Solid Polymer Films Research Articles

Optical Trapping of Photosoftened Solid Polymers

We present evidence of optical trapping of solid polymer films by a tightly focused near-infrared (NIR) laser beam (785 nm) when the polymer is softened by green laser (532 nm) irradiation, which is uniformly distributed over the film surface. While the whole film is softened by the green laser, only the part which is subjected to the NIR laser is trapped. The film, which is transparent in the NIR range and strongly absorbs the visible light, is deposited on a glass substrate. The NIR laser is focused at the sample plane and attracts the polymer to the laser focus, by the optical gradient force, during the green light irradiation, indicating that molecular mobility is strongly reduced and the optical gradient force of the NIR laser is inefficient in moving the polymer below the glass-transition temperature of the polymer without photosoftening. The observations are consistent with the theory of photochemical tweezing, which rests on the assumption that photosensitive polymers, containing azo dyes, are softened, i.e., molecular mobility is enhanced, by photoisomerization of the azo dyes during green light irradiation, and are moved in gradients of light fields. We also found that this two-color laser tweezing scheme is sensitive to light polarization, owing to the polarization sensitivity of the azo dye chromophores.

Surface Enhanced Visible Absorption of Dye Molecules in the Near-Field of Gold Nanoparticles

Surface enhanced absorption is a plasmonic effect parenting to surface enhanced fluorescence and Raman scattering, and it was clearly reported to occur in the infrared region of the spectrum of light. In this paper, we unambiguously show that it also occurs in the visible region of the spectrum by using a dye; i.e. an azo-dye, which exhibits a good light absorption in that region, and gold nanoparticles, which act as plasmonic nanoantennas that capture and re-radiate light, when the azo-dyes and the nanoparticles are incorporated in the bulk of solid films of polymer. In such a configuration, it is possible to use a dye concentration much larger than that of the nanoparticles and absorption path lengths much larger than those of the molecularly thin layers used in surface enhanced effects studies. In addition, the dye undergoes shape and orientation change; i.e. isomerization and reorientation, upon polarized light absorption; and the observation of surface enhanced visible absorption is done by two separate experiments; i.e. UV-visible absorption spectroscopy and photo-induced birefringence, since the signals detected from both experiments are directly proportional to the extinction coefficient of the dye. Both the dye’s absorption and photoorientation are enhanced by the presence of the nanoparticles.

Structure-properties relationship of tetrafluorostyrene-based monomers and polymers containing different donor moieties

A new series of monomers consisting of electron-deficient tetrafluorobenzene fragment and electron-donating units such as carbazole, di-tert-butyl carbazole, 9,9-dimethyl acridan and phenothiazine was prepared. Polymers containing well-defined donor-acceptor side chains were obtained via classical free radical polymerization of previously synthesized monomers. Comparative study of photophysical, electrochemical and thermal properties of the synthesized compounds was carried out. It was shown, that emission colour of the compounds from violet to yellow can be effectively adjusted by manipulation of the connected electron-donating fragments. The energy gaps of the compounds can also be fine-tuned by changing the moieties linked to the para-position of pentafluorostyrene moiety. Experimental optical energy gap values varied from 3.57 eV and 3.62 eV for carbazole based monomer and polymer to 2.99 eV and 3.24 for phenothiazine based monomer and polymer. Band gap values of polymers were found to be close to those of the corresponding monomers. The monomers demonstrated violet to yellow fluorescence in the solid state with quantum yields ranging from 1 to 22%. The solid films of polymers demonstrated blue to greenish fluorescence in the region of 456–512 nm with fluorescence quantum yields varying from 1 to 9 %. Monomers exhibited aggregation induced emission enhancement. Pholuminescence quantum yields of their solid samples were found to be higher than those of dilute solutions. Polymers exhibited higher thermal stability, in respect to the corresponding monomers, with 5% weigh loss temperatures reaching 411 °C.

