19th Century: The earliest models were very simple, as they suggested that lipid soluble substances entered cells faster than water soluble substances; scientists in those days had also figured out that the layers of lipid were layers of fat. However, the downfall of the evidence provided was that scientists back in the day were not able to provide information, as to how a lipid layer could remain stable in contact with the water surrounding the cell in its environment, since lipids are repelled by water.
20th century: Due to chemical analysis of isolated membranes, it was discovered that the membrane is largely made up of phospholipids and cholesterol. Digging deeper, it was revealed that phospholipids were amphiphilic: one head, which was soluble in water, and two tails, which would face inwards towards each other. This added to the bilayer remaining stable.
1934: A new model was proposed by Davson-Danielli, since the new model suggested both sides of the bilayer to be coated with water-soluble proteins. Therefore, through extensive chemical analysis, it was revealed that there was a lot of protein in the membranes. Even though membranes were thought to be more permeable to lipids than water, the membrane was able to absorb water faster than a pure phospholipid layer.
1970: Davson-Danielli’s model and theory was still accepted, since micrographs showed that membranes had a three-layered-structure.
Before the fluid-mosaic model: Due to advances in chemistry and biology, Davson-Danielli didn’t seem to explain coherently how such fluidity could occur without tearing or breaking bonds. Due to new chemical methods, it was stated that the proteins of membranes were highly variable in both quantity and type.
Sixty five years later: The fluid mosaic model was invented, which described the agreement of many scientists’ view on the cell membrane.