Reversible Assembly and Disassembly of Amphiphilic Assemblies by

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Reversible Assembly and Disassembly of Amphiphilic Assemblies by Electropolymerized Polyaniline Films: Effects Rendered by Varying the Electropolymerization Potential Kingshuk Dutta* and Patit P. Kundu* Advanced Polymer Laboratory, Department of Polymer Science and Technology, University of Calcutta, 92, A.P.C. Road, Kolkata −700 009, India S Supporting Information *

ABSTRACT: Polymer films that respond to a variety of stimuli are attractive candidates for location-specific guest molecule delivery. These systems release the guest molecules by polymer erosion; thus, these are mono-use systems. If a polymer film is used to disassemble amphiphilic assemblies containing sequestered guest molecules, the polymer erosion issue can be circumvented. However, charge-bearing vinyl polymers, upon interaction with amphiphilic assemblies, are known to adapt to a conformation that results in encapsulating guest molecules instead of releasing them. On the contrary, it has earlier been reported that a rigid, charge-bearing, and water-insoluble conjugated polyaniline film can effectively disassemble amphiphilic assemblies without causing much harm to the film. Herein, we demonstrate the effect rendered by varying the electropolymerization potential on the interaction efficiency between the positive charge-bearing polyaniline film and oppositely charged amphiphilic assemblies. In addition, it is also demonstrated that a film of oxidized polyaniline can be regenerated for repetitive disassembly of the amphiphilic assemblies, and concomitant guest molecule delivery.

1. INTRODUCTION Polymers capable of releasing guest molecules in the absence1,2 and in the presence of stimuli, such as pH,3,4 ionic strength,5 light,6,7 electric potential,8−10 and temperature,11,12 have been investigated toward integrating them on a device and developing pharmacy-on-a-chip.13−15 Among the stimuli, electrical potential is preferable because it can be applied rapidly, locally, and using miniaturized equipment under biological conditions.16 Irrespective of the stimuli employed in these systems, the polymer films erode to release guest molecules; hence, these are mono-use systems. Considering this, it is enticing to develop an approach that releases guest molecules by a nonerodible mechanism, as this will render the possibility of longevity and reuse. In general, if the guest molecules are encapsulated in the polymer film, their release is possible only with the erosion of the film. Thus, for a nonerodible mechanism to operate, the guest molecules should not be a part of the polymer film. On the other hand, there exists another class of nanoscopic release systems that have hydrophilic exteriors with stimuli-sensitive functionalities.17−24 They have been widely explored for encapsulation and release of payloads. Considering these two systems, it is enticing to develop a nonerodible polymeric substrate, in which, if used to trigger the disassembly of the nanoscale assemblies, a synergistic alike result should evolve (Figure 1). In this context, it is easier to conceive that a polyelectrolyte bearing charges opposite to that of the nanoscopic assemblies © 2013 American Chemical Society

Figure 1. Schematic representation of surface triggered guest molecule release from amphiphilic assemblies.

should, by rationale, stimulate the disassembly process owing to the strong attractive interactions between them. However, in the case of unsupported polymers, it is known that such an interaction essentially leads to the formation of other assemblies, having both orientation and features similar to their virgin counterpart.25−27 This is due to the flexible polymer’s ability to adapt to new conformations.28−31 Taking this into account, it Received: March 20, 2013 Revised: June 3, 2013 Published: June 6, 2013 7797

