Studies of thermoluminescence properties of liquid crystalline N-phenyl substituted phenyl polysiloxane hydroxamic acids.

The investigation of thermoluminescence (TL) glow curves in liquid crystalline side chain N-phenyl-substituted phenyl polysiloxane hydroxamic acids (PHAs) has yielded significant insights. These polymers demonstrated TL behavior when exposed to ß-radiation between 0 and 220°C, indicating inherent luminescent properties when irradiated. Notably, a dose-dependent relationship was observed in reported derivatized polymers; this study elucidates the diverse TL characteristics exhibited by various liquid crystalline side chain N-phenyl-substituted phenyl PHAs when exposed to ß-radiation. Understanding these dose-dependent and dose-independent behaviors enhances the knowledge of their luminescent properties and potential applications in radiation detection.

Synthesis and Properties of Bipolar Ladder-Like Polysiloxane with Carbazole and Triphenylphosphine Oxygen Groups.

In this study, a series of ladder-like polysiloxanes are synthesized by introducing double-chain Si-O-Si polymer as the backbone and the carbazole and triphenylphosphine oxide with high triplet energy as side groups. The ladder-like structures of polysiloxanes are achieved through a controlled polymerization method that involves the monomer self-assembly and subsequent surface-restricted solid-phase in situ condensation through freeze-drying. The introduction of siloxane improves thermal stability of the polymers and inhibits the conjugation of the polymers between the side groups, leading to an increase in the triplet energy level. Therefore, all these polymers perform higher triplet energy levels than phosphorescent emitter (FIrpic). The cyclic voltammetry measurements demonstrate that the bipolar polymer exhibits a high highest occupied molecular orbital (HOMO) value of -5.32 eV, which is consistent with the work function of ITO/PEDOT:PSS, consequently facilitating hole injection. Furthermore, the incorporation of triphenylphosphine oxide promotes electron injection. Molecular simulations reveal that the frontier orbital distributions of the bipolar polymer are located on the carbazole and triphenylphosphine groups, respectively, which facilitate the transport of electrons and holes.

Donor-Acceptor Stenhouse Adduct-Polydimethylsiloxane-Conjugates for Enhanced Photoswitching in Bulk Polymers.

Donor-acceptor Stenhouse adducts (DASAs) are a rapidly emerging class of visible light-activated photochromes and DASA-functionalized polymers hold great promise as biocompatible photoresponsive materials. However, the photoswitching performance of DASAs in solid polymer matrices is often low, particularly in materials below their glass transition temperature. To overcome this limitation, DASAs are conjugated to polydimethylsiloxanes which have a glass transition temperature far below room temperature and which can create a mobile molecular environment around the DASAs for achieving more solution-like photoswitching kinetics in bulk polymers. The dispersion of DASAs conjugated to such flexible oligomers into solid polymer matrices allows for more effective and tunable DASA photoswitching in stiff polymers, such as poly(methyl methacrylate), without requiring modifications of the matrix. The photoswitching of conjugates with varying polymer molecular weight, linker type, and architecture is characterized via time-dependent UV-vis spectroscopy in organic solvents and blended into polymethacrylate films. In addition, DASA-functionalized polydimethylsiloxane networks, accessible via the same synthetic route, provide an alternative solution for achieving fast and efficient DASA photoswitching in the bulk owing to their intrinsic softness and flexibility. These findings may contribute to the development of DASA-functionalized materials with better tunable, more effective, and more reversible modulation of their optical properties.

Corrosion Resistance and Electrical Conductivity of Hybrid Coatings Obtained from Polysiloxane and Carbon Nanotubes by Electrophoretic Co-Deposition.

