329,825 research outputs found
POSS-Containing Bioinspired Adhesives with Enhanced Mechanical and Optical Properties for Biomedical Applications
No full textA new terpolymer
adhesive, poly(2-methoxyethyl acrylate-co-N-methacryloyl 3,4-dihydroxyl-l-phenylalanine-co-heptaisobutyl substituted polyhedral
oligomeric silsesquioxane propyl methacrylate) (poly(MEA-co-MDOPA-co-MPOSS) was synthesized by thermally initiated
radical polymerization. In this study, we investigated the effect
of the POSS component on adhesion, mechanical, and optical properties
of the catechol-group containing bioinspired adhesives. The terpolymer
contains the catechol group which is known to improve the adhesion
properties of polymers. Only a very small amount of the POSS-containing
monomer, MPOSS, was included, 0.5 mol %. In the presence of POSS,
the synthesized poly(MEA-co-MDOPA-co-MPOSS) demonstrated strong adhesion properties, 23.2 ± 6.2
J/m2 with 0.05 N preloading and 300 s holding time, compared
to many previously prepared catechol-containing adhesives. The mechanical
properties (Young’s modulus and stress at 10% strain) of the
POSS-containing terpolymer showed significant increases (6-fold higher)
over the control polymer, which does not contain POSS. Optical transmittance
of the synthesized terpolymer was also improved significantly in the
visible light range, 450–750 nm. Cell testing with human embryonic
kidney cells (HEK293A) indicates that the new terpolymer is a promising
candidate in biomedical adhesives without acute cytotoxicity. The
synthesized poly(MEA-co-MDOPA-co-MPOSS) is the first example of POSS-containing pressure sensitive
bioinspired adhesive for biomedical applications. The study of poly(MEA-co-MDOPA-co-MPOSS) demonstrated a convenient
method to enhance two important properties, mechanical and optical
properties, by the addition of a very small amount of POSS. Based
on this study, it was found that POSS can be used to strengthen mechanical
properties of bioinspired adhesive without the need for a covalent
cross-linking step
Characterization of octamethylsilsesquioxane (CH3)8Si8O12 fillers in polypropene matrix
No full textThe results of Raman microspectroscopy measurements of octamethylsilsesquioxane (om-POSS) (3-wt %) in polypropylene (PP) are presented and compared with theoretical spectra calculated by ab initio density functional theory (DFT) based methods. The internal structure of this dielectric composite at the micrometer level was obtained by Computerized X-ray microtomography (CX?T) which reveals how micron-scale filler particles are distributed in the matrix media. The X–ray powder diffraction (XPD) was used to determine the om-POSS inner crystallite size that is in a nanometer range. Transmission electron microscopy (TEM) images confirm that the composite contains both nano and micron sized particles. The multiscale analysis indicates that in the composite om-POSS crystalline nanoparticles having a size from tens to hundreds of nanometers tend to agglomerate together with preferred orientation to form elongated micron sized particles. Orientation of crystallites affects the relative intensity of various Raman peaks. Appearance of Raman images thus depends on the choice of the peak used in the analysis
A novel POSS-coated quantum dot for biological application
No full textSarwat B Rizvi,1 Lara Yildirimer,1 Shirin Ghaderi,1 Bala Ramesh,1 Alexander M Seifalian,1,2 Mo Keshtgar1,21UCL Centre for Nanotechnology and Regenerative Medicine, Division of Surgery and Interventional Science, University College London, United Kingdom; 2Royal Free Hampstead NHS Trust Hospital, London, United KingdomAbstract: Quantum dots (QDs) are fluorescent semiconductor nanocrystals that have the potential for major advancements in the field of nanomedicine through their unique photophysical properties. They can potentially be used as fluorescent probes for various biomedical imaging applications, including cancer localization, detection of micrometastasis, image guided surgery, and targeted drug delivery. Their main limitation is toxicity, which requires a biologically compatible surface coating to shield the toxic core from the surrounding environment. However, this leads