JPH09257606A - Device for measuring precision shear stress - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure rheology behavior by connecting a divided cylindrical priezo-element vertically disposed on a sample to a spring perpendicular to a sample surface, and driving the element by a battery to detect horizontal displacement of the spring. SOLUTION: A connection member 4 is connected to the free ends of two springs vertical to the measuring surface of a silica lens 1 to provide a four- divided cylindrical piezo-element 5 vertical to a lens 1 on the other end. A holding member 1 extends downward the element 5 to hold the lens 1. Displacement of the member 4 is detected with a displacement gage probe 7. In measurement of this electro-static capacity method, and electro-static capacity is measured to find a distance (d) between the probe 7 and an opposed wall. In this case, the power source of a capacitive displacement gage 25 connected to the probe 7 used a nickel cadmium battery 26 to reduce electric fluctuation and noise. This is effective particularly in a case where rheology behavior is researched in a minute space of a nanometer scale.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the lubrication and friction of a sample surface, the deformation of a polymer adsorption layer, the structure formation and the collapse of a liquid or a liquid crystal trapped in a narrow space, based on a precise measurement of shear stress on a nanometer scale. The present invention relates to a precision shear stress measuring device for measuring in.

[0002]

2. Description of the Related Art Conventionally, a "shear stress measuring device" is used to precisely control the distance and interaction between two surfaces and horizontally shift them periodically to measure the stress against shearing.
Is being developed to study surface lubrication and friction. FIG. 10 is a block diagram of such a conventional shear stress measuring device.

As shown in this figure, reference numeral 101 is a liquid or liquid crystal sample for examining the characteristics of a liquid confined in a narrow space. Numerals 102 and 104 are sample surfaces, and the sample surface 102 is driven by a piezo element or the like to move the surfaces in parallel with high precision. 103 spring for detecting shear stress, 105
Is a measuring system using a spring for measuring the surface force. Here, a constant distance d is set between the two sample surfaces 102 and 104. It should be noted that there may be no sample 101 and the sample surfaces 102 and 104 may be directly displaced.

[0004]

[Problems to be solved] By the way, Israel
Lachvili et al., “Science, 240, 18
9 (1988) ”, (1) as a mechanism for accurately moving the surface in parallel, (2) a system using a stainless steel spring and a strain gauge for surface stress measurement is reported.

This system applies a stress of 10 ⁻⁶ to 10 ⁻³ N to a surface which moves several tens of μm on the order of “minute”.
That is the measurement range. for that reason,
This system has a problem that it is not suitable for measuring weak stress and rapid shear change. Also, Klein et al.
, 352, 143 (1991) ”, (1)
As a mechanism for accurately moving the surface in parallel, (2) using a stainless steel spring and an air capacitance method for surface stress measurement, while moving very precisely in the horizontal direction (± 0 (Transfer of 1 nm and 3 μm possible) 10
^-A system for measuring stress of ^-7 N or more is reported.

However, this system has a problem that it is difficult to measure even a weak stress with higher accuracy due to vibration and noise from the electric system. The present invention eliminates the above-mentioned problems, and reduces the noise coming from the electric system by using a battery that is isolated from the outside as a power source, thereby reducing rheological behavior in a nanometer-scale minute space. It is also an object of the present invention to provide a precision shear stress measuring device capable of highly accurate measurement.

[0007]

Means for Solving the Invention

(1) In a nanometer-scale precision shear stress measuring device, a spring arranged vertically to a sample and a divided cylindrical piezo element connected to this spring and arranged vertically to the sample. The driving means for the piezo element, the capacitance type displacement gauge for detecting the displacement of the spring in the horizontal direction, and the drive battery for the capacitance type displacement gauge are provided.

[0008] As described above, by using the battery that is isolated from the outside as the power source, it is possible to reduce the noise coming from the external electrical wiring and peripheral equipment. In particular, when researching rheological behavior in a nanometer-scale minute space, the noise reduction effect is great. In shear stress measurement, not only the strength but also the phase shift is often predicted between the waveform of the voltage applied to the piezo element (that is, the functional form of the movement of the surface) and the output of the shear stress, and the phase shifts. And, it becomes difficult to use a lock-in amplifier, which is generally used for noise reduction,
The reduction of noise in the output signal is of essential importance. However, when the output of the shear stress is the same as the waveform of the voltage applied to the piezo element in both waveform and phase, the use of the lock-in amplifier is also effective.

