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US 20110250252A1

(19) United States (12) Patent Application Publication (10) Pub. No.: US 2011/0250252 A1 (43) Pub. Date:

Canham et al. (54) COLOURING TECHNIQUES (76) Inventors:

Leigh Canham, Worcestershire (GB); Armando Loni, Worcester (GB); Alastair Godfrey,


Foreign Application Priority Data

Sep. 30, 2008

(GB) ................................. .. 08179400

Publication Classi?cation

(21) App1.N0.:


Int. Cl. A61K 8/25 A23L 1/27 A61K 8/02

(22) PCT Filed:

Sep. 30, 2009

A61Q 1/02 A61Q 11/00


PCT No.:


§ 371 (0X1), (2), (4) Date:

Jun. 2, 2011

Hampshire (GB)

Oct. 13, 2011




(2006.01) (2006.01) (2006.01)

(2006.01) (2006.01)

US. Cl. ............ .. 424/401; 424/63; 424/49; 426/262


A method for masking the appearance of silicon in a range of

compositions is described.

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US 2011/0250252 A1


or animal body. For example, the release may be triggered by contact With gastrointestinal tract ?uid such as saliva, gastric


This invention relates to the use of silicon in a range

of compositions Wherein the appearance of the silicon is masked. BACKGROUND OF THE INVENTION

[0002] There is a tendency to associate certain colours With certain ?avours and foodstuffs and certain colours With spe ci?c consumer goods. Speci?c colours or speci?c mixtures of

colours are frequently used by companies to help brand their consumer goods. [0003] Also, in the consumer care and food industries, vari

?uid, intestinal ?uid or sWeat. The release of the at least one

further ingredient and/or the masking material may be trig gered by one or more of a range of responses. These include,

for example, contact With Water of a particular temperature, for example, Warm Water during hair Washing. [0010] Loading the silicon With at least one further ingre dient includes Wherein the silicon is used to coat or partially coat one or more ingredients. For example, in food composi tions, the silicon may be used to coat or partially coat break fast cereals and the like or a product or products suitable for

making beverages, such as coffee granules, coffee poWder, tea, cocoa poWder, chocolate poWder. For example, When the ingredient is a microparticle (about 1-1000 pm in diameter),

ous methods are used to stabilise various ingredients and to

such as a poWder or a small granule, or is a macroparticle

control the timing and release of said ingredients. Such meth

(about 1 mm-20 mm), such as a granule or a typical cereal,

ods enable the protection of food components to ensure against nutritional loss and to mask or preserve ?avours and aromas. Suitable methods of protection also increase the sta bility of vitamin or mineral supplements Which are normally

or microparticles. [0011] The present inventors have also found that the use of

sensitive to light, UV radiation, metals, humidity, tempera ture and oxygen. Similar issues affect a range of consumer

care products such as hair care compositions, oral hygiene

compositions and cosmetics. [0004]

There is a continued need for alternative methods

and/ or products for protecting, controlling the release of, and/ or masking the taste of ingredients in the consumer care

and food industries Without compromising the appearance of

said ingredient may be coated With silicon nanoparticles and/

partially oxidised porous silicon is particularly effective in retaining the colour of the masking material, at least in part, through the effects of photostabilisation or photoprotection. The present inventors have found that the presence of the partially oxidised surface results in the colour of the masking material (eg a White or colour pigment) not being unduly affected by the surface of the porous silicon Which Would otherWise comprise a hydride surface. The partially oxidised

of partially oxidised porous silicon, and especially partially

porous silicon serves to maintain the original hue of the masking material more effectively than other modi?ed sur faces. As such, in a further aspect of the present invention, there is provided the use of partially oxidised porous silicon as a photostabiliser or photoprotector for a masking agent in a composition. There is also provided the use of partially oxidised porous silicon as a photostabiliser or photoprotector for a White or colour pigment. The modi?ed porous silicon serves to assist in retaining the colour of the masking agent. Advantageously, the porous silicon may be mesoporous sili

oxidised mesoporous silicon.


said products. [0005] The present invention is based on the surprising ?nding that the colour of silicon may be modi?ed and blended With other components of various compositions and not be distinguishable to the human eye. The present inventors have also found that the colour of the modi?ed silicon may be retained over extended periods of time. In particular, this colour retention may be achieved in connection With the use


The partially oxidised porous silicon may possess


an oxide content corresponding to betWeen about one mono

[0006] According to a ?rst aspect of the present invention, there is provided a method for masking the appearance of

layer of oxygen and a total oxide thickness of less than or equal to about 4.5 nm covering the entire skeleton.

particulate elemental silicon in a composition, comprising modifying the colour of the particulate elemental silicon so that the silicon is not distinguishable to the human eye When blended With the other components of the composition.


