Fabrication of Functional Polymer Structures through Bottom-Up

Subscriber access provided by UNIV OF SCIENCES PHILADELPHIA

Interface-Rich Materials and Assemblies

Fabrication of Functional Polymer Structures through Bottom-up Selective Vapor Deposition from Bottom-up Conductive Templates Chih-Yu Wu, Hung-Pin Hsieh, Shih-Ting Chen, Ting-Yu Liu, and Hsien-Yeh Chen Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b04008 • Publication Date (Web): 20 Mar 2018 Downloaded from http://pubs.acs.org on March 20, 2018

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

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

Page 1 of 24 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

Fabrication of Functional Polymer Structures through Bottom-up Selective Vapor Deposition from Bottom-up Conductive Templates

Chih-Yu Wu1,£, Hung-Pin Hsieh1,£, Shih-Ting Chen1,£, Ting-Yu Liu2, and Hsien-Yeh Chen1,*

1

Department of Chemical Engineering, National Taiwan University, Taipei, 10617

(Taiwan). 2

Department of Materials Engineering, Ming-Chi University of Technology, New Taipei

City 24301 (Taiwan).

Keywords: nanostructure; bottom up; selected deposition; colloidal lithography; multifunctional

1

ACS Paragon Plus Environment

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

Page 2 of 24

Abstract An electrically induced bottom-up process was introduced for the fabrication of multifunctional

nanostructures

of

polymers.

Without

requiring

complicated

photolithography or printing techniques, the fabrication process first produced a conducting template by colloidal lithography to create an interconnected conduction pathway. By supplying an electrical charge to the conducting network, the conducting areas were enabled with a highly energized surface that generally deactivated the adsorbed reactive species and inhibited the vapor deposition of poly-p-xylylene polymers. However, the template allowed the deposition of ordered poly-p-xylylene nanostructures only on the confined and negative areas of the conducting template, in a relatively large centimeter-scale production. The wide selection of functionality and multifunctional capability of poly-p-xylylenes naturally rendered the synergistic and orthogonal chemical reactivity of the resulting nanostructures. With only a few steps, the construction of a nanometer topology with the functionalization of multiple chemical conducts can be achieved, and the selected deposition process represents a state-of-the-art nanostructure fabrication in a simple and versatile approach from the bottom up.

2


Page 3 of 24 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

Introduction Nanostructures on the surface of a material have provided not only a topologically induced impact but also sophisticated physical and chemical properties at the material interface by integration through a functionalization process. Methods to generate nanostructures on a surface extensively rely on top-down techniques based on light,1-2 electrons,3 ions,4 manipulated atomic beams,5 dip-pen nanolithography,6-7 imprinting methods (collectively termed “nanoimprinting lithography”), and chemical depositions8-10 to transfer replica nanostructures onto a surface.11 On the other hand, a collection of bottom-up techniques to generate nanostructures using self-assembled molecules has also been reported, mostly based on the interactions of phase separation, intermolecular forces at

interfaces,

thermodynamic

equilibrium,

charge

interactions,

and

chemical

interactions.12-15 From the surface chemistry point of view, the functionalization of the nanostructures requires the use of additional functional materials (e.g., functional polymers, composites with functional additives, etc.) during the fabrication, or a post-modification method that is applied after the nanostructures are established.16-18 Although the resulting functional (nano-)structures are readily provided with both physical and chemical controllable parameters for a more advanced and synergistic manipulation of the materials’ interface, the required extensive knowledge in molecular/surface physics and chemistry to perform these techniques is prohibitive, and it is difficult to perform the multiple steps to establish these functional structures.19-20 In the present study, we demonstrate a versatile and simple approach to generate functionalized surface structures in the nanometer domain from the bottom up. Two independent bottom-up processes were exploited by first generating a nanometer-scale 3


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

and ordered conducting template containing an interconnected conduction pathway based on a colloidal lithography technique, and subsequently the selected vapor deposition of poly-p-xylylene polymers (also from the bottom up) on the negative and confined regions of the conducting template. The functionalization of the nanostructures was naturally enabled by the selection of the substituted poly-p-xylylene derivative (with a wide range of functionalities that are already established commercially)21 during the deposition process. The rationale of the selective deposition of poly-p-xylylenes was enlightened based on the inhibition behavior of high-energy surfaces including transition metals and their corresponding oxides,22-23 and electrically charged surfaces;24 therefore, a nanostructured surface of a conductive substrate was hypothesized for the preparation and construction of nano-sized poly-p-xylylene structures on the surface by selected chemical vapor deposition (CVD) polymerization. A cost-effective method of nanocolloidal lithography was utilized to generate an ordered arrangement of conductive metals on a surface, and the selective deposition of functionalized poly-p-xylylenes including amine, active ester, and a state-of-art multifunctional combination of the two groups was demonstrated for the fabrication of ordered structures with nanometer dimensions on the surface. The materials’ surface structuring and functionalization were demonstrated on a large scale (centimeter) and without requiring complicated photolithography and printing processes. The resulting structured surface provided, physically, a controlled surface morphology, and chemically, reactive accessibility towards specific reactions and/or orthogonal multifunctionality. The introduced technology is the first dry process that uses a charged force to fabricate a polymer nanostructure from the bottom up.

