Properties of Porous PDMS and Stretchability of Flexible Electronics in Moist Environment

2020 ◽  
Vol 87 (10) ◽  
Author(s):  
Peng Pan ◽  
Zuguang Bian ◽  
Xin Song ◽  
Xiaoliang Zhou
Keyword(s):  
Experimental Data ◽  
Elastic Modulus ◽  
Flexible Electronics ◽  
Mechanical Performance ◽  
Homogenization Method ◽  
Good Choice ◽  
Moisture Concentration ◽  
Moisture Expansion ◽  
Moist Environment ◽  
Coefficient Of Moisture Expansion

Abstract Polydimethylsiloxane (PDMS) is a good choice for the substrate and encapsulation of clinical flexible electronics, since it possesses some distinguished characteristics such as high elasticity, excellent optical characteristic, good biocompatibility, and stability. In the present study, the emulsion polymerization technique was used once more to fabricate porous PDMS, which is expected to assure the sweat penetration through the flexible electronics, and therefore to reduce the irritation to the skin due to the flexible electronics. To assess the mechanical performance of flexible electronics with moisture, the saturated moisture concentration, coefficient of moisture expansion, and elastic modulus of porous PDMS for different relative wetness fraction were measured in experiment. Meanwhile, an asymptotic homogenization method (AHM) was adopted to predict these parameters theoretically. Results indicate that the saturated moisture concentration is linear to the porosity, while the coefficient of moisture expansion is independent of the porosity, both of which are well verified by the experimental data. The fitted formula on the elastic modulus for different porosities suggested in our previous study was developed to take account of the relative wetness fraction based on the experimental data. These three parameters were finally applied in calculating the stretchability of a flexible electronic with serpentine interconnects in moist environment. Numerical stimulation reveals that the stretchability increases with the porosity and relative wetness fraction of the substrate and encapsulation. The present work is hoped to pave the way for flexible electronics in clinical applications.

Experimental and Theoretical Study on Mechanical Properties of Porous PDMS

2018 ◽  
Vol 85 (4) ◽  
Author(s):  
Chen Huang ◽  
Zuguang Bian ◽  
Chengfeng Fang ◽  
Xiaoliang Zhou ◽  
Jizhou Song
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Flexible Electronics ◽  
Poisson’S Ratio ◽  
Mechanical Design ◽  
Homogenization Method ◽  
Poisson's Ratio ◽  
Design And Optimization ◽  
Volume Porosity ◽  
Asymptotic Homogenization Method

Polydimethylsiloxane (PDMS) is extensively used in clinical flexible electronics, due to its biocompatibility and stability. When it is employed in a stretchable epidermal sensor for long-term monitoring, PDMS must have open pores within it to assure the sweat penetration. In the present paper, we focus on the mechanical properties of porous PDMS with different volume porosities at different temperatures. The emulsion polymerization technique is applied to fabricate porous PDMS. By controlling the ratio of water to PDMS prepolymer, different porosities of PDMS were obtained, and elastic moduli of such porous PDMS were measured in experiment. Results indicate that the elastic modulus increases nonlinearly as its temperature rises from 0 °C to 40 °C (a temperature range frequently encountered in clinical applications). Meanwhile, an asymptotic homogenization method (AHM) is employed to theoretically predict the elastic modulus and Poisson's ratio of porous PDMS, whose reliability is testified by comparing the results with experimentally measured data. Further theoretical discussions on mechanical properties are carried out, and results show that the pore size of porous PDMS has almost no effect on the elastic modulus and Poisson's ratio for certain porosities. Porosity of porous PDMS, however, has significant effect on both of these two mechanical parameters. Two fitted nonlinear formulas are then proposed to estimate the elastic modulus and Poisson's ratio of porous PDMS for any volume porosity less than 50%. All the results in the present paper are essential for mechanical design and optimization of clinical flexible electronics based on porous PDMS.

