液体表面特性的光学可视化

【作者】 朱峰；

【导师】 苗润才；

【作者基本信息】 陕西师范大学 ， 声学， 2008， 博士

【摘要】 光学技术是探测液体表面特性重要手段,通过研究光在液体表面的衍射、干涉、反射和折射等现象,可以探测液体表面特性。液体表面特性的光学可视化研究分为两部分:一部分是动态液面的研究,即激光衍射法探测毛细波及液体表面特性。另一部分是静态液面的研究,即激光边界反射法和掠射法探测润湿效应弯曲液面及液体表面特性。本文围绕液体表面特性的光学可视化研究,主要进行了以下几个方面的工作:(1)建立了斜入射情况下毛细波的激光衍射理论。当激光斜入射到几十至几百赫兹毛细波上,观察到稳定的、清晰的衍射图样。运用傅立叶光学中正弦位相光栅衍射理论对实验现象进行了理论分析,完善了斜入射情况下毛细波的激光衍射理论,利用该理论分析了衍射图样的缺级现象和衍射光斑的位置不对称分布,并对斜入射情况下毛细波的衍射光场进行理论仿真,并与实验结果进行了对比分析,理论仿真与实验结果完全符合。(2)激光衍射法探测毛细波的波长、振幅和色散关系。通过测量衍射光斑间距,进而实时、准确地测量出不同频率毛细波的波长。通过测定衍射图样中不同级别衍射光斑的光强比,求出了毛细波振幅的大小。探测了单一液体毛细波的色散关系,实验数据和理论曲线基本符合,并利用色散关系求得不同温度下液体的表面张力,实验所测表面张力与标准值基本吻合。理论上建立了液体薄膜毛细波的色散关系,分别探测了薄膜厚度不变时,毛细波的角频率和波数的关系;毛细波的频率不变时,波数和薄膜厚度的关系,实验数据和理论曲线基本符合,提出了利用激光衍射法探测较小厚度薄膜的方法。(3)激光入射角与衍射光强的关系。利用傅立叶光学中正弦位相光栅理论分析了不同入射角的激光在毛细波上的衍射,给出了衍射光斑光强分布与入射角的解析关系。实现了不同入射角的激光在毛细波上衍射,发现随着激光入射角的变化,衍射光斑的光强和间距随入射角的变化而变化,并且有缺级现象出现,激光入射角越大,衍射角的位置不对称性越明显,并将实验结果和理论分析加以比较,二者基本吻合。(4)激光衍射法测定表面张力、表面压和毛细波波速。利用激光衍射法测定了蒸馏水和煤油的表面张力,同时验证了毛细波的色散关系。测定了不同温度下蒸馏水的表面张力,用最小二乘法对实验数据进行拟合,得出了表面张力和温度的解析关系,表面张力随着温度的增加是递减的,并和温度呈近似线性关系。实现了不溶性单分子膜毛细波的激光衍射,测定了苯单分子膜的表面压。测定了不同频率下毛细波的相速度和群速度,研究了毛细波波速与频率和波长之间的关系,毛细波波速随着频率的增大而增大,随着波长的增大而减小,呈非线性关系。最后,测定了不同温度下毛细波波速,用最小二乘法对实验数据进行拟合,给出了毛细波波速与温度的解析关系,毛细波波速随着温度增加而减小,并和温度呈近似线性关系。(5)润湿效应弯曲液面的边界反射及应用。基于激光在润湿效应形成的弯曲液面上边界反射,研究了弯曲液面的特性。当平行激光束垂直入射到平板、细棒、双平板和圆柱形管润湿效应形成的弯曲液面时,弯曲液面的边界反射光随着弯曲液面的变化而变化,产生特殊地反射图样。反射图样中有清晰的干涉条纹,反射图样的形状随边界入射光束宽度的变化而迅速地变化,分析了反射图样的形状与边界入射光束的宽度关系,得出了平板和双平板润湿效应弯曲液面斜率和上升高度的拟合曲线及其解析表达式,细棒和圆柱形管润湿效应弯曲液面斜率的拟合曲线及其解析表达式,进一步计算出弯曲液面上升的最大高度和液体的接触角。建立了一种利用弯曲液面边界反射来实时测量液面特性的新方法。(6)光线掠射法和斜板法测定接触角。当平行激光束掠入射到平板润湿效应弯曲液面时产生特殊的反射图样,反射图样的中间为暗场,两侧为亮场。分析了暗场宽度和弯曲液面的最大高度关系,通过测量反射图样的暗场宽度计算出弯曲液面的最大高度,进而计算出弯曲液面的接触角。在斜板法测定接触角实验中,对传统斜板法做了较大改进。平行激光束垂直照射到液体表面,当改变平板的插入角度,平板润湿效应产生的弯曲液面形状也会随着发生变化,同样照射到弯曲液面的反射光也会发生变化,通过观测反射图样,可判断出何时弯曲液面完全平坦,进而通过测定平板转过角度计算出接触角。更多还原

