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•The incorporation of azobenzene moieties into a bridged silsesquioxane led a material with light-induced healing ability.•The photoisomerization of the azobenzene increases the ...mobility and allows the material to flow in the damaged area.•A complete recovery of the damage was observed after only 30 s of UV irradiation.
Intrinsic healable polymers are materials capable of repairing itself through its chemical nature, in order to improve stability and durability and to restore the lost functionalities or properties.
In this study, azobenzene (AZO) moieties were incorporated into a previously reported bridged silsesquioxane based on the reaction of isocyanatepropyltriethoxysilane (IPTS) with bisphenol A (BPA), by replacing a small fraction of BPA by a bisazophenol (4,4′-dihydroxyazobenzene, AZOH). The incorporation of these AZO moieties led to a material with UV light-induced healing abilities. The underlying healing mechanism is attributed to the intra-molecular conformational changes of the azo-chromophores that are induced by the trans to cis photoisomerization of the azobenzene. These changes temporary increased its mobility and allowed the material to flow in the damaged area, followed by a process of restoring the physical hydrogen bonds. This process was monitored following the viscoelastic properties during successive cycles of turning ON and OFF the UV irradiation. Remarkably, the resultant healed material has not significant observed mechanical differences with the original one.
Conventional drug delivery systems often have several pharmacodynamic and pharmacokinetic limitations related to their low efficacy and bad safety. It is because these traditional systems cannot ...always be selectively addressed to their therapeutic target sites. Currently, target-specific and controlled drug delivery is one of the foremost challenges in the biomedical field. In this context, stimuli-responsive polymeric nanomaterials have been recognized as a topic of intense research. They have gained immense attention in therapeutics - particularly in the drug delivery area - due to the ease of tailorable behavior in response to the surroundings. Light irradiation is of particular interest among externally triggered stimuli because it may be specifically localized in a contact-free manner. Light-human body interactions may sometimes be harmful due to photothermal and photomechanical reactions that lead to cell death by photo-toxicity and/or photosensitization. However, these limitations may also be overcome by the use of photo-responsive polymeric nanostructures. This review summarizes recent developments in photo-responsive polymeric nanocarriers used in the field of drug delivery systems, including nanoparticles, nanogels, micelles, nanofibers, dendrimers, and polymersomes, as well as their classification and mechanisms of drug release.
This work presents the synthesis of all‐optical polymer dispersed liquid crystals (PDLC) devices, in which the reversible trans–cis photoisomerization of azobenzene groups is used to induce the ...transition in the liquid crystal (LC) phase, activating the film from an opaque to a translucent state. The appropriate morphology is obtained through a reaction‐induced phase separation strategy using an epoxy–amine matrix modified with azobenzene precursors and the addition of a thermoplastic polymer (polystyrene, PS), which promotes the phase separation and the preferential location of the LC in separated domains. Formulations with liquid crystal content of 50 wt%, 5 wt% of modifier (PS), and 10 wt% of azo‐precursor present a reversible on–off optical response when irradiating the sample with the activation beam at λ = 488 nm. It is demonstrated that the liquid crystal responds according to the expected cooperative movement of orientation with the azobenzene groups. Based on the study of the PDLC devices obtained, its potential technological application can be confirmed.
An all‐optical polymer dispersed liquid crystal (PDLC) device is prepared, triggering its response with azobenzene moieties activated by linearly polarized light. A reaction‐induced phase separation strategy is exploited to achieve the desired morphology. The liquid crystal responds to a cooperative orientation with the azobenzene groups. Based on the study of the devices obtained, its potential technological application can be confirmed.
Photocontrol of molecular alignment is an exceptionally-intelligent and useful strategy. It enables us to control optical coefficients, peripheral molecular alignments, surface relief structure, and ...actuation of substances by means of photoirradiation. Epoxy linear polymers with azobenzene and alkyl side groups were synthesized and studied. They showed interesting and variable photo-response upon visible-light irradiation due to trans–cis–trans photoisomerization of the azobenzene units. The influence of physical crosslinks between alkyl chains on optical and mechanical properties was also investigated. Mechanical characterization of the polymers was done by nanoindentation. Light induced reversible or irreversible changes in the polymer after being irradiated with visible light, depend on the polarization states of light used. When using circularly polarized light, reversible mechanical response is observed. Permanent structural changes in films are related to anisotropic alignment of azobenzene molecules (after being illuminated with linear polarized light) and/or physical crosslinks of alkyl chains. This study demonstrated the importance of the polymer architecture and the presence of domains of alkyl chains on the potential photo responsiveness.
