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I recently read a paper by Lyulin et al. [1] where they talk about thin films and bulk polymers, I just don't quite understand what they mean by "bulk". Can someone please explain?

References

  1. Lyulin, A. V.; Balabaev, N. K.; Baljon, A. R. C.; Mendoza, G.; Frank, C. W.; Yoon, D. Y. Interfacial and Topological Effects on the Glass Transition in Free-Standing Polystyrene Films. The Journal of Chemical Physics 2017, 146 (20), 203314. https://doi.org/10/ggcghf.
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I think the meaning of the word "bulk" — as it is used in English language — is preserved here despite chemical context. I suspect that it's been used to stress some aspects or features of the surface chemistry: thin film is a 2D object, whereas bulk polymer is a 3D object (e.g. continuous in three directions) possessing a significant volume.

From IUPAC's Compendium of polymer terminology and nomenclature [1, p. 199]

3.12 continuous phase domain
matrix phase domain

Phase domain consisting of a single phase in a heterogeneous mixture through which a continuous path to all phase domain boundaries may be drawn without crossing a phase domain boundary.
Note: In a polymer blend, the continuous phase domain is sometimes referred to as the host polymer, bulk substance, or matrix.

More general from McGraw-Hill dictionary of chemistry [2, p. 171]:

gross sample [ANALY CHEM] One or more increments taken from a larger quantity of a material that is to be analyzed. Also known as bulk sample […]"

Gooch's Encyclopedic Dictionary of Polymers [3, p. 98] keeps it even simpler:

Bulk Material n A material or product in large quantity such as a drum or sack.

References

  1. IUPAC “Purple Book” Compendium of Polymer Terminology and Nomenclature; International Union of Pure and Applied Chemistry, Jones, R. G., Eds.; RSC Pub.: Cambridge, 2009. ISBN 978-0-85404-491-7.
  2. McGraw-Hill Dictionary of Chemistry, 2nd ed.; McGraw-Hill: New York, 2003. ISBN 978-0-07-141046-5.
  3. Encyclopedic Dictionary of Polymers; Gooch, J. W., Ed.; Springer New York: New York, NY, 2011. https://doi.org/10.1007/978-1-4419-6247-8.
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  • $\begingroup$ Yes it means a piece of polymer having almost comparable xyz dimensions. It is important as for a lot of properties of thin and very thin films differs from those within a big piece of solid. Sometimes it is said that thin films are a further state of the matter. *This is dictated - as the answer suggests - by characteristics of the surface weighing more or, sorry but it even helps, of the "bulk" within the film. The polymer/material arrangement might be dictated by the interaction with the substrate if any. Also the process used for casting might lead to out of equilibrium frozen states. +1 $\endgroup$ – Alchimista Nov 6 '19 at 9:20
  • $\begingroup$ In this case. Otherwise there is bulk polymerisation, bulk as in bulk chemicals, etc. $\endgroup$ – Alchimista Nov 6 '19 at 9:50
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I agree with the interpretation given by andselisk. The authors wish to differentiate thin films vs. bulk of the same polymeric material. One of meanings of bulk given in the unabridged Oxford English Dictionary [by subscription] is

Magnitude in three dimensions; volume.

1825 J. R. McCulloch Princ. Polit. Econ. ii. ii. 141 They [gold and silver] possess great value in small bulk. 1878 T. H. Huxley Physiogr. (ed. 2) 57 Sea water is denser or heavier, bulk for bulk, than fresh water.

For example, when the authors say:

Our studies reveal that the fraction of the chain-end groups is larger in the interfacial layer with its outermost region approximately 1 nm below the surface than it is in the bulk.

You can interpret that as "Our studies reveal that the fraction of the chain-end groups is larger in the interfacial layer with its outermost region approximately 1 nm below the surface than it is in the three dimensional body of the [polymer]."

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