scholarly journals Properties of composite systems based on polymethylsiloxane and silica in the water environment

Surface ◽  
2020 ◽  
Vol 12(27) ◽  
pp. 100-136
Author(s):  
T. V. Krupska ◽  
◽  
V. M. Gun'ko ◽  
I. S. Protsak ◽  
I. I. Gerashchenko ◽  
...  
Keyword(s):  
Interfacial Energy ◽  
Composite System ◽  
Close Contact ◽  
Water Environment ◽  
Heterogeneous Systems ◽  
Adsorption Properties ◽  
Mechanical Loads ◽  
Composite Systems ◽  
System A ◽  
Hydrophilic Particles

The formation of a composite system based on equal amounts of hydrophobic, porous polymethylsiloxane and hydrophilic nanosilicon A-300 was studied. It is shown that during the formation of a composite system the specific surface of the material is significantly reduced, which is due to the close contact between hydrophobic and hydrophilic particles. When water is added to the composite system, in the process of homogenization under conditions of dosed mechanical loading, the effect of nanocoagulation is manifested – the formation of nanosized particles of hydrated silica inside the polymethylsiloxane matrix, recorded on TEM microphotographs. When measuring the value of the interfacial energy of PMS and PMS/A-300 composite by low-temperature 1H NMR spectroscopy, it was found that the effect of nanocoagulation is manifested in a decrease (compared to the original PMS) energy of water interaction with the surface of the composite obtained under small mechanical conditions. its growth when using high mechanical loads. In the process, the binding of water in heterogeneous systems containing PMS, pyrogenic nanosilica (A-300), water and surfactants – decamethoxine (DMT) was studied. Composite systems were created using metered mechanical loads. It is shown that when filling the interparticle gaps of PMS by the method of hydrosealing, the interphase energy of water in the interparticle gaps of hydrophobic PMS with the same hydration is twice the interfacial energy of water in hydrophilic silica A-300. This is due to the smaller linear dimensions of the interparticle gaps in PMS compared to A-300. In the composite system, A-300/PMS/DMT/H2O there are non-additive growth of binding energy of water, which is probably due to the formation, under the influence of mechanical stress in the presence of water, microheterogeneous areas consisting mainly of hydrophobic and hydrophilic components (microcoagulation). Thus, with the help of mechanical loads, you can control the adsorption properties of composite systems and create new materials with unique adsorption properties.

scholarly journals Use of microcoagulation effect to control water binding in a heterogeneous polymethylsiloxane/silica/water system

2020 ◽  
Vol 21 (1) ◽  
pp. 132-139
Author(s):  
V. V. Turov ◽  
I. I. Gerashchenko ◽  
T. V. Krupskaya ◽  
N. Yu. Klymenko ◽  
K. O. Stepanuk
Keyword(s):  
Interfacial Energy ◽  
Mechanical Load ◽  
Heterogeneous Systems ◽  
Water System ◽  
Bound Water ◽  
Water Binding ◽  
Mechanical Loads ◽  
Composite Systems ◽  
System A ◽  
Surface Active

The binding of water in heterogeneous systems containing polymethylsiloxane (PMS) pyrogenic nanosilica (A-300) water and the surface-active substance decametoxin (DMT) was studied. Composite systems were created using metered mechanical loads. The low-temperature 1H NMR spectroscopy was used to measure the structural and thermodynamic parameters of bound water. It is shown that when filling PMS interparticle gaps with hydrocompaction, the interfacial energy of water in the interparticle gaps of hydrophobic PMS with the same hydration is twice as large as the interfacial energy of water in hydrophilic silica A-300. This is due to the smaller linear dimensions of the interparticle gaps in the ICP compared with the A-300. In the composite system, A-300/PMS/DMT/H2O, a non-additive growth of water binding energy is observed, which is likely due to the formation, under the influence of mechanical load in the presence of water, of microheterogeneous sites, consisting mainly of the hydrophobic and hydrophilic components (microcoagulation). Thus, using mechanical loads, you can control the adsorption properties of composite systems.

scholarly journals Interphase interactions of hydrophobic powders based on methilsilica in the water environment

