Silica Polymer Research Articles

Low Power Consumption Hybrid-Integrated Thermo-Optic Switch with Polymer Cladding and Silica Waveguide Core

Taking advantage of the large thermo-optical coefficient of polymer materials, a hybrid-integrated thermo-optic switch was designed and simulated. It is also compatible with the existing silica-based planar light-wave circuit (PLC) platform. To further reduce the power consumption, we introduced the air trench structure and optimized the structural parameters of the heating region. This scheme is beneficial to solving the problem of the large driving power of silica-based thermo-optic switches at this stage. Compared with the switching power of all-silica devices, the power consumption can be reduced from 116.11 mW (TE) and 114.86 mW (TM) to 5.49 mW (TE) and 5.96 mW (TM), which is close to the driving power of the reported switches adopting polymer material as the core. For the TE mode, the switch's rise and fall times were 121 µs and 329 µs. For the TM mode, the switch times were simulated to be 118 µs (rise) and 329 µs (fall). This device can be applied to hybrid integration fields such as array switches and reconfigurable add/drop multiplexing (ROADM) technology.

Advances in aptamer-based drug delivery vehicles for cancer therapy.

Overall, aptamers are special classes of nucleic acid-based macromolecules that are beginning to investigate because of their capability of avidity binding to a specific target for clinical use. Taking advantage of target-specific medicine led to more effective therapeutic and limitation of side effects of drugs. Herein, we discuss several aptamers and their binding capability and capacity for selecting tumor biomarkers and usage of them as targeting ligands for the functionalization of nanomaterials. We review recent applications based on aptamers and several nanoparticles to rise efficacy and develop carrier systems such as graphene oxide, folic acid, gold, mesopores silica, and various polymers and copolymer, polyethylene glycol, cyclodextrin, chitosan. The nanocarriers have been characterized by particle size, zeta potential, aptamer conjugation, and drug encapsulation efficiency. Hydrodynamic diameter and Zeta potential can used in order to monitor aptamers' crosslinking, in-vitro drug release, intracellular delivery of nanocarriers, and cellular cytotoxicity assay. Also, they are studied for cellular uptake and internalization to types of cancer cell lines such as colorectal, breast, prostate, leukemia and etc. The results are investigated in in-vivo cytotoxicity assay and cell viability assay. Targeted cancer therapy seems a good and promising strategy to overcome the systemic toxicity of chemotherapy.

Effect of Curing Temperature on the Properties of a MgO-SiO2-H2O System Prepared Using Dead-Burned MgO.

The hydration of M-S-H prepared using silica fume (SF) and dead-burned MgO cured at 20 °C, 50 °C, and 80 °C was investigated, and the properties and performance of this M-S-H were measured. The formation of M-S-H was characterized using XRD, FTIR, TGA, and 29Si MAS-NMR. Results show that the compressive strength of paste prepared using MgO calcined at 1450 °C for 2 h reached 25 MPa after 28 d. The shrinkage of mortar made with low reactivity MgO was lower than that made with high reactivity MgO. The pH value of MgO/SF paste mixed with dead-burned MgO did not exceed 10.4 at room temperature. The shrinkage of M-S-H prepared using dead-burned MgO was less than that prepared using more active MgO, and its strength did not decrease over time. No (or only a small amount of) Mg(OH)2 was formed, which is why the strength of M-S-H prepared with dead-burned MgO continually increased, without decreasing. The promotion of curing temperature favor process of MgO hydration and is beneficial for degree of silica polymerization. The sample cured in 50 °C water showed the highest relative degree of reaction.

Exploring the In Situ Formation Mechanism of Polymeric Aluminum Chloride-Silica Gel Composites under Mechanical Grinding Conditions: As a High-Performance Nanocatalyst for the Synthesis of Xanthene and Pyrimidinone Compounds.

