Ellipsometric study of nonionic polymer solutions

Noskov, Boris A.; Akentiev, Alexander V.; Grigoriev, D. O.; Loglio, G.; Miller, R.

doi:10.1016/j.jcis.2004.08.068

Cited by 16 publications

(14 citation statements)

References 39 publications

(77 reference statements)

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“…Particularly, the well-known Gibbs adsorption equation has been extensively applied, − mostly in its simple form, which does not take into account the polydispersity in size inherent to polymers. Especially the weak dependence of surface tension at intermediate concentrations, mentioned above in point iii, makes difficult the application of the Gibbs adsorption equation and even leads to the following paradox not fully understood yet. , Taking Gibbs’ equation to be valid in this range, the large molar area of polymer chains results in a small adsorption; therefore, the increase in surface tension with decreasing logarithmic concentration should be rather gradual. Moreover, adsorption must decrease upon dilution; thus, according to Gibbs’ equation, a plot of surface tension versus the logarithmic concentration must be always concave downward.…”

Section: Introductionmentioning

confidence: 99%

Adsorbed and Spread Films of Amphiphilic Triblock Copolymers Based on Poly(2,3-dihydroxypropyl methacrylate) and Poly(propylene oxide) at the Air−Water Interface

2009

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The adsorption behavior of the novel type of water-soluble amphiphilic triblock copolymers PGMA-b-PPO-b-PGMA at the air-water interface is studied by tensiometry and monolayer techniques. In particular, (PGMA(14))(2)-PPO(34) is found to be strongly surface active (Pi(max) approximately 38.1 mN/m, cmc approximately 50 microM), in spite of having a relatively short hydrophobic PPO middle block. Time-dependent adsorption measurements exhibit two different types of adsorption kinetics depending on concentration. Monolayers deposited by spreading form pseudo-Langmuir films, in spite of (PGMA(14))(2)-PPO(34) high water solubility. The transition from a dilute to a semidilute regime during compression of the monolayer occurs at a mean molecular area around 4424 A(2)/molecule (Pi = 0.03 mN/m). Above Pi = 2.1 mN/m (1291 A(2)/molecule) PGMA segments begin to change from a flat two-dimensional conformation to loops and tails protruding into the subphase. The onset of the conformational change for PO segments takes place at a mean molecular area of approximately 625 A(2)/molecule (Pi = 15.5 mN/m). In the range Pi approximately 21.4-23.8 mN/m the PPO blocks adopt a three-dimensional conformation. A new methodology for the estimation of the amount of polymer absorbed at the interface (Gamma) as a function of the solution bulk concentration from tensiometry measurements in pseudo-Langmuir spread films is proposed. The obtained adsorption isotherm suggests the occurrence of a conformational change of the PPO block segments toward conformations having smaller molar areas for actual bulk concentrations above 6.0 x 10(-8) M. The surface tension versus polymer bulk concentration curve (gamma vs ln C) exhibits a sharp break at low concentrations, which is probably due to a conformational change within the adsorbed layer. A theoretical multiple conformation model reproduces satisfactorily the experimental dependency of surface pressure on polymer adsorption (Pi vs Gamma) at low and intermediate ranges of polymer concentrations in the solution bulk. A ratio of approximately eight between the average molecular areas at low coverage and at full coverage confirms that (PGMA(14))(2)-PPO(34) chains are highly flexible and able to adopt very different conformations during the transition of the adsorbed polymer film from a highly diluted to a nearly saturated state. There are some experimental indications that nonequilibrium effects might determine a bimodal conformational distribution within the adsorbed (PGMA(14))(2)-PPO(34) layer, which departs substantially from the equilibrium adsorption picture.

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Section: Introductionmentioning

confidence: 99%

Adsorbed and Spread Films of Amphiphilic Triblock Copolymers Based on Poly(2,3-dihydroxypropyl methacrylate) and Poly(propylene oxide) at the Air−Water Interface

2009

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“…Previously, the interfacial behavior of PNIPAM adsorbed layers at the air−water interface has been studied by mean of surface tension, − ellipsometry, , surface light scattering, neutron reflectivity measurements, − and dynamic surface dilatation rheology. , The PNIPAM chains have been shown to absorb significantly at the air−water interface in both good and bad solvent conditions. , When the temperature is increased up to the LCST and above, the adsorbed amount as well the thickness of the adsorbed layer has been shown by Jean et al to increase significantly. , Above the LCST, the polymer chains have been observed to form highly heterogeneous thin-liquid films due to the formation of hydrophobic interfacial microgels, resulting in very slow drainage times . Recently, Noskov et al have studied the adsorption kinetics of dilute PNIPAM solutions (10 -9 −10 -1 wt %) at ambient temperature by means of ellipsometry and surface dilatational rheology using the capillary-wave and the oscillating-barrier methods .…”

