LIQUID COMPOSITION

FIELD OF THE INVENTION

The invention relates to a liquid composition for an electrowetting device/liquid lens, and to a method of manufacturing the liquid composition

BACKGROUND OF THE INVENTION

Electrowetting is a breakthrough innovation causing a revolution in liquid lenses. The proper operation of an electrowetting liquid lens is dependent on the properties of an electrowetting liquid. A liquid composition for electrowetting comprises one polar liquid and one non-polar liquid, so the properties of the liquid composition are affected by the properties of the polar liquid and the non-polar liquid. To get a proper liquid composition for an electrowetting device, in theory, the polar liquid and non-polar liquid may need to fulfill the following requirements:

- the polar liquid and the non-polar liquid are immiscible with each other;

- the polar liquid and the non-polar liquid are transparent;

- the polar liquid and the non-polar liquid are colorless;

- the densities of the polar liquid and the non-polar liquid are equal;

- the polar liquid and the non-polar liquid are chemically stable;

- the polar liquid and the non-polar liquid are inert;

- a large refractive index difference exists between the polar liquid and the non-polar liquid;

- the polar liquid and the non-polar liquid have a specific difference in Abbe number (the wavelength dependence of refractive index);

- the polar liquid and the non-polar liquid have a low melting point; and

- the polar liquid and the non-polar liquid have a high boiling point.

However, in practice, finding a liquid composition that fulfills all requirements as mentioned above is very difficult. In most cases, the polar liquid has a higher density than the non-polar liquid. In order to eliminate gravity effects, it is therefore important to make the density of the non-polar liquid/polar liquid equal to that of the polar/non-polar liquid.

A method of manufacturing a liquid composition, which comprises a non-polar liquid having an equal density as a polar liquid, comprises blending a specific non-polar liquid having a lower density with another non-polar liquid having a higher density, so as to increase the density of the specific non-polar liquid, and then combine the specific non-polar liquid with the polar liquid.

The current method of increasing the density of the specific non-polar liquid to be equal to the density of the polar liquid may generate unwanted properties in the liquid composition. For example: a polar liquid is water, which has a density of 1.00g/cm3, and a non-polar liquid is dodecamethylpentasiloxane, which has a density of 0.918g/cm3. In order to obtain a density equal to that of water, l,l,5,5-tetraphenyl,l,3,3,5-tetramethyltrisiloxane, which has a density of 1.07g/cm3, is blended with the dodecamethylpentasiloxane. After the blending, the non-polar liquid has a density equal to that of water, but a very low Abbe number, which may make the electrowetting liquid unsuitable for some applications, such as achromatic lenses.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved liquid composition for an electrowetting device/liquid lens, and a method of manufacturing the liquid composition.

The liquid composition comprises:

- a first liquid, and

- a second liquid formed from an initial liquid by replacing a type of atom included in the initial liquid with a corresponding isotope of the atom, so that a density difference between the second liquid and the first liquid is reduced, wherein the second liquid and the first liquid are non-miscible or separated by a flexible membrane. The method of manufacturing comprises:

- replacing a type of atom, which is included in an initial liquid and has a corresponding isotope, with the corresponding isotope of the atom to form a second liquid, so that a density difference between the second liquid and a first liquid is reduced, wherein the second liquid and the first liquid are non-miscible or separated by a flexible membrane, and the initial liquid is a liquid used for generating the second liquid; and

- combining the second liquid with the first liquid.

The advantage of the proposed liquid composition for an electrowetting device/liquid lens and the corresponding manufacturing method is that using isotopes to reduce the density difference between the first liquid and the second liquid hardly affects the optical and chemical properties of the liquid composition. This can be ascribed to the fact that the optical and chemical properties are based on electronicorbitals, and the electronicorbitals are hardly affected by different isotopes.

In an embodiment of the invention, an electrowetting device comprises the liquid composition. The shape and/or movement of the electrowetting device are controlled by a pressure variation of the liquid composition.

In another embodiment of the invention, a liquid lens comprises the liquid composition. The liquid lens is an optical or acoustic lens of which the shape and/or movement is controlled by a pressure variation of the liquid composition.

The invention further provides an electronicsystem comprising the liquid lens or the electrowetting device.

DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become more apparent from the following detailed description considered in connection with the accompanying drawings, in which: Fig. 1 depicts a schematic diagram for a liquid composition according to an embodiment of the invention;

Fig. 2 depicts a schematic diagram for a method of manufacturing a liquid composition according to an embodiment of the invention.

