軟物質(zhì)中的固體表面張力和表面彈性
Surface Tension and Surface Elasticity of Soft Solids
許欽 博士 Qin Xu, Ph.D.
瑞士蘇黎世聯(lián)邦理工學(xué)院材料系，軟物質(zhì)和生物材料實(shí)驗(yàn)室
Laboratory of Soft and Living Materials, Department of Materials
ETH Zurich, Swissland
2018年5月9日（周三）10:00-11:00
新主樓A849
Surface tension describes in-plane force per unit length required to deform a material interface. While the concept is widely used to characterize capillarity on liquid interfaces, solid surface tensions are overlooked as they are too weak to significantly deform bulk solids. However, recent works have shown that solid surface tension is essential to understand contact mechanics on soft solid interfaces at micro- to nano-meter scales. For a solid material with Young modulus, E, and surface tension, Υ, soild capillarity has been shown to dominate over bulk elasticity at scales smaller than the elastocapillary length scale, le=Υ/Ε. In this regime, the significant force contribution from surface tension Υ fundamentally alters experimental behavior, and consequently the interpretation of many materials characterization techniques. In this talk, by studying microscopic profiles of the contact-line geometry of a partially wetting droplet on a strained polymeric gels, we directly measure the strain dependent surface stress, and associated surface elasticity. We find the surface tension of soft polymeric gels significantly depends on applied strain.
表面張力是用來描述材料界面上單位長度受力的物理量。這一概念對于液體表面力學(xué)性質(zhì)的研究尤為重要并有廣泛的實(shí)驗(yàn)應(yīng)用。然而對于固體表面的力學(xué)問題，表面張力卻很少被提及。這是因?yàn)橄鄬τ隗w彈性，固體表面張力對于固體形變的貢獻(xiàn)通?？梢院雎圆挥?jì)。然而，近期的各項(xiàng)研究發(fā)現(xiàn)：在軟物質(zhì)體系中，固體表面張力對各類接觸力學(xué)的性質(zhì)卻起到了關(guān)鍵性作用。 當(dāng)一個(gè)材料的體楊氏模量為E，表面張力為Y，我們可以定義一個(gè)新的長度尺寸：彈性-張力尺寸，le=Υ/E（Elasto-capaillary length）。在這個(gè)空間尺度范圍內(nèi)，固體表面張力將對體系的力學(xué)性質(zhì)起到關(guān)鍵性的影響。很多軟物質(zhì)的實(shí)驗(yàn)現(xiàn)象和經(jīng)典的材料表征技術(shù)都應(yīng)該考慮固體表面張力從而進(jìn)行修正。在這個(gè)報(bào)告中，通過研究液滴在高分子膠體表面的浸潤，以及各相張力在固體微觀尺寸的特征。我們在實(shí)驗(yàn)上系統(tǒng)研究了固體表面張力隨材料表面形變的變化，從而發(fā)現(xiàn)了隨應(yīng)變調(diào)控的固體表面張力，同時(shí)揭示了軟性高分子材料的表面彈性性質(zhì)。
Reference (相關(guān)文獻(xiàn))：
[1] Direct measurements of surface stress of stretched soft solids
Qin Xu, Katharine E. Jensen, Rostislav Boltyanskiy, Raphael Sarfati, Robert Style, and Eric R. Dufresne
Nature Communications 8, 555 (2017)
[2] Surface Elastic Constants of a Soft Solid
Qin Xu, Robert W. Style and Eric R. Dufresne
Soft Matter, 14, 916-920 (2018)
[3] Strain-dependent solid surface stress and the stiffness of soft contacts
Katharine E. Jensen, Robert Style, Qin Xu and Eric R. Dufresne
Physical Review X, 7, 041031 (2017).
[4] The mechanical equilibrium of soft solids with surface elasticity
Robert W. Style and Qin Xu
arXiv:1801.07744
Accepted by Soft Matter
聯(lián)系人：徐曄（ye.xu@buaa.edu.cn）