The use of mechanical ball milling to facilitate the synthesis of organic compounds has attracted intense interest from organic chemists. Herein, we report a new process for the preparation of xanthene and pyrimidinone compounds by a one-pot method using polymeric aluminum chloride (PAC), silica gel, and reaction raw materials under mechanical grinding conditions. During the grinding process, polymeric aluminum chloride and silica gel were reconstituted in situ to obtain a new composite catalyst (PAC–silica gel). This catalyst has good stability (six cycles) and wide applicability (22 substrates). The Al–O–Si active center formed by in situ grinding recombination was revealed to be the key to the effective catalytic performance of the PAC–silica gel composites by the comprehensive analysis of the catalytic materials before and after use. In addition, the mechanism of action of the catalyst was verified using density functional theory, and the synthetic pathway of the xanthene compound was reasonably speculated with the experimental data. Mechanical ball milling serves two purposes in this process: not only to induce the self-assembly of silica and PAC into new composites but also to act as a driving force for the catalytic reaction to take place. From a practical point of view, this “one-pot” catalytic method eliminates the need for a complex preparation process for catalytic materials. This is a successful example of the application of mechanochemistry in materials and organic synthesis, offering unlimited possibilities for the application of inorganic polymer materials in green synthesis and catalysis promoted by mechanochemistry.

Atomic Details of Biomineralization Proteins Inspiring Protein Design and Reengineering for Functional Biominerals

Biominerals are extraordinary materials that provide organisms with a variety of functions to support life. The synthesis of biominerals and organization at the macroscopic level is a consequence of the interactions of these materials with proteins. The association of biominerals and proteins is very ancient and has sparked a wealth of research across biological, medical and material sciences. Calcium carbonate, hydroxyapatite, and silica represent widespread natural biominerals. The atomic details of the interface between macromolecules and these biominerals is very intriguing from a chemical perspective, considering the association of chemical entities that are structurally different. With this review I provide an overview of the available structural studies of biomineralization proteins, explored from the Protein Data Bank (wwPDB) archive and scientific literature, and of how these studies are inspiring the design and engineering of proteins able to synthesize novel biominerals. The progression of this review from classical template proteins to silica polymerization seeks to benefit researchers involved in various interdisciplinary aspects of a biomineralization project, who need background information and a quick update on advances in the field. Lessons learned from structural studies are exemplary and will guide new projects for the imaging of new hybrid biomineral/protein superstructures at the atomic level.

Testing the use of the silica deposition fluorescent probe PDMPO to estimate in situ growth rates of diatoms

AbstractThe fluorophore [2‐(4‐pyridyl)‐5{[4‐dimethylaminoethyl‐aminocarbamoyl‐methoxy]phenyl}oxazole], in short PDMPO, is incorporated in newly polymerized silica in diatom frustules and thereby provides a tool to estimate Si uptake, study diatom cell cycles but also determine mortality‐independent abundance‐based species specific‐growth rates in cultures and natural assemblages. In this study, the theoretical framework and applicability of the PDMPO staining technique to estimate diatom species specific‐growth rates were investigated. Three common polar diatom species, Pseudo‐nitzschia subcurvata, Chaetoceros simplex, and Thalassiosira sp., chosen in order to cover a broad range of species specific frustule and life‐cycle characteristics, were incubated over 24 h in control (no PDMPO) and with 0.125 and 0.6 μM PDMPO addition, respectively. Results indicate that specific‐growth rates of the species tested were not affected in both treatments with PDMPO addition. The specific‐growth rate estimates based on the PDMPO staining patterns (μPDMPO) were comparable and more robust than growth rates estimated from the changes in cell concentrations (μcc). This technique also allowed to investigate and highlight the importance of the illumination cycle (light and dark phases) on cell division in diatoms.

