| 1. |
- Iruthayaraj, Joseph, et al.
(författare)
-
Adsorption of Low charge Density Polyelectrolyte Containing Poly(ethylene oxide) Side chains on Silica : Effects of Ionic strength and pH
- 2005
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:14, s. 6152-6160
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorption characteristics of a random copolymer of poly(ethylene oxide) monomethyl ether methacrylate and methacryloxyethyl trimethylammonium chloride (PEOMENIA:METAC) on silica were studied using stagnation point adsorption reflectometry (SPAR), quartz crystal microbalance with dissipation (QCM-D), and contact angle techniques. The PEOMEMA:METAC copolymer used in this study is a low charge density polyelectrolyte, with 2% of the monomer units carrying permanent positive charges and 98% containing poly(ethylene oxide) side chains that are approximately 45 repeating units long. The surface excess was determined as a function of pH and concentration of indifferent electrolyte. It was found that the presence of a small amount of 1: 1 electrolyte decreases the adsorbed amount significantly. Further, increasing the pH at a constant ionic strength, 10 mM, results in decreasing surface excess. It is suggested that the adsorption is realized via a combination of non-Coulomb interactions between the poly(ethylene oxide), PEO, grafts and protonated silanol groups at the silica-solution interface and an electrostatic interaction between the charged segments and the oppositely charged surface. Increasing pH and/or salt concentration results in progressive charging of the silica surface with the consequent decrease in affinity between silica and PEO, explaining the decrease in the adsorbed amount of the polymer.
|
|
| 2. |
- Moglianetti, Mauro, et al.
(författare)
-
Interaction of sodium dodecyl sulfate and high charge density comb polymers at the silica/water interface
- 2009
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 5:19, s. 3646-3656
-
Tidskriftsartikel (refereegranskat)abstract
- The structures of interfacial layers formed from mixtures of comb polymers, comprising a high charge density cationic backbone and poly(ethylene oxide) (PEO) side-chains, with the anionic surfactant sodium dodecyl sulfate (SDS) at the silica/water interface, have been determined using neutron reflectivity measurements. The use of mixtures in which only the isotopic composition of the surfactant is changed has made it possible to determine the interfacial volume fraction profiles for both the polymer and the surfactant. For the polymer with 90% of the segments charged and 10% of the segments carrying PEO side-chains, there are four regimes of interfacial behavior with increasing surfactant composition of the bulk solution. First there is adsorption of surfactant to the polymer-covered surface, then, slightly above polymer charge stoichiometry, there is adsorption of near-neutral polymer/surfactant complexes followed by the adsorption of polymer/surfactant aggregates, with a well-defined internal structure. If the concentration of SDS is increased directly from below polymer charge stoichiometry to above the cmc, micelles or polymer/micelle complexes interact with the pre-existing polymer layer. Increasing the fraction of segments carrying PEO side-chains to 25% suppresses the formation of charge-neutral polymer/surfactant complexes at the interface. There is an increase in the adsorption of surfactant, which interacts with the pre-existing layer of polymers. This results in the surface aggregation of SDS and a swelling of the PEO side-chains from a mushroom to a brush-like configuration.
|
|
| 3. |
- Naderi, Ali, et al.
(författare)
-
Desorption of bottle-brush polyelectrolytes from silica by addition of linear polyelectrolytes studied by QCM-D and reflectometry
- 2008
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 323:2, s. 223-228
-
Tidskriftsartikel (refereegranskat)abstract
- The possibility of exchanging adsorbed layers of PEO(45)MEMA:METAC-X brush polyelectrolytes (with two different charge densities, 10 and 75 mol%, denoted by X), with poly(MAPTAC), a highly charged linear polyelectrolyte, was investigated by quartz crystal microbalance with dissipation and reflectometry. The studies were conducted on a silica substrate at pH 10, conditions under which only electrostatic interactions are effective in the adsorption process. Based on the results, it was concluded that PEO(45)MEMA:METAC-10 forms an inhomogeneous layer at the interface through which poly(MAPTAC) chains can easily diffuse to reach the surface. On the other hand, the PEO(45)MEMA:METAC-75 layer was not affected when exposed to a poly(MAPTAC) solution. We argue that the observed effect for PEO(45)MEMA: METAC-75 is due to the formation of a homogeneous protective brush layer, in combination with the small difference in surface affinity between the bottle-brush polyelectrolyte and poly(MAPTAC), together with the difficulty of displacing highly charged polyelectrolyte chains once they are adsorbed on the oppositely charged surface. We also use the combination of QCM-D and reflectometry data to calculate the Water content and layer thickness of the adsorbed layers. (c) 2008 Elsevier Inc. All rights reserved.
|
|
| 4. |
- Naderi, Ali, et al.