Preferably, the colour of the particulate elemental

silicon is modi?ed prior to blending With the other compo nents.


The colour of the silicon particles may be modi?ed

by one or more of a range of techniques. For example, the silicon may be contacted With a suitable masking material in order to mask the appearance of the silicon and tailored to a

suitable colour for the end product. The masking material may coat the silicon. When the silicon is selected from porous silicon, some, or all, or substantially all of the pores may be

partially or completely ?lled With masking material, said masking material optionally being suitable for delivery to the human or animal body. In addition to the masking material, the silicon may be loaded With at least one further ingredient

Which is different from the masking material. [0009] The at least one further ingredient and/or the mask ing material may be released after interaction With the human




As used herein, and unless otherWise stated, the

term “silicon” refers to solid elemental silicon. For the avoid ance of doubt, and unless otherWise stated, it does not include

silicon-containing chemical compounds such as silica, sili cates or silicones, although it may be used in combination With these materials. [0014] The purity of the silicon may depend to some extent on the ?nal application of the silicon. For example, the silicon may be about 95 to 99.99999% pure, for example about 96 to 99.9% pure. So-called metallurgical silicon Which may be suitable in a range of applications, including foodstuffs, has a purity of about 98 to 99.5%. [0015] The physical forms of silicon Which are suitable for use in the method according to the present invention include one or more of amorphous silicon, single crystal silicon and

polycrystalline silicon (including nanocrystalline silicon, the grain siZe of Which is typically taken to be 1 to 100 nm) and

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US 2011/0250252 A1

including combinations thereof. Any of the above-mentioned

Which is another conventional method for making porous

types of silicon, Which are suitable for use in the present

silicon. This method involves the immersion of a silicon

invention, may be porosi?ed to form porous silicon, Which

sample in a hydro?uoric acid solution containing a strong oxidising agent. No electrical contact is made With the sili con, and no potential is applied. The hydro?uoric acid etches

may be referred to as “pSi”. The silicon may be surface

porosi?ed or more substantially porosi?ed. Suitable forms of porous silicon include mesoporous, microporous or macroporous silicon. Microporous silicon contains pores

the surface of the silicon to create pores.

possessing a diameter less than 2 nm; mesoporous silicon contains pores having a diameter in the range of 2 to 50 nm; and macroporous silicon contains pores having a diameter greater than 50 nm. [0016] The average pore diameter is measured using a

sinski in Current Opinions in Solid State & Materials Science

9, 73 (2005). These techniques include “stain-etching”, “gal vanic etching”, “hydrothermal etching” and “chemical

knoWn technique. Mesopore diameters are measured by very

vapour etching” techniques. Stain etching results from a solu

high resolution electron microscopy. This technique and other suitable techniques Which include gas-adsorption-des orption analysis, small angle x-ray scattering, NMR spectros

tion containing ?uoride and an oxidant. In galvanic or metal assisted etching, metal particles such as platinum are also

[0021] Mesoporous silicon may be generated from a vari ety of non-porous silicon poWders by so-called “electroless electrochemical etching techniques”, as revieWed by K. Kola

involved. In hydrothermal etching, the temperature and pres

copy or thermoporometry, are described by R. Herino in

sure of the etching solution are raised in closed vessels. In

“Properties of Porous Silicon”, chapter 2.2, 1997. Micropore

chemical vapour etching, the vapour of such solutions, rather than the solution itself is in contact With the silicon. Mesopo

diameters are measured by xenon porosimetry, Where the Xe129 nmr signal depends on pore diameter in the sub 2 nm

