Fabrication of Liquid Crystalline Polyurethane/Polyhedral Oligomeric Silsesquioxane Nanofibers via Electrospinning.

A series of fibrous meshes based on liquid crystalline polyurethane/POSS composites were prepared. Two types of polyhedral oligomeric silsesquioxanes (POSSs) of different structures were chosen to show their influence on electrospun fibers: aromatic-substituted Trisilanolphenyl POSS (TSP-POSS) and isobutyl-substituted Trisilanolisobutyl POSS (TSI-POSS) in amounts of 2 and 6 wt%. The process parameters were selected so that the obtained materials showed the highest possible fiber integrity. Moreover, 20 wt% solutions of LCPU/POSS composites in hexafluoroisopropanol (HFIP) were found to give the best processability. The morphology of the obtained meshes showed significant dependencies between the type and amount of silsesquioxane nanoparticles and fiber morphology, as well as thermal and mechanical properties. In total, 2 wt%. POSS was found to enhance the mechanical properties of produced mesh without disrupting the fiber morphology. Higher concentrations of silsesquioxanes significantly increased the fibers' diameters and their inhomogeneity, resulting in a lower mechanical response. A calorimetric study confirmed the existence of liquid crystalline phase formation.

Effects of Segment Length and Crosslinking via POSS on the Calorimetric and Dynamic Glass Transition of Polyurethanes with Aliphatic Hard Segments.

The glass transition in polyurethanes is a complicated phenomenon governed by a multitude of factors, including the microphase separation, which in turn depends strongly on the molar mass of the hard and soft segments, as well as the presence of additives. In this work, we study the effects of the segments' length on the microphase separation and consequently on the calorimetric and dynamic glass transition of a polyurethane with aliphatic, "flexible" hard segments. It is found that the dependence of the calorimetric glass transition follows the same principles as those in systems with aromatic hard segments. Strikingly, however, the dynamic glass transition, as studied by dielectric spectroscopy, shows a slowing down of its dynamics despite a decrease in Tg. This discrepancy is discussed in terms of the strong dielectric response of the flexible segments, especially those close to the interface between the hard domains and soft phase, as opposed to a weak thermal one. In addition, polyhedral oligomeric silsesquioxanes (POSS) are introduced in the soft phase of the three matrices as crosslinking centres. This modification has no visible effect on the calorimetric glass transition; nevertheless, it affects the microphase separation and the dielectric response in a non-monotonic manner.

Examining the Water-Polymer Interactions in Non-Isocyanate Polyurethane/Polyhedral Oligomeric Silsesquioxane Hybrid Hydrogels.

Non-isocyanate polyurethane (NIPU) networks physically modified with octa(3-hydroxy-3-methylbutyldimethylsiloxy)POSS (8OHPOSS, 0-10 wt%) were conditioned in environments of different relative humidities (up to 97%) to study water-polymer interactions. The equilibrium sorption isotherms are of Brunauer type III in a water activity range of 0-0.97 and are discussed in terms of the Guggenheim (GAB) sorption model. The study shows that the introduction of 8OHPOSS, even in a large amount (10 wt%), does not hinder the water affinity of the NIPU network despite the hydrophobic nature of POSS; this is attributable to the homogenous dispersion of POSS in the polymer matrix. The shift in the urethane-derived carbonyl bands toward lower wavenumbers with a simultaneous shift in the urethane N-H bending bands toward higher wavenumbers exposes the breakage of polymer-polymer hydrogen bonds upon water uptake due to the formation of stronger water-polymer hydrogen bonds. Upon water absorption, a notable decrease in the glass transition temperature (Tg) is observed for all studied materials. The progressive reduction in Tg with water uptake is driven by plasticization and slaving mechanisms. POSS moieties are thought to impact slaving indirectly by slightly affecting water uptake at very high hydration levels.

Alginate Hydrogels with Aloe vera: The Effects of Reaction Temperature on Morphology and Thermal Properties.

In this study, we investigated the impact of reaction temperature on the physicochemical, structural, morphological, and thermal properties of sodium alginate/poly (vinyl alcohol)-based hydrogels, both in the pure form and with the addition of 20% (v/v) Aloe vera solution. The materials were prepared by chemical crosslinking at temperatures in the range of 65-75 °C. Poly (ethylene glycol) diacrylate was used as a crosslinking agent. The extent to which the crosslinking reaction proceeded was studied as a function of the reaction temperature, along with the thermal properties and morphology of the final materials. A measurement of gel fraction, in agreement with differential scanning calorimetry and Fourier transform infrared spectroscopy, showed that a higher temperature of reaction promoted the crosslinking reaction. On the basis of the aforementioned techniques, as well as by energy dispersive X-ray analysis under an electron microscope, it was also shown that the bioadditive Aloe vera promoted the crosslinking reaction.

