Azo Polymers for Reversible Optical Storage. 10. Cooperative Motion of Polar Side Groups in Amorphous Polymers

Azobenzene Functionalized "T-Type" Poly(Amide Imide)s vs. Guest-Host Systems-A Comparative Study of Structure-Property Relations

This paper describes the synthesis and characterization of new “T-type” azo poly(amide imide)s as well as guest-host systems based on the “T-type” matrices. The matrices possessed pyridine rings in a main-chain and azobenzene moieties located either between the amide or imide groups. The non-covalent polymers contained the molecularly dispersed 4-phenylazophenol or 4-[(4-methyl phenyl)diazinyl]phenol chromophores that are capable of forming intermolecular hydrogen bonds with the pyridine rings. The FTIR spectroscopy and the measurements of the thermal, optical and photoinduced optical birefringence were employed for the determination of the influence of H-bonds and the specific elements of polymer architecture on physicochemical properties. Moreover, the obtained results were compared to those described in our previous works to formulate structure-property relations that may be considered general for the class of “T-type” azo poly(amide imide)s.

Synthesis of photoresponsive main-chain oligomers with azobenzene moieties via ADMET oligomerization and their micellization properties

We report the synthesis of azobenzene functionalized linear unsaturated/saturated polyolefin-oligomers.

Near-field Raman dichroism of azo-polymers exposed to nanoscale dc electrical and optical poling

Azobenzene-functionalized polymer films are functional materials, where the (planar vs. homeotropic) orientation of azo-dyes can be used for storing data. In order to characterize the nanoscale 3D orientation of the pigments in sub-10 nm thick polymer films we use two complementary techniques: polarization-controlled tip-enhanced Raman scattering (TERS) microscopy and contact scanning capacity microscopy. We demonstrate that the homeotropic and planar orientations of the azo-dyes are produced by applying a local dc electrical field and a resonant longitudinal optical near-field, respectively. For a non-destructive probe of the azo-dye orientation we apply a non-resonant optical near-field and compare the intensities of the Raman-active vibrational modes. We show that near-field Raman dichroism, a characteristic similar to the absorption dichroism used in far-field optics, can be a quantitative indicator of the 3D molecular orientation of the azo-dye at the nanoscale. This study directly benefits the further development of photochromic near-field optical memory that can lead to ultrahigh density information storage.

Synthesis and characterization of new photoswitchable azobenzene-containing poly(ε-caprolactones)

A novel and efficient strategy in obtaining mono- and bi-armed azobenzene-containing poly(ε-caprolactone)s is described, starting from a commercially available azobenzene dye.

Safety and efficacy of composite collagen-silver nanoparticle hydrogels as tissue engineering scaffolds

The increasing number of multidrug resistant bacteria has revitalized interest in seeking alternative sources for controlling bacterial infection. Silver nanoparticles (AgNPs), are amongst the most promising candidates due to their wide microbial spectrum of action. In this work, we report on the safety and efficacy of the incorporation of collagen coated AgNPs into collagen hydrogels for tissue engineering. The resulting hybrid materials at [AgNPs] < 0.4 μM retained the mechanical properties and biocompatibility for primary human skin fibroblasts and keratinocytes of collagen hydrogels; they also displayed remarkable anti-infective properties against S. aureus, S. epidermidis, E. coli and P. aeruginosa at considerably lower concentrations than silver nitrate. Further, subcutaneous implants of materials containing 0.2 μM AgNPs in mice showed a reduction in the levels of IL-6 and other inflammation markers (CCL24, sTNFR-2, and TIMP1). Finally, an analysis of silver contents in implanted mice showed that silver accumulation primarily occurred within the tissue surrounding the implant.