Surface ◽  
2020 ◽  
Vol 12(27) ◽  
pp. 53-99
Author(s):  
V. V. Turov ◽  
◽  
V. M. Gun’ko ◽  
T. V. Krupskaya ◽  
I. S. Protsak ◽  
...  
Keyword(s):  
Interfacial Energy ◽  
Water Environment ◽  
Heterogeneous Systems ◽  
Stable State ◽  
Water System ◽  
Water Concentration ◽  
Binding Energies ◽  
Concentrated Suspension ◽  
Mechanical Loads ◽  
Hydrophobic Silica

Using modern physicochemical research methods and quantum chemical modeling, the surface structure, morphological and adsorption characteristics, phase transitions in heterogeneous systems based on methylsilica and its mixtures with hydrophilic silica were studied. It is established that at certain concentrations of interfacial water, hydrophobic silica or their composites with hydrophilic silica form thermodynamically unstable systems in which energy dissipation can be carried out under the influence of external factors: increasing water concentration, mechanical loads and adsorption of air by hydrophobic component. When comparing the binding energies of water in wet powders of wettind-drying samples A-300 and AM-1, which had close values of bulk density (1 g/cm3) and humidity (1 g/g), close to 8 J/g. However, the hydration process of hydrophobic silica is accompanied by a decrease in entropy and the transition of the adsorbent-water system to a thermodynamically nonequilibrium state, which is easily fixed on the dependences of interfacial energy (S) on the amount of water in the system (h). It turned out that for pure AM-1 the interfacial energy of water increases in proportion to its amount in the interparticle gaps only in the case when h < 1 g/g. With more water, the binding energy decreases abruptly, indicating the transition of the system to a more stable state, which is characterized by the consolidation of clusters of adsorbed water and even the formation of a bulk phase of water. Probably there is a partial "collapse" of the interparticle gaps of hydrophobic particles AM-1 and the release of thermodynamically excess water. For mixtures of hydrophobic and hydrophilic silica, the maximum binding of water is shifted towards greater hydration. At AM1/A-300 = 1/1 the maximum is observed at h = 3g/g, and in the case of AM1/A-300 = 1/2 it is not reached even at h = 4 g/g. The study of the rheological properties of composite systems has shown that under the action of mechanical loads, the viscosity of systems decreases by almost an order of magnitude. However, after withstanding the load and then reducing the load to zero, the viscosity of the system increases again and becomes significantly higher than at the beginning of the study. That is, the obtained materials have high thixotropic properties. Thus, a wet powder that has all the characteristics of a solid after a slight mechanical impact is easily converted into a concentrated suspension with obvious signs of liquid.

The Analysis and Synthesis of Vibrating Systems

1954 ◽  
Vol 58 (526) ◽  
pp. 703-719 ◽  
Author(s):  
R. E. D. Bishop
Keyword(s):  
Composite System ◽  
Frequency Equation ◽  
Computational Effort ◽  
Analytical Treatment ◽  
Principal Mode ◽  
Oscillatory Systems ◽  
Composite Systems ◽  
Analysis And Synthesis ◽  
Simple Systems ◽  
Vibrating Systems

SummaryComplicated oscillatory systems may be broken down into component “ sub-systems ” for the purpose of vibration analysis. These will generally submit more readily to analytical treatment. After an introduction to the concept of receptance, the principles underlying this form of analysis are reviewed.The dynamical properties of simple systems (in the form of their receptances) may be tabulated. By this means the properties of a complicated system may be found by first analysing it into convenient sub-systems and then extracting the properties of the latter from a suitable table. A catalogue of this sort is given for the particular case of conservative torsional systems with finite freedom.The properties of the composite system which may be readily found in this way are (i) its receptances and (ii) its frequency equation. Tables are given of expressions for these in terms of the receptances of the component sub-systems. All of the tables may easily be extended. The tabulated receptances may also be used for determining relative displacements during free vibration in any principal mode.A method of presenting information on the vibration characteristics of machinery, which is effectively due to Carter, is illustrated by means of an example. More general adoption by manufacturers of this method (which requires no more computational effort than must normally be made) would lead to enormous savings of labour in calculating natural frequencies of composite systems.

