DE102019113061A1 - METHOD OF CHARACTERIZATION OF MICROCAPSULES - Google Patents

Abstract

The invention relates to the field of measurement technology and relates to a method for characterizing microcapsules, such as can be used, for example, for determining the mechanical properties of microcapsules. The object of the invention is therefore to provide a simple and inexpensive method for characterizing microcapsules with respect to Their behavior when exposed to tensile, compressive and / or shear loads. The object is achieved by a method for characterizing microcapsules with regard to their behavior when exposed to tensile, compressive and / or shear stress on the microcapsules and / or on their surroundings , in which at least one microcapsule is introduced into a transparent or translucent elastomer and subsequently the elastomer and / or the microcapsule are deformed and the change in shape is monitored optically, the deformation being implemented by means of tensile, compressive and / or shear stress, and the deformation the microcapsule and / or the microcapsule shell and / or the elastomer is determined as a function of the applied tensile, compressive and / or shear stress.

Description

The invention relates to the fields of polymer chemistry and measurement technology and relates to a method for characterizing microcapsules, as can be used, for example, to determine the mechanical properties of the microcapsules, in order to then make statements for their use, for example in medical diagnostics of drug delivery Systems or for "self-healing" in materials.

The use of microcapsules nowadays extends across a large number of branches and branches of industry.
For several years, the medical and therapeutic use of microcapsules has been the subject of research and development, for example for local drug delivery ( AG Skirtach et al .: Chemical Communications, 2011, 47, 12736-12746 ; AM Pavlov, et al .: Soft Matter 7, 2011, 4341-4347 ; H. Gao et al .: Journal of Materials Chemistry B, 2015, 3, 1888-1897 ).

Another object of research and development regarding the use of microcapsules is the initiation of an autonomous regeneration of the mechanical properties of rigid plastics when cracks occur ( G. Li et al .: 35, 2012, 59-67 ; SR White et al .: Nature, 409, 2001, 794-797 ). In this case, microcapsules are present in a plastic, and the shell of the microcapsules in the plastic can be connected to the plastic by adhesion. In the event of a crack in the plastic, this crack hits one of the microcapsules, the shell of which is destroyed and materials present inside the microcapsules are released. The material from the interior of the capsule is distributed in the crack, at least partially fills it and, depending on the material, can harden, as a result of which the crack in the plastic can be regenerated.

It is therefore desirable to know the conditions for the destruction of the capsule shell in different environments in order to realize a destruction of the capsule shell only under the desired conditions, at the desired time and / or at the desired location. This in turn requires that the capsule shells can be sufficiently characterized and, in particular, their mechanical properties can be determined.

• - unter Einwirkung von Druckkräften untersucht, wie bei der Rasterkraftmikroskopie, Mikrokompression oder Nanoindentation, bei denen Mikrokapseln zwischen zwei Platten oder mit Kugel mit Druck belastet werden ( A. Ghaemi et al.: Chemical Engineering Science 142, 2016, 236-243 ),
• - auf eine Verformung durch osmotische und adhäsive Effekte untersucht ( C. Gao et al.: The European Physical Journal E, 2001, 5: 21-27 ),
• - auf eine Verformung durch eine zentrifugal angreifende Kraft untersucht (Spinning-Drop Tensiometer) ( G. Pieper et al.: Journal of Colloid and Interface Science 202, 1998, 293-300 ).

For the characterization of such microcapsules and the determination of mechanical parameters within the quality control in the production process, only capsule-specific procedures are mostly available. So are microcapsules;

• - examined under the influence of compressive forces, as in atomic force microscopy, microcompression or nanoindentation, in which microcapsules are loaded with pressure between two plates or with a ball ( A. Ghaemi et al .: Chemical Engineering Science 142, 2016, 236-243 ),
• - examined for deformation due to osmotic and adhesive effects ( C. Gao et al .: The European Physical Journal E, 2001, 5: 21-27 ),
• - examined for deformation caused by a centrifugal force (spinning-drop tensiometer) ( G. Pieper et al .: Journal of Colloid and Interface Science 202, 1998, 293-300 ).