4


Page 4 of 24

Page 5 of 24 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

EXPERIMENTAL SECTION Fabrication of conducting templates Glass substrates (18 x 18 mm, Paul Marienfeld GmbH, Germany) were cleaned by concentrated sulfuric acid and 30% hydrogen peroxide (in a ratio of 3:1) before use. A polystyrene (PS) latex bead solution (10%, 0.4 µm mean particle size) was purchased commercially from Sigma-Aldrich, USA, and a new solution was prepared containing 80% ethanol and 20% PS solution with 15 min sonication. The prepared PS solution was then cast on the cleaned glass substrates and was spin-dried at 2000 rpm for 30 sec and 500 rpm for 10 sec in ambient conditions at 20 °C. Metal layers of Ag, Au, and Fe were deposited separately on the resulting PS/glass samples using a thermal evaporation system (Kao Duen Technology, Taiwan) with a thickness of approximately 80 nm. A 20 nm Ti layer was deposited as an adhesion layer before each metal deposition. Oxygen plasma with a radio frequency generator (13.56 MHz) plasma source (Advanced Energy, USA) and with an oxygen flow rate of 25 sccm at a power of 15 W was used to etch and decrease the size of PS if necessary before the metal layer deposition. The treatment time of oxygen plasma was controlled between 60 sec and 120 sec with respect to the size of PS required.

Selected CVD polymerization Dichloro[2,2]paracyclophane (Galxyl C) was purchased commercially from Galentis, Italy. Substituted-[2,2]paracyclophanes including 4-aminomethyl-[2,2]paracyclophane, and 4-trifluoroacetyl-[2,2]paracyclophane were synthesized following previously

5


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

Page 6 of 24

reported routes.25-26 The CVD polymerization process was performed using a self-designed CVD that was comprised of two independent dimer feeding sources, each containing a sublimation zone and a pyrolysis zone, and the two sources were connected to a center deposition chamber. For the deposition of mono-substituted poly-p-xylylenes, the dimer was first sublimated in a vacuum in the sublimation zone at a temperature of approximately 90-125 °C, depending on the substituted-[2,2]paracyclophane that was used. The sublimated species were then transferred in a stream of argon carrier gas (25 sccm) to the pyrolysis zone in which the temperature was adjusted to 670-750 °C, also depending on the starting materials of selection. Following pyrolysis, the resulting quinodimethanes (diradical monomers) were transferred into the deposition chamber, where polymerization occurred on a rotating holder maintained at 15 °C to ensure the uniform deposition of the polymer. For the deposition of multifunctional di-substituted poly-p-xylylene,

dimers

of

4-aminomethyl-[2,2]paracyclophane

and

4-trifluoroacetyl-[2,2]paracyclophane were fed from separated and independent dimer sources27-29 with a controlled feeding ratio of 1:1 (molar), which corresponded to a 1:1 ratio of the aminomethyl and trifluoroacetyl within the PPX-dual copolymer.30

The

pyrolysis temperatures were 670 °C for 4-trifluoroacetyl-[2,2]paracyclophane and 750 °C for 4-aminomethyl-[2,2]paracyclophane to transform them into the corresponding quinodimethanes. The copolymerization occurred similarly upon condensation on a cooled

sample

holder

at

15

°C

forming

poly[4-aminomethyl-p-xylylene-co-4-trifluoroacetyl-p-xylylene-co-p-xylylene] (PPX-dual). A pressure of 75 mTorr was regulated during the entire CVD (co-)polymerization process. Depending on specific study of interest, deposition rates

6


Page 7 of 24 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

were controlled at 0.5 Å/s - 10 Å/s, as monitored by an in situ quartz crystal microbalance (QCM) system. For selected deposition, an electrical current (DC) of 50 mA was supplied to the conducting substrates by a GPS 3030D power supply (Good Will Instrument, Taiwan) during the CVD (co-)polymerization process.