dx.doi.org/10.1021/jp402748w | J. Phys. Chem. B 2013, 117, 7797−7805

The Journal of Physical Chemistry B

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was conceived that a polymer film deposited on a support can resist conformational changes and, in principle, can induce oppositely charged assemblies to disaggregate instead of reforming assemblies. Conducting polymers (CPs) having a rigid conjugated backbone fulfill these criteria and are, thus, suitable candidates to be employed for this purpose.32 In addition, their oxidized form possesses delocalized positive charges that can efficiently interact with the oppositely charged hydrophilic faces of amphiphile units and, thus, can act as a stimulant. The relative ease of executing a command over the CP’s charge33 renders an effective control over the overall process of breakage and subsequent release of payloads from the amphiphilic assemblies (AAs). Furthermore, the charge on the CP can be easily regenerated after the payload release by applying a small potential, which affords the possibility of repeated release of guest molecules using the same CP substrate. This is in contrast to the existing erosion-based approaches, which rules out the possibility of reusing the system.16,34,35 On the basis of this idea, Dutta et al.36 demonstrated the disassembly of AAs of sodium dodecylsulfate (SDS) by rigid and water-insoluble oxidized polyaniline (OxPAni). They also showed that the disassembly process was a surface-induced phenomenon, and the rate of disassembly was, therefore, found to vary with different polymer surface morphologies. In addition, it was reported that the disassembled SDS amphiphilic molecules (AMs) remain attached onto the OxPAni film surface by virtue of electrostatic interaction. This particular phenomenon induced surface hydrophobic properties to the otherwise superhydrophilic OxPAni film surface. We recently demonstrated that a similarly induced surface wettability can be tuned by modulating the electropolymerization potential of OxPAni, as well as the concentration of SDS.37 These reports led us to conceive that the interaction efficiency and the rate of disassembly of AAs can be fine-tuned by varying the electropolymerization potential. In this article, we report that (a) the rate of disassembly of AAs and the amount of payload released can be fine-tuned by precisely controlling the applied potential and (b) a single OxPAni film can be utilized for reversible and repetitive disassembly of AAs by reversing the applied electric potential. In effect, the results reported in this article may profoundly impact the field of payload entrapment and delivery.

was maintained between 200 and 600 nm. The particle size of the assemblies was recorded with a Brookhaven 90plus particle size analyzer. Scanning electron micrographs (SEM) were recorded with a Jeol JSM 5600LV instrument. A Digidrop contact angle meter was used to measure water drop contact angles (WDCAs). 2.2. Electropolymerization of Ani. OxPAni films were prepared by electropolymerization of 0.1 M Ani dissolved in 0.1 M HCl solution. For this purpose, the monomer Ani was first completely dissolved in DI water (acidified with 0.1 M HCl), by thorough stirring. Ag/AgCl was used as the reference electrode for the electropolymerization process. Pt foils (99.9% purity) were used as both the working and the counter electrodes. Different films were prepared by applying different potentials of +0.1, +0.2, +0.3, +0.4, +0.5, +0.6, +0.7, +0.8, +0.9, and +1.0 V. All the films were prepared by repeatedly sweeping at 0.1 V s−1 over the range of −0.2 V to the respective upper potential values, using an electropolymerization time of 25 s for each film. Electropolymerization solutions were maintained at a temperature of 27 ± 2 °C. The used geometric area of the working electrode was 2.5 cm2, whereas that of the counter electrode was 3 cm2. The following parameters were employed during the electropolymerization process: (a) initial potential = −0.2 V, (b) low potential limit = −0.2 V, (c) high potential limit = +0.1 to +1.0 V, (d) scan rate = 0.1 V s−1, (e) segment = 20, (f) sample interval = 0.001 V, (g) quiet time = 2 s, (h) sensitivity = 0.001 A V−1. Figure S1 (Supporting Information) represents the cyclic voltammetry (CV) plot obtained for the electropolymerization of Ani at +0.6 V. After each electropolymerization, the respective films were rinsed thoroughly in HCl and subjected to CV characterization. CV characterization of the polymer films was done in deaerated 0.1 M HCl at 27 ± 2 °C by performing single scans at 0.1 V s−1 over the range of −0.2 V to the respective upper potential values. The anodic charge density was measured from the corresponding area under the curve. 2.3. Sample Preparation and Measurements. Solutions of SDS AAs were prepared by dissolving 6 mM SDS in 5 mL of DI water. The pyrene encapsulation was carried out by following the reported procedure, and the concentration of pyrene was maintained at 10−6 M for all the experiments.38 The pyrene molecule is a widely studied probe molecule that exhibits multiple emission peaks, and the ratio of the peak intensity at 372 nm (I1) to that at 384 nm (I3) provides information about the environment that faces the probe. For this study, pyrene was entrapped in SDS AAs, and I1/I3 was found to be 0.97, a value typical of pyrene’s presence in a hydrophobic environment.38 To study the disassembly and release of guest molecules, the films were immersed in solutions of pyrene-encapsulated SDS AAs and were allowed to stand quiescently. For UV−vis analysis, the same sample preparation, as described for fluorescence spectroscopy, was employed. For dynamic light scattering (DLS), aliquots from reaction vials, both before and after interaction, were subjected to particle size analysis. The samples were taken in a quartz cuvette after filtering through a 600 nm polycarbonate membrane. This step was taken as a precaution to avoid any interference from PAni during the DLS measurements. It should be noted that the size of the assemblies was found to be 6 nm,39 which is 100 times smaller than the pores (600 nm) of the membrane. Therefore, we anticipated the assemblies to remain unaffected during the filtration process. SEMs of the electropolymerized films were recorded to observe the presence of any micro/nanostructures. The SEM micrographs of gold-sputtered PAni films were recorded at a magnification of 10 000×, a voltage of 30.00 kV, det = ETD, and a WD of 7.7 mm. The SDS attached