With these known methods, the behavior of the materials of microcapsules is determined, especially under pressure.

The disadvantage of these characterization methods for microcapsules is the high expenditure of preparation and time, which means that in practice only a small number of samples can be examined.

Another disadvantage is that the known characterization methods essentially only measure the pressure load on microcapsules, but not the behavior under the action of tensile and / or shear loads up to the failure of the microcapsule with simultaneous visual tracking.

The object of the invention is therefore to provide a simple and inexpensive method for characterizing microcapsules with regard to their behavior when exposed to tensile, compressive and / or shear loads.

The object is achieved by the invention specified in the claims. Advantageous refinements are the subject matter of the subclaims, the invention also including combinations of the individual dependent claims in the sense of an and link, as long as they are not mutually exclusive.

In the method according to the invention for characterizing microcapsules with regard to their behavior when tensile, compressive and / or shear stresses are exerted on the microcapsules and / or their surroundings, at least one microcapsule is placed in a transparent or translucent elastomer and then the elastomer and / or deforms the microcapsule and optically monitors the change in shape of at least one microcapsule and / or the capsule shell of the at least one microcapsule, the deformation being implemented discontinuously or continuously by means of tensile, compressive and / or shear stress, and the Deformation of the microcapsule and / or the microcapsule shell and / or the elastomer is determined as a function of the applied tensile, compressive and / or shear stress.

The elastomer is advantageously crosslinked and cured to form a transparent or translucent molded part.

A large number of microcapsules are also advantageously incorporated into the elastomer.

Microcapsules are also advantageously used which are impermeable to the material or fluid inside the microcapsule without the action of tensile, compressive and / or shear stress.

Microcapsules whose shell is permeable to the material or fluid located inside the microcapsule or to the elastomer are also advantageously used.

It is also advantageous if microcapsules with their largest diameter of 1 mm, advantageously with diameters of 5-100 μm, still advantageously 20-80 μm, furthermore advantageously 60-80 μm, are used.

It is also advantageous if one or more silicones or silicone compounds are used as the elastomer.

It is also advantageous if the microcapsules are introduced into the elastomer by means of mixing, advantageously homogenizing.

And it is also advantageous if a substantially bubble-free elastomer is used as a molded part by evacuating fluids from the elastomer.

It is also advantageous if the optical monitoring of the microcapsule and / or microcapsule shell is carried out by means of a microscope and / or a camera, the focus of the optical monitoring on the microcapsule and / or microcapsule shell during the application of the tensile, pressure - and / or the shear stress on the elastomer and / or the microcapsules is readjusted.

It is also advantageous if the deformation of the microcapsule is carried out at least until the microcapsule and / or the microcapsule shell rupture or until the elastomer delaminates.

It is also advantageous if the tensile, compressive and / or shear stress at which the shell of the microcapsule breaks is determined.

With the solution according to the invention it is possible for the first time to characterize microcapsules simply and inexpensively with regard to their behavior when exposed to tensile, compressive and / or shear loads.

With the method according to the invention, the force at which the microcapsule deforms, breaks or at least breaks the closed microcapsule shell and the material inside the microcapsule becomes accessible can advantageously be quantified.

According to the invention, at least one, advantageously a large number of microcapsules are introduced into a transparent or translucent elastomer, and the microcapsules are advantageously mixed with the elastomer. One or more silicones or silicone compounds can advantageously be used as the elastomer.

The elastomer can advantageously be evacuated in order to remove any fluids that may be present, in particular gas bubbles, from the elastomer.

According to the invention, microcapsules are to be understood as meaning capsules whose largest diameter is 1 mm. The microcapsules that are characterized according to the invention advantageously have a diameter between 5 and 100 μm, more advantageously between 20 and 80 μm, more advantageously between 60 and 80 μm.

The microcapsules to be characterized can consist of a brittle or a soft, stretchable material.

