Interfacial and Monolayer Properties of Poly(vinylcaprolactam) (original) (raw)
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Interfacial rheology of polyelectrolytes and polymer monolayers at the air–water interface
Current Opinion in Colloid & Interface Science, 2010
In this review, we describe interfacial rheology studies of polymer monolayers at the air-water interface. Since polyelectrolytes are usually soluble in water, the formation of surface monolayers requires the presence of a surfactant of opposite charge. The first part of the review is dedicated to these mixed monolayers. The second part is related to neutral monolayers that can be either adsorbed or deposited at the interface. Interfacial rheology studies of these systems are still scarce, despite a considerable interest: insoluble polymer monolayers in two dimensions are suitable model systems for the tests of polymer theories in two dimensions, such as and glass transition. The rheology of soluble polymer monolayers has important connections with the dynamic properties of dispersions stabilized with these polymers.
The European Physical Journal B, 1998
Equilibrium surface tension measurements have been carried out on mixed solutions of a nonsurface active polyelectrolyte (polyacrylamide sulfonate) and cationic surfactants. A strong synergistic lowering of the surface tension is found in the concentration range where no appreciable complexation of surfactant and polymer occurs in the bulk solution (as seen from viscosity measurements). The surface tension decrease does not depend upon the polymer molecular weight, and there is a limited influence of the surfactant chain length. The influence of the degree of charge of the polymer is more important: for small degree of charge, the complexation is less cooperative, and the structure of the surface complex is looser.
Adsorption of water-soluble polymers with surfactant character
Journal of Colloid and Interface Science, 2007
A comparative study between Langmuir and Gibbs monolayers of a hyperbranched polyol, poly(propylene glycol) homopolymers, and poly(propylene glycol)-poly(ethylene glycol) copolymers with different structure and molecular weight, is reported. Dynamic surface tension (DST) and surface pressure measurements have been carried out to characterize these amphiphilic water-soluble polymers. The adsorption kinetics results are consistent with a rapid diffusion stage followed by a slow reorganization at the air-water interface. The characteristic times of these steps, calculated by the Joos model, point out differences among the polymers in the diffusion rate and rearrangement mechanisms for diluted solutions. Short time analysis of DST data leads to diffusion coefficients in qualitative agreement with the diffusion times calculated with Joos' model. Spread monolayers remain stable for long periods of time. The desorption process seems quite inoperative. As a consequence, the surface pressure of the spread monolayers can be studied over a broad surface concentration range. 2D first-order phase transitions have been evidenced from plateaux observed in Langmuir and Gibbs isotherms. It has been found that Gibbs monolayers lead to lower surface tension states than the Langmuir ones.
Polyelectrolyte adsorption at the solid/liquid interface
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998
The forces between negatively charged surfaces in the presence of an adsorbing cationic copolymer of acrylamide and 2(methacryloyloxy)ethyltrimethylammonium chloride have been investigated using an atomic force microscope. The results were compared with measurements from adsorption isotherm, electrophoretic mobility, stability, and light scattering experiments. The adsorbed amount of polyelectrolyte and adsorbed layer conformation at the solid/liquid interface were found to be strongly dependent on the polymer concentration from which initial adsorption takes place. At low polyelectrolyte concentrations unstable silica suspensions were observed from stability tests; light scattering experiments indicate a large aggregate size under equivalent conditions. The adsorbed amount was also seen to be low, well less than monolayer coverage, and force measurements indicated that the polymer was adsorbed in a flat conformation. At high polyelectrolyte concentrations, an increase in the adsorbed amount was observed which resulted in a higher surface coverage, a higher mobility and a stable suspension. Direct force measurements indicated the presence of an electrosteric barrier.
