Thermomechanical and Hydrophobic Characterization of Shape Memory Polymers

2009 ◽  
Author(s):  
P. Daniel Warren ◽  
Rafael R. Bernal ◽  
John L. Harper ◽  
Rachelann N. Herlihy ◽  
Jonathan P. Vande Geest
Keyword(s):  
Shape Memory ◽  
Crystalline Structure ◽  
Thermal Energy ◽  
External Load ◽  
Mechanical Load ◽  
Shape Memory Polymers ◽  
Direct Result ◽  
Molecular Architecture ◽  
Original Shape ◽  
Chemical Crosslinks

Shape memory polymers (SMPs) have generated a great amount of interest due to their capacity to recover a programmable shape under an applied stimulus, such as temperature change or light irradation [1, 2]. The SMP is initially synthesized with a specific original shape. This shape can be deformed under a mechanical load and at a temperature (TH) greater than the glass transition temperature, Tg. The application of this deformation coupled with subsequent lowering of the temperature (TC) to below the Tg, can fix the polymer in the newly altered formation even after removal of the external load. Increasing the temperature again, to a point above Tg, then activates the shape memory effect, whereby the original shape can be recovered. This shape memory ability is a direct result of specific molecular architecture. Chemical and physical crosslinks and macromolecular chain entanglements are part of this structure. Chemical crosslinks between segments give form to the original shape. Some of these segments are stimuli-sensitive, in other words, segments can become increasingly elastic with the application of thermal energy. This application of energy causes the crystalline structure of these segments to melt and be easily deformed under external load. This temporary shape can now be maintained with the removal of thermal energy leading to re-crystallization. Recoil in this state is prevented by both the new crystalline structure and entanglements of the segments caused by deformation. Physical crosslinks give the architecture permanence, since the linkages do not degrade with stimulus [3]. Different crosslinker formulations can result in varying types of chemical crosslinks. Variations in the structure lead to alterations in the material properties, such as mechanical characteristics and hydrophobicity.

scholarly journals Surface Structures, Particles, and Fibers of Shape-Memory Polymers at Micro-/Nanoscale

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Liangliang Cao ◽  
Liwei Wang ◽  
Cihui Zhou ◽  
Xin Hu ◽  
Liang Fang ◽  
...  
Keyword(s):  
Shape Memory ◽  
Preparation Method ◽  
Shape Memory Polymers ◽  
Polymeric Materials ◽  
Surface Structures ◽  
Smart Polymers ◽  
Molecular Architecture ◽  
Free Standing ◽  
Nanoscale Structures

Shape-memory polymers (SMPs) are one kind of smart polymers and can change their shapes in a predefined manner under stimuli. Shape-memory effect (SME) is not a unique ability for specific polymeric materials but results from the combination of a tailored shape-memory creation procedure (SMCP) and suitable molecular architecture that consists of netpoints and switching domains. In the last decade, the trend toward the exploration of SMPs to recover structures at micro-/nanoscale occurs with the development of SMPs. Here, the progress of the exploration in micro-/nanoscale structures, particles, and fibers of SMPs is reviewed. The preparation method, SMCP, characterization of SME, and applications of surface structures, free-standing particles, and fibers of SMPs at micro-/nanoscale are summarized.

Application of a Constitutive Modeling for Light Activated Shape Memory Polymer to Circular Shear

2012 ◽  
Author(s):  
Fangda Cui ◽  
I. J. Rao
Keyword(s):  
Shape Memory ◽  
Constitutive Modeling ◽  
Shape Memory Polymer ◽  
Shape Memory Polymers ◽  
Polymer Chains ◽  
Covalent Bonds ◽  
The Past ◽  
Original Shape ◽  
Multiple Natural Configurations ◽  
New Type

Shape memory polymers (SMP’s) are polymers that have the ability to retain a temporary shape, which can revert back to the original shape on exposure to specific triggers such as increase in temperature or exposure to light at specific wavelengths. A new type of shape memory polymer, light activated shape memory polymers (LASMP’s) have been developed in the past few years. In these polymers the temporary shapes are fixed by exposure to light at a specific wavelength. Exposure to light at this wavelength causes the photosensitive molecules, which are grafted on to the polymer chains, to form covalent bonds. These covalent bonds are responsible for the temporary shape and act as crosslinks. On exposure to light at a different wavelength these bonds are cleaved and the material can revert back to its original shape. A constitutive model of LASMP’s which based on the notion of multiple natural configurations has been developed (see Sodhi and Rao[1]). In this work we use this model to analyze the mechanical behavior of LASMP’s under a specific boundary value problem, namely, the problem of circular shear. We use this model problem to study the behavior of the LASMP’s when a temporary configuration is formed by exposing the polymer to light. In addition we show that these materials are able to undergo complex cycles of deformation due to the flexibility with which these temporary configurations can be formed and removed by exposure to light.

