Micro Optical Viscosity Sensor for in situ Measurement Based on a Laser-Induced Capillary Wave

Abstract

In this article, we demonstrate a novel micro optical viscosity sensor (MOVS) based on a laser-induced capillary wave with a focus control system that enables in situ monitoring of viscosity and surface tension changes in microliter-order liquid samples such as body fluids, polymer coating materials, lubricants, heavy oils and so on. The microfabricated sensor consists of two deep trenches (depth of 273 µm) holding photonic crystal fibers (PCFs), and three shallow trenches (depth of 125 µm) holding collimating lensed fibers (CLFs) for the probing laser. The capillary wave is excited by two pulsed laser beams generating optical interference, and the rapid motion of the capillary wave, which contains information regarding the viscosity and surface tension of the sample, is monitored by detecting the first-order diffracted beam of the probing laser irradiated onto the sample surface. In order to apply this sensor in manufacturing and clinical settings, the distance between the liquid level and the sensor must be properly adjusted because the sample surface is strongly influenced by evaporation and outside vibration disturbances under such conditions. In the MOVS, the specular reflection of the probing laser is detected by a symmetrically placed collimating lensed fiber. Maximizing the signal of specular reflection by using a piezo stage connected to the MOVS and PID controller, the focal points of the fibers (PCFs and CLFs) are adjusted on the sample surface. The high-reproducible measurement results under evaporation and outside disturbance indicate the validity of MOVS for in situ application.

Thermoelastic Model for Impulsive Stimulated Scattering Monitoring the Evolution from Capillary to Rayleigh Type Wave Propagation on the Surface of Viscoelastic Materials Throughout the Glass Transition

“…ISS is a technique that has proven its value for the thermal and elastic characterization of bulk solids [26], thin coatings [27], intermediate layers in multilayered systems [28], bulk fluids [4], fluid-solid interface [6], and the free liquid surface [11][12][13]29]. In the employed ISS scheme shown in Fig.…”

A review of hemorheology: Measuring techniques and recent advances

“…Such micro-devices have been used to measure the shear viscosity (Srivastava et al, 2005;Zeng and Zhao, 2009;Smith et al, 2010) and viscoelasticity (Brust et al, 2013;Kang and Lee, 2013) of blood. Microfluidic viscometers are based on a range of different principles as reviewed by Ong et al (2010), such as capillary pressure-driven flow (Srivastava et al, 2005), electrical impedance spectroscopy (Zeng and Zhao, 2009), laser-induced capillary wave (Taguchi et al, 2009) and oscillating micro-structure induced by an electrostatic driving force (Smith et al, 2010). For instance, in the micro viscometer proposed by Srivastava et al (2005), which is illustrated in Fig.…”

“…The device requires a sample volume of 600 nl and is able to perform the measurement in less than 100 s. However, microfluidic devices often require a syringe pump or, in some cases, a pressurized reservoir and connecting tubes to be combined with the microchip in order to promote the blood flow, which typically implies larger sample volumes. An exception is the micro-optical capillary sensor based on laser-induced capillary wave developed by Taguchi et al (2009), in which the sample is placed directly on the sensor. Measurements using distilled water with a pigment have been performed for a proof-of-concept, but the device is yet to be tested with real blood.…”

An Optical Fiber Viscometer Based on Long-Period Fiber Grating Technology and Capillary Tube Mechanism

“…This novel micro optical viscosity sensor consists of two deep trenches holding photonic crystal fibers for excitation laser, and two shallow trenches holding the lensed-fibers for probing laser. The optical interference fringe excited by two pulsed laser beams heats the sample surface, and the temporal behavior of surface geometry is detected as a first-order diffracted beam, which contains the information of liquid properties (viscosity and surface tension) [ 9 - 11 ]. The flow of oil films under gravity and centrifugal force may be adapted to give accurate absolute measurements of viscosity for silicon oils [ 12 , 13 ].…”