Effect Of Elevated Temperatures On Complete Concrete Deformation Diagrams

2019 ◽  
pp. 9-14
Keyword(s):  
Experimental Data ◽  
Elastic Modulus ◽  
Elevated Temperatures ◽  
Peak Load ◽  
Relative Deformation ◽  
Deformation Characteristics ◽  
Compression Tests ◽  
Strain Behavior ◽  
Different Temperatures ◽  
Deformation Diagrams

The analysis of the previous results of the study on concrete stress-strain behavior at elevated temperatures has been carried out. Based on the analysis, the main reasons for strength retrogression and elastic modulus reduction of concrete have been identified. Despite a significant amount of research in this area, there is a large spread in experimental data received, both as a result of compression and tension. In addition, the deformation characteristics of concrete are insufficiently studied: the coefficient of transverse deformation, the limiting relative compression deformation corresponding to the peak load and the almost complete absence of studies of complete deformation diagrams at elevated temperatures. The two testing chambers provided creating the necessary temperature conditions for conducting studies under bending compression and tension have been developed. On the basis of the obtained experimental data of physical and mechanical characteristics of concrete at different temperatures under conditions of axial compression and tensile bending, conclusions about the nature of changes in strength and deformation characteristics have been drawn. Compression tests conducted following the method of concrete deformation complete curves provided obtaining diagrams not only at normal temperature, but also at elevated temperature. Based on the experimental results, dependences of changes in prism strength and elastic modulus as well as an equation for determining the relative deformation and stresses at elevated temperatures at all stages of concrete deterioration have been suggested.

A Dynamic Test of Fully Prestressed Concrete Beams

2011 ◽  
Vol 368-373 ◽  
pp. 2483-2490
Author(s):  
Yao Ting Zhang ◽  
Yi Zheng ◽  
Hong Jian Li
Keyword(s):  
Experimental Data ◽  
Elastic Modulus ◽  
Theoretical Analysis ◽  
Natural Frequency ◽  
Axial Force ◽  
Prestressed Concrete ◽  
Concrete Beams ◽  
Dynamic Test ◽  
Modified Formula

A dynamic test of two unbonded fully prestressed concrete beams has been conducted. The results indicate that the natural frequency of beams increases with the prestress force, which is opposite to the analytical arguments for homogeneous and isotropic beams subject to axial force. This paper explains the change in frequencies by discussing the change in the elastic modulus. A modified formula is also proposed, and the experimental data agree well with the theoretical analysis.

A Cyclic Plasticity Modeling for Uniaxial and Multiaxial Ratcheting Simulation of Austenitic Steel

2012 ◽  
Author(s):  
Salim Meziani ◽  
Lynda Djimli
Keyword(s):  
Experimental Data ◽  
Stainless Steel ◽  
Constitutive Model ◽  
Data Base ◽  
Good Choice ◽  
Cyclic Plasticity ◽  
Strain History ◽  
Material Parameters ◽  
Plastic Shakedown

The first objective of this paper investigates the influence of the previous strain history on ratcheting of the 304 L stainless steel on ambient temperature. The identification is done using the Chaboche constitutive model. New tests were performed where different strain-controlled histories have been applied prior to ratcheting tests. It is demonstrated that under the same conditions, one can observe ratcheting, plastic shakedown or elasticity according to the prior strain-controlled history. The second objective points out the correlation between the experimental data base devoted to the identification of the material parameters and the quality of the predictions in cyclic plasticity. The results suggest that the choice of the tests should be closely linked to the capabilities of the model. In particular, the presence of non proportional strain-controlled tests in the data base may be not a good choice if the model itself is not able to represent explicitly such a character.

scholarly journals In silico stress fibre content affects peak strain in cytoplasm and nucleus but not in membrane for uniaxial substrate stretch

2019 ◽  
Author(s):  
Tamer Abdalrahman ◽  
Neil H. Davies ◽  
Thomas Franz
Keyword(s):  
Elastic Modulus ◽  
In Silico ◽  
Focal Adhesions ◽  
Element Model ◽  
Homogenization Method ◽  
Fibre Volume ◽  
Fibre Content ◽  
Peak Strain ◽  
Stress Fibre ◽  
A Cell

AbstractExisting in silico models for single cell mechanics feature limited representations of cytoskeletal structures that contribute substantially to the mechanics of a cell. We propose a micromechanical hierarchical approach to capture the mechanical contribution of actin stress fibres. For a cell-specific fibroblast geometry with membrane, cytoplasm and nucleus, the Mori-Tanaka homogenization method was employed to describe cytoplasmic inhomogeneities and constitutive contribution of actin stress fibres. The homogenization was implemented in a finite element model of the fibroblast attached to a substrate through focal adhesions. Strain in cell membrane, cytoplasm and nucleus due to uniaxial substrate stretch was assessed for different stress fibre volume fractions and different elastic modulus of the substrate. A considerable decrease of the peak strain with increasing stress fibre content was observed in cytoplasm and nucleus but not the membrane, whereas the peak strain in cytoplasm, nucleus and membrane increased for increasing elastic modulus of the substrate.

