Abrasion Indicators for Smart Surfaces Based on a Luminescence Turn‐On Effect in Supraparticles

Abstract

Many surfaces of man-made objects are equipped with a coating. The coating fulfills specific functions, for instance, as easy-to-clean, [1] scratch-resistant, [2] antireflexive, [3] or antimicrobial [4] agent. These functional properties are usually achieved via molecular building blocks, by nanoparticulate coating additives or by imprinting a surface texture. A certain degree of "smartness" can also be achieved by combining several additives [5,6] which may turn a surface into a gas sensor, [7] a corrosion protection layer, [8] or a self-healing layer. [9] Although there have always been solutions to identify deformations in components, such as in metals [10] or polymer parts, [11] the detection of damages within a surface coating which is only a few micrometers thick still remains a challenge. [12] Such a "scratch-detecting" surface indicator must be cheap, easy to manufacture, easy to detect and should be applicable to any type of surface. Some additives for bulk materials have already been presented which are able to detect scratches and repair them directly. [13] A disadvantage of these systems is, however, that they only do work in a bulk material and not in a coating of a few microns thickness. In this study, we report on shear stress indicators in the form of so-called supraparticles that can be used as damage detectors in thin coatings. These indicator supraparticles are micron-sized, hierarchically structured particles and are composed of nanoparticles. The great advantage of such supraparticles is that a number of very different properties can be combined by assembling different nanoparticle building blocks which carry specific attributes (e.g., magnetism, fluorescence, catalytic activity, etc.). [14] Forced assembly of nanoparticles can be achieved by spray-drying. This process is well-known and well established, for instance, in the pharmaceutical or food industry, to obtain dry powder products (such as granular drugs or instant coffee). [15] Complex architectures can be achieved by repeating this process: In a first spray-drying cycle, supraparticles can be formed from a nanoparticle dispersion. Within a second spray-drying cycle, the supraparticles resulting from the first spray-drying cycle can be coated with other nanoparticles to ultimately obtain core-shell supraparticles.

Supraparticles with a Mechanically Triggerable Color‐Change‐Effect to Equip Coatings with the Ability to Report Damage

“…First, a silanized rhodamine B dye is covalently incorporated into the silica network of 80 nm silica nanoparticles in a modified Stöber synthesis and the dye-doped nanoparticles are assembled into spherical supraparticles via spray-drying (Scheme 1a). [21] Scheme 1. Schematic process of the investigation of color change indicator supraparticles.…”

“…The overall detected decrease of fluorescence intensity-also with the rhodamine B dye-can be explained by particle loss mechanisms during the shear-off process. [21] Figure 4b depicts the relationship between the PBI-PA and rhodamine B dyes over the shear cycles. It can be seen that the ratio decreases over the entire shear process.…”

“…Synthesis of Dye-Doped Silica Nanoparticles: The synthesis of 80 nm silica nanoparticles was carried out according to the literature, [21] based on the Stöber process. [29] In a normal experiment, 300 ml of ethanol was mixed with 15 ml of aqueous ammonia solution (25 wt%).…”

A Simple Model Setup Using Spray‐Drying Principles and Fluorescent Silica Nanoparticles to Evaluate the Efficiency of Facemask Materials in Terms of Virus Particle Retention

“…The dye aliquot was prepared by dilution of 9 mg (0.017 mol) of rhodamine B isothiocyanate in 2 mL dimethyl sulfoxide and mixing with 13 µL (0.055 mmol) 3-aminopropyltriethoxysilane. [20] Mask Material Test Setup Parameters: In this study, mainly fabrics were tested which are relevant to the everyday life of the general population and are used for so-called everyday masks/community masks. A polyester tissue, a cotton fabric (one and two layers) as well as a simple paper towel (one, two, and three layers), which can be used for the construction of a homemade mask, were subject to investigations.…”

Hybrid Inorganic–Organic Luminescent Supraparticle Taggants with Switchable Dual‐Level ID

“…A precondition to achieve this is that the quantity ratios of core and shell material are chosen wisely. [76][77][78] The equally mass-weighted ratios of differently colored PS:dye NPs (1:1:1) and the ratio of organic to inorganic components (core:shell, 50:1) were kept equal to the priorly co-spray-dried intermixed SP sample.…”