Novel self-dyed wholly aromatic polyamide-hydrazides covalently bonded with azo groups in their main chains: 1. Structure-property relationships

Twelve novel intrinsically colored wholly aromatic azopolyamide-hydrazides containing various proportions of para- and meta-phenylene units were successfully synthesized by a low temperature (−10 °C) solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide (4A3HBH) or 3-amino-4-hydroxybenzhydrazide (3A4HBH) with an equimolar amount of either 4,4′-azodibenzoyl chloride (4,4′ADBC), 3,3′-azodibenzoyl chloride (3,3′ADBC), or mixtures of various molar ratios of 4,4′ADBC and 3,3′ADBC in anhydrous N,N-dimethyl acetamide (DMAc) containing 3% (wt/v) LiCl as a solvent. The structures of the polymers were proven by elemental analysis, FTIR, ¹H- and ¹³C-NMR spectroscopy. The polymers’ properties were strongly affected by their various structures. The intrinsic viscosities of the polymers were ranged from 0.7 to 4.75 dL g⁻¹ and increased with the para-phenylene units content. The polymers are partially soluble in DMAc, dimethyl formamide (DMF) and N-methyl-2-pyrrolidone (NMP). Their solubility increases with the introduction of meta-phenylene moieties into the polymer chains. The polymers exhibit a great affinity for water sorption. Their hydrophilicity increases as a function of the content of meta-phenylene rings incorporated into the polymer. Mechanical properties of the polymer films are improved markedly by substitution of para-phenylene units for meta-phenylene units. The completely para-oriented type polymer has the best thermal and thermo-oxidative stability relative to those of the other polymers.

The biocompatibility and antibacterial properties of collagen-stabilized, photochemically prepared silver nanoparticles

Spherical 3.5 nm diameter silver nanoparticles (AgNP) stabilized in type I collagen (AgNP@collagen) were prepared in minutes (5-15 min) at room temperature by a photochemical method initiated by UVA irradiation of a water-soluble non-toxic benzoin. This biocomposite was examined to evaluate its biocompatibility and its anti-bacterial properties and showed remarkable properties. Thus, while keratinocytes and fibroblasts were not affected by AgNP@collagen, it was bactericidal against Bacillus megaterium and E. coli but only bacteriostatic against S. epidermidis. In particular, the bactericidal properties displayed by AgNP@collagen were proven to be due to AgNP in AgNP@collagen, rather than to released silver ions, since equimolar concentrations of Ag are about four times less active than AgNP@collagen based on total Ag content. This new biocomposite was stable over a remarkable range of NaCl, phosphate, and 2-(N-morpholino)ethanesulfonic acid concentrations and for over one month at 4 °C. Circular dichroism studies show that the conformation of collagen in AgNP@collagen remains intact. Finally, we have compared the properties of AgNP@collagen with a similar biocomposite prepared using α-poly-L-Lysine and also with citrate stabilized AgNP; neither of these materials showed comparable biocompatibility, stability, or anti-bacterial activity.

Long-term stability at high temperatures for birefringence in PAZO/PAH layer-by-layer films

Optical memories with long-term stability at high temperatures have long been pursued in azopolymers with photoinduced birefringence. In this study, we show that the residual birefringence in layer-by-layer (LbL) films made with poly[1-[4-(3-carboxy-4 hydroxyphenylazo)benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) alternated with poly(allylamine hydrochloride) (PAH) can be tuned by varying the extent of electrostatic interactions with film fabrication at different pHs for PAH. The dynamics of both writing and relaxation processes could be explained with a two-stage mechanism involving the orientation of the chromophores per se and the chain movement. Upon calculating the activation energies for these processes, we demonstrate semiquantitatively that reduced electrostatic interactions in films prepared at higher pH, for which PAH is less charged, are responsible for the longer stability at high temperatures. This is attributed to orientation of PAZO chromophores via cooperative aggregation, where the presence of counterions hindered relaxation.

All-optical subdiffraction multilevel data encoding onto azo-polymeric thin films

By exploiting photoinduced reorientation in azo-polymer thin films, we demonstrate all-optical polarization-encoded information storage with a scanning near-field optical microscope. In the writing routine, five-level bits are created by associating different bit values to different birefringence directions, induced in the polymer after illumination with linearly polarized light. The reading routine is then performed by implementing polarization-modulation techniques on the same near-field microscope in order to measure the encoded birefringence direction.