Enhancement of Random Laser Properties on Solid Polymer Films by Increasing Scattering Effect

We study the properties of solid-based random lasers by observing spectral emission shape, emission intensity, emission line width, and lasing threshold. Random lasers based on solid polymer film are prepared by combining titania nanoparticles with rhodamine 640 in poly(vinyl alcohol) (PVA) water solution. We compare samples with and without scatterers. Adding nanoparticles to the samples narrows the emission spectrum, and the lasing threshold can be observed. The amount of titanium dioxide (TiO2) or titania nanoparticles is varied and affects the properties of random lasers. The spectral emission line width becomes narrower, and the lasing threshold decreases when the amount of titania increases. Results obtained show that the properties of solid-based random lasers can be improved by increasing scattering, which enhances the feedback mechanism. The enhanced properties of random lasers are very useful for creating a reliable optical device for future applications in medical and biosensing fields.

Electromechanical Decoupling by Porous Aerogel Conducting Polymer

In the field of biointerface electronics, electromechanical decoupling—electrical performance independent of mechanical deformation—can ensure reliability of measured signals, which is critical in stable electrode. Herein, Chen et al. report such a decoupled and stretchable conductive polymer foam.

In-Situ Imaging of Electrochemical Polymerization of Functionalized Thiophenes Using Transmission Electron Microscopy

There is considerable continuing interest in developing conjugated polymer materials like the functionalized thiophene poly(3,4-ethylenedioxythiophene) (PEDOT) to interface ionically conducting living tissue with electronically conducting metallic or semiconducting biomedical devices. These versatile conjugated polymers can also be used in organic solar cells, anti-static coatings and flexible organic electronic devices. Electrochemical polymerization can be used to synthesize thin-films of conjugated polymers. Typically, a 3-electrode system comprising of a working, counter and reference electrodes is used for this process. It is initiated by the electrochemical oxidization of the monomers, followed by the formation of higher molecular weight products that precipitate from solution, forming a thin-film of the conjugated polymer on the working electrode (anode). The reaction can be controlled either potentiostatically (constant voltage) or galvanostatically (constant current).This technique has several advantages over vapor-phase and chemical polymerization such as the facile control of polymer morphology (rough and bumpy under normal conditions) and the ability to coat patterned surfaces. However, the factors that determine the development of these structures during electrodeposition are not yet well established. This makes it difficult to design new systems and optimize device performance. Considering that the morphology of electrochemically-polymerized thin-films can be fine-tuned by controlling the early stage nucleation and growth of the oligomeric clusters, we have used in-situ, low dose Transmission Electron Microscopy to image and obtain a detailed understanding of the fundamental processes occurring at the electrode-solution interface, especially the evolution of the mobile oligomers that precede solid polymer film formation. The observation and quantification of these electrochemical reactions are made possible using a commercial holder designed by Protochips, Inc. The liquid (monomer solution) is sandwiched between a top chip and a spacer chip. The spacer chip is used to control the amount of liquid to be imaged (typically 500 nm – 1000 nm). This system can either be used in a static mode (no flow) or flowing mode depending on the requirements. The top chip is equipped with the electrical connections required to perform electrochemical reactions and watch the process in-situ. During the experiments, we observed individual nuclei forming, merging and growing in size and thickness with increasing charge density. These droplets correspond to more mobile, oligomer-rich clusters which further react with the monomers in the solution to form the solid polymer (PEDOT) deposit. This mechanism of precipitation and solidification provides a reasonable explanation for the usual bumpy morphology of the electrochemically polymerized films. We observed that the deposition occurs in 2 regimes. The first regime corresponds to an increase in nucleation density (the nucleation regime) and the second (the growth regime) where the clusters start to merge and increase in size causing a decrease in the nucleation density. During the deposition, certain droplets were found to gradually decrease in size and mass thickness, indicating some degree of reversibility of the process which was not previously appreciated. In addition to this, we have found substantial variations when the chemistry of the monomer is changed, including a dramatic increase in the nucleation density when a more hydrophilic, carboxylic acid substituted EDOT was used as a comonomer. The total electron doses we used for these experiments were around 10-20 mC/cm2. These were well below the critical dose for electron damage of the PEDOT, which is about 0.1 C/cm2. Further, using a macromolecular counter-ion, poly(acrylic acid) (PAA) during the electrodeposition facilitates the formation of highly anisotropic nano-fibrils of PEDOT thereby reducing the overall impedances due to increase in the effective surface area. The basic understanding is that PAA prevents the lateral growth of PEDOT which results in the nano-fibrillar morphology. Using operando electron microscopy, we have observed the nucleation and growth of these fibrils in an oriented, dendritic manner at the solution-electrode interface, allowing us to better understand the nano-fibril formation mechanisms. These experiments have presented us with unprecedented insights about the processes occurring at the nanoscale during the early stage nucleation and growth of electrodeposition of PEDOT and PEDOT copolymers. Figure 1

