WO2018015734A1

WO2018015734A1 - Using metal nanoparticles to control the colour, lustre and iridenscence of cosmetics

Info

Publication number: WO2018015734A1
Application number: PCT/GB2017/052106
Authority: WO
Inventors: Robert Davidson Binns; Christopher Robin BINNS; John William Patrick KINMONTH
Original assignee: Cossme Ltd
Priority date: 2016-07-20
Filing date: 2017-07-18
Publication date: 2018-01-25
Also published as: GB201612561D0; GB2537777A; GB2552556A; GB201617162D0

Abstract

The invention provides a cream comprising non-spherical electromagnetic nanoparticles, in which the non-spherical electromagnetic nanoparticles are embedded in the cream in a first arrangement in which the long axes of the electromagnetic nanoparticles are randomly orientated relative to each other, and in which the electromagnetic nanoparticles are rotatable on exposure to an electric field to form a second arrangement having a predetermined degree of alignment of the long axes of the electromagnetic nanoparticles relative to each other.

Description

USING METAL NANOPARTICLES TO CONTROL THE COLOUR, LUSTRE AND

IRIDENSCENCE OF COSMETICS

The present invention relates to the use of nanoparticles within a cosmetic cream wherein the visual appearance of the cream can be altered by exposing the cream to an electric field. BACKGROUND TO THE INVENTION

Skin types and colours vary significantly between different ethnic backgrounds, age, the level of exposure to the elements etc. and this can strongly influence the preferred choice of cosmetics for application to the skin surface. Getting good colour matching to the skin can be difficult. In addition, getting even coverage can be a problem depending on the texture and condition of the natural skin surface. Cream based cosmetics have therefore been developed to address these issues and the cream compositions developed to support the addition of pigments and conditioning agents to improve the look of the surface of the skin.

On application of the cream to the skin, the finished appearance of the skin depends on the colour, lustre and iridescence of the cream and its interaction with the skin surface e.g. levels of cream absorption into the skin, the colour of the underlying skin surface etc. In addition, the lighting in the immediate environment can also have a significant impact. For example, the high level of stage lighting when filming or performing on stage requires a different type of make-up with different properties to that used in normal day to day lighting conditions. However, the choice of cosmetics used is a compromise as, once applied to the skin, the appearance cannot be altered depending on personal preference that particular day, the natural light quality in the immediate surroundings or the various artificial lighting environments that may be encountered during the course of the day. Changing the appearance of the skin after application of the cosmetics would require removal of the cosmetics and subsequent re-application using alternative products, which is both time consuming and expensive, not to mention often impractical throughout the course of a day.

There is therefore a need for a cosmetic application whose visual appearance can be controlled to suit the preferences of the user. SUMMARY OF THE INVENTION

The present invention seeks to address the problems of the prior art.

Accordingly, a first aspect of the present invention provides a cream comprising non-spherical metal nanoparticles, in which the non-spherical metal nanoparticles are embedded in the cream in a first arrangement in which the long axes of the metal nanoparticles are randomly orientated relative to each other, and in which the metal nanoparticles are rotatable on exposure to an electric field to form a second arrangement having a predetermined degree of alignment of the long axes of the metal nanoparticles relative to each other.

Metal nanoparticles exhibit strong absorption of specific wavelengths of light and this property can be made angle-dependent, leading to iridescence. The optical properties of nanoparticles can be controlled in a variety of ways, including changing the particle size, particle shape, constituent material and the carrier medium. By using a cosmetic cream as a carrier medium and controlling the optical properties of the nanoparticles as described herein, it is possible to control the colour and/or lustre and/or iridescence of creams, such as for example cosmetic creams. The metal nanoparticles are capable of forming a dipole in the presence of an electric field. The metal nanoparticles are preferably present within the cream without any additional surface coatings being applied to the metal nanoparticles.