Furthermore, the microcapsules are advantageously impermeable to the material, the fluid or the elastomer located inside the microcapsule, without the action of tensile, compressive and / or shear stress, so that it is optically recognizable if the material or fluid present inside the microcapsule is in a Crack emerges from the microcapsule. However, the permeation of the material in the microcapsule through the capsule shell can also be detected if the material of the shell of the microcapsule is permeable for the material or fluid located inside the microcapsule and / or for the elastomer.
This is a great advantage over the solutions of the prior art, since such results have not yet been demonstrable.

The stress-strain behavior of the elastomer to be used can be used in advance to calculate capsule-specific parameters be characterized. Serve as the basis for this DIN 53504 and ISO 37 . The stress and strain behavior and the behavior in the event of transverse contraction of the respective elastomer are then known before the method according to the invention is implemented.

According to the invention, at least one microcapsule must be introduced into the transparent or translucent, preferably bubble-free elastomer in order to carry out a characterization.

After the microcapsule (s) has been introduced into the elastomer, advantageously by means of mixing, still advantageously by means of homogenization, and also advantageously after evacuation of the elastomer, the advantageously essentially bubble-free elastomer is poured into a mold, advantageously in a band, strip or strip shape Wide-flat shape, since with such a shape of the elastomer with the microcapsule (s) the optical monitoring of the microcapsules can be realized more easily.

The elastomer is then advantageously crosslinked and cured if such an elastomer is used.
The elastomer can be crosslinked and cured by storage at or above room temperature (20 ° C.), by irradiation with UV light and / or by thermal crosslinking at higher temperatures.

Advantageously, additives, auxiliaries, fillers, vulcanizing agents, curing agents, crosslinking agents, accelerators, activators and / or catalysts can be added to the elastomer prior to crosslinking and curing.

The molded part made of the, advantageously crosslinked and cured, elastomer can then be processed in such a way that the molded part can be viewed under an optical monitoring unit, for example a microscope or a camera. The processing can be done, for example, by cutting a film-shaped molded part into smaller pieces.

Next, the machined or unmachined molded part is positioned in a clamping device under the optical monitoring unit, advantageously the clamping device of a microscope, the clamping device being positionable on or in the microscope.
The focus of the microscope is aligned and adjusted to a microcapsule. This is followed by the discontinuous or continuous deformation of the elastomer and / or the microcapsule, the focus on the microcapsule being adjusted at the same time as the deformation of the elastomer and / or the microcapsule progresses.

The at least one optically monitored microcapsule is advantageously not located on the edge of the molded part made of the elastomer, but with a minimum distance from the edge of the molded part of 3 mm, advantageously in the center of the elastomer molded part, so that the deformation of the elastomer ensures a uniform application of force and thus a uniform deformation of the Microcapsule is realized.

The deformation by tensile, compressive and / or shear stresses can be realized by stretching, applying pressure and / or by shearing the elastomer and / or the microcapsule, for example by manually applying a tensile, compressive, or non-continuous tensile or compressive action to the elastomer in 1-5 mm steps - and / or shear stress, advantageously a shear stress, is exposed and thus deformed. The deformation can also take place continuously.

The focus of the optical monitoring on the microcapsule and / or microcapsule shell is advantageously readjusted during the application of the tensile, compressive and / or shear stress to the elastomer and / or the microcapsules, so that the desired point to be monitored is always the focus of the monitoring lies.

The deformation takes place advantageously at least until the microcapsule and / or microcapsule shell rupture or until the microcapsules delaminate from the elastomer. If a large number of microcapsules are used and several microcapsules are monitored in the molded part at the same time, one or more microcapsules can break and / or delaminate sooner or later. According to the method, it is important to know when a microcapsule or microcapsule shell is broken for the first time or when it is delaminated from the elastomer.

The tensile, compressive and / or shear stress at which the shell of the microcapsule breaks or the microcapsule delaminates from the elastomer is determined.

