Russian chemists created polymer materials with a unique property – their rigidity or elasticity modulus gradually changes in given direction in such a way, that one side of material is a solid plastic and the other – soft rubber. Such materials are called “gradient materials”, and their elasticity modulus can change between 3 and 2000 megapascals within one piece of material without any layers or interfaces.

Traditional means for adjusting properties of polymer materials include their level-to-level alignment by means of expensive thermal sealing or glueing, which require high labour intensity, and resulting materials have weak interlayer adhesion.

Russian researchers suggested a curious technology for producing materials with controlled properties in given directions – synthesizing gradient polymer materials based on two polymers: a highly elastic and a glassy one. Moreover, this technology has nothing to do with simple mixing of two polymers, which cannot give gradual change in desired properties, but deals with synthesis of two types of cross-linked polymers, various concentrations of which can be found in the same material. These cross-linked polymers were first constructed via computer modeling, which allowed calculating their properties using their chemical structure and “virtually” synthesize polymers with desired properties. Later researchers performed real synthesis and investigated mechanical properties of new materials.

 

 

Gradient polymeric materials can work within temperature range of -50 - +330 degrees Centigrade without softening or decomposing. They show high durability, elasticity and wear resistance. New materials are promising for medicine, footwear industry, household appliances and various industrial enterprises. The laboratory has already started experimental production of orthopedic footwear, in which tension loads affect rubber part of a shoe, and plastic part accepts compression loads. The heel is rigid, but gets softer towards the toe.

As for medicine, gradient materials can be good implants, where rigid material imitates bone tissue, and soft material – cartilaginous tissue. Tests of new materials, which were performed on rabbits, showed reliability and good biocompatibility of gradient polymers.

Reinforced gradient polymers can be used in automotive and aeronautical engineering, in textile industry as rollers and gears, which are noiseless and almost non-wearing. Central part of such details is extremely rigid, and tooth area has low elasticity modulus.

Gradient materials can be good for building vibration-absorbing constructions, for instance bearings for various devices (radio equipment, household appliances and various instrumentation), which have elasticity modulus changing from rigid plastic to soft rubber along their width. A stand for any instrument, for instance, can be both elastic and rigid, thus being very easy to secure and requiring no shell. Secure mounting of a plastic part of stand to a device case helps expanding operation life, and a soft rubber part can dampen unwanted vibrations.

Source: Science & Life

Kizilova Anna