Physical chemistry of polymers

Thursday August 9th, 2012 Popov Anatoliy News, Articles No Comments

The role of polymers is so great in human life today that the standard of living can be judged by the level of consumption of these materials. UN experts predict that polymer production, including composite materials, will develop a faster pace compared to other materials. Hence, researchers take a tender interest in almost all sectors of polymer science, the range of problems of which is extremely broad and covers many areas of expertise.

Physical chemistry of polymers is one of the most important parts of modern polymer science and covers the following problems:

  • Development of the theoretical problems of reactions in polymer mixtures covers the flow conditions of macromolecular reactions, interdiffusion of components, changes in the composition and properties of the reaction mixture under the combined influence of macromolecular reactions and interdiffusion, phase separation of the components in an incompatible mixture, etc. The mechanism of chemical interaction of functional monomers with macromolecules is unclear when the reaction is performed in polymer alloys under the influence of unsteady heat and force fields. It is typical for a modern reaction processing. Theoretical problems related to electrical and thermal conductivity of organic polymers, as well as electroluminescence are purely physical.
  • Theoretical research in the field of physics of liquid-crystal polymer systems, as well as studies on the generation of liquid-crystal order in polymer systems is very essential.
  • Progress in the field of heterogeneous polymer composite materials is not possible without further development of physical and chemical understanding of phase-boundary phenomena in polymer-solid systems (including hard non-polymer ultrafine particles that are prone to cluster formation), as well as polymer-polymer and polymer-liquid systems.
  • One of the challenges of physical chemistry of polymers is the use of theoretical concepts and experimental techniques developed for the analysis of natural systems in order to establish a correlation between structure and properties. As a result, we are to find an answer to the question: how do complex biocomposite structures operate, and make a contribution to the evolution of our understanding of the laws of nature.

Largely through the efforts of physicists, physical chemists and specialists on polymers a curtain on understanding the structure of biocomposites has been slightly opened. Thus, three rules for complex macromolecular assemblies have been formulated.

The first rule says that the structure of a composite is based on the principle of discrete levels or scales. Experiments show that the minimum number of sub-levels in bioobjects is never less than four. It is found that all biocomposite systems have four structural sub-levels: molecular, nano-, micro- and macroscopic scale.

The second rule states that the different structural levels are maintained in a compact form due to specific interactions between the components. Whatever the nature of the relationships between the elements of the structure is, a sufficient level of adhesion including mechanical nature is required to ensure the integrity and efficiency of the entire system.

The third rule refers to the fact that these strongly interacting with each other structural sub-levels are organized in a composite system of complex hierarchy so as to satisfy a wide range of functional requirements, which in some cases have to be adaptive.

Properties of materials with complex hierarchical structure to a large extent depend on the formation of interfaces between elements of different size and composition. Electronic images of mollusk shell nacre show that it is a complex composite. Thin interlayers of ultra-thin layers of complex aminopolysaccharide coated with protein are observed between thick layers of aragonite (calcium carbonate).

The above mentioned puff structures typical for bioobjects can be obtained at the stage of polymer processing, for example by the method of coextrusion.

When layers have a relatively great thickness (49 layers), the material is destroyed immediately after crossing the yield point, indicating that the dominant role is played by the more fragile PSAN – component. However, when the fibers are small enough (776 layers), the system is able to stretch considerably after necking indicating that the more ductile PC plays a crucial role in the process. The reason for this transformation of the process determined only by the layer thickness can be obtained from the analysis of microstrain (crazing) processes that control the ability to stretch.

Wide spectrum of problems is covered by rapidly developing supramolecular chemistry. One of the issues is the implementation of the transition from molecular chemistry to molecular and supramolecular devices.

The creation of such devices should include, at least, three main stages:

  • Design and synthesis of organic molecules carrying a specific function. It is the task of molecular chemistry, which is responsible for the organization of individual atoms, binding them together and locating them in a certain way relative to each other in order to give a desired spatial structure to the molecule.
  • Establishment of organized multimolecular ensembles. Obviously, the available technologies of orientation of polymer materials, such as stretching, crystallization and orientation in the flow are not suitable for derivation of molecular-sized ensembles. This problem is solved in other ways, primarily by self-assembly and forced organization. Spontaneous formation of the double helix of nucleic acids which includes the recognition and selective base-pairing is a classic example of self-assembly. Creation of molecular (supramolecular) devices. To acquire the status of a device, the molecular structure must be able to perform a specific function.

There are solutions known at a higher scale level, such as in the existing storage and information processing devices, using only one physical effect. The tendency towards miniaturization of electronic devices down to the molecular ones entails the problem of implementation and integration of various physical effects in one device. Being limited only by the “tunnel security,” which sets the distance between key – molecules of 5 – 10 nanometers, the technology would allow packing of molecular electronic components with the density of 1018 units per 1 cm³.

ТThus, to create molecular devices it is necessary to search for molecular components that can perform a given function and are suitable for implementation in a certain way into an organized system, formed by different types of molecular assemblies. The main feature of such components and devices is that they function on the basis of the properties of molecules and supramolecules/

The use of organic polymeric photoconductors in electrophotography is the first and for the moment the only example of a large-scale industrial use of these polymers as materials with unique electronic properties. Suffice to say that at present most copiers, laser printers and other electrophotographic devices use organic polymeric photoreceptors as the main active element.

Despite a large number of experimental and theoretical works on electron transport in dielectric polymers published in recent years, there is still no widely accepted theoretical model. In the problem of electron transport in disordered organic dielectric layers two subjects are closely interwoven. First is an interest in the fundamental issues – the mechanism of electron transfer between identical centers in the organic medium, the effect on the transfer of physical and chemical characteristics of the environment, the formation of the recombination excited states emitting light – and, secondly, the need to maximize the electrical and light-emissive parameters of organic layers in widely used and newly developed optoelectronic devices. Understanding, describing and modeling of a complex of these processes will help to have new interesting scientific and practical results and accelerate the development of the problem as a whole.

Laboratory of filtering technology “Cribrol” has been for more than 10 years carrying out a research in the practical application of composite materials in various industries. Introduction of innovations at enterprises by our company brings not only economic benefits associated with a decrease in the cost of energy processes, supplies, improvement of the quality of products, etc., but also simplifies the production cycle, and cares about the environment.

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