Morphological transitions in polymer monolayers under compression

Srivastava, S and Basu, JK and Sprung, M and Wang, J (2009) Morphological transitions in polymer monolayers under compression. In: Journal of chemical physics, 130 (17).

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Abstract

We present a systematic investigation of morphological transitions in poly vinylacetate Langmuir monolayers. On compression, the polymer monolayer is converted to a continuous membrane with a thickness of similar to 2-3 nm. Above a certain surface concentration the monolayer, on water, undergoes a morphological transition-buckling, leading to formation of striped patterns of period of lambda(b)similar to 160 nm, as determined from in situ grazing incidence small angle x-ray scattering measurements. The obtained value is much smaller than what has been typically observed for Langmuir monolayers on water or thin films on soft substrates. Using existing theories for buckling of fluidlike films on fluid substrates, we obtain very low values of bending rigidity and Young's modulus of the polymer monolayer compared to that observed earlier for lipid or polymeric monolayers. Since buckling in these monolayers occurs only above a certain surface concentration, we have looked at the possibility that the buckling in these films occurs due to changes in their mechanical properties under compression. Using the model of Huang and Suo of buckling of solidlike films on viscoelastic substrates, we find values of the mechanical properties, which are much closer to the bulk values but still significantly lower. Although the reduction could be along the lines of what has been observed earlier for ultrathin polymer film or surface layers of polymers, the possibility of micromechanical effects also determining the buckling in such polymer monolayers cannot be ruled out. We have provided possible explanation of the buckling of the poly vinylacetate monolayers in terms of the change in isothermal compression modulus with surface concentration.

Item Type:	Journal Article
Publication:	Journal of chemical physics
Publisher:	American Institute of Physics
Additional Information:	Copyright for this article belongs to American Institute of Physics.
Keywords:	bending; buckling; Langmuir-Blodgett films; monolayers; polymer films; solid-state phase transformations; viscoelasticity; X-ray scattering; Young's modulus
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	11 Dec 2009 11:11
Last Modified:	19 Sep 2010 05:34
URI:	http://eprints.iisc.ac.in/id/eprint/20840

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