Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Kitao, Sagiri

Suzuki, Michio

Yamada, Tomoaki

English

Nonlinear Earnings Dynamics and Inequality over the Life Cycle: Evidence from Japanese Municipal Tax Records

Tohoku University博士（情報科学）thesi

Chen, Guangyu

Size tuning of visual spatial attention

三橋, 勇太

Japanese

若者における観光行動の意思決定過程―新型コロナウイルス感染症の影響を踏まえて―

宮西, 祐香子

英語デジタル教科書の利用履歴に基づく操作パターンの特徴とリスクの把握

山本, 泰平

Ranque-Hilsch効果のメカニズム解明を目的とした円管内に発生する非定常高速旋回流の数値的研究

Tohoku University博士（工学）要約のみthesi

LUO, QINGYAO

  ルオ  チンヤオ 
氏 名   LUO QINGYAO 
研究科，専攻の名称 東北大学大学院工学研究科（博士課程）ファインメカニクス専攻 
学 位 論 文 題 目          Surface Heterogeneity Effects on Thermal Transport across Solid–
Liquid Polymer Interfaces: A Molecular Dynamics Study (固液ポリマー界面の熱輸送におけ
る表面不均一性の効果：分子動力学法による研究） 
論 文 審 査 委 員          主査 東北大学教授 小原 拓  東北大学教授 徳増 崇 
  東北大学教授 岡部 朋永 東北大学准教授 菊川 豪太 
論文内容要約 
Electronic devices often contain solid–liquid interfaces where efficient heat transfer is crucial for thermal 
management. As device sizes shrink to the scale of mean free path of phonons, interfacial thermal resistance (ITR) at 
these interfaces becomes a significant bottleneck, impeding heat dissipation and limiting further improvements in 
device performance. A comprehensive understanding of the microscopic mechanisms governing interfacial thermal 
transport is therefore essential for optimizing thermal management strategies. Surface modifications serve as the one of 
primary methods for altering ITR. This thesis investigates the influence of surface heterogeneities, introduced by these 
modifications, on ITR across solid–polymer liquid interfaces using non-equilibrium molecular dynamics (NEMD) 
simulations.  
Chapter 1 introduces the research background, outlining the fundamental concepts of solid-liquid interfacial thermal 
transport and reviewing prior studies on surface heterogeneities. Despite progress in understanding surface effects on 
interfacial properties, the literature lacks a systematic investigation of how surface heterogeneity impacts ITR across 
solid–polymer liquid interfaces. This chapter sets the research objectives and outlines the thesis structure.  
Three representative types of surface heterogeneities, i.e., hard surface morphological heterogeneity (Chapter 2), 
chemical heterogeneity (Chapter 3), and soft surface morphological heterogeneity (Chapter 4), are systematically 
explored in this work through NEMD simulations to understand their effects on ITR and the underlying mechanisms.  
Chapter 2 focuses on hard surface morphological heterogeneity produced by surface texturing on solid substrates. 
The system consists of platinum surfaces with varying roughness (flat, small grooves, and large grooves) in contact with 
liquid n-alkanes of different chain lengths. The study investigates the combined effects of surface roughness scale, 
polymer chain length, and solid-liquid affinity on ITR. Results demonstrate that grooved surfaces generally exhibit 
higher ITR than flat surfaces at low affinity, but lower ITR at high affinity, due to differences in groove filling. Larger 
grooves provide more space to enable more favorable polymer chain orientations for heat transfer, leading to reduced 
ITR compared to smaller grooves. However, long polymer chains predominantly align parallel to the interface, limiting 
their ability to facilitate heat transfer perpendicular to the surface. These findings highlight that optimizing roughness 
and polymer chain length is crucial for efficient heat transfer.  
Chapter 3 examines chemical heterogeneity, modeled as periodic surface patterns with alternating patches of high 
and low solid-liquid affinity. Using the same materials as in Chapter 2, the study explores the patch size effects on ITR. 
Larger patch sizes result in non-uniform temperature distributions across the interface due to the fact that liquid atoms 
in weak-affinity regions are too far away to interact effectively with strong-affinity regions. This non-uniformity leads to 
larger ITR compared to surfaces with smaller patch sizes, which exhibit more uniform interfacial liquid and 
temperature distributions, and thereby smaller ITR. The parallel thermal resistance model, created based on the 
analogy to conventional electrical resistance model, accurately predicts ITR for systems with small patch sizes, as the 
uniform temperature distribution aligns with the assumption of equal voltage drop in the electrical analogy, However, it 
underpredicts ITR for large patch systems, due to non-uniform temperature at the interfaces. More complex models 