Modeling the Circular Shear in Light Activated Shape Memory Polymers With Three Networks

2013 ◽  
Author(s):  
Fangda Cui ◽  
I. J. Rao
Keyword(s):  
Shape Memory ◽  
Deformation Process ◽  
Shape Memory Polymer ◽  
Shape Memory Polymers ◽  
Polymer Chains ◽  
Covalent Bonds ◽  
The Past ◽  
Original Shape ◽  
Multiple Natural Configurations ◽  
New Type

Shape memory polymers (SMP’s) are polymers that have the ability to retain a temporary shape, which can revert back to the original shape on exposure to specific triggers such as increase in temperature or exposure to light at specific wavelengths. A new type of shape memory polymer, light activated shape memory polymers (LASMP’s) have been developed in the past few years. In these polymers the temporary shapes are fixed by exposure to light at a specific wavelength. Exposure to light at this wavelength causes the photosensitive molecules, which are grafted on to the polymer chains, to form covalent bonds. These covalent bonds are responsible for the temporary shape and act as crosslinks. On exposure to light at a different wavelength these bonds are cleaved and the material can revert back to its original shape. A constitutive model of LASMP’s which based on the notion of multiple natural configurations has been developed (see Sodhi and Rao [1]). It has been applied to model the circular shear of light activated shape memory polymer with two networks. In this work we use this model to analyze the mechanical behavior of LASMP’s with three different networks undergoing a circular shear deformation cycle. This involves study of the behavior of the LASMP’s when two temporary configurations are formed by exposing the polymer to light at different time during the deformation process. In addition, we show that these materials are able to undergo complex cycles of deformation due to the flexibility with which these temporary configurations can be formed and removed by exposure to light.

Modeling the Mechanics of Crystallizable Shape Memory Polymers With Two Crystallizing Phases for Crystallization Under Constant Strain

2012 ◽  
Author(s):  
Swapnil Moon ◽  
I. Joga Rao
Keyword(s):  
Shape Memory ◽  
Crystalline Phase ◽  
Smart Materials ◽  
Phase 1 ◽  
Polymer Networks ◽  
Shape Memory Polymers ◽  
Original Shape ◽  
Aerospace Technology ◽  
Multiple Natural Configurations ◽  
External Stimuli

Shape Memory Polymers are a promising class of smart materials with applications ranging from biomedical devices to aerospace technology. SMPs have a capacity to retain complex temporary shapes involving large deformations and revert back to their original shape when triggered by external stimuli such as heat. Crystallizable SMPs are a subclass of SMPs where the transient shape is retained by formation of a crystalline phase and return to the original shape is due to melting of this crystalline phase [1]. Recently CSMPs with multiphase polymer networks containing two different crystallizable segments have been reported which have the capability to switch between three shapes when stimulated by changes in temperature [2,4]. These properties open up many new possibilities for applications. Our research is focused upon modeling the mechanics associated with these CSMPs. The model is developed using a framework based upon theory of multiple natural configurations [3]. The developed model is then used to simulate results for typical boundary value problems.

Modeling and Simulation of Structurally Dynamic Crystallizable Shape Memory Polymers With Light-Induced Bond Exchange Reaction

2015 ◽  
Author(s):  
Fangda Cui ◽  
I. Joga Rao ◽  
Swapnil Moon
Keyword(s):  
Shape Memory ◽  
Exchange Reaction ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Shape Memory Polymers ◽  
Infrared Light ◽  
Covalent Bonds ◽  
Thermally Induced ◽  
New Class ◽  
Original Shape

Shape Memory polymers (SMPs) is a novel class of smart polymeric materials that have been attracted tremendous scientific interest within the last decades. SMPs have the ability to “remember” their original shape even after undergoing significant deformation into a temporary shape. For most first generation of SMPs, the shape memory effect was accomplished by a thermally induced process, triggered in many different ways, such as heating/cooling, electromagnetic field and infrared light. The transient shape in thermally induced SMPs is due to a glassy phase or a semi-crystalline phase. The thermally induced SMPs which temporary shape is fixed through crystallization is called crystallizable shape memory polymers (CSMPs). For traditional CSMPs, their original shape is predefined and is not able to be reprogrammed. This limits the applications of the CSMPs. Recently, a new class of CSMPs has been developed. These materials can perform a typical thermally induced shape memory cycle, but their original shape can be reprogrammed through exposing to UV light. The shape reprogramming effect is governed by light induced covalent bonds exchange reaction, while the shape memory effect-as typical CSMPs-is due to solid-phase crystallization. In this work, we focus on modeling the mechanical behavior of this new class of structurally dynamic CSMPs. The framework used in developing the model is built upon the theory of multiple natural configurations[1]. The model has been applied to solve a specific boundary condition problem, namely uni-axial tension. Furthermore, we implement our model through Abaqus (commercial finite element package) subroutine UMAT to simulate 3D behavior of this attractive material.

