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Host-guest self-assembly in block copolymer blends.

Park WI, Kim Y, Jeong JW, Kim K, Yoo JK, Hur YH, Kim JM, Thomas EL, Alexander-Katz A, Jung YS - Sci Rep (2013)

Bottom Line: Our self-consistent field theory (SCFT) simulation results theoretically support that the precise registration of a spherical BCP microdomain (guest, B-b-C) at the center of a perforated lamellar BCP nanostructure (host, A-b-B) can energetically stabilize the blended morphology.As an exemplary application of the hybrid nanotemplate, a nanoring-type Ge2Sb2Te5 (GST) phase-change memory device with an extremely low switching current is demonstrated.These results suggest the possibility of a new pathway to construct more diverse and complex nanostructures using controlled blending of various BCPs.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea.

ABSTRACT
Ultrafine, uniform nanostructures with excellent functionalities can be formed by self-assembly of block copolymer (BCP) thin films. However, extension of their geometric variability is not straightforward due to their limited thin film morphologies. Here, we report that unusual and spontaneous positioning between host and guest BCP microdomains, even in the absence of H-bond linkages, can create hybridized morphologies that cannot be formed from a neat BCP. Our self-consistent field theory (SCFT) simulation results theoretically support that the precise registration of a spherical BCP microdomain (guest, B-b-C) at the center of a perforated lamellar BCP nanostructure (host, A-b-B) can energetically stabilize the blended morphology. As an exemplary application of the hybrid nanotemplate, a nanoring-type Ge2Sb2Te5 (GST) phase-change memory device with an extremely low switching current is demonstrated. These results suggest the possibility of a new pathway to construct more diverse and complex nanostructures using controlled blending of various BCPs.

No MeSH data available.


Related in: MedlinePlus

Self-assembled morphologies of pure BCPs and blended BCPs treated by various mixed solvent vapors.(a) Morphologies of single-component PDMS-b-PS (DS45) and PS-b-PFS (SF35) in response to different solvent vapors. Cylindrical (top-left), hexagonally perforated lamellar (top-center), and lamellar (top-right) morphologies were obtained from the same PDMS-b-PS BCP by changing the volume ratio of heptane (VHep) and toluene (VTol). PS-b-PFS maintained the same spherical morphology (bottom) for the different solvent vapor treatment conditions. (b) Morphological variation of the BCP blends (PDMS-b-PS and PS-b-PFS) treated by mixed solvent vapors. The BCP blending ratio (VDS45/VSF35) was fixed at 2.5. Uniform host-guest assembly between the two BCPs were achieved at VHep/VTol = 1.2.
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f2: Self-assembled morphologies of pure BCPs and blended BCPs treated by various mixed solvent vapors.(a) Morphologies of single-component PDMS-b-PS (DS45) and PS-b-PFS (SF35) in response to different solvent vapors. Cylindrical (top-left), hexagonally perforated lamellar (top-center), and lamellar (top-right) morphologies were obtained from the same PDMS-b-PS BCP by changing the volume ratio of heptane (VHep) and toluene (VTol). PS-b-PFS maintained the same spherical morphology (bottom) for the different solvent vapor treatment conditions. (b) Morphological variation of the BCP blends (PDMS-b-PS and PS-b-PFS) treated by mixed solvent vapors. The BCP blending ratio (VDS45/VSF35) was fixed at 2.5. Uniform host-guest assembly between the two BCPs were achieved at VHep/VTol = 1.2.