The same reference numerals are used to denote similar parts throughout the Figures.

DETAILED DESCRIPTION OF THE INVENTION

Fig.l depicts a schematic diagram for a liquid composition according to an embodiment of the invention. The liquid composition is used for an electrowetting device/liquid lens.

The liquid composition (10) comprises:

- a first liquid (11), and

- a second liquid (12) formed from an initial liquid by replacing a type of atom included in the initial liquid with a corresponding isotope of the atom, so that a density difference between the second liquid (12) and the first liquid (11) is reduced, wherein the second liquid (12) and the first liquid (11) are non-miscible or separated by a flexible membrane.

Fig.2 depicts a schematic diagram for a method of manufacturing a liquid composition according to an embodiment of the invention. The method of manufacturing comprises:

- replacing (21) a type of atom, which is included in an initial liquid and has a corresponding isotope, with the corresponding isotope of the atom to form a second liquid, so that a density difference between the second liquid and a first liquid is reduced, wherein the second liquid and the first liquid are non-miscible or separated by a flexible membrane, and the initial liquid is a liquid used for generating the second liquid; and - combining (22) the second liquid with the first liquid.

In an embodiment of the invention, either the first liquid or the second liquid is a polar liquid.

The type of atom included in the initial liquid can be replaced in a predefined percentage according to an initial density difference between the initial liquid and the first liquid.

A meniscus surface (13, as shown in Fig. 1) can be formed between the first liquid and the second liquid.

The density of the second liquid may be equal to the density of the first liquid, after replacing the atom with the corresponding isotope of the atom. But, normally, the initial liquid and/or other liquids may be blended with the liquid the atom of which is replaced with an isotope of the atom, so that the density of the second liquid can be equal to the density of the first liquid.

The initial liquid is a liquid formed of chemicals, and the initial liquid may form isotope ratios naturally. Replacing the atom with a corresponding isotope of the atom may be implemented by a chemical synthesis, a substitution reaction, or an enriching process for a naturally occurring isotope ratio, such as separation of heavy water (D ₂ O) from normally occurring water (H ₂ O plus traces OfD ₂ O).

In the following, six examples are given to illustrate replacing the atom with the corresponding isotope of the atom.

Example 1 (increasing density by replacing an atom with the corresponding isotope)

The density of octane is 0.703 g/cm . The hydrogen atoms of octane can be replaced by deuterium atoms, and then octane becomes octane-dis which has a higher density than octane. In example 1, replacing an atom with an isotope of the atom, which can be called Deuterating or synthesis, can easily be implemented by using deuterium instead of hydrogen during the replacing operation. The density of the octane-dig is 0.815 g/cm ³ , equal to the density of another liquid of a liquid composition. Compared with octane, the octane-dis has a 16% increase in density. However, other properties of octane-dis are hardly changed, such as the refractive index of octane-dis decreases by only 0.3% compared to octane.

Example 2 (increasing density by replacing an atom with the corresponding isotope)

The density of dodecamethylpentasiloxane is 0.918g/cm ³ . Using deuterium to replace hydrogen, the density of dodecamethylpentasiloxane can be increased by 9%, and reach 1.00 g/cm ³ , equal to the density of water. After replacing hydrogen, by deuterating or the substitution in example 2, if the density of dodecamethylpentasiloxane becomes higher than the density of another liquid of a liquid composition, blending of the non-deuterated liquid with the deuterated liquid can form a desired density which is equal to the density of another liquid of the liquid composition.

Example 3 (increasing density by replacing an atom with the corresponding isotope)

With a high refractive index and a high Abbe number, the liquid perhydrofluorene is suitable for zoom lenses. The density of perhydrofluorene is 0.92 g/cm ³ . Due to its the low density, perhydrofluorene is not suitable to be combined with water to form a liquid composition for zoom lenses. Based on replacing an atom with the corresponding isotope, substituting (deuterium) hydrogen atoms can increase the density of perhydrofluorene to 1.034 g/cm , which is an increase of 12%. Then, blending of 70% deuterated perhydrofluorene and 30% non-deuterated perhydrofluorene results in a density of 1.00 g/cm ³ , which is equal to the density of water.

Example 4 (increasing density by replacing (an) atom(s) with the corresponding isotope(s))

The density of octane and polydimethylsiloxane can be increased by using ¹³ C to replace ¹² C by a substitution reaction.