Application of an electric field electrically polarises the non-spherical metal nanoparticles. Application of the electric field therefore induces a dipole moment in the non-spherical metal nanoparticles, thereby creating a torque which causes the non-spherical metal nanoparticles to rotate within the cream to align with or towards the applied field. The torque created is sufficient to overcome the viscous forces resisting rotation of the nanoparticles within the cream. It is to be understood that the electric field could be generated by any suitable mechanism, such as for example by passing or positioning a charged dielectric object adjacent the cream or the area to which the cream has been applied.

The nanoparticles are orientated randomly relative to each other in the first arrangement within the cream. Preferably, the cream has a first visual appearance when the long axes of the metal nanoparticles are orientated randomly relative to each other in the first arrangement. This random orientation of nanoparticles relative to one another is the natural arrangement of nanoparticles in a soft matrix.

The degree of alignment of the long axes of the metal nanoparticles in the second arrangement may vary depending on the duration of exposure to an electric field and/or the strength of the electric field.

By controlling the exposure of the cream to the electric field, the degree of alignment of the long axes of the metal nanoparticles may be controlled.

In one embodiment, in the second arrangement, the long axes of the metal nanoparticles may be substantially aligned with each other. It is however to be understood that the long axes of the metal nanoparticles may have any suitable degree of alignment with each other within the second arrangement depending on the particular requirements for the cream.

Preferably, the cream has a second visual appearance when the metal nanoparticles are in the second arrangement. For example, when the long axes of the nanoparticles are substantially aligned relative to one other the cream has a second visual appearance.

Preferably, the first and second visual appearances of the cream are visually distinct from each other. In a preferred embodiment, the visual appearance of the cream can be changed from the first visual appearance to the second visual appearance on exposure of the cream to an electric field. Preferably, exposure to the electric field is controlled in order to provide a second arrangement of nanoparticles having a predetermined degree of alignment relative to each other in order to provide the desired second visual appearance.

In one embodiment, the change in visual appearance between the first and second visual appearances is a change in the colour and/or lustre and/or iridescence of the cream. The cream may provide at least two visually different visual appearances, for example the first visual appearance when the metal nanoparticles are in the first arrangement and a second visual appearance when the metal nanoparticles are in the second arrangement. It is however to be understood that the cream may provide more than two, for example three or more visually different visual appearances depending on the degree of alignment of the long axes of the metal nanoparticles when in different arrangements within the cream.

The long axes of the nanoparticles within the cream are preferably rotatable between a first arrangement in which the long axes of the nanoparticles are arranged randomly relative to one another, and a second arrangement in which the long axes of the nanoparticles are substantially aligned relative to one another. It is however to be understood that the long axes of the metal nanoparticles may have any suitable degree of alignment relative to each other in the second arrangement in order to provide a desired second visual appearance.

The non-spherical nanoparticles may have any suitable shape. Preferably, the non-spherical nanoparticles have dimensions within the range of between lnm and 100 nm. In a preferred embodiment, the nanoparticles are nano-rods. Each nano-rod has a length which is greater than its diameter. The aspect ratio (i.e. the length divided by the diameter) is preferably between about 3 and about 5. A particular feature of non-spherical nanoparticles, such as nano-rods, is that the optical properties change as a function of viewing angle. Where the nanoparticles are nano-rods, the nanoparticles may be more efficiently aligned relative to one another compared with other non-spherical nanoparticles. Application of an electric field to a cream comprising non-spherical metal nanorods polarises the nanorods and creates a greater torque causing more efficient rotation than for other non-spherical nanoparticles.

The metal non-spherical nanoparticles, for example nano-rods, may be composed of one or more noble metals or alloys thereof. For example, the non-spherical nanoparticles, for example nanorods, are composed of one or more of: gold (Au), silver (Ag) and/or copper (Cu), and/or alloys thereof.

Preferably, the cream takes the form of a cosmetic, emollient, salve or therapeutic composition for topical application. Preferably, the cream is a cosmetic cream. In one embodiment, the cream is an aqueous solution of non-spherical metal nanoparticles.