Comparative efficiency of silica gel, biochar, and plant growth promoting bacteria on Cr and Pb availability to Solanum melongena L. in contaminated soil irrigated with wastewater

Crop irrigation with untreated wastewater is a routine practice in developing countries that causes multiple human health consequences. A comparative study was performed to regulate total Cr and Pb stress in soil and Solanum melongena L. plant. For this purpose, 0.2% chitosan polymerized silica gel (CP-silica gel), 1.5% zinc-enriched biochar (ZnBc), and three bacterial species such as Trichococcus sp. (B1), Pseudomonas alcaligenes (B2), and Bacillus subtilis (B3) were selected. Initially, a biosorption trial was conducted to test the heavy metal removal efficiency of three bacterial species B1, B2, and B3 for 24 h. Hence, B3 showed maximum Cr and Pb removal efficiency among the studied bacterial isolates. Then, a pot study was conducted with 12 different treatments having three replicates. After harvesting, different growth and biochemical parameters such as chlorophyll concentration, proteins, phenolics, reactive oxygen species, and antioxidant enzymes were analyzed. The results demonstrated that wastewater application significantly (p ≤ 0.01) reduced the fresh and dry weights of the root, stem, and leaves due to high total Cr and Pb toxicity. However, CP-silica gel and ZnBc treatments performed best when applied in combination with B3. The concentration of leaf total Cr was significantly decreased (91 and 85%) with the application of ZnBc + B3 and CP-Silica gel + B3, respectively, as compared to control. There was a reduction in stem hydrogen peroxide (87%) and malondialdehyde (81%) recorded with CP-silica gel + B3 treatment due to enhanced activities of antioxidant enzymes viz. ascorbate peroxidase (6-folds) and catalase (7-folds) relative to control. Similarly, leaf total phenolics (3-folds) and protein (6-folds) contents were enhanced with CP silica gel+B3 application relative to control. Overall, CP-silica gel and ZnBc with B3 application proved to be the most appropriate treatments and can be used in developing countries to limit the deleterious effects of total Cr and Pb pollution.

Effect of Hexane Addition on Mesoporous Silica Crystal Size Using Na2SiO3 from Chert Stone

Mesoporous silica is a silica solid with pores between 2-50 nm which can be used in the fields of adsorption, medicine, catalyst synthesis, material purification and stationary phase for chromatography. Mesoporous silica is generally synthesized using TEOS or TMOS, but these precursors are relatively expensive. Na2SiO3 is a precursor of mesoporous silica which is more economical and easy to obtain. Basic materials that contain a lot of silica such as chert can be synthesized into Na2SiO3. Mesoporous silica synthesis generally uses surfactants as templates for the polymerization of silica, therefore a cosolvent is needed that can act as a crystal size enlarger by interacting with surfactants. The purpose of this study was to determine the effect of the addition of hexane on the synthesis of mesoporous silica symbolized by SM and SMH5. Mesoporous silica was synthesized using the sol-gel method with the basic ingredients of Na2SiO3 from chert, P104 as a surfactant, HCl as a solvent and n-hexane as an additive to increase crystal size. Mesoporous silica was characterized using XRD. The results of measurements using XRD showed that the X-ray difragtogram pattern showed peaks at an angle of 2ϴ = 22.29o and 25.33o for SM and SMH5 products, respectively.

Gas permselectivity of novel polypyrrolone—Silica hybrid membranes

AbstractGas permselectivity behaviors of novel thermally‐rearranged polypyrrolone (PPL)—silica hybrid membranes obtained by applying thermal rearrangement of poly(ortho‐amino imide) as a precursor polymer and sol–gel reaction using tetraethoxysilane were investigated. Gas permeability of neat PPL membranes improved with the increase in rearranged temperature, which was brought by the increased fractional free volume attributed to the enlargement of intermolecular chain distance. H2/CH4 and CO2/CH4 separation abilities of the PPL—silica hybrid membranes improved and tended to cross‐corresponding upper bound trade‐off lines as the silica content increased. The admirable H2/CH4 and CO2/CH4 separation abilities would be provided by the cooperative effect of high fractional free volume derived from the conversion toward PPL and expansion‐suppressed free volume elements at the polymer—silica interfaces.