Nanocomposites developed based on siloxanes modified with carbon nanoforms are materials with great application potential in the electronics industry, medicine and environmental protection. This follows from the fact that such nanocomposites can be endowed with biocompatibility characteristics, electric conductivity and a high mechanical durability. Moreover, their surface, depending on the type and the amount of carbon nanoparticles, may exhibit antifouling properties, as well as those that limit bacterial adhesion. The paper reports on the properties of polysiloxane (PS) and carbon nanotubes (CNT) nanocomposite coatings on metal surfaces produced by the electrophoretic deposition (EPD). A comparison with coatings made of pure PS or pure CNT on the same substrates using the same deposition method (EPD) is provided. The coatings were examined for morphology and elemental composition (SEM, EDS), structural characteristics (confocal Raman spectroscopy), electrical conductivity and were tested for corrosion (electrochemical impedance spectroscopy-EIS, potentiodynamic polarization-PDP). The results obtained in this study clearly evidenced that such hybrid coatings conduct electricity and protect the metal from corrosion. However, their corrosion resistance differs slightly from that of a pure polymeric coating.

New Antiadhesive Hydrophobic Polysiloxanes.

Intrinsic hydrophobicity is the reason for efficient bacterial settlement and biofilm growth on silicone materials. Those unwelcomed phenomena may play an important role in pathogen transmission. We have proposed an approach towards the development of new anti-biofilm strategies that resulted in novel antimicrobial hydrophobic silicones. Those functionalized polysiloxanes grafted with side 2-(carboxymethylthioethyl)-, 2-(n-propylamidomethylthioethyl)- and 2-(mercaptoethylamidomethylthioethyl)- groups showed a wide range of antimicrobial properties towards selected strains of bacteria (reference strains Staphylococcus aureus, Escherichia coli and water-borne isolates Agrobacterium tumefaciens, Aeromonas hydrophila), fungi (Aureobasidium pullulans) and algae (Chlorella vulgaris), which makes them valuable antibacterial and antibiofilm agents. Tested microorganisms showed various levels of biofilm formation, but particularly effective antibiofilm activity was demonstrated for bacterial isolate A. hydrophila with high adhesion abilities. In the case of modified surfaces, the relative coefficient of adhesion for this strain was 18 times lower in comparison to the control glass sample.

Artificial Muscles: Dielectric Elastomers Responsive to Low Voltages.

The lack of soft high-dielectric-permittivity elastomers responsive to a low voltage has been a long-standing obstacle for the industrialization of dielectric elastomer actuators (DEA) technology. Here, elastomers that not only possess a high dielectric permittivity of 18 and good elastic and insulating properties but are also processable in very thin films by conventional techniques are reported. Additionally, the elastic modulus can be easily tuned. A soft elastomer with a storage modulus of E = 350 kPa, a tanδ = 0.007 at 0.05 Hz, and a lateral actuation strain of 13% at 13 V µm-1 is prepared. A stable lateral actuation over 50 000 cycles at 10 Hz is demonstrated. A stiffer elastomer with an E = 790 kPa, a tanδ = 0.0018 at 0.05 Hz, a large out-of-plane actuation at 41 V µm-1 , and breakdown fields of almost 100 V µm-1 is also developed. Such breakdown fields are the highest ever reported for a high-permittivity elastomer. Additionally, actuators operable at a voltage as low as 200 V are also demonstrated. Because the materials used are cheap and easily available, and the chemical reactions leading to them allow upscaling, they have the potential to advance the DEA technology.

Antimicrobial and Antibiofilm N-acetyl-L-cysteine Grafted Siloxane Polymers with Potential for Use in Water Systems.

Antibiofilm strategies may be based on the prevention of initial bacterial adhesion, the inhibition of biofilm maturation or biofilm eradication. N-acetyl-L-cysteine (NAC), widely used in medical treatments, offers an interesting approach to biofilm destruction. However, many Eubacteria strains are able to enzymatically decompose the NAC molecule. This is the first report on the action of two hybrid materials, NAC-Si-1 and NAC-Si-2, against bacteria isolated from a water environment: Agrobacterium tumefaciens, Aeromonas hydrophila, Citrobacter freundii, Enterobacter soli, Janthinobacterium lividum and Stenotrophomonas maltophilia. The NAC was grafted onto functional siloxane polymers to reduce its availability to bacterial enzymes. The results confirm the bioactivity of NAC. However, the final effect of its action was environment- and strain-dependent. Moreover, all the tested bacterial strains showed the ability to degrade NAC by various metabolic routes. The NAC polymers were less effective bacterial inhibitors than NAC, but more effective at eradicating mature bacterial biofilms.