range. Macropore diameters are measured by electron

microscopy. Alternative techniques include mercury poro

rous silicon can be made by techniques that do not involve

etching With hydro?uoric acid. An example of such a tech nique is chemical reduction of various forms of porous silica


as described by Z. Bao et al in Nature vol. 446 8th March 2007

[0017] Other suitable forms of silicon include: submicron diameter polycrystalline particles; submicron diameter amor

p172-175 and by E. Richman et al. in Nano Letters vol. 8(9) p3075-3079 (2008). If this reduction process does not pro ceed to completion then the mesoporous silicon contains varying residual amounts of silica. [0022] Following its formation, the porous silicon may be dried. For example, it may be supercritically dried as

phous silicon particles; holloW silicon microparticles; agglomerated silicon nanoparticles; amorphous silicon coat ings; micronised silicon alloys; micronised metallurgical

grade silicon; cold pressed silicon particles. [0018] The surface area and the siZe of the pores in the silicon may to some extent depend on What application the porous silicon is to be used for. For example, the BET surface area of the porous silicon is preferably in excess of 0.1 m2/ g

described by Canham inNature, vol. 368, (1994), pp133-135. Alternatively, the porous silicon may be freeZe dried or air

dried using liquids of loWer surface tension than Water, such as ethanol or pentane, as described by Bellet and Canham in

for microorganism entrapment, and preferably greater than 100 m2/g for biodegradability in intestinal ?uid. The BET

Adv. Mater, 10, pp487-490, 1998. [0023] Silicon hydride surfaces may, for example, be gen

surface area is determined by a BET nitrogen adsorption method as described in Brunauer et al., J. Am. Chem. Soc., 60, p309, 1938. The BET measurement is performed using an

erated by stain etch or anodisation methods using hydro?uo ric acid based solutions. When the silicon, prepared, for

Accelerated Surface Area and Porosimetry Analyser (ASAP 2400) available from Micromeritics Instrument Corporation,

comprises porous silicon, the surface of the porous silicon may or may not be suitably modi?ed in order, for example, to improve the stability of the porous silicon in the composition. In particular, the surface of the porous silicon may be modi

Norcross, Ga. 30093. The sample is outgassed under vacuum at 3500 C. for a minimum of 2 hours before measurement.


The methods for making various forms of silicon

Which are suitable for use in the present invention are Well knoWn in the art.


In PCT/GB96/01863, the contents of Which are

example, by electrochemical etching in HF based solutions,

?ed to render the silicon more stable in alkaline conditions. The surface of the porous silicon may include the external

and/or internal surfaces formed by the pores of the porous silicon.

incorporated herein by reference in their entirety, it is


described hoW bulk crystalline silicon can be renderedporous

may result in partial oxidation of the porous silicon surface. The surfaces of the porous silicon may therefore be modi?ed

by partial electrochemical dissolution in hydro?uoric acid

In certain circumstances, the stain etching technique

based solutions. This etching process generates a silicon structure that retains the crystallinity and the crystallographic orientation of the original bulk material. Hence, the porous silicon formed is a form of crystalline silicon. Broadly, the

to provide: silicon hydride surfaces; silicon oxide surfaces

method involves anodising, for example, a heavily boron

hydride surfaces may be produced by exposing the porous

doped CZ silicon Wafer in an electrochemical cell Which contains an electrolyte comprising a 20% solution of hydrof

silicon to HP.

Wherein the porous silicon may typically be described as

being partially oxidised; or derivatised surfaces Which may possess SiiO4C bonds and/or Si4C bonds. Silicon

luoric acid in an alcohol such as ethanol, methanol or isopro

[0025] Silicon oxide surfaces may be produced by subject ing the silicon to chemical oxidation, photochemical oxida

pylalcohol (IPA). Following the passing of an anodisation

tion or thermal oxidation, as described for example in Chapter

current With a density of about 50 mA cm '2, a porous silicon

5.3 of Properties of Porous Silicon (edited by L. T. Canham, IEE 1997). PCT/GB02/03731, the entire contents of Which are incorporated herein by reference, describes hoW porous