Section: Introductionmentioning

confidence: 99%

Shear Surface Rheology of Poly(N-isopropylacrylamide) Adsorbed Layers at the Air−Water Interface

et al. 2006

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We investigate the shear surface rheology of a thermosensitive polymer, PNIPAM (poly(N-isopropylacrylamide)), adsorbed at the air−water interface using an interfacial stress rheometer. This polymer is characterized by a lower critical solution temperature, LCST, of 32 °C; i.e., PNIPAM chains undergo a coil to globule transition as the temperature is increased above the LCST. We measure a spectacular increase in the surface shear elasticity and viscosity of PNIPAM layers as a function of the temperature around the LCST due to an increase in the amount of adsorbed species as the solvent quality decreases for PNIPAM chains. Moreover, the layers undergo a transition from a Newtonian liquidlike state to an elastic state due to an increase in intermolecular entanglements. We also show that the heating protocols have a strong influence on the rheological properties of the layers. In particular, we show that when the solutions are continuously heated from ambient temperature to well above the LCST, PNIPAM chains can be trapped in a nonequilibrium state at the air−water interface above the LCST. Last, we report on the influence that the PNIPAM bulk concentration and molecular mass have on the surface rheological properties at the air−water interface.

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“…The shape of the surface pressure−area isotherm implicates two main types: the condensed and the expanded polymer layers, , the behavior of which was interpreted on the basis of the molecular structure. Nevertheless, only indirect information was available on the structure of the Langmuir monolayer until it became possible to determine exact parameters such as the thickness − and structural details within the layer , with the aid of ellipsometry and neutron reflectometry, respectively.…”

Section: Introductionmentioning

confidence: 99%

Adsorbed and Spread Layers of Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) Block Copolymers at the Air−Water Interface Studied by Sum-Frequency Vibrational Spectroscopy and Tensiometry

et al. 2006

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The surface properties of three water-soluble and amphiphilic PEO−PPO−PEO triblock copolymers of different composition (Pluronic 6100, 6400, and 6800) are investigated by tensiometry and sum-frequency vibrational spectroscopy. We compared the concentration dependence of the structure of surface layers prepared by three different methods: (i) adsorption from aqueous solution, (ii) dropwise spreading from an organic solution onto a surface of constant area, and (iii) compression of the spread film in a Langmuir trough. The surface density and conformation of the polymers were deduced from the vibrational band intensities of the methyl groups of the central hydrophobic PPO block and from the surface tension isotherms. A transition range related to a conformational change was observed by tensiometry for the adsorbed and the compressed Langmuir films of Pluronics with short PEO blocks, whereas the Pluronic with longest PEO blocks displays a gradual change of surface pressure without the sign of a phase transition. This difference reveals the effect of the relative lengths of the hydrophilic and hydrophobic blocks on the structural changes in the surface layers of block copolymers. A clear indication of the influence of the hydrophilic blocks on the structure of the whole molecule at the interface was also observed in the sum-frequency experiments. Above a given concentration the Pluronic with longest PEO chains exhibited lower sum-frequency intensities and methyl symmetric/asymmetric amplitude ratios than the other Pluronic compounds for all of the layers formed by the various methods. The differences in the surface properties of the dropwise spread layers and of the compressed Langmuir layers exposed the importance of the kinetic aspects of polymer monolayer formation. In the case of the spread films the possible large degree of nonequilibrium chain entanglements might hinder the accomplishment of preferred orientation and conformation of the polymer chains.

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Ellipsometric study of nonionic polymer solutions

Cited by 16 publications

References 39 publications

Adsorbed and Spread Films of Amphiphilic Triblock Copolymers Based on Poly(2,3-dihydroxypropyl methacrylate) and Poly(propylene oxide) at the Air−Water Interface

Adsorbed and Spread Films of Amphiphilic Triblock Copolymers Based on Poly(2,3-dihydroxypropyl methacrylate) and Poly(propylene oxide) at the Air−Water Interface

Shear Surface Rheology of Poly(N-isopropylacrylamide) Adsorbed Layers at the Air−Water Interface

Adsorbed and Spread Layers of Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) Block Copolymers at the Air−Water Interface Studied by Sum-Frequency Vibrational Spectroscopy and Tensiometry

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