Non-classical control of solid-state aggregation-induced enhanced circularly polarized luminescence in chiral perylene diimides

Organic fluorescent molecules are gaining importance because of their potential applications in many devices. Optically active N,N′-bis((1R)-1-naphthylethyl)perylene-3,4,9,10-tetracarboxylic diimide [(R,R)-1-BNP] and N,N′-bis((1R)-2-naphthylethyl)perylene-3,4,9,10-tetracarboxylic diimide [(R,R)-2-BNP] and their antipode, [(S,S)-1-BNP and (S,S)-2-BNP], emit aggregation-induced enhanced (AIEnh) circularly polarized luminescence (CPL) on both a solid organic polymer film (poly(methyl methacrylate)) and solid inorganic KBr pellet. An opposite chirality is essential for generating CPL of inverted sign. However, a pair of enantiomeric organic molecules may not always be easy to prepare. Interestingly, the chiral perylene fluorophores synthesized in this study can emit both positive and negative AIEnh-CPL in the solid state, depending on their position on the naphthylene groups. In addition, no CPL was observed in these compounds from their dilute solutions.

Ultrasonic Studies of Solid Azobenzene-Decorated Polymer Thin Films.

This work investigates the effect of ultrasound on switching of cis azobenzene isomers to their trans counterparts in solid films of methyl methacrylate and methacryloyloxyazobenzene copolymers [P(MMA/MOAB)]. Ultraviolet–visible and 1H nuclear magnetic resonance spectroscopies demonstrate that 46% of the cis isomer converts to the trans form purely by ultrasonic agitation and 46% converts to the trans isomer by localized ultrasound-induced heating effects. Comparative studies of isomerization by ultrasound wave, heat, and visible irradiation show that ultrasound exposure requires a longer time to switch the cis-to-trans conformation. The estimated activation energy for the cis-to-trans conversion in solid polymer films is shown to be comparable to previous values of azobenzene isomerization, indicating that incorporation of the chromophore in a polymeric system affects the kinetics of transition but not the barriers to conformational change.

Structural, electrical and ion transport properties of free-standing blended solid polymeric thin films

Blended solid polymeric thin films based on PEO–PVP complexed with LiBOB were synthesized by solution cast technique. The effect of salt on morphology, structure and electrochemical properties was examined. The XRD and FESEM analyses reveal the enhancement of amorphous content on salt addition. The FTIR spectroscopy evidences the complex formation and presence of various microscopic interactions. The ionic conductivity for the optimized system has been estimated and found to be two orders higher than the salt-free system, i.e., ~ 5.1 × 10−6 S cm−1 (@40 °C), and remains increasing with temperature i.e. 6.5 × 10−4 S cm−1 (@100 °C) for O/Li = 16. The enhancement of ionic conductivity is attributed to increase in the number density of mobile ions as concluded by the Rice and Roth model. The high tion (~ 0.99) evidences the ionic nature of complexed electrolyte. DSC analysis evidences the suppression of crystallinity and shift of glass transition and melting temperature toward lower temperature implies the enhancement of the amorphous content and forms the rubbery nature of the thin films which support the faster ion conductions. Finally, an interaction scheme is proposed for a better explanation of the ion transport on the basis of experimental findings.

Photoswitchable Self-Assembly/Disassembly of Near-Infrared Fluorophores.