to an increase in QD size that may lead to problems of excretion and systemic sequestration. We describe a one pot synthesis, characterization, and in vitro cytotoxicity of a novel polyhedral oligomeric silsesquioxane (POSS)-coated CdTe-cored QD using mercaptosuccinic acid (MSA) and D-cysteine as stabilizing agents. Characterization was performed using transmission electron microscopy Fourier transform infrared spectroscopy, and photoluminescence studies. POSS-coated QDs demonstrated high colloidal stability and enhanced photostability on high degrees of ultraviolet (UV) excitation compared to QDs coated with MSA and D-cysteine alone (P value < 0.05). In vitro toxicity studies showed that both POSS and MSA-QDs were significantly less toxic than ionized salts of Cd+2 and Te-2. Confocal microscopy confirmed high brightness of POSS-QDs in cells at both 1 and 24 hours, indicating that these QDs are rapidly taken up by cells and remain photostable in a biological environment. We therefore conclude that a POSS coating confers biological compatibility, photostability, and colloidal stability while retaining the small size and unique photophysical properties of the QDs. The amphiphilic nature of the coating allows solubility in aqueous solutions and rapid transfer across cell membranes, enabling the use of lower concentrations of the QDs for an overall reduced toxicity particularly for prolonged live cell and in vivo imaging applications.Keywords: quantum dots, polyhedral oligomeric silsesquioxane, surface coating, cytotoxicit
Polyheral Oligomeric Silsesquioxanes (POSS) based Polymer Nanocomposites
No full textThis work reports on the preparation and characterization of polyhedral oligomeric
silsesquioxanes (POSS)-containing polymer nanocomposites. The nanocomposites
investigated in this study consist of two different types of POSS particles [octamethyl-T8-
POSS and poly((propylmethacryl-heptaisobutyl-POSS)-co-(methyl-methacrylate))] dispersed
in two different polymer matrices such as linear low-density polyethylene (LLDPE) and
poly(methyl methacrylate) (PMMA). The melt-blending technique was used for the
preparation of various nanocomposites. The morphology and structure of various
nanocomposites were characterized by using x-ray diffraction (XRD), small angle x-ray
scattering (SAXS), field-emission scanning electron microscopy (FE-SEM) and polarized
optical microscopy (POM). The influence of different loadings of POSS particles on the
thermal, thermomechanical, tensile, impact, and melt-state viscoelastic properties of
nanocomposites was investigated.
The morphology of the freeze-fractured surfaces of the LLDPE/POSS nanocomposites
investigated by means of FE-SEM, revealed a homogeneous dispersion of the octamethyl-T8-
POSS particles into the LLDPE matrix at a low filler content. The thermal properties of pure
LLDPE and various nanocomposites showed double melting behaviour of the neat LLDPE
matrix and the nanocomposite samples. The thermomechanical properties were investigated
by stress-strain controlled rheometry using a solid-state rectangular fixture. The results
showed a moderate improvement in both the storage and loss moduli of the neat LLDPE upon
the incorporation of the POSS particles. The thermal stability of pure LLDPE and its
nanocomposites was investigated in both air and nitrogen atmospheres. Two degradation steps
were observed for all studied samples under nitrogen atmosphere. An improvement in the
thermal stability of the samples studied in air in the high-temperature region was observed.
The melt-state rheological properties measurements showed that the POSS particles were
highly immiscible with the LLDPE matrix. POSS-containing LLDPE composites did not
show any improvement in tensile properties. A decrease in impact properties of the LLDPE at
higher POSS loadings was observed. The heat distortion temperature of the LLDPE samples
increased with increasing the POSS loading in the polymer matrix. In the case of PMMA/POSS nanocomposites, the FE-SEM results did not give any
information about the dispersion of the POSS particles in the PMMA matrix. However, the
XRD studies indicated that the POSS particles were dispersed throughout the PMMA matrix.