The cream may comprise a soft-matrix material within which the non-spherical nanoparticles are embedded. The expression 'cream' is to be understood to include, but not be restricted to any of paste, salve, emollient, emulsion, unguent, moisturiser, foundation, cosmetic, ointment, medical, and any other suitable cream known to the skilled person. It is also to be understood that, where the cream is a cosmetic, the cosmetic may comprise, but is not restricted to, cosmetic moisturiser, cosmetic primer, foundation, liquid foundation, cream foundation, cream eye shadow, lipstick, lip salve, lip gloss, cream blusher, cream bronzer, cream concealer, eyeliner, mascara and any other similar cosmetic known to the skilled person.

A second aspect of the present invention provides a method of manufacture of a cream with changeable visual properties, the method comprising the steps of: a. providing an aqueous dispersal of non-spherical metal nanoparticles;

b. embedding the non-spherical metal nanoparticles in a cream in a first arrangement in which the long axes of the non- spherical metal nanoparticles are orientated randomly relative to each other wherein the visual appearance of the cream can be switched between a first visual appearance and a second visual appearance on exposure of the cream to an electric field.

A third aspect of the present invention provides a method of altering the visual appearance of a cream, the method comprising the steps of: a. providing non-spherical metal nanoparticles dispersed in an aqueous or non-aqueous solution;

b. embedding the non-spherical metal nanoparticles in a cream in a first arrangement in which the long axes of the non-spherical metal nanoparticles are orientated randomly relative to each other

c. forming a film of the cream, the film having a first visual appearance; and

d. exposing the film to an electric field to rotate the metal nanoparticles of the matrix to provide a second arrangement having a predetermined degree of alignment of the long axes of the metal nanoparticles relative to each other to provide a second visual appearance.

The second visual appearance is preferably visually distinct from the first visual appearance. The film of the cream may be formed by application of a cream to surface, for example by topical application of the cream to an area of skin on a user.

A fourth aspect of the present invention provides a method of controlling the visual properties of a cream according to a first aspect of the invention, the method comprising exposing the cream to an electric field to control the degree of alignment of the long axes of the metal nanoparticles relative to each other.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a schematic illustration of the first arrangement of non-spherical metal nanoparticles in a cream according to one embodiment of the present invention; and Figure 2 is a schematic illustration of the second arrangement of non-spherical metal nanoparticles in the cream of Figure 1 during and/or after exposure of the cream to an electric field.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention will now be described, by way of example only. A cosmetic cream comprises a plurality of metal non-spherical nanoparticles composed of gold (Au). It is however to be understood that the non-spherical nanoparticles may be composed of any suitable metal. Preferably, the metal non-spherical nanoparticles are composed of one or more noble metals and/or alloys thereof.

The nanoparticles are non-spherical in shape, and have a length which is greater than the diameter. Typically nanoparticles have sizes in the range 1 to 100 nm and have novel optical properties due to the specific absorption and scattering mechanisms not found in the supporting substrate alone, in this case soft matrix material. The nanoparticles exhibit strong absorption of specific wavelengths of light and this property can be made angle-dependent, leading to iridescence. The optical properties of nanoparticles can be controlled in a variety of ways, including changing the particle size, particle shape, constituent material and the carrier medium. By using a cosmetic cream as a carrier medium and controlling the optical properties of the nanoparticles as described herein, it is possible to control the colour and/or lustre and/or iridescence of creams, such as for example cosmetic creams. In particular, the appearance of the cream of the present invention is dependent on the orientation of the nanorods within the cream.

When the non-spherical nanoparticles are exposed to light, the oscillating electromagnetic field of the light induces a collective coherent oscillation of the free electrons (free band electrons) of the gold. This electron oscillation around the particle surface causes a charge separation forming a dipole oscillation along the direction of the electric field of the light. The amplitude of the oscillation reaches maximum at a specific frequency known as surface plasmon resonance (SPR). The SPR induces a strong absorption of the incident light. The SPR band is much stronger for noble nanoparticles, such as for example gold nanoparticles, than for other metals. The SPR band intensity and wavelength depends on factors affecting electron density charge on the particle surface such as the metal type, particle size, shape, structure, composition, and the dielectric of the surrounding medium. The optical properties of the non-spherical nanoparticles may therefore be adjusted by controlling one or more of the shape, composition, structure and/or alignment of the nanoparticles within the cream.

