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  Solution Properties of Polymers, Chemistry tutorial

Introduction 

Liquid crystals when heated have structure of solids but by freedom of movements as in liquids at sharp transition temperatures. The dissimilar alignments of liquid crystal molecules are responsible for the diverse orders. Such solution properties are used in our modern electronic devices as calculators, cellular phones, laptops, mobile media players

Main content 

Solids usually pass openly from solid to liquid phase on heating. Instead of this several substances as polymers when heated pass through an intermediate liquid crystalline phase that has structure of solids but by freedom of movements as in liquids. The partial orderliness in it makes it extremely viscous and has properties of both liquid and solid phases. Region in which they exhibit above property is marked via sharp transition temperature. We will be considering molecular principles of liquid crystals through special optical properties. 

F. Reintzer a botanist the year (1888) was the 1st to examine this while handling organic compound: cholesteryl benzoate, which on heating melted at 1450C to a viscous milky liquid. But on reaching 1790C the liquid became clear. On cooling it repealed. For example it turns viscous and milky at 1790C, while the liquid solidifies at 1450C. Today this phenomenon is termed 'liquid crystal'. Most of our modern electronic devices are depends on these technologies: liquid crystal displays (LCDs) and light-emitting diodes (LEDs). 

The principles liquid crystal operates 

For polymers, they pass through intermediate liquid crystalline phase that has both structures of solids in addition to freedom of motion as liquids; it can be accounted for via their partial ordering, therefore the sharp conversion temperature they have. The weak intermolecular forces, which hold the molecule mutually in liquid crystal, are simply affected via temperature, pressure and electrical field changes. There are different kinds of the liquid crystalline phases, depending on the orientation and alignments. Polymers have long, elongated, rodlike molecules, through polar groups atimes [for example C=O, C=N, COOH, R-O-R, OH, CONH, C-X]; therefore by intermolecular forces [H-bondings, van der Waals forces and dipole-dipole attractions]. In ordinary situation polymers are oriented randomly. [NB: Lengths of the molecules are greater than their widths]. But the liquid crystalline phases have dissimilar orderings. The different alignments of liquid crystal molecules are responsible for the different orders. They can be demonstrated therefore:                                                                                                      

844_The principles liquid crystal operates.jpg

Fig: The principles liquid crystal operates

Nematics have its molecules in one dimensional ordering, aligned along their long axes as handful of pencils by non-aligned ends. Smetic molecules have 2 dimensional orderings; molecules are aligned along their long axes and in layers. Molecules of cholesteric are in successive layers. Their orientation is at trait angles to adjacent layers, therefore no repulsive interactions and provides a screwlike axis.

Some importance and applications of solution properties of polymers

The liquid crystal displays (LCDs) in several of our modern electronic devices as calculators, cellular phones, laptops, mobile media players employ the solution property. They have wide applications in temperature and pressure sensors in addition to displays of electrical devices of the above mentioned and wireless devices. They are utilized in monitoring devices for example the cholesteric liquid crystal is utilized in monitoring temperature changes in situations where conventional techniques aren't possible. Like taking skin temperature of infants; detecting hot spots in micro-electronic circuits that can signal presence of flaws. 

Some molecules of liquid crystals

 (i)

1852_Changes between solidification-viscous liquid.jpg

CH3O CH N C4H9 [Changes between solidification-viscous liquid] at 21-470C 

(ii) 

905_CH3 (CH2)7 O COOH.jpg

CH3 (CH2)7 O COOH   [Changes between solidification-viscous liquid] at 108-1470C

(iii) Dow Industrial Specialty Polymers in Electronics Applications Activity A: Discover details of (iii) Dow Industrial Specialty Polymers in Electronics Applications 

More examples

(i) Solutions of the polymer polyvinyl alcohol (PVA) and polyvinyl acetate can be made into gels via addition of a borax solution. Borax cross-links the polymer chains, to provide interesting properties of gels. 

(ii) 'Slime' is a polyvinyl alcohol polymer. 

(iii) 'Glue' is a polyvinyl acetate polymer.

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