When any substance which takes the shape and conforms of the container in which it’s kept without necessarily filling it is said to be in liquid state. Water at atmospheric pressure could exist as a liquid below zero degree C which is its normal freezing point.
Water is super cooled when this happens and similarly water could be heated beyond 100 C degree and we aptly call this as super heated water. We need to take precaution of not allowing super cooled water to freeze and super heated water to boil. The suspended impurities and vibrations and other irregularities on the walls of the container could trigger the appearance of a new phase.
The super cooled or super heated water exists in a state of precarious equilibrium. We could expand the range by removing suspended or dissolved impurities and by minimizing contact with the rough bounding surface. The extraneous impurities merely facilitate what the spontaneous molecular motion can accomplish slowly and drive the system towards a condition of greater stability through the formation of a new phase.
If we raise the temperature of a solid it will commonly become liquid and then on further heating it will evaporate to become a gas and while in this sequence of states the liquid is the intermediate state between solids and gaseous states.
The intermediate position is a reflection of the fact that the arrangement of atoms or molecules in a liquid is intermediate between the crystalline order of the solid state and the random molecular motions of the gaseous state.
The most properties of liquids could be understood by explanations that begin by saying that liquids are similar to solids but are more disordered and less dense. It could be stated that liquid atoms are similar to gaseous ones but more ordered and much denser.
Properties of Liquids are:
- Critical temperature: to turn a gaseous material into a liquid state material, the temperature is brought below the boiling temperature. This apart the other method would be to increase the pressure on the gaseous materials
- Critical pressure: liquids reach a boiling temperature when the vapour pressure of the material is equal to the surrounding pressure of the liquid system
- Surface tension: the liquid molecules have a force of attraction in between. This force becomes maximum when the liquid stops flowing and take the appropriate shape which maximises this force. The force of cohesion in between the molecules is found to be same all across while the liquid surface the net attraction force keeps them inside the liquid when the liquid occupies smallest surface area. The force magnitude which manages the shape of liquid is better known as surface tension. This magnitude grows as bonds in between the liquid becomes larger.
- Viscosity: it is a measure the resistive force which acts against the flow of liquid. This is calculated when a liquid flows into a glass tube of a certain cross section at a specific rate. The water viscosity is about 1 centipoise whereas gasoline has 0.4 – 0.5 centipoise.
The reason the liquid has a variable shape is due to the movement of particles and liquid will tend to flow filling the containers lowest portion, take the shape of the container but the volume doesn’t change. The limitation of space between the liquid particles also specifies that it cannot be compressed.
- The attraction that exists between similar kinds of particles is known as cohesion. The cohesive force is responsible for the liquids surface tension. It works as a skin and they are strongly attracted to each other rather than the particles around them. These are strong attraction force unless disturbed.
- The particles in any liquid state are in constant motion and keep colliding against the wall of the container as well as against each other. These results in energy transfer from one particle to next and this value eventually overcome the surface tension and escape after gaining enough kinetic energy.
- The property of volatility is nothing but the tendency to show how quickly a substance will vaporize at room temperature. In case we are looking at a very high volatile substance then it might go through sublimation at normal temperature. If the process takes place within a closed system then the evaporated particles will not escape and once the kinetic energy of these particles is lost it condenses back into the liquid.
Liquid crystal science and applications now spread across all segments ranging from industrial display to individual homes and many office spaces. The non-display applications in non-linear optics, optical communication along with data signal or images processing.
- The feature sizes have shrunk from microns to nano meters, while optical non linearity like refractive index coefficients have enhanced from 10-3 to 103 per cm2.
- Liquid crystals are wonderful materials and exhibit intermediate phase where they flow like liquids and yet possess the physical attributes of a crystals.
- Materials showing these unusual phases are termed as mesogens and since they could exist in various phases they are termed mesophase
- As a function of temperature or depending on the constituents, concentration, substituents etc. these liquids crystals exist in many so called mesophase like nematic, smectic or cholesteric.
- These are basically aromatic rings and include saturated cyclohexane or unsaturated phenyl or biphenyl in various combinations
- Many of the liquid crystals are benzene derivatives and apart from these there are hetero-cyclics, organometallics, sterols and other organic salts or fatty acids.
- The set of physical and optical properties are governed by the constituent groups and also on how these chemically synthesized together
- Since the molecules are quite large and anisotropic, they are not treated for molecular structural architecture in same manner which leads to different set of physical properties.
Any liquid matter would will evaporate at a temperature below its boiling point and this process continues till the gaseous phase matter reaches equilibrium after condensation. The rate of condensation and rate of evaporation is same at the point of equilibrium. A liquid when reaches its boiling point will evaporate quicker than the gas could condense at the given pressure.
At any temperature below the point of freezing a liquid tends to crystallise and change into a solid state. The transition to gas is quite different than changing into a solid state where there is no equilibrium in a given pressure and hence unless the liquid super cools the liquid will turn into a crystal. Liquid solutions:
Liquids could also show immiscibility and any immiscible solutions can be separated by fractional distillation or with the help of separating funnel. Example would be water and toluene.