(2) Precision shear stress measurement described in (1) above
In the device, the piezoelectric element has an outer electrode divided into four parts.
Has a curved shape, grounds the common part of the inner electrode, and
V _A= -V_cA voltage is applied.
Therefore, with a simple configuration, for example, ± 27 nm, 30
Surface drive in the X direction of Hz (1.6 μm / sec) is possible
And the frictional force at that time is 3 × 10^-6Get N
be able to.

(3) In the precision shear stress measuring device described in (1) above, the sample portion has a lens-like shape and is exchangeable, and the measurement surface is held by two springs perpendicular to the surface, The piezo element is such that the surface is driven horizontally at a constant speed. Therefore, it is possible to easily set the shear stress measurement of various samples.

(4) In the precision shear stress measuring device described in (3) above, the sample may be a solid surface such as glass or mica, or a chemically modified solid surface thereof. Therefore, the shear stress of the sample can be measured with high precision on the nanometer scale. (5) In the precision shear stress measuring device according to (1) above, a lock-in amplifier is provided in the capacitive displacement meter.

Therefore, the accuracy is further increased to ± 0.3n.
It is possible to measure about m. (6) In a nanometer-scale precision shear stress measuring device, a spring arranged perpendicular to the sample surface and a divided cylindrical piezo connected to the spring and arranged perpendicular to the sample. An element, a driving means for this piezo element, and a capacitive displacement gauge for detecting the horizontal displacement of the spring are used as an exchange attachment, and if necessary, liquid is filled between the sample surfaces or the sample part is hermetically sealed. It is designed to be immersed in the liquid inside.

Therefore, it is possible to measure the structural type of the liquid confined in the narrow space between the surfaces. Particularly, a surface force measuring device for precisely measuring the force in the vertical direction [Fig. 2 (b)]
And FIG. 8] can be easily replaced with the one sample surface [the piezo element tube 15 of FIG. 2 (b) and the shear stress measuring portion 35 of FIG. 8] as a replacement attachment.
The reliability of the measurement can be enhanced, and therefore, the vertical distance and the interaction between the two sample surfaces can be easily set.

By incorporating in the surface force measuring device, while controlling (variable) the distance between two surfaces (determined by interference fringe measurement using white light, see FIG. 8) and the force applied perpendicularly, Shear stress can be measured. When the displacement measurement is performed by the capacitance method, the distance is measured by utilizing that the capacitance between the surface facing the probe is inversely proportional to the distance d ₀ (see FIG. 1).

At this time, for example, the electrostatic capacity is measured from a current (AC current) flowing at that time by applying a high-frequency potential from the electrode on the probe. Actually, the current is converted into a voltage by the circuit and output. The measured capacitance C is the capacitance C of the space formed by the surface facing the actual probe.
It is the sum of _s and the capacitance C ₀ of unknown origin coming from the circuit of the device.

In the present measurement, as shown in FIG. 4, it is necessary to measure a minute displacement of nanometer order from a certain constant distance d ₀ . As described above, since the high-frequency potential change is applied, it is effective at that time to reduce the electrical fluctuation by the battery as the power source according to the present invention. By doing so, the capacitance C _{0 of} unknown origin is also stable, and more precise measurement is possible.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a precision shear stress measuring device showing an embodiment of the present invention, FIG. 2 is a diagram showing an assembled state of the precision shear stress measuring device, FIG. 3 is a block diagram of the precision shear stress measuring device, and FIG. Is an explanatory diagram of displacement measurement by the capacitance method, FIG. 5 is a configuration diagram of a piezo element that generates shear stress, FIG. 6 is a diagram showing a voltage applied to the piezo element, and FIG. 6 is an output of a displacement meter. It is a figure. Here, an example of measuring the frictional force between the glass and the surface of the mica will be described.