2. EXPERIMENTAL METHODS 2.1. Materials and Instruments. Aniline (Ani), sodium dodecylsulfate (ACS reagent), cetyltrimethylammonium bromide (CTAB), and pyrene were of analytical grade and were purchased from Sigma Aldrich. Reagent grade HCl was purchased from Loba Chemie. All the chemicals were used as received. Deionized (DI) water was used for all the experiments and was collected from a Millipore Q Gard water purifier and further purified by filtering through a 30 nm polycarbonate membrane purchased from SPI pore. The 30 nm pore membrane was mounted on a stainless steel filter holder, which was then fitted onto a plastic syringe. Electropolymerization of Ani was done with a CH Instruments 600D potentiostat/galvanostat. Pure Pt foils (99.9%), purchased from Arora Matthey Ltd., were used as working and counter electrodes. Fluorescence emission spectra were recorded with a Cary Eclipse fluorescence spectrophotometer. Excitation was done at 331.5 nm, and emissions were recorded in the 340−450 nm wavelength range. The slit width was fixed at 2.5 nm. The scan rate was fixed at normal. UV−vis absorption spectra were recorded with a Cary Eclipse UV−vis spectrophotometer. The wavelength window 7798



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Figure 2. DLS correlation function plots of (a) initial SDS AAs, (b) disassembled amphiphiles obtained after interaction of SDS AAs with OxPAni film, (c) intact SDS AAs after interaction with NeuPAni film, (d) initial CTAB AAs, and (e) intact CTAB AAs after interaction with OxPAni film.

films were subjected to WDCA measurements. For this purpose, 3 μL of DI water was dropped onto the PAni film surface from a hydrophobized needle mounted on a microsyringe. Each image of the water drop was taken a few seconds later, to avoid any problems arising due to drying of the drop. Five separate measurements were taken for each sample at different positions on the film surface, and the average value was adopted. All the dipping steps were carried out at 27 ± 2 °C. All the experiments were repeated at least five times, and the average value was adopted and reported.

