Polymer Monolayer Dynamics

Esker, Alan R.; Kim, Chan-Joong; Yu, Hyuk

doi:10.1007/12_2007_113

Cited by 24 publications

(35 citation statements)

References 108 publications

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“…When compressed, a ''stable'' monolayer (formed by polymers possessing an ''amphiphilic'' character) transforms into a multi-molecular layer. 3 Using the Langmuir film balance technique, the surface/ interfacial tension of a Langmuir polymer monolayer can be measured as a function of the monolayer area. The surface/ interfacial tension (g) is defined as the amount of free energy required to increase the surface/interface area by a unit amount at constant temperature and pressure, that is, g ¼ @G @A T;P .…”

Section: Introductionmentioning

confidence: 99%

Humidity-dependent compression-induced glass transition of the air–water interfacial Langmuir films of poly(d,l-lactic acid-ran-glycolic acid) (PLGA)

et al. 2015

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Constant rate compression isotherms of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA) show a distinct feature of an exponential increase in surface pressure in the high surface polymer concentration regime. We have previously demonstrated that this abrupt increase in surface pressure is linked to the glass transition of the polymer film, but the detailed mechanism of this process is not fully understood. In order to obtain a molecular-level understanding of this behavior, we performed extensive characterizations of the surface mechanical, structural and rheological properties of Langmuir PLGA films at the air-water interface, using combined experimental techniques including the Langmuir film balance, X-ray reflectivity and double-wall-ring interfacial rheometry methods. We observed that the mechanical and structural responses of the Langmuir PLGA films are significantly dependent on the rate of film compression; the glass transition was induced in the PLGA film only at fast compression rates. Surprisingly, we found that this deformation rate dependence is also dependent on the humidity of the environment. With water acting as a plasticizer for the PLGA material, the diffusion of water molecules through the PLGA film seems to be the key factor in the determination of the glass transformation properties and thus the mechanical response of the PLGA film against lateral compression. Based on our combined results, we hypothesize the following mechanism for the compression-induced glass transformation of the Langmuir PLGA film; (1) initially, a humidified/non-glassy PLGA film is formed in the full surface-coverage region (where the surface pressure shows a plateau) during compression; (2) further compression leads to the collapse of the PLGA chains and the formation of new surfaces on the air side of the film, and this newly formed top layer of the PLGA film is transiently glassy in character because the water evaporation rate in the top surface region is momentarily faster than the humidification rate (due to the initial roughness of the newly formed surface); (3) after some time, the top layer itself becomes humidified through diffusion of water from the subphase, and thus it becomes non-glassy, leading to the relaxation of the applied compressive stress.

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Section: Introductionmentioning

confidence: 99%

Humidity-dependent compression-induced glass transition of the air–water interfacial Langmuir films of poly(d,l-lactic acid-ran-glycolic acid) (PLGA)

et al. 2015

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“…[3][4][5] Langmuir monolayers at the air/water surface are good systems for studying polymer systems in quasi-two dimensions, and have been extensively described leading to a set of theories and models within the framework of quasi-bidimensional polymer solutions. 6,7 It has been found that the surface pressure, P, and the equilibrium elasticity, 3 0 , of polymer monolayers follow power laws of the surface concentration, G, with exponents that depend on the so-called solvent-quality of the interface for a given polymer and temperature. 8,9 The availability of experimental techniques for measuring the interfacial dilational and shear rheology over a broad frequency range, u, has allowed to measure the complex viscoelastic moduli pointing out that the interfacial elasticity and viscosity can also be described by power laws of u and of G. [10][11][12] Moreover, the exponents of these laws depend on the solvent-quality of the interface, 13 and coincide with those of the equilibrium properties.…”

Section: Introductionmentioning

confidence: 99%

“…6,7 It has been found that the surface pressure, P, and the equilibrium elasticity, 3 0 , of polymer monolayers follow power laws of the surface concentration, G, with exponents that depend on the so-called solvent-quality of the interface for a given polymer and temperature. 8,9 The availability of experimental techniques for measuring the interfacial dilational and shear rheology over a broad frequency range, u, has allowed to measure the complex viscoelastic moduli pointing out that the interfacial elasticity and viscosity can also be described by power laws of u and of G. [10][11][12] Moreover, the exponents of these laws depend on the solvent-quality of the interface, 13 and coincide with those of the equilibrium properties. 14 However, there has been some discussion about the dynamical mechanism of polymer chains confined to a quasi-two dimensional space, as in a monolayer.…”

Section: Introductionmentioning

confidence: 99%

Surface rheology: macro- and microrheology of poly(tert-butyl acrylate) monolayers

et al. 2011

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We have studied the surface shear viscoelasticity of poly(tert-butyl-acrylate) Langmuir monolayers spread at the air/water interface, by tracking the Brownian motion of tracer particles with different sizes and surface chemical nature, trapped at the same interface. Surface shear moduli have been extracted from the particles mean square displacements (MSD), using different approaches: hydrodynamic calculations of drag coefficients and direct inversion of the MSD by means of the generalized Stokes-Einstein equation. It has been found that these different theoretical approaches lead to comparable values of the shear interfacial viscosity independent of the polymer concentration and molecular weight. In addition, no effect of the size or chemical nature of the probe has been detected. The results have demonstrated the consistency of the microrheological techniques used, and confirm the existence of entanglements in PtBA monolayers, as recently deduced from dilational elasticity and viscosity measurements, [Maestro et al., Soft Matter, 2010, 6, 4407]. An unexpected result was that the interfacial viscosity values obtained from microrheology have been found to be several orders of magnitude lower than the ones obtained with macroscopic interfacial shear rheometers. At the moment there is no clear explanation for this disagreement, although it is not related to the probe size or their chemical nature. Furthermore, this discrepancy is not related to the analysis methodology used, including the calculation of the two-point correlation function used in 3D microrheology when there are heterogeneities present within the range of the probe size.

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“…12,15,17 In this context the Langmuir-Blodgett (LB) technique provides an ideal platform to study morphology and surface mechanical properties of polymers under extreme confinement at the air-water interface. [19][20][21][22][23][24][25][26] Langmuir monolayers of poly(vinyl acetate) (PVAc) 21,24,25,[27][28][29][30][31][32] and poly(methyl methacrylate) (PMMA) 23,27,33 have been extensively studied to explore their thermodynamic and rheological properties. These polymers are also known to form good Langmuir films at the liquid sub-phase, unlike most of the organic polymers which either tend to aggregate or dissolve into the sub-phase.…”

Section: Introductionmentioning

confidence: 99%