In FIGS. 1 and 2, 1 is a silica lens, 2 is a fixed portion, 3 is two springs perpendicular to the measurement surface of the silica lens 1, and 4 is a connecting member connected to the free end of the spring 3. The other end of the connecting member 4 is bent inward and upward. A piezoelectric element 5 is fixed to the other end of the connecting member 4 and is arranged perpendicularly to the silica lens 1 (a piezo element having a four-divided cylindrical shape, Morgon, PZT).
8-8031-5H), 6 extends below the piezoelectric element 5 and holds the silica lens 1, 7 is a displacement gauge probe for detecting the displacement of the connecting member 4, 11 is a silica lens, and 12 is a silica lens. Mica fixed on the surface of 11,
Reference numeral 13 is a spring constituting a vertical force (force in the Z-axis direction), 14 is a top plate, 15 is a piezo element tube, 16 is a measuring surface, 17 is a double cantilever (the same as the spring 13), and 18 is a diagram. , 19 is a shaft, and 20 is a translation stage.

Shear measuring device A shown in FIG.
Is the upper surface sample portion 15 of the surface force measuring device of FIG.
And is assembled to the portion of the top plate 14. In FIG. 3, reference numeral 21 is a function generator, 22 is a first piezo power source that generates a V _A voltage (see the upper part of FIG. 5) in the piezo element 5, and 23 is a V _C voltage (see the lower part of FIG. 5) in the piezo element 5. A second piezo power source to be generated, 24 shear stress measurement system, 25 is a capacitance type displacement gauge connected to the displacement gauge probe 7, 26 is a battery as a power source of the capacitance type displacement gauge 25, for example, nickel-cadmium battery, Reference numeral 27 is an oscilloscope, which can simultaneously measure the outputs of the power supplies 22 and 23 for the piezo elements and the output of the capacitive displacement meter 25 as a function of time and display them on the screen.

Displacement measurement by the capacitance method will be described. The distance is measured by utilizing the fact that the capacitance between the surface facing the displacement gauge probe 7 is inversely proportional to the distance d (see FIG. 1). . At this time, the capacitance is measured, for example, by applying a high-frequency potential from the electrode on the displacement gauge probe 7 and measuring the current (AC current) flowing at that time. actually,
The current is converted into a voltage by the circuit and output. The capacitance C to be measured is the sum of the capacitance C _{s of the} space formed by the surface facing the actual displacement gauge probe 7 and the capacitance C ₀ of unknown origin coming from the circuit of the measuring device.

C = C _s + C ₀ = (KA / d) + C ₀ where K is the permittivity and A is the area of the probe. In the present measurement, as shown in FIG.
Small displacements on the order of nanometers from ₀ must be measured. Since a high-frequency potential is applied in this manner, it is effective at that time to reduce electrical fluctuations than the battery as the power source according to the present invention.

By doing so, the electrostatic capacitance C _{0 of} unknown origin is also stabilized, and more precise measurement becomes possible. In this way, the surface of the glass-mica can be freely exchanged with other sample surfaces, and a system designed to be incorporated in a usual surface force measuring device (FIG. 2) was designed. The exchange attachment holds the measurement surface with two springs 3 which are perpendicular to the surface, and further allows the surface to be driven horizontally at a constant speed by a piezo element 5.

As shown in FIG. 5, the piezo element 5 is a cylindrical piezo element in which the outer electrode is divided into four (A, B, C, D), and the inner electrode is grounded (E). Figure 5 (A) to indicate the four-division (A, B, C, D ) in a cylindrical piezoelectric element, as shown in FIG. 6, the triangular wave V _A = -V _C
Voltage is applied. Then, as shown in FIG.
The maximum movement in the X direction is a few μm (208 nm / 100V),
It is driven at a cycle of 0 to several hundred Hz.

For driving the surface, as shown in FIG. 3, the signal of the function generator 21 is supplied by a piezo power source (ENP-made by Echo Electric Co., Ltd.).
2001A) 22 and 23 are amplified. Horizontal force F ₁
Refers to the horizontal displacement (ΔX) of the two springs 3 that hold the surface vertically, and the air gap capacitance method (manufactured by Japan ADE, Microsense non-contact micro displacement meter 3401HR).
-01) and the spring constant (K _{1 to} 320 N / m) was used to calculate from F ₁ = K ₁ ΔX. As will be seen below, the current ΔX accuracy is ± 1 nm. Further, the upper limit of the driving frequency of the surface when driven by a triangular wave is several hundreds Hz, except for the vicinity of 100Hz which is the resonance frequency of the device. Further, the resonance frequency changes depending on the design of the holding portion and the like and the spring constant used.