layer is produced Which may be separated from the Wafer by increasing the current density for a short period of time. The effect of this is to dissolve the silicon at the interface betWeen

the porous and bulk crystalline regions. Porous silicon may

silicon may be partially oxidised in such a manner that the sample of porous silicon retains some elemental silicon. For

also be made using the so-called stain-etching technique

example, PCT/GB02/03731 describes hoW, folloWing anodi

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US 2011/0250252 A1

sation in 20% ethanoic HF, the anodised sample Was partially


oxidised by thermal treatment in air at 500° C. to yield a

con nanoparticles include vaporation and condensation in a

partially oxidised porous silicon sample. [0026] Following partial oxidation, an amount of elemental

subatmospheric inert-gas environment. Various aerosol pro ces sing techniques have been reported to improve the produc tion yield of nanoparticles. These include synthesis by the

silicon Will remain. The silicon particles may possess an oxide content corresponding to betWeen about one monolayer of oxygen and a total oxide thickness of less than or equal to about 4.5 nm covering the entire silicon skeleton. The porous silicon may have an oxygen to silicon atomic ratio betWeen

Other examples of methods suitable for making sili

folloWing techniques: combustion ?ame; plasma; laser abla tion; chemical vapour condensation; spray pyrolysis; electro spray and plasma spray. Because the throughput for these

about 0.04 and 2.0, and preferably betWeen 0.60 and 1.5.

techniques currently tends to be loW, preferred nanoparticle synthesis techniques include: high energy ball milling; gas

Oxidation may occur in the pores and/or on the external

phase synthesis; plasma synthesis; chemical synthesis;

surface of the silicon. [0027] Derivatised porous silicon is porous silicon possess ing a covalently bound monolayer on at least part of its surface. The monolayer typically comprises one or more organic groups that are bonded by hydrosilylation to at least part of the surface of the porous silicon. Derivatised porous silicon is described in PCT/GB00/01450, the contents of

sonochemical synthesis. [0030] In the present invention, particle siZe distribution

Which are incorporated herein by reference in their entirety. PCT/GB00/01450 describes derivatisation of the surface of silicon using methods such as hydrosilyation in the presence of a LeWis acid. In that case, the derivatisation is effected in order to block oxidation of the silicon atoms at the surface and so stabilise the silicon. Methods of preparing derivatised porous silicon are knoWn to the skilled person and are

described, for example, by J. H. Song and M. J. Sailor in Inorg. Chem. 1999, vol 21, No. 1-3, pp 69-84 (Chemical Modi?cation of Crystalline Porous Silicon Surfaces). Derivi tisation of the silicon may be desirable When it is required to

increase the hydrophobicity of the silicon, thereby decreasing its Wettability. Preferred derivatised surfaces are modi?ed With one or more alkyne groups. Alkyne derivatised silicon

may be derived from treatment With acetylene gas, for example, as described in “Studies of thermally carboniZed porous silicon surfaces” by J. Salonen et al in Phys Stat. Solidi

(a), 182, pp123-126, (2000) and “Stabilisation of porous sili con surface by loW temperature photoassisted reaction With acetylene”, by S. T. Lakshmikumar et al in Curr. Appl. Phys.

3, pp185-189 (2003). Mesoporous silicon may be derivatised during its formation in HF-based electrolytes, using the tech niques described by G. Mattei and V. Valentini in Journal

American Chemical Society vol 125, p9608 (2003) and Val entini et al., Physica Status Solidi (c) 4 (6) p2044-2048

(2007). [0028] Methods for making silicon poWders such as silicon microparticles and silicon nanoparticles are Well knoWn in the art. Silicon microparticles are generally taken to mean par ticles of about 1 to 1000 pm in diameter and silicon nanopar ticles are generally taken to mean particles possessing a diam eter of about 100 nm and less. Silicon nanoparticles therefore typically possess a diameter in the range of about 1 nm to about 100 nm, for example about 5 nm to about 100 nm. Methods for making silicon poWders are often referred to as

“bottom-up” methods, Which include, for example, chemical synthesis or gas phase synthesis. Alternatively, so-called

measurements, including the mean particle siZe (dso/um) of the silicon particles are measured using a Malvem Particle

SiZe AnalyZer, Model MastersiZer, from Malvem Instru ments. A helium-neon gas laser beam is projected through a transparent cell Which contains the silicon particles sus pended in an aqueous solution. Light rays Which strike the

particles are scattered through angles Which are inversely proportional to the particle siZe. The photodetector array measures the quantity of light at several predetermined angles. Electrical signals proportional to the measured light ?ux values are then processed by a microcomputer system, against a scatterpattern predicted from theoretical particles as de?ned by the refractive indices of the sample and aqueous dispersant to determine the particle siZe distribution of the silicon.