Thermal Expansion of Composite System Epoxy Resin/Recycled Carbon Fibers

2020 ◽  
Vol 994 ◽  
pp. 162-169
Author(s):  
Štěpánka Dvořáčková ◽  
Dora Kroisová
Keyword(s):  
Experimental Study ◽  
Thermal Expansion ◽  
Epoxy Resin ◽  
Carbon Fibers ◽  
Composite System ◽  
Linear Thermal Expansion Coefficient ◽  
Linear Thermal Expansion ◽  
Carbon Fibres ◽  
Sample Matrix ◽  
Composite Systems

This experimental study deals with the problematics of thermal expansion α [10-6/K] of the composite systems based on recycled carbon fibres reinforced epoxy resin. The epoxy resin CHS – EPOXY 520 (EPOXY 15), cured with the hardener P11 (Districhem, s.r.o.), was chosen as a sample matrix. Recycled carbon fibres with a diameter of 7 μm and a length of 100 μm (Easy Composites Ltd.) were the filler. In the experiment, samples with the fulfilment of 10, 20, 40, 60, 80, 90 and 100 phr were prepared. The samples were being poured into silicone molds, cured at an overpressure of 0.7 MPa and a temperature of 23 ± 2 °C for 24 hours. A thermomechanical analyzer was used to determine the thermal expansion of composite systems. The addition of recycled carbon fibers to epoxy resin can reduce the coefficient of linear thermal expansion at 20°C in half, from the original α = 45 to 55 × 10-6/K for non-filled epoxy resin to α = 25 to 27 × 10-6/K for filled epoxy resin. Optimal filling is at the level of 40 phr, with higher filling there is no further reduction of the linear thermal expansion coefficient.

DESIGN OF THE STATE OBSERVER WITH D-STABILITY FOR UNCERTAIN SYMMETRIC CIRCULANT COMPOSITE SYSTEMS

2005 ◽  
Vol 08 (02n03) ◽  
pp. 193-208
Author(s):  
MAN LIU ◽  
YOU ZHANG ◽  
YUAN-WEI JING ◽  
SI-YING ZHANG
Keyword(s):  
Uncertain Systems ◽  
Composite System ◽  
Uncertain System ◽  
Original System ◽  
State Observer ◽  
Pole Assignment ◽  
The State ◽  
Special Structure ◽  
Composite Systems ◽  
Decentralized Observer

The design of the state observer for a kind of uncertain symmetric circulant composite systems based on regional pole assignment is studied. The "decentralized observer gain matrices" have been obtained by taking use of the special structure of the system. The central observer gain matrix for such a system has the same block symmetric circulant structure as the original system and can be constructed by the "decentralized observer gain matrices." Thus, the problem of designing state observer for such an uncertain system with n·N dimensions based on regional pole assignment can be transformed into the subproblems for N/2+1 or (N + 1)/2 uncertain systems with n dimensions. The central D-stabilizable state observer is also a symmetric circulant composite system. And the design of the observer makes best use of the advantage of interconnections of the system.

Thermal Expansion Behavior of the Multiphase Composite System

2004 ◽  
Vol 449-452 ◽  
pp. 765-768
Author(s):  
Chong Sung Park ◽  
Hyun Seok Hong ◽  
Myung Ho Kim ◽  
Chong Mu Lee
Keyword(s):  
Thermal Expansion ◽  
Composite System ◽  
Welding Process ◽  
High Volume ◽  
Volume Percent ◽  
New Approach ◽  
Composite Systems ◽  
Expansion Behavior ◽  
The Matrix ◽  
Multiphase Composite

A new approach for the CTE on the basis of Ashelby.s cutting and welding process was made for the analysis of the thermal expansion behaviors of Al-Si alloys and composites. In this theoretical approach, it was considered that relaxation of residual stress could create an elastoplastic zone in the matrix around a particle during cooling. A comparison of the measured CTEs with the calculated ones for the Al-Si-SiCp and Al-Si-Al2O3 composite systems was performed in terms of the volume percent and the size of reinforced phases. The calculated results revealed that the linear CTE of the both composite depends on the size of the reinforce phases, especially at the composite systems with a low volume percent of the reinforce phases. The increase in the volume percentages of Al2O3, SiCp and Si phase lowers the linear CTEs of the systems. The measured CTEs was deviated less than about ten percents from the calculated ones at composites with a high volume percent. The deviations of the CTEs of reinforced phases are about 4 - 6 vol% from real composite systems.

scholarly journals Delamination mechanisms in fiber-reinforced composites structures tested at different loadings

