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Year of fee payment: The invention relates to amphiphilic, nanoscalar particles comprising lipophilic hydrolyzable astonishing nails acrylic liquid pump on their surface. The invention also relates to methods for producing amphiphilic, nanoscalar particles and to compositions containing said particles. The present invention relates to amphiphilic nanoscale particles, to processes for their production and to their use.
The production of nanoscale particles usable in industrial processes has long been an interesting objective. When nanoparticles are produced by means of sol-gel or other precipitation techniques, agglomeration can be prevented by applying a surface charge double-charge cloud.
These connections were identified by Stem as early as the start of the 20th century. The colloid stability achieved as a result leads to the ability to keep nanoparticulate suspensions, also known as sols, stable over prolonged periods. This is referred to as electrosteric stabilization. The charge-stabilized nanosuspensions or sols can thus be destabilized at the so-called isoelectric point, i.
Aggregates or else gels are then formed if the aggregates combine to larger units. In addition to these stabilization forms by means of the application of charges, there is yet a further form in which the surface of the nanoparticles is provided with groups which are very similar to the surrounding liquid. This can be achieved, for example, with SiO 2 particles whose surface is covered fully with OH groups.
The result of this is that, even at the isoelectric point, silicas, for example in aqueous systems, do not precipitate out because the free interface enthalpy between the surface and the surrounding liquid itself is already at a minimum and no enthalpy gain occurs by aggregation. Such stabilizations are typical mainly for aqueous silica sols SiOH groups. The avoidance of agglomerates or aggregates is of crucial significance for the further industrial processing of the nanoparticles.
This applies both to the production of shaped bodies from such particles and to their dispersion in a matrix material. The interesting properties of nanoparticles, for example interface effects or transparency, can only come into full effect when they are homogeneously dispersible. While, in the case of electrostatic stabilization without additional groupsespecially in the case of oxidic but also in the case of nonoxidic systems, strong interaction via the formation of chemical bonds for example SiOSi bonds, significantly stronger in the case of TiOTi or ZrOZr occurs in the case of formation of aggregates, which enables redispersibility, for example, only with use of strong acids usually undesired in process technology, it is possible in the case of surface modifications with functional groups astonishing nails acrylic liquid pump do not react chemically with one another for aggregates to occur under certain conditions, which, however, can be returned back to the starting particles in an easily reversible manner with changed conditions.
This principle of chemical surface modification is described in the literature and is frequently used to increase redispersibility. However, the disadvantage of this surface modification is that a complicated chemical step is needed for this purpose, in which the surface-modifying molecule has to be converted to a stable bond with groups on the surface of the particles. An additional factor is that this surface modification virtually has to be tailored to the particular dispersion medium.
For example, hydrophilically surface-modified nanoparticles can be dispersed in aqueous or water-like solvents but not in nonpolar solvents, and vice versa. The object of the present invention was thus directed to the development of nanoparticles for which such surface modification is not required, but which, without further process steps, can be dispersed either in organic solvents or in aqueous solvents.
The invention shall additionally solve the problem of significantly reducing the costs for the production of nanoparticles, by virtue firstly of the surface modification as such being unnecessary, and also adjustment and dependency of the dispersion medium required in each case by different surface modifiers no longer being required.
Surprisingly, the object of the present invention can be achieved by providing amphiphilic nanoscale particles which, on the surface, have hydrolyzable radicals which are lipophilic. The hydrolyzable radicals stem in particular from the hydrolyzable precursors of the particles. The invention further relates to a process for producing amphiphilic nanoscale particles which have, on the surface, hydrolyzable radicals which are lipophilic, said process comprising a the hydrolysis and condensation of one or more hydrolyzable compounds which include at least one lipophilic hydrolyzable group with a substoichiometric amount of water and b the removal of solvent in order to obtain the resulting amphiphilic particles with hydrolyzable radicals as powder.
The hydrolyzable compounds are understood to mean the hydrolyzable monomers or condensation products thereof.
The hydrolyzable compounds are also referred to as hydrolyzable precursors of the particles. For the production, in the case of hydrolyzable compounds as precursors of the particles, for example alkoxides, a nucleation and growth process can be set in motion with a relatively small amount of hydrolysis agent for example water, aqueous acids or aqueous bases and leads either to crystalline or amorphous inorganic solid-state nanoparticles whose surface is still covered with unhydrolyzed precursors.
In the context of the present invention, it is particularly astonishing that the particles can be concentrated by evaporation to dryness without losing their amphiphilicity. The particles according to the present invention can surprisingly be dispersed directly both in aqueous and in organic media, without requiring additional surface modification.