If a liquid comprises two or more types of atoms and each type of atom has two or more types of corresponding isotopes, the two or more types of atoms can also be replaced with two or more corresponding types of isotopes, respectively, to increase the density of the liquid. For example, in siloxanes, ¹⁶ O atoms can be replaced by ¹⁷ O atoms or even ¹⁸ O atoms, and ²⁸ Si may be replaced by ²⁹ Si or even ³⁰ Si.

Example 5 (decreasing density by replacing (an) isotope(s))

It may be also possible to decrease the density of a liquid by using lighter isotopes. However, most lighter isotopes are not stable. Based on replacing (an) isotope(s), an example of a stable solution is the use of ³⁵ Cl instead Of ³⁷ Cl by a substitution reaction, to decrease the density of a liquid. For instance, the density of CCl ₄ can be decreased from 1.59 g/cm ³ to 1.57 g/cm3 by replacing ³⁷ Cl with ³⁵ Cl.

Example 6 (increasing density by replacing (an) atom(s) with the corresponding isotope(s))

For some special liquid lenses, such as the large lens of a high-quality digital still camera, both densities and thermal expansions of two liquids of a liquid composition are important to be matched to each other. For instance, a liquid lens is composed of a liquid composition, and the liquid composition comprises water and siloxane oil. The densities of water and siloxane can be matched at 20 ⁰ C. The cubic thermal expansion coefficient of water is 0.0002/ ⁰ C and the thermal expansion of siloxane is about 0.0015/ ⁰ C. When the temperature is 40 ⁰ C, the density of the water is (1+20x0.0013) 1.026 times the density of siloxane. The 2.6% density difference may have a big impact on gravity effects for the liquid composition._

A solution is to replace water by methanol, since methanol has a thermal expansion coefficient comparable to the thermal expansion coefficient of siloxane. However, methanol has a density of 0.79 g/cm ³ which is much lower than the density of siloxane. Based on replacing (an) atom(s) with the corresponding isotope(s), a type of atom of methanol can be substituted by at least one type of isotope atom, so as to increase the density of methanol. For example, replacing one ¹³ C and four ² H atoms increases the density of methanol to 0.92 g/cm ³ . Siloxanes can match said density of 0.92g/cm ³ . After said replacing with (an) isotope(s), not only the densities of methanol and siloxanes are equal, but also the thermal expansion coefficients are equal. Thus, the liquid lens can be used in a wide temperature range. Suppose an electrowetting device is used for ultrasound focusing. Matching the impedances Z of two liquids is important then for preventing reflections on the meniscus. Furthermore, for ultrasound focusing, a large sound velocity difference c between two liquids is also important for obtaining a strong lens effect. According to an embodiment of the invention, replacing (an) isotope atom(s) not only can affect the density of a liquid, but also the velocity of sound c=(kp)-0.5 and the impedance Z=(p/k)0.5, wherein k is the compressibility and p is the density of a liquid, so that matching the impedances and overcoming the large sound velocity difference can be reached by replacing isotopes.

The advantage of the embodiment of the invention: using (an) isotope(s) to reduce the density difference of two liquids hardly affects the optical and chemical properties of the liquid composition formed by the two liquids,since the optical and chemical properties are based on electronicorbitals, and the electronicorbitals are hardly affected by different isotopes. Only physical properties of a liquid, such as density, boiling point, freezing point, and acoustic properties, are affected. Boiling point and freezing point are, however, not affected as much by isotopes as density. For instance, D ₂ O has a density 10.7% higher than the density of H ₂ O, but the boiling point (101.4 ⁰ C) of D ₂ O is only 0.4% higher than the boiling point of H ₂ O, and the melting point (3.8 ⁰ C) Of D ₂ O is 1.4% higher than the melting point of H ₂ O. Thus, using isotopes to change the density of a liquid provides a powerful tool to design a liquid composition with desired properties suitable for electrowetting devices or liquid lenses.

In an embodiment according to the invention, an electrowetting device comprises the liquid composition.

In another embodiment according to the invention, a liquid lens comprises the liquid composition. The liquid lens can be an optical lens or an acoustic lens.

The shape or/and the movement of the liquid lens and electrowetting device is controlled by the pressure variation of the liquid composition. The electrowetting device/liquid lens can be applied in an electronic system. The electronic system can be a camera phone, endoscope, display, ultrasound catheter etc.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be constructed as limiting the claim. The word 'comprising' does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements and by means of a suitable programmed computer. In the means claims enumerating several means or steps, several of these means or steps can be embodied by one and the same item of hardware. The usage of the words first, second and third, etcetera does not indicate any ordering. These words are to be interpreted as names.