Both differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA)
showed a single glass transition for all the investigated samples. A decrease in the glass
transition temperature was observed with increasing POSS loading in the polymer matrix. The
rheological studies showed a gel-like character for all the investigated samples. An increase in
the storage modulus for the 5 wt % POSS-containing sample was observed when compared
with pure PMMA.Department of Science and TechnologyCouncil for Scientific and Industrial Research, Republic of South Afric
Polyoctahedral Silsesquioxane-Nanoparticle Electrolytes for Lithium Batteries: POSS-Lithium Salts and POSS-PEGs
No full textNanocomposite electrolytes have been prepared from mixtures
of
two polyoctahedral silsesquioxanes (POSS) nanomaterials, each with
a SiO1.5 core and eight side groups. POSS-PEG8 has eight polyethylene glycol side chains that have low glass transition
(Tg) and melt (Tm) temperatures and POSS-benzyl7(BF3Li)3 is a Janus-like POSS with hydrophobic phenyl groups and −Si–O–BF3Li ionic groups clustered on one side of the SiO1.5 cube. The electron-withdrawing POSS cage and BF3 groups
enable easy dissociation of the Li+. In the presence of
polar POSS-PEG8, the hydrophobic phenyl rings of POSS-benzyl7(BF3Li)3 aggregate and crystallize,
forming a biphasic morphology, in which the phenyl rings form the
structural phase and the POSS-PEG8 forms the conductive
phase. The −Si–O–BF3– Li+ groups of POSS-benzyl7(BF3Li)3 are oriented toward the polar POSS-PEG8 phase and dissociate
so that the Li+ cations are solvated by the POSS-PEG8. The nonvolatile nanocomposite electrolytes are viscous liquids
that do not flow under their own weight. POSS-PEG8/POSS-benzyl7(BF3Li)3 at O/Li = 16/1 has a conductivity
of σ = 2.5 × 10–4 S/cm at 30 °C,
which is 17 times greater than that of POSS-PEG8/LiBF4, and a low activation energy (Ea ∼ 3–4 kJ/mol); σ = 1.6 × 10–3 S/cm at 90 °C and 1.5 × 10–5 S/cm at
10 °C. The lithium ion transference number was tLi+ = 0.50 ± 0.01, as a result of the
reduced mobility of the large, bulky anion, and the system exhibited
low interfacial resistance that stabilized after 3 days (both at 80
°C)
Coating stent materials with polyhedral oligomeric silsesquioxane-poly(carbonateurea)urethane nanocomposites
No full textThe long-term efficacy of coronary or peripheral stenting is limited by in-stent
restenosis (ISR), which occurs in 15 to 30% of patients and is attributed primarily to
neointimal hyperplasia. By adding a drug-eluting coating, this rate has been reduced
to about 5% or less. However, recently longer-term follow-up data has highlighted
problems with drug-coated stents, including late stage thrombosis. A bio-stable
poly(carbonate-urea)urethane has been used for stent coating and the surface
properties of the polymer have been optimised by incorporating the polyhedral
oligomeric silsesquioxane molecule. These POSS polymers improve the adhesion and
the growth of endothelial cells. The work described in this thesis, presents an
innovative approach in self-expanding/balloon expandable coronary stent design that
incorporates a NiTi/stainless steel alloy scaffold with a polyhedral oligomeric
silsesquioxane- poly (carbonate-urea) urethane nanocomposite polymer (POSS-PCU)
coating. Electrohydrodynamic spraying and ultrasonic atomization spraying of the
non-biodegradable nanocomposite polyhedral oligomeric silsesquioxane (POSS)
polymer have been investigated in detail for coating metallic stent materials and
compared with dip coating. Because of the tight geometry of coronary stents, these
new coating techniques have been shown to offer advantages over traditional coating
techniques. These advantages include, reduced polymer consumption, precise coating
thickness as low as 10 μm and a highly controllable spray which leads to consistent
reproducible results. However, poor adhesion, or bond deterioration over the lifespan/
deployment of the device could reduces the efficiency and could impart even more
complexity to the implant including formation of debris which can induce thrombus
formation. Changing the surface physical property/chemical composition through the
proposed protocol has been shown to increase the bonding strength by up to three
times. This study has identified a new process and conditions which can be used in
stent coating research
Crosslinked Fluorinated Poly(arylene ether)s with POSS: Synthesis and Conversion to High-Performance Polymers