The amphiphilic particles according to the invention can, for example, astonishingly be dispersed directly without further treatment both in water and in toluene. When the amphiphilic particles are dispersed with nonpolar solvents, it should be ensured that the solvent is essentially anhydrous in order to avoid hydrolysis of the hydrolyzable groups. As shown in the examples below, the same inventive amphiphilic particle can be dispersed directly in such different solvents as water, methanol, toluene and hexane, and the particles, provided that no hydrolysis proceeds, can be freed from the dispersion medium and then redispersed again in the same or another solvent, i.
Without wishing to be bound to a theory, it is suspected that this surprising effect can be explained by the lipophilic hydrolyzable radicals present on the particle surface being highly compatible with nonpolar organic solvents and agglomeration thus being prevented.
The easy dispersibility in water can be explained, for example, by the hydrolyzable lipophilic astonishing nails acrylic liquid pump being hydrolyzed in the water, such that only hydrophilic groups which are readily compatible with the polar dispersion medium remain on the surface. Such amphiphilic particle systems can, for example, be freed of solvents and the resulting powder can be redispersed again at any time.
When additional functions are required, it is also possible to carry out appropriate surface modifications, dopings or other adjustments, as described below. The invention therefore provides nanoscale particles which, on the surface, have hydrolyzable radicals which are lipophilic. The expressions nanoscale particles and nanoparticles are used here synonymously.
Amphiphilicity here describes the property of the particles of being dispersible both in water as a polar or hydrophilic solvent and in nonpolar or lipophilic solvents such as toluene or hexane.
This compatibility results, with regard to the nonpolar media, from the lipophilic groups present on the surface of the particles, and, with regard to water, from the hydrolyzability of the lipophilic groups present which are hydrolyzed in water to leave hydrophilic groups such as hydroxyl groups on the surface of the particles. In addition to the hydrophilic groups formed by the hydrolysis, the particles may also already have hydrophilic groups on the surface before the hydrolysis.
Lipophilic and hydrophobic groups have the tendency not to penetrate into water and to remain therein, while hydrophilic groups have the tendency to penetrate into water and to remain therein. Lipophilic compounds or groups have the tendency to disperse or to dissolve in a nonpolar medium, astonishing nails acrylic liquid pump example an organic solvent, for example hexane or toluene, while hydrophilic compounds or groups have the tendency to disperse or to dissolve in a polar medium, for example water.
The hydrophilic character can arise, for example, as a result of astonishing nails acrylic liquid pump, oxy, oxide, carboxylate, sulfate, sulfonate functions, generally ionic astonishing nails acrylic liquid pump or hydrophilic polyether chains, while lipophilic astonishing nails acrylic liquid pump is present, for example, typically in the case of hydrocarbon radicals such as alkyl radicals or aromatic radicals. Astonishing nails acrylic liquid pump the amphiphilic particles according to the present invention, the hydrolyzable radicals are lipophilic, i.
For example, in the case of a hydrolyzable alkoxy group on the surface of a particle, the lipophilic character arises by virtue of the lipophilic alkyl group of the alkoxy group. These hydrolyzable radicals can, as a whole, be referred to as lipophilic groups. The amphiphilic particles according to the invention are nanoscale particles, i. Unless stated otherwise, particle size is understood here to mean the mean volume-average particle diameter, for which a UPA Ultrafine Particle Analyzer, Leeds Northrup laser optics, dynamic laser light scattering can be used for the measurement.
The mean particle diameter is preferably not more than nm, more preferably not more than nm, for example from 1 to nm, preferably from 2 to nm, for example from 2 to 50 nm. To determine very small particles in this range, it is also possible to use electron microscopy methods for example by means of HR-TEM. They may optionally also be fibrous particles. In this case, the mean particle size relates to the length which can, for example, also be determined visually with microscopic methods.
The nanoscale particles are in particular nanoscale inorganic solid particles. The nanoparticles are preferably of astonishing nails acrylic liquid pump, including metal alloys, metal or semimetal compounds, especially metal chalcogenides. For this purpose, all metals or semimetals hereinafter also abbreviated astonishing nails acrylic liquid pump as M may be used. It is possible to use one type of nanoparticles or a mixture of nanoparticles.
The nanoparticles may preferably be composed of metal or semimetal compounds. Nanoscale particles can conventionally be produced in various ways, for example by flame pyrolysis, plasma methods, colloid techniques, astonishing nails acrylic liquid pump processes, controlled seeding and growth processes, MOCVD methods and emulsion methods. These processes are described comprehensively in the literature. The amphiphilic nanoscale particles according to the invention are preferably produced by a astonishing nails acrylic liquid pump process to form the nanoscale particles.