PEG-POSS Star Molecules Blended in Polyurethane with Flexible Hard Segments: Morphology and Dynamics.

A star polymer with a polyhedral oligomeric silsesquioxanne (POSS) core and poly(ethylene glycol) (PEG) vertex groups is incorporated in a polyurethane with flexible hard segments in-situ during the polymerization process. The blends are studied in terms of morphology, molecular dynamics, and charge mobility. The methods utilized for this purpose are scanning electron and atomic force microscopies (SEM, AFM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and to a larger extent dielectric relaxation spectroscopy (DRS). It is found that POSS reduces the degree of crystallinity of the hard segments. Contrary to what was observed in a similar system with POSS pendent along the main chain, soft phase calorimetric glass transition temperature drops as a result of plasticization, and homogenization of the soft phase by the star molecules. The dynamic glass transition though, remains practically unaffected, and a hypothesis is formed to resolve the discrepancy, based on the assumption of different thermal and dielectric responses of slow and fast modes of the system. A relaxation α', slower than the bulky segmental α and common in polyurethanes, appears here too. A detailed analysis of dielectric spectra provides some evidence that this relaxation has cooperative character. An additional relaxation g, which is not commonly observed, accompanies the Maxwell Wagner Sillars interfacial polarization process, and has dynamics similar to it. POSS is found to introduce conductivity and possibly alter its mechanism. The study points out that different architectures of incorporation of POSS in polyurethane affect its physical properties by different mechanisms.

Physicochemical and Biological Characterisation of Diclofenac Oligomeric Poly(3-hydroxyoctanoate) Hybrids as ß-TCP Ceramics Modifiers for Bone Tissue Regeneration.

Nowadays, regenerative medicine faces a major challenge in providing new, functional materials that will meet the characteristics desired to replenish and grow new tissue. Therefore, this study presents new ceramic-polymer composites in which the matrix consists of tricalcium phosphates covered with blends containing a chemically bounded diclofenac with the biocompatible polymer-poly(3-hydroxyoctanoate), P(3HO). Modification of P(3HO) oligomers was confirmed by NMR, IR and XPS. Moreover, obtained oligomers and their blends were subjected to an in-depth characterisation using GPC, TGA, DSC and AFM. Furthermore, we demonstrate that the hydrophobicity and surface free energy values of blends decreased with the amount of diclofenac modified oligomers. Subsequently, the designed composites were used as a substrate for growth of the pre-osteoblast cell line (MC3T3-E1). An in vitro biocompatibility study showed that the composite with the lowest concentration of the proposed drug is within the range assumed to be non-toxic (viability above 70%). Cell proliferation was visualised using the SEM method, whereas the observation of cell penetration into the scaffold was carried out by confocal microscopy. Thus, it can be an ideal new functional bone tissue substitute, allowing not only the regeneration and restoration of the defect but also inhibiting the development of chronic inflammation.

Co-nonsolvency in concentrated aqueous solutions of PNIPAM: effect of methanol on the collective and the chain dynamics.

The polymer dynamics in concentrated solutions of poly(N-isopropyl acrylamide) (PNIPAM) in D2O/CD3OD mixtures is investigated in the one-phase region. Two polymer concentrations (9 and 25 wt%) and CD3OD contents in the solvent mixture of 0, 10 and 15 vol% are chosen. Temperature-resolved dynamic light scattering (DLS) reveals the collective dynamics. Two modes are observed, namely the fast relaxation of polymer segments within the blobs and the slow collective relaxation of the blobs. As the cloud point is approached, the correlation length related to the fast mode increases with CD3OD content. It features critical scaling behavior, which is consistent with mean-field behavior for the 9 wt% PNIPAM solution in pure D2O and with 3D Ising behavior for all other solutions. While the slow mode is not very strong in the 9 wt% PNIPAM solution in pure D2O, it is significantly more prominent as CD3OD is added and at all CD3OD contents in the 25 wt% solution, which may be attributed to enhanced interaction between the polymers. Neutron spin-echo spectroscopy (NSE) reveals a decay in the intermediate structure factor which indicates a diffusive process. For the polymer concentration of 9 wt%, the diffusion coefficients from NSE are similar to the ones from the fast relaxation observed in DLS. In contrast, they are significantly lower for the solutions having a polymer concentration of 25 wt%, which is attributed to the influence of the dominant large-scale dynamic heterogeneities. To summarize, addition of cosolvent leads to enhanced large-scale heterogeneities, which are reflected in the dynamic behavior at small length scales.