Characterizations Real-time mass spectrometry was detected by a residual gas analyzer (RGA, Hiden Analytical, UK) under 10 -7 mbar and a mass detection range of 0-500 amu with an electron ionization energy of 70 eV and ionization emission current of 20 µA. The RGA system was mounted on the deposition chamber of the CVD system. For infrared reflection absorption spectroscopy (IRRAS), spectra were recorded using a 100 FT-IR spectrometer (PerkinElmer, USA) equipped with a liquid nitrogen-cooled MCT detector and with an advanced grazing angle specular reflectance accessory (AGA, PIKE Technologies, USA). The spectra were recorded using 128 scans and a 4 cm-1 resolution from 500 cm-1 to 4000 cm-1. The resulting spectra were corrected for any residual baseline shifts. Scanning electron microscopy (SEM) was performed using a NovaTM NanoSEM 230 system (FEI, USA) and was operated at a primary energy of 5 keV at a pressure of 5 × 10-6 Torr in the specimen chamber. For the elemental analysis, energy dispersive X-ray spectroscopy (EDS) mode was operated with the same SEM system. The surface topology and roughness were analyzed using an atomic force microscope (MultiMode 8, Bruker, USA) equipped with with the acquisition of a peak force tapping mode. Silicon nitride tips (Bruker, USA) with a tip radius of 12 nm and a spring constant of 0.04N/m were used during the acquisitions.

7


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

Immobilizations Fluorescence molecules of Alexa Fluor® 350-conjugated NHS ester (Thermo Fisher Scientific, USA) and Alexa Fluor® 488-conjugated hydrazide (Thermo Fisher Scientific, USA) were used to verify the reactivity and specificity of the functional groups on the resulting nanostructures for PPX-amine, PPX-TFA, and PPX-dual. For PPX-amine nanostructures, 150 µg/ml of Alexa Fluor® 350 NHS ester in bovine serum albumin (PBS) was first allowed to react with the nanostructured sample for 120 min. After rinsing three times with PBS solution (containing 0.1% (wt/vol) bovine serum albumin and 0.02% (vol/vol) Tween 20) and deionized water, a nitrogen stream was used to gently dry the stent sample. For PPX-TFA, the Alexa Fluor® 488-conjugated hydrazide solution, prepared at a concentration of 250 µg/ml in phosphate-buffered saline (PBS, pH 7.4) was allowed to react with the PPX-TFA nanostructures sample in an acidic condition (pH=3 ~ 4). After 10 min of reaction, the excess and unreacted hydrazide solution was rinsed off using PBS (containing 0.1% (wt/vol) bovine serum albumin and 0.02% (vol/vol) Tween 20) and deionized water. For the multifunctional PPX-dual, a two-step conjugation process was performed by first allowing 150 µg/ml Alexa Fluor® 350 NHS ester to react with the nanostructured sample for 120 min, and after the aforementioned rinsing process with PBS and deionized water, 250 µg/ml Alexa Fluor® 488 hydrazide was then reacted with the same sample for 10 min in an acidic condition. Finally, the sample was rinsed several times with PBS (containing 0.1% (wt/vol) bovine serum albumin and 0.02% (vol/vol) Tween 20) and deionized water, and similarly a nitrogen stream was used to gently dry the sample. For the detection of the resulting fluorescence signals, the samples

8


Page 8 of 24

Page 9 of 24 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

were examined using a Leica TCS SP5 STED ultra-analytical multiphoton spectroscopy microscope (Leica Microsystems, Germany).

RESULTS AND DISCUSSION The behavior of selective deposition for poly-p-xylylenes was first verified in the study. Substrates of choice including gold (Au), silver (Ag), and iron (Fe) metals were examined

for

the

deposition

of

polydichloro-p-xylylene

poly[4-aminomethyl-p-xylylene-co-p-xylylene]

(PPX-C), (PPX-amine),

poly[4-trifluoroacetyl-p-xylylene-co-p-xylylene] (PPX-TFA), and a multifunctional poly[4-aminomethyl-p-xylylene-co-4-trifluoroacetyl-p-xylylene-co-p-xylylene] (PPX-dual). These poly-p-xylylenes were chosen for the demonstration based on the wide commercial availability for PPX-C (extra high chemical inertness and biocompatibility, United States Pharmacopeia Class VI polymer)31-34, the representative amine and ketone reactive functionality for the PPX-amine and PPX-TFA, and particularly, the multifunctional PPX-dual that comprises two distinct and side-by-side anchoring sites of amine and ketone and is synthesized in one step via CVD copolymerization.27,