3. RESULTS AND DISCUSSION 3.1. Dynamic Light Scattering Analysis. The OxPAniinduced disassembly process was first studied by the DLS technique. The aggregate size of the SDS AAs was determined to be 6 nm. The corresponding correlation function plot is shown in Figure 2a. To monitor the disassembly process, OxPAni-coated Pt electrodes, prepared at different electropolymerization potentials, were dipped in vials containing 5 mL of 6 mM SDS solutions. This quantity was maintained for all the experiments. It 7799



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Figure 3. (a) Changes in pyrene fluorescence emission intensity ratios with time of interaction for OxPAni films prepared at different potentials. (b) Maximum pyrene release percentages obtained for OxPAni films prepared at different potentials. (c) UV−vis spectra of pyrene showing progressive decrease in the absorbance of the 338 nm peak, indicating release of entrapped pyrene upon interaction with OxPAni film prepared at +0.6 V potential. (d) Variation of rate of pyrene release.

was observed that, in the case of films electropolymerized at +0.6, +0.7, +0.8, +0.9, and +1.0 V, the peak corresponding to 6 nm completely disappeared, which essentially indicates the complete disassembly of AAs.36 The representative correlation function plot obtained for OxPAni film prepared at +0.6 V, after interaction with SDS AAs, is shown in Figure 2b. From this plot, we could not determine any particle size. However, in the case of the films electropolymerized at +0.1, +0.2, +0.3, +0.4, and +0.5 V, we observed no or incomplete disassembly. Because the efficiency of electrostatic interaction between the negatively charged AAs and the positive charge-bearing OxPAni film was dependent on the charge density present on the OxPAni film, it was anticipated that disassembly was likely to occur only above a certain applied electrical potential. We reported in an earlier work that the maximum charge density was formed for films electropolymerized at potentials of +0.6 V and above.37 The results obtained here indicate that the best interaction efficiency takes place at and above this potential value. To confirm that the disassembly of SDS AAs took place only due to the electrostatic interaction between the positive charges on the OxPAni films and the negative charges of the AAs, we performed two control experiments: (a) interaction of SDS AAs with neutral PAni (NeuPAni) film possessing no charges and (b) interaction of positive charge-bearing AAs of CTAB with OxPAni film prepared at +0.6 V. Both of these control experiments produced no disassembly, as can be seen in Figure 2c−e.

3.2. Fluorescence Emission Spectroscopic Analysis. To determine the effect rendered by the different electropolymerization potentials on the rate of release of entrapped payload, we performed fluorescence emission spectroscopy of a well-studied probe molecule, pyrene. For this purpose, the change of I1/I3 was monitored against time of interaction. From Figure 3a, it can be seen that the same films that induced disassembly of AAs exhibited a maximum release of pyrene from the core of the assemblies into the surrounding aqueous medium. This was realized from corresponding changes in the intensity ratio values from the initial 0.97 to about 1.5.36,38 On the other hand, the films electropolymerized at +0.5, +0.4, +0.3, +0.2, and +0.1 V resulted in a change of intensity ratio from the initial 0.97 to 1.1, 1.03, 0.99, 0.97, and 0.97, respectively. This result was due to the fact that the films electropolymerized at potentials of +0.6 V and above possessed maximum charge density, whereas the films electropolymerized at lower potentials than +0.6 V possessed lesser charge densities. In addition, the charge density decreased with decreasing potential below +0.6 V. This finding compliments our previously reported work on surface wettability,37 as well as the work reported by Dutta et al.36 From Figure 3a, it can also be realized that the presence of a maximum charge density induces a faster rate of disassembly of AAs. The films prepared at potentials of +0.6 V and above exhibited an almost constant disassembly time of about 80 min. Because the other films effected no or incomplete disassembly, determination of rates of 7800



