, they have the magnetic responses at saturation magnetizations of 17.5 emu g-1 and 59.5 emu g-1, respectively, indicating that the hybrid MJNPs do not exhibit hysteresis at low magnetic field and room temperature. From the FT-IR spectrum of the composite MJNPs (Figure S10a), we could find that the characteristic peak of the -OH stretch at 3437 cm-1 and the O=C-O at 1726 cm-1 belongs to the JNPs. The peak at 594 cm-1 is assigned to the Fe-O group, demonstrating the adsorption of the OACIONs in the hydrophobic domain. In order to estimate the crystalline structure of the MJNPs, XRD analysis was employed. Figure S10b shows the patterns of the JNPs, the MJNPs and the OACIONs. The two strong diffraction peaks at 2θ = 21.4̊ (110) and 23.8̊ (200) observed in the XRD pattern correspond to the SU-PCL copolymer. The apparent peaks at 2θ = 31.28̊ (220), 35.68̊



(311) and 43.28̊ (400) are attributed to the OACIONs. Moreover, these characteristic peaks can also be observed in the XRD pattern of composite MJNPs. The results demonstrate that the crystallinities of the OACIONs and the cross-linked PCL segment are not affected after containing in the composite MJNPs. In order to further investigate the distribution of the occurred Janus nanostructure for the MJNPs, EDS mapping analysis was carried out. The corresponding EDS elemental mappings illustrate the actual distribution of O, C and Fe elements, respectively, as shown in Figure S11. The location of Fe element corresponds to the OACIONs and O element corresponds to both Fe3O4 nanoparticles and the JNPs, while the location of C element includes the JNPs, which certify that the OACIONs are mainly distributed in the PCL segment of the JNPs. The MJNPs have not only an asymmetric organic-inorganic hybrid structure but also the superparamagnetic properties, showing the unique property. We demonstrated the shape memory effect of the hybrid MJNPs with the different weight ratios of the OACIONs. Figure S12 shows the TEM images of the composite with the weight ratios of Fe3O4 at 3, 5, 10 and 15%, respectively. From these micrographs, we clearly observe that with the OACIONs component adding, the amount of the OACIONs in the composite MJNPs gradually increase. These result indicates that the magnetic OACIONs can be used to selectively label the PCL side of the JNPs by the hydrophobic effect and the sizes of the magnetic domain in the Janus nanostructure are facilely controlled by changing the amount of the OACIONs. The shape recovery behaviors of the MJNPs are shown in Figure S13. The shape


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recovery ratio decreases with the increase of the OACIONs content in the composite. When OACIONs contents are from 0 to 5%, the MJNPs show the desirable shape recovery effect. However, when the OACIONs content is higher than 5%, the shape recovery ratio decreases sharply due to the excessive OACIONs coated on the PCL chains, which can restrict the recovery movement of PCL molecular chains. We can also see the same recovery process of the MJNPs with the OACIONs at a weight ratio of 3% and 15%, respectively, from the Figure S14.

CONCLUSION In summary, we have successfully developed a novel procedure to fabricate the amphipathic JNPs using sudden negative pressure technique. The amphipathic structure of the JNPs composed of hydrophilic sucrose and hydrophobic cross-linked PCL parts, which possess the switchable ability to recover to the initial spherical shape at a temperature above Tm. We have also investigated the shape memory process at nanoscale using the monitorable methods such as TEM test, the WCA test and the DLS test. Furthermore, the statistical analysis of t test for the independent samples of three tests accurately evaluated the relativity of the switchable nanostructures in the shape memory and recovery process of the JNPs. More interestingly, the anisotropic Janus nanostructure may change from the hydrophilic/hydrophobic copolymer for JNPs to amphipathic/magnetic hybrid for MJNPs. When the amounts of the OACIONs are less than 3%, the MJNPs display an excellent shape memory effect. The unique property of the switchable nanostructures in shape memory process for the novel responsive nanomaterial may be used in the broad miniaturization fields such as



drug delivery, catalysis, nanorobot and electromagnetic devices. Moreover, the facile analysis methods in this paper pave a new prospect for mornitoring the multiple changes of the amphipathic structures at the nanoscale.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org. Additional information includes FTIR spectra, WCA image of the UPNPs, CPNPs and JNPs. TEM images, Particle sizes and WCA data of JNPs in shape recovery process at different temperatures and times. Student's t test about the average shape deformation ratio and shape recovery ratio for the independent samples from the DLS test, the TEM test and the WCA test. FTIR spectra, XRD patterns, EDS mapping, TEM images and shape recovery ratios of MJNPs.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected], [email protected] Notes The authors declare no competing financial interests.

ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China under Grant (51203130), the Central Universities under Grant (2682013CX001), and


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Sichuan Province Youth Science and Technology Innovation Team (Grant No. 2016TD0026).

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Figure 1. Schematic of preparing CPNPs through self-assembly of amphiphilic SU-PCL copolymer in water and cross-linking of PCL molecules under UV illumination.


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Figure 2. (a) The schematic molecular mechanism of preparing cross-linked network structure. The characterization of UPNPs and CPNPs. (b) XRD curves, (c) the degrees of crystallinity and (d) DSC curves. CMC of (e) the UPNPs and (f) the CPNPs, derived from the plot of I339/I333 ratio versus logarithm of micellar concentrations. After calculation, CMC of the UPNPs was 5.623×10-3 mg/mL, while the CPNPs was 0.759×10-3 mg/mL.



Figure 3. (a) Programming of the spherical CPNPs to JNPs under sudden negative pressure. (b) The schematic molecular mechanism of preparing JNPs during the shape memory process. (c) TEM image and (d) the size distribution of the CPNPs prepared from SU-PCL copolymer. (e) TEM image and (f) the size distribution of the amphipathic JNPs.


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Figure 4. (a) Schematic, (b) TEM images, (c) WCA images and (d) DLS images of the amphipathic JNPs in shape memory and recovery process.



Figure 5. (a) Schematic of the preparing process of the hybrid MJNPs switching to the new Janus nanostructure from JNPs. (b) TEM image and (c) highresolution TEM image of of the OACIONs. Inset: selected area electron diffraction (SAED) pattern of the OACIONs. (d) TEM images of the MJNPs and highresolution TEM image of of the OACIONs/PCL segment. (e) Magnetization hysteresis curve of the OACIONs and the MJNPs.


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