Development of N,N,N′,N′-tetra-2-ethylhexyl-thiodiglycolamide silica-based adsorbent to separate useful metals from simulated high-level liquid waste

A novel silica-based adsorbent was synthesized by impregnating macroporous silica polymer composite (SiO2-P) particles with a mixture of N,N,N',N'-tetra-2-ethylhexyl-thiodiglycolamide (TEHTDGA) and tri-n-octylamine (TOA). Then, the possibility of separating Pd(II) and other metal ions from simulated high-level liquid waste (HLLW) using the newly synthesized adsorbent (TEHTDGA+TOA)/SiO2-P was evaluated based on various adsorption characteristics obtained via batch-adsorption experiments, such as the HNO3 concentration, contact time, reaction temperature, adsorption isotherm, and chemical stability of the adsorbent. Furthermore, column separation experiments were performed based on the characteristics obtained from the batch-adsorption experiment, and the possibility of simultaneous separation of multiple metal ions was examined. The experimental results revealed that (TEHTDGA+TOA)/SiO2-P performs well in the separation of multiple metal ions from simulated HLLW.

Effect of Catalyst Support in B12-Based Heterogeneous Catalysts for Catalytic Alkane Oxidations

Abstract Heterogeneous catalysts composed of a vitamin B12 derivative with a polymer or mesoporous silica were synthesized and characterized. These two types of catalysts were used in alkane oxidation reactions with mCPBA oxidant, and improved catalytic efficiency was obtained using the polymer supported B12 catalyst with a monolith structure compared to that of the monomeric B12 catalyst. The catalytic effects were also evaluated in several alkane substrates and the polymer supported B12 catalyst showed a better performance in all reactions compared to the silica-supported B12 catalyst.

Chitosan Polymerized Silica Composite as a Potential Silicon Source: Modulation on Antioxidant Enzymes, Ionic Homeostasis, and Grain Quality in Maize Plants Under Na+ Stress

Chitosan Polymerized Silica Composite as a Potential Silicon Source: Modulation on Antioxidant Enzymes, Ionic Homeostasis, and Grain Quality in Maize Plants Under Na+ Stress

Development of coarse-grained potential of silica species

ABSTRACT Understanding the molecular transformation of silica aggregates during silica polymerisation is crucial to control the properties of final products such as zeolite, nanoparticles, mesoporous silica and other polymorphs. Nevertheless, molecular events during synthesis are challenging to probe using experimental techniques. Computational tools are beneficial to probe molecular length and time scales; however, the complex systems with significant degrees of freedom require significant computational resources. In this work, we have developed coarse-grained (CG) potentials for silica system wherein every silica tetrahedron (Si(OH)O) having ‘z’ number of bridging oxygen is mapped to a unique CG silica bead (). Different composition of these CG silica beads represent a polymerised silica system with varying degrees of condensation. We performed molecular dynamics (MD) simulations of all-atom silica system to obtain reference radial distribution functions between various silica species (), which was used in Monte Carlo simulations of the CG system to obtain CG potentials. We iteratively refined the CG potentials using iterative Boltzmann inversion and inverse Monte Carlo techniques. We found two attractive minima in the CG potential between arising due to direct and indirect interactions of species representing first and second coordination shells. The strength of CG potential increases for both of minima with increasing number of bridging oxygen in species. We performed MD simulations of CG silica beads using developed CG potentials at two degree of condensations and found equilibrium structure of spherical silica nanoparticle. We found that and species are predominantly located at the centre of nanoparticles, whereas species are present uniformly.

Organic geochemistry and mineralogy suggest anthropogenic impact in speleothem chemistry from volcanic show caves of the Galapagos

SummaryThe network of lava tubes is one of the most unexploited natural wonders of the Galapagos Islands. Here, we provide the first morphological, mineralogical, and biogeochemical assessment of speleothems from volcanic caves of the Galapagos to understand their structure, composition, and origin, as well as to identify organic molecules preserved in speleothems. Mineralogical analyses revealed that moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves were composed of calcite, opal-A, and minor amounts of clay minerals. Extracellular polymeric substances, fossilized bacteria, silica microspheres, and cell imprints on siliceous minerals evidenced microbe-mineral interactions and biologically-mediated silica precipitation. Alternating depositional layers between siliceous and carbonate minerals and the detection of biomarkers of surface vegetation and anthropogenic stressors indicated environmental and anthropogenic changes (agriculture, human waste, and cave visits) on these unique underground resources. Stable isotope analysis and Py-GC/MS were key to robustly identify biomarkers, allowing for implementation of future protection policies.