29, 35

During the deposition process, an in situ mass spectrometric residual gas analyzer (RGA) was used to separately monitor the ingredients of the gas vapor in the deposition chamber, and the results revealed the presence of characteristic chloro-p-quinodimethane (monomer of PPX-C) at 139 amu, aminomethyl-p-quinodimethane at 132 amu, and trifluoroacetyl-p-quinodimethane at 200 amu, and particularly, both the 132 amu and 200 amu signals for the multifunctional PPX-dual throughout the entire process (Figure 1a), indicating the dimers were successfully decomposed into their corresponding reactive

9


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

monomer species that were ready for polymerization and deposition. Subsequently, after the depositions were completed, the substrates (Au, Ag, and Fe) were examined using Fourier transform infrared spectroscopy (FT-IR). Interestingly, the results showed no deposition (inhibition) of PPX-C on the Ag and Fe substrates but a successful deposition on the Au substrate, as shown in Figure 1b. In contrast, the depositions of PPX-amine, PPX-TFA, and PPX-dual were successful (no inhibition) on all the three substrates. These data showed good consistency with previously reported results.22-23 Although the exact mechanism of the selective deposition is inconclusive, it is believed that the high surface energy of a substrate, such as Ag and Fe (or other transition metals and their oxides), can neutralize the reactive species of the monomer p-quinodimethane to become deactivated and prevent further polymerization and propagation of PPX-C;22 the surprisingly divergent result of nonselective deposition was, however, achieved for similar poly-p-xylylenes with reactive side groups (-amine and -TFA for the present case) because the compromising neutralization might occur at the side groups.23 In addition, the hypothesis of enhanced surface energy on the metal surface was tested by supplying charge/current to the metal surfaces, and the resulting surfaces were examined by FT-IR. A universal inhibition was indeed found for all the poly-p-xylylenes (PPX-C, PPX-amine, PPX-TFA, and PPX-dual), regardless of the side group substitution; no trace of signals from either substituted side groups or the poly-p-xylylene backbones were detected (Figure 1c). It is believed that the charged surfaces provided a sufficient energy barrier of deactivation for the adsorbed p-quinodimethane no matter the reactive side group. The examinations collectively supported the hypothesis that a charged conductive surface can be exploited for the confinement of deposition/growth of poly-p-xylylenes and its

10


Page 10 of 24

Page 11 of 24 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

derivatives. To create regions/patterns where the selected deposition of poly-p-xylylenes can occur, and more importantly, have the nanometer-scale confinement of such a selective technology be exploited from the bottom up, we utilized the simple and inexpensive technique of colloidal lithography, which has been demonstrated to produce nanometer-scale patterns of polymers,36 metals,37 and inorganic materials,38 without requiring high-end photolithography and lift-off processes. Briefly, colloidal polystyrene nanospheres with a 0.4 µm diameter were spin-dried on a glass substrate forming a two-dimensional (2D) particle monolayer that served as a mask. Subsequently, by sputtering a metal (Au, Ag, Fe, or others) with a coating thickness of approximately 30 nm into particle interstices, a thin film of a conductive layer with an ordered and continuous pattern on the nanometer scale was produced.

Finally, the removal of the

polystyrene sphere mask by toluene yielded the interconnected metal conductive pattern (Figure 2b-c). A nano-scaled metal template containing an interconnected conduction pathway was fabricated from a bottom-up approach by such a colloidal lithography technique with high reproducibility and large-scale production (centimeter, data are included in the supporting information in Figure S1); theoretically a meter-scaled production has been reported.39 Oxygen plasma was used during the colloidal lithography to etch the polystyrene spheres, reducing their size to flexibly control the resulting aspect ratio of the conductive pattern.

The resultant conductive template possessed an

averaged 1.2×103 Ω resistance compared with 1.9 Ω for a non-patterned homogeneous Ag conducting surface of the same area size. The CVD polymerization of poly-p-xylylenes was therefore conducted on the fabricated conductive templates (with a