A new photoswitchable near-infrared fluorophore (TDI-4DTE) with a symmetric structure exhibited reversible photo-controllable self-assembly and disassembly. The modification of π-conjugated terrylenediimide with four dithienylethene groups not only induced photoswitchable near-infrared fluorescence, but also photoregulated reversible precipitation-dissolution with microscopic and macroscopic polymorphism. Upon 302 nm UV-light irradiation, a noticeable precipitation was observed within seconds. The precipitate was gradually dissolved again in half an hour upon visible light irradiation. Different microscopic morphologies of the precipitates, including nanoparticles, nanofibrils and nanosheets, were observed when altering the intensity of the 302 nm light irradiation, indicating the dynamic control process of self-assembly. Upon UV-light irradiation, TDI-4DTE nanosheets were also obtained as a solid polymeric film, whereas well-defined nanoribbons with molecular monolayer thickness formed at the oil/water interface with slower assembly dynamics.

Chirality Construction from Preferred π-π Stacks of Achiral Azobenzene Units in Polymer: Chiral Induction, Transfer and Memory.

The induction of supramolecular chirality from achiral polymers has been widely investigated in composite systems consisting of a chiral guest, achiral host, and solvents. To further study and understand the process of chirality transfer from a chiral solvent or chiral molecules to an achiral polymer backbone or side-chain units, an alternative is to reduce the components in the supramolecular assembled systems. Herein, achiral side-chain azobenzene (Azo)-containing polymers, poly(6-[4-(4-methoxyphenylazo) phenoxy] hexyl methacrylate) (PAzoMA), with different Mns, were synthesized by atom transfer radical polymerization (ATRP). Preferred chirality from supramolecular assembled trans-Azo units of PAzoMAs is successfully induced solely by the neat limonene. These aggregates of the polymers in limonene solution were characterized by circular dichroism (CD), UV-vis spectra, and dynamic light scattering (DLS) under different temperatures. The temperature plays an important role in the course of chiral induction. Meanwhile, supramolecular chirality can be constructed in the solid films of the achiral side-chain Azo-containing polymers that were triggered by limonene vapors. Also, it can be erased after heated above the glass transition temperature (Tg) of the polymer, and recovered after cooling down in the limonene vapors. A chiroptical switch can be built by alternately changing the temperature. The solid films show good chiral memory behaviors. The current results will facilitate studying the mechanism of chirality transfer induced by chiral solvent and improve potential application possibilities in chiral film materials.

Laser synthesis of selenium nanoparticles in liquid monomers

The paper presents the results of selenium nanoparticles synthesis in various liquid monomers by laser ablation. The following substances were selected as the condensation liquids for laser ablation: isodecyl acrylate (IDA, Isodecylacrylate, Aldrich), carboxyethyl acrylate (2Car, 2-carboxyethyl acrylate, Aldrich), ethylene glycol phenyl acrylate (Aldrich), ethylene glycol phenyl acrylate, an available blend of Ebecryl monomers (Cytec Industries Inc.), currently one of the possible components of modern lacquer coatings for nail plates. Thus, a method is proposed for simultaneous synthesis and incorporation of selenium nanoparticles into a polymer matrix. It is established by scanning microscopy method that the sizes of the obtained nanoparticles are from 50 to 200 nm. Infrared spectroscopy results of obtained colloidal solutions showed zero interactions of selenium nanoparticles with monomers. Stable colloidal solutions of selenium nanoparticles were obtained, and solid polymer films promising for biomedical applications were synthesized. The polymerization of colloidal solutions with added monomers and/or mixtures of oligomers was carried out using photo initiator of polymerization 2.2-dimethoxy-2-fenilatsetofenol, sensitive in the UV region (365 nm). The results of IR spectroscopy of the obtained colloidal solutions and polymer nanocomposites showed the absence of interactions of selenium nanoparticles with monomers and polymer matrices. Such nanocomposites could be perspective for biomedical applications, for example, as fungicidal coatings of different surfaces.

AIE-Active Polyamide Containing Diphenylamine-TPE Moiety with Superior Electrofluorochromic Performance.