Assessment of the skin sensitisation hazard of functional polysiloxanes and silanes in the SENS-IS assay.

In the context of a larger testing programme that aimed at assessing the skin sensitisation potential of functional polysiloxanes and silanes, this investigation complements the available in vitro and in vivo data with data in the SENS-IS assay, a human in vitro 3D skin-based model. The SENS-IS assay allowed testing of all functional polysiloxanes and silanes without any solubility issues or limitations related to the multiconstituent nature of the commercial grade test substances. It appeared to encompass skin metabolism, a factor which we considered important for the skin sensitisation hazard assessment particularly of aminofunctionalised siloxanes and silanes. These three technical aspects posed significant challenges in the first part of the in vitro programme with the OECD-validated in vitro assays. The SENS-IS assay delivered promising results for this group of substances. On its own, it was the best performing model, as it did not pose any technical issues with the assay and it matched all in vivo outcomes. Considering its performance and avoidance of any limitations due to lack of solubility or chemical composition aspects, we concluded that the SENS-IS assay to be a suitable starting point for an integrated testing strategy for skin sensitisation for the group of functional polysiloxanes and silanes.

Directed In Situ Shaping of Complex Nano- and Microstructures during Chemical Synthesis.

Chemical composition and shape determine the basic properties of any object. Commonly, chemical synthesis and shaping follow each other in a sequence, although their combination into a single process would be an elegant simplification. Here, a pathway of simultaneous synthesis and shaping as applied to polysiloxanes on the micro- and nanoscale is presented. Complex structures such as stars, chalices, helices, volcanoes, rods, or combinations thereof are obtained. Varying the shape-controlling reaction parameters including temperature, water saturation, and the type of substrate allows to direct the reaction toward specific structures. A general mechanism of growth is suggested and analytical evidence and thermodynamic calculations to support it are provided. An aqueous droplet in either gaseous atmosphere or in a liquid organic solvent serves as a spatially confined polymerization volume. By substituting the starting materials, germanium-based nanostructures are also obtained. This transferability marks this approach as a major step toward a generally applicable method of chemical synthesis including in situ shaping.

Evaluation of in vitro assays for the assessment of the skin sensitization hazard of functional polysiloxanes and silanes.

The skin sensitization potential of chemicals has traditionally been evaluated in vivo according to OECD testing guidelines in guinea pigs or the mouse local lymph node assay. There has lately been a great emphasis on establishing in vitro test methods reflecting the key biological events in the adverse outcome pathway (AOP) for skin sensitization as published by the OECD. Against this background, a group of 8 polysiloxanes and silanes, seven of them aminofunctionalised, for which in vivo data were already available, has been tested in vitro in the direct peptide reactivity assay (DPRA), the KeratinoSens™ and the human cell line activation test (h-CLAT) and in the modified myeloid U937 skin sensitization test (mMUSST) as far as technically feasible. The main objective of the programme was to determine the utility of these systems for this heterogeneous group of silicone-based substances, recognizing that some substances are outside the assays applicability domains. The presented data provided some interesting mechanistical insights into the performance of these assays for functionalised siloxanes and silanes. The data also allow for a preliminary evaluation of proposed integrated testing strategies (ITS) to determine the skin sensitization potential of chemicals which were not considered in the training sets of the respective ITS.

Improved Antifouling Properties of Polydimethylsiloxane Films via Formation of Polysiloxane/Polyzwitterion Interpenetrating Networks.