11


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

supplied current of 50 mA) with the deposition selectivity of the charged high-energy surface; the deposition of poly-p-xylylenes occurred only on the regions where the conductive metal was absent (Figure 2a). The outcome of such a selected deposition on the patterned conducting template resulted in discrete and ordered nanostructures of poly-p-xylylenes, which were universally verified for all the studied variations of poly-p-xylylenes including PPX-C, PPX-amine, PPX-TFA, and PPX-dual. In the demonstration, aspect ratios ranging from 0.5 – 3.5 were fabricated, and the characterization by scanning electron microscopy (SEM) (Figure 3a) indicated the deposition footprint of the poly-p-xylylene nanostructure on the anticipated areas, with the ordered circular structures’ averaged size ranging from 120 ± 3.4 nm to 140 ± 5.2 nm according to the corresponding aspect ratio. The resulting structure size and the aspect ratio between structures were found correlated to the plasma treatment conditions, and a structure size down to approximately 73 ± 6.1 nm was demonstrated. The data are included in the supporting information in Figure S2. The analysis by energy dispersive X-ray spectroscopy (EDS) elemental mapping further provided direct evidence of the selectively formed nanostructures of PPX-C, PPX-amine, PPX-TFA, and revealed the confined distribution of chlorine signal for PPX-C, nitrogen signal for PPX-amine, and fluorine signal for PPX-TFA (Figure 3b). The atomic force microscopy (AFM) analysis in Figure 3c showed a more detailed surface morphology of these structures and have also confirmed the depositions of the polymers in the selected areas. The AFM images also suggested a result of varied aspect ratio for the structures that was time-controlled during the plasma treatment process. The three-dimensional height profile analysis from AFM also suggested the smooth and half-oval shape of the nanostructure with

12


Page 12 of 24

Page 13 of 24 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

dimensions of 143 nm in diameter and 100 nm in height (Figure 3d). A relatively smooth surface roughness was discovered for the polymer structures formed under a relative low growth rate (0.5 Å/s) by comparing to the roughness of such structures fabricated for higher growth rates (10 Å/s), and the compared results are shown in the supporting information, Figure S3. Potential limitations of the resultant pattern size are the size available for nanocolloids templates used and the combined control parameters that are manageable with current plasma treatment technology,40 and the selectivity may be lost due to a maximum thickness of polymer growth is reached.22, 24 Finally, from the surface functionality point of view, the nanostructures of PPX-amine and PPX-dual readily exhibited reactivity towards amine-reactive, and particularly both amine- and ketone-reactive molecules (for the multifunctional PPX-dual). In the demonstration, Alexa Fluor® 350 N-hydroxysuccinimide (NHS) ester molecules and Alexa Fluor® 488 hydrazide were used for the detection and reaction of the PPX-amine, PPX-TFA, and PPX-dual structures. The reactive ketones underwent the reaction route of nucleophilic addition with hydrazides to yield hydrazones, while the amines coupled specifically with NHS-ester through hydrolysis to form amide bonds. These two reactions were completed with high specificity and rapid reaction kinetics. As indicated in Figure 4, the resultant fluorescence signals were characterized using an ultra-sensitive multiphoton microscope. Strong signals of Alexa Fluor® 350 (blue) were visualized on the structured areas for PPX-amine, and on the other hand, Alexa Fluor® 488 (green) signals for PPX-TFA and PPX-dual samples. These fluorescence data were indicative of a high reaction yield and efficient bonding between the fluorescent biomolecules and the structure surface. The reaction specificities have previous been verified for similar polymer systems, and the

13


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

concerns of potential cross reactions can be eliminated.28, 30, 41 Additionally, and more importantly, both Alexa Fluor® 350 and Alexa Fluor® 488 signals were detected for PPX-dual indicating the multifunctional concept, and the merged image revealed the parallel immobilization and synergistic presence of the two biomolecules on the same structure, as well as the indication that the two orthogonal reactions were specific without cross contamination. These bottom-up structures provided readily reactive sites without requiring post functionalization procedures, and more attractively, the multifunctional capability (more than three functionalities theoretically) has enabled multitasking possibility in the controlled nanometer scale. Additional experiments were conducted to successfully remove the metal template after the polymer structures were constructed (supporting information, Figure S4), as well as applying the reported technique on varied flexible substrates (supporting information, Figure S5), which these results have widening the applications of using these nanostructures.

Conclusion Nanometer-scaled polymer structures were fabricated based on the selected deposition of conductive substrates from the bottom up. State-of-art, multifunctional, ordered nanostructures with both topological and chemical attributes were produced using a simple approach and on a relatively large scale. The bottom-up technique required inexpensive colloidal lithography, and subsequently, an accessible engineering parameter using the deactivation of the reactive species to enable selected deposition of materials on confined areas of a substrate surface. The technology is encouraged to be exploited for more vapor deposition systems of both organic and inorganic materials.

14


Page 14 of 24

Page 15 of 24 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

Owing to the excellent optical property for the poly-p-xylylenes and the flexible conjugation capacity of using the polymers, devices fabricated using the reported technology are beneficial from these merit properties in applications such as solar cells, electrochemical devices, optical devices, sensor devices, and prospective bioMEMS devices.

