The State-of-Art Testing and Measurement Instruments
Automatic Micro Contact Angle Meter
The micro contact angle meter is specially designed for the pioneers in the micro/nano fields. The instrument is equipped with a unique capillary liquid dispensing system that has an inner diameter of 5-50µm, for making a liquid drop <30µm in size and picoliter in volume. In addition, the instrument comes with high magnification optics for accurately placing and measuring such small drops on micrometer features, and CCD cameras with a high capturing speed of 60 frames per second for studying dynamic characteristics of interaction of micron size liquids with solid surfaces. The technique is sensitive and capable of detecting monolayer molecules.
The unmatched instrument capabilities and usefulness for contact angle measurement at microscale have been exemplified through results obtained on fibers, medical guide wires, patterned organic light emitting display and microcircuits. Its advantageous high speed capturing capability is demonstrated by measuring the strong dependency of contact angles on time at millisecond intervals. The recorded feature-rich dynamics of contact angles of micron size drops is deemed valuable for investigating sensitive surface chemistry, vapor evaporation, wettability, and hydrophilicity/hydrophobicity changes at micro/nano scales.
The Fully Automatic Contact Angle Meter
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The DM-701 Front View
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The close-up view of the automatic liquid dispenser, stage, camera and cool LED light source
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90 degree titled position for sliding angle measurement
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The DM-701 Fully Automatic Contact Angle Meter with sliding angle measurement capability is the top line of Kyowa’s contact angle meters. Complementary to the microscopic contact angle meter MCA-3, the DM 701 provides a more macro scale and conventional approach to a full spectrum of contact angle measurements. It combines Kyowa’s over 60 years of expertise in designing and manufacturing surface/interface scientific instruments with the latest and advanced technologies in fast imaging and data processing. DM-701 represents the state of art and quality instrumentation for performing surface and interface study of liquids, solids and their interactions. It enables users to acquire accurate measurements with easy operation through the FAMAS measurement and analysis software package.
The instrument as shown above is capable of automated stage positioning and dispenser control. Automatically the stage moves along the x and z axes and can be rotated from 0° to 90° along with the dispenser, camera and light source. The dispenser is capable of repeatedly producing droplets in the micro-liter to mili-liter range. A long lasting cool LED acts as the light source for use during experimentation. This feature minimizes the heat effect on the contact angle measurement if any. Each measurement is recorded by a 3 zoom CCD camera. The camera has a capturing speed of 60 frames per second for use in dynamic contact angle measurements. The varying zoom levels allow for the testing of super hydrophilic surfaces where deposited droplets can extend outside the range of the standard zoom level.
The instrument can perform a variety of contact angle measurements including sessile drop, advancing angle, receding angle and sliding angle. The sensitivity of contact angle measurements is useful for determining surface characteristics. These test results can be useful for characterizing solid surfaces or liquid solutions. The contact angle can determine whether the surface is either hydrophobic or hydrophilic in nature. This in turn gives an understanding of the surface’s wettability. By combining the contact angle measured via different liquids, the surface free energy can be calculated by means of one of 5 common methods. The fluid used in determining the contact angle does not necessarily need to be liquid. With the three-state setup, the contact angle of gas can be determined. The contact angle can be measured in the dynamic sense. The ability to record the change in contact angle over time is useful for determining the absorption rate. This is useful for materials with sponge-like characteristics. The instrument can also measure the surface tension of a liquid. The same imagining equipment can measure the surface tension of a liquid by using the pendent drop method.
The Delsa Nano C Particle and Zeta Potential Analyzer
The Beckman Coulter Delsa Nano C Particle Analyzer provides desirable solutions to your nanoparticle size and Zeta potential analysis needs. The DelsaNano C utilizes Photon Correlation Spectroscopy (PCS) and Electrophoretic Light Scattering techniques to determine particle size and zeta potential of materials. Offering an excellent degree of accuracy, resolution and reproducibility, the DelsaNano C has been designed to simplify submicron particle size and zeta potential analyses. The DelsaNano C provides accurate size measurements in the range from 0.6 nm to 7 μm with sample concentration ranging from 0.001% to 40%. It can perform the analysis of aqueous and non-aqueous samples as well as Zeta potentials of solid surfaces and membranes. It has been serving a wide variety of applications in industries such as nanotechnology, electronics, pharmaceuticals, inks, food & beverage, biomedical, textile. Figure 1 is a picture of the DelsaNano C.
Particles suspended in liquids are in Brownian motion due to random collisions with solvent molecules. This motion causes the particles to diffuse through the medium. The diffusion coefficient, D, is inversely proportional to the particle size according to the Stokes-Einstein equation:
Where D is the diffusion constant, kB the Boltzmann’s constant, T the absolute temperature, ƞ0 the viscosity, d the spherical particle diameter.
Photon Correlation Spectroscopy, sometimes also referred as dynamic light scattering, is a technique used to determine the diffusion coefficient of small particles in a liquid. The coefficient is determined by accurately measuring the light scattering intensity of the particles as a function of time. As the particles of interest diffuse through the sample cell due to Brownian motion, an incident beam of laser light illuminates the particles. The particles scatter the light, producing fluctuations in the scattering intensity as a function of time. The scattered light is collected at a chosen angle, and is measured by a highly sensitive detector. Since the diffusion rate of particles is determined by their size, information about their size is contained in the rate of fluctuation of the scattered light. The intensity fluctuations are collected as photon counts and correlated to generate the auto correlation function (ACF). The diffusion coefficient is determined by fitting the ACF using the Cumulants method from which the mean size is obtained using the Stokes-Einstein equation.
The particle analyzer measures both size and zeta potential by use of its patent pending dual laser system and specialized sample holding cells. Each cell is designed specifically to measure either particle size, zeta potential or both. One cell is specially designed to measure the zeta potential of a flat solid surface. Highly sensitive light detectors measure the changes in light intensity that is caused by the scattering created by the particles. This process can detect particle size as small as 0.6nm or as large as 7µm. By applying a current to the appropriate cell, an electric field is created within the cell. This causes the particles to move to the electrode with the opposite charge. The same light detectors used for determining size can measure the frequency change and determine the particle velocity for use in zeta potential. A heating and cooling stage can adjust the cell temperature from 15°C below the ambient room temperature to 90°C. An auto titrator can be used in conjunction with the particle analyzer to adjust the pH level within the solution.
The particle sizing and zeta potential are applicable to fields such as adhesives, beverages, biotechnology, membranes, nanoparticles, paints, pharmaceuticals and surface coatings. The sizing can measure the actual diameter of the particles in a solution. The zeta potential of those particles will give a better understanding on the stability of the particles in the solution. Typically, a value of +/-30mV is used as the border between a stable system and a system with high flocculation. By using the solid surface cell, the zeta potential gives an indication of the surface charge. This is useful for thin film membranes and data recording devices. Using the auto titrator to adjust the pH level changes the zeta potential as well. At a certain pH level, the zeta potential will be neutral and thus determining the isoelectric point of the surface.