【Abstract】 Optical technique is important to probe the substance properties. Of course, this method is a good choice for the liquid surface research. When the optical effects, including interference, diffraction, reflection and refraction, occur on the liquid surface, some parameters of liquid surfaces can be measured. Visualization of liquid surfaces by means of the optical method includes two aspects: one is study on the dynamic liquid surface, in other words, probing of capillary waves and liquid surface properties by laser diffraction. The other is study on the static liquid surface, in so many words, measurement of the curved liquid surfaces and liquid surface properties by laser boundary reflection and glancing incidence. Visualization of liquid surfaces by means of the optical method is investigated in detail in this dissertation. The main work can be summarized as follows.(1) The theory of investigating capillary waves using optical diffraction in a case of oblique incidence is found. When the laser beam obliquely impinges on capillary waves at a certain angle, steady and visible diffraction spots are formed. The capillary wave acts as a sinusoidal reflection phase grating for the laser beam, and the theory is further developed from the theory of Fourier Optics. Missing order and asymmetry of diffraction patterns are investigated in some detail, both theoretically and experimentally. A combination of simulation and experiment is proposed to trace out light diffraction from capillary waves at a certain angle. The theoretical analysis and experimental results are in good agreement.(2) Measurement of the wavelength, the amplitude, and the dispersion relation of capillary waves by laser diffraction. The wavelength of capillary waves is real time determined with great precision by measuring the distance of diffraction spots. The amplitude of capillary waves is calculated by measuring the diffraction intensity ratio of different order. The data give the dispersion relation of capillary waves and provide an accurate method for determining the relation between the surface tension and the temperature, and the standard value and experimental results are in good agreement. The dispersion relation of liquid film surfaces is discussed. The relation between angular frequency and wave number at a fixed film thickness and the relation between wave number and film thickness at a fixed angular frequency are verified with experiments, and experimental data agree well with theoretical curves. A new method for measurement of liquid film thickness is presented in a no-contact way.(3) Study on the relation between the diffraction intensity and the angle of incidence. The theory of laser diffraction from capillary waves at a different angle of incidence is found from the theory of Fourier Optics, and the relation between the diffraction intensity and the angle of incidence is obtained. When the laser beam obliquely impinges on capillary waves at a different angle, steady and visible diffraction spots are formed. The diffraction intensity and the distance of diffraction spots vary with the change of an angle of incidence, and there is the phenomenon of missing orders in the diffraction spectrum. Asymmetry of diffraction patterns increases with the increasing of an angle of incidence. The theoretical and experimental results are in good agreement.(4) Measurement of liquid surface tension, surface pressure of insoluble monolayer surface film and velocity of capillary waves by laser diffraction. Surface tension of distilled water and kerosene are measured using laser diffraction, subsequently, the theory of dispersion relations is well consistent with the experimental data. The analytic expression of the surface tension and the temperature was derived by the non-linear least square fit to the data. Surface tension of distilled water decreases with the increasing temperature. The approximate relation between surface tension and temperature is linear. When laser falls on the insoluble monolayer surface film capillary waves, in the experiment steady and visible diffraction patterns are obtained. Surface pressure of Benzene is measured carefully. Phase velocity and group velocity of capillary waves are investigated. Velocity of capillary waves increases with the increasing frequency of capillary waves, velocity of capillary waves decreases with the increasing wavelength of capillary waves, and the relation is obviously nonlinear. At last, the velocity of capillary waves is measured at a different temperature, the analytic expression of the velocity and the temperature was derived by the non-linear least square fit to the data. Velocity of capillary waves decreases with the increasing temperature, and the approximate relation between velocity and temperature is linear.(5) Boundary reflection from curved liquid surfaces and its application. A simple technique for investigating the curved liquid surface (CLS) was developed, which is based on analyzing the reflection patterns from the CLS. When a collimated light beam vertically illumined the CLS which is caused by the effect of the wetting a smooth flat plate, a rod, a double parallel flat and a columned glass tube, the special reflective patterns, which correspond to the boundary light reflection from a deformed liquid surface, are experimentally obtained. In fact, there are the visible interference fringes in the reflective patterns, and the width of patterns varies with the change of the decreasing width of the incident beam. By analyzing the relation between the reflective patterns and the CLS, the analytic expressions of the slope and height of the CLS around a smooth flat plate and a double parallel flat are derived. According to the same method, the analytic expressions of the slope of the CLS around a rod and a columned glass tube are derived. Furthermore, the contact angle and the surface maximal height of the sample liquid are obtained by the analytic expression. It is believed that the boundary reflection principle is capable of real time describing the measurement of the characterization of CLS.(6) A novel contact angle measurement by laser glancing incidence method and tilting plate method. When an expanded and collimated laser beam impinges on the CLS around a smooth flat plate at glancing incidence, special reflective patterns of a strip-shape dark region in the center and the bright region on both sides are observed. The relation of the dark region width and the maximal height of the CLS is derived theoretically. The contact angle of distilled water on the glass slides is calculated directly by utilizing the dark area width of the reflection pattern. A contact angle measurement by traditional tilting plate method is improved. When a collimated light beam vertically illumined the CLS, the distribution of the reflected light from the CLS will change with the surface deformation. It is possible to measure the surface deformation by determining the change of the reflective light from the CLS. A contact angle is direct calculated by the angle of rotation of a plate.更多还原