Light and Temperature as Dual Stimuli Lead to Self-Assembly of Hyperbranched Azobenzene-Terminated Poly(N-isopropylacrylamide)

Light-Tuning Surface Activity and Emulsion Stability of Macromolecular Surfactants Based on the Host-Guest Interaction

Supramolecular chemistry provides more possibilities to design responsive macromolecular surfactants. In this study, poly(N-isopropylacrylamide) (Pnipam) with (azobenzene) AZO as the end group (Pnipam-AZO) was synthesized (P1 and P2), and then an inclusion complex was formed by Pnipam-AZO and β-cyclodextrin-modified poly(ethylene oxide) (PEO-CD). The host-guest interaction was characterized by using UV-vis spectra and GPC. The surface activity of P2 and the PEO-CD inclusion complex (P2@CD-PEO) was studied. Compared with Pnipam-AZO, the surface tension of P2@CD-PEO was higher. The inclusion of the hydrophobic AZO by CD and the attachment of the hydrophilic PEO to P2 lead to the decreasing adsorption amount of Pnipam, which results in increasing surface tension of P2@CD-PEO. Under UV light, the photoisomerization of AZO leads to decoupling of P2 and PEO-CD. Accordingly, the surface tension decreased, and this process was recyclable. The aggregation behaviors of P2@CD-PEO were studied by dynamic laser light scattering. The size and structure of the aggregates formed by P2@CD-PEO were light-responsive. The decoupling of PEO-CD and Pnipam-AZO made the size of the aggregates increase under UV light due to the increasing hydrophobicity of Pnipam-AZO. The emulsification study showed that P2@CD-PEO was an effective emulsifier, which could form oil-in-water emulsion for the petroleum ether and water system. The SEM images of the freeze-dried emulsion showed that the emulsion was stabilized by P2@CD-PEO aggregates that adsorbed at the oil and water interface. Also, demulsification occurs under UV light, and the emulsification and demulsification processes are recyclable.

Compatible Photochromic Systems for Opto-electronic Applications

Today, a lot of attention is paid to remote controlled opto-electronic devices. Many of them are commonly used in the society, industry, and science. Accessories dedicated to the particular utilization are desired. The point is to find a simple way to obtain smart and functional appliances. Materials engineering faces such problems and provides a variety of solutions concerning advanced material design, preparation, and utilization. Photochromic materials represent one of the already known materials, which still find other objectives in new fields of life. In our work, we present two differently constructed photoresponsive polymers, which give significantly different nonlinear optical (NLO) response visible as noticeable optical signal modulation. By playing with diversified laser light energy or its frequency, NLO output characterized appealing, and individual characteristics (doubled Δn ∼0.02 vs 0.04 and entirely different kinetics for two similar materials and the same laser pumping). Interestingly, high output signal repeatability and stability were achieved, which indicate the investigated materials as promising candidates in the construction of various opto-electronic devices. Additionally, a set of photoresponsive studies, reflectometry, and theoretical insights was performed and included in this work.

Temperature and Photo Dual-Stimuli Responsive Block Copolymer Self-Assembly Micelles for Cellular Controlled Drug Release

To well adapt to the complicated physiological environments, it is necessary to engineer dual- and/or multi-stimuli responsive drug carriers for more effective drug release. For this, a novel temperature responsive lateral chain photosensitive block copolymer, poly[(N-isopropylacrylamide-co-N,N-dimethylacrylamide) -block-propyleneacylalkyl-4-azobenzoate] (P(NIPAM-co-DMAA)-b-PAzoHPA), is synthesized by atom transfer radical polymerization. The structure is characterized by ¹ H nuclear magnetic resonance spectrometry and laser light scattering gel chromatography system. The self-assembly behavior, morphology, and sizes of micelles are investigated by fluorescence spectroscopy, transmission electron microscope, and laser particle analyzer. Dual responsiveness to light and temperature is explored by ultraviolet-visible absorption spectroscopy. The results show that the copolymer micelles take on apparent light and temperature dual responsiveness, and its lower critical solution temperature (LCST) is above 37 °C, and changes with the trans-/cis- isomerization of azobenzene structure under UV irradiation. The blank copolymers are nontoxic, whereas the paclitaxel (PTX)-loaded counterparts possessed comparable anticancer activities to free PTX, with entrapment efficiency of 83.7%. The PTX release from the PTX-loaded micelles can be mediated by changing temperature and/or light stimuli. The developed block copolymers can potentially be used for cancer therapy as drug controlled release carriers.

Synthesis and Self-Assembly of Multistimulus-Responsive Azobenzene-Containing Diblock Copolymer through RAFT Polymerization

This paper gathered studies on multistimulus-responsive sensing and self-assembly behavior of a novel amphiphilic diblock copolymer through a two-step reverse addition-fragmentation transfer (RAFT) polymerization technique. N-Isopropylacrylamide (NIPAM) macromolecular chain transfer agent and diblock copolymer (poly(NIPAM-b-Azo)) were discovered to have moderate thermal decomposition temperatures of 351.8 and 370.8 °C, respectively, indicating that their thermal stability was enhanced because of the azobenzene segments incorporated into the block copolymer. The diblock copolymer was determined to exhibit a lower critical solution temperature of 34.4 °C. Poly(NIPAM-b-Azo) demonstrated a higher photoisomerization rate constant (kt = 0.1295 s-1) than the Azo monomer did (kt = 0.088 s-1). When ultraviolet (UV) irradiation was applied, the intensity of fluorescence gradually increased, suggesting that UV irradiation enhanced the fluorescence of self-assembled cis-isomers of azobenzene. Morphological aggregates before and after UV irradiation are shown in scanning electron microscopy (SEM) and dynamic light scattering (DLS) analyses of the diblock copolymer. We employed photoluminescence titrations to reveal that the diblock copolymer was highly sensitive toward Ru3+ and Ba2+, as was indicated by the crown ether acting as a recognition moiety between azobenzene units. Micellar aggregates were formed in the polymer aqueous solution through dissolution; their mean diameters were approximately 205.8 and 364.6 nm at temperatures of 25.0 and 40.0 °C, respectively. Our findings contribute to research on photoresponsive and chemosensory polymer material developments.

Photochromic Materials by Postpolymerisation Surface Modification

Photochromic materials are available by a postpolymerization surface modification of diverse polymers in a multistep sequential process mediated, first, by carbene insertion chemistry, second, by diazonium coupling with a tethered precursor, and finally by coupling to a spiropyran. This three-step sequence is efficient, and surface loading densities of 10¹³ molecules cm^-2 are typically achievable, leading to materials with observable photochromic and wettability behavior, which operate over multiple cycles without significant photobleaching or loss of efficacy. Materials suitable for application in this process include both reactive, but also lower surface energy polymers. Although the process is particularly efficient for high surface area materials, surface modification onto lower surface area substrates, while being intrinsically less efficient, is nonetheless sufficiently effective that changes in macroscopic photochromic properties are readily observable.