(författare)
-
Effect of Polymer Architecture on the Adsorption Properties of a Nonionic Polymer
- 2008
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:13, s. 6676-6682
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of a linear- and bottle-brush poly(ethylene oxide (PEO))-based polymer, having comparable molecular weights, was studied by means of quartz crystal microbalance with dissipation monitoring ability (QCM-D) and AFM colloidal probe force measurements. The energy dissipation change monitored by QCM-D and the range of the steric forces obtained from force measurements demonstrated that linear PEO forms a more extended adsorption layer than the bottle-brush polymer, despite that the adsorbed mass is higher for the latter. Competitive adsorption studies revealed that linear PEO is readily displaced from the interface by the bottle-brush polymer. This was attributed to the higher surface affinity of the latter, which is governed by the number of contact points between the polymers and the interface, and the smaller loss of conformational entropy.
|
|
| 5. |
- Naderi, Ali, et al.
(författare)
-
Interactions between Bottle-Brush Polyelectrolyte Layers : Effects of Ionic Strength and Oppositely Charged Surfactant
- 2008
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 323:1, s. 191-202
-
Tidskriftsartikel (refereegranskat)abstract
- Interactions between cationic bottle-brush polyelectrolyte layers adsorbed on mica across salt and oppositely charged surfactant solutions were investigated with the interferometric surface force apparatus, and the results were compared with what is known for similarly charged linear polyelectrolytes. Ellipsometric measurements demonstrated that the bottle-brush polyelectrolytes, which contain 45 units long poly(ethylene oxide) side chains, are more readily desorbed than linear equivalents when the ionic strength of the solution is increased. It is argued that this is due to the steric repulsion between the poly(ethylene oxide) side chains that reduces the surface affinity. The preadsorbed bottle-brush polyelectrolyte layers were also exposed to sodium dodecyl sulfate (SDS) solutions. It was found that the presence of SDS affected the force profiles less than observed for similarly charged linear polyelectrolytes. This observation was attributed to excluded volume constraints imposed by the poly(ethylene oxide) side chains that reduces the accessibility of the charged polyelectrolyte segments and counteracts formation of large aggregates within the layer.
|
|
| 6. |
- Naderi, Ali, et al.
(författare)
-
Surface Properties of Bottle-Brush Polyelectrolytes on Mica : Effects of Side Chain and Charge Densities
- 2007
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:24, s. 12222-12232
-
Tidskriftsartikel (refereegranskat)abstract
- Surface properties of a series of cationic bottle-brush polyelectrolytes with 45-unit-long poly(ethylene oxide) side chains were investigated by phase modulated ellipsometry and surface force measurements. The evaluation of the adsorbed mass of polymer on mica by means of ellipsometry is complex due to the transparency of mica and its birefringence and low dielectric constant. We therefore employed a new method to overcome these difficulties. The charge and the poly(ethylene oxide) side chain density of the bottle-brush polymers were varied from zero charge density and one side chain per segment to one charge per segment and no side chains, thus spanning the realm from a neutral bottle-brush polymer, via a partly charged brush polyelectrolyte, to a linear fully charged polyelectrolyte. The adsorption properties depend crucially on the polymer architecture. A minimum charge density of the polymer is required to facilitate adsorption to the oppositely charged surface. The maximum adsorbed amount and the maximum side chain density at the surface are obtained for the polymer with 50% charged segments and the remaining 50% of the segments carrying poly(ethylene oxide) side chains. It is found that brushlike layers are formed when 25-50% of the segments carry poly(ethylene oxide) side chains. In this paper, we argue that the repulsion between the side chains results in an adsorbed layer that is non-homogeneous on the molecular level. As a result, not all side chains will contribute equally to the steric repulsion but some will be stretched along the surface rather than perpendicular to it. By comparison with linear polyelectrolytes, it will be shown that the presence of the side chains counteracts adsorption. This is due to the entropic penalty of confining the side chains to the surface region.
|
|
| 7. |
- Olanya, Geoffrey, et al.
(författare)
-
Adsorption characteristics of bottle-brush polymers on silica : Effect of side chain and charge density
- 2008
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:10, s. 5341-5349
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption behavior of bottle-brush polymers with different charge/PEO ratio on silica was studied using optical reflectometry and QCM-D. The results obtained under different solution conditions clearly demonstrate the existence of two distinct adsorption mechanisms depending on the ratio of charge/PEO. In the case of low-charge density brush polymers (0- 10 mol %), the adsorption occurs predominantly through the PEO side chains. However, the presence of a small amount of charge along the backbone (as low as 2 mol %) increases the adsorption significantly above that of the uncharged bottle-brush polymer in pure water. As the charge density of the brush polymers is increased to 25 mol % or larger the adsorption occurs predominantly through electrostatic interactions. The adsorbed layer structure was studied by measuring the layer dissipation using QCM-D. The adsorbed layer formed by the uncharged brush polymer dissipates only a small amount of energy that indicates that the brush lie along the surface, the scenario in which the maximum number of PEO side chains interact with the surface. The adsorbed layers formed by the low-charge density brush polymers (2- 10 mol %) in water are more extended, which results in large energy dissipation, whereas those formed by the high-charge density brush polymers (50- 100 mol _%) have their backbone relatively flat on the surface and the energy dissipation is again low.
|
|
| 8. |
- Peron, Nicolas, et al.