Journal of Physical Chemistry B, 2005
The surface pressure of monolayers of an insoluble surfactant, didodecyldimethylammonium bromide (DODAB), has been measured onto subphases with different concentrations of poly(styrenesulfonate) (PSS) and at different temperatures. The presence of PSS in the subphase shifts the surface-pressure (Π) curves to larger areas per DODAB molecule, A, and shifts the surface phase transition to higher Π's. The presence of PSS chains decreases the surface electric potential; the decrease is higher than expected from the formation of a double layer between the DODAB molecules and the PSS segments. Increasing the temperature shifts the surface-pressure curves to higher areas and also increases the values of Π of the surface phase transition. The effect of the PSS chains on the Π versus A curves is contrary to the one induced by the presence of inert electrolytes in the subphase. The behavior is consistent with the existence of a dense layer of PSS segments beneath the DODAB monolayer at low PSS concentrations, c. Two PSS layers exist at higher concentrations, a dense layer immediately below the DODAB and a less-dense layer, below the first one, that protrudes deep into the subphase. The surface-pressure relaxation curves have been found to be bimodal through the whole range of surface pressures and at all the values of polymer concentration studied. These results point out that the adsorption layers behave mainly as elastic bodies, with zero-frequency elasticity, (ω ) 0), which agrees with the equilibrium compressibility modulus. The increase [ (ω ) 1) -(ω ) 0)] has been found to be independent of both polymer concentration and molecular weight. The zero-frequency-dilational viscosity, κ(ω ) 0), strongly increases with Π in the two-dimensional condensed-liquid region. The surface viscosity strongly decreases with increasing frequency; the decreasing rate is higher than the one found for the monolayers of nonionic insoluble polymers. κ(ω ) 0) has also been found to be independent of both polymer concentration and molecular weight. These results seem to indicate that it is the film formed by the DODAB molecules and the first dense polymer layer that determines the surface viscoelastic moduli of this system.
Colloid and Polymer Science, 1998
The surface pressure (Π) vs surface concentration (Γs) curves of the hydrogen-bonded polymer blend poly(vinylacetate)+ poly(4-hydro-xystyrene) (PVAc+P4HS) have been measured at 25 °C onto a water subphase at pH=2.0. While PVAc forms extended monolayers, and the free surface of water is found to be a good solvent for it, P4HS forms compressed monolayers, and the surface is a near Θ-type solvent for it. PVAc and P4HS form miscible non-ideal monolayers until near the collapse pressure through the whole concentration range. The composition dependence of the Π–Γs curves is rather complex. Contrary to what might be expected, the addition of PVAc to the blend does not reduce the rigidity of the monolayer until its weight fraction is larger than 0.5. The compressibility data of the P4HS-rich monolayers suggest the existence of a second maximum at high surface coverages, a result already observed in some polysiloxanes.
Phase behaviour of poly(N-vinyl caprolactam) in water
Polymer, 2000
The solution behaviour of the system poly(N-vinyl caprolactam)/water has been studied. Experiments and theoretical calculations indicate a typical Flory-Huggins (Type I) demixing behaviour with a lower critical solution temperature (LCST). The critical concentration and LCST shift to lower values with increasing molar mass of the polymer. The phenomenological description of such a system predicts a continuous temperature controlled swelling behaviour of the corresponding network. A comparison with literature data confirms this prediction.
Polymer, 2000
Dynamic light scattering measurements have been performed for aqueous solutions of thermosensitive linear poly(N-vinylcaprolactam) (PVCa) macromolecules in the presence of NaCl and different water soluble amphiphilic organic compounds: pyrogallol (neutral amphiphilic compound), cetylpyridinium chloride (cationic surfactant) and sodium dodecylsulfate (anionic surfactant). A decrease in the macromolecular hydrodynamic diameter is observed upon addition of ionic surfactants (SDS, CPC) at low surfactant concentrations. This trend changes to an increase in the macromolecular hydrodynamic diameter at high surfactant concentration at temperatures below the temperature of polymer aggregation. This effect is in contrast with the behaviour of the systems of PVCa-non-ionic organic compounds (pyrogallol) and NaCl where we always observed the weak monotonic decrease of the hydrodynamic diameter with the increase in the concentration of organic compound, NaCl.