After characterizing microcapsules by determining the tensile, compressive and / or shear stresses at which the shell of the microcapsule breaks or the microcapsule delaminates from the elastomer, conclusions can be drawn about the properties of the elastomer and / or the environment of the microcapsules or the elastomer to be hit.

It was further surprisingly found that, under certain conditions, when the tensile, compressive and / or shear stresses are exerted, microcapsules deform to the extent that the capsule shell not only breaks, but depending on the material the capsule shell, the capsule shell can also deform inward, so that part of a capsule wall moves to its opposite capsule wall and thus the microcapsule is quasi folded instead of being stretched or torn apart.

In the event of delamination between the elastomer and the microcapsule, further deformation is neither possible nor sensible, since the microcapsule can no longer break or deform.

The data obtained up to the point of delamination can nevertheless provide conclusions as to the compressive, tensile or shear stress up to which the microcapsule is break-proof. The data obtained can also be used to draw conclusions about the adhesion or material compatibility between the microcapsule and the elastomer.

Characterizations with regard to modulus of elasticity, elongation, plastic deformation and / or fracture behavior under tensile, compressive and / or shear stress of the microcapsules can advantageously be carried out.

The characterization is advantageously carried out during continuous deformation of the molded elastomer part with microcapsules, which can be recorded as a stop motion or as a video.

From a specific stress-strain curve for a cross-linked and cured elastomer without microcapsules, which is either known or determined in advance, the force that is necessary to deform or break microcapsules or delamination of the microcapsule shell can be determined bring about the elastomer in this elastomer. From this value of the force, further mechanical parameters, such as modulus of elasticity, elongation, plastic deformation, or also the breaking behavior under tensile, compressive and / or shear stress can be determined.

In this way, specific conditions for the destruction of the capsule shell or its delamination in the vicinity of a certain elastomer can be specified, so that the capsule shell or its delamination in such an elastomer can be destroyed under desired conditions, at the desired time and / or at the desired location .

The invention is explained in more detail below using several exemplary embodiments.

Example 1:

A polyurethane elastomer is produced from two components by mixing 10 g of polyisocyanate and 8 g of polyol to form a pourable elastomer with a Shore hardness of 83.
Then 10 mg of polyurea-based microcapsules with an average diameter between 20 and 120 μm, the cavities of which are filled with the fluorescent dye rhodamine B, are added to the elastomer and mixed with one another.

The elastomer with the microcapsules is poured into a mold measuring 10 cm x 3 cm x 5 mm. The elastomer cross-links and cures within 2 hours at 70 ° C. The molded part made from the elastomer with the microcapsules is then cut to a sample size of 3 cm × 8 mm.

This sample is positioned in a clamping device in a light microscope, the focus is set on a microcapsule and the sample is stretched discontinuously. The expansion takes place in steps of 1 mm, during the expansion the focus of the microscope on the microcapsule has to be readjusted. The expansion takes place until the microcapsule shell ruptures.

A known stress-strain curve specific to the elastomer is used to determine the force that is necessary to cause the microcapsule shell of the monitored microcapsule to break, which in the present case occurs at a force of 12 mN.
From this value, further mechanical parameters, such as modulus of elasticity, plastic deformation, or the fracture behavior under tensile or shear stress can be determined.

After the capsule shell has broken, the dye escapes from the inside of the capsule into the elastomer and it can be seen at which point in the elastomer sample a microcapsule has broken.

Example 2:

A silicone elastomer is produced from two components by mixing 10 g of a siloxane mixture and 1 g of hardener to form a pourable elastomer. Then 10 μg of polyelectrolyte-based microcapsules with an average diameter between 20 and 120 μm, the cavity of which is filled with trimethylhexamethylenediamine, are added to the elastomer and mixed with one another.

The elastomer with the microcapsules is poured into a mold measuring 10 cm x 3 cm x 3 mm. The elastomer crosslinks and hardens within 7 Days at room temperature. The molded part made from the elastomer with the microcapsules is then cut to a sample size of 3 cm × 3 cm.