Shape Memory Polymers: Viscoelastic Thermomechanical Constitutive Modeling

2014 ◽  
Author(s):  
Olaniyi A. Balogun ◽  
Changki Mo
Keyword(s):  
Constitutive Model ◽  
Shape Memory ◽  
Stimulus Change ◽  
Viscoelastic Model ◽  
Engineering Application ◽  
Shape Memory Polymers ◽  
Recovery Process ◽  
Elastic Stiffness ◽  
Molecular Architecture ◽  
Strain Storage

Shape memory polymers (SMPs) are known to change their elastic stiffness as they respond to change in induced stimulus such as temperature. Under appropriate loading and pre-deformation, a shape memory effect can be captured as the stimulus change. From the nature of polymers, the pre-deformation can tend to be large and can in turn be memorized by SMPs. Due to this characteristic of SMPs, it makes a great candidate for morphing structures. To analyze complex structures a simple but yet practical constitutive model needs to be developed for commercial engineering application. In this paper, a thermomechanical constitutive model is proposed making use of the standard linear viscoelastic model. The total strain during the shape memorization process is defined by mechanical, thermal and storage strains. The rheological model defined is an elastic element in parallel with a Maxwell element, which in turn are both in series with storage and thermal element. Inclusion of a storage strain within the model reveals the internal strain storage mechanism as the temperature of the material drops. Similar work done in the past requires material parameters that can be arduous to determine in the laboratory. This model proposes a simplified approximate material parameter called a binding factor which accounts for the polymer’s molecular architecture and morphology as the temperature changes. Finally, the model is applied to a four step shape memorization and stress-free recovery process. For this study, the four steps considered are a) Pre-loading of the material at high temperature b) Constant strain fixity c) unconstrained relaxation at low temperature d) unconstrained free strain recovery. The developed model is validated by comparing the predictions to experimental results in literature.

Shape Memory Polymers: Energy Method Superposition Constitutive Modeling

2014 ◽  
Author(s):  
Olaniyi A. Balogun ◽  
Changki Mo
Keyword(s):  
Free Energy ◽  
Constitutive Model ◽  
Shape Memory ◽  
Energy Function ◽  
Shape Memory Polymers ◽  
Rate Of Change ◽  
Free Energy Function ◽  
Molecular Architecture ◽  
Binding Factor ◽  
The Individual

Shape memory polymers (SMPs) have the capacity to stored strain energy under appropriate stimulus and pre-deformation conditions. Temperature is a good stimulus and predominantly used to activate the shape memory effects of SMPs. Complex engineering application use of SMPs are being developed or proposed and it becomes imperative to develop a simple but yet practical constitutive model that will capture the deformation and recovery of SMPs appropriately under different constraints and loading conditions. In this study, a thermo-mechanical constitutive model is developed for SMPs. A four step shape memorization and recovery is considered and a thermo-mechanical energy balance (first principles of thermodynamics) is done on the individual steps. For this study, the four steps considered are a) Pre-loading of the SMP at high temperature b) Constant strain at negative rate of change of temperature c) constraint release and shape fixity at low temperate and d) unconstrained free strain recovery. A free energy function is developed for the individual steps and superposition principle is used to define the storage free energy in the third step. Applying the second law of thermodynamics in Clausius-Duhem form, the stress-strain relation was developed. Also, in order to account for the polymer’s molecular architecture and morphology resulting in shape memory effect, a binding factor was approximately defined. The binding factor is primarily a function of temperature and secondarily a function of the viscosity of the material at high and low temperatures. The storage strain was assumed to be an internal variable that is generated from the mechanical loading of the SMP. The general model is reduced down to a specific viscoelastic model based on the assumption of the free energy function. The developed model is validated by comparing the predictions to experimental results in literature.

Tissue Integration of Two Different Shape-Memory Polymers with Poly(ε-Caprolactone) Switching Segment in Rats

2008 ◽  
Author(s):  
Bernhard Hiebl ◽  
Dorothee Rickert ◽  
Rosemarie Fuhrmann ◽  
Friedrich Jung ◽  
Andres Lendlein ◽  
...  
Keyword(s):  
Shape Memory ◽  
Shape Memory Polymers ◽  
Tissue Integration
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