•Photoresponsive linear epoxy polymers with widely tunable optical/mechanical properties were obtained.•Light induced reversible or irreversible changes in the polymer after being irradiated with visible light.•When using circularly polarized light, reversible mechanical response is observed.•Permanent structural changes in films are related to anisotropic alignment of azobenzene units and/or to physical crosslinks.
Azopolymers are highly versatile materials due to their unique photoresponsive properties. In this contribution, a novel azo‐modified epoxy network is synthesized by cationic homopolymerization with ...boron trifluoride monoethylamine (BF3.MEA) complex as initiator. The effect of the addition of a fixed content of amino‐functionalized azo chromophore, Disperse Orange 3, into the polymer matrix is studied in detail. First of all, the thermal curing cycle is optimized by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) measurements. Then, the resulting bulk azo‐modified epoxy networks are characterized by means of thermogravimetric analysis (TGA), FTIR, DSC, UV–vis spectroscopy, and rheological measurements. Finally, the optical response of thin films of these materials is determined. The results evidence that azo‐modified epoxy networks obtained by cationic polymerization with optimized curing cycle display high Tg values, high maximum photoinduced birefringence, fast writing speed, and exceptionally high remnant anisotropy. Therefore, this material is a promising candidate to be used for optical storage applications.
A new type of azo‐modified epoxy network has been prepared by the way of cationic homopolymerization with boron trifluoride monoethylamine (BF3·MEA) complex as initiator. The resulting networks are promising materials for optical storage applications.
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•Polymers containing azobenzene units and alkyl side chains were synthesized.•Azobenzene groups contribute to light response, alkyl chains form physical crosslinks.•Domains of alkyl ...chains are an alternative for optimizing photoinduced anisotropy.
The influence of physical crosslinks on the photoinduced anisotropy in epoxy linear polymers with azobenzene and alkyl side groups was studied. Two series of linear epoxy-based polymers were synthesized by reaction between diglycidyl ether of bisphenol A (DGEBA), Disperse Orange-3 (DO3), and dodecylamine (DA). Two strategies of synthesis were employed in order to analyse the optical behavior of the polymers with their architecture. As a result, a polymer with randomly distributed amine groups (one-step polymerization), and another with both amines forming blocks (two-step polymerization) were synthesized. The experimental evidence derived from different techniques confirmed that isothermal annealing at several temperatures produced association of DA alkyl chains. The rate of this physical gelation process could be varied with the annealing temperature and the polymer architecture. The association strength of the alkyl chains was higher for the block polymer. The rate of the physical gelation process increased as the annealing temperature did. UV–visible spectroscopy showed interactions between the azo groups and aggregated alkyl chains only for the polymer prepared in two steps. For the same chromophore content, block polymers yielded higher birefringence than random ones did. The increment in the information stored (remnant birefringence) for annealed samples was considerable only for block polymers. This study demonstrates the importance of the polymer architecture and the presence of domains of alkyl chains on its potential photo responsiveness.
Azobenzene containing epoxy networks are a class of photosensitive materials characterized by high thermal, optical and mechanical stability, promising for reversible optical storage applications. ...Here, we propose an encouraging two-step method to fabricate crosslinked coatings by simply reacting an amine-functionalized azobenzene and an epoxy resin in bulk for specified times to get soluble products (network precursors). Thin films based on these precursors were prepared, and thermally crosslinked in order to obtain high-Tg materials. The optical response of the materials was determined, both before and after crosslinking. In the case of the samples as prepared, the dynamic time response of the system is fast, as well as the relaxation of the photoinduced birefringence, as expected due to the high mobility of the chromophore. On the other hand, crosslinked systems have a slightly slower response, but higher values of remnant birefringence, providing stability of the photoinduced orientation, what makes them promising materials to use in optical storage applications. Besides, further analysis on the effect of temperature on the induced birefringence of the polymeric networks was also conducted to help optimization of material design. Finally, we had presented some preliminary investigations of surface relief grating recording in the obtained new materials.
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