Structure and internal dynamics of a side chain liquid crystalline polymer in various phases by molecular dynamics simulations: a step towards coarse graining

Side chain liquid crystalline polymer with relatively long spacer was modeled on a semiatomistic level and studied in different liquid crystalline phases with the aid of molecular dynamics simulations. Well equilibrated isotropic, polydomain smectic and monodomain smectic phases were studied for their structural and dynamic properties. Particular emphasis was given to the analysis on a coarse-grained level, where backbones, side chains, and mesogens were considered in terms of their equivalent ellipsoids. The authors found that the liquid crystalline phase had a minor influence on the metrics of these objects but affected essentially their translational and orientational order. In the monodomain smectic phase, mesogens, backbones, and side chains are confined spatially. Their diffusion and shape dynamics are frozen along the mesogen director (the one-dimensional solidification) and the reorientation times increase by one to one-and-half orders of magnitude. In this phase, besides obvious orientational order of mesogens and side chains, a stable detectable order of the backbones was also observed. The backbone director is confined in the plane perpendicular to the mesogen director and constantly changes its orientation within this plane. The backbone diffusion in these planes is of the same range as in the polydomain smectic phase at the same temperature. A detailed analysis of the process of field-induced growth of the smectic phase was performed. The study revealed properties of liquid crystalline polymers that may enable their future fully coarse-grained modeling.

Langmuir and Grafted Monolayers of Photochromic Amphiphilic Monodendrons of Low Generations

Four generations of monodendrons with multiple dodecyl alkyl tails (AA-N, N representing number of alkyl tails from 1 to 8), an azobenzene spacer group, and a carboxylic acid polar head have been studied at the air-water and air-solid interface using AFM, GIXD, X-ray reflectivity, and UV-vis spectrometry. The one and two tail molecules formed orthorhombic lateral packing with long-range intramonolayer ordering. Good agreement between molecular models and thickness measurements indicated that the one and two tail molecules orient along the surface normal. The increase in the cross-sectional mismatch caused by the presence of the multiple chains for the higher generations disrupted the long-range ordering and forced the alkyl tails to adopt quasi-hexagonal structure. The higher generations (AA-4 and AA-8) formed a kinked structure with the alkyl tails oriented perpendicular to the surface with the azobenzene group tilted at a large degree toward the surface. The photoisomerization behavior in dilute solutions, at the air-water interface, and for grafted layers demonstrated that lower generation monodendrons maintained the photochromic behavior after chemical grafting to the silicon substrates, although the confinement of the molecules in monolayers significantly increased the reorganization time.

Synthesis, characterization, and optical properties of a novel azo-dye bearing an oligo(ethylene glycol) methyl ether side chain in solution and in the solid state

A novel azobenzene compound bearing a short poly(ethylene glycol) methyl ether side chain, N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(3,6,9,12,15,18,21,24-octaoxapentacos-1-yl)amine (RED-PEGM-8) was synthesized and characterized. RED-PEGM-8 exhibits a thermal behavior similar to that of Disperse Red-1; however, its thermal stability, as well as its Tg and Tm values, are lower because of the presence of the PEGM segment. The optical properties of this compound in solution and in the solid state were studied by UV–vis spectroscopy. The appearance of a blue-shifted band in aqueous solutions at high concentrations of the chromophore reveals the existence of H-type aggregates, resulting from π–π intermolecular interactions between the azobenzene units. Strong intermolecular interactions were also confirmed by 1H NMR measurements. Optical properties of RED-PEGM-8 in the solid state (thin film) also suggest the presence of H aggregates. However, a tail is also detected in the red region of the absorption spectrum, which could be because of the formation of J-type aggregates in the thin film.Key words: aggregation, azo-dye, poly(ethylene glycol) methyl ether.