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(Figure 3b). The gradual change in the absorption intensity of the 338 nm peak of pyrene obtained upon interaction of SDS AAs with OxPAni film electropolymerized at +0.6 V is shown in Figure 3c. The films prepared at +0.7, +0.8, +0.9, and +1.0 V induced a pyrene release of 93.4, 93.6, 93.3, and 93.4%, respectively (Figure 3b). Although these values are lower than the value of 93.8% obtained for the film prepared at +0.6 V, the differences are negligible and can be considered to be within the range of instrumental error. Nevertheless, the films polymerized at +0.5, +0.4, +0.3, +0.2, and +0.1 V resulted in a corresponding release percentages of 32.1, 15.9, 5.7, 1.5, and 1.7%, respectively (Figure 3b). As pointed out earlier, because these films effected no or incomplete disassembly, comparing the rates of disassembly for these films with that prepared at +0.6 to +1.0 V seems irrelevant. However, from the time required to achieve a certain percentage of pyrene released, it can be easily realized that the presence of higher charge density resulted in faster release (Figure 3d). The control experiments, as expected, exhibited no release of entrapped pyrene (Figure 3d). From the above results, it can be safely concluded that the films possessing maximum charge density resulted in the maximum extent of disassembly, rate of disassembly, and rate and amount of payload release. One reason for concern involved in studying the disassembly of AAs using pyrene as a probe molecule is the possibility of interaction between pyrene’s aromatic rings and Ani monomers. In an earlier work, we showed that pyrene can be effectively used as a plug molecule to fill the hydrophilic voids created on an electropolymerized OxPAni film by the uneven distribution of the long hydrocarbon tails of SDS amphiphiles.37 In fact, pyrene got entrapped within the voids due to the hydrophobic surrounding of the hydrocarbon tails, and complete entrapment took place after dipping the SDS-attached OxPAni film in an aqueous solution of pyrene for about 24 h. However, in this present work, the much less dipping time of about 2 h was not sufficient for the entrapment of pyrene molecules within the voids. The high I1/I3 and percent pyrene release values obtained suggest that the whole amount of pyrene that got released upon disassembly was present in the aqueous solution.38,40,41 Nevertheless, we carried out a control pyrene fluorescence emission experiment, wherein we dipped an OxPAni film prepared at +0.6 V into a 10−6 M aqueous solution of pyrene, containing no amphiphiles. The result obtained is plotted in Figure S2 (Supporting Information), from which we can see that the initial I1/I3 value of about 1.5 remained constant over a time period of 120 min. This result further confirms that, within the time period involved in the disassembly process, the pyrene molecules did not interact with the polymer film. 3.4. Water Drop Contact Angle (WDCA) and SEM Analysis. We have, in an earlier article, reported that OxPAni films, after interaction with SDS AMs, exhibited an initial superhydrophilic-to-hydrophobic transition.37 The reason found to be responsible behind this transition of surface wettability was (a) charge neutralization of positive charges on the OxPAni film surface by the negative charges present in the head groups of the attached AMs and (b) covering of the surface of the OxPAni film by the long hydrocarbon tails of the attached AMs. In addition, the amphiphile-attached OxPAni film exhibited a strong adhesive force toward a drop of water, preventing it from rolling or dropping down. In effect, the amphiphile-attached OxPAni film was shown to exhibit two important effects, namely, the “Lotus effect” and “Petal effect”.42−45 This present work created a situation, whereby the disassembled AMs shall remain attached onto the OxPAni film surface and, thus, shall induce surface

Figure 4. WDCA images representing surface hydrophobicity of (a) untreated OxPAni film prepared at +0.6 V potential, and after interaction with SDS AAs of films prepared at (b) +0.1, (c) +0.2, (d) +0.3, (e) +0.4, (f) +0.5, and (g) +0.6 V potentials.

disassembly for these films seems irrelevant. However, from the time required to achieve a certain change of the intensity ratio, it can be easily realized that the presence of higher charge density resulted in faster disassembly. For example, for inducing a change of intensity ratio from 0.97 to 1.1, the film prepared at +0.6 V required a time of about 20 min, whereas the film prepared at +0.5 V required a time of about 40 min (Figure 3a). 3.3. UV−vis Absorption Spectroscopic Analysis. Determination of the amount of payload released is extremely important in realizing the efficiency of a delivery mechanism. Therefore, we carried out the UV−vis absorption spectroscopy of the probe molecule pyrene and determined the percentage of pyrene released upon interaction by employing the following relation40 % Pyrene release = (1 − I /I0) × 100

where I0 is the absorption intensity of the 338 nm peak before interaction, whereas I is the same obtained at different time intervals after the start of interaction. The gradual decrease in the absorption intensity at 338 nm indicated the release of pyrene payload from SDS AAs.40,41 From the above relation, we found that the film electropolymerized at +0.6 V showed the maximum release percentage, that is, 93.8% 7801