No full textThis study reports on a series of crosslinked poly(arylene ether)s with POSS in the main chain. The fluorinated and terminated poly(arylene ether)s were first synthesized by the nucleophilic reaction of diphenol POSS and decafluorodiphenyl monomers, including decafluorobiphenyl, decaflurobenzophenone, and decafluorodiphenyl sulfone. They were then reacted with 3-hydroxyphenyl acetylene to produce phenylacetylene-terminated poly(arylene ether)s. The polymers were of excellent processability. When heated to a high temperature, the polymers converted into a crosslinked network, exhibiting a low range of dielectric constant from 2.17 to 2.58 at 1 HMz, strong resistance against chemical solutions, low dielectric losses, and good thermal and hydrophobic properties
PCL/POSS Nanocomposites: Effect of POSS Derivative and Preparation Method on Morphology and Properties
No full textThe incorporation of polyhedral oligomeric silsesquioxanes (POSS) molecules as nanoparticles into polymers can provide improved physico-chemical properties. The enhancement depends on the extent of dispersion of the nanofiller, which is determined by the compatibility with the polymer that is by the POSS type, and the processing method. In this study, poly(epsilon-caprolactone)/POSS derivatives nanocomposites (PCL/POSS) were obtained via solution-casting and melt compounding. Two amino-derivatives containing different alkyl substituents, and ditelechelic POSS-containing hybrid PCL masterbatch were used as nanofillers. The effect of preparation method, POSS content and type on the morphology, thermal, mechanical, and surface properties of nanocomposites were studied. Morphological analysis evidenced the formation of POSS crystalline aggregates, self-assembled POSS molecules of submicrometer size dispersed in the polymer matrix. The best dispersion was achieved using the ditelechelic POSS-containing hybrid PCL masterbatch, and comparing the two amino-POSS derivatives, the one with longer alkyl chain of substituents exhibited better degree of dispersion independent of preparation method. DSC analysis showed the role of POSS derivatives as nucleating agents for PCL. The incorporation of POSS derivatives into the PCL matrix improved thermal stability. The preparation method, POSS type and content had influence on mechanical properties of nanocomposites. POSS nanoparticles enhanced the surface hydrophobicity of PCL.This research was funded by the Basque Government (SAIOTEK 2012 S-PE12UN006) and the University of the Basque Country (UFI11/56)
PIM-1 Membranes Containing POSS - Graphene Oxide for CO2 Separation
No full textPIM-1 mixed matrix membranes (MMMs) were fabricated with polyhedral oligomeric silsesquioxane (POSS) and graphene oxide (GO) functionalized with POSS (GO-POSS), and tested for CO2/N2 (single gas) and CO2/CH4 (1:1, v:v gas mixture). The CO2 permeability of the best performing fresh MMM (containing 0.05 wt% GO-POSS) was ∼ 12000 Barrer, which is 69% higher than that of the neat PIM-1 membrane, with about the same selectivity (CO2/CH4 selectivity ∼ 12 and CO2/N2 selectivity ∼ 20). In both cases, the gas separation data surpass the 2008 Robeson upper bound. In addition to the initial CO2 permeability enhancement, the use of GO-POSS is an efficient strategy to slow down physical aging. The MMM at a filler loading of 0.75 wt% showed less than half of the reduction in CO2 permeability than the neat PIM-1 membrane 160 days after preparation (26% for the MMM vs 58% for the purely polymeric one)
Recent Findings in (Ti)POSS-based Polymer Systems
No full textNovel polymer hybrids based on a Ti-containing polyhedral oligomeric silsesquioxane-(Ti)POSS-and two polymer matrices-polyamide 6 (PA6) and a styrene-maleic anhydride copolymer (PSMA)-have been prepared by different approaches (namely, in situ polymerization, melt blending, grafting) in order to investigate the dispersion level of (Ti)POSS within the organic polymer matrices in view of potential in situ catalytic activity of the metal. The chemical characterization of the prepared hybrid systems, performed by infrared spectroscopy and nuclear magnetic resonance, and their morphological analysis, evaluated by electron microscopy and X-ray diffraction, have shown that it is possible to homogeneously distribute and finely disperse (Ti)POSS at nanometric level within PA6 and PSMA. In this manner, an easy incorporation of metal functionalities into the above polymer matrices has been achieved and extension to other polymer systems can be foreseen
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