Exploring the structural relaxation in 2-ethyl-1-hexanol by neutron spin echo: from intermolecular and supramolecular correlations to long-range density fluctuations

IF 5.2 2区化学 Q2 CHEMISTRY, PHYSICAL

Journal of Molecular Liquids Pub Date : 2025-09-30 DOI:10.1016/j.molliq.2025.128600

S. Arrese-Igor , J. Colmenero , J. Allgaier , M.D. Ruiz-Martín , B. Farago , A. Arbe

{"title":"Exploring the structural relaxation in 2-ethyl-1-hexanol by neutron spin echo: from intermolecular and supramolecular correlations to long-range density fluctuations","authors":"S. Arrese-Igor , J. Colmenero , J. Allgaier , M.D. Ruiz-Martín , B. Farago , A. Arbe","doi":"10.1016/j.molliq.2025.128600","DOIUrl":null,"url":null,"abstract":"<div><div>The combination of neutron spin echo experiments on protonated and deuterated samples has provided direct insight into the hydrogen (H) self (incoherent) and collective (coherent) dynamics of the monoalcohol 2-ethyl-1-hexanol (2E1H) over a wide range of scattering vector (<math><mi>Q</mi></math>) values. Thereby we have covered length scales from the intermolecular ones (at the structure factor peak <math><msub><mi>Q</mi><mrow><mtext>max</mtext></mrow></msub><mo>∼</mo><mn>1.4</mn></math> Å<math><msup><mspace></mspace><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>) to long-range density fluctuations (<math><mi>Q</mi><mo>∼</mo><mn>0.1</mn><mo>−</mo><mn>0.3</mn></math> Å<math><msup><mspace></mspace><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>) including also the relevant length scale for the supramolecular structures developed by H-bonding (pre-peak at <math><mi>Q</mi><mo>≈</mo><mn>0.5</mn></math> Å<math><msup><mspace></mspace><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>). Away from the main structural peak, incoherent contributions to the measured echoes have been properly subtracted to isolate the coherent scattering. The structural relaxation of long-wavelength fluctuations and intermolecular correlations as well as the incoherent H-motions reveal two processes, a non-dispersive (local) one and diffusion. Their relative weight to the structural relaxation dramatically varies from low-<math><mi>Q</mi></math> (<math><mn>0.1</mn><mo>≲</mo><mi>Q</mi><mo>≲</mo><mn>0.4</mn></math> Å<math><msup><mspace></mspace><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>) – where relaxation is dominated by the non-dispersive process – to <math><msub><mi>Q</mi><mrow><mtext>max</mtext></mrow></msub></math> – where it takes place mainly by diffusion –. The opposite tendency is shown by incoherent scattering. These results corroborate for 2E1H the observations recently reported in other systems with different interactions and molecular sizes, and support the assignment of the local process as that responsible for stress relaxation. Moreover, the NSE results at the pre-peak reveal a much slower relaxation than at intermolecular level. Comparison of the NSE timescales at the different characteristic lengths investigated with those obtained by relaxation techniques (dielectric spectroscopy, oscillatory shear rheology, depolarized light scattering, NMR, and calorimetry) sheds light on the origin of these processes.</div></div>","PeriodicalId":371,"journal":{"name":"Journal of Molecular Liquids","volume":"438 ","pages":"Article 128600"},"PeriodicalIF":5.2000,"publicationDate":"2025-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Molecular Liquids","FirstCategoryId":"92","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0167732225017775","RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}

引用次数: 0

Abstract

The combination of neutron spin echo experiments on protonated and deuterated samples has provided direct insight into the hydrogen (H) self (incoherent) and collective (coherent) dynamics of the monoalcohol 2-ethyl-1-hexanol (2E1H) over a wide range of scattering vector (

Q

) values. Thereby we have covered length scales from the intermolecular ones (at the structure factor peak

Q_{max} \sim 1.4

^{- 1}

) to long-range density fluctuations (

Q \sim 0.1 - 0.3

^{- 1}

) including also the relevant length scale for the supramolecular structures developed by H-bonding (pre-peak at