15


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

Figure 1. Verification of the deposition selectivity. (a) in situ mass spectrometric analysis for the vapor species within the deposition chamber during the CVD polymerization process of PPX-C, PPX-amine, PPX-TFA, and the multifunctional PPX-dual. (b) FT-IR spectra showed the selected deposition of PPX-C, PPX-amine, PPX-TFA, and PPX-dual on bare metal surfaces including Au, Ag, and Fe. (c) FT-IR spectra showed the general inhibition of the deposition for PPX-C, PPX-amine, PPX-TFA, and PPX-dual on conducting surfaces of Au, Ag, and Fe. An electrical current of 50 mA was supplied to the metal surfaces during the CVD polymerization process.

16


Page 16 of 24

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

Langmuir

Figure 2. (a) Schematic illustration of the bottom-up process to fabricate polymer nanostructures based on the selected vapor deposition of functional polymers on a conducting template that was formed by colloidal lithography. The deposition of poly-p-xylylenes were inhibited by the high surface energy of a conducting surface. (b) SEM images show the nanometer scale conducting template of Ag containing interconnected conducting pathways, which was fabricated by the colloidal lithography process. (c) EDS analysis showing the Ag elemental map for the conducting template.

17


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

Figure 3. Formation of polymer nanostructures by selected deposition. (a) SEM images show the selected deposition of poly-p-xylylene on the confined and negative areas of the conducting template. Various aspect ratios of the nanostructures were fabricated. (b) EDS analysis confirmed the elemental distribution on these confined areas for PPX-C (Cl, chlorine map), PPX-amine (N, nitrogen map), and PPX-TFA (F, fluorine map). (c) AFM height analysis of the nanostructure verified the selective deposition of the polymer structures and revealed a half-oval shape for the structure. (d) An example of a nanostructure possessing dimensions of approximately 143 nm in diameter and 100 nm in height.

18


Page 18 of 24

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

Langmuir

Figure 4. Fluorescence probes were used to confirm the reactivity and specificity of the functional nanostructures of (a) PPX-amine, (b) PPX-TFA, and (c) PPX-dual. The overlaid images in (c) with blue and green channels indicated the synergistic and orthogonal reactivity of the PPX-dual nanostructures.

19


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

ASSOCIATED CONTENT Supporting Information. SEM images of the conducting template, control experiments of the nanostructures fabricated under high flow rate, removed conducting template, and forming structures on varied and flexible substrates. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * Fax: (+)886-2-33669476 E-mail: [email protected] Author Contributions £

C.-Y. Wu, H.-P. Hsieh, and S.-T. Chen contributed equally to this work.

Notes The authors declare no competing financial interests. ACKNOWLEDGMENT H.-Y. Chen gratefully acknowledges financial support from the Ministry of Science and Technology of Taiwan (104-2628-E-002-010-MY3), National Taiwan University (103R7745 and 104R7745).

