研究者詳細 - 大久保　光

This paper reports the thermally activated ultralow friction of 100% cellulose nanofiber (CNF) molding. The mechanism of friction reduction was investigated using a laboratory-built in-situ Raman tribometer. Our experimental results showed that a CNF molding exhibited an ultralow friction coefficient of below 0.04 in a CNF ring and steel disk tribopair under high-temperature conditions (T > 100°C). The results of the temperature-rise friction test showed that the friction coefficient of the CNF molding strongly depended on the temperature and decreased linearly with increasing temperature. The in situ tribo-Raman monitoring results, during friction, indicated a change in the structure of the CNF molding. Therefore, the crystallinity indices and lengths of the CNF fibers gradually changed as the temperature increased. Moreover, transfer tribofilms were observed on the counter-steel surface against the CNF rings. When the CNF molding exhibited thermally activated ultralow friction, the tribofilm was mainly composed of cellulose and graphitic carbon. Our results suggest that the thermal and friction-activated structural transformations of CNF molding and CNF-derived transfer film formation are pivotal factors contributing to the ultralow friction phenomenon observed in CNF molding at high temperatures.

Layered Structure and Wear Mechanism of Concentrated Polymer Brushes

Okubo, H; Kagiwata, D; Nakano, K; Tsujii, Y

LANGMUIR 39 ( 50 ) 18458 - 18465 2023年12月 [査読有り]

DOI Web of Science PubMed

記述言語：英語掲載種別：研究論文（学術雑誌）共著

Operando tribo-Raman spectroscopic observation for wear processes of superlow frictional concentrated polymer brushes at frictional interface

Hikaru Okubo , Daiki Kagiwata , Shinya Sasaki , Yoshinobu Tsujii , Ken Nakano

Polymer Testing 127 2023年9月 [査読有り]

DOI Web of Science

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）共著

Novel Environmentally Superior Tribomaterial with Superlow Friction: 100% Cellulose Nanofiber Molding

Okubo Hikaru, Hashiba Hiromi, Inamochi Toru, Sato Kaisei, Sasaki Shinya, Yamada Kazushi, Nakano Ken

TRIBOLOGY LETTERS 71 ( 3 ) 2023年9月 [査読有り]

DOI Web of Science

記述言語：英語掲載種別：研究論文（学術雑誌）共著

a-C:H DLC膜の潤滑性能に及ぼす多層フラーレン粒子の効果

大久保光, 中野健, 佐々木信也

日本機械学会論文集 89 ( 924 ) 23-00126 - 23-00126 2023年5月 [査読有り]

DOI CiNii Research

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本機械学会共著

Suitable friction modifiers and anti-wear additives for hydrogenated amorphas carbon (a-C:H) films have been investigated by many research groups for a decade since it is well-known that the combination of the a-C:H film and the conventional additives hardly exhibits good tribological performances under boundary lubrication. In this study, to confirm the effectiveness of nano-carbon additives for improving the tribological performance of a-C:H films, the tribological performances of the combination of the a-C:H film and multi-walled fullerenes (MWFs) containing oil was investigated under boundary lubrication. Especially, we compared the effects of the MWFs on the tribological performances of two DLCs: a-C:H and tetrahedral amorphous carbon (ta-C) using a ball-on disk tribometer and in-contact Raman tribometer that can monitor the chemical structure of frictional interfaces. All our results suggest that the combination of a-C:Hs and MWFs exhibits an ultralow friction and remarkable wear reduction compared to non-MWF added oils due to the formation of MWF tribofilms uniformly at the frictional interfaces.

Tribological properties of 100% cellulose nanofiber (CNF) molding under dry- and boundary lubrication-conditions at CNF/steel contacts

H. Okubo , R. Nakae , D. Iba , K. Yamada , H. Hashiba , K. Nakano , K. Sato , S. Sasaki

Cellulose 2023年5月 [査読有り]

DOI

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）単著

Analysing the Relationship between Mechanical Properties and Inner Structure of LLDPE Virgin Film for Optimizing Extrusion Condition

Maho Toshimitsu, Hikaru Okubo, Shigeru Yao & Yosuke Matsukuma

Journal of Chemical Engineering of Japan 2023年1月 [査読有り]

DOI

記述言語：英語掲載種別：研究論文（学術雑誌）単著

AFM摩擦面その場観察によるZDDPと有機系FM複合添加潤滑油中の反応膜の生成過程と潤滑メカニズムの調査

佐藤魁星, 大内春花, 大久保光, 渡部誠也, 佐々木信也

トライボロジスト 67 ( 5 ) 354 - 365 2022年5月 [査読有り]

DOI CiNii Research

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本トライボロジー学会共著

Zinc dialkyldithiophosphate (ZDDP) improves wear resistance by forming a tribo-film on the sliding surface. However, the tribo-film is known to cause an increase in the friction coefficient. In order to reduce the friction coefficient as well as the wear, it is expected to combine an organic friction modifier (OFM) with ZDDP. In this study, a macro-friction test was conducted using a reciprocating sliding tester under the lubrication with the combined oils of ZDDP and OFMs. In order to understand the lubrication mechanism of the combined oils, the formation process of tribo-film was evaluated by using AFM in-situ observation. NMR analysis of the combined oil and XPS analysis of the sliding surface were performed. Glycerol monooleate (GMO) was found to suppress the formation of ZDDP-derived tribo-film. On the other hand, it was found that tallow diethanolamine (TDEA) changes the composition and mechanical properties of the ZDDP-derived tribo-film and exerts a friction-reducing effect. It was considered that the combined effect of OFM is due to the competitive adsorption phenomenon and the change of ZDDP molecular structure in the mixed oil.

Time-resolved ex situ Raman/FT-IR spectroscopic study of structural changes in polymeric gears during operation: Towards the development of operando spectroscopic systems for polymer gears

H. Okubo , K. Kobayashi , D. Iba , I. Moriwaki , S. Yao , S. Sasaki

Polymer Testing 113 107675 - 107675 2022年 [査読有り]

DOI

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）単著

Ultralow Friction of a Tetrahedral Amorphous Carbon Film Lubricated with an Environmentally Friendly Ester-Based Oil

大久保光

トライボロジスト 66 ( 12 ) 931 - 932 2021年12月

DOI CiNii Research

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本トライボロジー学会単著

Frictional Properties of Element- and Compound-Doped Diamond-Like Carbon Films under Boundary Lubrication with Synthetic Base Oil

Hikaru Okubo, Shinya Sasaki

Trans Tech Publications　Defect and Diffusion 2021年