Q \approx 0.5

^{- 1}

). Away from the main structural peak, incoherent contributions to the measured echoes have been properly subtracted to isolate the coherent scattering. The structural relaxation of long-wavelength fluctuations and intermolecular correlations as well as the incoherent H-motions reveal two processes, a non-dispersive (local) one and diffusion. Their relative weight to the structural relaxation dramatically varies from low-

Q

(

0.1 ≲ Q ≲ 0.4

^{- 1}

) – where relaxation is dominated by the non-dispersive process – to

Q_{max}

– where it takes place mainly by diffusion –. The opposite tendency is shown by incoherent scattering. These results corroborate for 2E1H the observations recently reported in other systems with different interactions and molecular sizes, and support the assignment of the local process as that responsible for stress relaxation. Moreover, the NSE results at the pre-peak reveal a much slower relaxation than at intermolecular level. Comparison of the NSE timescales at the different characteristic lengths investigated with those obtained by relaxation techniques (dielectric spectroscopy, oscillatory shear rheology, depolarized light scattering, NMR, and calorimetry) sheds light on the origin of these processes.

查看原文本刊更多论文

用中子自旋回波探索2-乙基-1-己醇的结构弛豫：从分子间和超分子相关到远程密度波动

结合质子化和氘化样品的中子自旋回波实验，可以直接了解单醇2-乙基-1-己醇（2E1H）在大范围散射矢量(Q)值上的氢(H)自（非相干）和集体（相干）动力学。因此，我们涵盖了从分子间的长度尺度（在结构因子峰Qmax ~ 1.4 Å−1）到远程密度波动（Q ~ 0.1−0.3 Å−1），包括由氢键形成的超分子结构的相关长度尺度（在Q≈0.5 Å−1的前峰）。在远离主结构峰的地方，测量回波的非相干贡献被适当地减去，以隔离相干散射。长波波动的结构弛豫和分子间的相互关系以及非相干h运动揭示了两个过程，即非色散（局部）和扩散。它们对结构弛豫的相对权重从低Q值（0.1≤Q≤0.4 Å−1）到Qmax值（主要由扩散过程引起）变化很大。非相干散射则表现出相反的趋势。这些结果证实了最近在其他具有不同相互作用和分子大小的系统中报道的2E1H观察结果，并支持了局部过程作为应力松弛的原因的分配。此外，峰前的NSE结果显示了比分子间水平慢得多的弛豫。将不同特征长度的NSE时间尺度与弛豫技术（介电光谱、振荡剪切流变学、去偏振光散射、核磁共振和量热法）所得的时间尺度进行比较，揭示了这些过程的起源。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

求助全文

约1分钟内获得全文求助全文

来源期刊

Journal of Molecular Liquids 化学-物理：原子、分子和化学物理

CiteScore

10.30

自引率

16.70%

发文量

2597

审稿时长

78 days

期刊介绍： The journal includes papers in the following areas: – Simple organic liquids and mixtures – Ionic liquids – Surfactant solutions (including micelles and vesicles) and liquid interfaces – Colloidal solutions and nanoparticles – Thermotropic and lyotropic liquid crystals – Ferrofluids – Water, aqueous solutions and other hydrogen-bonded liquids – Lubricants, polymer solutions and melts – Molten metals and salts – Phase transitions and critical phenomena in liquids and confined fluids – Self assembly in complex liquids.– Biomolecules in solution The emphasis is on the molecular (or microscopic) understanding of particular liquids or liquid systems, especially concerning structure, dynamics and intermolecular forces. The experimental techniques used may include: – Conventional spectroscopy (mid-IR and far-IR, Raman, NMR, etc.) – Non-linear optics and time resolved spectroscopy (psec, fsec, asec, ISRS, etc.) – Light scattering (Rayleigh, Brillouin, PCS, etc.) – Dielectric relaxation – X-ray and neutron scattering and diffraction. Experimental studies, computer simulations (MD or MC) and analytical theory will be considered for publication; papers just reporting experimental results that do not contribute to the understanding of the fundamentals of molecular and ionic liquids will not be accepted. Only papers of a non-routine nature and advancing the field will be considered for publication.