As the surface, a mica 12 having a smooth molecular level was fixed on a cylindrical (curvature, R-20 mm) silica (quartz) lens 11. The two lenses are placed with their axes perpendicular to each other, and one surface is spring (K ₂ ~ 1).
00 N / m) 13 is held at one end. The distance between the surfaces is measured by the color-order interferometry method, and the force (F = KΔz) in the vertical direction is obtained from the displacement (Δz) of the spring 13.

Note that a sine wave, a rectangular wave, or the like may be used instead of the triangular wave. [Measurement Example] (1) Displacement of Spring The displacement of the spring 3 was measured using the air gap capacitance method. When reading ΔX with an accuracy of ± 1 nm, noise from the power supply cannot be ignored, and in order to obtain a stable response, the power supply of the capacitive displacement meter 25 was changed to a storage battery as the DC power supply 26. Furthermore, it was confirmed that the measurement of about ± 0.3 nm is possible by using the lock-in amplifier.

However, the following measurement (2) is performed without using the lock-in amplifier. (2) Friction between the glass and the surface of the mica The glass and the surface of the mica are brought into contact with each other, and the surface is 30 Hz in the X direction
The stress due to friction when repeatedly moved at was investigated.

FIG. 6 shows the input voltage (× 1) to the piezo element.
/ 100), and FIG. 7 shows the monitor signal corresponding to the displacement ΔX of the spring at that time. (2 mV / div is 5n
It corresponds to the displacement of m). When the two surfaces are separated, ΔX becomes almost zero. 1.6 μm / sec from these data
The frictional force when driven at 30 Hz (actual moving distance ± 2.7 nm) is 3 × 10 ⁻⁶ N.

As described above, since the battery is driven in order to reduce the noise from the power source, the noise can be reduced. In particular, when studying the rheological behavior of periodic surface movement in a nanometer-scale minute space, the noise reduction effect is great. FIG. 8 is a diagram showing the displacement of the spring in the case of AC drive and DC drive, where the vertical axis is 2 mV / Div (1 graduation 2 mV) and the horizontal axis is 10 msec / Div (1 graduation 1
0 msec).

As is apparent from this figure, the displacement of the spring 3 is more stable in the case of DC drive shown in FIG. 8 (b) than in the case of AC drive shown in FIG. 8 (a). I understand. The improvement of the stability of displacement of the spring 3 in the DC drive can exert a great effect in improving the accuracy of shear stress measurement on the nanometer scale. Further, in the shear stress measuring device of the present invention, the sensitivity of stress is 10 ⁻⁷ N, but by further including a low pass filter, a high pass filter, etc., it is possible to further improve the sensitivity, and an equivalent system. In particular, it has an advantage that electric fluctuations on a long time scale are not included.

FIG. 9 is a sectional view showing the construction of another embodiment of the present invention, which is incorporated into a surface force measuring apparatus. In this figure, 31 is an airtight container, 32 is an aqueous solution enclosed in the airtight container 31, 33 is a spring, 34 is a Z direction distance drive unit having a spring 33, and 35 is a sample for incorporating the above-mentioned exchange attachment. It is a department.

With this configuration, it is possible to measure the structural form of the liquid confined in the narrow space between the surfaces. In particular, as the exchange attachment, the shear stress measuring unit (X-direction displacement measuring unit) can be easily replaced, the reliability of measurement can be improved, and the setting thereof is easy.

Further, various samples can be set in place of the above-mentioned sample in which glass-mica is contacted.
For example, a solid surface such as glass or mica may be brought into contact with the chemically modified surface, and an appropriate liquid sample may be sandwiched. In that sense, the surfaces do not necessarily have to be in contact. In shear stress measurement, the waveform of the voltage applied to the piezo element (that is, the functional form of the surface movement)
In many cases, not only the strength but also the phase shift is predicted during the output of the shear stress, and if the phase shift occurs, it becomes difficult to use a lock-in amplifier, which is generally used for noise reduction, and the output signal Noise reduction is essentially important. However, when the output of the shear stress is the same as the waveform of the voltage applied to the piezo element in both waveform and phase, the use of the lock-in amplifier is also effective.

It should be noted that the present invention is not limited to the above embodiment, but various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0035]

As described in detail above, according to the present invention, the following effects can be achieved. (1) According to the first aspect of the invention, since the driving battery is used as the driving power source, it is possible to reduce the noise coming from the external electric wiring and peripheral devices as compared with the AC power source. You can In particular, when studying rheological behavior in a nanometer-scale minute space, the noise reducing effect is remarkable.