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Figure 5. SEM micrographs of OxPAni films exhibiting no change in surface morphologies upon changing the electropolymerization potentials: (a) +0.2, (b) +0.4, (c) +0.6, (d) +0.8, and (e) +1.0 V (magnification: 10 000×; scale: 10 μm).

hydrophobicity. Therefore, it was interesting to check whether the varying electropolymerization potential, and the resulting interaction with SDS AAs, brought about any changes to these effects. Accordingly, we carried out WDCA analyses of the different films prepared at different potentials. From Figure 4, it can be seen that, upon increasing the applied potential from +0.1

to +0.6 V, the WDCA exhibited a progressive increase. However, upon a further increase in potential beyond +0.6 V, the WDCA showed no further increase and remained almost constant. These results compliment well with the results we obtained so far, wherein the films prepared at potentials at and above +0.6 V were able to disassemble the AAs. 7802



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3.5. Charge Density Calculation of the Electropolymerized OxPAni Films. Because the disassembly process is a direct consequence of the electrostatic interaction between the positive charges on the polymer film and the negative charges on the amphiphiles, and both the rate and the extent of disassembly were found to be directly affected by the variation of the values of the surface charges of the films, it is very important to determine these values for the films prepared at different potentials. The anodic charge density (Qa) of the films prepared at +0.1 to +0.6 and +1.0 V were determined from the area under the curve of their respective CVs. Table 1 represents the calculated values of the anodic charge density. Again, during the electropolymerization of the individual films, the anodic current measured during each potential sweep was integrated to yield the anodic electropolymerization charge density (Qe). Table 1 represents the obtained values. From the table, it can be clearly seen that both Qa and Qe increased with increasing applied potential from +0.1 to +0.6 V. However, the films prepared at +0.6 and +1.0 V showed almost identical Qa and Qe. These results tally exactly with the results obtained so far, and further confirm our observations. 3.6. Reversibility and Repeatability of the Disassembly Process. The prospect of achieving reversible, repeatable, and controlled assembly and disassembly is very exciting, and has been reported by several authors.47−49 In the context of this work, the positive charges on the OxPAni films can be easily withdrawn by applying a reduction potential of −0.2 V with respect to a quasi reversible Pt reference electrode. Under this condition, the OxPAni film gets converted to NeuPAni film, and thus, the amphiphiles get ejected from the polymer surface and move into the aqueous solution. Because the attachment of the AMs onto the polymer film was solely due to the prevailing electrostatic interaction, there remains no urge for the AMs to remain attached onto the film surface after the positive charges on the film get withdrawn. If all the AMs that were bound to the OxPAni surface get released, then this shall lead to the concentration of AMs within the solution to reach the initial critical micelle concentration (CMC). This, in turn, shall lead to reformation of AAs and subsequent entrapment of pyrene within the reformed assemblies. We studied this possibility by employing the pyrene fluorescence emission spectroscopy and were gratified to observe that the detached AMs indeed reassembled to reform the AAs (Figure 6a). Moreover, we were able to repeat this disassembly assembly phenomenon for over a period of 12 cycles, after which the quantity of release decreased, possibly owing to the degradation of the polymer. A representative percentage of pyrene release versus number of cycles plot obtained for the OxPAni film prepared at +0.6 V is represented in Figure 6b. From a different viewpoint, using the same OxPAni substrate to reversibly disassemble and assemble the AAs for 12 cycles essentially implies the repeatability and reusability of the substrate films prepared at and above a +0.6 V potential. In addition, we were able to reuse the same film substrate to cause various predetermined amounts of payload release by precisely adjusting the applied potential between +0.3 and +0.6 V. This result shall be particularly prospective at conditions when different doses of payload release are required at different points of time.

