2021 Fiscal Year Research-status Report
Hierarchical liquid crystal assemblies based on large graphene oxide sheets and nonionic organic compounds
| Project/Area Number |
20K03887
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| Research Institution | Waseda University |
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Principal Investigator |
GUEGAN Regis 早稲田大学, 理工学術院, 准教授(任期付) (50822483)
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| Co-Investigator(Kenkyū-buntansha) |
山田 貴壽 国立研究開発法人産業技術総合研究所, 材料・化学領域, 研究グループ長 (30306500)
畠山 一翔 国立研究開発法人産業技術総合研究所, 材料・化学領域, 研究員 (30773965)
菅原 義之 早稲田大学, 理工学術院, 教授 (50196698)
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| Project Period (FY) |
2020-04-01 – 2023-03-31
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| Keywords | Nanosheets / colloids / hierarchical assemblies / nonionic surfactants / excluded volume |
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| Outline of Annual Research Achievements |
The C12E8-GO mixtures were measured by small angle X-ray scattering (SAXS) at different concentrations and temperatures and a phase diagram of the different assemblies of C12E8-GO-H2O system could be determined. SAXS profiles of bulk C12E8 sample (at 40 wt%) and C12E8-GO samples (40 wt% C12E8 and 0.8 wt% GO dispersion). The sample with short lateral size GO remained in a spherical micellar phase (L1 phase) , but the sample with large GO transits in a hexagonal phase (H1 phase). In the presence of GO, the phase transitions L1-H1 and H1-V1 (cubic phase) shifted to the low concentration. The presence of water located onto the GO surface at large content, combined with the excluded volume (non-accessible volume) of GO, reduces the available free water molecules for C12E8 leading to a phase transition and reorganization of the micelles of the C12E8 in hexagonal assemblies. The mixtures were also studied by rheo-SANS (experiments carried out at J-Parc) but, interestingly, no phase changes occurred under the shear measurements even for the mixtures prepared at large concentration of GO, only an anisotropy effect of the micelles assembled in hexagonal assembly (H1 phase) was observed. Furthermore, under shear measurements, a slight shift (to low angle value) of the first Bragg reflection related to the hexagonal lattice was observed but cannot be only attributed to the impact of the shear but could more likely related to a change of the concentration of the surfactant due to an evaporation of the solvent in rheological cell during the long rheo-SANS measurements.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
The understanding of the stability and the formation of different assemblies of the mixtures of inorganic and organic colloids (here graphene oxide sheets and nonionic surfactant) represent an important effort and fundamental step for the possible preparation of hierarchical advanced materials. A phase re-organization to a hexagonal phase (H1 phase) in the presence of large GO with the observation of a shift of about 5 wt.% for the L1-H1 boundary could be confirmed by the rheo-SANS measurements, that can be explained by excluded volume effect. The GO nano sheets occupy a certain volume mobilizing water molecule that is no more accessible to the surfactant leading to locally an increase of the volume fraction of the nonionic surfactant micelles that undergo a phase transition, shifting to low concentration the L1-H1 phase transition. Now the research efforts focus on the understanding of the impact of the size and oxidation rate of GO nano sheets on the change of phases made by nonionic surfactants showing different hydrophilic lipophilic balance: C12E5-8 and octylphenol ethoxylate (TX-100 that can be the precursors for the synthesis of hybrid materials with potential supercapacitor like applications.
Thus, we are currently investigating:
- the excluded volume effect of large GO with the different surfactants showing diverse HLB and showing similar phase diagrams as C12E8
- the interaction between the surfactants with different hydrophilic-lipophilic balance and GO surface (adsorption isotherms)
- numerical simulation of the colloidal dispersion
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| Strategy for Future Research Activity |
A complete understanding of the phase reorganization of the nonionic surfactant species will be done by the study using small angle X-ray scattering of other amphiphilic molecules of the CnEm series and probably other nonionic surfactants and even other nonionic systems showing a L1-H1 phase transition. Indeed, the hydrophilic-lipophilic balance (HLB) as well as the aggregation number (number of surfactants forming micelles) tune the rigidity of the micelles and even their ability to aggregate. Rigid micelles are likely to be more sensitive to excluded volume in contrast to flexible micelles incorporating a large number of surfactants. In addition to the amphiphilic molecules, an improvement of the GO synthesis for a more accurate and monodisperse selection of the lateral size has to be undertaken. Indeed, the ability of the inorganic nanosheets to form the liquid crystalline phase mainly depend on the lateral size as well as its polydispersity.
In addition, the affinity between the syrfactantts of different hydrophilic-lyotropic balance (HLB): C12E5-8 and TX-100 and GO with different lateral size will be determined by total organic carbon (TOC) experiment and the obtention of adsorption isotherms. To calculate the amount of surfactant absorbed on GO, TOC that can measure the concentration of the organic carbons that dissolved in water was used.
Depending on the progresses of the research, we may also investigate the behavior of other phases made by nonionic surfactants and GO and perform the preparation of the composites and investigate their electro-chemical performances.
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| Causes of Carryover |
Since a lot of experiments were and are planned to be done in the frame of some collaborations, we plan to use some of the funds to cover the business trips to carry out the experiments at the NIMS in Tsukuba (SAXS, rheological measurements), and/or at the CROSS in Tokai (SALS, rheological measurements as well) and probably in Kobe (Jelena Muncan, Kobe U.).
It is likely that the Langmuir-Blodgett equipment will not be purchased within this project, but instead we may use the funds for electro-disposition set-up cells in addition to other devices and items for layer by layer equipment in order to obtain uniform composite films.
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Research Products
(4 results)