Nonspecific adsorption of proteins is a challenging problem for the development of biocompatible materials, as well as for antifouling and fouling-release coatings, for instance for the marine industry. The concept of preparing amphiphilic systems based on low surface energy hydrophobic materials via their hydrophilic modification is being widely pursued. This work describes a novel two-step route for the preparation of interpenetrating polymer networks of otherwise incompatible poly(dimethylsiloxane) and zwitterionic polymers. Changes in surface hydrophilicity as well as surface charge at different pH values are investigated. Characterization using atomic force microscopy provides thorough insight into surface changes upon hydrophilic modification. Protein fouling of the materials is assessed using fibrinogen as a model protein.

Water-Soluble Blue Fluorescence-Emitting Hyperbranched Polysiloxanes Simultaneously Containing Hydroxyl and Primary Amine Groups.

In this Communication, novel water-soluble hyperbranched polysiloxanes (WHPSs) simultaneously containing hydroxyl and primary amine groups are developed. The polymers are constructed via melt polycondensation, that is, transesterification reaction between ethoxyl groups of (3-aminopropyl)triethoxysilane and hydroxyl groups of dihydric alcohols, using a one-step process under catalyst-free conditions. Surprisingly, the resultant WHPSs can emit bright blue fluorescence in the 100% solid state under the irradiation of UV light, and their photoluminescence intensities in aqueous solutions continuously go up along with increasing concentrations. Interestingly, their hydrolyzates display more intense luminescence compared to the unhydrolyzed. The efficient and easily controllable preparation strategy provides a remarkable and versatile platform for the fabrication of neoteric fluorescent materials for various potential applications.

Green polymer chemistry: enzyme catalysis for polymer functionalization.

Enzyme catalyzed reactions are green alternative approaches to functionalize polymers compared to conventional methods. This technique is especially advantageous due to the high selectivity, high efficiency, milder reaction conditions, and recyclability of enzymes. Selected reactions can be conducted under solventless conditions without the application of metal catalysts. Hence this process is becoming more recognized in the arena of biomedical applications, as the toxicity created by solvents and metal catalyst residues can be completely avoided. In this review we will discuss fundamental aspects of chemical reactions biocatalyzed by Candida antarctica lipase B, and their application to create new functionalized polymers, including the regio- and chemoselectivity of the reactions.

Polarity responsive polysiloxanes with twisting intramolecular charge transfer effect for monitoring lipophagy process and the detection of volatile organic compounds.

Polarity plays a critical role in biology and materials science, serving as a complex parameter. Imbalances in polarity within subcellular organelles are closely associated with various diseases. Moreover, volatile organic compounds (VOC) with low polarity pose significant health and safety risks, therefore, researchers have shown great interest in accurately detecting polarity. However, precise observation of polarity changes within organisms and identification of low-polarity volatile organic solvents are formidable challenges. To overcome these difficulties, we developed a versatile polymeric twisting intramolecular charge transfer (TICT) effect Polysiloxane-n (PDMS-n), utilizing polysiloxane molecular chains as "smart guides" to connect TICT molecules, inspired by the concept of "threading a needle." With the aid of PDMS-n, the process of polarity changes during cellular lipophagy was monitored in situ with high accuracy. Remarkably, the polarity changes of the local microstructure of the PDMS films were successfully visualized. PDMS-Films were also constructed, which enabled the recognition of Dichloromethane (DCM) gas during swelling. This work will contribute to the understanding of changes in cellular physiological processes, and facilitate the sensitive detection of VOCs.

Topical gel containing Polysiloxanes and hyaluronic acid for skin scar: Formulation design, characterization, and In vivo activity.

