/pdf/honeycomb-carbon-a-review-of-graphene-bjl5wl6ai8.pdf

Honeycomb Carbon: A Review of Graphene

Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.

Graphene: The New Two-Dimensional Nanomaterial

Biomaterials have played an enormous role in the success of medical devices and drug delivery systems. We discuss here new challenges and directions in biomaterials research. These include synthetic replacements for biological tissues, designing materials for specific medical applications, and materials for new applications such as diagnostics and array technologies.

Designing materials for biology and medicine

A review of shape memory alloy research, applications and opportunities

Graphene oxide: preparation, functionalization, and electrochemical applications.

Shape-memory polymers

The thermally-induced shape-memory effect (SME) is the capability of a material to change its shape in a predefined way in response to heat. In shape-memory polymers (SMP) this shape change is the entropy-driven recovery of a mechanical deformation, which was obtained before by application of external stress and was temporarily fixed by formation of physical crosslinks. The high technological significance of SMP becomes apparent in many established products (e.g., packaging materials, assembling devices, textiles, and membranes) and the broad SMP development activities in the field of biomedical as well as aerospace applications (e.g., medical devices or morphing structures for aerospace vehicles). Inspired by the complex and diverse requirements of these applications fundamental research is aiming at multifunctional SMP, in which SME is combined with additional functions and is proceeding rapidly. In this review different concepts for the creation of multifunctionality are derived from the various polymer network architectures of thermally-induced SMP. Multimaterial systems, such as nanocomposites, are described as well as one-component polymer systems, in which independent functions are integrated. Future challenges will be to transfer the concept of multifunctionality to other emerging shape-memory technologies like light-sensitive SMP, reversible shape changing effects or triple-shape polymers.

/pdf/multifunctional-shape-memory-polymers-11fu0v0rum.pdf

Multifunctional Shape-Memory Polymers

Shape-memory polymers are stimuli-responsive materials. Upon exposure to an external stimulus, they have the capability of changing their shape. A change in shape initiated by a change in temperature is called thermally induced shape-memory effect. The shape-memory effect results from the polymer's structure, that is, its morphology in combination with a certain processing and programming technology.



The polymer is processed into its permanent shape by conventional methods. Afterwards, it is deformed and the desired temporary shape is fixed. The latter process is called programming. Heating the programmed polymer above a temperature higher than the transition temperature Ttrans results in activating the shape-memory effect. As a consequence, the recovery of the memorized, permanent shape can be observed. The described effect is called a “one-way” shape-memory effect.



The shape-memory effect can be quantified by cyclic thermomechanical investigations. Important quantities describing the shape-memory properties of the material for a certain strain ɛm are the strain recovery rate Rr and the strain fixity rate Rf. The strain recovery rate Rr quantifies the ability of the material to memorize its permanent shape. The strain fixity rate Rf describes the ability of the material to fix the mechanical deformation ɛm which has been applied during the programming process.


Keywords:

block copolymers;
elastomers;
networks;
shape-memory polymers;
stimuli-sensitive polymers;
structure–property relations

Shape-Memory Polymers

Free-standing copolymer network samples with two types of crystallizable domains are capable of a fully reversible bidirectional shape-memory effect. One set of crystallizable domains determines the shape-shifting geometry while the other provides the thermally controlled actuation capability.

Reversible bidirectional shape-memory polymers.

Polymeric materials are clinically required for medical devices, as well as controlled drug delivery systems. Depending on the application, the polymer has to provide suitable functionalities, for example, mechanical functions or the capability to actively move, so that an implant can be inserted in a compact shape through key-hole incisions and unfold to its functional shape in the body. Shape-memory polymers, as described herein regarding their general principle, compositions and architectures, have developed to a technology platform that allows the tailored design of such multifunctionality. In this way, defined movements of implants triggered either directly or indirectly, tailored mechanical properties, capability for sterilization, biodegradability, biocompatibility and controlled drug release can be realized. This comprehensive review of the scientific and patent literature illustrates that this technology enables the development of novel medical devices that will be clinically evaluated in the near future.

https://www.tandfonline.com/doi/pdf/10.1586/erd.10.8

Marc Behl

Papers

Shape-memory polymers

Multifunctional Shape-Memory Polymers

Shape-Memory Polymers

Reversible bidirectional shape-memory polymers.

Shape-memory polymers as a technology platform for biomedical applications