In the sol-gel process, hydrolyzable compounds are commonly astonishing nails acrylic liquid pump with water, optionally under acidic or basic catalysis, and optionally at least partly condensed. Suitable adjustment of the parameters, for example degree of condensation, solvent, temperature, water concentration, duration or pH, allows the amphiphilic sol comprising nanoscale particles to be obtained.
Further details of the sol-gel process are described, for example, in C. According to the invention, the hydrolysis and condensation reaction is carried out such that the hydrolyzable compounds are incompletely hydrolyzed and nanoparticles are formed, i. The person skilled in the art faced with the task of incomplete hydrolyzing the hydrolyzable compounds is familiar with how this astonishing nails acrylic liquid pump achieved by suitable adjustment of the abovementioned parameters.
Some preferred conditions are explained below. The hydrolysis and condensation can be carried out in a solvent, but they can also be carried out without solvent, in which case solvents or other liquid constituents can be formed in the hydrolysis, for example in the hydrolysis of alkoxides.
The removal of the solvent can include the removal of liquid constituents present. Preference is astonishing nails acrylic liquid pump to effecting the hydrolysis with a substoichiometric amount of water, i. The molar ratio is preferably greater than 0. A preferred molar ratio is, for example, from 0. As stated, the hydrolysis can be acid- or base-catalyzed, preference being given to acid catalysis.
In a further preferred embodiment, the hydrolysis is effected with heating and pressure hydrothermal reactionfor example by heating in a closed vessel. By their nature, suitable reaction conditions depend on the starting compounds astonishing nails acrylic liquid pump, so that, for example, a wide range of suitable conditions may be appropriate depending on the stability of the starting compound. The person skilled in the art can select suitable conditions immediately depending on the compounds selected.
It is also possible to employ organyls with metal-carbon bonds. Useful metal or semimetal compounds are in principle all metals or semimetals of the main and transition groups from which alkoxides or other hydrolyzable compounds can be prepared.
The semimetals used in addition to the pure metals are, for example, Si, B or Ge. The hydrolyzable compounds useable for this purpose are illustrated further below. Suitable hydrolyzable compounds are in principle hydrolyzable metal or semimetal compounds, for example of the metals and semimetals M which have been listed above and, in addition to hydrolyzable groups, may optionally also have non-hydrolyzable groups. It is possible to use one or more hydrolyzable compounds.
It should be noted at this point that, as known to the astonishing nails acrylic liquid pump skilled in the art, the hydrolyzability of the group of course also depends upon the central atom M to which the group is bonded, so that a certain group may be hydrolyzable or non-hydrolyzable, depending on which M it is bonded to. These connections are known to those skilled in the art.
For example, an alkyl group which is bonded to Si is not hydrolyzable, while the alkyl group on another central atom, for example zirconium, may be hydrolyzable. In the case of the latter central atoms, lipophilic alkyl radicals are then also conceivable as hydrolyzable groups. In addition, for example, in the case of some metals, for example astonishing nails acrylic liquid pump the case of bis acetylacetonate zinc, zinc acetate or calcium acetate, carboxylate or acetylacetonate groups are hydrolyzable, while these groups are no longer hydrolyzable in the case of larger metals, for example Ti, Zr or Fe.
The astonishing nails acrylic liquid pump hydrolyzable groups which are present on the surface of the inventive particles include a astonishing nails acrylic liquid pump radical, the lipophilic radical having in particular at least 4 and preferably at least 5 carbon atoms.
Specific lipophilic hydrolyzable groups are lipophilic alkoxy, alkenyloxy, alkynyloxy, aryloxy, aralkyloxy, alkaryloxy, acyloxy, ether such as alkoxyalkoxy or alkoxyalkoxyalkoxy, and acyl radicals, particular preference being given to alkoxy radicals. The lipophilic radicals astonishing nails acrylic liquid pump also include corresponding cyclic radicals, for example cycloalkyloxy radicals. As stated, the hydrolyzability of the group also depends upon the central atom to which it is bonded.
The lipophilic radicals preferably have a saturated, unsaturated or aromatic, branched or unbranched hydrocarbon radical having at least 4 and preferably at least 5 carbon atoms. Examples or astonishing nails acrylic liquid pump alkoxy groups are C 4 -C 20 -alkoxy, preferably C 4 -C 10 -alkoxy, such as n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, linear or branched pentoxy, hexoxy, heptoxy or octoxy such as 2-ethylhexoxy, cyclohexyloxy.
The alkoxy group may be branched or preferably linear; an advantageous branched alkoxy group is, for example, 2-ethylhexoxy. The alkenyloxy group may be branched or preferably linear; the double bond may be at any position.