BACKGROUND: Scar formation is undesirable both cosmetically and functionally. It shows that silicone gel is effective in preventing and improving scars formed due to a wound formation after injury. OBJECTIVES: This study investigates whether a silicone gel composition based on a novel concept of infusing a biologically active material such as hyaluronic acid and/or salts with various polysiloxane derivatives in a specific proportion to achieve desired viscosity range and their action has a synergistic beneficial effect on skin scar after injury. METHODS: We have developed a topical gel utilizing a combination of emulsifiers, sodium hyaluronate, polysiloxane, and its derivatives. The method of preparation comprises mixing of aqueous phase dispersion and polysiloxanes blend under stirring at room temperature. RESULTS: It results in the formation of a homogenous smooth gel formulation. The developed topical gel formulation was characterized for physicochemical properties, rheology, stability, and anti-scar activity in Wistar rats. It was found that the developed formulation system consists of desirable attributes for skin applications. In vivo investigation of developed polysiloxane gel formulation for anti-scar activity shown promising outcomes compared to marketed product (Kelo-cote scar gel). Furthermore, a histopathology study of healed skin tissues observed the formation of microscopic skin structures compared to the Kelo-cote scar gel. CONCLUSIONS: It indicates that the combination of polysiloxanes and sodium hyaluronate resulting an improvement in anti-scar activity compared to the marketed product containing polysiloxanes alone.

Are telechelic polysiloxanes better than hemi-telechelic for self-cleaning applications?

HYPOTHESIS: Polysiloxanes are becoming new trend in self-cleaning (oil- and water-repellent) applications due to their low-cost and environmentally friendly nature. Lower phase separation of polysiloxanes in coating matrix is critical to obtain excellent self-cleaning properties. We hypothesize that telechelic polysiloxanes can bind to coating matrix at both ends and thus will suppress phase separation of polysiloxane as compared to hemi-telechelic analog and thus will offer excellent self-cleaning properties. EXPERIMENT: Eight PDMS additives were prepared via the free-radical polymerization of telechelic and hemi-telechelic methacryloxypropyl-based PDMS precursors with methylmethacrylate (MMA) and glycidylmethacrylate (GMA). The compositions of the prepared polysiloxane additives were optimized to obtain excellent self-cleaning performance. FINDINGS: Our breakthrough development confirms that telechelic polysiloxanes (PDMS-T) incorporated into epoxy-based anti-smudge coatings outperform hemi-telechelic polysiloxanes (PDMS-HT) by offering excellent repellency against difficult to repel liquids. These breakthrough findings will vertically advance Science and innovations in the self-cleaning field by offering robust guidelines for choosing suitable polysiloxane for self-cleaning applications.

Poly(silsesquioxanes) and poly(siloxanes) grafted with N-acetylcysteine for eradicating mature bacterial biofilms in water environment.

Bacteria adapt to their living environment forming organised biofilms. The survival strategy makes them more resistant to disinfectants, which results in acute biofilm-caused infections, secondary water pollution by biofilm metabolites and bio-corrosion. New, efficient and environmentally friendly strategies must be developed to solve this problem. Water soluble N-acetyl derivative of L-cysteine (NAC) is a non-toxic compound of mucolytic and bacteriostatic properties that can interfere with the formation of biofilms. However, it can also be a source of C and N for undesired microorganisms, as well as a reason for some adverse human health effects. Consequently, novel procedures are required, that would decrease the take-up of NAC but not reduce its antibacterial properties. We have grafted N-acetyl-l-cysteine onto linear poly(vinylsilsesquioxanes) and poly(methylvinylsiloxanes) via thiol-ene addition. Antibacterial activity of the obtained hybrid materials (respectively, NAC-Si-1 and NAC-Si-2) was determined against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus strains. Native NAC inhibited growth of planktonic cells for the tested bacteria at concentration 0.25% w/v. Inhibition with equivalent solutions of the polymer derivatives was less effective due to the lack of SH groups. However, the tested polymers proved to be quite effective in eradication of mature biofilms. Treatment with 1% w/v emulsions of the hybrid polymers resulted in a significant reduction of viable cells in biofilm matrix despite the absence of thiol moieties. The effect was most pronounced for mature biofilms of S. aureus eradicated with NAC-Si-2.

Fluoro-substituted tetraphenyl-phenyl grafted polysiloxanes as highly selective stationary phases for gas chromatography.

