Facile Phase‐Separation Approach to Encapsulate Functionalized Polymers in Core–Shell Nanoparticles

Abstract

Core-shell nanoparticles fi lled with a reactive hydrophobic azide-terminated polyisobutylene are prepared by a combination of miniemulsion and solvent evaporation techniques. Successful encapsulation is achieved by the rational selection of the polymer pair that displays a large difference in solubility parameters ( δ ) and interfacial tensions with water ( γ polymer/water ). By labeling the two polymers with different fl uorescent dyes, core-shell structures can be visualized by fl uorescence microscopy. After extraction of the polymer present in the core, hollow morphologies are observed by transmission electronic microscopy. The encapsulation effi ciency of the reactive polymer increases with decreasing surfactant concentration, with values as high as 90%. This study presents a simple and reaction-free method to encapsulate reactive polymers. Considering the drawbacks of self-healing agents with low molar mass, such as volatility and higher propensity for leakage from nanocapsules, the encapsulation of reactive polymers in nanocontainers is an interesting and new alternative for selfhealing materials. damaged materials by polymerization or solvent-assisted welding. [17][18][19][20] In their pioneering work, White et al. [ 21 ] encapsulated dicyclopentadiene in poly(urea formaldehyde) microcapsules. Autonomic healing behavior was observed when mechanical damage occurred to the matrix. Since then, a large variety of SH agents such as triethylene glycol dimethacrylate, [ 22 ] hexamethylene diisocyanate, [ 23 ] or reactants based on azides and alkynes for copper-catalyzed "click" chemistry [24][25][26] were successfully encapsulated in microcapsules. In order to apply encapsulating SH agents in thin fi lms and microelectronic coatings, we recently developed a general and mild method to encapsulate monomers, [ 27,28 ] solvents, [27][28][29] and plasticizers [ 27 ] as SH agents, fl uorescent dyes [ 30,31 ] and contrast agents, [ 32 ] in nanocontainers based on commercially available [ 27 ] or synthesized copolymers. [28][29][30] The method is a combination of miniemulsion and emulsion-solvent evaporation techniques and benefi ts from the advantages of both methods: the miniemulsion droplets are colloidally stable and are not subjected to coalescence, [ 33,34 ] and the preparation of the nanocontainers does not require any reaction

CuAAC-Based Click Chemistry in Self-Healing Polymers

“…[22][23][24]28,50,51 Overall there is an excellent interplay of click reactions and self-healing, as reflected in our own work during the past decade, 16−26,54−61 showing a strong success in achieving autonomous as well as damage-triggered self-healing via balanced cross-linking chemistries. In this Account, we discuss the advantages of the CuAAC-based click chemistry displayed in self-healing materials at room temperature or below, not only enabling healing of damage under ambient conditions with a large variety of substrates and materials [16][17][18][19][20][21][22][23][24][25][26][27][28]54,62 but also allowing damage reporting 20,25 and the visualization of material failure triggering click reactions by mechanical force. 20 We therefore systematically have used a large variety of potential healing agents [16][17][18][19]21,26,54 varying in molecular weight, architecture, and the number and density of functional groups (Figure 2A−D).…”

“…In this Account, we discuss the advantages of the CuAAC-based click chemistry displayed in self-healing materials at room temperature or below, not only enabling healing of damage under ambient conditions with a large variety of substrates and materials − ,, but also allowing damage reporting , and the visualization of material failure triggering click reactions by mechanical force . We therefore systematically have used a large variety of potential healing agents − ,,, varying in molecular weight, architecture, and the number and density of functional groups (Figure A–D). Moreover, the applied Cu­(I) catalysts have been optimized, starting with commercial Cu­(I) salts, − ,, then using immobilized heterogeneous carbonaceous supported catalysts, − ,, and ending up with initially latent mechanocatalysts that are directly activated by the damage event itself (Figure E–G).…”

Towards the Development of Antioxidant Cerium Oxide Nanoparticles for Biomedical Applications: Controlling the Properties by Tuning Synthesis Conditions

“…The first one is based on the addition of an amphiphilic molecule to the external surface of the NPs, without the removal of the capping agent. The hydrophobic interaction between the two amphiphilic molecules creates a two-layer structure exposing a hydrophilic surface, on the surface of the NP, thus allowing the dispersion in water [ 29 , 30 , 31 ]. The second kind of functionalization is based on the substitution of the capping agent used in the synthesis by replacing it with a bi-functional molecule formed by a functional group able to bind to the NPs surface and a second polar group that makes the compound soluble in water [ 32 , 33 , 34 , 35 ].…”

Improving Kinetics of “Click-Crosslinking” for Self-Healing Nanocomposites by Graphene-Supported Cu-Nanoparticles

“…Of particular importance is the ability to tune the temperature at which crosslinking takes place, thus enabling self-healing at room temperature or even below [ 11 , 17 ]. The central principal of action is the use of encapsulated low molecular weight azides [ 19 , 22 ] or azide-functionalized polymers [ 11 , 14 , 15 , 17 , 20 , 27 ], and low molecular weight alkynes [ 15 , 19 , 20 , 22 ] or alkyne-functionalized polymers [ 11 , 14 ], embedded within capsules sized from 100 nm up to microns [ 13 , 15 , 19 , 54 ]. Whereas the uncatalyzed process is conventionally taking place at temperatures close to ~160 °C [ 55 , 56 ], the use of Cu(I) as catalyst can significantly lower the crosslinking temperature, together with an increase in crosslinking efficiency [ 49 , 50 , 51 ].…”