Introduction of block copolymer self-assembly
Introduction
- Basic principle of block copolymer self-assembly and their application
- Major factor affecting the aggregates in solvent system
- Block copolymer nanolithography for nano-template
- Synthesis of arranged inorganic nanoparticle using block copolymer nano-template 15
Schematic illustration of various micelle structures formed by self-assembled amphiphilic block copolymer in the selective solvent.10. They used the low-molecular-weight block copolymer as a template, and Si ions were loaded onto the template.21 As a result, well-ordered porous silica was obtained. The first method is that metal ions are directly covered with a selective block in solution system.22 Second method is that metal ions are loaded onto prepared block copolymer thin film template.23 And the morphology of block copolymer can be controlled by annealing process.24 .
In this step, crystalline metal oxides may form during calcination, depending on the temperature used.22 Another method is that a self-assembling thin film of block copolymer has been prepared in advance as a nano-template. Before the metal ions are charged, the patterns of the block copolymer thin film are changed by an annealing process23,24. The block copolymer thin films are defined by a degree of confinement within the film thickness that is comparable to the distance between the polymer domain.
Two main categories of insulation are defined for substrate-supported block copolymer thin films: "hard" insulation and "soft" insulation. However, perpendicular structures are preferred over parallel structures for block copolymer nano-template applications. In addition to thermal annealing of the block copolymer above Tg, solvent vapor annealing (SVA) also induces morphological changes.
The solvent molecules affect block copolymer mobility and significantly enhance lateral ordering of the block copolymer microdomains. Both, the concentration of block copolymer and the type of solvent influence the obtaining of film with well-ordered microdomains. The amount of swelling of the block copolymer thin film depends on the chemical nature of the blocks, the quality of the solvent and the molecular weight of the block copolymer during SVA system.
And then the removal of solvent causes the breakdown of order due to the confinement of the block copolymer thin film. As various application areas using nanostructures are increasing, block copolymer self-assembly is attracting attention for the nanolithography. Because block copolymer nanolithography is required for relatively low cost and simple fabrication process compared to photolithography process.
On the other hand, block copolymer self-assembly, block copolymer microphase separation, forms a uniform nanostructure without additional complex manufacturing processes. Accordingly, we confirmed that the block copolymer nano template is suitable for nanolithography of inorganic materials.
Experimental section
- Block copolymer solution and thin film
- Solvent vapor annealing system
- Block copolymer inorganic nano-template
The block copolymer thin film was immersed in metal precursor solution for a sufficient time to load the metal ion into the pyridine group of the specific block P4VP or P2VP. The PS-b-P4VP block copolymer dissolved in toluene at 1 wt% was spin-coated on the Si substrate to prepare an inorganic nano-template using self-assembled block copolymer micelles. And then various metal precursors can be loaded with specific location of the cores in block copolymer micelles such as pyridine group of P4VP block copolymer with polar-polar interaction.
And its size and distance can be controlled depending on the amount of precursors and the molecular weight of block copolymer. Figure 1.8 shows scanning electron microscope (SEM) images of uniformly arranged titanium oxide nanoparticles using block copolymer self-assembly. The titanium tetraisopropoxide (TTIP) was added in block copolymer solution (titanium ion/pyridine molar ratio = 1) and stirred for sufficient time so that the metal precursor was attached to the block copolymer.
1 wt% PS-b-P4VP was dissolved in toluene, and then iron nitrate or TTIP was added in a block copolymer solution (metal ion/pyridine molar ratio = 1). After reducing the metal ions, the Ag-PS-b-P4VP or Au-PS-b-P4VP solution was spin-coated onto Si substrate. a) SEM image of arranged titanium oxide nanoparticles using PS(37.5K)-b-P4VP(16K) block copolymer. Moreover, the specific location of the nuclei in block copolymer micelles, such as the pyridine group of P4VP block copolymer, can charge the metal ion via polar-polar interaction.
Based on the theories in this chapter, we apply block copolymer self-assembly to energy-related applications. In the next chapter, I introduce the energy-related application using the block copolymer scaffold, especially in relation to the gas sensor application. Fabrication of TiO2 Nanopatterned Au Nanosheet for Gas Sensing: The resulting purple wafer coated with copolymer film floated on the surface of 1 wt% hydrofluoric acid (HF) aqueous solution and transferred to deionized (D.I.) water.
Herein, nanopatterned TiO2 was used as active material, and Au nanosheet and elastomeric SBS block copolymer film were used as stretchable electrode. We easily synthesized nanopatterned TiO2 for active material via self-assembly of block copolymers and solvent vapor annealing process to increase the gas-sensitive area. The Au nanosheet with SBS block copolymer thin film gained stretchability for the gas sensor.
Result and Discussion
Conclusion
Stretchable gas sensor application
- Introduction
- Sensing properties of titanium oxide
- Synthesis of TiO 2 nanomaterials
- Gas sensing mechanism
- Experimental Section
- Fabrication of Au nanosheet substrate
- Synthesis of TiO 2 nanoparticles
- Fabrication of stretchable gas sensor
- Results and Discussion
- Analysis of Au nanosheet
- TiO 2 patterned AuNS stretchable gas sensor and their gas sensing performance
- Conclusion
Therefore, according to doping types (n-doping/p-doping), it causes the change of the depletion region and the band bending on the surface, which leads to the change of conductivity. For example, when reducing gases are adsorbed on the anionic oxygen, electrons will be injected from gases into TiO2. On the other hand, when oxidizing gases are adsorbed on the anionic oxygen, electrons transfer to TiO2.
Fabrication of Au nanosheet substrate: First, Au nanosheet dispersed in 1-butanol and petri dish filled with D.I. When the monolayer film was built on the water surface, Si wafer was put into petri dish and the Au nanosheet film was scooped up. Gas sensor material fabricated on Si substrate was stamped with PDMS stamp and transferred onto PDMS stamp.
The gas sensor measures the change in current or resistance due to the detected gas. For this purpose, the gas sensor requires an active layer that traps the gas and an electrode layer that detects changes in resistance or current. The hydrogen tetrachloroaurate trihydrate (HAuCl4·3H2O) and L-arginine were used as synthetic materials in the Au nanosheet.
In this paper, the Au nanosheet is only used as a stretchable substrate and electrode that maintains the conductivity, and the UV-vis spectroscopy confirmed that the absorbance was similar to that of bulk Au rather than Au nanoparticle. The size of the Au nanosheet was about 20μm. c), (d) represent AFM images of a TiO2 nano-patterned on the Au nanosheet. The shaded area shown in Figure 2.8(c) is indicated by the height difference of the Au nanosheets.
Finally, we also confirmed that the conductivity as an electrode is preserved when the TiO2 nanopatterned Au nanosheet is folded for use as a stretchable gas sensor. As the gas injection was turned on and off, the change in flow was observed. a, b) SEM images of Au nanosheet at different scales. a) UV–vis spectroscopy of Au nanosheet. SEM images of Au nanosheets with TiO2 nanopatterned (a) Au nanosheets, (b) TiO2 with line pattern, and AFM images of Au nanosheets with TiO2 nanopatterned (c), (d) TiO2 with line pattern on Au nanosheets, and (e) photograph of TiO2 nanopatterned Au nanosheets on stretchable substrate. a) Real-time flow response of stretchable gas sensors at a fixed NH3 gas concentration (2000 ppm).
In conclusion, we demonstrated stretchable gas sensor using nanopatterned TiO2 coated on Au nanosheet. Therefore, it has been confirmed that the stretchable gas sensor has selective gas sensing capability.