would be needed for large patch systems, although the model might become simpler again when the patch size reaches 
the macroscale. These findings demonstrate the potential for precise ITR modulation through chemical heterogeneity.  
Chapter 4 investigates soft surface morphological heterogeneity introduced by self-assembled monolayers (SAMs) 
with heterogeneous chain lengths grafted onto solid surfaces. In contrast to hard surface morphological heterogeneity, 
the soft and flexible nature of SAMs introduces additional complexity. Hydrophobic alkanethiol SAMs, with higher 
stiffness, maintain well-defined patterned structures and increase liquid contact area, thereby reducing ITR compared 
to flat surfaces. Conversely, hydrophilic polyethylene glycol (PEG)-COOH SAMs are soft, with short SAMs being 
covered by longer SAMs, that limits the increase of liquid contact area and the reduction of ITR. Liquid adsorption 
density is the primary factor influencing the ITR of SAM-based surfaces. For systems involving polar liquids, hydrogen 
bond density becomes another key factor affecting ITR. In such cases, ITR may even exceed that of non-patterned 
surfaces because, in patterned systems, the formation of hydrogen bonds between short SAMs and polar liquid 
molecules is constrained by being covered by longer SAMs. These findings underscore the importance of optimizing 
SAM stiffness and arrangement for efficient thermal management at interfaces involving soft morphological 
heterogeneity.  
Across these studies, governing mechanisms for surface heterogeneity effects on ITR are concluded in Chapter 5:  
1. The additional surface area from hard surface morphological heterogeneity enables greater liquid adsorption, 
effectively reducing ITR by increasing heat paths. Compared to small-scale heterogeneity, larger-scale 
heterogeneity provides more freedom for liquid molecules to adopt favorable orientations, enhancing heat 
transfer efficiency and resulting in lower ITR.  
2. The imposed interfacial chemical heterogeneity results in a heterogeneous interfacial temperature distribution, 
introducing additional sources of thermal resistance. The uniformity of interfacial temperature distribution 
governs the ITR.  
3. The increased surface area from soft surface morphological heterogeneity is not guaranteed because of the soft 
nature of SAMs. While stiff, heterogeneous SAMs maintain their pattern and increase the liquid contact area; 
soft, long SAMs covering shorter ones limit the expansion of this area, reducing the number and efficiency of 
heat paths. When hydrogen bonds are present, hydrogen bond density becomes another key factor affecting ITR, 
alongside liquid adsorption density. The restricted hydrogen bond formation due to the long SAMs coverage 
results in higher ITR compared to non-patterned surfaces.  
Based on these mechanisms, the following design principles and optimizing strategies are proposed:  
1. Liquid molecules with smaller sizes, ideally shorter than both the height and width of surface grooves, are 
recommended to reduce ITR, as this allows the molecules inside the grooves to adopt favorable orientations that 
enhance heat transfer.  
2. For precise tuning of ITR, producing chemical heterogeneity with carefully optimized patch sizes is effective. The 
combination of chemical and morphological heterogeneities may offer further opportunities for ITR control by 
inducing specific liquid chain orientations.  
3. For high-resolution patterned surfaces aimed at reducing ITR, densely packed SAMs with high stiffness, such as 
alkanethiols, and alternating chain lengths are recommended.  
4. Framing the long hydrophilic SAMs with long stiff SAM boundaries, alongside short hydrophilic SAMs to create 
a patterned surface, may achieve both a large liquid contact area and a high hydrogen bond density, further 
reducing the ITR.  
This thesis provides fundamental insights into the role of surface heterogeneity in interfacial thermal transport and 
offers practical strategies for optimizing ITR at solid–polymer liquid interfaces. It contributes to the development of 
advanced thermal management solutions for nanodevices, paving the way for more efficient and reliable electronic 
devices. 
  
 
 
 
 


Surface Heterogeneity Effects on Thermal Transport across Solid-Liquid Polymer Interfaces: A Molecular Dynamics Study

GUO, YAN

Enhancing Robustness in Inertial Sensor-based Gait Analysis Using Temporal Convolutional Network and Its Clinical Application

春山, 大地

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