This sample is positioned in a fixture in a light microscope, the focus is set on a microcapsule and the sample is continuously sheared. During the shear, the focus of the microscope on the microcapsule is automatically readjusted.
The shear continues until the microcapsule delaminates from the elastomer.

A specific stress-strain curve determined for the elastomer is used to determine the force that is necessary to cause delamination of the monitored microcapsule, which in the present case takes place at a force of 1.9 mN.

Example 3:

The sample preparation takes place as in Example 1, the stretching of the sample in the clamping device takes place continuously.
The microcapsules have a colored, ethanolic betanin solution in their cavity.

The microscope's focus is readjusted automatically.

The expansion takes place until the colored capsule filling material permeates through the capsule shell, without any direct breakage of the microcapsule.

A specific stress-strain curve known for the elastomer is used to determine the force that is necessary to bring about the permeation of the colored capsule filling material, which in the present case takes place at a force of 1.7 mN.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Non-patent literature cited

• A.G. Skirtach et al .: Chemical Communications, 2011, 47, 12736-12746 [0002]
• AT THE. Pavlov, et al .: Soft Matter 7, 2011, 4341-4347 [0002]
• H. Gao et al .: Journal of Materials Chemistry B, 2015, 3, 1888-1897 [0002]
• G. Li et al .: 35, 2012, 59-67 [0003]
• S.R. White et al .: Nature, 409, 2001, 794-797 [0003]
• A. Ghaemi et al .: Chemical Engineering Science 142, 2016, 236-243 [0005]
• C. Gao et al .: The European Physical Journal E, 2001, 5: 21-27 [0005]
• G. Pieper et al .: Journal of Colloid and Interface Science 202, 1998, 293-300 [0005]
• DIN 53504 [0030]
• ISO 37 [0030]

Claims (13)

Method for characterizing microcapsules with regard to their behavior when tensile, compressive and / or shear stresses are exerted on the microcapsules and / or on their surroundings, in which at least one microcapsule is introduced into a transparent or translucent elastomer and then the elastomer and / or the Microcapsule are deformed and the change in shape of at least one microcapsule and / or the capsule shell of the at least one microcapsule is optically monitored, the deformation being implemented discontinuously or continuously by means of tensile, compressive and / or shear stress, and the deformation of the microcapsule and / or the Microcapsule shell and / or the elastomer is determined depending on the applied tensile, compressive and / or shear stress. Procedure according to Claim 1 , in which the elastomer is crosslinked and cured to form a transparent or translucent molded part. Procedure according to Claim 1 , in which a large number of microcapsules are inserted into the elastomer. Procedure according to Claim 1 , in which microcapsules are used that are impermeable to the material or fluid inside the microcapsule without the action of tensile, compressive and / or shear stress. Procedure according to Claim 1 , in which microcapsules are used whose shell is permeable to the material or fluid located inside the microcapsule or to the elastomer. Procedure according to Claim 1 , in which microcapsules with their largest diameter of 1 mm, advantageously with diameters of 5-100 μm, still advantageously 20-80 μm, furthermore advantageously 60-80 μm, are used. Procedure according to Claim 1 , in which one or more silicones or silicone compounds are used as the elastomer. Procedure according to Claim 1 , in which the microcapsules are introduced into the elastomer by means of mixing, advantageously homogenizing. Procedure according to Claim 1 , in which a substantially bubble-free elastomer is used as a molded part by evacuating fluids from the elastomer. Procedure according to Claim 1 , in which the optical monitoring of the microcapsule and / or microcapsule shell is carried out by means of a microscope and / or a camera. Procedure according to Claim 10 , in which the focus of the optical monitoring on the microcapsule and / or microcapsule shell is readjusted during the application of the tensile, compressive and / or shear stress to the elastomer and / or the microcapsules. Procedure according to Claim 1 , in which the deformation of the microcapsule is carried out at least until the microcapsule and / or the microcapsule shell rupture or until the elastomer delaminates. Procedure according to Claim 1 , at which the tensile, compressive and / or shear stress at which the shell of the microcapsule breaks is determined.