Formulation of nanohybrid coating based on essential oil and fluoroalkyl silane for antibacterial superhydrophobic surfaces

This paper reveals the role of microstructures formed on the surface of aluminum substrates created by acid etching. A wettability study showed that using a fluorinated silica polymer (PF) and the essential oil of eucalyptus (ECA) with adequate surface texture promoted antibacterial activity. Scanning electron microscope (SEM) images showed that the micro-nanostructure enhanced the possibility of loading the ECA as an antibacterial agent. Fourier Transform Infrared (FTIR) spectroscopy analysis confirmed the chemical linkage between the different components of the surface. Antibacterial tests carried out using inhibition discs displayed the antibacterial behavior of the surface's components against Bacillus cereus and Escherichia coli bacteria. The direct tests on the surface confirmed its capacity to limit bacterial adherence when exposed to bacteria contamination, 99.19% and 97.28% in the case of B. cereus with (PF) and ECA:PF-based coatings. In the case of E. coli these were 94.65% and 98.69% with PF and ECA:PF respectively.

Engineering silica-polymer hybrid nanosystems for dual drug and gene delivery.

In recent years, it has been shown that a combination of different antitumour strategies involving distinct therapeutic agents, such as chemical compounds and genetic material, could result in an effective therapeutic activity that is much higher than that obtained by conventionally used individual approaches. Therefore, the main goal of this work was to develop a new hybrid nanosystem based on mesoporous silica nanoparticles and polymers to efficiently transport and deliver drug and plasmid DNA into cancer cells. Moreover, its potential to mediate a combinatorial antitumour strategy involving epirubicin and herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) gene therapy was evaluated. For this purpose, various cationic polymers were assessed, including poly(β-amino ester) homopolymer, gelatine type A, gelatine type B, and poly(ethylene glycol)-b-poly(2-aminoethyl methacrylate hydrochloride) block copolymer. The obtained results show that using different polymers leads to nanosystems with different physicochemical properties and, consequently, different biological activities. The best formulation was obtained for hybrid nanosystems coated with PEG-b-PAMA. They demonstrated the ability to cotransport and codeliver an anticancer drug and plasmid DNA and effectively mediate the combined antitumour strategy in 2D and 3D tumour cell culture models. In summary, we developed a novel silica- and polymer-based nanosystem able to mediate a dual chemotherapeutic and suicide gene therapy strategy with a much higher therapeutic effect than that obtained through the use of individual approaches, showing its potential for cancer treatment.

Hydration Characterization of Two Generations of MTA-Based Root Canal Sealers

Since the setting characterization of a root canal sealer has an impact on its biological behavior of final obturation, this study evaluated the setting characterization of mineral trioxide aggregate MTA-Fillapex versus MTA-Bioseal compared with epoxy resin (Adseal) root canal sealers. Freshly mixed sealer was inserted into the mold (n = 10). The initial and final setting times were evaluated using a Vicat needle and were then statistically analyzed by one-way ANOVA at p < 0.05. The raw pastes and the stages of the setting reaction were analyzed using Fourier Transform Infrared (FTIR) Spectroscopy. The phase compositions were evaluated using X-ray diffraction (XRD). A significant and fast setting time was recorded by Adseal (4.7 ± 0.46 h) followed by MTA-Bioseal (11.4 ± 1.34 h) at p < 0.001. The MTA-Fillapex did not set completely in three months. The FTIR and XRD of both MTA-Bioseal and Adseal detected bands of the polymerized phases, while those of MTA-Fillapex detected partial polymerization with a low percentage of polymerized silica. MTA-Bioseal and Adseal met the ISO standards for setting times. However, MTA-Fillapex did not fulfill the ideal requirement for the sealer. Although the raw pastes of both MTA-sealers had nearly similar compositions, they behaved differently during the hydration reaction. MTA-Bioseal set completely, while MTA-Fillapex was not completely set.