2020 ◽  
Vol 12 (1) ◽  
pp. 175-182 ◽  
Author(s):  
Adriana STEFAN ◽  
George PELIN ◽  
Alina DRAGOMIRESCU ◽  
Alexandra PETRE ◽  
Sorina ILINA
Keyword(s):  
Carbon Fibers ◽  
Composite System ◽  
High Strength ◽  
Fiber Reinforced Composites ◽  
Reinforced Composites ◽  
Mechanical Loads ◽  
Synthetic Fibers ◽  
Low Weight ◽  
Mechanical And Physical Properties ◽  
Strength And Stiffness

Composite materials are a special class which has some advantages like low weight, high strength and stiffness. For a composite system they are very suitable for aerospace, marine and auto applications due to the low density. Among all the synthetic fibers, carbon fibers are now considered the first material to be used for reinforcement due to their proper cost, as compared to aramid, and better mechanical and physical properties. This paper is an experimental work and presents the preliminary results regarding the evaluation of CFRP prepreg based on M18/1 carbon fiber prepreg developed by manual lay-up/autoclave curing. The obtained materials were tested at different mechanical loads and the failure mode was analyzed with the aim of evaluating their performances. The mechanism by which the fibers are delaminated in the composite system is assessed. To verify if the structure has defects that can interfere with the delamination process, ultrasonic nondestructive testing has been used. Also, for a better understanding of the delamination mechanism, the numerical simulation was used.

scholarly journals A Review Of Mechanisms And Fracture Mechanics Of Moisture Ingress In Composite Systems

2021 ◽  
Author(s):  
Janani S. Gopu
Keyword(s):  
Fracture Mechanics ◽  
Composite Structures ◽  
Composite System ◽  
Aerospace Industry ◽  
Weight Ratio ◽  
High Strength ◽  
Honeycomb Structure ◽  
Sandwich Composite ◽  
Composite Systems ◽  
Water Accumulation

Composite materials help realize high strength to weight ratio requirements of the Aerospace Industry. Composite structures and sandwich composite structures are susceptible to moisture ingress. Moisture ingress causes degradation of thermo-mechanical properties of the composite panels. Water accumulation in sandwich composite structures causes rapid degradation of face to core bondline, damage of cells frozen water and even blow off skins owing to sudden pressure build up in the cells of the honeycomb structure. Mechanisms of moisture ingress can be broadly classified into direct and indirect mechanisms. Direct ingress occurs through pre-existing pathways formed by defects in the composite system. Indirect mechanisms are diffusion, Capillary actions, Wicking actions, and Osmosis. The first form of damage in FRP materials is microcracking. The rate of microcracking increases with moisture ingress. Microcracking fracture toughness is a material property for the susceptibility of a composite system to the formation of microcracks. This work implores the mechanisms and the fracture mechanics dominating the formation of microcracks.

scholarly journals Supramolecular interactions in the mixtures of hydrophobic and hydrophilic pyrogenic silicas

2021 ◽  
pp. 93-107
Author(s):  
Vladimir V. Turov ◽  
◽  
Tetyana V. Krupska ◽  
Vladimir M. Gun'ko ◽  
Mykola T. Kartel ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Interfacial Energy ◽  
1H Nmr Spectroscopy ◽  
Point Of View ◽  
Supramolecular Interactions ◽  
Mechanical Loads ◽  
Hydrophobic Substances ◽  
Adsorption Processes ◽  
Hydrophobic Particles ◽  
Air Removal

In order to study the peculiarities of the interaction of hydrophobic particles with water, the binding of water in composite systems based on structurally modified mixtures of 1/1 hydrophilic (A-300) and hydrophobic (AM-1-300) silica was studied by low-temperature 1H NMR spectroscopy. It is shown that with equal amounts of hydrophobic and hydrophilic components, the dependence of the interfacial energy on the value of surface hydration has a bell-shaped appearance with a maximum at h = 3000 mg/g. The obtained dependence is explained from the point of view of restructuring of the composite system under the influence of mechanical loads and the possibility of air removal and adsorption processes in the interparticle gaps of hydrophobic and hydrophilic components, as well as the phenomenon of nanocoagulation. Increasing the concentration of the hydrophilic component does not increase the binding energy of water. Under the influence of liquid hydrophobic substances, depending on the bulk density of the composite, there may be an increase or decrease in interfacial energy. The growth is due to the restructuring of the hydrophobic and hydrophilic components (nanocoagulation), and the decrease is due to the displacement of water from the surface into pores of larger radius. For n-decane, the effect of increasing the melting temperature by several tens of degrees was registered in the interparticle gaps.

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