Table 1. Variation of Anodic Charge Density (Qa) and Anodic Electropolymerization Charge Density (Qe) with Applied Electropolymerization Potential electropolymerization potential (V) +0.1 +0.2 +0.3 +0.4 +0.5 +0.6 +1.0

anodic charge density (Qa) (C cm−2) −7

8.09 × 10 2.01 × 10−6 2.55 × 10−6 1.11 × 10−4 2.40 × 10−4 2.10 × 10−3 2.07 × 10−3

anodic electropolymerization charge density (Qe) (C cm−2) −5

3.26 × 10 8.10 × 10−5 1.02 × 10−4 4.53 × 10−3 9.78 × 10−3 8.49 × 10−2 8.45 × 10−2

Qe/Qa 40.3 40.3 40.0 40.8 40.7 40.4 40.8

Figure 6. (a) Reversibility of the assembly disassembly phenomenon of SDS AAs, and (b) reusability of OxPAni film substrates for disassembly of AAs.

The increase in surface hydrophobicity has often been attributed to an increase in surface roughness.42−46 Therefore, the increase in amphiphile-attached OxPAni surface hydrophobicity with an increase in applied potential demands an investigation of whether the increase in applied potential brought about any changes in the films’ surface morphology. Figure 5 represents the SEM micrographs of the OxPAni films electropolymerized at different potentials. From the micrographs, no changes in surface morphology could be identified. Therefore, this confirms that the interaction between the OxPAni film surface and the SDS AAs was exclusively responsible for the observed increase in surface hydrophobicity.

4. CONCLUSIONS In summary, we have utilized a charge-bearing, water-insoluble, and rigid OxPAni film to disassemble AAs. The disassembly phenomenon took place due to the prevailing electrostatic 7803



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interaction between the positive charges on the OxPAni film and the negatively charged head groups of the AAs. This phenomenon was characterized by the DLS, pyrene fluorescence emission, and UV−vis absorption analyses. We have also demonstrated that the extent of disassembly, the rate of disassembly, and the rate and amount of payload release can be fine-tuned by precisely controlling the electropolymerization potential. Film synthesized at and above a potential of +0.6 V resulted in maximum interaction efficiency with the AAs by virtue of possessing the maximum charge density. The fastest disassembly time of about 80 min was observed, with a corresponding payload release of about 94%. In addition, the interaction pattern with the AAs was also found to be dependent on the applied electrical potential, as indicated by the WDCA analysis. Most importantly, the disassembly process was found to be reversible and could be tuned by altering the applied potential between +0.6 and −0.2 V. In addition, the OxPAni film substrates were found to be reusable for over a period of 12 cycles, as indicated by the repeatability of the disassembly process induced by them. Furthermore, the amount of payload release could be fine-tuned by precisely adjusting the applied potential.

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ASSOCIATED CONTENT

S Supporting Information *

Cyclic voltammetry plots representing the electropolymerization of Ani at +0.6 V and fluorescence emission analysis of the interaction between pyrene and OxPAni film. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (P.P.K.), kingshukdutta.pst@ gmail.com (K.D.). Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS K.D. would like to thank Dr. K. Krishnamoorthy for valuable discussions and to the Council of Scientific and Industrial Research (CSIR), India, for a Senior Research Fellowship.

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REFERENCES

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Article

NOTE ADDED AFTER ASAP PUBLICATION This paper was published ASAP on June 17, 2013. Figure 3c has been replaced. The corrected version was reposted on June 27, 2013.

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Reversible Assembly and Disassembly of Amphiphilic Assemblies by

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