20


Page 20 of 24

Page 21 of 24 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

REFERENCE 1. Rai-Choudhury, P., Handbook of Microlithography, Micromachining, and Microfabrication. Volume 1: Microlithography. 1997. 2. Cerrina, F., X-ray imaging: applications to patterning and lithography. J. Phys. D: Appl. Phys. 2000, 33 (12), R103. 3. Yao, N. W., Z. L., Handbook of Microscopy for Nanotechnology. 2005. 4. Tseng, A. A., Recent Developments in Nanofabrication Using Ion Projection Lithography. Small 2005, 1 (6), 594-608. 5. Meschede, D.; Metcalf, H., Atomic nanofabrication: atomic deposition and lithography by laser and magnetic forces. J. Phys. D: Appl. Phys. 2003, 36 (3), R17. 6. Piner, R. D.; Zhu, J.; Xu, F.; Hong, S.; Mirkin, C. A., "Dip-Pen" Nanolithography. Science 1999, 283, 661-663. 7. Salaita, K.; Wang, Y.; Mirkin, C. A., Applications of dip-pen nanolithography. Nat Nano 2007, 2 (3), 145-155. 8. Kronholz, S.; Rathgeber, S.; Karthäuser, S.; Kohlstedt, H.; Clemens, S.; Schneller, T., Self-Assembly of Diblock-Copolymer Micelles for Template-Based Preparation of PbTiO3 Nanograins. Adv. Funct. Mater. 2006, 16 (18), 2346-2354. 9. Calzada, M. L.; Torres, M.; Fuentes-Cobas, L. E.; Mehta, A.; Ricote, J.; Pardo, L., Ferroelectric self-assembled PbTiO 3 perovskite nanostructures onto (100)SrTiO 3 substrates from a novel microemulsion aided sol–gel preparation method. Nanotechnology 2007, 18 (37), 375603. 10. Grosso, D.; Boissière, C.; Smarsly, B.; Brezesinski, T.; Pinna, N.; Albouy, P. A.; Amenitsch, H.; Antonietti, M.; Sanchez, C., Periodically ordered nanoscale islands and mesoporous films composed of nanocrystalline multimetallic oxides. Nature Materials 2004, 3, 787. 11. Guo, L. J., Nanoimprint Lithography: Methods and Material Requirements. Adv. Mater. 2007, 19 (4), 495-513. 12. Shimomura, M.; Sawadaishi, T., Bottom-up strategy of materials fabrication: a new trend in nanotechnology of soft materials. Curr. Opin. Colloid. In. 2001, 6 (1), 11-16. 13. Cai, J.; Ruffieux, P.; Jaafar, R.; Bieri, M.; Braun, T.; Blankenburg, S.; Muoth, M.; Seitsonen, A. P.; Saleh, M.; Feng, X.; Mullen, K.; Fasel, R., Atomically precise bottom-up fabrication of graphene nanoribbons. Nature 2010, 466 (7305), 470-473. 14. Zhang, S., Fabrication of novel biomaterials through molecular self-assembly. Nat Biotech 2003, 21 (10), 1171-1178. 15. Hawker, C. J.; Russell, T. P., Block Copolymer Lithography: Merging “Bottom-Up” with “Top-Down” Processes. MRS Bull. 2011, 30 (12), 952-966. 16. Joshi, R. K.; Schneider, J. J., Assembly of one dimensional inorganic nanostructures into functional 2D and 3D architectures. Synthesis, arrangement and functionality. Chem. Soc. Rev. 2012, 41 (15), 5285-5312. 17. Lu, Y.; Chen, S. C., Micro and nano-fabrication of biodegradable polymers for drug delivery. Adv. Drug Del. Rev. 2004, 56 (11), 1621-1633. 18. Zhang, J.; Li, Y.; Zhang, X.; Yang, B., Colloidal Self-Assembly Meets Nanofabrication: 21


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

From Two-Dimensional Colloidal Crystals to Nanostructure Arrays. Adv. Mater. 2010, 22 (38), 4249-4269. 19. Ozin, G. A.; Hou, K.; Lotsch, B. V.; Cademartiri, L.; Puzzo, D. P.; Scotognella, F.; Ghadimi, A.; Thomson, J., Nanofabrication by self-assembly. Mater. Today 2009, 12 (5), 12-23. 20. Gates, B. D.; Xu, Q.; Love, J. C.; Wolfe, D. B.; Whitesides, G. M., UNCONVENTIONAL NANOFABRICATION. Annual Review of Materials Research 2004, 34 (1), 339-372. 21. Lahann, J.; Langer, R., Novel poly(p-xylylenes): Thin films with tailored chemical and optical properties. Macromolecules 2002, 35 (11), 4380-4386. 22. Vaeth, K. M.; Jensen, K. F., Transition metals for selective chemical vapor deposition of parylene-based polymers. Chem. Mater. 2000, 12 (5), 1305-1313. 23. Chen, H.-Y.; Lai, J. H.; Jiang, X.; Lahann, J., Substrate-Selective Chemical Vapor Deposition of Reactive Polymer Coatings. Adv. Mater. 2008, 20 (18), 3474-3480. 24. Wu, C.-Y.; Sun, H.-Y.; Liang, W.-C.; Hsu, H.-L.; Ho, H.-Y.; Chen, Y.-M.; Chen, H.-Y., Electrically charged selectivity of poly-para-xylylene deposition. Chem. Commun. 2016, 52 (14), 3022-3025. 25. Lahann, J.; Klee, D.; Höcker, H., Chemical vapour deposition polymerization of substituted [2.2]paracyclophanes. Macromol. Rapid Commun. 1998, 19 (9), 441-444. 26. Rozenberg, Valeria I.; Danilova, T. yana I.; Sergeeva, Elena V.; Shouklov, I. A.; Starikova, Zoya A.; Hopf, H.; Kühlein, K., Efficient Synthesis of Enantiomerically and Diastereomerically Pure [2.2]Paracyclophane-Based N,O-Ligands. Eur. J. Org. Chem. 2003, 2003 (3), 432-440. 27. Tsai, M.-Y.; Chen, Y.-C.; Lin, T.-J.; Hsu, Y.-C.; Lin, C.-Y.; Yuan, R.-H.; Yu, J.; Teng, M.-S.; Hirtz, M.; Chen, M. H.-C.; Chang, C.-H.; Chen, H.-Y., Vapor-Based Multicomponent Coatings for Antifouling and Biofunctional Synergic Modifications. Adv. Funct. Mater. 2014, 24 (16), 2281-2287. 28. Elkasabi, Y.; Lahann, J., Vapor-Based Polymer Gradients. Macromol. Rapid Commun. 2009, 30 (1), 57-63. 29. Chen, H.-Y.; Lin, T.-J.; Tsai, M.-Y.; Su, C.-T.; Yuan, R.-H.; Hsieh, C.-C.; Yang, Y.-J.; Hsu, C.-C.; Hsiao, H.-M.; Hsu, Y.-C., Vapor-based tri-functional coatings. Chem. Commun. 2013, 49 (40), 4531-4533. 30. Elkasabi, Y.; Chen, H.-Y.; Lahann, J., Multipotent Polymer Coatings Based on Chemical Vapor Deposition Copolymerization. Adv. Mater. 2006, 18 (12), 1521-1526. 31. Nichols, M. F.; Hahn, A. W. Apparatus for applying a composite insulative coating to a substrate. 16 June, 1992. 32. Hassler, C.; von Metzen, R. P.; Ruther, P.; Stieglitz, T., Characterization of parylene C as an encapsulation material for implanted neural prostheses. Journal of Biomedical Materials Research Part B: Applied Biomaterials 2010, 93B (1), 266-274. 33. Fontaine, A. B.; Koelling, K.; Dos Passos, S.; Cearlock, J.; Hoffman, R.; Spigos, D. G., Polymeric Surface Modifications of Tantalum Stents. J. Endovasc. Surg. 1996, 3 (3), 276-283. 34. Schurmann, K.; Lahann, J.; Niggemann, P.; Klosterhalfen, B.; Meyer, J.; Kulisch, A.; Klee, D.; Gunther, R. W.; Vorwerk, D., Biologic response to polymer-coated stents: In vitro analysis and results in an iliac artery sheep model. Radiology 2004, 230 (1), 151-162. 22