Sticky-MARTINI as a reactive coarse-grained model for molecular dynamics simulations of silica polymerization

We report a molecular modeling paradigm to describe silica polymerization reactions in aqueous solutions at conditions that are representative of realistic experimental processes like biosilicification or porous silica synthesis – i.e. at close to ambient temperatures and over a wide range of pH. The key point is to describe the Si-O-Si chemical bond formation and breakage processes through a continuous potential with a balance between attractive and repulsive interactions between suitably placed virtual sites and sticky particles. The simplicity of the model, its applicability in standard parallelized molecular dynamics codes, and its compatibility with the widely used MARTINI coarse-grained force-field allows for the study of systems containing millions of atoms over microsecond time scales. The model is calibrated to match experimental results for the temporal evolution of silica polymerization in aqueous solution close to the isoelectric point, and can describe silica polymerization and self-assembly processes during encapsulation of a surfactant micelle.

MANIPULATING MEMBRANE HYDROPHOBICITY BY INTEGRATING POLYTHYLENE-COATED FUME SILICA IN PVDF MEMBRANE

Membrane gas absorption (MGA) as an emerging technology exhibits superior advantages in comparison to conventional carbon dioxide (CO2) absorption processes. However, the decrease in membrane flux, induced by membrane wetting is a significant issue to be pondered upon. Thus, fabrication of an anti-wetting composite membrane is essential to retain and sustain the MGA performance. In this work, silica nanoparticles (SiNPs) is first coated with hydrophobic low-density polyethylene (LDPE). Then, integrating LDPE-HMDS/SiNPs fillers into the polyvinylidene fluoride (PVDF) matrix to increase its hydrophobicity. The incorporation of LDPE-coated silica into PVDF polymer enhanced the contact angle values from 71.8° to 111.8°, indicates the improvement of membrane anti-wetting ability. Despite the similar finger-like layer laid on top of the sponge-like structure for pristine and composite membranes, the incorporation of LDPE-HMDS/SiNPs has reduced in the length ratio of finger-like to sponge-like layer. The changed in the membrane morphology induced higher membrane hydrophobicity which prevent membrane from getting wet easily especially in long term of operation. In addition, EDX surface mapping and lining profiles clearly proved that the LDPE-HMDS/SiNPs were distributed evenly in the composite membranes indicates the good interfacial compatibility between PVDF polymer and LDPE-coated silica. In term of CO2 absorption flux, the embedment of LDPE-HMDS/SiNPs in PVDF polymer matrix demonstrated 2.4x10-3 mol/m2.s which was 2 times higher than that of the pristine membrane. This means the incorporation of LDPE-HMDS/SiNPs into the PVDF membrane has still played a pivotal role in overcoming membrane wetting drawbacks when in contact with the liquid absorbents.

Phase Separation of Oppositely Charged Polymers Regulates Bioinspired Silicification

AbstractIn nature, simple organisms evolved mechanisms to form intricate biosilica nanostructures, far exceeding current synthetic manufacturing. Based on the properties of extracted biomacromolecules, polycation–polyanion pairs were suggested as moderators of biosilica formation. However, the chemical principles of this polymer‐induced silicification remain unclear. Here, we used a biomimetic polycation–polyanion system to study polymer‐induced silicification. We demonstrate that it is the polymer phase separation process, rather than silica–polymer interactions, which controls silica precipitation. Since ionic strength controls this electrostatic phase separation, it can be used to tune the morphology and structure of the precipitates. In situ cryo electron microscopy highlights the pivotal role of the hydrated polymer condensates in this process. These results pave the road for developing nanoscale morphologies of bioinspired silica based on the chemistry of liquid‐liquid phase separation.