(2) According to the invention described in claim 2, ± 27 nm, 30 Hz (1.6 μm / se) with a simple structure.
Surface driving in the X direction of c) was possible, and 3 × 10 ⁻⁶ N could be obtained as the frictional force at that time. (3) According to the invention described in claim 3, the shear stress measurement of various samples can be easily set.

(4) According to the invention described in claim 4, the shear stress of the medium set between the glass and the mica or between the glass and the mica can be measured with high precision on the nanometer scale. (5) According to the invention of claim 5, the accuracy is further improved,
It is possible to measure ± 0.3 nm.

(6) According to the invention described in claim 6, it is possible to measure the structural form of the liquid confined in the narrow space between the surfaces. In particular, it can be easily replaced with a shear stress measuring unit (X-direction displacement measuring unit) as a replacement attachment, and the reliability of measurement can be improved and its setting is easy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a precision shear stress measuring device showing an embodiment of the present invention.

FIG. 2 is a diagram showing an assembled state of a precision shear stress measuring device showing an embodiment of the present invention.

FIG. 3 is a block diagram of a precision shear stress measuring device showing an embodiment of the present invention.

FIG. 4 is an explanatory diagram of displacement measurement by a capacitance method showing an example of the present invention.

FIG. 5 is a diagram showing a configuration of a piezo element that generates shear stress according to an embodiment of the present invention.

FIG. 6 is a diagram showing a voltage applied to a piezo element showing an example of the present invention.

FIG. 7 is a diagram showing an output of the displacement meter showing the embodiment of the present invention.

FIG. 8 is a diagram showing the stability of distance measurement by the capacitance method in the case of AC driving and battery driving showing an example of the present invention.

FIG. 9 is a sectional view showing the configuration of a surface force measuring device for replacing and incorporating a precision shear stress measuring device according to another embodiment of the present invention.

FIG. 10 is a configuration diagram of a conventional shear stress measuring device.

[Explanation of symbols]

1 silica lens 2 fixing part 3,13,33 spring 4 connecting member 5 piezo element (a piezo element of a four-divided cylindrical shape) 6 holding member 7 displacement gauge probe 11 mica fixed on the surface of the silica lens 12 normal force (Z axis direction) Force generator 22 a function generator 22 a first piezo power supply 23 a second piezo power supply 24 a shear stress measurement system 25 a capacitive displacement meter 26 a battery 27 an oscilloscope 31 a closed container 32 an aqueous solution 34 a distance in the Z direction Drive mechanism 35 Attachment exchange part in surface force measuring device

Claims (6)

[Claims] 1. In a nanometer-scale precision shear stress measuring device, (a) a spring arranged perpendicular to a sample surface, and (b) a spring connected to the spring and arranged perpendicular to the sample surface. Divided cylindrical piezo element, (c) driving means for the piezo element, (d) a capacitive displacement meter for detecting horizontal displacement of the spring, and (e) the capacitive displacement meter. A precision shear stress measuring device, comprising: 2. The precision shear stress measuring device according to claim 1, wherein the piezo element has a shape divided into four parts.
Grounding the common portion of the upper end, precise shear stress measurement apparatus for applying the V _A = -V _c voltage of the triangular wave. 3. The precision shear stress measuring device according to claim 1, wherein the sample portion has a lens-like shape and is replaceable, the measurement surface is held by two springs perpendicular to the surface, and the piezo Precision shear stress measurement device that drives the surface horizontally at a constant speed with an element. 4. The precision shear stress measuring device according to claim 3, wherein the sample is a solid surface such as glass or mica, or the solid surface is chemically modified. 5. The precision shear stress measurement device according to claim 1, wherein the capacitive displacement gauge includes a lock-in amplifier. 6. A nanometer-scale precision shear stress measuring device, wherein a spring arranged perpendicular to a sample surface and a divided cylindrical shape connected to the spring and arranged perpendicular to the sample. The piezo element, the driving means for the piezo element, and the capacitive displacement gauge for detecting the horizontal displacement of the spring are used as an exchange attachment, and the liquid is sandwiched between the two surfaces of the sample section, or A precision shear stress measuring device characterized by immersing a liquid in a closed container.