Using Exponential Cubic Splines to Predict Low Temperature Behavior of Elastomeric Materials

1994 ◽  
Author(s):  
Terry E. Shoup ◽  
George R. Fegan
Keyword(s):  
Experimental Data ◽  
Elastic Modulus ◽  
Low Temperatures ◽  
Analytical Techniques ◽  
High Sensitivity ◽  
Considerable Difficulty ◽  
Spline Curves ◽  
Different Types ◽  
Elastomeric Materials ◽  
Energy Absorbing

Abstract Because of their desirable elastic and energy absorbing properties, elastomeric materials have been widely used as shock mounts and pressure seals. The high sensitivity of the elastic modulus of these materials to changes in temperature has been a source of considerable difficulty to the development of robust design methods based on analytical techniques. This paper presents a simple analytical method for predicting the elastic modulus for a group of five different types of elastomers when used at low temperatures. The method is based on the application of exponential cubic spline curves to smooth experimental data. The method is applied to experimental data from the literature to illustrate its usefulness.

Cost-effective silver ink for printable and flexible electronics with robust mechanical performance

2019 ◽  
Vol 373 ◽  
pp. 355-364 ◽  
Author(s):  
Kiesar Sideeq Bhat ◽  
Umesh T. Nakate ◽  
Jin-Young Yoo ◽  
Yousheng Wang ◽  
Tahmineh Mahmoudi ◽  
...  
Keyword(s):  
Flexible Electronics ◽  
Mechanical Performance ◽  
Cost Effective ◽  
Silver Ink

Simulation of sub-micron indentation tests with spherical and Berkovich indenters

2001 ◽  
Vol 16 (7) ◽  
pp. 2149-2157 ◽  
Author(s):  
A. C. Fischer-Cripps
Keyword(s):  
Experimental Data ◽  
Elastic Modulus ◽  
Material Properties ◽  
Indentation Testing ◽  
Depth Sensing ◽  
Displacement Response ◽  
Analysis Methods ◽  
Detailed Treatment ◽  
Indentation Tests ◽  
Load Displacement

The present work is concerned with the methods of simulation of data obtained from depth-sensing submicron indentation testing. Details of analysis methods for both spherical and Berkovich indenters using multiple or single unload points are presented followed by a detailed treatment of a method for simulating an experimental load–displacement response where the material properties such as elastic modulus and hardness are given as inputs. A comparison between simulated and experimental data is given.

scholarly journals Grafting of Polypyrrole-3-carboxylic Acid to the Surface of Hexamethylene Diisocyanate-Functionalized Graphene Oxide

Nanomaterials ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 1095 ◽  
Author(s):  
José Antonio Luceño-Sánchez ◽  
Ana Maria Díez-Pascual
Keyword(s):  
Graphene Oxide ◽  
Carboxylic Acid ◽  
Flexible Electronics ◽  
Mechanical Performance ◽  
Ester Group ◽  
Hexamethylene Diisocyanate ◽  
Acyl Chloride ◽  
Functionalized Graphene Oxide ◽  
Modified Graphene Oxide ◽  
Grafting Reactions

A polypyrrole-carboxylic acid derivative (PPy-COOH) was covalently anchored on the surface of hexamethylene diisocyanate (HDI)-modified graphene oxide (GO) following two different esterification approaches: activation of the carboxylic acids of the polymer by carbodiimide, and conversion of the carboxylic groups to acyl chloride. Microscopic observations revealed a decrease in HDI-GO layer thickness for the sample prepared via the first strategy, and the heterogeneous nature of the grafted samples. Infrared and Raman spectroscopies corroborated the grafting success, demonstrating the emergence of a peak associated with the ester group. The yield of the grafting reactions (31% and 42%) was roughly calculated from thermogravimetric analysis, and it was higher for the sample synthesized via formation of the acyl chloride-functionalized PPy. The grafted samples showed higher thermal stability (~30 and 40 °C in the second decomposition stage) and sheet resistance than PPy-COOH. They also exhibited superior stiffness and strength both at 25 and 100 °C, and the reinforcing efficiency was approximately maintained at high temperatures. Improved mechanical performance was attained for the sample with higher grafting yield. The developed method is a valuable approach to covalently attach conductive polymers onto graphenic nanomaterials for application in flexible electronics, fuel cells, solar cells, and supercapacitors.

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