Theoretical and empirical approaches to understanding the effect of phosphonate groups on the thermal degradation for two chemically modified PMMA

The influence of phosphonated groups on thermal degradation and flammability has been investigated in the case of two chemically modified PMMA. Thermogravimetric analysis as well as pyrolysis combustion flow calorimetry have been used to define the efficiency of phosphorus in both condensed and vapor phases. A theoretical study was also performed to determine the contribution of phosphonated groups to the effective heat of combustion, residue content and heat release capacity. Empirical and theoretical approaches agreed to highlight that PMMA modified with monophosphonated comonomer is more efficient in both condensed and vapor phases in terms of flammability and char formation. These results were attributed to the ability of phosphonate groups to interact with ester groups and also to the weakness of the P–C–N bonds. Moreover, this study proposes a method for designing the chemical environment of phosphonate group in polymers to achieve better flame retardancy.     

Antimicrobial photodynamic therapy with two photosensitizers on two oral streptococci: an in vitro study

Laser Physics - Periodontal diseases are caused by infection of tissues supporting the teeth due to complex aggregate of bacteria known as biofilm and firstly colonized by streptococci. The aim of...     

Injectable poloxamer/graphene oxide hydrogels with well‐controlled mechanical and rheological properties

Although significant progress has been made in the design and application of injectable hydrogels for biomedical applications, concurrent control of rheological and mechanical properties of injectable hydrogels has remained as an open challenge to the researchers. In this work, we introduce and put into practice a photo‐curable poloxamer (also known as Pluronic)/graphene oxide (Plu/GO) injectable hydrogel with well‐controlled rheological and mechanical properties. Acrylate group was anchored to hydrogel structure to endow photo‐crosslinking ability through decelerating degradation rate of poloxamer hydrogels after injection. It was found that the modified Plu remains stable in biological media for a long‐term period without significant weight loss. Rheological properties of hydrogels were also carried out as essential prerequisite for an ideal injectability via frequency sweep, flow curve, recovery, and yield stress before and after modification, signifying shear‐thinning behavior of Plu/GO hydrogels with high recoverability. The viscosity of shear‐thinning‐like hydrogels dropped at higher shear stress, which facilitated injection process. Moreover, mechanical behavior of Plu was optimized by manipulating the content of Plu, degree of modification with reactive precursor, curing, and particularly incorporation of GO without deteriorating effects on rheological behavior of Plu.     

Influence of modified mesoporous silica SBA‐15 on the flammability of intumescent high‐density polyethylene

This work aims to investigate the fire retardant properties of a novel type of high‐density polyethylene composites. Our intumescent system consists in using classical flame retardants such as ammonium polyphosphate, pentaerythritol in combination with porous mesostructured silica (SBA‐15) fillers. Prior to use, SBA‐15 was chemically modified using different organic and inorganic grafts in order to obtain some specific properties, such as an improved compatibility with the polymer, or different types of surface acidity in order to increase charring reactions. Limiting oxygen index, UL‐94, pyrolysis flow combustion calorimetry and thermogravimetric analysis were used to assess the burning behavior and thermal stability, respectively, of the processed composites. By keeping the total amount of additives always equal to 25 wt%, the better flammability characteristics were in general obtained at low SBA‐15 loadings (<2 wt%). X‐ray diffraction and Fourier transform infrared spectroscopy analyses of the residues showed that the formation of a barrier mainly constituted by crystalline silicon phosphates is probably a key to enhance the fire properties. Further slight improvements brought by the surface modification of SBA‐15 nanofillers are discussed according to type of incorporated particles. Copyright © 2016 John Wiley & Sons, Ltd.     

Integration of geographic and hierarchical routing protocols for energy saving in wireless sensor networks with mobile sink

Wireless Networks - Wireless sensor networks (WSNs) is used for the internet of things, and Pervasive/Ubiquitous computing. These networks consist of intelligent nodes which sense data and forward...     

Correction to: Integration of geographic and hierarchical routing protocols for energy saving in wireless sensor networks with mobile sink

Wireless Networks - The original version of this article unfortunately contained an error in the author’s affiliation.     

Experimental investigation of the adhesion force of single and double-layer coatings on MEMS surfaces

Adhesion force is one of the most important factors in microelectromechanical systems (MEMS), especially for microassembly. It depends on operating conditions and is affected by the contact area. In this study, the adhesion force between MEMS materials and AFM tips was analysed using AFM's point-mode spectroscopy. The aim was to study the effectiveness of various coatings in MEMS adhesion surfaces. For this purpose, five silicon surfaces were used, four of which were coated, and one was noncoated. Two of them were deposited by single-layer coating (Au and Ag). The other two were deposited by double-layer coating (TiO₂/Au, TiO₂/Ag) on a Si (1 0 0) substrate. The depositing was accomplished by the thermal evaporation method. Composite materials and analysis were reviewed by observing the SEM image. The experimental results showed that the method of deposition helped to decrease the adhesion force between the probe tip and the surface of the specimens, and double-layer coating had stronger effect on decreasing the adhesion force than the single-layer coating.     

Multiscale programming to manage the air pollution problem using the level crossing method

Problems regarding pollution must be handled very carefully and precisely, which requires a well-organized and accurate program. In this article, we suggest that different programs should be used for different time scales (short-term or long-term programs) to manage and control the pollution, which we call multiscale programs. Here, we follow the level crossing (LC) method to introduce an optimum program for different time scales to manage pollution. It might be useful to mention that we have used the historical pollution data available for Tehran.     

Comparison of the adhesion forces in single and double-layer coatings on the MEMS surfaces by JKR and DMT models

In many medical and industrial applications, some strategies are needed to control the adhesion forces between the materials, because surface forces can activate or hinder the function of the device. All actual surfaces present some levels of roughness and the contact between two surfaces is transferred by the asperities on the surfaces. The force of the adhesion, which depends on the operating situations, can be influenced by the contact region. The aim of the present study is to predict the adhesion force in MEMS surfaces using the JKR and DMT models. The surfaces of the coating material in this research consisted of the single-layer coating of Gold and Silver, and the double-layer coating of TiO₂/Gold and TiO₂/Silver on the silicon (100) substrates. The depositing was done by the thermal evaporation method. The results showed that the double-layer coating developed by the new deposition method helped the reduction of the adhesion forces between the probe tip and the specimen surface. The predicted adhesion forces between the probe and the specimens with DMT and JKR models were compared with the experimental results. For all specimens, the simulated data by applying the JKR theory were in a good agreement with the adhesion force experimental values.     

Synthesis of new aromatic polyamides containing α-amino phosphonate with high thermal stability and low heat release rate

The new aromatic polyamides containing α-amino phosphonate were synthesized from phosphorus-based dicarboxylic acid 4 and various aromatic diamines by direct polycondensation reaction. Dicarboxylic acid 4 was successfully synthesized from trimethyl phosphite, 4-aminobenzoic acid and terephthaldehyde via a three-component reaction. The polymerization reaction produced the polyamides 6a–f with high yield and desirable inherent viscosities. The thermal properties of the all samples were investigated by thermo-gravimetric analysis (TGA). The TGA results in N₂ exhibited the 10% mass loss temperatures (T₁₀) in the ranges of 324–345 °C, while the T₁₀ resulted from thermo-oxidative degradation were higher than those. The main data obtained by microscale combustion calorimetry revealed acceptable combustion properties such as very low peak of heat release rate for the synthesized polyamides 6a–f. The all of the results indicated that these polyamides can be potentially utilized as additive for improvement of thermal resistance and combustion behavior of thermoplastic materials.