Covalently Modulated and Transiently Visible Writing: Rational Association of Two Extremes of Water Wettabilities

Abstract

Anticounterfeiting measures are of ever-increasing importance in society, e.g., for securing the authenticity of and the proof of origin for medical drugs.Here, an arms race of counterfeiters and valid manufacturers is taking place, resulting in the need of hard-to-forget, yet easyto-read out marks. Anticounterfeiting measures based on micropatternswhile being attractive for their need in not widely available printing methods while still being easily read out with fairly common basic optical equipmentare often limited by being too easy to be destroyed by wear or handling. Here, nature-inspired wettability is rationally exploited for developing an unprecedented anticounterfeiting method, where hidden information can be only identified under direct exposures to an aqueous phase or mist and disappears again on air-drying the interface. A chemically reactive and hierarchically featured dip coating, capable of spatially selective covalent modification with primary amine containing small molecules, is developed for abrasion-tolerant patterning interfaces with two extremes of water wettabilities, i.e., superhydrophilicity and superhydrophobicity. Arbitrary handwriting with glucamine followed by chemical modification with octadecylamine, provided "invisible" text on the synthesized interface. The glucaminetreated region selectively becomes optically transparent and superhydrophilic due to rapid infiltration of the aqueous phase on exposure to liquid water or mist. The remaining interface remains opaque and superhydrophobic due to metastable entrapment of air. The hidden text became transiently and reversibly visible by the naked eye under exposure to liquid water/mist. Furthermore, microchannel-cantilever spotting (μCS) is adopted for demonstrating well-defined chemical patterning on the microscale. These patterns are at the same time highly resistant against wear and scratching because of the bulk functionalization, retaining the wetting properties (and thus pattern readout) even on serious abrasion. Such a simple synthesis of spatially controlled, direct, and covalently modulated wettability could be useful for various applied and fundamental contexts.

“Writing biochips”: high-resolution droplet-to-droplet manufacturing of analytical platforms

“…Lastly, a recent report from Das and coworkers showed the possibility to produce glucamine patterns onto amine-reactive interfaces subsequently treated with octadecylamine. 101 The patterns were visible only when in a wet environment and were used to produce a microscale Data Matrix barcode.…”

Michael Addition Reaction Assisted Derivation of Functional and Durable Superhydrophobic Interfaces

“…Taking advantage of the pH responsive switchable superhydrophobicity, spatially selective bulk patterns with unperturbed superhydrophobicity and self-cleaning ability were demonstrated on the polymeric material via exposure to acidic droplets of rhodamine 6G dye as shown in Figure 11G−I. Separately, Das et al extended another chemically "reactive"but hydrophobicdip-coating to integrate extremes of water wettability, i.e., both superhydrophilicity and superhydrophobicity, for demonstrating anticounterfeiting application. 67 The embedded hydrophobicity and residual chemical reactivity of the polymeric dip-coating allowed the covalent immobilization of glucamine moleculesdirectly from aqueous solutionwithout any arbitrary spillage. The subsequent postmodification of the same interface with ODA provided a spatially selective, invisible, superhydrophilic/superhydrophobic patterned interface as shown in Figure 11J,K.…”

“…Such characteristics are of utmost importance for realistic and diverse applications of the bioinspired coating. In this regard, the environment-friendly Michael addition reaction between amine and acrylate requiring mild operational conditions would provide a prospective platform to tailor the bioinspired water wettability and other relevant physical properties (Figure )including transparency, mechanical property, porosity, etc.following simple and scalable fabrication processes. − In the past, the catalyst-free Michael addition reaction was successfully extended to produce amplified “reactive” surfaces. , Ford et al studied the ability of growing different nanostructures on selected substrates following the catalyst-free aza-Michael addition reaction between branched polyethylenimine (BPEI) and dipentaerythritol penta-acrylate (5-Acl) that resulted in hyperbranched poly­(ester amines) cross-linked thin films with surface amplified functional groups . In 2012, Bechler et al capitalized on this concept of a nanostructured, “reactive” polymeric film of BPEI/5Acl to construct a relatively thick (∼750 nm) multilayer coating following the layer-by-layer deposition approach .…”

“…To overcome this challenge, the Michael addition reaction between BPEI and 5Acl was employed strategically to achieve rapid and controlled growth of chemically “reactive” nanocomplexes (CRPNCs) in solution phase, instead of on a solid surface. The research group of Manna et al introduced and extended these solution phase CRPNCs for developing porous, three-dimensional superhydrophobic monoliths and flexible polymeric superhydrophobic coatings for applications in oil/water separation, ,,− ,,− ,, drug delivery, ,, patterned interfaces, ,,, etc. The controlled growth of CRPNCs through Michael addition reaction and its strategic postcovalent modifications allowed different durable bioinspired wettabilities to be adoptedincluding controllable adhesive/nonadhesive superhydrophobicity, hydrophilic/superhydrophobic patterns, chemically “reactive” superhydrophobicity, and stimuli-responsive superhydrophobicityfollowing simple and scalable fabrications processes. − The as fabricated chemically “reactive” interfaces with tailorable water wettability exhibited impeccable durability and performance at even chemically harsh and challenging settings.…”

High‐Resolution Patterned Functionalization of Slippery “Liquid‐Like” Brush Surfaces via Microdroplet‐Confined Growth of Multifunctional Polydopamine Arrays

“…[20,31] Photolithography has been utilized to create slippery regions for selective oil infusion. [26,[32][33][34] Moreover, ink-jet printing [18,35] or scanning-probebased microspotting [36,37] could offer a post-functionalization approach to chemically modify the nanostructured or smooth liquid-attached surfaces. Nevertheless, the above-mentioned demonstrations usually involve sophisticated apparatus, tedious processing steps, or specific chemical design.…”