The preferred methods of producing silicon nano

particles are described in more detail.

High-Energy Ball Milling [0032]

High energy ball milling, Which is a common top

doWn approach for nanoparticle synthesis, has been used for the generation of magnetic, catalytic, and structural nanopar ticles, see Huang, “Deformation-induced amorphiZation in

ball-milled silicon”, Phil. Mag. Lett., 1999, 79, pp305-314. The technique, Which is a commercial technology, has tradi

tionally been considered problematic because of contamina tion problems from ball-milling processes. HoWever, the availability of tungsten carbide components and the use of inert atmosphere and/or high vacuum processes has reduced impurities to acceptable levels. Particle siZes in the range of about 0.1 to 1 pm are most commonly produced by ball

milling techniques, though it is knoWn to produce particle siZes of about 0.01 pm. [0033] Ball milling can be carried out in either “dry” con ditions or in the presence of a liquid, i.e. “Wet” conditions. For Wet conditions, typical solvents include Water or alcohol based solvents.

Gas Phase Synthesis

“top-doWn” methods refer to such knoWn methods as elec

[0034] Silane decomposition provides a very high through put commercial process for producing polycrystalline silicon

trochemical etching or comminution (e.g. milling as described in Kerkar et al. J. Am. Ceram. Soc., vol. 73, pages

about $30/kg) is expensive, so called “?nes” (microparticles

granules. Although the electronic grade feedstock (currently

2879-2885, 1990). PCT/GB02/03493 and PCT/GB01/

and nanoparticles) are a suitable Waste product for use in the

03633, the contents of Which are incorporated herein by ref erence in their entirety, describe methods for making particles

present invention. Fine silicon poWders are commercially available. For example, NanoSiTM Polysilicon is commer cially available from Advanced Silicon Materials LLC and is a ?ne silicon poWder prepared by decomposition of silane in

of silicon, said methods being suitable for making silicon for use in the present invention. Such methods include subjecting silicon to centrifuge methods, or grinding methods.

a hydrogen atmosphere. The particle siZe is 5 to 500 nm and

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US 2011/0250252 Al

the BET surface area is about 25 m2/ g. This type of silicon has

case of porous silicon, ?lls at least some, or all, or substan

a tendency to agglomerate, reportedly due to hydrogen bond ing and Van der Waals forces.

tially all of the pores and/or coats the outside of the silicon

Plasma Synthesis [0035] Plasma synthesis is described by Tanaka in “Produc tion of ultra?ne silicon poWder by the arc plasma method”, J.

Mat. Sci., 1987, 22, pp2192-2198. High temperature synthe sis of a range of metal nanoparticles With good throughput may be achieved using this method. Silicon nanoparticles (typically 10-100 nm diameter) have been generated in argon hydrogen or argon-nitrogen gaseous environments using this method.

ful?l the dual purpose of being at least one ingredient to be delivered to the human or animal body. The masking material

may also comprise a layer of nanoparticles, effectively form ing a coating or capping layer. [0041] Suitable masking materials may include the use of high opacity materials, such as titania, Which is White, or

vividly coloured pigments or speci?c ingredients normally used in the composition. Examples of suitable masking mate rials include the folloWing colouring agents Which may be used in order to effect the desired colour: Whiteiamydon;

yelloWisaffron, turmeric, annatto; greeniparsley, spinach,

Chemical Synthesis [0036]

particles forming a capping layer. The masking material may

sorrel; redilycopene, carmine, sWeet potato extract, red cab

bage; blueiblueberry, mulberry extracts; purpleigrape

Solution groWth of ultra-small (