Mentions: As we demonstrated in our previous study3435, an unusual degree of geometrical tunability of BCP patterns can be achieved through an annealing treatment with mixed vapors composed of preferentially swelling solvent molecules. For PDMS-b-PS (DS45), with a molecular weight of 45.5 kg/mol and a minority volume fraction of = 33.7% in the dry state, the sample morphologies showed significant variation depending on the ratio between heptane and toluene used for the solvent-annealing of the BCP, because heptane preferentially swells the PDMS block. Morphological transitions are due to selective swelling of PDMS by heptane and a consequent increase in its effective volume fraction of PDMS () during solvent annealing34. After the completion of the solvent vapor treatment, the rapid removal of solvent molecules from the BCP samples quenches in-plane morphologies36, due to predominant out-of-plane shrinkage of the film thickness and due to the rise of the effective glass transition temperature (Tg) of the matrix PS block above room temperature. All the solvent vapor treatments in this study were performed at 85°C for accelerated self-assembly37. The morphologies were observed using electron microscopy after subjecting the BCP samples to a two-step sequential CF4 plasma and oxygen plasma treatment process to remove the thin PDMS top layer and PS matrix, respectively38. As shown in Figure 2a, the pure PDMS-b-PS BCP presented cylindrical and HPL morphologies when treated with vapors of pure toluene and a 1:1 mixture of heptane and toluene, respectively. In the HPL (or lamellar catenoid structure)39, the minority block (PDMS) forms a lamellar sheet with well-aligned PS perforations having overall six-fold symmetry. Uniform thru-pores were generated by the removal of the PS domains, as can be seen in the SEM image (Figure 2a, top-middle). The average pore diameter and center-to-center distance were 36 and 58 nm, respectively. In contrast, the morphologies of PS-b-PFS (SF35), with a molecular weight of 35 kg/mol and a minority volume fraction of = 11.5%, did not present any noticeable change by varying the fraction of heptane in the treatment vapor, as shown in Figure 2a (bottom). This can be attributed to the small difference in the solubility parameters between PS and PFS4041, which may induce almost symmetric swelling for the two constituent blocks, thereby preserving the morphology regardless of the treatment conditions. These results on the respective di-BCPs suggest that the effective volume fraction of PDMS () can be selectively tunable in the blends of PDMS-b-PS and PS-b-PFS via the controlled incorporation of a preferential solvent (heptane).


Host-guest self-assembly in block copolymer blends.

Park WI, Kim Y, Jeong JW, Kim K, Yoo JK, Hur YH, Kim JM, Thomas EL, Alexander-Katz A, Jung YS - Sci Rep (2013)

Self-assembled morphologies of pure BCPs and blended BCPs treated by various mixed solvent vapors.(a) Morphologies of single-component PDMS-b-PS (DS45) and PS-b-PFS (SF35) in response to different solvent vapors. Cylindrical (top-left), hexagonally perforated lamellar (top-center), and lamellar (top-right) morphologies were obtained from the same PDMS-b-PS BCP by changing the volume ratio of heptane (VHep) and toluene (VTol). PS-b-PFS maintained the same spherical morphology (bottom) for the different solvent vapor treatment conditions. (b) Morphological variation of the BCP blends (PDMS-b-PS and PS-b-PFS) treated by mixed solvent vapors. The BCP blending ratio (VDS45/VSF35) was fixed at 2.5. Uniform host-guest assembly between the two BCPs were achieved at VHep/VTol = 1.2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC3824169&req=5

