Process for subsequent surface modification of finely structured structures

A process comprising:

• a) providing a structure formed from a hard inorganic material, the structure having, in at least one spatial direction, a material thickness M of not more than 1000 nm and as an overall structure having, in at least one spatial direction, a measurement which is at least 5 times the material thickness M;
• and
• b) subsequently treating the structure provided in step a) with an organic liquid comprising at least one reactive substance which can react with atoms of the inorganic material to form a chemical bond and having at least one reactive functional group selected from the group consisting of hydroxyl groups, carboxyl groups, carbonate groups, and oxygen atoms bonded to phosphorus atoms, the treating being effected under conditions under which the organic liquid is under supercritical conditions, resulting in a surface modification of the structure, wherein the treating comprises introducing the structure under subcritical conditions into the organic liquid and then heating to bring the organic liquid to the supercritical conditions,
• wherein the structure is selected from the group consisting of:
• i. hollow spheres, the sphere shell of which has a thickness of not more than 100 nm, and wherein the ratio of sphere diameter to thickness of the sphere shell is at least 5;
• ii. fibers having a fiber thickness of not more than 1000 nm, and an aspect ratio of at least 50;
• iii. platelets having a thickness of not more than 100 nm and a ratio of diameter to thickness of at least 5;
• and
• iv. agglomerates of particles having a mean particle diameter of not more than 100 nm, the proportion by volume of the inorganic material, based on the total volume of the agglomerate, being in the range from 1 to 20% by volume;
• wherein the inorganic material is selected from metal oxides and semimetal oxides and has a Mohs hardness of greater than 4 and comprises at least one oxide selected from the group consisting of silicon dioxide, zinc oxide, tin(IV) oxide, titanium(IV) oxide and aluminum oxide in an amount of 90 to 100% by weight, based on the total weight of the inorganic material, and wherein the reactive substance is selected from the group consisting of C1-C6-alkanols, C1-C6-alkanecarboxylic acids, C2-C6-alkanepolycarboxylic acids, C2-C6-alkanepolyols, C2-C4-alkylene carbonates and mixtures thereof.