Examining the Influence of Re-Used Nanofiller-Pyrolyzed Montmorillonite, on the Thermal Properties of Polypropylene-Based Engineering Nanocomposites.

Pyrolysis of the polypropylene/montmorillonite (PP/OMMT) nanocomposites allows for recovery of the filler that can be then re-used to produce PP/pyrolyzed MMT (PMMT) nanostructured composites. In this work, we discuss the thermal properties of PP/PMMT composites investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). It has been found that effect of PMMT (5 wt. % and 10 wt. %) on matrix thermal stability occurs at temperatures above 300 °C. Addition of 5 wt. % and 10 wt. % of PMMT into polypropylene system gave good stabilization effect, as confirmed by the overall stabilization effect (OSE) values, which increased by 4% and 7%, respectively, compared to the control sample (PP). Interestingly, the presence of 1 wt. % and 3 wt. % of pyrolyzed clay stabilizes the system better than the same concentrations of organoclay added into polypropylene melt. DSC data revealed that pyrolyzed clay has still the same tendency as organoclay to enhance formation of the α and ß crystalline PP phases only. The pyrolyzed MMT causes an improvement of the modulus in the glassy as well as rubbery regions, as confirmed by DMA results.

Immune responses induced by nano-self-assembled lipid adjuvants based on a monomycoloyl glycerol analogue after vaccination with the Chlamydia trachomatis major outer membrane protein.

Nanocarriers based on inverse hexagonal liquid crystalline phases (hexosomes) show promising potential as vaccine delivery systems. Their unique internal structure, composed of both lipophilic domains and water-containing channels, renders them capable of accommodating immunopotentiating compounds and antigens. However, their adjuvant properties are poorly understood. We hypothesized that the supramolecular structure of the lyotropic liquid crystalline phase influences the immunostimulatory activity of lipid-based nanocarriers. To test this, hexosomes were designed containing the lipid phytantriol (Phy) and the immunopotentiator monomycoloyl glycerol-1 (MMG-1). Self-assembly of Phy and MMG-1 into nanocarriers featuring an internal hexagonal phase was confirmed by small-angle X-ray scattering and cryogenic transmission electron microscopy. The effect of the nanostructure on the adjuvant activity was studied by comparing the immunogenicity of Phy/MMG-1 hexosomes with MMG-1-containing lamellar liquid crystalline nanoparticles (liposomes, CAF04). The quality and magnitude of the elicited immune responses were determined after vaccination of CB6/F1 mice using the Chlamydia trachomatis major outer membrane protein (MOMP) as antigen. MMG-1-based hexosomes potentiated significantly stronger MOMP-specific humoral responses than CAF04 liposomes. The liposome-based vaccine formulation induced a much stronger MOMP-specific cell-mediated immune response compared to hexosome-adjuvanted MOMP, which elicited minimal MOMP-specific T-cell stimulation after vaccination. Hence, our data demonstrates that hexosomal and liposomal adjuvants activate the immune system via different mechanisms. Our work provides valuable insights into the adjuvant potential of hexosomes and emphasizes that engineering of the supramolecular structure can be used to design adjuvants with customized immunological properties.

Superhydrophobic Silicon Nanocrystal-Silica Aerogel Hybrid Materials: Synthesis, Properties, and Sensing Application.

Silicon nanocrystals (SiNCs) are abundant and exhibit exquisitely tailorable optoelectronic properties. The incorporation of SiNCs into highly porous and lightweight substrates such as aerogels leads to hybrid materials possessing the attractive features of both materials. This study describes the covalent deposition of SiNCs on and intercalation into silica aerogels, explores the properties, and demonstrates a prototype sensing application of the composite material. SiNCs of different sizes were functionalized with triethoxyvinylsilane (TEVS) via a radical grafting approach and subsequently used for the synthesis of photoluminescent silica hybrids. The resulting SiNC-containing aerogels possess high porosities, SiNC-based size-dependent photoluminescence, transparency, and a superhydrophobic macroscopic surface. The materials were used to examine the photoluminescence response toward low concentrations of 3-nitrotoluene (270 µM), demonstrating their potential as a sensing platform for high-energy materials.