Electrofluorochromism has attracted great attention due to the intelligence optoelectronic and sensing applications. The intrinsically switchable fluorophores with high solid-state fluorescence are regarded as key for ideal electrofluorochromic materials. Here, we reported an AIE-active polyamide with diphenylamine and tetraphenylethylene units, showing high fluorescence quantum yield up to 69.1% for the solid polymer film and stable electrochemical cycling stability. The polyamide exhibited reversible color and emission switching even in hundreds of cycles, and the fluorescence on/off contrast ratio was determined up to 417, which is the highest value to our knowledge. Furthermore, as the response time is vital for the real-life applications, to speed up the response of electrofluorochromism, a porous polymer film was readily prepared through a facile method, notably exhibiting high fluorescence contrast, long-term stability and obviously improved response, due to the sharply increased surface area. Therefore, the AIE-functionalization combining the porous structure strategy will synergistically and dramatically improve the electrofluorochromic performance, which will also promote their practical applications in the near future.

Polymer Composition Influence on Optical Properties of Laser-Generated Au Nanoparticles Based Nanocomposites

Au nanoparticles (AuNPs) stable colloid solution were prepared by laser ablation and fragmentation in liquid monomer isodecyl acrylate (IDA). Sizes of obtained nanoparticles were determined by scanning transmission electron microscopy (STEM) and were about 20 nm. Nanocomposites films were prepared from obtained stable colloid solution by UV-photocuring. To prepare solid polymer films different crosslinking diacrylates were used. Third-order nonlinear optical responses of prepared nanomaterials with different polymer matrix compositions were estimated by z-scan technique and compared.

Synthesis and spectroscopic properties of a new fluorescent acridine hyperbranched polymer: Applications to acid sensing and as antimicrobial agent

The synthesis of a hyperbranched polyesteramide functionalized with 6 acridine groups (P1000-ACRID) is described, and its photophysical properties compared with its low molecular weight reference compound (ACRIDyne). The hyperbranched polymer does not show aggregation of the acridine groups neither in solution nor in solid polymer matrices. The behavior of both chromophores as fluorescent acid sensors has been studied in solution and in solid polymer films, showing an increase in their fluorescence emission. The stoichiometry of the protonation reaction has been calculated, showing that ACRYDyne is able to protonate twice both in solution and in solid polymer matrices, whereas P1000-ACRID only protonates once. The sensing sensitivity of the compounds is consistent with this. The antimicrobial activity of the hyperbranched polymer has been tested against five bacteria (Gram positive and Gram negative) and two yeasts, showing high antimicrobial activity. The biocompatibility of low- and high-molecular weight compounds has been studied towards two mammalian cell lines (C2C12 and Swiss3T3), and the hyperbranched polymer shows higher biocompatibility than its low-molecular weight reference compound. P1000-ACRID allows enough cellular viability when used in its biofunctional concentration range.

Polymer composition influence on optical properties of laser-generated Au nanoparticles based nanocomposites

AbstractAu nanoparticles (AuNPs) stable colloid solution were prepared by laser ablation and fragmentation in liquid monomer isodecyl acrylate (IDA). Sizes of obtained nanoparticles were determined by scanning transmission electron microscopy (STEM) and were about 20 nm. Nanocomposites films were prepared from obtained stable colloid solution by UV-photocuring. To prepare solid polymer films different crosslinking diacrylates were used. Third-order nonlinear optical responses of prepared nanomaterials with different polymer matrix compositions were estimated by z-scan technique and compared.

Preparation and characterization of new nanocomposite polymer films containing NiO nanofillers

ABSTRACTNanocomposite solid polymer films based on the poly(exo‐N‐phenyl‐7‐oxanorbornene‐5,6‐dicarboximide) (PPhONDI)/LiClO4/NiO system have been designed, and the effect of inorganic NiO nanofiller in different amounts on the film properties has been examined. The exo‐PPhONDI/LiClO4/NiO polymer system is the first solid nanocomposite polymer electrolyte film example based on a ring‐opening metathesis polymerization (ROMP) host polymer. The NiO nanoparticles were prepared by two‐step chemical syntheses, and the thermoplastic host polymer, exo‐PPhONDI, was synthesized via ROMP. Composite polymer films were prepared by the solution‐casting method. The amount of nanoparticles was varied from 1 to 15 wt % of NiO. The conductivity of the nanocomposite solid polymer systems was influenced by the NiO nanofiller concentration. The composite films based on exo‐PPhONDI ROMP polymer with the highest conductivity were achieved for the composition with 8 wt % of NiO nanofiller and 10 wt % of LiClO4 dopant. The prepared films were characterized using X‐ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy (SEM). The SEM results showed that the filler was well distributed in the polymer matrix. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45938.