Page 22 of 24

Page 23 of 24 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

35. Yuan, R.-H.; Wu, C.-Y.; Tung, H.-Y.; Hsieh, H.-P.; Li, Y.-J.; Chiang, Y.-C.; Chen, H.-Y., Multifunctional Surface Modification: Facile and Flexible Reactivity toward a Precisely Controlled Biointerface. Macromol. Biosci. 2017, 17 (4), 1600362. 36. Singh, G.; Griesser, H. J.; Bremmell, K.; Kingshott, P., Highly Ordered Nanometer-Scale Chemical and Protein Patterns by Binary Colloidal Crystal Lithography Combined with Plasma Polymerization. Adv. Funct. Mater. 2011, 21 (3), 540-546. 37. Tessier, P. M.; Velev, O. D.; Kalambur, A. T.; Lenhoff, A. M.; Rabolt, J. F.; Kaler, E. W., Structured Metallic Films for Optical and Spectroscopic Applications via Colloidal Crystal Templating. Adv. Mater. 2001, 13 (6), 396-400. 38. Jiang, P.; Bertone, J. F.; Colvin, V. L., A Lost-Wax Approach to Monodisperse Colloids and Their Crystals. Science 2001, 291, 453-457. 39. Gao, P.; He, J.; Zhou, S.; Yang, X.; Li, S.; Sheng, J.; Wang, D.; Yu, T.; Ye, J.; Cui, Y., Large-Area Nanosphere Self-Assembly by a Micro-Propulsive Injection Method for High Throughput Periodic Surface Nanotexturing. Nano Lett. 2015, 15 (7), 4591-4598. 40. Oehrlein, G. S.; Phaneuf, R. J.; Graves, D. B., Plasma-polymer interactions: A review of progress in understanding polymer resist mask durability during plasma etching for nanoscale fabrication. Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena 2011, 29 (1), 010801. 41. Chen, Y.-C.; Sun, T.-P.; Su, C.-T.; Wu, J.-T.; Lin, C.-Y.; Yu, J.; Huang, C.-W.; Chen, C.-J.; Chen, H.-Y., Sustained Immobilization of Growth Factor Proteins Based on Functionalized Parylenes. ACS Appl. Mater. Inter. 2014, 6 (24), 21906-21910.

23


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

Table of Contents Nanometer-scale and multifunctional polymer structures were fabricated using selected deposition on conductive substrates from the bottom up.

24


Page 24 of 24

Fabrication of Functional Polymer Structures through Bottom-Up

Recommend Documents