Dynamic glass transition of the rigid amorphous fraction in polyurethane-urea/SiO2 nanocomposites.

We report molecular dynamics in the rigid amorphous fraction (RAF) of the polymer bound at the interfaces with nanoparticles in polymer nanocomposites and calculate the glass transition temperature, Tg, for this bound layer of polymer. We follow the '3-phase-model' for semicrystalline polymers where the polymer matrix consists of the crystalline fraction (CF), the mobile amorphous fraction (MAF) and the RAF. While the amorphous polymer bound by crystallites is completely rigid, neither contributing to the glass transition, nor displaying molecular dynamics, the amorphous polymer bound at the interfaces with filler displays decelerated dynamics, as compared to the bulk polymer. Reports in the literature suggest a discrepancy between Tg values obtained by Differential Scanning Calorimetry (DSC) and by Dielectric Relaxation Spectroscopy (DRS). As a plausible explanation we suggest that DRS results in Tg values taking into account the bound polymer, whereas DSC does not. For this investigation we use semicrystalline polyurethane-urea/SiO2 nanocomposites and employ, next to DSC and DRS, SEM, SAXS and WAXS for morphological characterization. It is our intention to use DRS as a tool for investigating the RAF.

pH Responsiveness of hydrogels formed by telechelic polyampholytes.

We investigate the influence of pH on the rheological and structural properties of hydrogels formed by hydrophobic association of the sticky ends of the triblock terpolymer poly(methyl methacrylate)-b-poly(2-(diethylamino)ethyl methacrylate-co-methacrylic acid)-b-poly(methyl methacrylate) (PMMA-b-P(DEA-co-MAA)-b-PMMA). The middle block is a weak polyampholyte having a pH dependent charge density and sign, which enables tuning of the rheological and structural properties by pH variation. Small-angle neutron scattering (SANS) studies of solutions in D2O at 0.05 wt% and pH 3.0 reveal clusters of interconnected spherical micelles having PMMA cores, stabilized by repulsive ionic interactions in the middle polyampholyte block. With increasing pH, the degree of ionization of the DEA units decreases, whereas the one of the MAA units increases, resulting in a complete loss of the correlation between these micelles. At a concentration of 3 wt% at low pH values, the system forms a gel with charged fuzzy spheres from PMMA interacting via a screened Coulomb potential. With increasing pH, the gel disintegrates due to the decrease in the effective charge on the micelles. At both concentrations, the hydrophobic aggregation of micelles is observed near the isoelectric point. At pH 3.0-7.4, the autocorrelation functions measured by rotational dynamic light scattering at 3 wt% exhibit a decay steeper than single exponential, which confirms that the gels are frozen, presumably due to the glassy PMMA cores and hydrophobic interpolyelectrolyte complexes. At pH 11, the diffusion of single micelles is observed in addition to the frozen dynamics.

Bandgap-Tuning in Triple-Chalcogenophene Polymer Films by Thermal Annealing.

The authors study adjustable bandgap properties of the novel triple chalcogenophene-based polymer poly-(3-hexyl-2(3-(4-hexylthiophene-2-yl)-4,5-butylselenophene-1-yl)-5-(4,5-butyltellurophene-1-yl)thiophene) through a combination of morphological, spectroscopic, and computational techniques. The bandgap can be tuned after polymerization by means of mild temperature annealing, which will allow for a partnership with a broader range of donor/acceptor molecules, a property that makes it potentially suitable for organic photovoltaic implementation. The bandgap is modified by selection of the annealing temperatures, and the process is arguably related to the aggregation of tellurophene units, as similar effects are observed in polytellurophenes. Moreover, adequate chemistry engineering ensures easy solution processability and attainment of homogeneous films, which is also essential for applications.

Pressure-Dependence of Poly(N-isopropylacrylamide) Mesoglobule Formation in Aqueous Solution.

Above their cloud point, aqueous solutions of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) form large mesoglobules. We have carried out very small-angle neutron scattering (VSANS with q = 0.21-2.3 × 10-3 Å-1) and Raman spectroscopy experiments on a 3 wt % PNIPAM solution in D2O at atmospheric and elevated pressures (up to 113 MPa). Raman spectroscopy reveals that, at high pressure, the polymer is less dehydrated upon crossing the cloud point. VSANS shows that the mesoglobules are significantly larger and contain more D2O than at atmospheric pressure. We conclude that the size of the mesoglobules and thus their growth process are closely related to the hydration state of PNIPAM.