Hello Ershad,

A membrane is essentially a thin film but it is often used in the field of biology when one talks about the cells. A membrane is any layer or boundary that separates the interior of the cells from the external environment. Thickness of a cell membrane is usually 3-9nm. So a thin film is something when we talk about a planar geometry like a very thin layer of oil on water whereas a membrane is used for 3d objects such as living cells, balloon, where we want to segregate 2 regions essentially. Hope that makes some sense to you.

Regards,

Vinita

Dear Vinty,

Nice to get your answer. But, a membrane not only used in biology field but there is a lot of membrane based applications in chemical/polymer industry as well, like membrane based gas separation, pervaporation, proton exchange membrane for fuel cells etc. Actually i'm working on Proton exchange membrane and noticed that in some of the journal, authors are using the term "thin film" whereas maximum authors are using the term "membrane". Our membranes(free standing) are usually 40-80 nm in thickness and we are using the term "membrane" although it needs plannar geometry for membrane-electrode assembly. I apprieciate  your answer but expect more clear answer from the scintific community. As per my understanding, generally a thin film need some substrate over which it can form (like SiC or, ZnO thin film over glass substrate)  whereas a membrane generally means a "free standing" or "stand alone film".

Appreciate your clarification. Thanks Ershad.

Dear Ershad

Anisotropic membranes consist of an extremely thin surface layer (Thin Film)

supported on a much thicker, porous substructure.

and this thin layer to increase the rejection of salt ions

thanks Obaid...

Membrane is the thin film that must be have some characteristics such as suitable pore size, pores distribution  and chemical selectivity to a one compound.

Dear Ershad, also in my opinion membrane and thin films are eqivalent terms. Your efforts to give a different means respect to their condition of freestanding,  it is not totally correct: in gas separation membranes technology, is ordinary speak  of "composite membrane" for membrane with support, that, obviously, are not freestandig. Anyway I thank you for your questions becasue the matter is not so clear

Many thanks Giuseppe...

Dear Ershad, I've to correct myself: Some definition from Goldbook IUPAC Compendium of Chemical Terminology:

MEMBRANE

Structure, having lateral dimensions much greater than its thickness, through which transfer may occur under a variety of driving forces.

Source:

PAC, 1996, 68, 1479 (Terminology for membranes and membrane processes (IUPAC Recommendations 1996)) on page 1482

FILM

A generic term referring to condensed matter restricted in one dimension.

Source:

PAC, 1994, 66, 1667 (Thin films including layers: terminology in relation to their preparation and characterization (IUPAC Recommendations 1994)) on page 1671

THIN FILM

Also contains definition of: thick film

A film whose thickness is of the order of a characteristic scale or smaller. Since a film may 'look' operationally thin or thick, according to the procedure applied, it is also recommended that the measurement procedure employed be specified (e.g. ellipsometrically thin film, optically thin film, etc.). It is recommended that the physical specification of the film thickness be used, whenever possible (e.g. thick compared to the electron mean free path, thin compared to the optical wavelength,

etc.)

Source:

PAC, 1994, 66, 1667 (Thin films including layers: terminology in relation to their preparation and

characterization (IUPAC Recommendations 1994)) on page 1672

Following this defintion Membrane, IS NOT EQUIVALENT TO THIN FILMS. Respect to thin film, membrane has to be a medium through which some transfert

Giuseppe

Many thanks Giuseppe... Nice to see your answer.. Now it is clear to me...

depending on its application: through the polymeric film is there mass flow? in this case is more appropriate called membrane

Dear Ershad Ali Mistri,

The difference between membrane and thin film are

Membranes are permeable

Thin films are not permeable

please tell the difference between thin film and thick film technology.