(författare)
-
Competitive Adsorption of Neutral Comb Polymers and Sodium Dodecyl Sulfate at the Air/Water Interface.
- 2008
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 112:25, s. 7410-7419
-
Tidskriftsartikel (refereegranskat)abstract
- The interfacial behavior of aqueous solutions of four different neutral polymers in the presence of sodium dodecyl sulfate (SDS) has been investigated by surface tension measurements and ellipsometry. The polymers comprised linear poly(ethylene oxide) with low and high molecular masses (10 (3) and 10 (6) Dalton (Da), respectively), and two high molecular mass methacrylate-based comb polymers containing poly(ethylene oxide) side chains. The adsorption isotherms of SDS, determined by Gibbs analysis of surface tension data, are nearly the same in the presence of the high molecular mass linear polymer and the comb polymers. Analysis of the ellipsometric data reveals that while a single surface layer model is appropriate for films of polymer alone, a more sophisticated interfacial layer model is necessary for films of SDS alone. For the polymer/surfactant mixtures, a novel semiempirical approach is proposed to determine the surface excess of polymer, and hence quantify the interfacial composition, through analysis of data from the two techniques. The replacement of the polymer due to surfactant adsorption is much less pronounced for the high molecular mass linear polymer and for the comb polymers than for the low molecular mass linear polymer. This finding is rationalized by the significantly higher adsorption driving force of the larger polymer molecules as well as by their more amphiphilic structure in the case of the comb polymers.
|
|
| 9. |
- Pettersson, Torbjörn, et al.
(författare)
-
Lubrication Properties of Bottle-Brush Polyelectrolytes : An AFM Study on the Effect of Side Chain and Charge Density
- 2008
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:7, s. 3336-3347
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of side chain to charge ratio on the frictional properties of adsorbed layers formed by bottle-brush polyelectrolytes with poly(ethylene oxide) side chains has been investigated. The brush polyelectrolytes were preadsorbed from 0.1 mM NaNO3 solutions onto mica and silica surfaces; the interfacial friction was then measured in polyelectrolyte-free solutions via AFM (with the silica surface acting as the colloidal probe). It was concluded that the decisive factor for achieving favorable lubrication properties is the concentration of nonadsorbing poly(ethylene oxide) side chains in the interfacial region. However, contrary to what may be expected, the results showed that an ideal brush layer structure with the adsorbed polymers adopting comb-like conformation is not necessary for achieving a low coefficient of friction in the asymmetric mica-silica system. In fact, the lowest coefficient of friction (< 0.01) under applied pressures as high as 30 MPa was observed for a system with a side chain to charge ratio of 9: 1, incapable of forming brush-like layers.
|
|
| 10. |
- Shovskyy, Oleksandr, 1978-, et al.
(författare)
-
Formation and Stability of Water-Soluble Molecular Polyelectrolyte Complexes : Effects of Charge Density, Mixing Ratio and Polyelectrolyte Concentration
- 2009
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:11, s. 6113-6121
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of complexes with stoichiometric (1:1) as well as nonstoichiometric (2:1) and (1:2) compositions between oppositely charged synthetic polyelectrolytes carrying strong ionic groups and significantly different molecular weights is reported in this contribution. Poly(sodium styrenesulfonate) (NaPSS) was used as polyanion, and a range of copolymers with various molar ratios of the poly(methacryloxyethyltrimethylammonium) chloride, poly(METAC), and the nonionic poly(ethylene oxide) ether methacrylate, poly(PEO45MEMA), were used as polycations. Formation and stability of PECs have been investigated by dynamic and static light scattering (LS), turbidity, and electrophoretic mobility measurements as a function of polyelectrolyte solution concentration, charge density of the cationic polyelectrolyte, and mixing ratio. The data obtained demonstrate that in the absence of PEO45 side chains the 100% charged polymer (polyMETAC) formed insoluble PECs with PSS that precipitate from solution when exact stoichiometry is achieved. In nonstoichiometric complexes (1:2) and (2:1) large colloidally stable aggregates were formed. The presence of even a relatively small amount of PEO45 side chains (25%) in the cationic copolymer was sufficient for preventing precipitation of the formed stoichiometric and nonstoichiometric complexes. These PEC’s are sterically stabilized by the PEO45 chains. By further increasing the PEO45 side-chain content (50 and 75%) of the cationic copolymer, small, water-soluble molecular complexes could be formed. The data suggest that PSS molecules and the charged backbone of the cationic brush form a compact core, and with sufficiently high PEO45 chain density (above 25%) molecular complexes are formed that are stable over prolonged times.
|
|
