Russian physicists developed and tested a technique for making polymethylmethacrylate (known under trade name Plexiglas) surfaces smoother in nanometer and subnanometer range. The technique involves exposure to vacuum ultraviolet radiation with wavelength of about 124 nanometers.

Polymethylmethacrylate is a transparent thermoplastic, a polymer usually known as organic glass or Plexiglas and widely used in various fields of science and technology, in nano-electronics, for instance, as electron, ultraviolet and X-ray-sensitive resist, or as a construction material for electromechanical systems. Polymethylmethacrylate got a good account of itself in transplantology as a nontoxic biocompatible material for artificial human organs, like eye lenses, dental prostheses, bone cement and etc.

In order to fulfill various tasks, surface of Plexiglas should be modified according conditions, specific for each problem. One of important parameters is surface roughness in nanometer range, which affects operating characteristics of a polymer item. When polymethylmethacrylate film is used as a resist, surface thickness and irregularities are crucial factors in determining minimal size of an element after nanolithography. When Plexiglas works as a construction material, relief of rubbing surfaces would determine force of friction, therefore, energy losses due to friction and thermal deformation of a tiny mechanism. In microfluidic devices, surface of micro- and nano-channels specifies flow pattern and velocity of fluids, used in mentioned devices. In medicine, changing roughness of a transplant surface can result in enhanced biocompatibility of artificial organs.

 

 

Russian scientists suggested and already tested a technique for smoothing surfaces of polymethylmethacrylate by means of vacuum ultraviolet radiation with wavelength of about 124 nanometers. Since air is a good sorbing agent for ultraviolet radiation with wavelengths between 10-200 nanometers, the polymer is exposed to UV in vacuum. In this case, energy of falling photons is enough to break intermolecular bonds in Plexiglas. Moreover, ultraviolet launches a cascade of chemical reactions, caused by light photons – photolysis. Parts of polymer molecules and volatile photolysis products are constantly removed from working chamber by means of a vacuum pump. The whole lot of processes, taking place under UV irradiation, leads to smoothening of polymer surface defects of nanometer size. One of the main advantage o0f the technique is almost no heating of a sample, and modifications take place in a very thin surface layer of the polymer, without involving the whole bulk.

Scientists have also found a simple and convenient test-object for accurate registering of changes, which take place on Plexiglas surface after exposing it to vacuum ultraviolet radiation. This object is an extremely thin polymethylmethacrylate film, applied on a polished silicon plate by means of centrifugation and modified in oxygen radio-frequency plasma.

Source: Science & Technologies

Kizilova Anna