It has been found that the SPR band of the non-spherical nanoparticles is split into two bands. A first band corresponding to electron oscillations along the long axis (known as the longitudinal band) of the nanoparticles, and a second band corresponding to electron oscillations along the transverse axis (known as the transverse band). As a result, the visual appearance of the cream of the present invention can be altered on application of an electric field whereby causing rotation of the nanoparticles and altering which SPR band is more dominant and/or the degree to which a particular SPR band is more dominant. Preferably, the metal nanoparticles are resonant in the optical part of the spectrum, i.e. at a wavelength of less than 700 nm.

With reference to Figure 1, in cosmetic cream, prior to and during application to an area of skin, the metal non-spherical nanoparticles assume a first arrangement whereby the long axes of the non-spherical nanoparticles are randomly oriented with respect to each other, giving the cosmetic a specific first visual appearance.

An electric field is applied to the cosmetic cream at the area of application, either during or after application to the area of skin. As shown in Figure 2, by applying a controlled electric field to the cosmetic cream, the long axes of the metal nanoparticles become aligned to a certain predetermined degree. The degree of alignment of the long axes of the nanoparticles relative to each other is controlled by the degree of exposure of the cream to the electric field and/or by the strength of the electric field. The degree of alignment of the long axes of the nanoparticles maybe maintained for a significant time period after exposure to an electric field, preferably for at least an hour, more preferably for at least four hours.

The electric field may be applied by any suitable means capable of inducing a dipole moment in the nanoparticles. For example, the electric field could be generated by passing a charged dielectric object such as a plastic comb close to where the cream is applied thus changing the appearance as the object is passed over. In one embodiment, the electric field could be generated by passing a statically charged rod or wand close to the area of application of the cream so as to change the visual appearance of the cream as the rod is passed over. The rod or wand may be composed of any suitable material(s) having electrostatic properties, such as for example polyethylene. The rod or wand may become electrostatically charged by friction caused when removing the rod or wand from a sleeve or container. Applying an electric field will induce a dipole moment in the metal nanoparticles and hence create a torque that will rotate the metal nanoparticles to align with or towards the field. This rotation cause the long axes of the nanoparticles to align to a predetermined extent with each other within the cream. The cream therefore comprises the metal nanoparticles in a second arrangement having a predetermined degree of alignment of the long axes with each other. The second arrangement of nanoparticles has a second visual appearance.

A particular feature of non-spherical nanoparticles, for example, nano-rods, is that the optical properties change as a function of viewing angle. Therefore, by altering the orientation of the long axes of the nanoparticles within the cream or at an area to which the cream in applied it is possible to alter the visual appearance of the cream. For example, the optical properties of the metal nanoparticles within the cream are changed due to rotation from the first arrangement to the second arrangement, thereby causing a visual alteration in one of more of the colour and/or lustre and/or iridescence of the cream. By controlling exposure to the electric field it is possible to control the degree of alignment of the metal nanoparticles relative to each other within the cream and to therefore control the adjustment in the optical properties of the cream. The present invention also has the advantage that the visual adjustments to the cream can be facilitated in specific discrete areas on the skin of the user as and when required. The degree of visual alteration between for example the first visual appearance and the second visual appearance may vary depending on for example the difference in aspect ratio, ie. the difference between the longitudinal dimension and transverse dimension of the non-spherical nanoparticles.

EXAMPLE - Eye shadow

Cream eye shadow comprising a colloidal suspension of non-spherical metal nanoparticles may be applied by a user to provide a first visual appearance. The applied cream comprises a plurality of non-spherical metal nanoparticles in a first arrangement in which the long axes of the nanoparticles are randomly aligned. The user may during the day or evening wish to alter the visual appearance provided by the applied cream eye shadow. For example, the user may wish for the eye shadow to appear lighter during the day, and darker in the evening. The first visual appearance of the eye shadow may for example provide a light tone. The user may therefore wave a wand composed of electrostatically charged material across or near the applied eye shadow. The electric field created by the wand causes rotation of the non-spherical metal nanoparticles within the applied cream eye shadow from the first arrangement towards a second arrangement in which the metal nanoparticles are aligned with or towards the direction of the applied field to provide a second visual appearance of the cream. The degree of alignment of the non-spherical metal nanoparticles may be controlled by controlling the strength of the electric field and/or the duration of exposure to the electric field. The second visual appearance of the cream may be darker than the first visual appearance of the cream.