In this work, two new types of polycyclic aromatic grafted polysiloxanes, namely, 3,4-bis(4-fluoro phenyl)-2,5-diphenyl polysiloxane (FPP) and 3,4-bis(3,4,5-trifluoro phenyl)-2,5-diphenyl polysiloxane (TFPP), were synthesized and statically coated onto capillary columns as stationary phases for gas chromatography (GC). Based on their McReynolds constants, both columns exhibited moderate polarity. The efficiencies of the FPP and TFPP columns were 3316 (k=3.96, naphthalene; 0.25mm inner diameter) and 3768 (k=4.14, naphthalene; 0.25mm inner diameter) plates/m, respectively. The thermostability of the polymers was tested by thermogravimetric analysis (TGA), and results revealed that both TFPP and FPP began to decompose slightly at 380°C. Separation of polyethylene pyrolysis products showed that the upper working temperature of the two columns can reach up to 360°C. Relying on their unique polarizable characteristics in combination with other types of interactions, such as H-bond acceptor, dipole-dipole, and dispersive interactions, the newly synthesized polarizable stationary phases offered unique selectivity for aromatic isomers and substituted benzenes. A slight separation difference between TPP and TFPP was observed. TFPP also exerted excellent selectivity for polycyclic aromatic hydrocarbons, fatty acid esters, and fatty alcohols. Overall, FPP and TFPP demonstrated considerable potential for further applications because of their unique structures and outstanding separation performance.

7,10-Diphenylfluoranthene grafted polysiloxane as a highly selective stationary phase for gas chromatography.

A novel 7,10-diphenylfluoranthene grafted polysiloxane (DPFP) was synthesized and statically coated on a fused-silica capillary column. High column efficiency (3864 plates per m) was achieved for naphthalene at 120°C. Thermo-gravimetric analysis showed that the DPFP polymer began to decompose at 380°C. The chromatogram of polyethylene pyrolysis products indicated that the maximum allowable temperature of the DPFP column could reach 360°C. By relying on its specific π-π stacking and dipole-induced dipole interactions with aromatic solutes, the DPFP stationary phase achieved excellent resolution for substituted benzene and aromatic hydrocarbons with satisfactory peak shapes, as well as showed superiority to current stationary phases that failed to resolve some critical pairs. Moreover, DPFP also showed good selectivity and resolving ability for Grob test mixtures, fatty acid esters, and ethers.

Characterization of stationary phases based on polysiloxanes thermally immobilized onto silica and metalized silica using supercritical fluid chromatography with the solvation parameter model.

Stationary phases (SP) prepared by immobilization of polymers on silica or metalized silica are interesting for use in reversed-phase high-performance liquid chromatography (RP-HPLC) due to better protection of residual silanols or Lewis acid sites, as well as ease of preparation. On the other hand, there are no previous reports of the use of such phases in packed column supercritical fluid chromatography (SFC). Fourteen different SPs based on polysiloxanes (phenyl, C1, C8, C14, C18) thermally immobilized onto different supports (silica, titanized silica, zirconized silica) and one chemically bonded and end-capped C18 stationary phase having a doubly zirconized silica support, were characterized with identical SFC conditions (CO2 with 10% of methanol, 25°C, 15.0 MPa backpressure). Characterization was achieved based on retention factors measured for 85 test compounds and linear solvation energy relationships (LSER), namely the solvation parameter model based on Abraham descriptors. The polysiloxane SP were compared to a commercial C18-bonded silica (Kromasil C18), and to the native silica and metalized silica supports to better unravel the effects of stationary phase chemistry on chromatographic behavior. Together, 19 stationary phases were compared. The results highlight the variety of polarities provided by the column set. The polysiloxane backbone contributes significantly to the SP polarity as evidenced by the comparison to a classical alkylsiloxane-bonded SP. Metalization also appears to modify the polar characteristics of the SP, particularly toward basic compounds. Sample applications illustrate the applicability of these SP in SFC to the analysis of compounds of interest to the pharmaceutical and cosmetic industries.