Block-type proton exchange membranes prepared by a combination of radiation-induced grafting and atom-transfer radical polymerization

We prepared proton exchange membranes (PEMs) composed of block-type polymers by a combination of radiation-induced graft polymerization (RIGP) and atom-transfer radical polymerization (ATRP). This process involves the following three steps: (i) RIGP of styrene (St) and chloromethylstyrene (CMS) into poly(ethylene-co-tetrafluoroethylene) (ETFE) films; (ii) the ATRP of ethyl styrene sulfonate (EtSS) starting from the grafted CMS units; and (iii) hydrolysis of the EtSS-grafted film, converting poly(EtSS) to poly(styrene sulfonic acid) (PSSA). The ATRP of EtSS (step (ii)), the key process in our preparation method, was successfully performed by controlling the catalyst concentration at a relatively-low temperature (50 ºC), under the condition of which undesirable thermal polymerization was suppressed. The grafting degree during ATRP could be controlled and ranged from 24% to 240%, resulting in the preparation of PEMs with ion exchange capacities ranging from 0.96 to 2.9mmol/g. Thus, we have demonstrated that ATRP reactions can be carried out inside solid polymer films. At 30% relative humidity and 80 ºC, the block-type PEMs exhibited higher proton conductivities and water contents than those of the conventional RIGP-PEMs. In the block-type PEMs, the hydrophilic proton-conducting PSSA grafts are separated from the ETFE matrix by the hydrophobic polystyrene grafts. Hence, the PSSA-graft-chain aggregation occurs, creating a well-connected ion channel network, which in turn results in increased proton conduction.

Aggregation-enhanced emission (AEE)-active polyamides with methylsulfonyltriphenylamine units for electrofluorochromic applications

In this work, a series of AEE-active polyamides containing methylsulfonyltriphenylamine units were prepared from a newly synthesized diamine “4,4′-diamine-4″-methylsulfonyltriphenylamine” and three dicarboxylic acids, which were highly soluble in various organic solvents and exhibited outstanding thermostability. The resulting polymer films showed one reversible redox couple along with apparent color changing from colorless to purple. The polymer solutions revealed relatively weak fluorescence with quantum yields in the range of 2.2–26.2%, which could be enhanced by induced aggregation in poor solvents. Furthermore, the bright fluorescence of the solid polymer film could be reversibly tuned by direct electrochemical redox of triphenylamine with a high contrast ratio (Ioff/Ion) of 234. Overall, this comprehensive investigation of their interesting electrochromic and electrofluorochromic bifunctional properties not only supplies a deep understanding of the optical essence upon electrical stimuli but also paves the way for their future intelligent applications.

White Light from a Single Fluorophore: A Strategy Utilizing Excited-State Intramolecular Proton-Transfer Phenomenon and Its Verification

This article is devoted to the development of a strategy for the design of a single fluorophore emitting white light due to the excited-state intermolecular proton-transfer (ESIPT) phenomenon. The key parameters of this strategy include (i) selection of an effective blue emitter, (ii) its structural modification to enable ESIPT, and (iii) adjustment of ESIPT parameters to assess similar fluorescence intensities of both emission bands. The important factor which determines similar intensity of these bands was found to be energetic closeness of the species participating in ESIPT (Δ298G°ESIPT ≈ 0), which makes this phototransformation reversible. Verification of the proposed strategy was carried out by design and synthesis of a new ESIPT fluorophore, which exhibits white light under certain conditions. Spectral features of this compound were investigated in various liquid solutions and solid polymeric films by means of steady-state electronic absorption and steady-state, time-resolved, and temperature-depend...