Although the cream eye shadow of the Example is discussed in terms of providing a first and second visual appearance which differ with regards to tone, it is to be understood that the first and second visual appearances may differ with regards to one or more of: colour and/or lustre and/or iridescence of the cream.

Furthermore, although this Example illustrates the use of a cream as an eye shadow, it is to be understood that the cream may be used as any suitable cosmetic cream. For example, the cream may be used as, and not limited to, foundation and/or moisturiser and/or blusher.

Although aspects of the invention have been described with reference to the embodiment shown in the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment shown and that various changes and modifications may be effected without further inventive skill and effort. For example, not only can the visual appearance of the cosmetic cream be changed by controlled application of an electric field, the creams may also contain additional components to enhance their therapeutic or dermatological properties. For example, the cream may also include retinol or epidermal growth factors or other anti-aging components. Alternatively (or in addition), the cream may also contain silver nanoparticles which are powerful anti-bacterial agents which are known to have therapeutic benefits for skin conditions such as, but not limited to, impetigo. The cream may be any suitable cream, such as for example a medical cream or ointment, and is not limited to a cosmetic cream.

Claims

1. A cream comprising non-spherical metal nanoparticles, in which the non-spherical metal nanoparticles are embedded in the cream in a first arrangement in which the long axes of the metal nanoparticles are randomly orientated relative to each other, and in which the metal nanoparticles are rotatable on exposure to an electric field to form a second arrangement having a predetermined degree of alignment of the long axes of the metal nanoparticles relative to each other.

2. A cream according to claim 1, wherein the non-spherical metal nanoparticles are nano- rods.

3. A cream according to any preceding claim, wherein the non-spherical nanoparticles are operable to rotate within the electric field such that the long axes of the non-spherical nanoparticles become substantially aligned relative to one another in the second arrangement.

4. A cream according to any preceding claim, wherein the cream has a first visual appearance when the non-spherical nanoparticles are in the first arrangement.

5. A cream according to claim 4, wherein the cream has a second visual appearance when the non-spherical nanoparticles are in the second arrangement, and in which the second visual appearance is visually distinct from the first visual appearance.

6. A cream according to claim 5 wherein the change in visual appearance from the first to the second visual appearance is a change in one or more of: the colour and/or lustre and/or iridescence of the cream.

7. A cream according to any preceding claim, wherein the cream is provided in the form of an emollient, salve or therapeutic composition for topical application.

8. A cream according to any preceding claim, wherein the cream is an aqueous solution.

9. A method of manufacture of a cream with changeable visual properties, the method comprising the steps of:

a. providing an aqueous dispersal of non-spherical metal nanoparticles; b. embedding the non-spherical metal nanoparticles in a cream in a first arrangement in which the long axes of the non-spherical metal nanoparticles are orientated randomly relative to each other, wherein the visual appearance of the cream can be switched between a first visual appearance and a second visual appearance on exposure of the cream to an electric field.

10. A method of altering the visual appearance of a cream, the method comprising the steps of:

a. providing non-spherical metal nanoparticles dispersed in an aqueous solution; b. embedding the non-spherical metal nanoparticles in a cream in a first arrangement in which the long axes of the non-spherical metal are orientated randomly relative to each other;

c. forming a film of the cream, the film having a first visual appearance; and d. exposing the film to an electric field to rotate the metal nanoparticles of the matrix to provide a second arrangement having a predetermined degree of alignment of the long axes of the metal nanoparticles relative to each other to provide a second visual appearance.

11. A method of controlling the visual properties of a cream according to any one of claims 1 to 8, the method comprising exposing the cream or film of the cream to an electric field to control the degree of alignment of the long axes of the metal nanoparticles relative to each other.