f2: Self-assembled morphologies of pure BCPs and blended BCPs treated by various mixed solvent vapors.(a) Morphologies of single-component PDMS-b-PS (DS45) and PS-b-PFS (SF35) in response to different solvent vapors. Cylindrical (top-left), hexagonally perforated lamellar (top-center), and lamellar (top-right) morphologies were obtained from the same PDMS-b-PS BCP by changing the volume ratio of heptane (VHep) and toluene (VTol). PS-b-PFS maintained the same spherical morphology (bottom) for the different solvent vapor treatment conditions. (b) Morphological variation of the BCP blends (PDMS-b-PS and PS-b-PFS) treated by mixed solvent vapors. The BCP blending ratio (VDS45/VSF35) was fixed at 2.5. Uniform host-guest assembly between the two BCPs were achieved at VHep/VTol = 1.2.
Mentions: As we demonstrated in our previous study3435, an unusual degree of geometrical tunability of BCP patterns can be achieved through an annealing treatment with mixed vapors composed of preferentially swelling solvent molecules. For PDMS-b-PS (DS45), with a molecular weight of 45.5 kg/mol and a minority volume fraction of = 33.7% in the dry state, the sample morphologies showed significant variation depending on the ratio between heptane and toluene used for the solvent-annealing of the BCP, because heptane preferentially swells the PDMS block. Morphological transitions are due to selective swelling of PDMS by heptane and a consequent increase in its effective volume fraction of PDMS () during solvent annealing34. After the completion of the solvent vapor treatment, the rapid removal of solvent molecules from the BCP samples quenches in-plane morphologies36, due to predominant out-of-plane shrinkage of the film thickness and due to the rise of the effective glass transition temperature (Tg) of the matrix PS block above room temperature. All the solvent vapor treatments in this study were performed at 85°C for accelerated self-assembly37. The morphologies were observed using electron microscopy after subjecting the BCP samples to a two-step sequential CF4 plasma and oxygen plasma treatment process to remove the thin PDMS top layer and PS matrix, respectively38. As shown in Figure 2a, the pure PDMS-b-PS BCP presented cylindrical and HPL morphologies when treated with vapors of pure toluene and a 1:1 mixture of heptane and toluene, respectively. In the HPL (or lamellar catenoid structure)39, the minority block (PDMS) forms a lamellar sheet with well-aligned PS perforations having overall six-fold symmetry. Uniform thru-pores were generated by the removal of the PS domains, as can be seen in the SEM image (Figure 2a, top-middle). The average pore diameter and center-to-center distance were 36 and 58 nm, respectively. In contrast, the morphologies of PS-b-PFS (SF35), with a molecular weight of 35 kg/mol and a minority volume fraction of = 11.5%, did not present any noticeable change by varying the fraction of heptane in the treatment vapor, as shown in Figure 2a (bottom). This can be attributed to the small difference in the solubility parameters between PS and PFS4041, which may induce almost symmetric swelling for the two constituent blocks, thereby preserving the morphology regardless of the treatment conditions. These results on the respective di-BCPs suggest that the effective volume fraction of PDMS () can be selectively tunable in the blends of PDMS-b-PS and PS-b-PFS via the controlled incorporation of a preferential solvent (heptane).

Bottom Line: Our self-consistent field theory (SCFT) simulation results theoretically support that the precise registration of a spherical BCP microdomain (guest, B-b-C) at the center of a perforated lamellar BCP nanostructure (host, A-b-B) can energetically stabilize the blended morphology.As an exemplary application of the hybrid nanotemplate, a nanoring-type Ge2Sb2Te5 (GST) phase-change memory device with an extremely low switching current is demonstrated.These results suggest the possibility of a new pathway to construct more diverse and complex nanostructures using controlled blending of various BCPs.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea.

ABSTRACT
Ultrafine, uniform nanostructures with excellent functionalities can be formed by self-assembly of block copolymer (BCP) thin films. However, extension of their geometric variability is not straightforward due to their limited thin film morphologies. Here, we report that unusual and spontaneous positioning between host and guest BCP microdomains, even in the absence of H-bond linkages, can create hybridized morphologies that cannot be formed from a neat BCP. Our self-consistent field theory (SCFT) simulation results theoretically support that the precise registration of a spherical BCP microdomain (guest, B-b-C) at the center of a perforated lamellar BCP nanostructure (host, A-b-B) can energetically stabilize the blended morphology. As an exemplary application of the hybrid nanotemplate, a nanoring-type Ge2Sb2Te5 (GST) phase-change memory device with an extremely low switching current is demonstrated. These results suggest the possibility of a new pathway to construct more diverse and complex nanostructures using controlled blending of various BCPs.

No MeSH data available.


Related in: MedlinePlus